TECHNICAL REPORT WA/90/14 Geology and land-use planning: Morpeth--

Part 1 LAND-USEPLANNING

I Jackson and D J D Lawrence

This report has been generated from a scanned image of the document with any blank pages removed at the scanning stage. Please be aware that the pagination and scales of diagrams or maps in the resulting report may not appear as in the original BRITISH GEOLOGICAL SURVEY

TECHNICAL REPORT WA/90/14 Onshore Geology Series

Geology and land-use planning: Morpeth-Bedlington-Ashington

Part 1 LAND-USEPLANNING

1:25 000 sheets NZ28 andNZ 38

Parts of 1:50000 geological sheets 9 (), 10 (Newbiggin), 14 (Morpeth) and 15 (Tynemouth)

I Jackson and D J D Lawrence

This study was commissioned by the Department of the Environ- ment, but the views expressed in it are not necessarily those of the Department

Maps and diagrams in this book use topography based on Ordnance Survey mapping

Geographical index UK, ,

Subject index Land-use planning, thematic maps, resources, mining, engin- eering geology, Quaternary, Carboniferous

Bibliographic reference Jackson, I, and Lawrence, D J D. 1990. Geology and land- use planning: Morpeth- Bedlington-Ashington. Part 1: Land-use planning. British Geological Survey Technical Report WA/90/14

0 NERC copyright 1990 Keyworth,Nottingham British Geological Survey1990 BRITISH GEOLOGICAL SURVEY

The full range of Survey publications is available through the Keyworth, Nottingham NG12 5GG Sales Desks at Keyworth, Murchison House, Edinburgh, and at Plumtree (06077) 6111 Telex378173 BGSKEY G the BGS London Information Office in the Geological Museum. Fax 06077-6602 The adjacent Geological Museum bookshop stocks the more popular books for sale over the counter. Most BGS books and Murchison House, West Mains Road, Edinburgh EH9 3LA reports are listed in HMSO’s Sectional List 45, and can be bought from HMSO and through HMSO agents and retailers. 031-667 1000 Telex 727343 SEISED G Maps are listed in theBGS Map Catalogue and theOrdnance Fax 031-668 2683 Survey’s Trade Catalogue, and can be bought from Ordnance Survey agents as well as from BGS. London Information Office at theGeological Museum, Exhibition Road, South Kensington, London SW7 2DE The British Geological Survey carries out the geological survey 071-589 4090 Fax 071-584 8270 of Great Britain and Northern Ireland (the latteras an agency 071-938 9056/57 service for the governmentof Northern Ireland), and of the surrounding continental shelf; as well as its basic research 19 Grange Terrace, Edinburgh EH9 2LF projects. It also undertakes programmesof Britishtechnical aid 031-667 1000 Telex 727343 SEISED G in geology in developing countries as arranged by the Overseas Development Administration. St Just,‘30 Pennsylvania Road, Exeter EX4 6BX Exeter (0392)78312 Fax 0392-437505 The British Geological Survey is a component bodyof the * Natural Environment Research Council. Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed SY23 4BY * Aberystwyth (0970)611038 Fax 0970-624822

Windsor Court, Windsor Terrace, NE2 4HB 091-281 7088 Fax 091-2819016

Geological Survey of Northern Ireland, 20 College Gardens, Belfast BT9 6BS s Belfast (0232)666595 Fax 0232-662835

Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB Wallingford (0491)38800 Telex 849365 HYDROL G Fax 0491-25338

Parent Body Natural Environment Research Council Polaris House, North Star Avenue, Swindon, SN2 1EU Swindon(0793) 411500 Telex 444293 ENVRE G Fax 0793411501 Data used inpreparing this report and PREFACE associated maps are lodged at the Newcastle uponTyne office of theBritish Geological Thisreport is one of twodescribing the Survey. Anyenquiries concerning these resultsof a survey of the geology of the documents should be directed to that office. Morpeth-Bedlington-Ashington district. Thisvolume, Part I, reviews the geological factorsrelevant to land-use planning and Reportsare alsoavailable for the following development. A secondvolume, Part 11, 1:25 000 sheets: describes the geology of the area in detail. Thedistrict is coveredby 1: 10 000 sheets NZ 15: Chopwell,Rowlands Gill, Consett NZ 28 NW, NE, SW, SE and NZ 38NW, and Stanley NZ25: Kibblesworth,Birtley, SW and lies within 150 000 geological CragheadChester-le-Streetand NZ27: sheets(Rothbury), 9 10 (Newbiggin), ,Killingworth and Wide Open 14 (Morpeth)and 15(Tynemouth). The NZ17E & 18E: -Morpeth district was firstsurveyed at the six-inch scale byH.H. Howell and W. Topleyand published on Northumberland Old Meridian County mapsbetween 1867 and 1879. A resurveyby G.A. Burnett, V.A. Eyles and A. Fowlerbetween 1929 and 1950was published on the New Meridian. Thepresent survey, which was funded jointly by the Departmentjointlythe by of the Environmentand the British Geological Survey,revised the geologicalmaps and prepared thematic maps designed for use by NOTES plannersand developers. The survey was undertakenbetween 1986 and 1989 by All National Grid referencesin this report I. Jackson(NZ 28 NE, SE, NZ 38 SW) and lie withinthe 100 kmsquare NZ. Grid D.J.D. Lawrence(NZ 28 NW, referencesare given to either eight figures sw, NZNW). 38 R.A.Monkhouse, BGS (accurateto within lOm), orsix figures for HydrogeologyResearch Group,provided extensive locations. informationon groundwater resources and pollutionwhile A. Forsterand Eachborehole or shaft registered with BGS M.G.Culshaw of the BGS Engineering is identifiedby a four-elementcode (e.g. ResearchtheadvisedGroup on NZ 28SE 58). Thefirst elements define establishment of thegeotechnical database the 10 kmsquare (of theNational Grid) in and subsequentand analyses.data The whichthe borehole is situated;the third programmemanagers were Dr. D.J. Fettes element defines the quadrant of that square, (BGS) and Mr. H. Mallett (DOE). andthe fourth is the accession number of that borehole. Inthe text of thereport the borehole/shaft is normallyreferred to by thelast threeelements alone (e.g. 28 SF, F.G. Larminie, OBE, Director 58). British Geological Survey Keyworth Theword 'district' unqualified, thisin Nottingham NG12 5GG account means the whole ground covered by NZ 28NW, NE, SW, SE andNZ 38 NW January 1990 and SW.

1

This page is blank CONTENTS 5. SUMMARY OF GEOLOGICAL FACTORSFOR CONSIDERATION IN EXECUTIVE SUMMARY LAND-USE PLANNING (MAP 10)

1 INTRODUCTION 5.1 SHALLOW MINING 5.2 SOFT GROUND 1.1 OBJECTIVES 5.3 FILL AND ARTIFICIAL DEPOSITS 1.2 GEOGRAPHICAL SETTING (MADE GROUND) 1.3 DATA SOURCES AND 5.4 LANDSLIPS METHODOLOGY 5.5 SAND AND GRAVEL RESOURCES 1.4 PRESENTATION OF RESULTS 5.6 WATER RESOURCES 1.5 LIMITATIONS 1.6 CONFIDENTIALITY SELECTED BIBLIOGRAPHY 1.7 ACKNOWLEDGMENTS GLOSSARY

2 GEOLOGICALSUMMARY (MAPS 1-4) APPENDIX A: DATA SOURCES APPENDIX B: THE BOREHOLE 2.0 INTRODUCTION DATABASE 2.1 SOLIDGEOLOGY APPENDIX C: THE GEOTECHNICAL 2.2 DRIFTGEOLOGY DATABASE

3 LAND STABILITY ANDGROUND FIGURES CONDITIONS (MAPS 5 - 8) 3.0 INTRODUCTION 1. Locationdiagram. 3.1 COAL MINING 2. Generalizedvertical section. 3.2 ENGINEERING GEOLOGY 3. Solid geology. 3.3 SLOPE STEEPNESS AND 4. Horizontalsections. STABILITY 5. Drift geology. 3.4 FLOODING 6. Rockheadelevation. 3.5 EFFECTS OF COAL-MINING ON 7. Drift thickness. HYDROGEOLOGY 8. Shallow mining. 3.6 NATURAL DISCHARGE OF 9. EngineeringGeology. METHANE AND 10. Made and disturbed ground. DEOXYGENATED AIR 11. Slope steepness. 12. Flooding. 13. Mineral and water resources (excluding 4 MINERALWATERAND RESOURCES coal). (MAP 9) 14.factors Geological for consideration in land-use planning). 4.0 INTRODUCTION 4.1 COAL 4.2 SANDSTONE TABLES 4.3 MUDSTONE AND SILTSTONE 1. Presentation of results. 4.4 IRONSTONE 2. Coal seam nomenclature. 4.5 SEATEARTH 3. Former collieries with a take in the 4.6 IGNEOUS ROCK district. 4.7 METALLIFEROUS MINERALS 4. 4.8 SAND AND GRAVEL Opencast coal sites. 5. Engineering geology divisions 4.9 GLACIAL CLAYS 4.10 GROUNDWATER 6. Geotechnical properties. 7. Made ground. 8. Former sandstone quarries. 9. Former clay pits for brick and tile making.

2 MAPS 1:25 000 scale thematic maps [in folder] 1. Solid geology. 2. Drift geology. 3. Rockhead elevation. 4. Drift thickness. 5. Shallow mining. 6. Made and disturbed ground. 7. Borehole and shaft sites. 8. Engineering geology. 9. Mineral and water resources (excluding coal). 10. Geological factors for consideration in land-use planning.

1:lO 000 scale standard geological maps [available separately] NZ 28 NW NZ 28 NEAshington NZ 28 SW Nedderton NZ 28 SE Bedlington NZ 38 NW Newbiggin NZ 38 SW Blyth

COVER PHOTOGRAPH Woodhorn Colliery

Taken by Mr T Bain, BGS Photographic Unit

3 EXECUTIVE SUMMARY b) Tob) collect,evaluate andinterpret availableinformation on geology, INTRODUCTION geotechnicalgroundproperties, conditions,geomorphology, and The Morpeth-Ashington-Bedlington area hydrogeology. forms part of the Northumberland Coalfield. Coal mining and its decline has left a legacy of reclaimedand unreclaimed spoilheaps, c) To organise the information obtained into unchartedold workings, subsidence and a data-base/ archive. abandonedshafts. Large areas of variably restoredopencast coal andbrick clay workingsare equally common.This has d) To present basic data and interpretations givenrise tovariable ground conditions forselected parts of thestudy areas as whichcan pose problemsfor development thematic maps andaccompanying reports andderelict land reclamation. When set in a form easilyunderstood by planners againstthisbackground theneed for andothers nottrained in geology, comprehensiveand up-to-date information mining,civilengineering relatedor onthe geological environment is readily disciplines. apparent. e) Toidentifye) theneed forfurther investigationsspecialistor advice in Thisstudy was thereforeundertaken to relationspecific toplanning and examine and upgrade the geological database development objectives and proposals. and associateddatasets andpresent the results in a formto aid planners, engineers and geologists. Twosets of maps and METHODOLOGY accompanying reports have been prepared: Thework involved thecollation and interpretation of datafrom many different 1 (thisreport): A series of tenthematic sources:- a specially commissioned 1: 10 000 maps atthe 1:25 000 scalewith an scale field geological survey, coal explanatory text. explorationboreholes, deepmine and opencastcoalabandonment plans, site 2 (publishedseparately, WA/90/19): A investigationboreholes and reports, existing seriesofsixgeological maps theat geologicalmaps and memoirs andother 1: 10 000 scale with an explanatory text. archivalmaterial held bythird parties. Computeriseddatabases of boreholeand geotechnical information were established. Thestudy was fundedjointly bythe Department of theEnvironment and the CONCLUSIONS BritishGeological Survey (BGS). Thework was carriedout by BGS stafftheat 1. Thesurvey hascollated and interpreted Newcastleupon Tyneoffice,with availablegeological datafrom all known contributionsfrom staff of the BGS sources. It is the mostcomprehensive study EngineeringGeology andHydrogeology of the geologyof thedistrict for 50 years researchKeyworthgroups atand and has resultedin substantial revision of Wallingford. the geological maps. Theten 1:25 000 scale thematicmaps, sixnew 1:lO 000 scale geologicalstandards, explanatory texts and OBJECTIVES thecomputerised databases provide a sound The detailed objectives of the study were: basis forthe evaluation of geological issues in land-use planning decisions. a) Tocomplete, where necessary, new basic field geologicalmapping of thestudy 2. Almost all thedistrict has been area and produce revised maps. undermined for coal. Shalfow mine

4 workings,present inmany areas, are a 6. Despitethe long history of mininglarge potential cause ofland instability, whereas resources of coalremain and, leaving aside it is reasonableto assume that subsidence planningandenvironmental constraints, causedby deepmining is generally there is considerablepotential for opencast complete. Over 240 disused shafts and adits extraction. havebeen located andothers undoubtedly exist. 7. Sand graveland deposits occur extensively inthe area east of Morpeth. Littledetailed information theiron 3. Below thetop weathered zone, till, thicknesscompositionand exists but glacial sandand gravel and solid rock, inadvertentsterilization developmentby whichtogether cover alarge part of the prior to assessment should be avoided. district, provide good foundation conditions. More variable conditions exist in the buried valleys, where deposits of laminated silt and 8. Largersandstone units the inCoal clay may be present, and in the river valleys Measures are the principal aquifers. Mining andestuaries, where alluvial clay, silt and has caused significantmodification to the peat possess relativelyweak geotechnical naturalhydrogeological regime andits properties. effectsconsideredneedbe to when evaluating potential leachate movement from 4. Made ground and fill is extensive and of landfill sites. variablecomposition, consolidation and thickness. Many restored opencast coal sites exist but these are well documented; smaller 9. There is aremote risk of methaneor disused and infilled clay pits and sandstone oxygen-deficientair build-up incertain quarries may producefoundation problems areas, especially those aboveunventilated if not identified prior to construction. old mine workings.

Thisstudy has collatedand presented all 5. Slopes, especially those driftin available geological data but is not a sediments,may prove unstable and are substitute for on site investigation. Where liable toslip if oversteepenedor undercut mining is suspectedthe mine plans and by rivers and the sea or disturbed by man. shaft atlases maintained byBritish Coal should be consulted in the first instance.

5 1 INTRODUCTION incised valleys of therivers Blyth and andthe low sandstone hills upon whichBedlington andNorth Seatonstand. 1.1 OBJECTIVES Inthe west theground is moreundulating Thisreport describes the results of a andsouth of Morpeth rises toover 85 m research projectfunded jointly by the abovesea level. The riversBlyth and Department of theEnvironment and the Wansbeck whichdrain thearea, flow BGS (ContractPECD 7/1/241). The eastwardsthrough gorges tomeet the coast objectives of the project were to provide an at Blyth and . At Cambois the up-to-date ~ geological database forthe coastis a dune-fringedsandy baywhich Morpeth,Bedlington andAshington area as separates the low rockyheadlands of a fo-undationa for land-useplanning and Newbiggin and North Blyth. development,effective future geological research andthe safeguarding of mineral 1.3SOURCES DATA AND resources. The presentstudy is thethird METHODOLOGY DOE sponsoredapplied geological mapping projectsouth-eastin Northumberland, Severalcenturies of coalmining and, in previoussurveyscoveredhave the recent decades, an extensive search for coal Cramlington-Killingworth - NZ27 and seams which could be worked opencast have Ponteland-Morpethdistricts - NZ17E and provided a wealth of geological data for the 18E (see Figure 1). BGS has undertaken district.compilingIn thisreport and thesestudies as part of itsprogramme to accompanying maps data from the following maintainits coverage of 1: 10 000 scale sources were collated and interpreted: geological maps of the UK. * detailed geological field survey at 1: 10 000 scale 1.2 GEOGRAPHICALSETTING * deep mine coal boreholes and shaft The area described in this report lies to the records north of Newcastleupon Tynewithin the , and Wansbeck * deep mine coal abandonment plans districts of theCounty of Northumberland opencastcoal prospecting boreholes (Figure 1). Thebuilt-up areas of Blyth, * Morpeth,Ashington, Bedlington, Newbiggin * opencastcoal completion plans andStakeford make up significant a siteinvestigation boreholes, trial pits proportion (~25%)of the land areabut in * and reports the main the district is rural. The east coast railline andthe A1 trunk road cross the * existing geological maps district in the west. * aerialphotographs Coal mining was for centuries the dominant * Water Authoritydata industryand has leftitsmark onthe Local Authoritydata landscape inthe form of collierybuildings * andterraces, shafts, pitheaps and the * geological reportsand journals effects of subsidence.Although underground mining is now confined to one Thetype, quantity, quality and limitations small privatemine, opencast coal mining of each of these data sourcesis dealt with continuesand Butterwell, currently one of in Appendix A. the largest sites in Europe, is situated in the north-west of district.the With the Computeriseddatabases of borehole and exception of opencastmining andthe large geotechnicalinformation comprising more aluminiumelectricitysmeltingand than 40 600 recordswere established. Their generatingplants at Lynemouth and Blyth structureand value, bothcurrent and respectively, industryin the district inis describednow are potential, chieflybased on small light units in and AppendicesB and C. Computer-aidedand around the urban areas. conventionaltechniques were used to producethe 1: 10 000 scalestandard Topographically, the east of the district is a geological maps, the 1:25 000 scale thematic featurelesstill plain relieved only by the maps and the accompanying reports.

6 NORTH

NORTHUMBERLAND\

PONTELAND

- 70

KEY AI Major roads ---- Railways

-0-0- County boundarres (7 Urban area

Recent BGS survey areas

ICurrentsurvey area

0 5 10 krn I I I Scale

Figure 1. Location diagram

7 1.6 CONFIDENTIALITY 1.4 PRESENTATION OF RESULTS Confidentialdata, chiefly British Coal Opencast Executive prospecting information, Theresults of thestudy are detailed in has beentaken into account and used in a Table 1. generalizedway during the preparation of the geologicalmaps, butdetails of specific 1.5 LIMITATIONS boreholes are not individually quoted. Thisreport and accompanying mapshave beenproduced theby collation and 1.7 ACKNOWLEDGEMENTS interpretation of geological,geotechnical Thehelp and cooperation of thefollowing andrelated data from awide variety of are gratefully acknowledged: sources.However extensive this research may seem thedata are not comprehensive BritishCoal Deep Mines andOpencast anddo vary in quality. It is inevitablethat Executive thiswill bereflected inthe documents Northumberland County Council presented; local features and conditions may not be representedand manyboundaries Northumbrian Water Authority may be only approximate. Landownersand tenants in the survey area. Theaim hasbeen toproduce generala descriptionof the geological factors which arerelevant land-useto planning and development.This report and associated documentscan contribute to drafting and evaluatingstructure and local planpolicies, theymay alert planners, engineers and developers by highlighting particular aspects of the geology of thedistrict but they cannot and should not replacesite-specific surveysaimed at evaluatingpotential resources or hazards.Users must satisfy themselves by seekingthemselves by appropriate professionaladvice and bycarrying out groundsurveys that conditions are suitable for any particular land-use or development.

The maps were constructed in May 1989, no informationsubsequent tothat date has been taken into account.

8 Table 1. Presentation of Results

Part I: report with ten 1:25 000 scale maps listed below (This report)

MA P NUMBER TITLE DESCRIPTION TITLE NUMBER MAP

1 Solid geology major rockunits, named coals, faults.

2 Drift 2 geology Recent and glacial (superficial) deposits.

3 elevationRockhead Contours at 10m intervals on bedrock surface.

4 Drift thickness Thickness of superficial deposits contoured at 10m intervals.

5 Shallow mining Areas of known, probable and possible coal mining within 30 m of surface.

6 Made and disturbed Differentiation of ground artificial ground, location of landfill sites.

Borehole and shaft Location of shafts, sites boreholes, adits and trial pits.

Engineering geology Surface rocks and soils classified in geotechnical terms.

Mineral and water Potential mineral deposits resources (excluding and sites of extraction coal) 10 factorsGeological Significant elements from for consideration in individualthematic maps land-use planning presented together.

Part I1 report describing six 1:lO 000 scale standard geological maps listed below

M AP NUMBER NAMENUMBER MAP NZ 28 NW Pegswood NZ 28 NE Ashington NZ 28 SW Nedderton NZ 28 SE Bedlington NZ 38 NW Newbiggin NZ 38 SW Blvth 2. GEOLOGICALSUMMARY TheCoal Measures sequence includes the (MAPS 1-4) following lithologies: 2.0 INTRODUCTION Mudstone is the most dominant lithology The followingaccount is an introduction to and ranges in colour from light grey to dark the geology of the district; its purpose is to grey.Although fossiliferous immediately provide sufficientbackground toplace in abovea coal seam, mudstones are generally context the subsequent sectionson land-use devoid of organicremains elsewhere. The planningelements. Adetailed description mudstonesusually become increasingly silty of the geology is given ina second report upwardsand grade into siltstones, or pass (Part 11) which is published separately. by intercalationandinterlamination of sandybeds (striped-beds) into fine-grained Thedistrict is underlain by geological sandstone. deposits of twovery different ages. Firstly, thesolid rocks of theUpper Carboniferous Sandstone and Siltstone eitherform thin, periodwhich were deposited 300-320 widespreadsheets, less than5 m in millionyears ago andcomprise Coal thickness,elongateor channel deposits. Measuresstrata, underlain depthat by 'Washouts' occurwhere such channel Millstone Grit (Figures 2,and 3 4*). sandstones cutdown into, and remove the Secondly, Quaternary (Drift) depositswhich coal seams; the sandstone containing pebbles are less than 18 000 years old andform an and fragments of derived mudstone and coal unconsolidatedsuperficial layer which is ('scares'). Channel sandstonesalways have generally between 5 and 20 m thick (Figures coarse bases althoughoverall grain-size of 5 and 7). sandstonesdecreases theup succession. Sandstones are usually pale grey or cream at depth, but near the surface they weather to 2.1 SOLIDGEOLOGY (MAP 1) rustybrown or, less commonly,white. Theyare generallywell-cemented with 2.1.1 Carboniferous Rocks quartz being the dominant component. In Carboniferous timesthe area lay ina subsidingbasin - theNorthumberland Seatearths (fireclayorganister) underlie Trough. Vast deltasystems fedsediment everycoal seam andrepresent the soil from the surrounding land surfaces into the accumulationvegetationwhich on trough,accumulating succession a over flourished.There is nocorrelation between 2 000 mthick. The successioncomprises a the thickness or character of a seatearth and series of cycles of sedimentation.Each of that of theoverlying coal. Seatearths are these cycles began with an abrupt change of morepersistent thantheir associated coals relativelevelgivingsea marine or andgrade from sandstone(ganister) to near-marine conditions. The water mudstone(fireclay). They are distinguished shallowedas sediments built up to water from underlyingstrata by thepresence of level andthe full cycle ended with the rootletsandabsence,the extremeor establishment of forests and swamps on the disruption, of bedding with abundant highly newly formed land.Each cycle gave a polished (listric) surfaces. repeatedsequence of typesrock (cyclothem)**ideally starting with a basal Coals are of bituminousrank and range in marinemudstone and continuing upwards thickness fromthin coaltraces to about throughnon-marine mudstone, siltstone, 2 m. All seams varylaterally in thickness; sandstone andseatearth to coal. However some thinand die out, althoughtheir the cyclesthe rarelyare complete and position may beindicated by the associated commonly die out or split laterally. andmore persistent seatearth. Some seams are splitare by interdigitation of other The Figures reducedfrom the 1:25 * 000 sediment; splits may be on either a regional scalemaps aresimplified portrayals. The ora local scale.Many seams have2or appropriate map should always be consulted 3 cm3 of cannelcoal immediately above. for detailed information. The coal seams formedfrom vegetation ** A shortglossary of technicalterms used whichswampsgrewin which were in this report is presented on page 55. sufficientlyde-oxygenated for the partial

10

aregenerally less than 5 mwide and, in preservation of vegetablematter. The most cases, areboth laterally and vertically thicknessto which a coal seam developed discontinuous.Surface evidence of their andtheamount of splittingbyother presence is limitedto sections in opencast sediments was determinedby the rate of coalworkings, two possible quarries and a subsidence of the original vegetation surface formerexposure on the foreshore at Blyth and its potential inundation. [3185 82201. Thereare approximately 35 namedcoal seams inthe district, at least 22 of which havebeen mined. Despite (orperhaps 2.2 DRIFTGEOLOGY (MAP 2) because of)the longhistory of miningin Overmuch of thedistrict the bedrock or thearea, coal seamnomenclature suffers rockheadsurface is coveredby Quaternary considerably from homonyms (different coal deposits (Figure 5). Theform of the seamscalled the samename, e.g. High rockhead surface on which these deposits lie Main)and synonyms (the samecoal seams is illustratedbythe rockhead elevation called different names, e.g. Beaumont and contours of Figure 6 and MAP 3. These Harvey); some due to mis-correlation, others showa majorpre-glacial valley system introducedforcommercial reasons. The enteringthe district from the west and seamnames which appearon the geological south-westand declining to adepth well maps andin this report are for the most belowpresent sea level atCambois. In part those adoptedLandby (1974). thesevalleys varied glacial sediments, a Correlation has been made with the standard product of the last ice age, reach thicknesses classificationused by British Coal andthe in excess of 60 m (Figure 7 and MAP 4). appropriate seam indexletter has been Incontrast the interfluvial areas generally includedin the generalisedvertical section havea thin (less than 10 m) drift covering of each 1: 10 000 scale geological map, consistingalmost entirely oftill (boulder togetherwith commonly occurring local clay). The youngestdeposits (less than names and Table 2 lists the more significant 12000 yearsold andtherefore post-dating variations.Adetailed description can be the lastice sheet) are the silts, muds,sands found in the Part I1 report. and gravelswhich flankthe present rivers and coastline. SideriticIronstone (whin) is common, developedeither as nodules,generally 2.2.1 Till flattened parallelto bedding, or aslayers. In themetre or so abovecoal seams it Till(Boulder Clay) is present over much of typically forms laterally continuous beds up district.At depth, where it is unweathered, to about 10 cmin thickness. Ferruginous thetill usually comprises astiff grey to concretions are common in seatearths. grey-brownsilty, sandy, stony clay. Near surface however, in the first metre or so till is usuallyrepresented mottled a by 2.1.2 Structure orange-brown and pale grey silty, sandy and only sporadicallyonly Tillclay. stony Therocks were all foldedand faulted thicknesses of over 40m have been recorded duringlateCarboniferous times(about in boreholes and may exceed 60m inthe 280 millionyears ago). Subsequently,about Stobhill andStannington areas. Thin lenses 60 million years ago, they were tilted gently and partings of sand and gravel and silt and eastwardswith some furtherfaulting. The clay arecommonly found in the till and regional dip of thestrata is tothe east or stones andboulders, while generally less south-eastbut there is considerable local than 100mm,mayexceptionally reach variation(Figure 4). The estimatedposition several metres across. of thelarger faults is shownonthe geological map (MAP 1). 2.2.2 GlacialSand and Gravel 2.1.3 Igneous Dykes The mostextensive deposit of glacialsand Severaligneous dykes of Tertiary agehave and gravel occurs in the west of the district beenrecorded inmine workings inthe aroundPark House, Shadfen, Hepscott and district.These intrusions trend WNW-ESE, NorthChoppington tothe south of the

14 Table 2 Coalseam nomenclature

This report Local or county name(s) British Coal Index Letter

Moorland Blackclose DE 1

Ashington High Main, Upper High Main, Ashington High Main DE2

High Main Diamond, Top Main, New Main E

Me tal Top Main, Middle Main, Grey, Top Grey F1

Five-quarter Bottom Main, Bottom Grey F2

Bentinck Top Yard G1

Top Bensham Top Maudlin, Cowpen Bensham, Cambois Duke, Bensham H1

Bottom Bensham Bottom Maudlin, Stone, Cowpen Five- quarter, Cambois Five-quarter, Quarry, Six-quarter H2

Durham Low Five-quarter, Pegswood Band, Cowpen Brass Main Thill J

Northumberland Brass Thill, Pegswood Yard K Low Main

Plessey Hutton, Low Low Main L

Bottom Plessey Cheeveley, Lower Yard, Ruler M

Beaumont Harvey, Pegswood Tilley N

Tilley Widdrington Yard, Denton Low Main P

Top Busty Barmoor, Pegswood Harvey, Widdrington Five-quarter Q1

Bottom Busty Pegswood Top Busty, Splint, Old Man, Hepscott, Widdrington Main (or Top Main) Q2

Three-quarter Widdrington Main (or Bottom Main), Little, Pegswood Bottom Busty R

Brockwell Bandy S

Victoria Brockwell T

Marshall Green Choppington Victoria U

River Wansbeck. It consists of brownand 2.2.8 Blown Sand greymedium-grained sand and sandy silt These wind-transported sediments fringe the ranging to 18m in thickness* . coastdunes,as theinland edge of which are boreholesrecord apparently less persistent generallyindistinct. Like the deposits above deposits atvarying levels withinthe glacial theymay change their extent and thickness sequence. in a relatively short period of time. 2.2.3 Laminated Silt and Clay Thisdeposit has not been differentiated at surfaceknownbutis from borehole . .. evidenceand clay pit workings to bemost prevalenttheinburied valley between Choppingtonand Cambois. the deposits are usually finelylaminated andvirtually stone-freeand maybe intercalated with fine-grainedsand partings and thin till units.

2.2.4 River Terrace Deposits Theseare developed along the Wansbeck where they comprise sand and gravel which is hard-packedtowards the base andup to 4 m thick.Very fewother details are available.

2.2.5 Alluvium Sedimentdeposited by rivers and streams flanksmany of the watercourses inthe districtand is variable a deposit of sand/silt/clay/gravel ofcontaining ten . organicdebris. 2.2.6 Marineor Estuarine Alluvium Thesesediments occur below the Normal TidalLimit. The most extensivespread has beenmapped on the south bank of the Blyth Estuary [290 8221, where it consists of beds of silty,pebbly clay and sand and gravel. Thedeposit also occursbeneath the tidalflats of theriver Wansbeck buthere

' comprisesup to 11.6m of sandand gravel. 2.2.7 Marine Beach and Tidal Flat The beaches arechiefly of sandwith subordinateshingle. Tidal flats of mud and silt occurthein Blyth and Wansbeck estuaries.All of thesedeposits arein a dynamicsituation (likelyto be affected by the action of the rivers and the sea) and are thereforesubject to changes of extent, thickness and composition over a very short timescale.

17

3.1 COALMINING 3 LAND STABILITY AND GROUND Almost all the district has been undermined CONDITIONS (MAPS 5-8) and, in general, the number of seams which havebeen removed increases to the east (Table 3). However,with the closure of 3 .O INTRODUCTION Ashington Colliery in 1988, large scale deep mining of coal inthe district ceased. The Thissection describes factors which may presence of suchextensive underground affectground conditions and stability and workings poses twoquestions which should thereforehave important implications for always be asked prior to any development. planningand development. Coal Mining is These are: likelyto be theprincipal cause of potential ground instability in this district and mining 1) "Has the area been undermined?" methodsstabilitythe andproblems 2) If so, "at what depth and by what method? associated withthem are reviewed. MAP 5 indicatesareas which are thought tobe underlain by shallowmining and locates The last question is fundamental because the shaftsand adits know to BGS andBritish depthand style of anymining is directly Coal. Theparticular hazards posed by linkedto the subsequent stability of the shafts and adits are also detailed below. groundsurface. For this reason,ahistory of miningmethods inthe Northumberland coalfield is outlined below. Under Engineering Geology the rocks and superficialdeposits aredescribed in a 3.1.1 History of Mining Methods geotechnicalcontext, and the essentially qualitative descriptions are supplemented by Coal was probably worked in this region by information from adatabase created during theRomans, but the earliest documented theproject. MAP 8 classifies the deposits working is fromthe year 1236 whenthe exposed at surface in engineering terms and monks of Newminster,near Morpeth, were indicatesthe sites of thoseboreholes with grantedminingrightsnear Blyth geotechnicaltestresults. Made ground, (Galloway, 1882). Thefirst workings were depicted on MAP 8, is also the subject of a likely to have been at outcrop, either on the separatemap, MAP 6, wherethe extent of coastal cliffsor in the valleysides. By the disturbedlandscaped or ground is end of 13thcentury coal was being additionallyshown and made ground is extracted from shallow driftsor adits and subdivided on the basis of composition. frombell-pits. The latter consisted of a shaft, usually about 1 m across sunk through theoverlying strata thetocoal at a MAP 7 illustratessitesthe of all maximumdepth of about 12 m. The coal non-confidential boreholes, shafts, adits and was thenworked all around the shaft until trial pits held by BGS and for which further the unsupportedthe roof becameunsafe. informationis available. Slope movement Anotherpit was thensunk adjacent to the may cause foundation problems, therefore firstandthe processrepeated. The areas of steep slopeshave been delineated excavatedarea of coal was roughly circular on Figure 11 and known landslips are shown and no morethan 20 m across. Although in morein detail on MAP 8. Dataon crude, with careful management, the system flooding, actual and potential, was provided recoveredahigh percentage of the seam. by theNorthumbrian Water Authorityand Because of the depth limitation, only narrow this has beensupplemented by information strips close tothe outcrop could bemined fromthe BGS fieldsurvey (Figure 12). andthe potential reserves were accordingly Brief reviews of theeffects of coal mining small. No positiveexamples of bellpits on the local hydrogeology andthe potential have been noted in the district. problems of methane and deoxygenatedair conclude the section. It is of morethan academic interest that almost every major industrial dispute in the miningindustry (including the 1984 strike) has seen a return to these primitive methods

20 Table 3 Former collieries with a take within the district

Colliery Approximate Date workings Grid Reference abandoned of Mine Entrance

Ashington 266 880 1988 Barmoor 217 840 1911 Barrington 265 237 1938 Bates 306 823 1986 Bedlington A 274 830 1971 Bedlington D (or Doctor) 260 822 1968 Bedlington E (or West Sleekburn) 281848 1962 Bedlington F (or Bomarsund) 270 847 1968 Bessie Grey (New) 210 865 1937 Park 232 878 1961 Cambois 303 847 1968 Catchburn 203 831 1921 Choppington A 250 841 1966 Choppington B (or High) 242 848 1966 Choppington North 242 848 ? Clifton 203 827 1899 Clifton West 199 832 1947 Cottingwood West 205 873 1918 Cowpen 306 815 1946 Ewart Hill 246 807 1954 Hartford 269 794 1961 Hepscott 239 838 1924 Horton Grange (or ) 281 813 1962 Howburn 208 868 1962 Isabella (or Cowpen Isabella) 300 807 1966 Lilly 209 814 1926 238 890 1961 Longhirst Drift 233 887 1969 Longhirst Grange 215 881 1901 Mill (or Crofton Mill) 316 811 1969 Morpeth Banks 215 875 ? Morpeth Moor 211 870 1917 Netherton (or Hartley West) 233 819 1974 Netherton Hall 231837 1943 Newbiggin 309 885 1967 Newsham (or New Delaval) 292 802 1955 North Seaton 290 858 1966 Park House 214 861 1931 Pegswood 228 872 1969 Woodhorn 289 884 1981

Note: other small coal workings exist throughout the district Table 4 Opencast coal sites

Site Grid Date Coal seam(s) Coal Reference coaling worked recovered completed Mg (tomes) Active Butterwell 211810 - Victoria to ?Durham Low Main

Cowpen Road 286 814 - Moorland -

Abandoned

Abyssinia I+IIA 250 885 1955 High Main 18 860" and Metal

Acorn Bank + 255 805 1966 HighMain, Metal, 6830 871 Extensions Five-Quarter, Bentinck, Yard

Bebside 278 820 1985 Moorland ? (Furnance Bank)

Bebside 284 808 1970 Ryhope Five- 42 837 (Hathery Lane) Quarter, Ryhope Little

Bedlington 266 824 1983 Moorland 11794 Reclamation Heap

Climbing Tree 226 868 1957 Bensham, Durham Low 140 545 Main, Northumberland Low Main, Plessey, Bottom Plessey

Ewart Hill and 250 812 1954 High Main, Metal, 2 263 083 Ewart Hill Deep Five-Quarter

Fawdon House 217 872 1945 Durham Low Main 31 620

Netherton I+II 230 825 1948 Top Durham Low Main, 166132 Northumberland Low Main

Pegswood Moor 223 871 1945 Bensham, Durham 500" 118 Low Main, Northumberland Low Main

Stepping Stones 269 808 1958 Moorland 349 101 of working withlittle attempt to reinstate excavation has increased to more than shafts or workings afterwards. 100 m. One of the largest opencastsites in Europe is situated at Butterwelltothe In medieval times deeper resources of coal north-east of Morpeth [210 8901. A list of were worked by driving headings from a the opencast sites within the district is given shaft through the coal seams with cross cuts in Table 4. atirregular intervals. Adequate ventilation 3.1.2 Stability Problems caused by Mining was usually the limiting factor to the extent of the workings. This mining style The most serious hazard whichthe early progressively developed regulara pattern methods of working present to a planner or with roadways intersecting at right angles developer is that in most cases they are not and unmined pillars of coal leftsupporting documentedand any plans which do exist the roof - amethod known as pillar and are likely to be inaccurate. stall orbord and pillar. It became the established system of mining in the Althoughthis survey did notencounter NorthumberlandandDurham Coalfield, ancient bell pit workings it cannot be withinitial extraction rates of 40-50% assumed that they do not exist, or that they commonly increased by the practise of have necessarily collapsed andare now removing the pillars on retreating. Most satisfactorilycompacted. It is known from seams mined in thisdistrict have been other areas that bell pitswere commonly worked at some point by the pillar and stall only partlybackfilled and the state of method. Occasionally theearly irregular compaction was not good.If anyare mining is revealed when opencast workings presentthey are likely to occur within the cutinto in shallow seams, (e.g. Cowpen 30m limits shown on MAP 5. Shallow drifts Road, Bebside [286 8151). associated with outcrop workings (including those workedduring strikes) mayalso be Although a mechanized version of pillar and left in poor condition. stall mining is still used today at Ellington Colliery justnorth of thedistrict, by the Shallow pillar andstall workings have been beginning of the 19th century, many identified at a number of locations and are collieries were workinglarger areas of coal pxobably present elsewhere withinthe by theshortwall or panel method. This district.Nearsurface theycan pose system extracted coal from a broad face particular problems. Theydo not collapse withthe roof supported by wooden props, when mining has ceased sinceearth leaving a space which was subsequently pressures, at shallow depthswere not packed withdebris and small coal allowing sufficient. However, the roof becomes the roof to settledown steadily. Extraction weaker with time andsudden failure, rates of up to 80% were achieved andthe particularlythrough loading by new method was sometimes used inconjunction construction, may occur. with, or used to rework, areas of pillar and stall. Site investigations need to be properly designed andexecuted to identifythis type Longwall mining developed fromthis of working as much of the coal is left method and in its mechanized form was the undisturbed in pillars and, if too few last system of mining to beused inthe boreholes aredrilled or if theyare drilled district. Two parallel headings, typically on aregular grid, they may only find the about 200 m apart, are driven from a main pillars and miss the voids. development road. Between these headings the coal was excavated. As theface was Additionally, because packing of workings advancedthe roof behindthe working face with rock was not necessary, and where was allowed to collapse. roof measures have subsided to rest on the seatearthwith slight disturbance, the only In thetwentieth century, the development evidencein borehole cores may be alittle of mechanical earth-movers made powdered coalstained, aon slightly large-scale opencastmining practical. The weathered andperhaps rusty seatearth. It initial sites developed during the early 1940s is, thereforeimportant that inany site were seldom excavated deeperthan 20 m, investigationpotentialthe problems but since thenthe economic limit to associated with pillar and stall workingare

23 allowed andfor comprehensive a geotechnical and mining reportmininggeotechnical and Piggottand Eynon (1978) identifiedthe commissioned. squeeze of floor or roof strata as a common cause of failure of shallowcoal workings. Piggott andEynon (1978) notedthree In such cases, the strength of the coal pillars principalmechanisms of failure of pillar suchis thattheearth pressures are and stall workings:- transferredto the floor or roof strataand theirbearing capacity becomes criticala ' i) collapse of roof bedsspanning adjacent pillars factor. If thepillar is strongenough to carry the load, it will be 'punched' into the ii) pillar- failure roof orfloor measures, particularlywhere low strengthseatearths underlie the coal or iii) squeeze of floor or roof strata whereformer workings are flooded. The lastsituation may become more significant Suddencollapse of the bedsspanning the as minewater levels rise aresult of the stallsis themajor cause of ground as cessation of pumping (see 3.5). instabilityproblems. The voidpropagates upwardsunder the combined influences of Much has beenpublished on subsidence gravity and weathering, until the whole void induced by longwall mining (see Bell et al., becomes choke-filledwith debris, or more 1988). Generallythe amount of subsidence competentbeds are reached. If the void is a function of depth,the width of the reaches thesurface, it forms acrown hole panelmined and the thickness of strata (pitfall).wholeseries A of these removed.Subsidence occurs rapidly after depressionsoccur west of the mining and is usually complete about a year Ashington-EllingtonRoad [260 8861 where after extraction, although a small amount of shallowworkings inthe Ashington Seam residual subsidence may occur over the next havecollapsed. Piggott andEynon (1978) few years.Consequently while this method showedempirically thatthemaximum may cause problemscausemay for existing height of collapse in BritishCoal measures developments it poses few problems for is commonly up to 6 times the height of the subsequent development of the land. mine void but may, exceptionally exceed 10 times theheight. This relationship is also Subsidencecaused by all of thesemining consideredvalid by Garrard and Taylor methodswill usually extend beyond the (1988) although they have reservations about limit of working(the draw zone) and may the bulking theory and regard arching the as be influencedby natural faulting (2.1 2) dominantvoid-arresting mechanism; stating which is often reactivated by mining. that up to 70%of the old workings in their studywere likely to suffer some further 3.1.3 Shallow Mining(MAP 5) collapse if disturbed,(forinstance by additionalloading). However, as Carter Shallow coalworkings shownare on (1984) has noted,'safe-depth' rules are Figure8 and MAP 5 wherean attempt has often broken in real-life situations. beenmade delimitto areas of known, inferredand possiblemining atdepths of It is possible that the deterioration of pillars less than 30 m fromsurface. The areas may take place aftermany years but delineatedare generalized and do not take generallypillar failure is rarein shallow intoaccount subsidence draw zones which coalworking, provided that the original will extendbeyond the limits shown. In pillar geometry was sufficient to support the consideringparticular sites it is essential to roof.Piggott and Eynon (1978) commented consult the originaldocuments (heldby that the pillars left by ancient mining were BritishCoal Mining Records Office, Mine usually muchgreater in cross-section than Service Centre,Tursdale, Co. Durham, was requiredsupportto the over-lying DH65NT) from which much of the strata.However, failure may occurwhere information has beenabstracted. Workings pillars arevery small orhave been robbed knownfrom mine planscan beanticipated at latera date. Pillars may also collapse buttheareas of inferredor possible long aftermining has ceasedwhen piles workingshown on MAP 5 aremuch less associated withmodern construction, create certain. It is important to remember that highly concentrated loads. ancient, unrecorded workings -may occur at

24 shallow depth in any area where a coal thick enough to beworked lies near the surface 3. Presence of gas (see individual 1: 10 000 scale geological Various gases may be foundin standards for detailedinformation on coal unventilated old workings. These include positions). carbon dioxide and nitrogen (blackdamp), 3.1.4 Shafts and adits which may createan oxygen-deficient atmosphere and cause asphyxiation; The sites of shafts and aditsare shown on methane (firedamp), which is explosive MAPS 1, 5, 7 and 10 and also on the ina mixture of 5 - 15940 withair and 1: 10 000 scale geological standards. All finallycarbon monoxide and hydrogen shaftsand adits known to BGS and British sulphide(stinkdamp), both of which are Coal have been plotted but their positions in poisonous even at low concentrations. somecases may be inaccurateand it is not The escape of oxygen-deficientair claimed that all have been traced. during periods lowof atmospheric Particularcare should be taken in those pressure has proved aparticular problem areas wherethe Moorland (or Blackclose) inthe Cramlington and Seaton Delaval seam lies at shallow depth,for example at areas immediately south of the district. and around Blyth and Bedlington and north-east of Bridge. 4. Pollution of water supplies Old shafts provide artificial channels The location and condition of disused shafts allowing water topass from one aquifer clearly affectsthe safety of any proposed to another. If one aquifer becomes development and poses the following polluted, ashaft can act as apath for specific hazards. spreadingthe pollution to otheraquifers 1. Accidental Entry (see section on Effects of Coal Mining on Hydrogeology; 3.5). A fallA down shafta results almost inevitablyin serious injury or death. Much of this section has been drawnfrom Apart from afall, there is danger of National Coal Board publication "The drowning,suffocation or poisoning by Treatment Disusedof Mine Shafts and gas. Inan adit there isalso a danger Adits" (1982); this handbook contains useful from falls of roof strata. informationaboutthe location and treatment of disused shafts and adits and is 2. Movement or collapse of ground commended to planners and developers who The surface near a shaft may subside or may encounter unsuspected old workings. collapse. If the shaft lining has deteriorated,the collapse may not be confined to the diameter of the shaft but may spread to formcrater. a The diameter of the crater is afunction of thedepth to competentstrata and the angle of repose of the incompetent strata that collapses. Collapsesmay also occur beneath competent strata in a shaft; these may not immediately affectthe surface but thebut collapse may reduce the load-bearingcapacity of the ground around the shaft.

Old mine shafts may collapse because of changes in ground water levels, additional surface loadings due to new structures or tipping,vibration from traffic, mining subsidence or blasting. The collapse of one shaft may cause nearby shafts, linked by underground workings, becometo unstable.

26 3.2 ENGINEERING GEOLOGY (MAP 8) Table 6 summarises the geotechnical properties values andtheirvariation, The geological materials of the district have obtained from a simple statistical analysis of been allocated to fiveprincipal groups on the geotechnical database established for the the basis of their predicted behaviour in an project (see Appendix C). Apartfrom engineering context; incertain cases the simple visual checks of scatterplotsand engineering divisions splitor combine histograms, no attempt was made to validate geological units (Table 5). With the individual test results or to take account of exception of laminated silt and clay, MAP 8 the depth or location of samples, so that all (Figure 9) shows thenature of only the are equally 'weighted'. For most samples topmost material likely to be encountered only a few geotechnical tests had been during development or investigation. The carriedout and rarely was a full range of 5 m drift thickness contour is delineated on test results available for particular a the map an indication of the areas in as lithological/geotechnical unitwithin one which some foundationsor trenches for borehole. In mostcases, thedifference services may encounter solid rock; outside between the maximum and minimum values this area, MAPS 3 and 4 (Figures 6 and 7) is large. Theinformation should only be should be consulted foran indication of used,therefore, as a guide when planning a likely drift thickness or rockhead elevation. site investigation and not asa substitute for The geotechnical propertiesand behaviour a sampling and testing programme. of theengineering divisions and their constituent geological unitsare discussed Details of the tests andthe methods of below according to their engineering applying them insite investigations can be geology classification. foundin publications of the British Standards Institution, B.S. 1377 and B.S. 5930. A summary of the tests and their applications is given in Appendix C. Table 5 Engineering Geology Divisions

Description Lithology Geological Formation

ROCKS Sandstone, siltstone, Coal Measures and mudstone, coal Millstone Grit seatearth

SOILS Normally Clays and silts Alluvium consolidated Marine Beach and Tidal Flat cohesive Marine and Estuarine Alluvium Laminated Silt and Clay Overconsolidated Clay Till cohesive Non-cohesive Sand and gravel Blown Sand Alluvium Marine Beach and Tidal Flat Marine and Estuarine Alluvium Glacial Sand and Gravel Fill, made ground Highly variable Made Ground

27

3.2.1 Rock bridge piers are concerned. Chemical tests indicate that no special precautions need be Rock generally has adequate bearing taken against sulphateattack on concrete capacity for domestic and light industrial buried within sandstone. structures using normal foundations. However the weathering process commonly Mudstones and Siltstones range from weak reduces thestrength of a rock and weaker to strong, strength decreasing with material may beencountered where rock increasing weathering. Their clay minerals crops out, or at rockhead where drift covers are stable, but mudstones weather rapidly an old weatheredsurface. Consequently on exposure andexpand on contact with easeof excavation inthe rock generally water, making them liable to heave, so that varies with thedegree of weathering. excavations should be protected as far as is Geological faults,or displacement, within possible against wetting and will usually the solid rocks may have produced broken need support. Explosives are not generally rock orjuxtaposed rocks of varying type required in surface excavations; weathered and strength.Undermining may have mudstones are diggable, but they may need widened jointsin overlying rocks and ripping when fresh. As weathered material loosened blocks, particularly of sandstone, has a lower bearing capacitythan so that they are unstable in excavations or unweathered it may be necessary to place above tunnels and may require special foundations (e.g. footingsor piles) beneath support. the weathered materials. The weathered Few test results are available for the solid zonehas been recordedin boreholes up to rocks in the district. It should be noted that about4 m thick, for completely weathered on weathering the rocks gradually change rock, but the degree of weathering decreases into soils in situ and thatthe summary beneath this depth. Weathering is greater values given in Table 5 include a range of where drift cover is less. Thefew sulphate weathered to unweathered samples. determinationson the materials place them in classes 1and 2 of the BRE classifiction Sandstones fine-from vary to (Building Research Establishment, 1983). coarse-grained. of Some the However, disseminated pyrite may be coarser-grained sandstones aregritty and present withinthe rocks, rapid weathering highly abrasive, othersare quartz-cemented of which leads to ground water of high and extremely hard.Ganister, a variety of acidity(pH<4) in which abundantsulphate sandstone seatearthfound beneath some ions maybe present so thatthe possibility coalsis particularly a tough rock. of attackonburied concrete must be Excavation and tunnelling in sandstones considered. Trenchingin mudstones is generally presents fewsupport problems, generally relatively easy, but tunnelling at with the possible exception of undermined depths of12 mor less presents substantial areas (see above). Near rockhead weathered support problems. A recent useful sandstones will probably be rippable,but discussion of propertiesthe Coalof explosives maybe required to break up Measures mudrocks is given by Taylor unweathered rock to facilitate excavations. (1 988). Thedepth of weathering varies and probably exceeds 6 min places. It can be Seatearth mudstones probablyare the extremely difficultin boreholes to commonest lithology immediately underlying differentiate between basal drift deposits coal seams though locally they may occur containing sand and weathered sandstone unaccompanied by a coal. Theyare bedrock, especially where recovery is strikingly differentfrom the sandstone incomplete. Such differentiation is, seatearths (or ganisters) noted above and however, extremelyimportant as sandstones typically consist of readily-weathered clay commonly weather irregularly to produce an minerals andabundant random internal uneven rockhead surface. Loose sand from polished ("listric") surfaces, which make weathering can be adjacent to virtually them potentialy unstable both in excavations unweathered rock and the different bearing and under load. Disseminated pyrite may capacities of the adjacent materials must be alsobe present and comments made above allowed for foundation in design, concerning the weathering of this mineral in particularlywhere major structures such as mudstones apply here too.

29 SOLID ROCKS t 52 SANDSTONE 1 32( 1 21 ) 14.0 5l ____ 6-500 7.9-1 9.7 :ROCK: 74 26 5 7 7 32 25 "ISToNE AND 2.1 18 24 129(94) 7.1 (10.6) SILTSTONE 99(83) 2(0.14)1.72(0.18) W I 10-480 11.81 -2.4811.47-1.891 16-24 17-35 3-469 0-34

* see AppendixC for explan ation of Number of valuesStandard Deviation of values,classes useddescribeto theresults givenwhere at least 10 valuesof consolidation and sulphate tests. Mean value superscriptafter present.The are class value indicates the number of samples with that value. SULPHATE GRAVEL ItbblMlLl IY DRY DENSITY FuluI tN, Mv CLASS* Mv Mg/m3 Cv CLASS* % % % % %

7.0

4 C I 1 6.2 ‘1 5.5-6.9

2::511 5::9: 5::9: 2::511 16 4 6.4-7.0 109(21) 39 17 67 ;5 I 7.3(0.5)I 161 23 85-143 7-96 4-35 48-80 1-13 6.0-8.8 83 17 16 87 100 1 06(37) 44(2 5) 27(24) 7.1 (0.5) l852l1 9-1 82 5-94 4-95 5.0-8.1 4’33

~~ 3 3 3 2 2 34 51 7 .O 1 l5 13-50 43-55 45 5 41 5 73(25) 20(23) 6.8 1 8-99 1-75 6.5-7.5 9 8 83 19 45- 1 00 2-55 1 3 21 21 5 40 45 26 71 3 1.73(0.08) 14(2) 11 8(8; 1 19(15) 60(28) 1.60-1.91 1 1-1 7 1-32 2-29 2-60 2-98 4 1 13 13 13 63 69 73 3 1.81(0.26) 13(5) 33(35) 57(26) 36-96 1.25-2.08 8-22 1-99 10-99

The values given for geotechnical parameters are the result of an interpretation of data obtained from site investigation reports. Sampling was not done in a statistically valid way and the mean and standarddeviation are thereforenot statistically valid.However, theydo give a useful indication of values and spread of the geotechnical properties. It must beemphasised that many of the lithostatigraphical units are variablelaterally and vertically and that some sands may occur in predominantly clay units and clays may occur in predominantly sand units. 3.2.2 Normally Consolidated Cohesive Soils The grey or grey-brown clay of the Marine and Estuarine alluvium varies from very soft These soils are commonly very soft to soft, to stiff, but is generally firm with medium are highly compressible and are oflow compressibility anda medium to fairly bearing capacity. Even lightweight rapidrate of consolidation. Hydrostatic structures will commonly require special foundationsto spread the load or piles to pressures inthe estuarine alluvium may transferthe load to deeper,stronger fluctuate because of tidalinfluence. Groundwatercontrol for excavations, foundations. The deposits can vary laterally together with shoring are usually required. in composition, leading to possible differential settlement where structures cross 3.2.3 OverconsolidatedCohesive Soils compositional boundaries. Gravel layers withinthem may locally provide better Glacial till (boulder clay) is the only deposit foundation conditions. However, the in this category within the district. It is the thickness of the gravel andnature of the most widespread surface deposit and is the deposits underlying it must be determined. material on which most development has taken place, consequently it has yielded Laminated silt and clay consists of more geotechnical test datathan other blue-grey, brown weathering finely deposits (MAPS 2 and 8, Table 6). Thetill laminated clay, siltand silty clay. It is of usually has a distinct weathered upper layer, soft to stiff consistency with intermediate generally weaker, less dense, more plastic plasticity, low to moderate compressibility and with a higher moisture content than the and medium to fairlyfastrate of underlying unweathered material. This consolidation (owing to the drainage effect weathered layer was identified as a distinct of thesilty laminae). MAP 8 indicates the unitin several site investigation reports, areas in which it may be present within although it was not mapped as aseparate other glacial deposits; these areas are based unit. Its test results have been enteredinto on an interpretation of information derived the geotechnical database under the heading from boreholes andformer exposures. A of 'Superficial Mottled Clay'. It is a maximum known thickness 12of m is red-brownor mottled grey-brownand recorded formerthefrom Foggos orange-brown sandy siltyor clay with Brickworks [250 8351. Laminated clay and pebbles. Thedepth to which the till has silt have a low safe angle of rest and been affected by weathering varies. It is excavations need close support. commonly weathered to 3 or 4 m, adepth within which most normal foundations Peat has not been mapped at surface, but is would be placed and extends to at least 8 m known to be present within alluvial Northumberlandin (Eyles and Sladen, deposits, usually associated with soft grey 1981). organic clays, andbeneath sand dunes (e.g. Locally the undrained shear strength of the atNorth Blyth). Geotechnical data for peat Superficial Mottled Clay may be increased is available for only 3 boreholes within the near the surface where the clays are dry or district. It is essentially highly compressible with very a low bearing capacity. In where secondary effects have led to unusual excavations it may either stand well without compaction. Lower parts can besoft and plastic, particularlywhere in contact with support, or flow and require close boarding. Its propertiesare described indetail in underlying water- bearing strata (e.g. glacial sands and gravels), such was observed to Hobbs (1 986). as the souththe of Morpeth.The reversed strength gradient which thus can be induced Clay-rich alluvium is present along the must be takenfully into account in flanks of the rivers Blyth and Wansbeck and foundation design. It is an especial hazard theirtributaries above the Normal Tidal in open excavations which are reasonably Limitand also occurs commonly peaty as stable where the clays aredry,but flats on the surface of the glacial sand and dangerously unstable where lower parts of gravel. Fromthe few geotechnical data theprofile are wet. Sub-verticaljoints are available, the alluvium is believed to be a a major a source of weakness suchin variable materialwith low bearing capacity situationsand also lead to instabilityon and generally high compressibility. natural slopes, particular in where superficialstony clay overlies plastic

32 laminated clay. supportand "running" conditions are likely, such that below the water table de-watering Unweatheredtill is primarily a stiffgrey may, therefore, needed.be Cuttings stony clay of lowto intermediate plasticity, throughthese deposits require drainage low tomedium compressibility and with measures toremove water from perched mediumto slow rate of consolidation. Thin watertables andrelieve high water lenses of sand,gravel andlaminated, pressures inconfined aquifers (sands and stone-free silt and clay are also present and gravelsoverlain by less permeableclays) to lateralvariation lithologyin leads to avoid heaving or sagging on excavation. variation in bearingcapacity across the deposit. GlacialSand and Gravel occurswidely in the western half of the district (see MAP 2 Water- bearing deposits of granular materials andFigure 5), both largeirregular inthe till areprone to running or piping as spreadswith recorded thicknesses in excess and may cause high inflow of water during of 18 m, and smalleraccumulations or excavation.Laminated orstone-free clay as beds withinthe till. It is commonly layersin thetill may softenrapidly on associated withlaminated silt and clay in wetting leading to poor trafficability on site themajor drift-filled channels. It is a and unstable pit or trench walls. heterogeneousdeposit, but consists Generallytill provides satisfactory support predominantly of loose tomedium dense, for lightweightstructures withnormal fine-tomedium-grained brown sand with foundation design, although lateral variation subordinatesandyand, silt generally inbearing capacity on site-scalea may well-sorted,sand andgravel layers.No cause differentialsettlements. The possible specialprecautions against sulphate attack presence within the till of large boulders, or on buried concrete are indicated by the test even of largebodies of detachedbedrock, data. should also beconsidered. The failure to recognisesuch occurrences may lead toa No geotechnical data are available for blown misinterpretation of siteinvestigation data sand fromwithin the district. The sand is andsubsequent problems executingin generally fine-graineduniformlyand foundationdesign. Sulphate determinations graded.It is expectedbeto of loose indicatethat generally no special relative density. precautions are required to prevent sulphate attackon buried concrete, the majority of Marine Beach and Tidal FlatDeposits the samplesfalling in Class 1 of theBRE comprisethe surface deposits fringing the classification (Building Researchclassification(Building coast and extending up the rivers Wansbeck, Establishment, 1983). However,shouldit Blyth andSleekburn. The beach deposits be notedthat over 10Yo of determinations aremainly of sandin the bays andshingle wereBRE Class 2, andfour others in aroundandimmediately south of the Classes 3 and 4. Thesehigher values headlands. Thetidal flat deposits and the probablyresult from localgroundwater mouths of therivers consist of a thin layer contamination (see madeanddisturbed of greysilt and clay. Standard penetration ground below), butemphasise the need for test data for the sands indicate that they are carefulinvestigation determineto the generally medium dense to dense. geological andgeotechnical variability in threedimensions thescaleat of any The alluvium along theflanks of theriver particular site prior to development. Wansbeck betweenBothal and the Normal Tidal Limit consists mainly of non-cohesive 3.2.4 Non-Cohesive Soils sandand gravel. Inthe , marine and estuarine alluvium consists of up Thesegranular materials are composed of variableamounts of sandand gravel and to 11.6 m of gravel and medium dense sand. Thefew standard penetration testdata commonly contain clayey orsilty layers. available for thesedeposits show them to Where denseor very dense, the deposits providean adequate bearing capacity for range from very loose to dense. most domesticor light industrial purposes 3.2.5 Made and Disturbed Ground using normalfoundations. Where loose they havelower bearing capacities. Excavations Materialsin this category exhibit a wide evendensein material, usuallyrequire

33 range of geotechnical properties summarised fill must be expected thein years in Table 6. MAP 8 (Figure 9) indicates immediately following restoration,the their disposition separatedinto two main position formerand depth of the types: excavations is well documented and because of thiscan be takeninto account prior to (i) Fill placed inquarries, pits andother any development. Engineering problems are excavations, likely to be mainly dueto settlement; differential settlement may be a problem at Made Ground, artificial deposits which (ii) the margins of asite should development have been spread over thenatural land straddle the fill and undisturbed ground. surface.The recognition of such areas is importantanin engineering context, because of the variable foundation Miscellaneous Waste conditions which may exist within adjacent tipped materials and theircontrast with This category includes domestic, those of bordering natural deposits. agricultural, building, industrialand quarry waste. All waste disposal sites known to Additionally, the possible presence of voids, NorthumberlandCounty Council are shown methane-generatingand hazardous on MAP 6 and a list of the waste materials components and the potential of leachate to which may have been placed in them is contaminate areas outside the spread of given (Table 7).Some sites may not have made ground may have consequences on been located (two possible sites occur near health or lead to chemical attack on buried Willow Bridge [253 8331 andStakeford concreteand structures. Careful attention Bridge [273 8571). Domestic, agricultural should be given to site investigation in order and industrialrefuse is likely to be highly to takeinto account the problems outlined variable in composition and geotechnical above when areas of made ground are properties. Problems of includedwithin the boundaries of any methane-production, voids, differential proposed developments. settlement, toxic leachate or toxic solids, maybe anticipatedin association withthis MAP 6 (Figure 10) should be consulted for material. further information on thenature and composition of areas of made ground. The Restored and partially restored old clay pits following description of engineering are common inthe Choppington area and properties uses the categories illustrated on small disused and infilled sandstone quarries that map. arescattered throughout the district. Where known approximatethe limit of the (i) Worked-out opencast coal-seam areas. excavations is shown on MAP 6. Commonly thereare no clear surfaceindications of (ii) Miscellaneous waste. theirtrue extent (or in a few areas their (iii) Colliery waste. presence) andin most instances their location and limits have been derivedfrom (iv) Landscaped and disturbed ground. old topographic or geological maps. The latter however, do not provide any Worked-out Opencast Coal-Seam Areas indication of the nature of the fill material. These areas occur chiefly to the south-west Large parts of the town of Blyth are of Bedlington andnorth-east of Morpeth underlain by made ground. Inthe town (Table 4). Two of them, Butterwell centrea sizeable tidalcreek has been (currently active) and Acorn Bank (restored infilledand adjacent to theriver large in 1966), are extremely large inarea (137 quantities of ships’ ballast (chiefly flint and 342 hectares respectively) whilst the gravel fromthe Thames estuary) were remainderare generally less than tipped at the height of the coal t rade. 40 hectares. All the sites now restored and Immediately to thenorth of the town parts landscaped have been filled with the of both banks of theestuary have been overburden which was originally removed reclaimed and softer estuarine deposits may fromthem, the composition of the.fill is, occur below thefill which must be taken therefore, likely tobe relatively uniform. into account when designing site - Although settlementand compaction of the

35 Table 7 Made Ground

~~~ ~ ~~~~~~~~ ~ A: Miscellaneous waste: known landfill sites

Site Grid Licence or Classes Name Reference Resolution of waste Status Number

Alcan (UK) Ltd 299 896 1 12 Closed Spital House Farm 299 878 2 6,ll Closed Quarry Woods 210 866 4 6,ll Closed Barrington 263 383 11 6,9,11 Active Pegswood Colliery 231878 19 6 Closed North Blyth 312 828 22 6 Closed Links Quarry, 308 866 24 6,9,11 Closed Newbiggin Alcan (UK) Ash 308 888 25 9 Closed Lagoons, Stage 2 Alcan (UK) Pot 304 890 32 12,14 Active Linings Site 2 Alcan (UK) Ash 307 892 38 9 Active Lagoons, Stage 3 Links Quarry (East) 309 867 45 6 Closed Choppington Old 248 834 51 1,233, Active Brickfields 4,6,10 Bothal Barns Farm 246 869 56 6 Active Ellington Road 260 893 R22 1,29697 Active Stakeford 278 861 R23 1,637, Closed 10,11,12 Bomarsund 267 847 R28 1,637, Closed 10,11,12 Waste Classification

1. Domesticandcommercial waste (including 9. Pulverised fuel ash. street sweepings, litter, market refuse and gullycontents butnot wasts falling 10. Non-hazardous industrial waste - into the following categories) - untreated potentially combustible. 2. Domestic andcommercial waste (as above) 11. Non-hazardous industrial waste - inert - pulverised/composted and non-flammable. 3. Domesticand commercial waste (as above)- 12. Difficult waste. This will generally be baled. notifiable waste or waste contaminated with hazardous quantities or 4. Sewage sludge and pail closet contents. concentrations of notifiable waste, but also includes certain categories of waste 5. Incinerator residues. which may not be notifiable but which would cause difficulties in certain 6. Waste from construction or demolition. circumstances. 7. Medical,surgicalveterinary and waste. 13. Water treatment sludge. Old cars, vehicles and trailers. andvehicles cars, 8. Old 14. Farm wastes.

Compiled frominformation provided by NorthumberlandCounty Council updated May 1988.

\ B: Miscellaneous waste: fill unknown

Locality Grid Reference Excavation (if any)

Bebside 278 822 - Bedlington 272 835 clay pits Bedlington 2648 8260 - Bedlington 2805 8235 Blyth 3044 8170 clay pit Blyth 3075 8230 sandstone quarry Blyth 3076 8200 sandstone quarry Blyth 315 817 Blyth 318 806 clay pit Blyth 3188 8050 clay pit Blyth 3184 8032 clay pit Bomarsund 276 847 - Bothal Park 237 875 clay pit Cambois 305 843 Cambois 305 837 Cambois 2960 8345 Cambois 298 834 Cambois 303 832 - Choppington 254 834 clay pit Cowpen 297 818 clay pit Coney Garth 2515 8730 clay pit Fawdon House 2176 8833 sandstone quarry Morpeth 2076 8644 - Morpeth 2112 8658 sandstone quarry North Blyth 310 829 North Blyth 317 820 Pegswood 2181 8786 sandstone quarry Pegswood 2193 8768 sandstone quarry Pegswood 2156 8779 - Woodhorn 2995 8906 sandstone quarry Stobhillgate 2019 8502 clay pit C: Colliery Spoil Grid Locality Reference Condition

Ashington/Woodhorn Colleries 890270 Partially restored Barrington 265 836 Partially restored

Bates Pit, Blyth 306 823 Unrestored

-,. .. Bedlington A 829 270 Restored

Bedlington Doctor 260 823 Restored

Bomarsund 847 267 Restored

Cambois 847 303 Restored

Choppington840 250 Restored

Coney Garth 877 250 Restored

Cowpen South Pit, Blyth 815 306 Restored

Ellington Road, Ashington 894 261 Restored

H orton Grange Horton 281 813 Partially restored

Hepscott 837 223 Restored

Isabella Pit, Blyth 807 300 Partially restored

Longhirst 891 238 Partially restored

Mill Pit, Blyth 316 808 Restored

Newsham 802 292 Restored

/’ Netherton 827 238 Restored Netherton 827 229 Partially restored

Netherton 822 232 Unrestored

Newbiggin 884 311 Restored

Newbiggin 880 306 Restored

North Seaton 857 290 Restored

Pegswood 232 879 232 Pegswood Restored

P egswood 212 872 212 Pegswood Partially restored

West Sleekburn 847 263 Restored investigations prior to development and in geotechnical properties, deposited in a the design of the development itself. controlled mannerand compacted to a specified density.

Colliery Waste Untilrecent years conspicuous mounds of colliery spoil were a common feature of the local landscape; almost all have now been restored (Table 7).Whilst some arestill distinct artificial mounds, the reclamation of others has involved the redistribution of the spoil over large areas and dressing the surfacewith soil and sub-soil. In such areas, e.g. aroundThird House Farm [280 8901, the thickness of the spoil is highly variable andthe limits of the artificial ground difficult to fix.

Colliery waste is largely composed of rock fragments whose propertiesare well established (Taylor, 1978), but there may be substantialquantities of carbonaceous and pyritous material which may cause spontaneous combustion andthe production of toxic gases. Inthe past most colliery heaps inthe area were subject to periodic self ignitionand some burned for considerable periods. theDuring reclamation of the heaps it has been the practice to identify hot spots by drilling and special procedures have been adopted (exposure, cooling and compaction) to ensure thatthe possibility of any future ignition is remote. However problems caused by swelling of the mudstone (shale) fragments causing ground heave must be addressed foundation in design if development takes place. High sulphate levelsmay require sulphate-resisting mixes to be used in buried concrete.

Landscaped and Disturbed Ground This category includes the extensive veneer of man-made groundwithin urban areas, landscaped recreationand industrial areas, major road andrail lines, coal stockpiles and the restored areas on theperimeter of opencast excavations. In general the cover of landscaped ordisturbed ground in the built-up areas is patchy and usually less than 2 m thick. It is virtually impossible to accurately determinethedistribution of such deposits withouta highly detailed investigation. Fill placed for road orrail lines or as part of associated engineering projects will usually of be known

39 3.3SLOPE STEEPNESS AND STABILITY

Figure 11 illustratesthe slopesof the district classified by the degree of steepness. Thefigure was produced digitally by computer using 1:25 000 scale Ordnance Survey contourinformation. Because the contoursdo not show detailed variations in slope angle ordirection, a small scale generalized portrayal of slope steepness was judgedappropriate. From Figure 11 it can be appreciatedthat the terrain is relatively subduedand that steep slopes occur only along the incised river valleys and on the coast. Slope steepness should not be viewed in isolation as a guide to slope stability , but considered inconjunction with rock/soil composition and attitude and hydrogeology.

Landslips and rockfalls occur naturally in areas where the land surface has been oversteepened orundercut by rivers or the sea. In this district examples were noted on the sides of the WansbeckValley at Parkhouse [215 8601, Sheepwash [2518561 and North Seaton [297 8541 and on the coast between Cambois [306 8401 and Newbiggin [3 10 8701 (see MAP 8 and Figures 9 and 1 1) where active marine erosion is taking place and rock fallsand slips occur thein sandstone and low boulder clay cliffs. Coastal defence measures, includingthe emplacement of rock cubes and concrete sea walls, have been adoptedat both Cambois andNorth Blyth. Landslips mayalso occur where theground has been artificially oversteepened, incuttings, or by removing material from thefoot of a slope or by loading slopes during embankment construction.

40

3.4 FLOODING

Figure 12, Flooding, was compiled from dataprovided by theNorthumbrian Water Authoritybut, additionally, indicates the location of areas of waterlogged or flooded groundnoted during the BGS fieldsurvey and thought to be due in the main to recent mining subsidence.

TheNorthumbrian Water Authority have subdividedtheir information on flooding into four categories.

1. Areas which have been flooded. 2. Areas which could potentially flood. 3. Areas subject to tidal flooding. 4. Areas now protected by floodbanks which were once potentially liable to flood. Areas inthe first category include the floodplain of the Wansbeck at Morpeth, Bothal and Sheepwash, small tracts along Woodhorn, Hepscott and Sleek burnsand isolated areas of low-lying ground at Bedlington and Blyth. Included thein second category areparts of the Woodhorn Burn and Blyth Valley. The areas identified as subject to tidal flooding arethe Wansbeck and Blyth river courses up to the Normal TideLimit and a small part of Newbiggin town. The construction of an amenity weir at North Seatonhas reduced the prospect of tidal flooding inthe lower Wansbeck Valley and, similarly, flood protection measures at Morpeth and Blyth have removed thethreat of flooding in those areas.

42

3.5 THE EFFECTS OF COAL MINING reservoirs for gases(see 3.6). If,in places, ON HYDROGEOLOGY groundwater levels recover sufficientlythere are possible implications both for the release Coal mining has caused two significant of these gases theand geotechnical modifications theto local hydrogeology. properties of currentlyunsaturated rocks Thefirst change is inthe development of and deposits. vertical connections between water-bearing units by fracturingdue to subsidence and by shaftssunk forthe purpose of mining. Lateral movement of groundwater has also been greatlyfacilitated by the connection between workings instigated by a policy of passing mine drainage water from one mine to another towards the coast where it was finallypumped to the sea. As a result, any contaminantentering an old working, whetheran open pit or underground, may disperse widely and rapidly. Leachate from landfill waste disposal sites is one example of asource of such contaminants. While this appears to pose a potential problem, the volume of groundwater in storage within the old mine workings is very large, and the consequent dilution of thecontaminant is considered by Northumbrian Water Authority to be reduced to undetectable levels. However, Aldous et al. (1986) concluded that problems may occur if drainage is free and transmission rapidand moreover, thatit is relatively difficult to predicttheprobable effects wasteof disposal particulargroundwater on discharges. Certainly if water abstraction boreholes were to be constructed near the source of such contamination dilution would be insufficient.

The second effect of coal mining on the local hydrogeology is inthe lowering of groundwater levels. Dewatering operations in thein coal mines caused a general depression of groundwater head often amounting to many metres. Someof the dewatering took place through adits between adjacent mines. The result was to establish base drainage levels at a lower altitude than thenatural level. With the cessation of large-scale mining activityand therefore pumping, groundwater levels have risen (and may still be rising) although over most of thedistrict it is unlikely that they will attainthe levels of pre-mining days. There are, at present therefore, considerable voids (comprising old workings as well as joints, fissures and pores withinthe rock) present beneath theground surface and above the present water table which may act as

44 3.6 NATURAL DISCHARGE OF METHANE AND DEOXYGENATED AIR

A potentialA hazard which should be considered inthis district is the possibility of a build-up naturallyof occurring methaneand/or oxygen-deficient air, in excavations,basements, tunnels and other underground space. The up-to-date informationcontained in MAPS 1, 4 and 5 may usedbe evaluateto geological structure,thickness of coverand presence of oldworkings and shafts should the problem arise.

Stratacontaining hydrocarbons such ascoal tendto give off methaneas well as other gases. Normaloxidation processes also tend to generatecarbon dioxide and, during climaticperiods when atmospheric pressure is high,air may be drawn down into pore spaces or voidssuch as old workings and becomede-oxygenated. In places these gases becomemay trapped beneath impermeablecover (such as till) and may escapewhere this is thin,or breached (e.g. by shafts,fissures/faults, foundations, cellars),especially duringperiods of low atmospheric pressure.

Where there is nocontinuous, impermeable cover the discharge of gases still takes place. However,unless concentrated someby means, thedischarge is overa wide area, dilutionwith the air is rapid,and no particularrisk is present.Nonetheless, the construction of boreholes,sewers andwater pipelinescan form pathsthrough which gases canreadily pass andin whichthey may collect. Even housecellars, shallow wells and similar excavations can pose some risk. Adequateprecautions to ventilate such works and to disperse the gases are essential. Local problems in the Cramlington area and thedisastrous explosion at Abbeystead in Lancashire in 1983 (HMFI, 1985) where methane was ignitedin subsurface a chamberconsequentwith fatalities, emphasises these dangers.

45 4.2 SANDSTONE 4. MINERAL AND WATER RESOURCES (MAP 9) Sandstone was formerly quarried on a small scale manyat localities throughoutthe district (see MAP 9, Figure 13 and Table 8). 4.0 INTRODUCTION It was chiefly used as a local building stone, Nine different mineralproducts have been butone quarry at Hartford [241 8001 is extractedfrom thedistrict. They are reportedtohave supplied stone for the describedbriefly below and the sites of repair of the Houses of Parliament and two extractionand,where appropriate, the London Bridges. A thicksandstone above location of thedeposits are delineated on theKirkby’s Marine Band - theNorth MAP 9 (Figure 13). Coal was, and is, by Seaton or Woodhorn Sandstone - hasbeen far the most important mineral in the region particularlywidely worked, for grindstones but within this particular district brick clay (shippedmostly to Norway and Sweden), and sandstone were also significant. A brief andfor facings for buildings. Considerable discussion of groundwater resources is resources of sandstoneremain of varying includedin this section, but pollution and hueand grain-size, both inthe thicker theeffects of miningareconsidered persistentthelikeunits Woodhorn elsewhere (3.5). Sandstone,relativelytheandin thin discontinuous beds.

4.1 COAL 4.3 MUDSTONEAND SILTSTONE Deep-mined coal is no longer worked in the Theserock-types (often described as shale) districtBritishby Coal, the last pit, arecommon throughout the CoalMeasures Ashington,closed in 1988 but small a sequenceandresources aresubstantial. shallow private drift mine is still operated at Shale hasbeenquarried for use in ShadfenPark [222 8571. Substantial brick-making elsewhere in Northumberland, quantities of coal remain at depth but these but no suchquarries have been identified resourcesare currently regarded by British withinthe district. The shale (or ’brat’) Coaluneconomicas and furtherdeep roof of the Northumberland Low Main was miningappears unlikely. Opencast mining, formerly mined and extensively employed in introducedin the 19403, is stillactive both brick-makingAshingtonboth at and on asmall and largescale and,at the time Pegswood collieries, latterthe was of writing,further largeexploration producing 40 000 bricksper week in 1935 programmes are underway. (Fowler, 1936). Leavingplanningasideany and/or 4.4 IRONSTONE environmentalcontraints,are there considerablecoal resources in much of the Sideritic ironstone is commonly developed as areawith potential for opencast extraction. nodules or layersabove a number of coal The generallocation of theseresources can seams. Althoughthey have been worked in be deducedfrom study of the maps in this the past these deposits contain too little iron report, the 1:10,000 geologicalmaps and the andare too thinor discontinuous to be Part I1 Report. consideredeconomically viable today. At least twoformer ironstone mines are However,potentialthe for opencast recordedfrom the Netherton area of the extractionisdependent, notonly on the district [233 8231 wherebeds above the location of coalseams, but also onthe NorthumberlandLow Main Coalwere number,thickness and quality of individual worked.These mines supplied ore to the seams inany given area, the thickness of Bedlington Ironand Engine Works which overburden and the extent to which the coal was situated near Furnace Bridge beside the seams have already been removed by erosion River Blyth [278 8211. This works,now or by undergroundmining, or disturbed by demolished,played seminala role in the faulting. nationaland international development of A full description of coal seam distribution, earlyrailroads andlocomotives and is thickness and mining is given in the Part I1 closely associatedwith the names sf Report. Stephenson Longridge.and Curiously, although its original situation is said to be

46

4.9 GLACIAL CLAYS based on the presence ofwood, water, coal andiron nearby, the part of the coal Small disused pits andbrickfields which measures sequence exposed near the works formerly worked till or laminated clay have is not noted for significantquantities of been identified at many localities across the ironstone. district (see MAP 9 and Table 9) and it is probable that several other smaller workings 4.5 SEATEARTH have not been located. Clay pitsare most prevalent on theflanks of the Sleek Burn Thefireclays below the High Main and between Scotland Gate [250 8401 andRed Five-Quarter coals were formerly taken at Row [273 8381 and records indicatebrick Ashington Colliery for brick-making. The and tile making taking place early as the Seggar clay below the Northumberland Low as 18th century.The pits in thisarea appear Main Coal is also reported to have been to have worked lenses ("seams") of relatively mined locally Nethertonthein area stone-free (and probably laminated) clay [230 8271. within the more complex glacial sequence of theburied valley (see2.2). Although many 4.6 IGNEOUS ROCK of these pits closed because theirparticular seam of clay was exhausted, it is likely that Several dykes are recorded in mine considerable resources still exist elsewhere workings theindistrict but they are in the buried valley. generally narrow (usually less than 5 m) and with one exception,the West Sleekburn Dyke, discontinous both vertically and 4.10 GROUNDWATER laterally. Small quarries south of Bedlington [2648151 and on the east bank of the river Under natural conditions, the Coal Measures Wansbeck[2127 86121 probably worked a in this district form a multi-layered aquifer. valley side exposure of tholeiitic dolerite Groundwater is stored andin, flows from the Netherton-South Blyth Dyke. through,fissures in the sandstone beds and in the coals. Groundwater movement within 4.7 METALLIFEROUS MINERALS the enclosing mudstones and shales is slow, amounting only to seepage. The larger Mineral veins of pyrite, galena, sphalerite, sandstone units can potentially support calcite, ankeritebaryteand occur useful well yields, butfaulting tends to throughoutthe district but they rarely as divide these unitsinto discrete areal blocks exceed 2 mm inwidth they are of only to which natural replenishment may be academic interest. However, there is an slow. Consequently, yields which initially exception, at Choppington 'B' or High Pit maybe good tend to diminish with time where, "lead orein considerable quantity as the aquifer storage is depleted.Natural was foundin a fault (and was) worked for discharge is to the valleys of the river Blyth some time in 1948" (Martin). andthe Wansbeck where the boulder clay cover is absent. 4.8 SAND AND GRAVEL Sand and gravel occurs within blown sand, Recorded yields of boreholes constructed glacial andriver terrace deposits and into the Coal Measures vary widely, usually alluvium. The thickest and most extensive ranging from less than 70 cubic metres per development of sand and gravel is within day (m3/d) to more than 2000 m3/d. A few the glacial deposits flankingthe river boreholes have yielded only negligible Wansbeck inthe westof thearea, where it amounts. The large yields fromare has been worked in several small pits. boreholes of more than 100 mdepth, but Boreholes have also shown sand and gravel drawdowns tend to increase withdepth so to be present beneath varying thicknesses of thatthe specific capacity (yield divided by till overburden elsewhere in the district, but drawdown) actually decreases with depth. there is little or no available information on The number of abstraction boreholes in the its gradequality.or Blown sand was district toois small to permita useful worked locally in a small pit at Spital Point, analysis of performance (see MAP 9), but it Newbiggin [309 8681. would appearthat a borehole of100 m depth would have a specific capacity of the order of 35% less than one of 50 metres.

48 Thequality of groundwaterin undisturbed Coal Measures strata is rather variable, with the total dissolved solids generally less than 1000 milligrammes per litre (mg/l) inthe westof thedistrict, and rising towards 20 000 mg/lnear the coast. Thechloride ion concentration follows a similar pattern with less than 50 mg/l (as Cl) inthe west and more than 5 000 mg/l in the east. The sulphate ion concentration follows arather differentpattern, rising from less than 250 mg/l (as SO4) inthe western outcrop to more than 500 mg/l centrally,and then tending to fall towards the coast. Total hardness (as CaC03) also appears to increase eastwards to values above 1000 mg/l in parallel withthe increase in sulphate concentration.

Groundwater pumped from coal mines is generally more mineralised. At the Bates Colliery No. 3 shaft [3108231, the meanof the total hardness between 1978 and 1984 of the pumped water was over 6000 mg/l of which only some 300 mg/l was carbonate hardness (information provided by the Northumbrian Water Authority) . Although sulphate was not monitored over this period, it probably accounts for the high non-carbonate hardness.

Discontinuous lenses of sand and gravel withinthe boulder clay, andrather more extensive granular deposits on its surface, form small andunimportant aquifers which may, inthe past, have been exploited by a few small wells as formerly on the northern margin of thedistrict at Broomhill Farm [215 9021. No data on quality is available.

For details of the relationship between mineworkings, pollution and groundwater the section of thereport on the effects of coal mining on hydrogeology should be consulted (3.5).

49 Table 8 Former sandstone quarries

Locality GridLocality Lithology' Sandstone name Reference or position

Ashington 26 15 8646 "Brown, micaceous". Woodhorn/North Seaton Sandstonb Bebside Wood 2662 8082 "Massive, yellow". Below Moorland Coal Bedlington 26388096 Fine with medium- Below Moorland Coal grained yellow-brown. Blyth 82303075 - Below Moorland Coal Blyth 82003076 - Below Moorland Coal Fawdon House 2176 8827 "grey and brown, Above Bensham Coal micaceous, bedded and shaley". Hartford 80012408 - Above Durham Low Main Coal Humford Mill 2666 8058 Fine-medium-grained, Below Moorland Coal yellow-brown. Humford Mill 2678 8049 - Below Moorland Coal

Morpeth 2100 8666 - Above Three-quarter Coal Morpeth 2112 8658 - Above Three-quarter Coal Netherton 2332 8196 "Massive bedded, coarse- Above Bensham Coal grained" Newbiggin 3 143 8943 "Red and grey bedded" Woodhorn Sandstone Newbiggin 3165 8937 "Red and greyish white, Woodhorn Sandstone micaceous in partings". "Medium grain to fine grain". North Seaton 30738680 "fine brown" North Seaton Sandstone North Seaton 308866 "Medium grained, North Seaton Sandstone sparingly micaceous". North Seaton 29268555 "Massive". North Seaton Sandstone Pegswood 87862181 "Grey and greenish grey". Above Bedham Coal Pegswood 21938768 "Micaceous sandstone". Above Bensham Coal

Woodhorn 29748918 "Brownish yellow, Woodhorn Sandstone reddish, very micaceous in partings". Woodhorn 29958906 "Brown, reddish in Woodhorn Sandstone places, sparingly micaecous fine-grained". Stakeford 86302604 Massive, medium-grained, Above Burradon Coal vellow-brown. Note: 1. Descriptions in quotes = former exposures 2. Several small sandstone quarriesare also recorded south of FrontStreet, Bedlington. Table 9 Former clay pits worked for brick and tile making

Site Grid Reference Site Grid Reference

Barrington 263 840 Choppington 253 849

Barrington 2630 8375 Choppington 249 835

Barrington 2636 8358 Choppington 254 834

Bedlington 272 835 Choppington 2575 8340

Bedlington 2700 8340 Coney Garth 2515 8730

Blyth 3044 8170 Cowpen 897 818

Blyth 318 806 Hepscott 2223 8370

Blyth 3188 8050 Hepscott 2217 8358

Blyth 3184 8032 Hepscott Burn 235 837

Bothal Park 237 875 Howard House 2394 8270

Choppington 2510 8435 Morpeth 2076 8644

Choppington 2530 8424 Newbiggin 3107 8914

Choppington 252 841 Stobhillgate 2019 8502 "5.3 FILL AND ARTIFICIAL DEPOSITS 5. SUMMARY OF GEOLOGICAL (MADE GROUND) FACTORS FOR CONSIDERATION IN LAND-USE PLANNING These deposits are extensive and have a (MAP 10) variable composition, rate of consolidation and thickness. Many restored opencast coal MAP 10 is agraphic summary - it brings sites exist butthey are well documented; together specific elements fromindividual smaller disused andinfilled clay pits and thematic maps which are considered to have sandstone quarries (which may have been a significanta bearing . on planning and used as 'unofficial tips')may produce development. Such a compilation allows the foundation problems if not identifiedprior identification of areas where difficulties to construction.The possibility of may arise and, conversely, where problems hazardous or methane-generating are less likely. However, it is importantto components withinfill should always be realise that only selected aspects have been considered. abstracted andthat difficult geotechnical conditions may exist elsewhere. MAP 10 5.4 LANDSLIPS should be used therefore as aguide to the A small number of landslips have been relevant single theme maps which should be noted. They occur chiefly where thick drift consulted for contextand detail. The need sediments are undercut or oversteepened by for properlyfor designed and executed the River Wansbeck, but have also been site-speci f ic investigations cannotbe identified on the coast. overstated. 5.5 SAND AND GRAVEL RESOURCES In the following section each of the elements which may constrain development Sand and gravel commonly occurs within and which appear on MAP 10 (and Figure variable thicknesses of fluvialand marine 14) are briefly summarised. sediments but it is the glacial deposits, which are widespread inthe westof the 5.1SHALLOW MINING district, which may have potential as a source of aggregate. It is recommended that Almost all of districtthe has been in order to avoid sterilization an assessment undermined for coal but, whereas of thetrue extent and quality of any subsidence related to longwall deep mining resource should be made prior to extensive is probably complete, shallow workings, development. present in many areas, are a potential cause of land instability. Areas where shallow 5.6WATER RESOURCES mining is known from plans or for which there is otherevidence are delineated on The four active wells and two licensed MAP 10, which alsoshows the location of surface water abstraction points are located 240 shaftsand adits known to exist. Where on MAP 10. Large sandstone unitsin the mining is suspected acareful study of the Coal Measures arethe principal natural detailed mine plans and shaft atlases held by aquifersbut coal mining has caused British Coal should always be made. significantmodification to the hydrogeological regime and its affects 5.2SOFT GROUND should alwaysbe considered when evaluating potential leachate movement from Soft ground is associated mainly with recent landfill sites. alluvial andmarine sediments of the river valleys, estuariesand coast. The variable 5.7 NOTE sands, silts, clays and peats of which these Leaving aside any planning and/or deposits consist possess relatively weak environmentalconstraints, are there geotechnical properties. Additionally beds considerable coal resources in much of the of laminated silt and clay occur withinthe area with potential for opencast extraction. glacial sequence thein Choppington - The general location of these resources can Stakeford - Cambois areaand may provide be deduced from study of the maps in this lower bearing capacities than overlying report, the 1: 10,000 geological maps and the deposits. Part 11 Report.

52

and the CoalTrade. London.(First Series). SELECTED BIBLIOGRAPHY 1904. Annals of Coal Mining ALDOUS, P.J., SMART, P.L. and BLACK, and the CoalTrade. London. (Second J.A. 1986. Groundwatermanagement Series). problems in abandoned coal-mined aquifers: a case study of the Forest of Dean, England. GARRARD, G.F.G. andTAYLOR, R.K. Quarterly Journal of Engineering Geology, 1988. Collapse mechanisms of shallow Vol. 19, 375 - 388. coal-mineworkings fieldfrom measurements. In: Engineering Geology of ANON, 1982. Thetreatment of disused Underground Movements. 23rdAnnual mineshafts and adits. National Coal Board Conference of the Engineering Group of the Mining Department. Geological Society. (Eds.BELL, F.G., CULSHAW,M.G., CRIPPS, J.C., LOVELL, BELL, F.G., CRIPPS, J.C.,CULSHAW, M.A.) (London: GeologicalSociety M.G., LOVELL, M.A.1988. Areview of EngineeringGroup Special Publication groundmovements dueto civil and mining 5, 181-192. engineeringoperations. In Engineering NO Geology of Underground Movements. 23rd HER MAJESTY'S FACTORY AnnualConference of theEngineering INSPECTORATE, 1985. The Abbeystead Group of the Geological Society. (Eds. Explosion: Areport on the investigation by BELL, F.G., CULSHAW, M.G. and theHealth and Safety Executive into the CRIPPS, J.C., LOVELL, M.A.) (London: explosion on23 May 1984 atthe valve GeologicalSociety Engineering Geology house of the Lune/Wyre Transfer Scheme at SpecialPublication. No. 5. Abbeystead. HMSO. BORINGS AND SINKINGS, 1878-1910. HOBBS,N.B. 1986. Miremorphology and Council of the North of England Institute of the properties and behaviour of some British Mining and MechanicalEngineers. An andforeign peats. Quarterly Journal of account of the strata of Northumberland and Engineering Geology, Vol. 19, 7-80. Durham asproved by borings and sinkings. 7 volumes in 4 books. Newcastle upon JACKSON, I., LAWRENCE, D.J.D. and Tyne. FROST, D.V. 1985. Geological notes and local details for Sheet NZ27. Cramlington, B UILDING RESEARCH BUILDING Killingworthand Wide Open ESTABLISHMENT, 1983. Concrete in (SE Northumberland). OpenFile Report, sulphate - bearing soils andgroundwater. British Geological Survey. Digest 250 H.M.S.O., London. LAND, D.H.1974. Geology of the CARTER, P.G. 1984. Case Histories which TynemouthDistrict. Memoirs of the breakthe rules. In: Mineworkings 84. Geological Survey of Great Britain Sheet 15. Proceedings of the InternationalConference on Construction in areas of abandoned LAWRENCE, D.J.D. andJACKSON, I. mineworkings. FORDE,(Eds. M.C., 1986. Geology of thePonteland-Morpeth TOPPING, B.H.V. and WHITTINGTON, district. ResearchReport of theBritish H.W.). EngineeringTechnics Press, 20-29. Geological Survey. 1990. Geologyand EYLES, N. and SLADEN, J.A. 1981. land-use planning: Morpeth - Bedlington - Stratigraphyand geotechnical properties of Ashington.Part 11: Geology British w eathered lodgement till in tilllodgementweathered GeologicalSurveyTechnical Report Northumberland,England. Quarterly WA/90/19. Journal of Engineering Geology, Vol. 14, 129-141. MARTIN, E.S.B.1974. Bedlington Iron FOWLER, A. 1936. The geology of the andEngine Works (1736-1867). A New countryaround Rothbury, and History. NorthernHist0r.y Booklets. No52. Ashington. Memoirs the Geological of MARTIN, S.B. unknown.dates Survey of Great Britain Sheets 9 and 10. Bedlingtonshire Village History Series, GALLOWAY, R.L. 1882. Ahistory of coal "Bedlington", West Sleekburn", "Bomarsund mining in Great Britain, London. andStakeford", "Choppington Township", "Sleekburn", "Netherton". 1898. Annals of Coal Mining

54 GLOSSARY ORCHARD, R. J. 1964. Partial extraction and subsidence. Transactions of the ADIT Horizontal passage fromthe surface Institute of MiningEngineering, Vol.123, into a mine. 417-427. AQUIFER Bodyof rock sedimentor sufficiently permeable to conduct PIGGOTT, R.J. and EYNON, P. 1978. groundwater and yield significant quantities Ground movements arising fromthe of water to wells and springs. presence of shallow abandoned mine workings. In: Large ground movements and BED Basic unit of rock or sediment. structures. Proceedings of the Conference CANNEL Usually impure coal with glassy heldat the University of Wales Institute of fracture. Science and Technology andScience (Ed. GEDDES, J.D.), Cardiff 1977. Pentech CARBONACEOUS Rock orsediment rich Press, London, 749-780. in carbon. TAYLOR, B.J.,BURGESS, I.C., LAND, COMPETENT Able to withstand force. D.H.,MILLS, D.A.C., SMITH, D.B. and CYCLOTHEM Series of beds deposited in a WARREN, P.T.1971. Northern England. cycle. BritishRegional Geology (4th Edition) HMSO. DETAIC Laid down in a delta. TAYLOR, R.K. 1968. Site investigations DRAWDOWN Lowering of water level in a in coalfields: the problem of shallow mine well due to water withdrawal. workings. Quarterly Journal of Engineering DRIFT Unconsolidated sediments deposited Geology, Vol 1, 115-133. during the Quaternary. 1978. Properties of Mining GEOLOGICAL STANDARD 1: 10 000 scale Waste with respect to foundations. In: map of field geologist’s interpretation of all Foundation Engineering in Difficult Ground available data for a particular area intended (Ed. BELL, F.G.) (Newnes-Bullerworths for public examination. London) 175-203. HYDROGEOLOGY Groundwater geology. 1988.Coal Measures mudrocks: composition, classification and weathering HYDROSTATIC PRESSURE Pressure processes. Quarterly Journal of Engineering exerted by water at any given pointin a Geology, Vol 21, 85 - 89. body of water at rest. INCISED Describes riveror stream which has cut down into the land surface. INTERFLUVIAL Describes higher ground between streams or rivers. LEACHATE Solution produced by water passing through a substance. LITHOLOGY Physical character of a rock. OVERBURDEN Material overlying a mineral deposit. PYRITOUS Containing iron-sulphides. RANK Degree of metamorphism in coal;is the basis of coal classification. RESOURCE Totalamount of potentially workable mineral. ROCKHEAD Bedrock surface. SIDERITIC Containing ferrous carbonate. TILL Sediment deposited by a glacier; commonly a stiff stony clay.

55 became established at 2 chains to the inch and subsequently 1:2 500. They may be APPENDIX A: DATASOURCES large old linen documents or modern 1. Field survey plastic plans covering aground area of 2 km2. Coal mines prior to 1850 are only Undertakenat the 1:lO scale by a 000 patchily recorded and even after 1872, geologist foot.on It involves the when the keeping of accurate plans examination, recording and interpretation became mandatory, plans frequently only of surface morphology and naturaland showed the extent of the working and are man-made exposures. It attempts to oftendifficult to register withsurface delimit solid and drift deposits and topography. After 1947 the plans are checks for the existence ofold shafts, considered to be fully reliable and adits, underground workings and comprehensive (however these areoften abandonedand active pits and quarries. plans of the lower, deeper seams and Theamount of detailidentifiable is' therefore those which the heavily dependentonthe degree of planner/developer is least concerned). exposure naturetheand ,the of Almost all coal mine plans are held by landforms. In a largely drift covered the Mines Record Office of British Coal; arealike the current district there is a list of those plans withinthe survey oftenlittle evidence of the solid rocks. area is given in the Geology report (Part Mapping of thenatural drift deposits is 11). made difficult by the extensive built-up and man-made areas. 4. British OpencastCoal Executive prospecting boreholes 2. Deep-mined coal boreholesand shaft records These datefrom the early 1940's to the present day and were drilledin selected These provide a log of strata encountered prospecting areas, usually at a close down a borehole orshaft. They may spacing. They are largely openhole and startgroundat level fromor an many of the older boreholes are very underground position. The method of poorly logged; however, a small number drillingthe boreholes maybe either of diamond (cored) boreholes were put open-hole or cored. The earliest down to control thestratigraphy. Early borehole for which BGS holds a record sites were not usually deep (x20 m) and was drilledin 1731 and boreholes were thereforethe prospecting boreholes were still being drilledup until the closure of also shallow and oftendifficult to the Past colliery in 1988.Boreholes and correlate. With time progressively deeper shaftsare lodged inthe BGS archive as seams were exploited and boreholes in text butare conventionally converted to excessof 50 mdrilled. Prospecting by graphicform at a standard scale (1:480) British Coal nowis a much more forcorrelation. 233 shafts and 1 1 01 structured exercise butthe majority of deep-mined coal exploration boreholes holes are still not cored and are only are held for this district. The records are logged geophysically. Private licensed of variable qualityand the absence or operators have a varied approach to inadequacy of certain details, for example exploration and, because of their surface level, location, strata record, is commercial sensitivity, the boreholes are common. Theyare however the main rarely deposited with BGS. All the source of informationabout lithological British Coal Opencast Executive borehole variation across the district. data are confidential. 3. Deep-mined coal abandonment plans 5. Opencast coal completion plans These area record of underground Following completion of coaling at a working inindividual coal seams and, British Coal opencast sitea plan is ideally, will show theextent, date and routinely produced at 1:2 500 scale depth of the working, coal thicknesses, showing limit of working, surveyed faulting, presence of water and the coal-base contours, faulting, typical location of shafts and drifts transecting sections and coal overburdenand the seam. Initially their scale varied but thickness at specified points. They also

56 indicate the tonnage extracted from each contains ad hoc desk interpretations of seam and dates of working and mining and borehole information. restoration. These documents represent Although olderthe surveys were the results of a ''measured survey" and are undertakenwithout the benefit of much thereforea good datum if seam of the borehole, opencast and mining correlation is known, although inevitably data available to thecurrent revision a some of theearly plans are lacking in significant factor in their favour was the vital detail. Completion plans from lack of urban development and private sites tend .to be much less landscaping. Theytherefore had much comprehensive. more naturalexposure andthis is reflectedinthe amount of observed 6. Site investigationboreholes, trial pits detailon their fieldslips. They did not, and reports unfortunately,delimit areas of made In the past boreholes were only rarely put ground. down to investigate ground conditions prior to construction; the exceptions were 8. Aerial photographs structureslike bridge foundations or BGS holds no coverage for this region harbour works. Today almost every but was able to borrow stereogfaphically development, from minor residential to paired photographs takenin 197 1 for, major civil, is preceded by some form of NorthumberlandCounty Council and a site survey, that is, trial pit, or boreholes second set flown in 198 1 and held by the or probe. BGS holds records of 1 454 Department of Environment.the boreholes andtrial pits drilled for this Although the 1971 series were atan purpose inthe district and undoubtedly appropriate scale (approximately many more exist. They are usually only 1:lO 560) their usefulness was reduced by shallow explorations, with an average their age. The 1981 photographs were, depth ofless than 10m; they therefore unfortunately, at too small a scale tend to be restricted to the drift sequence (1:25 000) to allow accurate identification and use a method appropriate to those or delineation of salient features. deposits, that is shell and auger rig or mechanical excavator. Initially poor 9. Water authoritydata recording of the sediments has improved TheNorthumbrian Water Authority greatly but there is an engineering rather provided informationon flooding and thana geological bias.Samples are water abstraction and quality. usually taken for subsequent laboratory Additionally discussions took place testing and the results of this together between theAuthority and BGS on the with aninterpretive section andthe subject of mine water and leachate borehole results make up the conventional dilution. geotechnical report. 10. Local authority data 7. Existing.~ geological maps NorthumberlandCounty Council Waste There have been two previous full Disposal section provided information on surveys of district,the firstthe the location of known landfill sites and undertaken between 1860 and 1880 and a composition of deposited waste. The second between 1929 and 1950. These Land Reclamation Section of the County produced field slips and published Council gave access to data on the extent six-inch geological 'maps on the of reclamation schemes and the procedure Northumberland Old Meridian County for restoring colliery waste. Generaland Series and New Meridian County Series site specific discussions have taken place respectively. In additiona largely between theCounty Soils Engineerand desk-based revision of thesouth-eastern BGS, and his department has also part of thedistrict took place between provided a large quantity of site 1957-1961. The working maps (mostly investigation Informationdata. on mining slips) for this revision were based mineral within extraction onNew Meridian County Series but the Northumberland was obtained from the results were published on National Grid Mineral Planning section. The highways six-inch sheets. The BGS archive also departments of Blyth Valley and

57 Wansbeck district councils have provided copies of relevant site investigation reports. (Seealso aerial photographs.)

11. Geological reports and journals Thebibliography contains a selection of those documents consulted duringthe study,they range from memoirs describingthe geology of the region to academic papers concerning specific subjects.

58 APPENDIXB: BOREHOLETHE fromthe database and mostof thefigures DATABASE in the accompanying geological report (Part 11) were directly generated by computer. BGS holds an extensive collection of paper records which describestratathe List of fields in the Newcastle borehole encounteredsinkingduringthe of BGS database boreholes, mineshaftsand trial pits, and in sections measured by BGS geologists(see a) Index table Appendix A). These records represent a O.S.1: 10000 sheet Reliability major source of factual data, in some parts number* the only source, for geological investigations andinterpretations within the coalfield. Accession number Start point Thepaper borehole record is considered to and suffix' be theauthoritative primary record and National grid reference Inclination there has been no attempt to replicate it on and accuracy thecomputer. A computerised database for theproject area was seen as a wayof Borehole name Drilling date utilising the data held in the paper archive Comments Geologist to maximum effect by allowing rapidand flexibleretrieval of a wide range of Other borehole number Drilling method information. Surf ace level Borehole diameter and accuracy All borehole and shaft records in the project area have been coded following aformat Confidentiality Consulting engineer which has been developed within BGS. Purpose Drilling contractor This work has resulted in the establishment of a simple system by which borehole Originator Water strike information can be assigned to two tables of data, on the basis of the following criteria: b) Lithological table O.S.1: 10,000 sheet Stratigraphy a) All data which describes afeature of number* the borehole itself, for example, its name, its location by National gridreference, Accession number Reliability thedate it was drilled, height above (or and suffix' below) sea level. Depth Workings b) All information relating to samples Lithology Comments taken from point depths below the surface for that borehole. Base of bed A complete list of fieldsin each of these * "the primary key index" tables within the borehole database is given below.

Thedata is currently held inan ORACLE relational database management system running on a VAX 6410 computer at BGS Edinburgh.It can be interrogated by menu or specifically by using aquery language (SQL). It may be used as an index to available records orfor detailed geological analysis. Retrieveddata be may manipulated and displayed using a number of statistical graphicand application packages andit is possible to automatically producegraphic vertical sections, scatter plots, contour maps and three-dimensional diagrams. Several elements within the thematic maps were produced by retrievals

59 APPENDIX C: THE GEBTECHNICAL ANON, 1981. BritishStandard code of DATABASE practice for siteinvestigation, BS 5930. British Standards Institution, London. The classification of the geological formationsinto groups orunits of similar The Standard penetration test (SPT) is a engineering properties was carried out using dynamic test carried out at intervals during geotechnical dataextracted fromsite the drilling of a borehole, widely used to investigation reports on sites within the area give an indication of the relative density of of theproject. Data was abstracted, coded granular soils (very loose to very dense), onto a specially designed form and entered and the consistency of cohesive soils (very into an ORACLE relational database soft to hard). Correlations have also been management system maintained on a made between SPT and the bearing capacity VAX 6410 computer in BGS Edinburgh. of a soil. Geotechnical data were obtained for over Density of a soil, that is the mass per unit 14 000 individual tests [a single Standard volume, maybe measured in various ways. Penetration Test (SBT) counting as one test] The total or bulk density is the massof the from 913 boreholes. The location of each entire soil element (solids water)divided test was identified by both the Primary key + by the volume of theentire element. The index (see Appendix B)of the borehole dry density is the mass of dry solids divided from which it came and the depth of the by the volume of theentire soil element. tested sample in that borehole, thus enabling Soil density measurements maybe used to cross-referencing with all other assess various earth loads such soil mass, stratigraphical, lithological and location data as overburden pressure, surcharge pressure and held in the computerised borehole database. The sites of non-confidential boreholes with earth pressure on retaining walls. geotechnical test samples are shown on MAP The moisture content of a soil sample is 8. defined as the ratio of the weight of water The results of the following geotechnical in the sample to the weight of solids, tests and measurements (laboratory and in normally expressed as a percentage. It is a situ) were abstracted and enteredinto the basic soil propertyand influences soil database: behaviour with regard to compaction, plasticity, consolidation and shearstrength 1. Standard penetration test (SPT). characteristics. As moisture is removed Bulk density. 2. from a fine-grained soil it passes through a 3. Dry density. series of states, that is liquid, plastic, 4. Moisture content. semi-solid and solid. the moisture contents Liquid limit. 5. of a soil at the points where it passes from Plastic limit. 6. one state to the next are known 7. Plasticity Index. as 'consistency limits'. 8. Triaxial test (drained and undrained). The plasticlimit (PL) is the minimum 9. Consolidation. moisture contentat which the soil can be 10. Compaction. rolled into a thread 3 mm diameter without Particle size analysis (PSA). 11. breaking up. 12. California bearing ratio (CBR). 13. pH. The Liquid Limit (LL) is the minimum 14. Sulphate content. moisture content at which the soil flows 15. Rock quality designation (RQD). underits own weight. The range of A brief description of the tests and their moisture content over which the soil is applications is given below. The following plastic is known as the plasticity index (PI), British Standards Institution publications such that PI = LL - PL. should be consulted for further information: The factors controlling the behaviour of the ANON, 1975. Methods of test for soils for soil with regard to consistency are: the civil engineering purposes, BS 1377. British nature of the clay minerals present, their Standards Insititution, London. relative proportions, and the- amountand

60 proportions of silt, fine clay and organic 1979. Soil Mechanics (S.I. Version). material. A soil maybe classified in terms Wiley, New York. of its plastic behaviour by plotting plasticity index against liquidlimit on standarda The assignment to a class is mainly based on plasticity (or Casagrande) chart.The the mid-range values obtainedduring consistency charts also give an indication of progressive testing. soil strength and compressibility. Coefficient of volume compressibility Thetriaxial compression test is the most (Mv) Class widely used test for determiningthe shear m2/MN strength of cohesive soils, and a number of > 1.5 5 Very High different methods maybe used depending on theapplication of the results. The test 0.3 - 1.5 4 High maybe carriedout with the sample either 0.1 - 0.3 3 Medium drainedor undrained and thetype of test 0.05 - 0.1 2 Low will depend upon the site conditions and < 0.01 1 Very Low type of engineering works being undertaken.

Graphicalinterpretation of the results < 0.01 1 enables theshear strength of the soil tobe 0.1 - 1 2 determinedin terms of its cohesive and 1 - 10 3 frictional components: undrained (apparent) 10 - 100 4 cohesion, C,and angle of shearing resistance > 100 5 (internal friction), U. Consolidation test results areimportant for The vane test is used for soft materials that foundation design and calculating the likely settlements that will take place duringand wouldbe difficult to sample andprepare for otherstrength tests. The test enables afterconstruction. The test results also theundrained shear strength of the soil to enable the planning of phased construction be calculated and the residual shear strength stages to allow full consolidation settlement to be measured. Theundisturbed and (dissipation of pore pressure) to take place remoulded strengths of the soil will give a prior to successive load stages. measure of its sensitivity. The compaction test determinesthe If saturated cohesive soil is subjected to an 'optimum'moisture content at which a soil increase in loading the pressure of the water maybe compacted to its maximum dry in the pore spaces will increase by the same density. The drydensity of the compacted soil is plotted against its moisture content amount as theapplied stress. The water will therefore tend to flow towards areas of and the moisture content at which maximum compacted density maybe achieved is read lower pressure at arate controlled by the fromthe curve. The results of the soil permeability. The removal of water compaction test are usedto determinethe causes a decrease in volume of the soil, a optimum moisture conditions at which to process known consolidation. The as place a given soil general or embankment coefficientof volume compressibility Mv as fill. (m2/MN), is a measure of the amount of volume decrease that will take place fora The California Bearing Ratio test is an given increase in stress. The coefficient of empirical test carried out in the laboratory, consolidation, Cv (m2/year) is a measure of or in thefield,inor which compares the the rateat which the volume change will resistance a soil to penetration by a take place for a given increase in stress. of standard plunger to the resistance to The results of consolidation tests give Mv penetration shown by astandard crushed Cv atanumber of increasing loads. To stone: enable this range of values to be used in the database the ranges areconverted to classes CBR = Measured force using the tables which have been taken 'Standard Force' from: HEAD, K.H., 1982. Manual of Soil The CBR value of recompacted soil is very laboratorytesting. Pentach Press London sensitive to variations in moisture content and LAMBE, T.W. and WHITMAN,R.V.,

61 * and dry density.The results of the CBR Part of theappropriate table is reproduced test are used to assess the suitability of soils below, the document should be consulted for use as base, sub-base andsub-grade in for further information. road construction. A llocation to sulphateAllocation to class in Particle size distribution used is for concentrations of sulphate expressed as SO3 classifying soil in engineering terms. - Particle size distribution curves will give an Concentrations of sulphates indication of soil behaviour with regard to expressed as SO3 permeability, susceptibility to frost heave or in soil in groundwater liquefaction and will give some indication of strength properties. Particle size analysis Class Total SO3 SO3 in 2.1 g/1 does not, however, indicatestructure. For (%I water: soil example a sandy clay and a laminated sand extract and clay which may behave very differently 811 in situ, may show similar particle size 1 <0.2 <1 <0.3 distribution in bulk test sample. .o 2 0.2 to 0.5 1.01.90.3 to to 1.2 The pH of soil or groundwater is important when designing concretestructures below 3 0.5 to 1.O 1.9 to 3.1 1.2 to 2.5 ground surface.Ordinary Portland cement t is not recommended in situtions with a pH 4 1.0 to 2.0 3.1 to 5.6 2.5 to below 6, high alumina cement can beused 5.0 down to pH4 and supersulphated cement 5 >2 >5.6 ~5.0 has been used to pH 3.5. Acidic groundwaters can also cause corrosion in Rock qualitydesignation (RQD) was buried iron pipes. introduced to give anindication of rock qualityrelationin to thedegree of It is also important that the sulphate content fracturingfrom drill cores. It is defined of groundwaterand soil is known as as a sum of thecore sticks in excessof 100 ordinary Portland cement deteriorates in the mm in length expressed a percentage of presence of sulphate. Building Research as the total length of core drilled. RQD has Establishment Digest No. (1983)250 been used with uniaxial compressive discusses the factors responsible for sulphate strength to give indicationan of attackon concrete below ground level, and excavatibility,and one inputfor the recommends what can be done, by suitable as classification of rock masses to assist in the selection of cementtype and concrete design of tunnel support systems. quality, to resist attack by naturally occurring sulphates. For further information see: DEERE, D. K., 1964. Technical description of rock cores for engineering purposes. Rock Mechanics and Engineering Geology, 1, 1, 17-22.

62 MORPETH RD CO CON::.T MORPETH RD [ LNG10N C:P

59QOOOm 590000m

BRITISH GEOLOGICAL SURVEY / DEPARTMENT OF THE ENVIRONMENT

THEMATIC GEOLOGICAL MAPPING

Outer Carrs MORPETH - BEDLINGTON - ASHINGTON t' NZ 28/38

MAP 7 BOREHOLE AND SHAFT SITES

Scale 1 :25 000 ·1 NEWBIGGIN-By--rHE-SEA KEY LIST OF BRITISH COAL OPENCAST (UD) I PROSPECTING AREAS ." o Borehole terminated wIthin drift BGS 1 10000 SHEET BRITISH COAL BGS 1 10000 SHEET BRITISH COAL REFERENCE NUMBER SITE NAME REFERENCE NUMBER SITE NAME

Borehole proving sohd rock NZ 28 NW!l East Shield HIli I NZ 28 SW! , Netherton • , ButtelWell 14 Netherton II 3 Fawdon House 18 Netherton III 4 Underground borehole PegSlNOod Moor 1A Poland 44 Pegswood I 2B Warsaw 4B Pegswood II Ewart Hili Dee~nclJdes 5 Abvsslnla I o Trial Pit terminated Within drift Bedlington " ." ." 54 AbySSInia II Hartford Road 56 AbySSinia IIA Ewart Hili North ." ." ." 50 Abyssin a liB Ewart HIli South ." Pit or mine shaft, abandoned 50 AbYSSInia III 4 Red House 6 Climbing Tree 5 Howald House Includes J Sheepwash Meadow Dale Adlt or mine mouth. shOWing direction of entry 8 Jubilee SA Howard mdudes 9 longhlrst tane Howard Row 10 Watch House Howard House E~l Adlt or mine mouth, abandoned, shOWing direction of entry 11 Stonyflat 6 Frallt:ls North Choppmgton J The Lodg~ 13" South lodge 8 Diamond HIli ApproXimate limit of area prospected by British Coal Opencast 14 I..onghlrst I 9 Netherton LV ·...... hnghust II a 14A 10 Clifton Row z ...... Executive (Information from these areas has been used In the []B...... 1.·.·.·. 148 longitlfSt III :'i ...... · .. '" com pilat on of the geological map but details of the boreholes ~ · ...... 140 Longltirst IV 11 Hazelton W are confidential) The number refers to the list of opencast sites M 140 longhnst V Clifton Lane >: 15 Mmpetb I "13 Field House " 154 Morpeth II ~a ONLY NON· CONFIDENTIAL BOREHOLES ARE SHOWN 158 Morpeth III NZ 28 SEI Acom BanI:. z 16 Bothal I 2 Hathery tane DETAILS OF BOREHOLES EXCEPT THOSE WHICH ARE CONFIDENTIAL. MAY I 164 BOlhal1l 3 Bebs de BE CONSULTED ON APPLICATION TO THE OFFICER IN·CHARGE BRITISH 17 Cabin HIli 4 Humford ." GEOLOGICAL SURVEY. WINOSOR COURT. WINDSOR TERRACE. NEWCASTLE· ." 18 East Shield Hill II 5 StePPing Stones ." ~" UPON·TYNE NEZ 4HB 19 Bothal Bum Includes 6 Foggos Longhlrst II Wh 1st efforts have been made to trace the sites of shafts and edits It IS not claimed AbYSSInia III ·NZ 18 SE/ 2 Duddo HIli Bothal II 4 that all have been located Catch Burn 5 Glororum For Information on the exact pOSitIOn of mine shafts and adlts, application should NZ 28 NE/ Third House Includes be made to British Coal Woodhmn II *NZ27 NW!12 Church Where boreholes and shafts are very closely spaced some may have been omitted Lemoor ." for clarity Woodhom I • Sites registered on adjacent sheets

." Scale ." o 2 3 ." kilometres

LIMITATIONS This map provides only general indications of ground conditions and must not be relied upon as a source of detailed informati'on ." about specific areas, or as a substitute for site investigations or NW ground surveys. Users must satisfy themselves. by seeking appropriate professional advice and carrying out ground surveys r-----NZZ8--~~~ and site investigations if necessary, that ground conditions are suitable for any particular land-use or development. SW

ThiS map gives an mterpretatlon of data available to May 1 989. Based on a 1 10 000 geological survey by I Jackson and D J D Lawrence, ThiS map should be read ic conjunction With the report. Geology 1986·89 and land-use plannmg· Morpeth-Bedlington-Ashmgton.Parts 1 and D.H.Land, D J Fettes, (BGS) and H Mallett, (DOE) Programme Managers. 2 by I.Jackson and D J D.Lawrence F G.Larmlnie. OBE. Director British GeologIcal Survey

o U Se.,o~ Se" L Rocks ~ I X I

• GolfCou ... ." 28 29 35 CASTLE WARD RD S-ANN NGTON CP BL Y fH BORO ""01\ST Topographic information © Crown COPYright 1982 Drawn by K A.Arbon BGS Keyworth

Geological information © NERC 1989