Stability Risk Assessment.Pdf

Home , Chalk Group

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

GEOTECHNICAL

ENVIRONMENTAL

WYG ENVIRONMENTAL LTD.

MAYTON WOOD QUARRY

ENVIRONMENTAL PERMIT APPLICATION

Stability Risk Assessment Report

GEC NO: GE200243006

Geotechnical and Environmental Ltd

10 Seven Acres Road, Weymouth, Dorset. DT36DG Tel: +44 (0)800 0407051 www.geosure.co.uk

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

WYG ENVIRONMENTAL LTD.

MAYTON WOOD QUARRY

ENVIRONMENTAL PERMIT APPLICATION

Stability Risk Assessment

GEC NO: GE200240610

Document History:

Reference: GE20024/SRA/V1 Date of Issue Document Description Prepared

30/11/2020 Stability Risk Assessment Dr David Fall CGEOL FGS

GEOTECHNICAL AND ENVIRONMENTAL CONSULTING LTD., 10 Seven Acres Road, Weymouth, Dorset. DT3 6DG. Telephone: +44 (0)800 0407051 www.geosure.co.uk

GE200240610 i Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

CONTENTS

1.0 INTRODUCTION 1

2.0 STABILITY RISK ASSESSMENT 9

3.0 MONITORING 18

LIST OF TABLES

Table SRA1 Local Stratigraphy of the Application Area 3 Table SRA2 Groundwater Strikes during the Construction of the Boreholes 3 Table SRA3 Groundwater Monitoring Data 4 Bibliography of Published Sources used in the Determination of the Table SRA4 7 Characteristic Geotechnical Parameters of the Inert Waste Table SRA5 Side Slope Subgrade Stability – Summary of Characteristic Geotechnical Data 11 Table SRA6 Side Slopes Liner Stability – Summary of Characteristic Geotechnical Data 11 Table SRA7 Waste Mass Stability - Summary of Characteristic Geotechnical Data 11 Table SRA8 Partial Factors used in Design in Accordance with the UK National Annex to 12 EC7 Table SRA9 Side Slope Subgrade Stability – Summary of Results 13 Table SRA10 Side Slope Liner Stability – Summary of Results 14 Table SRA11 Waste Mass Stability – Summary of Results 15

LIST OF FIGURES Figure SRA1 Cross-Sections Through Side Slope Subgrade 6

LIST OF APPENDICES Appendix 1 SlopeW Worksheets Side Slope Subgrade Appendix 2 SlopeW Worksheets Side Slope Liner Appendix 3 SlopeW Worksheets Waste Mass

GE200460610 - ii - Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

1.0 INTRODUCTION

Report Context

1.1 The operator of the installation is Mick George Ltd. (MGL).

1.2 WYG Environmental Ltd. (WYG) have instructed Geotechnical & Environmental Consulting Ltd. (GEC) to undertake a Stability Risk Assessment (SRA) to form part of an Environmental Permit Variation Application for Mayton Wood Quarry.

1.3 This environmental permit application is for the permanent placement of inert material within the void formed by the extraction of minerals.

1.4 The following documents and drawings have been supplied by the Client and referred to in the compilation of this Report:-

• Mayton Wood Quarry, Environmental Permit Application, Environmental Setting and Site Design – WYG Report No A116126 dated November 2020.

• Mayton Wood Quarry Extension Groundwater Protection and Hydrogeological Impacts – TerraConsult Report No. 10152-RO5 dated June 2019.

• Mayton Wood Quarry, Environmental Permit Application – Operating Techniques - WYG Report No. A116126 dated November 2020.

• Mayton Wood Quarry Extension Geotechnical Design Report – TerraConsult Report No. 10152-RO6 dated November 2020.

1.5 This Report has been completed in conjunction with the Environmental Setting and Site Design Report (ESSD) (June 2018). It is not a standalone document and factual data related to the site, its setting and receiving environment are located in the ESSD and referred to in this document. All drawings referred to in this SRA are to be found in the ESSD unless otherwise stated.

1.6 This document has been prepared in accordance with the Stability Risk Assessment Report Template (Version 1 – March 2010).

Conceptual Stability Site Model

Location

1.7 This Stability Risk Assessment refers to the area that is included within the Environmental Permit Application boundary shown on Drawing No MGL/A116126/PER/01 of the Environmental Setting and Site Design Report and covers the area known as Mayton Wood Quarry Extension.

GE200240610 1 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

1.8 The application site is located approximately 700m to the west of the hamlet of Little Hautbois in Norfolk and approximately 12.6km NNE of the centre of Norwich. The centre of the site is located at NGR 624200,320969.

1.9 The application site comprises three fields to the south of the existing Mayton Wood Quarry site which are currently in agricultural use and are separated by hedgerows. The proposed facility will cover an area of approximately 32.2ha and is on gently north easterly sloping terrain (17mAOD to 15mAOD) towards the River Bure.

Regional Geology

Solid Geology

1.10 With reference to British Geological Survey Sheet 147 Alysham1:50000 Sold & Drift, the Application site is underlain by the Wroxham Crag Formation overlying units of the White Chalk Group which are up to 300m thick.

1.11 The BGS Lexicon of Named Rock Units describes the Wroxham Crag Formation a sheet of interbedded gravels, sands, silts and clays. The gravels are dominated by flint (up to c.80%) and by quartz and quartzite (up to c.60%), with far-travelled minor lithologies. The deposits are interpreted as being of estuarine and near-shore marine origin,

Superficial Geology

1.12 The geological map records superficial deposits across the site comprise the Happisburgh Glaciogenic Formation.

1.13 The Happisburgh Glaciogenic Formation consists of a range of diamictons, sands and gravels, sands and laminated silts and clays. The diamictons (Happisburgh Till, Corton Till and California Till members) are typically sandy matrix-supported diamictons that contain a high abundance of flint and quartzose lithologies

Structural Geology

1.14 No structural features are shown within the area of the permit application boundary.

Local Geology

1.15 14No. boreholes have been undertaken within the site area and reported in the Hydrogeological Risk Assessment. A precis of the stratigraphy encountered in these boreholes is presented as Table SRA1.

Table SRA1 Local Stratigraphy of the Application Area Stratigraphy Topsoil Sand & Gravels * Whi te Chalk Grou p Borehole No. From Thickness From Thickness From Thickness (mbgl) (m) (mbgl) (m) (mbgl) (m)

GE200240610 2 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

TerraConsult Borehole s 2016 BH1 GL 0.25 0.25 8.55 8.80 >6.70 BH2 GL 0.25 0.25 6.25 6.50 >7.50 BH3 GL 0.30 0.30 4.50 4.80 >5.70 BH4 GL 0.30 0.30 8.20 8.50 >2.50 BH5 GL 0.50 0.50 8.50 9.00 >3.00 BH6 GL 0.50 0.50 7.00 7.50 >4.50 BH7 GL 0.90 0.90 7.80 8.70 >3.30 BH8 GL 0.90 0.90 7.10 8.00 >5.00 MGL 2018 BH9 GL 3.70** 3.70 7.80 11.50 >7.00 BH10 GL 0.40 0.40 6.50 6.90 >14.10 MGL 2014 BHA Not Recorded (in GL 7.60 7.60 >7.40 quarry area) BHB Not Recorded (in GL 4.60 4.60 >11.40 quarry area) BHC GL 0.60 0.60 4.60 5.20 >10.30 BHD Not Recorded (in GL 5.70 5.70 9.30 quarry area) *Insufficient detail on borehole logs to allow discrimination between the Happisburgh Glaciogenic Formation and the Wroxham Crag Formation **Probable Made Ground

1.16 The borehole logs indicate the local ground conditions comprise up to 0.90m of Topsoil over 4.50 TO 8.55m of sands and gravels with units of the White Chalk Group forming the basal unit of the ground investigation. In BH9 3.70m of probable Made Ground was reported.

1.17 The major diagnostic feature used to discriminate between the Happisburgh Glaciogenic and Wroxham Crag Formations is the presence of exotic lithologies in the Wroxham Crag Formation. The level of description in the TerraConsult engineering logs is insufficient to make this differentiation; therefore, the two strata will be combined for the purposes of this SRA. There is sufficient similarity between the two materials to have no noticeable effect on the results of the side slope subgrade assessment.

Hydrogeology

1.18 Groundwater was encountered during the installation of the 8No. boreholes (Table SRA 2) overleaf

Table SRA2: Groundwater Strikes during the Construction of the Boreholes Borehole Water Strike Strata Description ID mbgl

BH1 13.50 Structureless light brown /cream Chalk

BH2 12.00 Structureless light brown yellowish gravelly Chalk

GE200240610 3 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Borehole Water Strike Strata Description ID mbgl

BH3 6.70 Structureless light brown / dark cream slightly gravelly Chalk

BH4 9.00 Structureless light brown / cream Chalk

BH5 9.00 Structureless light brown / yellowish cream Chalk

BH6 8.50 Structureless light brown / yellowish cream slightly gravelly Chalk

BH7 8.55 Structureless light brown / yellowish cream Chalk

BH8 9.70 Structureless very light brown / creamy yellow Chalk

BH9 15.30 Structureless white putty Chalk

BH10 15.80 Chalk with Flints

BHA 10.70 White flinty Chalk

BHB 10.70 White flinty Chalk

BHC 12.00 White flinty Chalk

BHD 10.80 White flinty Chalk

1.19 Groundwater strikes occurred at all locations and were consistently located within the White Chalk Group thus ensuring that dry working conditions will be maintained, as these boreholes were drilled during October and January when groundwater elevations are close to being at their maximum.

1.20 Groundwater monitoring has been undertaken in all boreholes since their construction. The range of groundwater depths recorded are presented in Table SRA 3.

Table SRA 3: Groundwater Monitoring Data BH ID BH1 BH2 BH3 BH4 BH5 BH6 BH7 Minimum Depth (mbgl) 11.54 11.20 6.36 7.46 7.46 10.14 11.85 Maxim um Depth ( mbgl) 13.04 13.53 8.95 9.20 8.69 10.55 12.74 Mean Depth (mbgl) 12.29 12.45 7.66 8.33 8.08 10.35 12.30

BH ID BH8 BH9 BH10 BHA BHB BHC BHD Minimum Depth (mbgl) 10.36 12.47 11.94 9.80 9.37 10.94 10.54 Maximum Depth (mbgl) 12.17 11.88 11.28 8.09 8.19 7.97 8.73 Mean Depth (mbgl) 11.27 12.08 11.56 9.21 9.14 9.24 9.70

1.21 According to the MAGIC website the application site is underlain by both a Secondary B and Principal Aquifers (the Chalk).

Hydrology

1.22 The application area lies within the catchment of the River Bure which flows to the southwest, passing approximately 410m at its closest point to the northeast of the site. There is currently a

GE200240610 4 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

surface water channel identified on OS maps which runs from west to east through the centre of the site along a field boundary. The channel is located within a valley feature from 14mAOD to 10mAOD and forms a tributary to the River Bure at <4mAOD.

1.23 It is noted that the stream is not identified on maps downstream of the site between the 10mAOD and 5mAOD contours, and a surface water feature only remerges at the bottom of the valley where there is a pond, which is likely to be spring fed at <5mAOD which discharges via a tributary to the River Bure. It is likely therefore that the stream indicated on the OS maps was an ephemeral stream which only contained surface run-off that does not immediately infiltrate through the clay rich soils after rainfall events.

1.24 The site is not located in flood warning area.

Basal Subgrade Model

1.25 The void will be created by the extraction of the sands and gravels of the undifferentiated Happisburgh Glaciogenic and Wroxham Crag Formations exposing both the Wroxham Crag Formation and the White Chalk Group in the base of the void.

1.26 The White Chalk is described as structureless chalk in the 8No. boreholes logs and therefore is considered consistent with CIRIA Grade D Chalk.

1.27 Based on the groundwater strikes recorded in the boreholes and subsequent monitoring groundwater levels will remain below the base of the void.

Basal Lining System

1.28 A basal lining system will be constructed using locally sourced material to create a basal liner 0.5m thick with a permeability of 5x10-8m/s or 1m thick with a permeability of 1x10 -7m/s.

Side Slope Subgrade Model

1.29 The side slope subgrade will be exposed during the mineral extraction works and will comprise sands and gravels of the Happisburgh Glaciogenic Formation and Wroxham Crag Formation. Similarities in the lithology of these two strata has made it impossible to differentiate between them so they will be dealt with as a single unit (Undifferentiated Sands and Gravels) in any further analyses. These Undifferentiated Sands and Gravels (USG) are described as dark orange sandy Gravel / gravelly Sand, the gravel component is fine to coarse and largely quartz although other minor lithologies may be present.

1.30 Cross sections through the side slope subgrade are presented in scheme specific HRA and reproduced herein as Figure SRA1 overleaf. These sections show the highest side slope will be approximately 9.00m along the western side of the void.

GE200240610 5 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Figure SRA 1 Cross-Sections Through Side Slope Subgrade

Side Slope Lining Model

1.31 It is likely that the side slope lining will be placed in stages as the waste level rises such that side slope lining is not left unsupported for long periods of time before being buttressed by the inert waste.

1.32 The side slope liner will comprise a geological barrier 1.00m thick with a minimum hydraulic conductivity of less than 1.0 x 10m -7 m/s or 0.5m thick with a hydraulic conductivity of 5.0 x 10 -8 m/s.

Inert Waste Mass Model

1.33 It is proposed that Mayton Wood Quarry Extension will be used for the placement of inert waste only.

GE200240610 6 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

1.34 The inert waste is liable to comprise locally derived arisings from earthworks, foundation construction works and demolition debris.

1.35 The geology of the local area is variable and comprises both coarse- and fine-grained materials. As most of the inert waste is likely to comprise locally derived materials. With respect to stability the worst case would be a waste mass comprised entirely of fine-grained materials. Therefore, the inert waste model will comprise a generic fine-grained material and the characteristic geotechnical parameters attributed to this material will be based on a number of sources.

Table SRA4: Bibliography of Published Sources used in the Determination of the Characteristic Geotechnical Parameters of the Inert Waste Author Date Title Carter M., & Bentley S.P. 2016 Soil Properties and Correlations 2 nd . Ed. Look B. 2007 Handbook of Geotechnical Investigation and Design Tables Duncan J.M., & Wright, 2005 Soil Strength & Slope Stability S.G. CIRIA C583 2004 Engineering in the Lambeth Group 1 Hight D.W., McMillan, F., 2003 Some Characteristics of the London Clay: IN Tan et Powell, J.J.M., Jardine, al. (Eds.) Characterisation and Engineering Properties R.J., & Allenou, C.P. of Natural Soils. 1 1 the inclusion of these two strata specific references should not be taken as a suggestion of the Inert Waste content.

1.36 The maximum temporary waste slope during placement operations will be restricted to 1(v):3(h).

1.37 The waste will be compacted in horizontal layers across the base of the cell to the pre- settlement restoration level.

Capping System Model

1.38 On completion of filling to final levels, the site will be capped with 1m of restoration soils comprising not less than 0.3m of topsoil. In accordance with the requirements of the Landfill Directive, an engineered cap (clay or plastic) is not required.

GE200240610 7 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

2.0 STABILITY RISK ASSESSMENT

Risk Screening

Basal Subgrade Screening

2.1 The basal subgrade will be formed of the in-situ White Chalk Group and / or the Wroxham Crag Formation. As the void will be formed by the excavation and extraction of material there will be a net unloading of the ground. The replacement of the excavated material with inert waste will not fully reload the soil as there is a difference in the unit weight of the excavated material and the replaced inert waste this will cause only limited elastic recompression of the basal subgrade.

2.2 The White Chalk like all carbonate materials can be prone to karstic weathering and the production of solution features. Although not considered a risk requiring stability analysis, it is recommended that careful inspection of the subgrade is undertaken prior to the placement of the basal liner. Further details and recommendations are presented in Section 3 of this SRA.

2.3 No stability analysis of this component is considered necessary.

Basal Lining System Screening

2.4 The basal liner is to comprise locally sourced fine-grained material that will be placed as either 1.00m of clay with a hydraulic conductivity of 1.0 x 10 -7m/s or 0.5m of clay with a hydraulic conductivity of 5.0 x 10 -8m/s.

2.5 Based on both the groundwater strike depths and subsequent groundwater monitoring data (Tables SRA2 and SRA3) groundwater will remain below the base of the void. Therefore, uplift on the underside of the basal liner is not considered a risk at this site and no further analyses of the basal liner is considered necessary.

Side Slope Subgrade Screening

2.6 The side slopes will be formed as part of the mineral extraction process carried out by a suitably qualified and experienced specialists and be subject to geotechnical appraisal under Regulation 33 of the Quarries Regulations. It can therefore be assumed that the void will have been designed to be stable during the extraction works. Given the stratigraphy and description of the side slope subgrade it is unlikely that the materials will become unstable during the inert waste placement phases of the works; however, a stability check of the side slope subgrade will be carried out for completeness.

GE200240610 8 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Side Slope Lining System Screening

2.7 An artificially established side-lining system, comprising either 1.0m of clay with a hydraulic conductivity of 1.0 x 10 -7m/s or 0.5m of clay with a hydraulic conductivity of 5.0 x 10 -8m/s is to be placed on the side slopes of the void. Given the expected gradient of the side slopes subgrade it is probable that the side slope lining system will be placed in sections; such that the side slope liner will not achieve drained conditions prior to the placement of inert waste.

2.8 Groundwater outflows into the void are not expected as the standing groundwater level is below the base of the void within the White Chalk.

2.9 Analysis of this component is considered necessary to investigate the short-and long-term stability of this element prior to the placement of the inert waste.

Waste Mass Screening

2.10 This component will require a detailed geotechnical analysis in order to assess the stability of the waste mass.

Capping System Screening

2.11 Based on the finished proposed finished contours presented in Drawing No. M35/F/19/04 a maximum gradient of 1(v):3 (h) will be created which will remain stable under all foreseeable ground conditions. Therefore, no stability analysis of the restoration soils is considered necessary.

Justification of Modelling Approach and Software

2.12 Two-dimensional limiting equilibrium stability analyses will be used in the assessment of the stability of the various components of the proposed Southern Extension. The method of analysis used in each case was determined from an examination of the form of failure being considered.

2.13 The stability analyses were carried out using the Slope/W computer programme.

2.14 The Morgenstern and Price Method was used in the analyses to determine the factor of safety against instability for both total stress and effective stress conditions.

Justification of Geotechnical Parameters Selected for Analyses

Parameters Selected for Side Slopes Subgrade Analyses

2.15 In-situ and laboratory geotechnical testing was carried out and reported in the Geotechnical Design Report (TerraConsult Report No. 10152 R06 dated January 2020) and characteristic geotechnical parameters for the side slope subgrade presented. The values presented in the TerraConsult Report have been reviewed and values checked and found to be appropriate for the USG (Table SRA5).

GE200240610 9 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Table SRA5: Side Slope Subgrade Stability – Summary of Characteristic Geotechnical Data Material Unit Weigh Total Stress Effective Stress

3 2 2 γ (kN/m ) cu (kN/m ) φu (˚) c’ (kN/m ) φ’ (˚) Undifferentiated Not Applicable Granular 17 0 37 Sands and Gravels Material

Parameters Selected for Side Slope Liner Analyses

2.16 The side slope liner is to be constructed using an appropriate fine-grained material. Typical values for clay materials have been used to define the characteristic geotechnical values of the side slope liner material (Table SRA5).

Table SRA6: Side Slope Liner Stability – Summary of Characteristic Geotechnical Data Material Unit Weigh Total Stress Effective Stress

3 2 2 γ (kN/m ) cu (kN/m ) φu (˚) c’ (kN/m ) φ’ (˚) Side Liner 19 50 0 2 25

Parameters Selected for Waste Analyses

2.17 The Parameters of the inert waste appropriate for this site were selected on the basis of the information presented in the various publications listed in Table SRA4. As stated previously the inclusion of stratum specific references should not be taken as guidance to what may be included within the Inert Waste but purely as another source to help define a generic fine- grained material. In reality, it is likely to comprise a mixture of fine- and coarse-grained materials and demolition materials. Therefore, the treatment of the inert waste as fine-grained will be the worst-case as the inclusion of any coarse-grained material will increase its characteristic angle of shearing resistance.

Table SRA7: Waste Mass Stability - Summary of Characteristic Geotechnical Data Material Bulk Unit Total Stress Effective Stress

Weight γk 3 2 2 (kN/m ) cuk (kN/m ) φuk (˚) c’ k (kN/m ) φ’k (˚) Waste 17 50 0 5 25 Mass

Selection of Appropriate Factors of Safety

2.18 The stability analyses have been carried out in accordance with EC7. The United Kingdom have adopted Design Approach 1 (DA1) Combination 1 & 2 (C 1 & 2) whereby partial factors

GE200240610 10 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

are applied to either the actions or the material properties and a resultant degree of utilisation of less than 1.00 is required.

Table SRA8: Partial Factors used in Design in Accordance with the UK National Annex to EC7 Design Combination Partial Factor Partial Factor Value Approach Sets Actions A1

Permanent (G) Unfavourable γG;dst 1.35

Favourable γG;stb 1.00

Variable (Q) Unfavourable γQ;dst 1.50

Favourable γG;dst 0 1 A1 + M1 + R1 Materials M1

Coefficient of shearing resistance ( tan φ) γφ’ 1.00

Effective cohesion (c’ ) γc’ 1.00

Undrained shear strength ( cu) γcu 1.00 Resistance R1

Resistance γR;e 1.00 1 Actions A2

Permanent (G) Unfavourable γG;dst 1.00

Favourable γG;stb 1.00

Variable (Q) Unfavourable γQ;dst 1.30

Favourable γG;dst 0 2 A2 + M2 + R1 Materials M2

Coefficient of shearing resistance ( tan φ) γφ’ 1.25

Effective cohesion ( c’ ) γc’ 1.25

Undrained shear strength ( cu) γcu 1.40 Resistance R1

Resistance γR;e 1.00

2.19 The values of the partial factors used are termed “nationally determined parameters” and EC7 (as published by CEN) allows these to be specified in National Annexes which recognise regional variations in design philosophy.

2.20 LFE4 – Earthworks in Landfill Engineering – Chapter 2 confirms the adoption of Design Approach 1 Combinations 1 and 2, and the nationally adopted partial factors.

Analyses

Side Slope Subgrade

2.21 The side slopes of the void will be formed during the mineral extraction phase of the works and will be subject to appraisal under Regulation 33 of the Quarries Regulations. However, for

GE200240610 11 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

completeness a stability of the side slope subgrade has been carried out using the cross sections provided as Figure SRA1.

2.22 The groundwater monitoring has shown that groundwater levels will remain below the base of the void and the free-draining nature of the coarse-grained sands and gravels means that porewater pressures will not affect the side slope subgrade.

2.23 Initially a 9.00m high slope in the USG has been analysed to determine the maximum face angle that will stand safely under DA1 Combination 1 and 2 Factoring.

2.24 The results of the side slope liner stability analyses are shown in Table SRA9 and the SlopeW worksheets presented in Appendix 1.

Table SRA9: Side Slope Subgrade Stability – Summary of Results Degree of Shear Strength Run File Name Utilisation Notes c φ C1 C2 E-W Section – Western End (Figure SRA1) 01 SSG1 0.76 Highest Slope 9.00m 0 37 Western End of E-W Section 02 SSG2 0.95 Steepest face gradient = 30° E-W Section - Eastern End (Figure SRA1)

03 SSG3 0.75 Assess the effect of the 0 37 04 SSG4 0.94 historic landfill to the east

Side Slope Liner Analyses

2.25 A side slope liner will be placed against the side slope subgrade. Based on the results of the side-slope subgrade analyses presented in Table SRA9 it is assumed that the side slopes are at 30°. The liner will be modelled as a 1.00m thick layer applied to the side slope subgrade applied to the side-slope subgrade, although in reality it is likely to be placed in lifts ahead of the inert waste placement. Both rotational failures entirely within the liner material and sliding along the side liner / side-slope subgrade will be considered.

2.26 The effects of long-term softening of the liner have been considered by reducing the effective cohesion of the liner material.

2.27 The results of the side slope liner stability analyses are shown in Table SRA10 and the SlopeW worksheets presented in Appendix 2.

Table SRA10: Side Slope Liner Stability – Summary of Results Characteristic Shear Degree of Liner Run File Name Strength Utilisation Thickness Notes c φ C1 C2 (m) Side Slope Gradient up to 30 °

GE200240610 12 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Rotational Failure Entirely within Side Slope Liner 01 SLINER1 0.11 0.50 02 SLINER2 0.10 50 0 Total stress 03 SLINER3 0.19 1.00 04 SLINER4 0.18

05 SLINER5 0.84 Long term 0.50 06 SLINER6 0.95 exposure – 25 Full effective 07 SLINER7 0.92 stress 2 1.00 08 SLINER8 0.96 conditions

09 SLINER9 0.97 0.50 Translational

10 SLINER10 0.96 1.00 failure

Waste Mass Analyses

2.28 The post extraction void may be up to 9m deep. Although considered unlikely that a 9m high waste face would be created given the phasing and placement of the inert waste in layers. However, to represent the worst case 9m high waste slopes will be considered in this analysis and the waste during placement operations will be restricted to 1(v) : 3(h).

2.29 Leachate pore fluid pressures may develop in the waste mass during filling due to infiltration. It is noteworthy that the term leachate as applied refers to direct precipitation or groundwater present within the inert waste at time of placement.

2.30 Given the composition (inert materials), landfill gas pressures are unlikely to develop within the waste mass.

2.31 Waste stability must be assessed as part of the design process for the temporary waste slope configuration. A Stability assessment is required for failure modes wholly within the waste body. The analyses of the failures wholly within the waste were based on Table 3.43 “Failure Wholly within the Waste” of the Environmental Agency R&D Technical Report P1-385/TR2.

2.32 Slope/W has been used to undertake the investigation into failures wholly within the waste mass for both total and effective stress conditions.

2.33 The effects of variations in leachate pressure were modelled by investigating the effects of increased leachate levels on the factor of safety against instability within the waste body.

2.34 Results of the analyses are presented in Appendix 3 and can be summarised as follows:

Table SRA11: Waste Mass Stability – Summary of Results Waste Leachate Degree of Run File Name Notes Strength Level Utilization

GE200240610 13 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

C1 C2 1 WMass1 0.24 Total Dry Total Stress 2 WMass2 0.21 13 WMass3 0.43 1.00m 04 WMass4 0.46 05 WMass5 0.43 Increasing leachate level 4.00 measured from base of 06 WMass6 0.46 Effective waste mass 07 WMass7 0.48 6.00 08 WMass8 0.53

09 WMass9 Not Present 0.59 Cohesion = 0kN/m 2

Assessment

Basal Subgrade

2.35 The basal subgrade is to comprise the in-situ White Chalk Group and / or the Wroxham Crag Formation which are both considered competent and with no net increase in stress at basal subgrade level predicted, no settlement other than short term elastic recompression is expected.

2.36 Therefore, subject to careful inspection prior to the placement of the basal liner system, the basal subgrade is considered appropriate without any significant re-engineering.

Basal Liner

2.37 A basal liner of locally sourced fine-grained material will be placed across the entire base of the void. The basal liner will comprise either 1.00m of clay with a hydraulic conductivity of 1.0 x 10 -7m/s or 0.5m of clay with a hydraulic conductivity of 5.0 x 10 -8m/s.

2.38 Groundwater monitoring undertaken since 2016 has shown that groundwater will not impinge on the void and uplift pressure on the base of the liner will not be generated. Therefore, the basal lining system is considered stable in the form set out herein.

Side Slope Sub-Grade

2.39 The side slopes of the void will be formed as part of the mineral extraction works. It is appropriate to assume that the extraction works will be subject to Geotechnical Appraisal under Regulation 33 of the Quarries Regulations and as part of that appraisal it will be demonstrated that the side slope subgrade is stable at the planned angle of excavation.

2.40 However, a stability assessment of the side slope subgrade has been carried and shows to achieve long term stability under Design Approach 1 Combination 2 factoring side slope

GE200240610 14 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

subgrade batter angles should not exceed 30°. At this angle, a degree of utilisation of 0.95 is achieved under Combination 2 factoring.

2.41 The stability assessment presented herein has used characteristic geotechnical parameters presented in the TerraConsult GDR. It is possible that these values are over-conservative as a result of sample disturbance caused by the percussive drilling techniques used and the conservatism built into all empirical relationships. It may be possible to reappraise the side slopes once mineral extraction works have commenced and direct observations can be made.

2.42 The side slope subgrade analysis has demonstrated that the existing waste east of the proposed extension has no discernible effect on the stability of the side slope subgrade provided the proposed 8.00m standoff is maintained.

2.43 Provided the side slope subgrade batter angle does not exceed 30° the void will remain stable under all foreseeable conditions.

Side Slope Liner

2.44 For the purposes of this stability assessment the full height of the side slope liner has been modelled although it is likely it will be placed in advance of the inert waste placement to avoid long term exposure and degradation. Both the 0.50m and the 1.00m thick options have been considered in this assessment.

2.45 Both the 0.50m and 1.00m thick side slope liner have been analysed and shown to be stable in the short term under total stress conditions with a maximum degree of utilisation of <0.20 being returned under Design Approach 1, Combination 1 and 2 factoring.

2.46 If left unsupported in the long-term such that fully drained effective stress conditions are achieved the liner remains stable with a maximum degree of utilisation of 0.95 and 0.96 for the 0.50 and 1.00m thick liner configurations under combination 2 factoring.

2.47 A full height translational failure of the liner along the interface with the side slope subgrade has been considered by fully defining the slip plane. Under these conditions both the 0.5m and 1.00 thick side slope liner remain stable with a degree of utilisation of 0.97 and 0.96 respectively.

2.48 Given the closeness of these two results it is probable that the thickness of the liner has negligible effect on the stability of the side slope liner in fully effective stress conditions.

2.49 It can be concluded that side liner will remain stable under all foreseeable conditions and there are no easily identifiable differences in stability as a result of side liner configuration.

Waste Mass

2.50 The stability of the temporary waste face was analysed using the computer programme SLOPE/W to calculate the degree of utilisation of the restoring forces to prevent failure through the waste body for a range of circular failure surfaces using Morgenstern and Price’s method.

GE200240610 15 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

2.51 The importance of different leachate levels within the waste and their effect on overall stability were assessed. The effect of reduction of shear strength from peak to residual values has also been investigated.

2.52 The waste slope has a Degree of Utilisation of <1.00 (<100%) for all leachate levels up to 6.00m from the base of the waste body. A leachate level of 6.00m is considered extremely unlikely to occur under normal operating conditions and therefore represents a worst-case situation.

2.53 The waste slope has a Degree of Utilisation of 0.59 even if the value of the cohesion intercept of the waste reduces from 5kN/m 2 to 0kN/m 2

2.54 It is concluded that a 1(v) : 3(h) waste slopes will be stable for the range of leachate levels anticipated.

Capping System

2.55 Not a consideration at this site.

GE200240610 16 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

3.0 MONITORING

The Risk-Based Monitoring Scheme

3.1 Monitoring of the stability of the site is proposed in the form set out below. The objectives are to identify any instances of overall settlement of the structure, identify instability of the waste mass itself and instability of the side slope subgrade and lining system at the earliest possible juncture.

Basal Subgrade Monitoring

3.2 Prior to the placement of the basal liner it is recommended that the basal subgrade is carefully inspected to identify any soft spots. Particular attention should be paid to the White Chalk Formation for evidence of solution features which may take the form of areas of gravel within the chalk surface. If such features are identified they should be dealt with the excavation of the infill and replacement with properly compacted granular fill material to a minimum depth of 2.00m. If large features are identified, it is recommended that the advice of a suitably qualified geotechnical engineer is sort to design a suitably robust backfill / capping solution.

Basal Liner Monitoring

3.3 The basal liner will comprise locally derived materials which would have undergone appropriate permeability testing to ensure they meet the relevant permeability requirements.

3.4 If the basal liner is left exposed for any length of time a programme of routine monitoring should be undertaken to identify cracking as a result of drying and shrinkage or softening as a result of exposure to wet inclement weather. If either of these features are identified, the affected area should be excavated and replaced prior to the placement of inert waste.

Side Slope Subgrade + Lining Monitoring

3.5 The side slopes should be visually monitored for instability during the waste placement operations. In the event of any instances of instability appropriate action should be taken which may include buttressing the toe of the slope using inert waste material.

3.6 Although not anticipated, if perched groundwater bodies are identified during the mineral extraction phases, additional works may be required to prevent hydrostatic forces causing separation between the liner and side slope subgrade. This may involve phasing of the waste placement to buttress the liner or the localised placement of a drainage composite behind the side slope liner. Although, as stated previously, the requirement for either of these actions is considered highly unlikely.

Waste Mass Monitoring

GE200240610 17 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

3.7 The temporary slopes in the waste should be visually monitored and appropriate actions taken on any sign of instability. This would typically include a reduction in slope angle of the temporary waste slopes. Capping System Monitoring

3.8 The condition of the surface of all restored areas will be monitored on a regular basis as part of the site inspection regimen.

3.9 The surface will be checked for incipient signs of failure that might result from the occurrence of differential settlement within these deposits. These would include cracking, development of depressions or ponding and seepage of water. In the event that any symptom of incipient failure is detected the Environment Agency will be informed and a site action plan for remediation agreed.

3.10 The Surface of the restored areas will be monitored by land survey techniques on a regular basis. These checks will be on a annual basis to the fifth year after restoration, when the periodicity reviewed with the Environment Agency.

GE200240610 18 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Appendix 1

SlopeW Worksheets – Side Slope Subgrade

GE200240610 19 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

0.760 (DoU)

Mayton Wood Quarry Variable construction surcharge 16 Side-Slope Subgrade

15 SlopeW File SSG1

Design Approach DA1 14 Combination 1 Partial factors applied to Actions 13

12 Name: Undifferentiated Sands and Gravels 11 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 0 kPa 10 Phi': 37 °

8 Elevation (mOD) Elevation Name: White Chalk Slope Amgle 30 degrees 7 Model: Mohr-Coulomb or Unit Weight: 20 kN/m³ 1(v):1.7(h) Cohesion': 5 kPa 6 Phi': 35 °

3 0 10 20 30 Distance (m)

0.950 (DoU)

Mayton Wood Quarry Variable construction surcharge 16 Side-Slope Subgrade

15 SlopeW File SSG2

14 Design Approach DA1 Combination 2 Partial factors applied to Materials and 13 Variable Actions

Name: Undifferentiated Sands and Gravels 11 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 0 kPa 10 Phi': 37 °

8 Elevation(mOD)

Name: White Chalk Slope Amgle 30 degrees 7 Model: Mohr-Coulomb or Unit Weight: 20 kN/m³ 1(v):1.7(h) Cohesion': 5 kPa 6 Phi': 35 °

3 0 10 20 30 Distance (m)

GE200240610 20 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

23 0.751 (DoU)

19 Mayton Wood Quarry

Side-Slope Subgrade

17 Name: Historic Landfill SlopeW File SSG3 Model: Mohr-Coulomb Unit Weight: 16 kN/m³ Design Approach DA1 Cohesion': 2 kPa Phi': 21 ° Combination 1 Partial factors Ru: 0.3 applied to Actions 15 Include Ru in PWP: Yes

Variable construction surcharge

13 Elevation (mOD) Elevation

11 8.0787 m

Name: Undifferentiated Sands and Gravels 9 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 0 kPa Phi': 37 ° Include Ru in PWP: No Slope Amgle 30 degrees 7 or 1(v):1.7(h)

Name: White Chalk Model: Mohr-Coulomb Unit Weight: 20 kN/m³ 5 Cohesion': 5 kPa Phi': 35 ° Include Ru in PWP: No

3 0 10 20 30 Distance (m)

23 0.939 (DoU)

Mayton Wood Quarry 21 Side-Slope Subgrade

SlopeW File SSG4

19 Design Approach DA1 Combination 2 Partial factors applied to Materials and Variable Actions

17 Name: Historic Landfill Model: Mohr-Coulomb Unit Weight: 16 kN/m³ Cohesion': 2 kPa Phi': 21 ° 15 Ru: 0.3 Include Ru in PWP: Yes

Variable construction surcharge

13 Elevation(mOD)

11 8.0787 m

9 Name: Undifferentiated Sands and Gravels Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 0 kPa Phi': 37 ° Include Ru in PWP: No Slope Amgle 30 degrees 7 or 1(v):1.7(h)

Name: White Chalk Model: Mohr-Coulomb Unit Weight: 20 kN/m³ 5 Cohesion': 5 kPa Phi': 35 ° Include Ru in PWP: No

3 0 10 20 30 Distance (m)

GE200240610 21 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Appendix 2

Slope W Worksheets – Side Slope Liner

GE200240610 22 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

0.110 (DoU) Mayton Wood Quarry

Side-Slope Liner Variable construction surcharge Name: Side Liner 16 Model: Mohr-Coulomb SlopeW File SLINER1 Unit Weight: 19 kN/m³ Cohesion': 50 kPa Total Stress Analysis 15 Phi': 0 ° Design Approach DA1 14 Combination 1 Partial factors applied to Actions 13

10 Slope Amgle 30 degrees or 9 1(v):1.7(h)

8 0.50m thick liner Elevation (mOD) Elevation

3 0 10 20 30 Distance (m)

0.102 (DoU) Mayton Wood Quarry

Side-Slope Liner

Variable construction surcharge Name: Side Liner SlopeW File SLINER2 16 Model: Mohr-Coulomb Unit Weight: 19 kN/m³ Total Stress Analysis Cohesion': 50 kPa 15 Phi': 0 ° Design Approach DA1 Combination 2 Partial factors 14 applied to Materials and Variable Actions 13

10 Slope Amgle 30 degrees or 9 1(v):1.7(h)

8 0.50m thick liner Elevation (mOD) Elevation

3 0 10 20 30 Distance (m)

GE200240610 23 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Mayton Wood Quarry

Side-Slope Liner 0.193 (DoU) SlopeW File SLINER3

Total Stress Analysis Variable construction surcharge Name: Side Liner 16 Model: Mohr-Coulomb Design Approach DA1 Unit Weight: 19 kN/m³ Combination 1 Partial factors Cohesion': 50 kPa applied to Actions 15 Phi': 0 °

10 Slope Amgle 30 degrees or 9 1(v):1.7(h)

8 1.00m thick liner Elevation (mOD) Elevation

3 0 10 20 30 Distance (m)

Mayton Wood Quarry

Side-Slope Liner

0.179 (DoU) SlopeW File SLINER4

Total Stress Analysis

Variable construction surcharge Name: Side Liner Design Approach DA1 16 Model: Mohr-Coulomb Combination 2 Partial factors Unit Weight: 19 kN/m³ applied to Materials and Cohesion': 50 kPa Variable Actions 15 Phi': 0 °

10 Slope Amgle 30 degrees 9 or 1(v):1.7(h)

8 1.00m thick liner Elevation (mOD) Elevation

3 0 10 20 30 Distance (m)

GE200240610 24 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

0.844 (DoU) Mayton Wood Quarry

Side-Slope Liner Variable construction surcharge Name: Side Liner 16 Model: Mohr-Coulomb SlopeW File SLINER5 Unit Weight: 19 kN/m³ Cohesion': 2 kPa Effective Stress Analysis 15 Phi': 25 ° Design Approach DA1 14 Combination 1 Partial factors applied to Actions 13

10 Slope Amgle 30 degrees 9 or 1(v):1.7(h)

8 0.50m thick liner Elevation (mOD) Elevation

3 0 10 20 30 Distance (m)

0.954 (DoU) Mayton Wood Quarry Side-Slope Liner

SlopeW File SLINER6 Variable construction surcharge Name: Side Liner 16 Model: Mohr-Coulomb Unit Weight: 19 kN/m³ Effective Stress Analysis Cohesion': 2 kPa 15 Phi': 25 ° Design Approach DA1 Combination 2 Partial factors 14 applied to Material and Variable Actions 13

10 Slope Amgle 30 degrees 9 or 1(v):1.7(h)

8 0.50m thick liner Elevation (mOD)

3 0 10 20 30 Distance (m)

GE200240610 25 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Mayton Wood Quarry

Side-Slope Liner 0.929 (DoU) SlopeW File SLINER7

Effective Stress Analysis Variable construction surcharge Name: Side Liner 16 Model: Mohr-Coulomb Design Approach DA1 Unit Weight: 19 kN/m³ Combination 1 Partial factors Cohesion': 2 kPa applied to Actions 15 Phi': 25 °

10 Slope Amgle 30 degrees 9 or 1(v):1.7(h)

8 1.00m thick liner Elevation (mOD)

3 0 10 20 30 Distance (m)

Mayton Wood Quarry

Side-Slope Liner 0.958 (DoU) SlopeW File SLINER8

Effective Stress Analysis

10 Slope Amgle 30 degrees 9 or 1(v):1.7(h)

8 1.00m thick liner Elevation(mOD)

3 0 10 20 30 Distance (m)

GE200240610 26 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Mayton Wood Quarry 0.966 (DoU) Side-Slope Liner Translational Failure

Variable construction surcharge Name: Side Liner SlopeW File SLINER9 16 Model: Mohr-Coulomb Unit Weight: 19 kN/m³ Effective Stress Analysis Cohesion': 2 kPa 15 Phi': 25 ° Design Approach DA1 Combination 2 Partial factors 14 applied to Material and Variable Actions 13

10 Slope Amgle 30 degrees or 9 1(v):1.7(h)

8 0.50m thick liner Elevation(mOD)

3 0 10 20 30 Distance (m)

Mayton Wood Quarry

Side-Slope Liner Translational Failure

0.948 (DoU) SlopeW File SLINER10

Effective Stress Analysis

10 Slope Amgle 30 degrees or 9 1(v):1.7(h)

8 1.00m thick liner Elevation (mOD) Elevation

3 0 10 20 30 Distance (m)

GE200240610 27 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Appendix 3

SlopeW Worksheets – Inert Waste

GE200240610 28 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Mayton Wood Quarry 0.236 (DoU) Waste Slope Analysis

SlopeW File WASTE1 Variable construction surcharge 16 Total Stress Analysis

15 Design Approach DA1 Name: Inert Waste Combination 1 Partial factors Model: Mohr-Coulomb applied to Actions 14 Unit Weight: 17 kN/m³ Cohesion': 50 kPa Phi': 0 ° 13 Waste Slope

Waste Slope 8 Elevation(mOD) 1(V) : 3(H)

3 0 10 20 30 40 Distance (m)

Mayton Wood Quarry

0.212 (DoU) Waste Slope Analysis

SlopeW File WASTE2 Variable construction surcharge 16 Total Stress Analysis

Design Approach DA1 15 Combination 2 Partial factors Name: Inert Waste applied to Materials and Model: Mohr-Coulomb Variable Actions 14 Unit Weight: 17 kN/m³ Cohesion': 50 kPa Phi': 0 ° 13 Waste Slope

Waste Slope 8 Elevation(mOD) 1(V) : 3(H) 7

3 0 10 20 30 40 Distance (m)

Mayton Wood Quarry

Waste Slope Analysis 0.427 (DoU) Leachate Level + 1.00m

SlopeW File WASTE3 Variable construction surcharge 16 Effective Stress Analysis

15 Design Approach DA1 Combination 1 Partial factors Name: Inert Waste applied to Actions 14 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 5 kPa 13 Phi': 25 ° Piezometric Line: 1 Waste Slope 12

Waste Slope 8 Elevation (mOD) Elevation 1(V) : 3(H)

3 0 10 20 30 40 Distance (m)

GE200240610 29 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Mayton Wood Quarry

Waste Slope Analysis Leachate Level + 1.00m 0.460 (DoU) SlopeW File WASTE4

Variable construction surcharge Effective Stress Analysis 16 Design Approach DA1 15 Combination 2 Partial factors applied to Materials and Name: Inert Waste Variable Actions 14 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 5 kPa 13 Phi': 25 ° Piezometric Line: 1 Waste Slope 12

Waste Slope 8 Elevation (mOD) 1(V) : 3(H) 7

3 0 10 20 30 40 Distance (m)

Mayton Wood Quarry

Waste Slope Analysis 0.427 (DoU) Leachate Level + 4.00m

SlopeW File WASTE5 Variable construction surcharge 16 Effective Stress Analysis

15 Design Approach DA1 Combination 1 Partial factors Name: Inert Waste 14 Model: Mohr-Coulomb applied to Actions Unit Weight: 17 kN/m³ Cohesion': 5 kPa 13 Phi': 25 ° Piezometric Line: 1 Waste Slope 12

Waste Slope 8 Elevation (mOD) Elevation 1(V) : 3(H)

3 0 10 20 30 40 Distance (m)

Mayton Wood Quarry

Waste Slope Analysis Leachate Level + 2.00m 0.460 (DoU) SlopeW File WASTE6

Variable construction surcharge Effective Stress Analysis 16 Design Approach DA1 15 Combination 2 Partial factors applied to Materials and Name: Inert Waste 14 Model: Mohr-Coulomb Variable Actions Unit Weight: 17 kN/m³ Cohesion': 5 kPa 13 Phi': 25 ° Piezometric Line: 1 Waste Slope 12

Waste Slope 8 Elevation (mOD) Elevation 1(V) : 3(H)

3 0 10 20 30 40 Distance (m)

GE200240610 30 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

Mayton Wood Quarry

Waste Slope Analysis 0.483 (DoU) Leachate Level + 6.00m

SlopeW File WASTE7 Variable construction surcharge 16 Effective Stress Analysis

Waste Slope 8 Elevation (mOD) Elevation 1(V) : 3(H) 7

3 0 10 20 30 40 Distance (m)

Mayton Wood Quarry

Waste Slope Analysis 0.533 (DoU) Leachate Level + 6.00m

SlopeW File WASTE8 Variable construction surcharge Effective Stress Analysis 16 Design Approach DA1 15 Combination 2 Partial factors applied to Materials and Name: Inert Waste Variable Actions 14 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 5 kPa 13 Phi': 25 ° Piezometric Line: 1 Waste Slope 12

Waste Slope 8 Elevation (mOD) Elevation 1(V) : 3(H)

3 0 10 20 30 40 Distance (m)

Mayton Wood Quarry

Waste Slope Analysis Long Term Softening 0.586 (DoU) c' = 0

SlopeW File WASTE9 Variable construction surcharge Effective Stress Analysis 16 Design Approach DA1 15 Combination 2 Partial factors applied to Materials and 14 Variable Actions

Name: Inert Waste 13 Model: Mohr-Coulomb Unit Weight: 17 kN/m³ Cohesion': 0 kPa 12 Phi': 25 °

Waste Slope 8 Elevation (mOD) Elevation 1(V) : 3(H)

3 0 10 20 30 40 Distance (m)

GE200240610 31 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd

GEOTECHNICAL & ENVIRONMENTAL CONSULTING

GE200240610 32 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd