ç's'<13 ENGIIÍEERING GEOLOGICåI, FÀCTORS ÀFFECTING SLOPE SÎÀBILIfY IN SOFT BROÍIN COÀI, DEPOSIÎS - A SOUTH ÀUSTRÀI,IÀIÜ E¡(ÀMPT,E (voLrrME 1) BY ANDREW GEORGE I(REMOR B.App.Sc., APP Geoloçry. (S.A.I.T) Grad,. Dip. CoaI Geology. (Newcastle) t992 DEPÀRTMENT OF GEOLOGY ÀND GEOPHYSICS UNIVERSITY OF ADELÀIDE Awor't]¡'tC ir-)lí-l'-; THIS THESIS IS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY STATETTEIIT OF ORIGIIIÀI,ITY This thesis contains no material which has been accepted for the award or any other degree or diploma in any university and, to the best of my knowled.ge and. belief , it contains no material- previously published or wri,tten by another person' except where due reference is made in the text. Andrew Kremor. I TÄBLE OF CONTSNTS I LIST OF FIGT]RES VI LIST OF TÀBLES XII ÀPPEIIDICES - VOLI]IÍE 2 XIII ÂCKNOIVLEDGEMEITTS xIv ÀBSTRÀCT XV Pacre No. 1.0 INTRODUCTION 1 1.1 Nature of engÍ.neeri-ng geological 2 aspects of soft brown coal nining areas I.2 The Lochiel Coal Deposit - Àn example 4 of a soft brown coal dePosit L.2.I Previous investigations 6 2.O GEOLOGICAI, SETÎINGS OF SOFT BROÍ|N COÀÉ I DEPOSITS - CLÀSSIFICÀTION OF TIIE S1 VIIICENT BASIIÚ 2.I Geotectonic and' d'epositionâI settings I of soft brown coal d'ePosits 2.2 Geotectonic setting of the Lochiel 10 CoaI DePosit 2.2.I Structure of the northern 11 part of the St Vincent Basin 2.2.2 Igneous activitY 16 2.2.3 Geotectonic controls and 18 Basin formation 2.2.4 SummarY 20 2.3 Depositional characteristics of coal 20 de¡rcsits on nidPlate continental margins 2.3.L EustacY and sedimentarY 2t sequences 2.3.2 SedimentarY environments 23 2.4 Palaeogeographical sett'ing of the 26 northern St Vincent Basin 2.4.L Sources of sediment 26 IT 2.4.2 Cainozoic hiatuses 28 2.4.3 Palaeoclimate 30 2.5 Stratigraphic success ion 30 2.5.L Tertiary - St. Vincent Basin 32 2.5.2 Tertiary Pirie Basin 37 2.5.3 Quaternary 38 2.6 Geotectonic and eustatic model for the 39 stratigraphic sequence of the northern St Vincent basin 2.7 Summary 43 3 . O IDENÎIFICÀTIOIT OF EIÜGIITEERING GEOLOGICÀL 45 FÀCTORS ÀFEECÎIIÚG SLOPE STABILIIY II5 TTIE LOCHIEL COAI, DEPCISIT 3.1 Generic modes of slope failure in weak 46 rock a¡rd soil 3.2 Mecha¡risms causing failure of slopes 49 in weak rock and soi-l 3.3 Review of slope stability analyses for 52 the Ëochiel CoaI DePosit 3.3.1 SummarY of stratigraPhY 52 3.3.2 SummarY of engineering 54 properties 3.3.3 Modes of fail-ure 56 3.3.4 Mechanisms causing failure 57 3.4 Review of engineering properties 60 3.4.1 Intact material strength 60 3.4.2 Physical components of shear 62 strength in fine grained soils 3.4.3 Residual angle of friction 64 versus mineralogrY and grain shape 3.5 Discontinuiti-es 69 3.5.1 Tectonic discontlnuities 69 3.5.2 SedimentarY vteak zones 70 III 3.6 Porewater movement 74 4. O METHODOLOGY ÀI{D DATÀ ÀVÀIT,ÀBILITY 78 4.I Data availability and limitations 79 4.2 Methodology 84 4.2.1 Principtes of geological 85 interpretation and modelling 4.2.2 Principles of engineering 94 geological interPretation and modelling 4.3 Stratigraphic nomenclature for the 95 Lochiel CoaI DePosit 5.O .âNALYSIS OF SEDIMEIITS OCCTIRRING BELOW TIIE 98 O\ÍERBI'RDEI{ 5.1 Bunbunga Sa¡rd. Formation - Na¡rtawarra 98 Sand llenber 5.1.1 LithologY and lateral 100 variatíon 5.L.2 Depositional environment 105 5.1.3 Engineering Properties LO7 5.2 Bunbunga Sand Formation - Darnleigh 108 Park Sand Ìlember 5.2.7 LithologY and lateral 108 variation 5.2.2 DePositional environments 111 5.3 Bunbunga Sand Formation - Condowie 113 SiIt Member 5.3.1 Litholog'Y and lateral 116 variation 5.3.2 Depositional environments 1-24 5.3.3 Properties of weak zones L29 5.4 Bumbunga Sand Fomation - Kooliata 131 CoaI Member 5.4.1 H zone 133 5.4.2 GH interseam sediments L42 IV 5 .4.3 G zone ]-44 5.4.4 FG interseam sediments L47 5 .4.5 F zone 150 5.4.6 Depos itional environments 151 5.4.7 Synthesis of geological 155 controls and engineering properties 5.5 Bunbunga Sand Formation - Slmthesis of 156 geological processes controlling the properties of weak zones and porewater movement 6.0 ÀNÀLYSIS OF OVERBITRDEN SEDII'ÍEI{TS 160 6.1 Stratigraphic nomenclature 160 6.2 Warrind.i SiIt Formation 163 6.2.1 Lithological d'escriPtion, r66 facies relationshì.Ps and depos itional Processes 6.2.2 SummarY of dePositional 193 processes 6.2.3 Engineering Properties t96 6.3 Tarella SiIt Fomation 202 6.3.1 LithologY and lateral 202 variation 6.3.2 SummarY of facies 272 relationshiPs and depos itional environments 6.4 Tectonic strrrctures in the TareIIa 2L5 Silt Fomation 6.4.I Data available 2r5 6.4.2 ExÈensi.onal structures 2L7 6.4.3 Shear structures 223 6.4.4 Origins of tectonic 230 structures v 6.5 Slmthesis of geological processes and 234 engineering properties for the TareIIa SiIt Formation 6.5. 1 Strength of the ÎarelIa Silt 234 Shear Zone 6.5.2 Porewater movement 23s 7 .O SUUTTARY OF ENGINEERING GEOLOGY OF THE 238 LOCHIEL COÄI, DEPOSIT 7.L Highwall Stability Design Sectors 239 8.0 SIJUIIÍARY ÀI{D COIÚCLUSIONS 249 8.1 Geological processes 25t 8.1.1 Bumbunga Sand Formation 25r a.2 Warrind.i SiIt and TareIIa SiIt 252 Formations 8.3 Key engineering geological factors 253 affecting slope stability 8.4 Relationship between engineering 256 geological factors affecting slope stability and tectonics, eustacy and depositional processes REEERENCES 258 VT LIST OF FTGURES CHAPTER 1 TITLE PÀGE NO. 1.1 Locality plan of the studY area. 5 L.2 Summary of sequence of investigati-ons. 7 CHAPTER 2 2.L Spatial relationship of major depositional 10 eñvironments for coal bearing sediments associated with coastal settings. 2.2 Geotectonic setting of the St Vincent T2 Basin including location of major structural elements and of the studY area. 2.3 North-south section through the northern 13 part of the St Vincent Basin illustrating tfre structural and stratigraphic relationships. 2.4 Structural setting and elements of the 15 Lochiel Coal Deposit including' structure contours of the basin floor. 2.5 Illustration of the concePts and 22 terminology of sequence stratigraphy. 2.6 Eustatic sea leve1 curves and relative 24 change in coastal onlap for the Midd1e Eocene to Late Oligocene. 2.7 Depositional environments and vertical 25 profiles for midplate continental margin settings. 2.4 Palaeogeographical reconstruction of the 28 northern St Vincent Basin for the Oligocene and Eocene. 2.9 Stratigraphic nomenclature and correlation 31 of Formations in the northern St Vincent Basin. 2.ro Sediment relation diagram and inferred 40 depositional setting for the northern part of the St Vincent Basin. CHÀPTER 3 3.1 Schematic representation of the 47 characteristics of the modes of failure for weak rock and soil. VII 3.2 Relationship between factors affecting 50 failure along a discontinuity. 3.3 Stratigraphy and lateral lithological 53 variation for the Lochiel CoaI Deposit. 3.4 Relationships between the key factors 57 affecting slope stability for the Lochiel Trial Pit site. 3.5 Radial and vertical drainage mechanisms 59 and their relationship with pumping bores. 3.6 Stratigraphic location of weak zones and 61 their relationship with rates of dewatering/depressurisation . 3.7 Relationship between residual friction 65 angle and clay fraction. 3.8 Relationship between residual friction 66 angle and plasticity index for the Lochiel Coal Deposit. 3.9 Summary of results of Àtterberg, xRD, total 67 organic carbon, clay mineralogY, moisture content and percentage clay fraction tests for the Tarella SiIt. 3 .10 Discontinuities associated with 7L tectonically formed shear zones. 3.11 Locations of weak zones in progradational 72 and aggradational sequences. 3.12 Summary of grain size analyses for sandy 76 sediments occurring within the Lochiel CoaI Deposit. 3.13 Summary of well test results. 77 CHÀPTER 4.O 4.7 Summary of number and types of data 80 collection sites. 4.2 Core and geophysical log response 91 i-nterpretation f lowpath. 4.3 Legend for stratigraphic symbols. 93 CHÀPTER 5.0 5.1 Thickness and lateral distribution of the 99 Nantawarra Sand Member. VIII 5.2 Nantawarra Sand Member Lateral variation 100 in lithology and vertical sequence' 5.3 Schematic representation of the 106 d.epositional setting for the Nantawarra Sand Member. 5.4 Thickness and Lateral distribution of the 109 Darnleigh Park Sand Member. 5.5 Darnleigh Park Sand Member - Geophysical 110 log resþonse and vertical lithological profile. 5.6 Thickness and. Iateral distribution of the LL4 Condowi-e SiIt Member. 5.7 Cond.owie Sitt Member - Geophysical log 115 response and vertical tithological profile. 5 .8a Thickness and' Iateral distribution of the r77 CN# unit - Condowie SiIt' Member. 118 5 .8b Thickness and lateral distribution of the CN2 unit - Condowie Silt Member' 119 5 .8c Thi.ckness and lateral distribution of the CN1 unit - Condowie Silt Member' 5.9 Condowie Silt Member - Thickness and 125 Iateral distribution of clean sand' 5 .10 Depositional setting for the Condowie Silt' L28 5 .11 Condowie Silt Member weak zones 130 Location of test sites and summary of results of strength testing. 5.L2 Thickness and. lateral distribution of the L32 Kooliata CoaI Member. 5.13a Kooliata Coal Member - Thickness of H 1-34 Zone coal and H Zone coal Partings' 5.13b Kooliata CoaI Member GH Interseam 135 sediments - lota1 thickness and facies d.istribution and thickness of clean sand' 5.13c Kooliata CoaI Member - Thickness of G 136 Zone coal and G Zone coal Partings' 5.13d Kooliata CoaI Member FG Interseam 1-37 sediments Tota1 thickness and facies distribution and thickness of clean sand' 5.13e Kooliata CoaI Member Thickness of F 138 Zone coal.