BUCKHILL COLLIERY SPOIL TIP DERWENT FOREST, BROUGHTON MOOR INSPECTION REPORT 2009/10 GC20549/G1/02 Issue: Rev. A, June 2010 Undertaken For: Allerdale Borough Council Cumbria County Council NWDA Inspection of Buckhill Colliery Spoil Tip Derwent Forest, Broughton Moor O.S.G.R. 305400E, 531900N DOCUMENT VERIFICATION Report Reference: GC20549/G2/02 Issue: Rev. A Date: 15/VI/10 Prepared by: S.J.J.Ferley BSc. MSc. CEng. MICE FGS Principal Geotechnical Engineer (For and on behalf of Capita Symonds Ltd.) Checked by: M.W.Penny BEng FGS Senior Geotechnical Engineer (For and on behalf of Capita Symonds Ltd.) Approved by: M.Briggs BSc, CEng, MICE Project Manager (For and on behalf of Capita Symonds Ltd.) Revision History Revision Date Description Prepared Checked Approved 0 31/III/10 SJJF MWP MB A 15/VI/10 Amendment to update §4.2.8 SJJF MWP MB This document has been prepared by Capita Symonds Limited within the terms of the Contract with the Client to whom this document is addressed. Capita Symonds Limited disclaims any responsibility to the Client and others in respect of matters outside the scope of the said contract. No person other than the Client and their professional advisors shall rely on it in any respect and no duty of care shall be owed to any such third party by Capita Symonds Limited. This document is of UK origin and is © Capita Symonds Limited. The contents of this document shall not in whole or in part be stored in any retrieval system nor be reproduced or transmitted in any form by photocopying or any optical, electronic, mechanical or other means, without the prior written permission of the Managing Director, Capita Symonds Limited, 1 Proctor Street, London WC1V 6DW. Capita Symonds, Kingmoor Business Park, Carlisle, Cumbria. CA6 4SJ Derwent Forest Three Year Holding Programme Cumbria County Council Buckhill Colliery Spoil Tip Inspection Report CONTENTS ............................................................................................................................... PAGE 1.0 INTRODUCTION .................................................................................................................. 1 1.1 BACKGROUND ...................................................................................................................... 1 1.2 PREVIOUS INVESTIGATIONS ............................................................................................. 1 2.0 SITE DESCRIPTION ............................................................................................................ 2 2.1 GENERAL ................................................................................................................................ 2 2.2 GEOLOGY ............................................................................................................................... 2 2.3 MINING HISTORY ................................................................................................................. 2 3.0 INSPECTION RESULTS ...................................................................................................... 3 3.1 DESK BASED RESEARCH .................................................................................................... 3 3.2 SITE OBSERVATIONS .......................................................................................................... 4 3.3 LABORATORY TEST RESULTS .......................................................................................... 4 4.0 ENGINEERING ASSESSMENT AND RECOMMENDATIONS .................................... 5 4.1 TIP STABILITY ....................................................................................................................... 5 4.2 CONCLUSIONS AND RECOMMENDATIONS ................................................................... 5 APPENDICES APPENDIX A: MAPS AND PLANS A/01 Site Location A/02 Layout Plan of Spoil tip APPENDIX B: LABORATORY TEST RESULTS APPENDIX C: PHOTOGRAPHS APPENDIX D: SOURCES OF INFORMATION D/01 Published Information D/02 General Sources of Information D/03 Ground Investigation Reports D/04 Computer Programs D/05 Standards, Statutes and Guidance on Statutes CAPITA SYMONDS Report GC20549/G1/02 Carlisle i Rev. A: 15/VI/10 Derwent Forest Three Year Holding Programme Cumbria County Council Buckhill Colliery Spoil Tip Inspection Report 1.0 INTRODUCTION 1.1 BACKGROUND 1.1.1 At the request of Allerdale Borough Council work was carried out on behalf of Allerdale Borough Council, Cumbria County Council and the Northwest Regional Development Agency, (The Clients) to inspect the spoil tip at the former Buckhill Colliery and assess the current condition. The tip is located in a large area of former MOD land near Broughton Moor, Cumbria, O.S. grid reference (NY) 305735E, 531945N. 1.1.2 The inspection regime required as part of the commission involves repeat visits annually for a total of three years. The subject of the current report is the second visit undertaken, in March 2010. 1.1.3 Existing desk-based information was researched as part of the study. This information is referenced in the relevant sections of the report, and a list of sources of information is included in Appendix C. 1.1.4 As part of the study site visits were undertaken between 6th and 13th January 2009 and 15th to 18th March 2010 to inspect the spoil tip and its surroundings, and to confirm the topography of site. 1.1.5 The comments given in this report and the opinions expressed assume that the site conditions do not vary outwith the extents revealed by this investigation. There may be, however, conditions within the site, particularly in relation to moisture content changes and weathering, which have not been disclosed by the investigation and consequently have not been considered in this report. Capita Symonds accepts no liability for the completeness or accuracy of third party records. 1.1.6 This document has been prepared by Capita Symonds Limited within the terms of the Contract with the Clients to whom this document is addressed. Capita Symonds Limited disclaims any responsibility to the Clients and others in respect of matters outside the scope of the said contract. No person other than the Clients, their professional advisors, and Beneficiaries under the Deed of Warranty shall rely on it in any respect and no duty of care shall be owed to any such third party by Capita Symonds Limited. 1.2 PREVIOUS INVESTIGATIONS 1.2.1 Reference was made to the Coal Authority, but no information regarding the spoil tip was located within their archives. 1.2.2 Capita Symonds have carried out investigations at the site in the past, including the determination of strength parameters for the spoil material. Results from this investigation are included in Appendix B. CAPITA SYMONDS Report GC20549/G1/02 Carlisle 1 Rev. A: 15/VI/10 Derwent Forest Three Year Holding Programme Cumbria County Council Buckhill Colliery Spoil Tip Inspection Report 2.0 SITE DESCRIPTION 2.1 GENERAL 2.1.1 The site is located near to Broughton Moor in West Cumbria at O.S.G.R. (NY) 305735E, 531945N. The site location is shown on Figure A/01. 2.1.2 The area is mixed in character, generally thickly wooded with conifer plantations in the Centre and West of the site, with rough gorse thickets to the North, and open grazing land to the South and East. Much of the site has been used for munitions storage from the late 1930’s when the Admiralty developed the facility until closure of the depot in the early 1990’s, and many storage magazines still remain, although in varying states of dereliction. The majority of the area in all some 300ha, including the former Buckhill Colliery, is ring fenced by concrete post and wire mesh fencing. 2.2 GEOLOGY 2.2.1 The superficial geology beneath the Made Ground of the spoil tip is indicated on the 1:50,000 and 1:10,000 scale maps published by the Geological Survey to consist of Glacial Till (Boulder Clay) of Devensian age. The Glacial Till is essentially composed of a heterogeneous unsorted mixture of lithology ranging from cobble and gravel down to a matrix of relatively impermeable boulder clay with isolated lenses of more sandy or gravelly material. The overall thickness of the Glacial Till varies significantly across the site in a complex manner, and the results of previous ground investigations indicate a superficial thickness varying from a few metres to up to thirty metres. Drift is generally thinner towards the North East of the site, but significant post-glacial erosion is evidenced by the deeply incised gills crossing the site, where it may be conjectured that the drift cover is thinner at the base of these valleys. The presence of buried pre-glacial stream channels where thicker drift occurs cannot be discounted. 2.2.2 The geological map shows that the site lies on solid geology of the Coal Measures, part of the Carboniferous. The Coal Measures are formed from superimposed cyclothems of shale, siltstone, coal and sandstone. The area is traversed by several intersecting major fault sets, leading to complexities in interpreting the precise correlation of cyclothems between adjacent faulted blocks. The fault zones between adjacent blocks will also cause significant disruption due to jointed and locally shattered zones. In addition, over the area of the site the cyclothem horizons may vary significantly, with individual units lensing out. It is known that local washouts or “nips” occur in coal seams in the area. 2.3 MINING HISTORY 2.3.1 Coal mining has historically been undertaken in the area by shallow methods (“bell pits”) and deeper