GROUND INVESTIGATION REPORT FOR THE EDEN DEEP … · investigation works comprised of the following exploratory holes: xFour boreholes (BH01 to BH04) between 23.0 and 50.0m deep were

July 2014

GROUND INVESTIGATION REPORT

FOR THE EDEN DEEP GEOTHERMAL

PROJECT PRE-ENABLING WORKS,

CORNWALL

Balfour Beatty Civil Engineering Ltd

3512819A-HHEFinal

Ground Investigation Report forthe Eden Deep Geothermal

Project Pre-Enabling Works,Cornwall

3512819A-HHE

Prepared forBalfour Beatty Civil Engineering Ltd

Roman House Chancel LanePinhoe, Exeter

Devon EX4 8JT

Prepared byParsons Brinckerhoff

Queen Victoria HouseRedland Hill

RedlandBristol BS6 6US0117 933 9300

www.pbworld.com

Ground Investigation Report for the EdenDeep Geothermal Project Pre-Enabling

Works, Cornwall

Eden Project GIR Rev 1G Prepared by Parsons BrinckerhoffFebruary 2014 for Balfour Beatty Civil Engineering Ltd

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CONTENTSPage

List of Abbreviations 3

Executive Summary 5

1 Introduction 61.1 Scope and Objective of the Report 61.2 Description of the Project 61.3 Geotechnical Category of the Project 101.4 Other Relevant Information 10

2 Existing Information 112.1 Topographical Maps 112.2 Aerial Photographs 112.3 Land Use 112.4 Hydrology 122.5 Flooding 122.6 Geological Maps and Memoirs 122.7 Records of Mines and Mineral Deposits 132.8 Previous Ground Investigations 142.9 Consultation with Statutory Bodies and Agencies 172.10 Hydrogeology 172.11 Contaminated Land 182.12 Archaeological and Historical Investigations 182.13 Other Relevant Information 18

3 Field and Laboratory Studies 193.1 Walkover Survey 193.2 Geomorphological/Geological Mapping 193.3 Ground Investigations 193.4 Drainage Studies 203.5 Geophysical Surveys 203.6 Pile Tests 213.7 Other Field Work 213.8 In Situ Testing 213.9 Laboratory Testing 21

4 Ground Summary 224.1 Geotechnical Investigation 224.2 Geophysical Investigation 234.3 Groundwater 23

5 Ground Conditions and Material Properties 245.1 Made Ground 245.2 Alluvium 245.3 Kaolinised Granite 25


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Eden Project GIR Rev 1G Prepared by Parsons BrinckerhoffJuly 2014 for Balfour Beatty Civil Engineering Ltd

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5.4 Geotechnical Parameters 285.5 Geochemical Parameters 28

6 Engineering Interpetation 296.1 Main Access Road 296.2 Rig Plant, Spill Containment Area and Drilling Rig Foundation Pad (including Wells) 296.3 Conductor Pipe 31

7 Geotechnical Risk Register 32

8 References 35

Appendix A – Figures 36

List of Tables

Table 1: Previous Ground Investigations .......................................................................................... 14Table 2: Drilling Methods for 2010 Ground Investigation .................................................................. 16Table 3: 2013 Ground Investigation Summary ................................................................................. 20Table 4: Laboratory Testing Summary ............................................................................................. 21Table 5: Summary of Strata Reduced Levels ................................................................................... 23Table 6: 2013 Groundwater Summary ............................................................................................. 23Table 7: Laboratory Testing Results in Alluvial Deposits .................................................................. 24Table 8: Classification Test Summary (Kaolinised Granite) .............................................................. 25Table 9: Summary of PSD Testing (Kaolinised Granite) ................................................................... 25Table 10: Summary of Derived Geotechnical Parameters ................................................................ 28Table 11: Geochemical Testing Summary ........................................................................................ 28Table 12: Geotechnical Risk Register .............................................................................................. 33


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LIST OF ABBREVIATIONS

ACEC Classification Aggressive Chemical Environment for Concrete Classification

BGS British Geological Survey

BH Borehole

BHD Buro Happold

CJA C J Associates

CPT Cone Penetration Testing

DS Class Design Sulphate Class

EA Environment Agency

EDGP Eden Deep Geothermal Plant

EGPS European Geophysical Services

EGS Engineered Geothermal Systems Limited

GI Ground Investigation

GIR Ground Investigation Report

GQA General Quality Assessment

mbgl Metres below ground level

mAOD Metres above Ordnance Datum

NGR National Grid Reference

PAH Poly Aromatic Hydrocarbons

SPT Standard Penetration Testing

TFL Terra Firma Limited

TP Trial Pit

TPH Total Petroleum Hydrocarbons

WS Window Sample Hole


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EXECUTIVE SUMMARY

Engineered Geothermal Systems Energy Limited in conjunction with the EdenProject are proposing to build the UK's first geothermal power plant generatingboth heat and electricity at The Eden Project, St Austell, Cornwall.

The Ground Investigation was completed in July 2013 and comprised ofboreholes, Cone Penetration Testing and geophysics. This was was scoped byParsons Brinckerhoff Ltd on and undertaken by C J Associates.

The objectives of this Ground Investigation Report are to:

Summarise any previous GI information;

Describe the 2013 GI undertaken;

Provide details of the ground and groundwater conditions as part of aground model;

Present preliminary geotechnical parameters for the works; and,

Develop a geotechnical risk register for the works.

The proposed enabling works include an access road, a cuttings pit, a waterstorage lagoon, two wells and drilling rig foundation (with cellars), a rig plantand spill containment area and a conductor pipe.

It is recommended that the conductor pipe is installed using drilling andgrouting as opposed to driving methods. This would need to be installed todepths of 5m greater than the level of competent rock.

The main risks highlighted in this report are the variability of material propertiesacross the site and the excessive and differential settlement of the underlyingalluvial deposits comprising soft clays and peat.

It is recommended that any foundations for the drilling rig are founded on theunderlying kaolinised granite at an approximate depth of 4mbg. The rig plantand spill containment area can be founded at a depth of at least 1 mbgl,provided that any very soft to soft or highly organise material at formation levelis dug out and replaced with suitable material.

This sheet is intended as a summary only.


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1 INTRODUCTION

1.1 Scope and Objective of the Report

1.1.1 Engineered Geothermal Systems (EGS) Energy Limited in conjunction with the EdenProject are proposing to build the UK's first geothermal power plant generating bothheat and electricity at The Eden Project, St Austell, Cornwall.

1.1.2 The current Ground Investigation was scoped by Parsons Brinckerhoff Ltd (PB) onbehalf of EGS Energy and undertaken by C J Associates (CJA). This was completedin July 2013 and comprised of:

Two boreholes (one fully logged, sampled and with in situ geotechnical testingand the other open holed since the main aim was to allow geophysics to beundertaken within the hole); and,

Seven Cone Penetration Tests (CPTs), the results of which were interpreted toinclude strata, angle of shearing resistance, undrained shear strength, relativedensity and equivalent SPT N-value, as appropriate.

1.1.3 The objectives of this Ground Investigation Report (GIR) are to:

Summarise any previous GI information;

Describe the 2013 GI undertaken;

Provide details of the ground and groundwater conditions as part of a groundmodel;

Present preliminary geotechnical parameters for the works;

Provide preliminary recommendations for the proposed works; and,

Develop a geotechnical risk register for the works.

1.2 Description of the Project

1.2.1 Background

1.2.2 The proposed Eden Deep Geothermal Plant (EDGP) is to be the UK’s first geothermalpower plant generating both heat and electricity to supply Eden and the equivalent ofaround five thousand households as well as heating for the biomes.

1.2.3 It will be made up of two boreholes, drilled to around 4km into the granite beneath thesite with water injected into the first borehole super-heated to temperatures of around185 C and returned to the surface via the second borehole.

1.2.4 The EDGP will cover an area a similar size to a rugby pitch with buildings no greaterthan 10m in height.

1.2.5 Site Location

1.2.6 The EDGP is to be located off Butts Lane, Bodelva, Cornwall next to the northernentrance at the Eden Project, National Grid Reference (NGR) 204310, 055710. A planshowing the site location can be found below.


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Reproduced from the 2007Ordnance Survey 1:25,000 St Austell & Liskeard Explorer map with the permission of OrdnanceSurvey on behalf of the Controller of Her Majesty’s Stationary Office. Crown Copyright AL100018516

Figure 1: Location Plan

1.2.7 The site is roughly rectangular in shape and at an approximate reduced level of130mAOD, occupies approximately 2.81 hectares and forms part of the Eden Projectand is commonly known as the ‘Tomato’. It is currently unoccupied and is covered bya mixture of rough grass, reeds, old tree stumps and rough ground.

1.2.8 Previous Investigations

1.2.9 Previous intrusive investigations have been undertaken on the site but were limiteddue to the following reasons:

Restricted access;

Uneven topography;

Dense vegetation;

EDGP Site

EdenProject

St Austell

NORTH


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Boggy ground; and,

Water courses.

1.2.10 In addition, the previous investigations concentrated on the potential contaminationrather than the geotechnical significance of the ground.

1.2.11 These investigations are discussed in further detail in Section 2.8.

1.2.12 Proposed Works

1.2.13 The major aspects of the enabling works consist of the following major units.

Main access road – into, around and out of the site, constructed of tarmac,capable of carrying loads greater than 40 tonnes;

Rig plant and spill containment area – a lipped concrete platform typicallycovering an area of 120x60m; within which are the following elements:

i A cuttings pit – approximately 400m2 surface area and volumetriccapacity of 1,000 – 1,250 m3;

ii A mud pit/ lagoon – approximately 1,400m2 surface area and volumetriccapacity of 4,000 – 4,400 m3; the western edge of which might be outsidethe containment area.

iii Drilling rig foundation pad and cellars – strong foundation padapproximately 15x25m capable of supporting 500 tonnes.

iv Two wells each with a cellar – 3m diameter by 4m deep constructed ofconcrete rings, centre of cellars 6-8m apart;

v Conductor pipe – anticipated to be around 50m in length.

1.2.14 These are discussed further in Section 6. A layout of the proposed works listed aboveis provided on the next page.


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NORTH


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1.3 Geotechnical Category of the Project

1.3.1 The scheme has been categorised as a Geotechnical Category 2 project, whichHD22/08 (Ref. 1) defines as “projects which include conventional types ofgeotechnical structures, earthworks and activities, with no exceptional geotechnicalrisks, unusual or difficult ground conditions or loading conditions.”

1.4 Other Relevant Information

1.4.1 None.


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2 EXISTING INFORMATION

2.1 Topographical Maps

2.1.1 A previously commissioned topographical survey of the site has been obtained. Thesurvey was undertaken in January and February 2010 for EGS Energy Ltd by KempEngineering and Surveying.

2.1.2 The survey shows the site to be at an approximate reduced level of 130mAOD.

2.1.3 Survey information is included in Drawing No. 3512819A-HHE/G/100/02 can befound in Appendix A of this report.

2.2 Aerial Photographs

2.2.1 No specific aerial photographs were taken for the scheme, however an aerialphotograph obtained from GoogleEarth can be found below:

Figure 2: Aerial Photograph

2.3 Land Use

2.3.1 Existing Land Use

2.3.2 The site is part of the Eden Project and is currently unoccupied and is covered by amixture of rough grass, reeds and overgrown hardcore.

2.3.3 Historic Land Use

NORTH

EDGP Site


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2.3.4 The historical maps included in the Envirocheck Report within the Buro Happold(BHD) Geoenvironmental Report (Ref. 2) have been reviewed and are summarisedbelow. These date back to 1882 with the most recent being 2009.

2.3.5 The site has remained undeveloped, comprising rough grassland, heath, woodlandand marshes and from the 1882 map has been divided into small plots.

2.3.6 Anecdotal evidence noted in the BHD report has suggested that the material used toraise site levels locally between January 1990 and June 1992 comprised demolitionrubble from a supermarket development in St Austell. During this time, the site was alicensed landfill.

2.3.7 During the previous GIs, a layer of Made Ground 1.4 – 3.8m thick was encountered,generally confirmed the anecdotal evidence.

2.4 Hydrology

2.4.1 According to the Envirocheck Report obtained as part of the BHD Geo-environmentalReport (Ref. 2), there are no licensed surface water abstractions located within 1kmof the site and that the site is classified as being at low risk from flooding.

2.4.2 Spring fed drainage channels were noted to run along the southern and western siteboundaries:

A channel running along the southern site boundary flows through a culvertbeneath The Eden Project access road which joins the Treverbyn Streamapproximately 800m north of the site.

A channel running along the western site boundary flows into an attenuationpond located in the north of the site, which in turn flows north towards TreverbynStream.

2.4.3 It should be noted that the Treverbyn Stream has been designated with an EAGeneral Quality Assessment (GQA) Grade of A (the highest quality).

2.4.4 A further attenuation pond is located approximately 25m to the north east of the site.

2.5 Flooding

2.5.1 According to the EA website (Ref. 4), the site is not within an area at risk of floodingfrom rivers or the sea.

2.6 Geological Maps and Memoirs

2.6.1 The geology of the site has been reviewed with reference to the British GeologicalSurvey (BGS) 1:50,000 sheet 347 (Bodmin) Drift Edition (Ref. 3).

2.6.2 The site is shown to be underlain by alluvium, likely to comprise silty clays, sands,gravels and peat, overlying granite. An extract of the geological map can be foundbelow reproduced from BGS 1:50,000 sheet 347 (Bodmin) by permission of theBritish Geological Survey © NERC. All rights reserved.


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[C08/060-CSL] British GeologicalSurvey © NERC. All rights reserved

Figure 3: Extract of Geological Map

2.6.3 The granite underlying the site is part of the St Austell Granite pluton which in turn ispart of the Cornubian batholiths (a group of associated granite intrusions whichunderlie the south west peninsula of the UK).

2.6.4 The site is located within the St Austell Granite batholiths, of Upper Carboniferousage. Research has shown that the granite consists of Topaz Granite.

2.6.5 The local alteration of the feldspars within the granite to kaolinite is known askaolinisation. The kaolinisation is typically structurally controlled and generally occursin association with sheeted greisen, tourmaline and abundant quartz veining. Thekaolinised zones are typically orientated parallel to NW-SE and ENE-WSW strikingstructures. The degree of alteration varies locally, with intensely kaolinised andrelatively unkaolinised granite present in varying proportions.

2.6.6 This alteration of the feldspars has locally formed large economic deposits of chinaclay (kaolinite) within the St Austell district. There are several historic and workingchina clay quarries in the vicinity of the site.

2.6.7 The nearby Eden Project visitor attraction is located in a reclaimed china clay pit.

2.6.8 The presence of Made Ground due to these historic industrial activities is expected.

2.7 Records of Mines and Mineral Deposits

2.7.1 Although there is no evidence of mining within the site boundaries, the site lies withinan area well known for china clay extraction.

EDGP Site

NORTH


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2.7.2 Several china clay pits and associated industrial activities have been noted on thehistorical maps and these include:

Methrose China Clay Works (800m to the northeast);

Restineas China Clay Works and associated shafts (800m to the south);

Wheal Ruby Iron Mine and associated shafts (850m to the west);

Teverlyn Iron Mines and associated shafts (1.1km to the north west);

Vounder China Clay Works, shafts and old quarries (950m to the south);

Wheal Par Tin mine and associated shaft (1km to the east);

Cornwall Works China Clay Pits (1.2km to the south east) – these werere-designated in 1933 as Carvear and Bodelva Works;

Pentruff China Clay Works (1.3km to the north west);

Carbis China Clay Works (1.5km to the north west);

Cannamanning China Clay Works (1.5km to the north west);

Garker China Clay Works (1km to the south);

Alseveot China Clay Works (750m to the north east);

Bodelva China Clay Works (500m to the south east) – where the Eden Project isnow located);

Trethurgy China Clay Works (450m to the southwest); and,

Wheal Rashleigh China Clay Works (700m to the south east).

2.7.3 The maps show the majority of the works listed above as being disused by the 1970sapart from the Imerys Trebal Refinery which is noted in 1973 at the site of the formerAlseveot Works.

2.8 Previous Ground Investigations

2.8.1 All previous GIs undertaken as part of this scheme are detailed in the Buro Happold,Geoenvironmental Interpretative Report (Ref. 2).

2.8.2 A summary of all previous GIs is presented below:

Table 1: Previous Ground Investigations

Year Undertakenby:

ExploratoryHole

Depth(mbgl) Instrument Filter Zone Strata

2002John

GrimesPartnership

5 No. trial pits (up to 4.2mbgl)Limited chemical testing (metals, phenol, polycyclic aromatic hydrocarbons (PAH),

total petroleum hydrocarbons (TPH), pH, sulphate, weight loss on drying and %stones)

2010 BuroHappold

BH01 14.50 11.50 – 14.50 Granite

BH02 15.00 5.00 – 5.00 Granite

BH03 25.00 15.00 – 25.00 Granite

BH04 13.50 4.50 – 13.50 Granite


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WS01 2.00 0.50 – 2.00 Made Ground

WS02 3.00 0.50 – 3.00 Made Ground

WS03 2.50 0.50 – 2.50 Made Ground

WS04 1.50 0.50 – 1.50 Made Ground

WS05 1.80 0.80 – 1.80 Made Ground

WS06 3.00 1.00 – 3.00 Made Ground

WS07 3.50 1.00 – 3.50 Made Ground and Peat



WS10 3.50 1.00 – 3.50 Made Ground

TP01 3.55 n/a

TP02 3.10 n/a

TP03 1.50 n/a

TP04 2.80 n/a

TP05 3.15 n/a

TP06 3.60 n/a

TP07 3.50 n/a

BHD scheduled a programme of chemical testing on soil samples based upon thesites historical use (unoccupied prior to its use as a landfill), known likely elevated

background concentrations of contaminants in the area: Heavy metals, otherinorganics, PAH, TPH and asbestos.

2.8.3 The exploratory holes undertaken as part of both these investigations generallyconfirmed the ground conditions as predicted by the published geology.

2.8.4 Drawing No. 3512819A-HHE/G/100/02 can be found in Appendix A and shows thelocations of the exploratory holes undertaken for the 2010 GI along with those for theGI undertaken in 2013.

2.8.5 The kaolinised granite was encountered at depths of 2.65 – 4.00mbgl overlain byMade Ground and Alluvial Deposits (soft dark brown amorphous silty and clayey peat)of varying thickness.

2.8.6 2002 Ground Investigation – John Grimes Partnership

2.8.7 A GI comprising five machine dug trial pits 2.4 – 4.2mbgl and limited chemicallaboratory testing was undertaken by John Grimes Partnership (JGP) in 2002 as partof a planning proposal to develop the site as a supplementary visitor car park.

2.8.8 The Made Ground encountered in these trial pits was found to include demolitionwaste comprising plastic, metal and wood. This was underlain by a thin layer of relicttopsoil, including peat, which was overlying soft grey gravelly silt and sand (assumedto be Alluvial Deposits). The results of the chemical testing indicated the site was nothighly contaminated.

2.8.9 Groundwater strikes and seepages were recorded within every trial pit between0.3-3.0mbgl.


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2.8.10 2010 Ground Investigation – Buro Happold

2.8.11 The 2010 GI was undertaken by Apex Drilling with logging undertaken by an engineersupplied by Terra Firms Ltd (TFL) and supervised by an engineer from BHD. Theinvestigation works comprised of the following exploratory holes:

Four boreholes (BH01 to BH04) between 23.0 and 50.0m deep were advancedusing the dynamic sampling technique with open hole and rotary follow-on whereapplicable. Disturbed and bulk samples were taken for laboratory testing and insitu testing in the form of Cone Penetration Tests were undertaken. These areStandard Penetration Tests (SPTs) but due to the nature of the material a solidcone rather than a split spoon was used and the test is still undertaken inaccordance with the standards for SPTs;

Ten window sample holes (WS01 to WS10) advanced to depths of between3.0m and 6.0mbgl; and

Seven trial pits (TP01 to TP07) to depths of between 1.5m and 3.6mbgl.

2.8.12 A summary of the drilling methods employed for the four boreholes is presentedbelow:

Table 2: Drilling Methods for 2010 Ground Investigation

Borehole No. Depth (mbgl) Reduced Level (mAOD) Drilling method

BH01

0.00 – 11.50 136.48 – 124.98 Dynamically sampled

11.50 – 14.50 124.98 – 121.98 Open hole

14.50 – 15.50 121.98 – 120.98 Rotary cored

15.50 – 23.00 120.98 – 113.48 Open hole

BH02


10.00 – 40.00 121.96 – 91.96 Open hole

40.00 – 43.00 91.96 – 88.96 Rotary cored

43.00 – 48.50 88.96 – 83.46 Open hole

48.50 – 50.00 83.46 – 81.96 Rotary cored

BH03


12.40 – 27.50 123.26 – 108.16 Open hole

27.50 – 31.50 108.16 – 104.16 Rotary cored

31.50 – 40.00 104.16 – 95.66 Open hole

40.00 – 44.50 95.66 – 91.16 Rotary cored

BH040.00 – 10.00 134.07 – 124.07 Dynamically sampled

10.00 – 40.00 124.07 – 94.07 Open hole

2.8.13 No geotechnical laboratory testing was undertaken as part of this investigation. Alllaboratory testing was purely for geo-environmental purposes.

2.8.14 The granite, where encountered, was logged in accordance to Geoguide 3: Guide toRock and Soil Descriptions (Ref. 5) and as noted on the logs was found to be varyingfrom Grade II to VI. The definitions for these particular grades are presented below:


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Grade IISlightly decomposed – not broken easily by geological hammer. Makesa ringing sound when struck by geological hammer. Fresh rock coloursgenerally retained but stained near joint surfaces.

Grade IIIModerately decomposed – Cannot usually be broken by hand; easilybroken by geological hammer. Makes a dull or slight ringing soundwhen struck by geological hammer. Completely stained throughout.

Grade IVHighly decomposed – can be broken by hand into smaller pieces.Makes a dull sound when struck by geological pick. Does not slakewhen immersed in water. Completely discoloured compared with freshrock.

Grade VCompletely decomposed – original rock texture preserved. Can becrumbled by hand and finger pressure into constituent grains. Easilyindented by point of geological pick. Slakes when immersed in water.Completely discoloured compared with fresh rock.

Grade VIResidual soil – original rock texture completely destroyed. Can becrumbled by hand and finger pressure into constituent grains.

2.8.15 50mm slotted standpipes were installed in all boreholes and window sample holeswith a granular response zone and a bentonite seal above and below this zone.

2.8.16 Groundwater was recorded as being encountered at elevations of between 130.27 –135.22mAOD. The factual report states that a high rate of groundwater flow withrunning sand conditions was recorded at 18.5mbgl and below in all rotary boreholes.

2.8.17 It should be highlighted that asbestos sheeting fragments were noted within the MadeGround encountered in TP01.

2.9 Consultation with Statutory Bodies and Agencies

2.9.1 Consultations with statutory bodies and agencies have not been undertaken as part ofthe 2013 GI.

2.10 Hydrogeology

2.10.1 The superficial deposits and granitic bedrock underlying the site are classified asSecondary A aquifer by the Environment Agency (EA). The EA (Ref. 4) gives thefollowing definition for a Secondary A aquifer: “permeable layers capable ofsupporting water supplies at a local rather than strategic scale, and in some casesforming an important source of base flow to rivers. These are generally aquifersformerly classified as minor aquifers”.

2.10.2 The site does not lie within a published Groundwater Source Protection Zone. Thenearest licensed groundwater abstraction is located 130m to the north-east at LittleCarne Farm (NGR 204542, 55798). Groundwater is used for general farming anddomestic applications.

2.10.3 A ground investigation was carried out in March 2010 which showed that the that thenatural geology beneath the site is as predicted from published geological maps,comprising Made Ground overlying in sequence, relic topsoil / peat, alluvium andalterated granite. Groundwater was present a varying depths within the alteratedgranite, generally associated with fracture zones within the stratum.


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2.10.4 Subsequent groundwater monitoring from the 2010 GI indicates that groundwaterwithin the alterated granite is present at 1.70 to 4.17mbgl (~133mAOD) whenunconfined. Some perched groundwater was identified within the Made Ground.

2.10.5 It has been noted on the published OS 1:25,000 topographic mapping that severalwater courses and bodies in the area have an elevation of between approximately100 – 110mAOD.

2.11 Contaminated Land

2.11.1 There was no visual or olfactory evidence of contamination noted during the 2013 GI.

2.11.2 There was little recorded visual or olfactory evidence of contamination during the2010 GI apart from the anthropogenic tipped material in TP02 and TP07 and thepresence of Crysolite (white) asbestos in TP01 mentioned in the BHD Geo-environmental Report (Ref. 2).

2.11.3 Some slight exceedences of the relevant screening criteria for residential andcommercial / industrial land use for arsenic and benzo(a)pyrene was also noted withinthe Made Ground.

2.11.4 Groundwater monitoring was carried out as part of the 2010 GI between April andMay 2010 with slight exceedences of copper and selenium recorded.

2.11.5 Ground gas monitoring was also carried out over a period of 7 week. Significantlyelevated concentrations of methane and carbon dioxide were recorded.

2.11.6 Additionally the site is an area where greater than 30% of homes within a 1km radiusof the site are above the radon action level.

2.11.7 The BHD report concluded that “based on the investigation carried out and the natureof the proposed development, the ground conditions present limited potential risk tohuman health or the environment”. The following recommendations were made:

A visual inspection for possible asbestos containing material (PACM’s) should beundertaken during any excavation works and if any are encountered, followingthe guidance given in the Control of Asbestos Regulations; and,

Gas protection measures to be installed for any permanent buildings to mitigatethe risk from carbon dioxide, methane and radon.

2.11.8 Further information regarding these aspects can be found in the report (Ref. 2).

2.12 Archaeological and Historical Investigations

2.12.1 PB are not aware of any existing archaeological or historical investigation in the areaof the site.

2.13 Other Relevant Information

2.13.1 None.


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3 FIELD AND LABORATORY STUDIES

3.1 Walkover Survey

3.1.1 No walkover survey was undertaken as part of this reporting.

3.2 Geomorphological/Geological Mapping

3.2.1 No specific geomorphological or geological mapping was undertaken as part of thisscheme.

3.3 Ground Investigations

3.3.1 The combined geotechnical and hydrogeological intrusive ground investigation wasdesigned by PB following a review of the existing ground investigation information andwith reference to the proposed works on the site, current at the time of theinvestigation.

3.3.2 The fieldwork, scheduled by PB was carried out by CJA between 8th July and 12thJuly 2013 and comprised rotary boreholes with associated in situ testing andsampling, in situ CPTs using a piezocone and down the hole geophysical testing inBHA2.

3.3.3 Prior to the 2013 GI being undertaken, the vegetation and tree stumps have beencleared in the area of the proposed drilling platform.

3.3.4 The location of the drilling platform was chosen away from the boggy ground andwater courses noted in previous investigations.

3.3.5 The GI was carried out generally in accordance with the following standards:

BS EN 1997: Part 2, including the UK National annex (Ref. 6);

BS5930:1999 + A2:2010 ‘Code of Practice for Site Investigation’(Ref. 7);

BS1377:1990 ‘Soils for Civil Engineering Purposes’ (Ref. 8)

ICE ‘Specification for Ground Investigation’ (Ref. 9);

BS EN 14688-1:2002 (Ref. 10);

BS EN 14688-2:2004 (Ref. 11); and,

BS EN 14689-1:2003 (Ref. 12).

3.3.6 All exploratory hole logs and factual information relating to the 2013 GI can be foundin the CJA Factual Report (Ref. 13)

3.3.7 The exploratory hole locations were determined by PB and are shown approximatelyon the Exploratory Hole Location Plan (Drawing No. 3512819A-HHE/G/100/02),included in Appendix A

3.3.8 All exploratory hole locations were scanned for buried services using a CableAvoidance Tool (CAT). In addition hand dug inspection pits were excavated to amaximum 1.2m depth before drilling/boring commenced to check for undergroundservices.


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3.3.9 A summary of the exploratory holes undertaken for this phase of ground investigationis shown below:

Table 3: 2013 Ground Investigation Summary

ExploratoryHole Ref Type In Situ Testing Depth

(m bgl) Installations

BHA1 Rotary cored borehole (airflush)

Standard PenetrationTesting (SPTs) 20.00

None (backfilledwith cement

bentonite grout)BHA2Rotary open hole drilling anddown the hole hammer (air

flush)

Geophysically loggedusing down hole 60.00

CPT01 Piezocone Penetration Test 0.56 n/a







3.3.10 Air was used as the flushing medium. Standard penetration tests (SPT’s), asdescribed below, were conducted in suitable materials.

3.3.11 Details of ground water conditions were noted where possible. Water levels may havebeen affected by the installation of casing to the boreholes or the use of air as aflushing medium. In addition, water level observations are those at the time of theinvestigation and do not necessarily reflect seasonal fluctuations. The boreholes werebackfilled on completion with cement bentonite grout.

3.4 Drainage Studies

3.4.1 No drainage studies were carried out as part of the 2013 investigations.

3.5 Geophysical Surveys

3.5.1 Down the hole geophysical surveys were undertaken in order to assess the conditionof the rock within the top 50m of BHA2, the results of which would determine therecommendation given in relation to the conductor pipe.

3.5.2 The following geophysical logging was undertaken by European GeophysicalServices (EGPS) within exploratory hole BHA2:

Fluid temperature and conductivity (between 42.5 – 60.6mbgl);

Caliper and Natural Gamma (between 42.5 – 60.6mbgl); and,

Gamma gamma density (between 3.0 – 60.6mbgl).


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3.6 Pile Tests

3.6.1.1 No pile tests were required.

3.7 Other Field Work

3.7.1 None.

3.8 In Situ Testing

3.8.1 Seventeen SPTs were undertaken within BHA1 on suitable materials.

3.8.2 No in situ geotechnical testing was undertaken in BHA2 since this was put downusing open hole techniques and undertaken specifically for the geophysical testing.

3.8.3 Seven piezocone penetration tests were undertaken, recording the followinginformation:

Correlated cone end resistance (MPa);

Sleeve friction (kPa);

Soil behaviour type index;

Relative density

Derived SPT N Value;

Pore Pressure Ratio;

Pore Pressure (kPa)

Derived shear strength (kPA) ; and,

Derived friction angle (degrees).

3.9 Laboratory Testing

3.9.1 As part of the 2013 GI, the following laboratory testing was scheduled to beundertaken on samples collected from BHA1:

Table 4: Laboratory Testing Summary

Laboratory Testing No of Tests

Geotechnical Testing Moisture Content 5

Atterberg Limits 4

Organic Content 1

Particle Size Distribution (PSD) 5

Geochemical Testing Sulphate and pH 6


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4 GROUND SUMMARY

4.1 Geotechnical Investigation

4.1.1 The 2013 intrusive GI confirmed the expected geological conditions describedpreviously, i.e. granite of varying stages of kaolinisation at an approximate depth of4.00 mbgl overlain by superficial deposits comprising Topsoil, Made Ground andAlluvial Deposits as tabulated below:

BoreholeNo. Stratum

Depth to topof stratum

(mbgl)Thickness

(m) Description

BHA1

Alluvial Deposits(Peat) 0.00 0.65 Spongy dark clayey pseudo amorphous

PEAT

Alluvial Deposits(Cohesive) 0.65 3.15 Soft slightly sandy slightly gravelly SILT

/ CLAY

Kaolinised Granite

3.80 0.20 Grade 4 Granite (recovered as soft greyslightly gravelly CLAY)

4.00 1.70Grade 4 Granite (recovered as medium

dense silty / clayey SAND andGRAVEL)

5.70 0.75Grade 4 Granite (recovered as firm to

stiff slightly sandy slightly gravelly SILT/ CLAY)

6.45 2.55 Grade 4 Granite (recovered as mediumdense very silty / clayey gravelly SAND)

9.00 11.00*Grade 4 Granite (recovered as stiff tovery stiff slightly gravelly sandy SILT /

CLAY)

*: Base of stratum not encountered

BHA2

Made Ground 0.00 2.30 Made Ground (driller’s description)

Alluvial Deposits(Peat) 2.30 1.00 PEAT (driller’s description)

Alluvial Deposits(Cohesive)

3.30 0.30 SILT (driller’s description)

3.60 0.40 Gravelly CLAY (driller’s description)

Kaolinised Granite4.00 12.90 Light grey highly weathered GRANITE

(driller’s description)

16.90 26.50 Highly weathered gravelly GRANITE(driller’s description)

Granite

43.40 9.50 Stronger grey GRANITE (driller’sdescription)

52.90 0.70 Very strong GRANITE (driller’sdescription)

53.60 1.20 Strong GRANITE (driller’s description)

54.80 5.20* GRANITE (driller’s description)

*: Base of stratum not encountered


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4.1.2 Casing was required up to a depth of 42.70mbgl in exploratory hole BHA2 and thegranite encountered up until a depth of 43.40mbgl was noted as being highlyweathered in the driller’s descriptions. This would suggest a weathered zone ofapproximately 45mbgl.

4.1.3 A summary of the strata encountered in during both the 2010 and 2013 GIs ispresented below:

Table 5: Summary of Strata Reduced Levels

Borehole No.BHA1 BHA2 BH01 BH02 BH03 BH04Level to top

of stratum (mAOD)

Made Ground N/A 135.00 136.48 131.96 135.66 134.07

Alluvium 133.00 132.70 134.33 129.46 131.66 131.22

Kaolinised Granite 129.20 131.00 133.25 126.36 124.66 128.57

4.1.4 It is assumed the structures are to be founded on the kaolinised granite.

4.2 Geophysical Investigation

4.2.1 The results of the geophysical investigation are presented in the CJA Factual Report(Ref. 13).

4.2.2 A reduction in density was noted between 19 – 23mbgl behind the casing in BHA2.As the site elevation is approximately 130mAOD, this is equivalent to 107-111mAOd,which is similar to the inferred elevation of the saturated zone to the south of the site,discussed in Section 2.10.

4.3 Groundwater

4.3.1 A summary of the groundwater encountered during the 2013 is presented below:

Table 6: 2013 Groundwater Summary

Exploratory Hole Depth togroundwater (mbgl) Comments

BHA11.00 Seepage noted

7.00 Strike with groundwater level rising to 6.95mbgl after 20minutes.

BHA210.80 Borehole noted as “damp”

17.20 Seepage noted

4.3.2 No groundwater monitoring was undertaken as part of the 2013 GI works so as not tointerfere with the proposed structures.


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5 GROUND CONDITIONS AND MATERIAL PROPERTIES

5.1 Made Ground

5.1.1 The presence of 2.30m of Made Ground (based on driller’s description) was noted atthe top of BHA2. No further details were noted. No Made Ground was noted in BHA1.

5.1.2 Made Ground was encountered in all trial pits and exploratory holes undertaken forthe 2011 GI.

5.1.3 No in situ or laboratory testing has been undertaken in this stratum.

5.1.4 It is assumed that no foundations will be founded on the Made Ground.

5.2 Alluvium

5.2.1 The alluvial despoils encountered in BHA1 comprised 0.65m of pseudo amorphouspeat overlying 3.15m of soft slightly sandy slightly gravelly clay.

5.2.2 1.00m of peat underlain by 0.30m of grey silt (from the driller’s description) wasencountered immediately underneath the Made Ground in BHA2.

5.2.3 The results for the laboratory testing undertaken within the alluvial deposits aresummarised below:

Table 7: Laboratory Testing Results in Alluvial Deposits

Laboratory Testing Value No of Tests

Peat

Moisture Content (%) 422 1

Liquid Limit (%) 386 1

Plastic Limit (%) 213 1

Plasticity Index (%) 173 1

Fines Content (%) 83 1

Organic Matter Content (%) 42 1

Cohesive


Liquid Limit (%) 32 1

Plastic Limit (%) 23 1

Plasticity Index (%) 9 1

Cobbles (%) 0.0 – 4.3 2

Gravel (%) 20.7 – 28.8 2

Sand (%) 26.9 – 37.6 2

Fines Content (%) 37.7 – 44.0 2


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5.2.4 It is assumed that no foundations will be founded on the Alluvial Deposits due to thehighly variable nature and low strength.

5.3 Kaolinised Granite

5.3.1 Kaolinised granite was encountered from 3.8 – 4.0mbgl and was classed as grade 4.Table 13 in BS EN ISO 14689-1 (Ref. 10) states that rock is completely weathered i.e.“all rock material is decomposed and/or disintegrated to soil. The original massstructure is still largely intact”. It should be noted that the classification is using adifferent grading scale to the one used in the 2010 GI.

5.3.2 The description for this stratum was predominantly soft grey slightly gravelly clay orsilt with a layer of medium dense light brown to orange slightly gravelly medium tocoarse sand between 4.0 – 5.7mbgl and a layer of medium dense very silty / clayeygravelly fine to medium sand at 6.45 – 9.00mbgl.

5.3.3 It should be noted that the majority of the kaolinised granite recovered during the2010 was described as medium dense to dense clayey fine to medium sand.

5.3.4 The results for the classification testing undertaken as part of the 2013 GI within thekaolinised granite are summarised below:

Table 8: Classification Test Summary (Kaolinised Granite)

Classification Testing Range of Values No of Tests


Liquid Limit (%) 37 – 39 2

Plastic Limit (%) 25 – 26 2

Plasticity Index (%) 11 – 14 2

5.3.5 Table 2 of BS 8002 (Ref. 14) recommended a value of 30 degrees for the angle ofshearing resistance for a clay soil with a plasticity index of 15% therefore this isdeemed an appropriate value for the cohesive component of the kaolinised granite.

5.3.6 The ReWaRD Reference Manual was reviewed and recommended an angle ofshearing resistance of 24 degrees for a low plasticity clay.

5.3.7 The results of the PSD testing undertaken as part of the 2013 GI within the kaolinisedgranite are summarised below:

Table 9: Summary of PSD Testing (Kaolinised Granite)

Grading Range of Values No of Tests

Cobbles (%) 0.0 3

Gravel (%) 13.2 – 37.7 3

Sand (%) 31.6 – 47.9 3

Silt (%) 20.9 – 48.0 3

Clay (%) 3.1 – 8.3 3


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5.3.8 Due to the presence of the granular component that it can be conservatively assumedthat there is no effective cohesion.

5.3.9 As there is no test data for the unit weight, Table 1 from BS 8002:1994 (Ref. 14) wasused in order to obtain values for the kaolinised granite, values from the ReWaRDReference Manual were also reviewed as a secondary source of information.

5.3.10 A unit weight of 19kN/m3 is deemed appropriate for the kaolinised granite material.

5.3.11 The SPT testing, in relation to reduced levels, undertaken for both the 2013 and 2010GIs are presented below. Values for the undrained shear strength, cu, for thecohesive have been correlated from N-values obtain during the GI using CIRIA report143 (Ref. 16).

5.3.12 The plots above show the SPT N-value in the kaolinised granite to generally increasewith depth, but also highly variable, thus indicating a possible value increase inundrained shear strength if a cohesive material or an increase in relative density if agranular material.

5.3.13 The equivalent SPT N-values derived from CPTs 04, 05 and 07 fall within the range of5 – 30 (shown on the graph above) and generally agree with the SPT N-values shownabove i.e. generally increase with depth.

5.3.14 CPTs 01, 02, 03 and 06 were stopped due to refusal within the superficial depositstherefore provide no information relating to the kaolinised granite.

105

110

115

120

125

130

135

0 20 40 60 80 100

Red

uced

Leve

l(m

AO

D)

N-Value

Kaolinised Granite: SPT N-Value Vs Reduced Level (mAOD) - 2010and 2013 GIs

BHA1 (2013)

BH01 (2010)

BH02 (2010)

BH03 (2010)

BH04 (2010)

Range on equivalentSPT N-values from CPT

results

SPT N-value Design Line


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5.3.15 The design line shown on the graph above takes into account the SPT testingundertaken as part of both the 2010 and 2013 GIs and the CPTs undertaken in 2013.

5.3.16 The values for cu for the cohesive kaolinised granite were derived from the in situSPTs undertaken within BHA1 and are presented below along with the design line.

5.3.17 The value for 80kPa is based on SPT testing within cohesive deposits and the valuesderived from the CPT testing undertaken whereas the increasing value at depthsbelow 10mbgl is based solely on SPT testing as the CPT testing was carried out onlywithin the top 10m.

5.3.18 A value of 35o for the angle of shearing resistance for the granular component of thekaolinised granite based of the values derived from the CPT testing.

5.3.19 A conservative value of 24o has been chosen for the kaolinised granite, taking intoaccount the cohesive component discussed previously.

4

6

8

10

12

14

16

18

20

22

24

70 80 90 100 110 120 130 140 150 160

Dept

h(m

bgl)

Undrained Shear Strength (kPa)Undrained Shear Strength (kPa) Vs Depth (mbgl)

Granular layer

Granular layer

Design line for undrainedshear strength


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5.4 Geotechnical Parameters

5.4.1 The following geotechnical derived parameters have been determined as discussedabove:

Table 10: Summary of Derived Geotechnical Parameters

StratumDerivedGeotechnicalParameter

Value Comment

Made Ground Unit weight,(kN/m3) 18 As recommended in BS8002 and the Reward

Manual based on descriptions.

Alluvial Deposits Unit weight,(kN/m3) 16 As recommended in BS8002 and the Reward


Kaolinised Clay

Unit weight,(kN/m3) 19 As recommended in BS8002 and the Reward


Undrained shearstrength, cu (kPa)[6 – 10mbgl]

80Results of in situ & laboratory testing. Verifiedusing Reward Manual based on descriptions.Undrained shear

strength, cu (kPa)[10 – 20mbgl]

80 – 140(increasing

linearly)

Angle of shearingresistance, ’(degrees)

24

Results of in situ testing and recommendations inBS 8002. Cohesive component taken intoconsideration. Verified using Reward Manualbased on descriptions.

Effectivecohesion, c’ (kPa) 0

Due to the presence of the granular componentthat it can be conservatively assumed that thereis no effective cohesion.

5.5 Geochemical Parameters

5.5.1 The results of the geochemical testing undertaken on samples from the alluvialdeposits and granite are summarised below.

5.5.2 This includes the determined characteristic values using the methods given in BRESpecial Digest 1 (Ref. 17) and the Design Sulphate (DS) class and the AggressiveChemical Environment for Concrete (ACEC) classification. Mobile groundwaterconditions were assumed. This ties in with a value of DS-1 and AC-1 determined forthe site in the BHD geo-environmental report.

Table 11: Geochemical Testing Summary

StrataCharacteristicWater Soluble

SO4 (g/l)pH No of Tests DS Class ACEC

Classification

Alluvial Deposits (Peat) <0.01 6.0 1 DS-1 AC-1

Alluvial Deposits (Clay) 0.01 5.3 2 DS-1 AC-2z

Kaolinised Granite 0.01 6.1 3 DS-1 AC-1


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6 ENGINEERING INTERPETATION

6.1 Main Access Road

6.1.1 The proposed main access road into, around and out of the site is to be constructedof tarmac and shall be capable of carrying loads greater than 40 tonnes.

6.1.2 In situ California Beating Ratio (CBR) testing or equivalent should be undertaken toinform appropriate pavement design for these roads. Clarity regarding the preciseloads will be required prior to any CBR testing being carried out.

6.2 Rig Plant, Spill Containment Area and Drilling Rig Foundation Pad (includingWells)

6.2.1 The ancillary plant associated with the drilling rig will be located within a single levelpaved area that will be a lipped concrete platform surrounding the drilling rigfoundation pad.

6.2.2 The ancillary plant comprises the following:

3 – 4 generator units;

SCR unit;

mud pumps;

water tanks;

mixing tanks and mud settling tanks;

2 fuel tanks;

Mud pit/lagoon; and,

Cuttings pit.

6.2.3 The drainage from the containment area will be channelled into the lagoon.

6.2.4 A foundation pad for the rig is to be constructed beneath the load-bearing sub-structure that supports the rig floor and mast. This pad has to be level and be capableof supporting a load of approximately 500 tonnes.

6.2.5 It is estimated that the foundation pad will cover an overall surface area ofapproximately 15 x 25 m and will need to be constructed and allowed sufficient timeto cure prior to the arrival of the drilling rig.

6.2.6 The two wells will be approximately 6 – 8 m apart at surface. Each well requires acellar, approximately 3m diameter by 4m depth constructed of concrete rings withinthe centre of the pad with the base of the cellar being concrete.

6.2.7 Assuming the load is spread over a 10 x 10m area, this results in an approximateeffective area of 86m2. The pressure acting across this area would be approximately60kPa.

6.2.8 Regarding founding on Made Ground, BS 8004 (Ref. 18) states that “all made groundshould be treated as suspect because of the likelihood of extreme variability. Anyproposal to found a structure on made ground should be investigated with extremecare.”


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6.2.9 BS 8004 (Ref. 18) states that peat and organic soils are “highly compressible, andeven lightly loaded foundations will be subject to considerable settlements over a longperiod if placed on them. For this reason these soils are not suitable for carrying theloads from important structures.” It continues, “in general, it is necessary to carryfoundations down through peat and organic soil to a reliable bearing stratum below”.

6.2.10 As differential settlements are required to be minimised, the foundations for both theconcrete pavement and rig foundation should be below the Made Ground and softalluvial deposits and founded in the kaolinised granite (encountered at a depth ofapproximately 4mbgl).

6.2.11 Table 1 from BS 8004 (Ref. 18), provides presumed allowable bearing values understatic loading for a variety of soil types. Based on the soil descriptions given in theexploratory hole logs, the following presumed allowable bearing pressures can beassumed:

Medium dense sand: 100 – 300kPa

Firm clay: 75 – 150kPa

6.2.12 Please note that no addition has been made for the depth of embedment of thefoundations, and the width of the foundations is no less than 1m. Groundwater levelhas been assumed to be at a depth not less than below the base of the foundation.

6.2.13 Using the following expression from Terzaghi and assuming a Factor of Safety of 3,an allowable bearing capacity was determined using the geotechnical parametersdetermined through in situ and laboratory testing:

qnu = cNc + p’o (Nq – 1) + ½ BN

Where:

Unit weight of the soil below the foundation level

c Cohesive shear strength of the soil

p’o Effective overburden pressure at foundation level

B Foundation width

Nc, Nq and N Bearing capacity factors (Terzaghi)

6.2.14 An allowable bearing capacity of approximately 500kPa was determined for thekaolinised granite.

6.2.15 If the foundations are to be based on the kaolinised granite, the net increased inpressure of this stratum is negligible therefore the amount of settlement is assumed tobe negligible.

6.2.16 Concrete Platform (Spill Containment Area)

6.2.17 The overall footprint of this concrete platform including the rig floor substructure andancillary plant is typically 120 x 60m. The thickness of this platform is unknown. Aconservative estimate of the pressure acting across this area, taking into account thesite offices and traffic, of 30kPa has been assumed.


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6.2.18 Based on a minimum undrained shear strength of 40kPa and a minimum angle ofshearing resistance of 30o, the rig plant and spill containment area should be foundedat a depth of at least 1.00mbgl. This is provided that any very soft to soft or highlyorganic material at formation level is dug out and replaced with suitable material.Consideration should be given to the use of geogrids installed to the manufacturer’srecommendations.

6.2.19 The net increase in pressure of the concrete platform is minimal therefore the amountof settlement is assumed to be negligible.

6.3 Conductor Pipe

6.3.1 The last part of the enabling works will be the installation of a 30” diameter steelconductor pipe in the base of each well cellar. This needs to be in place before thedrilling rig is mobilised. The purpose of the conductor is to isolate the subsoil and nearsurface weathered horizon and protect the near surface groundwater system.

6.3.2 The depth of this pipe depends on the near-surface geological conditions, but giventhe high degree of shallow kaolinisation at this site, it is anticipated that eachconductor may need to be in the region of 50m in length.

6.3.3 It is recommended that the conductor pipes are installed by drilling methods andbottom-grouted into place, as opposed to being driven, to prevent the potential forbuckling of the pipe within the kaolinised granite.

6.3.4 The pipes would need to be installed to a minimum depth of 5m into the competentrock, which, from the information obtained, would be to depths in the order of 50mbgl.This would provide between 25-30m of penetration into the saturated zone, whichshould be sufficient to mitigate the potential for the near-surface groundwater to beaffected. Should competent rock be encountered at depths of 25mbgl or less, whichis considered unlikely from the information obtained, the conductor pipes shouldextend to a minimum depth of 30mbgl for similar reasons.


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7 GEOTECHNICAL RISK REGISTER

7.1.1 A health and safety hazard and risk register has been compiled. As this is a livedocument, this will be regularly updated and guidance will be sought from all partiesinvolved in the design and implementation of the works.

7.1.2 Residual health and safety risks will be highlighted on the construction drawings.

7.1.3 The scoring system used in the register below is as follows:

Probability(P)

Impact/Consequence (I) Risk Rating Risk

(PxI=R) Response

Very likely 5 Very high 5 Intolerable 17 to 25 Unacceptable

Probable 4 High 4 Intolerable 13 to 16 Unacceptable

Likely 3 Medium 3 Substantial 9 to 12 Early attention

Unlikely 2 Low 2 Tolerable 5 to 8 Regularattention

Negligible 1 Very low 1 Trivial 1 to 4 Monitor

Ground Investigation Report for the Eden Deep GeothermalProject Pre-Enabling Works, Cornwall


- 33 -

Table 12: Geotechnical Risk Register

Feature HazardBeforeControl Risk Control Measure (RCM)

AfterControl

P I R P I R

Geotechnical

Variability of material properties acrosssite 4 3 12

Geotechnical parameters chosen are moderatelyconservative to take into account the variability of theground conditions.

2 3 6

Excessive and / or differential settlementof underlying alluvial deposits 4 3 12

Appropriate geotechnical recommendations (i.e. dig outunsuitable material and found foundations on competentstrata – the kaolinised granite) as detailed in Section 6.

2 3 6

Geochemical Aggressive ground conditions andsulphate attack on concrete and grout. 2 3 6 Implement all recommendations of BRE Special Digest 1

during detailed design of buried structures 1 3 3

ContaminationContaminated materials encounteredcausing delays and disposal/ treatmentcosts.

2 3 6

Limited extent of Made Ground (<3m thickness) identifiedduring the intrusive GI works. Appropriate treatment orremoval of materials identified due to potential presence ofasbestos.

1 3 3

Landowners Landowner objections causing delay toprogramme 3 4 12 Site wholly within Eden Project site boundaries 1 4 4

Archaeology Archaeological finds made during workscausing delays to programme. 1 2 2 No indication of archaeological features or materials in the

site vicinity 1 2 2

Hydrogeological Buckling of the conductor pipe duringinstallation 4 4 16 Installation using drilling and grouting as opposed to

driving methods. 1 4 4


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8 REFERENCES

1. Design Manual for Roads and Bridge (DMRB), Volume 4, Section 1, Part 2,HD22/08-Managing Geotechnical Risk

2. Buro Happold ‘026893 Eden Geothermal Geoenvironmental Interpretative Report July 2010

3. British Geological Survey (BGS) Sheet 347 Bodmin (Solid) scale 1:50,000, 1982

4. Environment Agency, www.environment-agency.gov.uk (accessed December 2013)

5. Geoguide 3: Guide to Rock and Soil Descriptions, Geotechnical Engineering Office, CivilEngineering Department, Government of the Hong Kong Special Administrative Region

6. BS EN 1997-2:2007 ‘Geotechnical Design- Part 2: Ground Investigation and Testing’, 2007

7. BS 5930:1999+A2:2010 ‘Code of Practice for Site Investigations’, 2010

8. BS 1377-1 to 9 ‘Methods for Test for Soils for Civil Engineering Purposes’, 1990

9. ICE Publishing, ‘Specification for Ground Investigations’, 2nd edition 2012

10. BS EN 14688 – Geotechnical Investigation and Testing – Identification and Classification ofSoil Part 1 Identification and Description, 2002.

11. BS EN 14688 – Geotechnical Investigation and Testing – Identification and Classification ofSoil Part 2 Principals for a Classification, 2004.

12. BS EN 14689 – Geotechnical Investigation and Testing – Identification and Classification ofRock Part 1 Identification and description, 2003

13. C J Associates ‘Ground Investigation No. AB0533 Factual Report The Eden DeepGeothermal Project Pre-enabling Works, Cornwall September 2013’

14. BS 8002:1994 Code of Practice for Earth Retaining Structures

15. ReWaRD Reference Manual Version 2.5

16. CIRIA Report 143 The Standard Penetration Test (SPT): Methods and Use 1995

17. BRE Special Digest 1:2005, ‘Concrete in Aggressive Ground’, Third Edition, 2005

18. BS 8004 – Code of Practise for Foundations , 1986

APPENDIX A – FIGURES

Date: Scale: Sheet:

Designed:

Drawn:

Approved:

Checked:

© Copyright Parsons Brinckerhoff

App

Chk

ByDescription

DateRev

A1

Plo

t D

ate

:

26

/0

6/2

01

3 0

9:1

2:3

9

G:\P

ro

je

cts\3

51

28

19

A-H

HE

E

de

n P

ro

je

ct G

eo

th

erm

al\H

D

wg

s\1

C

urre

nt\G

00

1_

2.d

wg

File

N

am

e:

14/06/2013

Gile

s, B

en

Lo

gin

:

Title:Site/Project:Client:

Tel: 44-(0)117-933-9300

Fax: 44-(0)117-933-9253

Queen Victoria House

Redland Hill, Redland

Bristol BS6 6US

Notes:

Project Number: Revision:Drawing Number:

BRG

IJK

IJK

IJK

1:500

Proposed Exploratory

Hole Locations

Eden GeothermalBalfour Beatty Regional

Civil Engineering

3512819A-HHEG/001

2

Borehole (Buro Happold, March 2010)

Trial Pit (Buro Happold, March 2010)

Window Sample (Buro Happold, March 2010)

Previous Investigation Locations

Dynamic Sampling/Rotary Cored Borehole

Proposed Investigation Locations

A1

1. This drawing is based on topographical survey data on Kemp

Engineering and Surveying drawing Nos. 10-1624-001C and 002C

dated 01-04-10 and the Proposed Layout of Deep Geothermal Site.

Rotary Percussive Hole & Down Hole Geophysical Logging

A2

1 19.03.13 Soakaway trial pits S1-S3 added. BRG IJK IJK

2 14.06.13 Proposed investigation locations revised. BRG KH IJK

Proposed Exploratory Hole

Co-ordinates

A1204323.90, 55650.22

A2204347.03, 55641.37

CPT1204284.55, 55623.94

CPT2204280.66, 55650.26

CPT3204296.54, 55678.97

CPT4204325.06, 55683.46

CPT5204368.91, 55683.28

CPT6204373.71, 55633.89

CPT7204324.68, 55627.98

Static Cone Penetrometer Testing

CPT1-7

Documents

GROUND INVESTIGATION REPORT FOR THE EDEN DEEP … · investigation works comprised of the following exploratory holes: xFour boreholes (BH01 to BH04) between 23.0 and 50.0m deep were