appendix 11 kingswood playing field interpretation report...

Appendix 11

Kingswood Playing Field Interpretation

Report on Ground Investigation

63

Geotechnical Engineering Ltd Centurion House, Olympus Park Quedgeley, Gloucester. GL2 4NF 01452 527743 www.geoeng.co.uk

KINGSWOOD PLAYING FIELD

INTERPRETATIVE REPORT ON GROUND INVESTIGATION

Prepared for KINGSWOOD PARISH COUNCIL

Report Ref: 27979

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Geotechnical Engineering Limited

www.geoeng.co.uk

2718


INTERPRETATIVE REPORT ON GROUND INVESTIGATION

Prepared for KINGSWOOD PARISH COUNCIL

Report Ref: 27979

PROJECT: Kingswood Playing Field

CONSULTANT: Complete Design Partnership VOLUME - VERSION STATUS ORIGINATOR CHECKER APPROVED DATE

1 of 1 – A DRAFT SCo CT - 19/06/2013

1 of 1 - A FINAL SCo CT CT 26/06/2013

ORIGINATOR APPROVER

Sophie Collins BSc (Hons) MSc CGeol EurGeol FGS Principal Geotechnical Engineer

Colin Thomas BSc PhD FGS Geotechnical Consultant

The report is not to be used for contractual or engineering purposes unless this sheet is signed and the

report designated “Final”. The report has been prepared for the sole use and reliance by Kingswood Parish Council. GEL accepts no

liability as a result of the use or reliance of this report by any other parties.

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RT01 v09 18/01/13 JH Report Ref: 27979 Page i

CONTENTS

REPORT PAGE

1. INTRODUCTION ............................................................................................................1

2. SITE LOCATION, DESCRIPTION AND GEOLOGY ............................................................2

3. PROPOSED WORKS ......................................................................................................3

4. GROUND INVESTIGATION ............................................................................................3

4.1 Fieldwork ..................................................................................................................3

4.2 Logging .....................................................................................................................5

4.3 Laboratory Testing ...................................................................................................5

5. DISCUSSION AND CONCLUSIONS .................................................................................7

5.1 Ground Conditions ...................................................................................................7

5.2 Geotechnical Appraisal ..........................................................................................10

5.2.1 Made Ground......................................................................................................10

5.2.2 Charmouth Mudstone ........................................................................................12

5.3 Excavations .............................................................................................................14

5.4 Pavement Design ....................................................................................................14

5.5 Soakaway Design ....................................................................................................15

5.6 Drainage Recommendations ......................................................................................16

6. REFERENCES ...............................................................................................................18

FIGURES Nos.

LOCATION PLAN 1

EXPLORATORY HOLE LOCATION PLAN 2

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RT01 v09 18/01/13 JH Report Ref: 27979 Page ii

APPENDICES

APPENDIX A FIELDWORK DATA

APPENDIX B LABORATORY TESTING

APPENDIX C GEOTECHNICAL DATA

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RT01 v09 18/07/12 JH Report Ref: 27979 Page 1

1. INTRODUCTION

It is proposed to undertake works to improve the drainage of existing playing fields and

construct a new car parking area at Kingswood Playing Fields, Kingswood, Wotton-under-

Edge. Geotechnical Engineering Limited (GEL) was instructed by Complete Design Partnership

acting on behalf of Kingswood Parish Council to carry out an investigation to determine the

ground conditions.

The scope of work and terms and conditions of appointment were defined in

correspondence by GEL, reference T16687 dated 21st February 2013.

This report describes the investigation, presents the findings and comments accordingly.

The comments given in this report and the opinions expressed assume that ground

conditions do not vary beyond the range revealed by this investigation. There may

however, be conditions at or adjacent to the site, which have not been disclosed by the

investigation and which, therefore, have not been considered in this report. Accordingly, a

careful watch should be maintained during any future ground works and the

recommendations of this report reviewed as necessary.

Many aspects of the proposed development have yet to be agreed/determined. The

comments given in this report should therefore be considered in the context of a general

overview of the site. It is recommended that the report is reviewed when the design is

finalised.

The recommendations given in this report should not be used for any other schemes on or

adjacent to this site without further reference to GEL.

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2. SITE LOCATION, DESCRIPTION AND GEOLOGY

The site is situated at Kingswood Playing Fields, Wickwar Road, Wotton-under-Edge,

Gloucestershire and may be located by its National Grid co-ordinates ST 744 916. A site

location plan is provided as Figure 1.

A site walkover survey was undertaken on 11th April 2013.

At the time of the site walkover, the site was found to comprise a variety of playing field

areas (football and cricket pitches), a village hall, children’s playground areas and car

parking areas/areas of hardstanding (around the village hall – access road) of

approximately two to three hectares in total area. Several small buildings (pavillion and

observation huts) were noted around the main football pitch area. The site is accessed via

a dedicated driveway from Wickwar Road through a barrier. Topographical survey

information provided for the site indicates a slight sloping downwards to the west,

however visual observation would indicate that the site is essentially flat.

The site was found to be surrounded by open fields to the north, east and west, being

bordered by residential gardens to the south. Several mature trees were noted along the

site boundaries with the site being bounded by hedgerows of between 1.5 to 2.0m in

height.

No visual or olfactory signs of contamination were observed.

The site was found to be wet underfoot at the time of the walkover and drainage ditches

were noted along the site boundaries (noted to be partially full of water). It is assumed

(although no evidence was observed) that water from these drainage ditches drains into

the local surface water sewer drainage. Anecdotal evidence provided by the Client and

Complete Design Partnership indicates that the playing fields have a history of and

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ongoing issue of waterlogging, at times causing parts of the pitches to be

unusable/unplayable.

British Geological Survey (BGS) England and Wales (Sheet No. 264, Bristol:) and the BGS

online geology (1:50,000) indicate the site is underlain by the Charmouth Mudstone

Formation (formerly Lower Lias Clay). Examination of the BGS 1:10 000 mapping for the area

(Sheet number ST 79 SW) confirms the above with additional detail/description given for the

site area of “Clay soil with limestone fragments”.

3. PROPOSED WORKS

Due to the ongoing issues of waterlogging and poor drainage of the existing sports

pitches, appropriate drainage solutions are required to remove excess water and to

ensure the pitches remain suitable for use at all times of the year. A proposed new car

parking area is also required on the site. At the time of preparing this report, details of

the likely remedial drainage solutions have not been agreed. This report will provide

ground investigation data and preliminary design parameters, together with

recommendations to enable the optimum selection and design of remedial drainage

option(s) and to facilitate the pavement design of the proposed car parking area.

4. GROUND INVESTIGATION

4.1 Fieldwork

The fieldwork was carried out in general accordance with BS5930:1999+A2:2010 on 29th April

2013 and comprised six machine dug trial pits, two soakaway tests and six dynamic cone

penetrometer (DCP) tests.

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The exploratory holes locations were selected and set out by this Company and are shown

on Figure 2. The ground level and co-ordinates at each exploratory hole location were not

established.

The trial pits, referenced TP01 to TP06 (Appendix A), were formed by a wheeled excavator

with a 0.60m wide backactor bucket. Trial pit logs are presented in Appendix A.

The ground surface at TP01 to TP06 consisted of grassed (turf) areas. Breaking out prior to

excavation was not required.

Representative disturbed samples were taken and retained in sealed plastic bags and

airtight containers to retain moisture content.

Hand vane tests were carried out in suitable cohesive material. The results are presented

on the trial pit logs and tabulated in Appendix A.

Soakaway tests were carried out in trial pits TP03 and TP05 in general accordance with

BRE 365 (2007). The excavation sides were squared using the excavator bucket and the

dimensions recorded within the test section. The trial pit was partially filled with clean

water using a dedicated bowser with a 75mm diameter outlet and the fall in level

recorded against time. The test was undertaken only once in each pit due to the

extremely slow rate of infiltration observed. The results are presented in Appendix A.

On completion all trial pits were backfilled with arisings compacted in suitable layers by

the excavator bucket. The ground surface was left slightly proud to accommodate the

future inevitable settlement of the backfill.

Dynamic Cone Penetrometer tests (DCP), referenced DCP01 to DCP06 (Appendix A), were

carried out using a CNS Farnell A2465 dynamic cone penetrometer. Probe depths were

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measured with respect to ground level and the number of blows for the penetration of

the probe was recorded. Equivalent CBR values have been calculated and presented with

the results in Appendix A.

On completion of fieldwork all samples were brought to this Company's laboratory for

testing and storage.

4.2 Logging

The logging of soils and rocks was carried out by an Engineering Geologist in general

accordance with BS5930:1999+A2:2010. A key to the exploratory hole logs is presented in

Appendix A.

Detailed descriptions of the samples are given in the trial pit logs, Appendix A, along with

details of sampling, in situ testing, groundwater ingress and relevant comments on drilling

techniques.

Hand vane tests were carried out on suitable samples. The results are summarised on the

trial pit logs and tabulated in Appendix A.

4.3 Laboratory Testing

A schedule of laboratory tests was prepared by this Company, the following tests being

carried out in accordance with BS1377:1990, unless stated otherwise. The number in

brackets refers to the test number given in that standard. The results are presented in

Appendix B.

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The natural moisture content [Part 2:3.2] was determined on twenty two selected

samples.

Liquid limit, plastic limit and plasticity index tests [Part 2:4.3, 5.3 and 5.4] were carried out

on six selected samples. An Atterberg line plot has also been presented.

Particle size distributions were determined for two samples by wet sieving [Part 2:9.2].

The fine fractions of both of these samples were further analysed by sedimentation using

the pipette method [Part 2:9.4]. The results are presented as grading curves.

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5. DISCUSSION AND CONCLUSIONS

5.1 Ground Conditions

The ground conditions revealed by the investigation generally confirm the strata indicated

by the geological records.

The ground conditions encountered in the exploratory holes are described in detail in the

exploratory hole logs presented in Appendix A. The general sequence of strata encountered

on the site is presented in Table 5.1 below.

Table 5.1 – Ground Summary

Stratum Age Stratum

Name

Typical Description(s) Approx depth to top

of stratum (m below

ground level (bgl))

Approx thickness

(m) 1, 2

Recent Made

Ground

(possibly

Topsoil)

Turf over firm SILT and CLAY (see

below and section 5.2 for detailed

descriptions)

Ground level Up to 0.85m (typically

0.15-0.30m, 0.85m in

TP03)

Jurassic Charmouth

Mudstone

Formation

(formerly

Lower Lias

Clay)

Stiff to very stiff (rarely firm)

CLAY (see below and section 5.2

for detailed descriptions)

0.15-0.20 (0.85m in

TP03)

Up to 2.2m encountered

(<2.2m)

Notes

1 thickness ranges based on data obtained from ground investigation, actual range of thicknesses may vary.

2 Base of stratum not proven

Made Ground (possibly Topsoil) was identified within all of the exploratory holes.

Encountered thicknesses typically ranged from 0.15-0.30m (0.85m observed in TP03).

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The Made Ground comprised turf over firm, greyish brown slightly sandy, slightly gravelly silt

with frequent roots and rootlets and firm greyish brown mottled orangish brown and bluish

grey, slightly gravelly clay (below 0.3m in TP03 only). The gravel constituent was found to

consist of subangular and subrounded fine and medium quartzite, mudstone, sandstone and

rare brick fragments. Rare medium gravel sized pockets of yellowish brown coarse sand were

observed in TP06. A land drain consisting of a 60mm diameter orange clay pipe was observed

at 0.60m depth within the Made Ground encountered in TP03.

Material described as Charmouth Mudstone (formerly known as the Lower Lias Clay) was

identified within all of the exploratory holes. Encountered thicknesses ranged from 0.95m -

2.2m. The base of the Charmouth Mudstone was not proven in any of the exploratory holes.

The Charmouth Mudstone was found to comprise up to 2.2m of stiff (rarely firm) orangish

brown, becoming light grey mottled orangish brown, slightly sandy, silty stiff clay overlying

very stiff thinly laminated dark bluish grey and grey slightly sandy clay with frequent fine to

coarse gravel sized calcareous mudstone lithorelicts, rare to frequent fossil fragments and low

to high limestone cobble content. A band of light grey subangular limestone cobbles and

boulders was encountered between 1.40 and 1.53m bgl in TP01 is considered to represent a

weathered limestone band within the Charmouth Mudstone. The Charmouth Mudstone

typically contains bands and lenses of mudstone and limestone (may be laterally and vertically

impersistent). Each of the trial pits were terminated upon refusal on possible rock bands at

depth varying between 1.3 – 2.5m bgl.

Groundwater

Groundwater was not encountered in any of the trial pits, during the short period they

remained open.

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Groundwater levels may vary seasonally, with significantly higher groundwater levels

expected in the winter/spring period or following periods of heavy rainfall, with levels in

summer or during periods of drought likely to be lower. The anecdotal evidence provided in

Section 2 of this report would suggest that significant waterlogging of the existing pitches

takes places, especially following heavy rainfall events. Groundwater levels may increase

following periods of heavy rainfall, however water may also pond at surface due to poor

infiltration characteristics of the relatively impermeable soils, inadequacy/poor function of

any existing land drainage and lack of a suitable gradient/fall across the existing pitches to

allow any excess surface water to drain away to the sides. The above should be taken into

account in the design of drainage measures.

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5.2 Geotechnical Appraisal

The general sequence of strata encountered during the ground investigation, together with

encountered thicknesses and elevations is summarised in Section 5.1 above. The material

parameters and derivation of appropriate suggested preliminary design parameters is

discussed below.

5.2.1 Made Ground

The material parameters for the Made Ground are as given below together with the

derivation of appropriate design parameters.

Classification

Seven natural moisture content tests were carried out on samples of Made Ground, which

ranged from 26 to 59 %. The results are summarised in Appendix B and presented

graphically in Appendix C. Near surface results (with 0.15m depth) typically gave higher

moisture content values (40-59%), likely reflective of the surface wetness of the pitch as

observed during the site walkover.

No plasticity index tests were carried out on samples of Made Ground.

One particle size distribution test was carried out on a sample of the deeper Made Ground

from TP03. The results are presented in Table 5.2 below. Appendix B presents a grading

curve for this material.

Table 5.2. Summary of Particle Size Distribution Tests

% Clay % Silt %Sand % Gravel

% Cobbles/boulders

Laboratory classification

46 50 3 1 0 Brown slightly sandy silty CLAY with a little fine gravel

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Bulk Unit Weight

No testing was undertaken on samples of Made Ground to obtain bulk density values,

however a value of 18kN/m3 is considered appropriate for the bulk unit weight of this

material.

Strength

One vane test was undertaken on a sample of Made Ground in TP03. This gave a value of

undrained shear strength of 44 KPa at 0.4m bgl (i.e. the deeper Made Ground).

An undrained shear strength in the range 40-50 kPa can be assumed for Made Ground on

the basis of the above result and material descriptions given on the exploratory hole log

(using typical strengths from BS8004, 1986).

Permeability

No data is available relating to the permeability of the Made Ground. Due to its cohesive

nature, the Made Ground is likely to be relatively impermeable, with a permeability in the

typical range for silts and clays (order of 10-5 m/s or less) (BS8004, 1986). The

permeability may vary both laterally and vertically with changes in the deposits (i.e. any

granular horizons may exhibit a higher permeability than cohesive).

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5.2.2 Charmouth Mudstone

The material parameters for the Charmouth Mudstone are as given below together with

the derivation of appropriate design parameters.

Classification

Fifteen natural moisture content and six Atterberg limit tests were carried out on samples

of the Charmouth Mudstone, which ranged from 20 to 39 %. The results are summarised

and presented graphically in Appendix B.

The results shows that the Charmouth Mudstone soils typically fall within the boundary of

Group CH and CV with one result on the boundary of Group CV and CE) as defined in

BS5930 (1999) and therefore generally classify as clays of high to very high plasticity.

Based upon the modified plasticity indices, this material is considered to be of high

volume change potential in response to changes in moisture content (NHBC, 2011). The

desiccation parameters - moisture content, and moisture content/liquid limit ratio, would

infer the soil is currently slightly desiccated to around 1m depth. It should be noted

however, that with depth, the parameters may reflect the less weathered, more

overconsolidated nature of the Charmouth Mudstone. Desiccation parameter profiles,

plotted against depth, are presented in Appendix C.

Moisture content profiles are presented in Appendix C, for TP01 to TP06 inclusive. Based

on the shape of these profiles, moisture contents measured in the top 0.3m begl are

significantly higher than those at greater depths, likely indicative of the of the wet ground

surface observed. The moisture content profiles typically show an initial decrease in

moisture content to depths of 0.6m bgl followed by a slight increase. This would likely

indicate a slight desiccation of the soil to around 0.6m, with the observed slight increase

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being indicative of the relatively high natural moisture content (undesiccated) of the

ground i.e. the initial observed decrease in moisture content is reflective of the near

surface desiccation. The observed pattern of moisture content with depth may also

possibly reflect the presence of existing land drains, which may be acting to partially drain

the site where present. A land drain was noted in TP 03 at 0.6m bgl.

Bulk Unit Weight

No specific testing was undertaken on samples of Charmouth Mudstone to obtain bulk

density values, however a value of 19kN/m3 is considered an appropriate design value for

the bulk unit weight of this material in accordance with the suggested range given for stiff

clays given in BS8002(1994).

Strength

Twelve vane tests were undertaken on samples of Charmouth Mudstone described as firm

and stiff. These gave values of undrained shear strength in the range 70-83 KPa. The

descriptions given on the exploratory hole logs would suggest a strength in the range 50-

150 kPa. For the purposes of preliminary design an undrained shear strength in the range

50-75 kPa (for firm clays), 75-150 kPa (for stiff clays), and 150 kPa or above (for very stiff

clays) can be assumed for the Charmouth Mudstone on the basis of the above results and

material descriptions given on the exploratory hole log (using typical strengths from

BS8004, 1986).

Rock bands encountered with the Charmouth Mudstone (limestone and mudstone) would

be expected to be of considerably higher strength.

A strength vs depth below ground level plot is presented in Appendix C based on the hand

vane results within the clay.

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Permeability

No fieldwork data is available relating to the permeability of the Charmouth Mudstone,

however these deposits are likely to be relatively impermeable, with a permeability in the

typical range for clays (order of 10-7 m/s or less) BS8004, 1986) as demonstrated by the

soakaway tests carried out in TP03 and TP05. The permeability may vary both laterally

and vertically with changes in the deposits (i.e. granular horizons may exhibit a higher

permeability than cohesive).

5.3 Excavations

Excavations may be required to allow the installation of appropriate drainage measures.

The extent and dimensions of these are not determined at the time of writing this report.

Excavations should be within the scope of conventional backhoe excavators. Recourse to

hydraulic breakers may be required to break out any existing obstructions and rock bands.

Excavations should remain stable in the short term, although minor spalling of the

excavation sides may occur.

If potentially unstable excavations or any excavations deeper than 1.00m are to be

entered then the sides should be battered back and/or shoring methods and equipment

should be utilised in accordance with the relevant Health and Safety Acts.

5.4 Pavement Design

Six dynamic cone penetrometer tests were carried out in the vicinity of the proposed car

parking area. On the basis of the results, California Bearing Ration (CBR) values of 2.5%

and greater may be obtained on the basis of the correlation given in IAN 73/06 (2009).

Higher values are likely to represent localised higher strength materials within the soils.

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An equilibrium subgrade California Bearing Ratio (CBR) value of 2% can be estimated from

plasticity indices based on table 5.1 of IAN 73/06 (2009). On the basis of the available

results, it is suggested that a CBR value of 2.5% be adopted for road and pavement design,

on the assumption that the formation subgrade for the car parking area will be within the

Charmouth Mudstone at a depth of at least 0.3m below ground level or greater.

The predominantly high plasticity nature of the soils indicates that these are relatively

unlikely to be frost susceptible. It is recommended that any material placed as sub

base/capping within 450mm depth of the proposed car park surface should be non-frost

susceptible in accordance with the Manual of Contract Documents for Highway Works,

Volume 1 Specification for Highway Works, Series 600 Earthworks, and tested according

to BS812: Part 124 (2009). Sub base and capping materials should be granular in nature

with a low fines content and not composed of any frost susceptible materials e.g

magnesian or oolitic limestones (as these are typically susceptible to frost heave).

The subgrade should be protected prior to placing sub base and capping materials in order

to protect the formation level from softening. In addition, adequate drainage should be

installed to ensure that water can be adequately drained from the area.

5.5 Soakaway Design

Soakaway tests were carried out in Trial Pits TP03 and TP05 in general accordance with

BRE 365 (2007). Due to the poor rate of infiltration observed (between 10 and 20mm

depth in three hours), it was not possible to calculate the soil infiltration rate.

Due to the poor infiltration observed, the use of soakaways to facilitate drainage on the

site is not considered to be appropriate.

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5.6 Drainage Recommendations

The following drainage options may be considered for the site. Specialist advice should be

sought from a drainage designer/contractor/supplier to determine a suitable option and

design, suitable depths, spacing, layout, extent etc. The capacity of existing surface and

groundwater drainage systems (sewers etc) and ability to accept additional run-

off/drainage from the site and connection details to these should also be established and

taken into account in the selection and design of a suitable remedial option. Drainage

ditches (partially filled) were observed to the perimeter of the playing field, however it is

not clear whether existing drainage from the site currently routes into these, or what the

capacity of these existing ditches is to receive additional water from proposed drainage

systems.

Clay land drains

Anecdotal evidence provided by the Client and Complete Design Partnership, suggests

that there may be some existing drainage beneath the surface of the playing fields in the

form of land drains. A clay land drain was located in TP03 at 0.6m. The extent or layout of

the existing drains is not known. Use of land drains (either re-use of the existing or

construction of new drains) would not be recommended on their own as it is evident from

the waterlogging of the playing fields that the existing land drains are not functioning

correctly and/or are inadequate in size, number, layout etc to adequately drain the field.

Sand and gravel slit trenches

Drainage of waterlogged soils may possibly be achieved through the use of sand and

gravel slit trenches. These would typically consist of narrow trenches to shallow depths

(less than 1m) filled with sand and/or gravel. These are connected laterally via plastic

pipes (connector drains) and then routed onwards into the main drainage system. The

effectiveness of this type of drainage may be enhanced using geotextile wrapped

connector drains e.g. Hydraway Sportsdrain (Turfdry drainage system) by increasing the

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surface area of the lateral connector drains and reducing the potential for clogging. Use

of this type of system may be effective for drainage of the site. Advice should be sought

from a specialist contractor/supplier for selection of an appropriate system, design and

installation.

Plastic pipe geocomposite systems

Drainage of waterlogged soils may possibly be achieved through the use of plastic pipe

drainage system geocomposites e.g Macaferri MacDrain or similar. These consist of a

HDPE drainage core attached to non-woven geotextile to prevent clogging one side or

both sides. These replace the function of traditional drainage materials such as sands and

gravels, meaning that they can be installed in narrow trenches without the addition of

surrounding imported filter materials (sand and gravel). These are then connected

laterally via connector drains and then routed onwards into the main drainage system.

Use of this type of system may be effective for drainage of the site. Advice should be

sought from a specialist contractor/supplier for selection of an appropriate system, design

and installation.

GEOTECHNICAL ENGINEERING LIMITED

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6. REFERENCES

British Standards Institution (1999): Code of practice for site investigations. BS 5930

incorporating Amendments No. 1 & 2. Amendment 1 removes text superseded by BS EN ISO

14688-1:2002, BS EN ISO 14688-2:2004 and BS EN ISO 14689-1:2003, and makes reference to

the relevant standard for each affected sub clause. Amendment 2 removes text superseded

by BS EN 22475-1:2006 and makes reference to the relevant standard for each affected sub

clause.

British Standards Institution (1990): Methods of tests for soils for civil engineering purposes.

BS 1377 Parts 1-9.

British Standards Institution (1986): Code of Practice for Foundations. BS 8004:1986.

Superseded/withdrawn, replaced by BS EN 1997-1:2004.

British Standards Institution (1994): Code of Practice for Earth Retaining Structures. BS

8002:1994. Superseded/withdrawn, replaced by BS EN 1997-1:2004.

British Standards Institution (2009): Testing aggregates. Method for determination of frost

heave. BS 812-124:2009

Building Research Establishment (2007): Soakaway Design. BRE 365.

Highways Agency (2009): Design Guidance for Road and Pavement Foundations (Draft

HD25). Interim Advice Note (IAN) 73/06 Revision 1.

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Highways Agency (1992, Amended 2009): Manual of Contract Documents for Highway

Works, Volume 1 Specification for Highway Works, Series 600 Earthworks. The Stationery

Office Ltd, (Amended 2009).

National House Building Council (2011): NHBC Standards. Chapter 4.2. Foundations:

Building near trees.

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SITE LOCATION PLAN

CLIENT KINGSWOOD PARISH COUNCILSITE KINGSWOOD PLAYING FIELDSCALE NTS CONTRACT FIGURE

Reproduced from the Ordnance Survey 1:50,000 Map sheet 183, Yeovil and Frome, 1999. With the permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office, Crown Copyright. Geotechnical Engineering Limited, Gloucester. AL100002447. 27979 1

N

SITE LOCATION

87

FIELDWORK DATA

2797

9

APPENDIX A


89

0.30

0.80

1.40

1.55

1.70

2.50

1

2

3

4

D*

B

B

B

H 79

H 74

0.15

0.30

0.35

0.75

1.00

1.80

- 0.50

- 1.20

- 2.00

Dry

Turf over firm greyish brown slightly sandy slightly gravelly SILT with frequentroots (up to 15mm diameter) and rare ash. Gravel is subangular and subroundedfine and medium quartzite. (MADE GROUND)

Stiff orangish brown and greyish brown slightly sandy silty CLAY.

Stiff light grey mottled orangish brown CLAY.

Light grey subangular limestone COBBLES and BOULDERS.


Very stiff dark bluish grey and light grey slightly sandy CLAY with frequent fine tocoarse gravel sized calcareous mudstone lithorelicts and rare fine and mediumgravel sized fossil remains.

Trial pit completed at 2.50m.

Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/06/

2013

10:

34:4

5 D

JO

End Date


depth level

(m)legend

CONTRACT CHECKED

Notes

TRIAL PIT LOG

(m)

Start Date

water

record

sample/test

TP01SITE

KINGSWOOD PARISH COUNCIL

2.50 m

27979EXPLORATORY HOLE LOGS SHOULD BE READ IN CONJUNCTION WITH KEY SHEETS

Sketch of Foundation - Not to scale. All dimensions in metres.

no/type

Trial pit excavated by JCB 3CX mechanical excavator.Groundwater not encountered.Trial pit sides remained stable and vertical.Trial pit dimensions 1.70x0.60x2.50m.Trial pit refused at 2.50m. Possible rock.On completion, the trial pit was backfilled with materials arising.

29 April 2013

29 April 2013

CLIENT


depth (m)description

Sheet 1 of 1

Scale 1 : 25

result

Depth

EW

90

0.20

0.60

0.80

1.30

1

2

3

4

D*

B

B

B

H 79

H 82

0.15

0.30

0.30

0.60

0.80

1.00

- 0.50

- 0.80

- 1.20

Dry

Turf over firm greyish brown slightly sandy slightly gravelly SILT with frequentrootlets. Gravel is subangular fine and medium quartzite. (MADE GROUND)

Stiff orangish brown and greyish brown slightly sandy silty CLAY with rare rootlets.


Very stiff dark bluish grey and grey slightly sandy CLAY with frequent fine andmedium gravel sized fossil remains and a high limestone cobble content.


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/06/

2013

10:

34:4

5 D

JO

End Date


depth level

(m)legend

CONTRACT CHECKED

Notes

TRIAL PIT LOG

(m)

Start Date

water

record

sample/test

TP02SITE


1.30 m



no/type


29 April 2013

29 April 2013

CLIENT



Sheet 1 of 1

Scale 1 : 25

result

Depth

EW

91

0.30

0.85

1.50

1.80

1

2

3

D*

B

B

H 44

H 70

H 82

0.25

0.30

0.40

0.90

1.50

1.60

- 0.50

- 1.60

Dry

Turf over firm greyish brown slightly sandy slightly gravelly SILT with frequentrootlets and rare fine gravel sized brick fragments. Gravel is subangular andsubrounded mudstone. (MADE GROUND)

Firm greyish brown mottled orangish brown and bluish grey slightly gravellyCLAY. Gravel is subangular fine to coarse mudstone and quartzite. (MADEGROUND)

0.60m: 60mm diameter orange clay land drain.

Firm greyish brown mottled orangish brown and bluish grey slightly sandy CLAY.

Stiff thinly laminated dark bluish grey slightly sandy CLAY with frequent fine andmedium gravel sized fossil remains.


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/06/

2013

10:

34:4

6 D

JO

End Date


depth level

(m)legend

CONTRACT CHECKED

Notes

TRIAL PIT LOG

(m)

Start Date

water

record

sample/test

TP03SITE


1.80 m



no/type


29 April 2013

29 April 2013

CLIENT



Sheet 1 of 1

Scale 1 : 25

result

Depth

EW

92

0.20

0.90

1.40

1

2

3

D*

B

B

H 82

H 77

0.15

0.30

0.30

0.65

1.00

- 0.50

- 1.20

Dry

Turf over firm greyish brown slightly sandy SILT with frequent roots (up to 10mmdiameter) and rare brick fragments. (MADE GROUND)

Stiff orangish brown and light greyish brown slightly sandy silty CLAY with rarerootlets.

Stiff light grey rarely mottled orangish brown and bluish grey CLAY with a lowlimestone cobble content.


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/06/

2013

10:

34:4

6 D

JO

End Date


depth level

(m)legend

CONTRACT CHECKED

Notes

TRIAL PIT LOG

(m)

Start Date

water

record

sample/test

TP04SITE


1.40 m



no/type


29 April 2013

29 April 2013

CLIENT



Sheet 1 of 1

Scale 1 : 25

result

Depth

EW

93

0.15

1.30

1.50

1.70

1

2

3

4

D*

B

B

B

H 74

H 82

0.15

0.20

0.30

0.70

1.30

1.50

- 0.50

- 1.50

- 1.70

Dry

Turf over firm greyish brown slightly sandy slightly gravelly SILT with frequentrootlets and rare brick fragments. Gravel is subangular and subrounded fine andmedium quartzite. (MADE GROUND)


0.50m: With rare cobble sized pockets of stiff light grey slightly sandy clay.

Stiff light grey CLAY with a high limestone cobble and boulder content.

Very stiff dark bluish grey and light grey slightly sandy CLAY with frequent fine tocoarse gravel sized calcareous mudstone lithorelicts.


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/06/

2013

10:

34:4

6 D

JO

End Date


depth level

(m)legend

CONTRACT CHECKED

Notes

TRIAL PIT LOG

(m)

Start Date

water

record

sample/test

TP05SITE


1.70 m



no/type


29 April 2013

29 April 2013

CLIENT



Sheet 1 of 1

Scale 1 : 25

result

Depth

EW

94

0.15

0.60

1.40

1.70

1

2

3

4

D*

B

B

B

H 77

H 83

0.15

0.30

0.30

0.60

0.80

1.40

- 0.50

- 0.80

- 1.60

Dry

Turf over firm greyish brown slightly sandy slightly gravelly SILT with frequentrootlets and rare medium gravel sized pockets of yellowish brown coarse sand.Gravel is subangular and subrounded fine and medium sandstone and mudstone.(MADE GROUND)


Stiff light grey CLAY with a high limestone cobble and boulder content.

Very stiff dark bluish grey and light grey slightly sandy CLAY with frequent fine tocoarse gravel sized calcareous mudstone lithorelicts and rare fine and mediumgravel sized fossil remains.


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/06/

2013

10:

34:4

7 D

JO

End Date


depth level

(m)legend

CONTRACT CHECKED

Notes

TRIAL PIT LOG

(m)

Start Date

water

record

sample/test

TP06SITE


1.70 m



no/type


29 April 2013

29 April 2013

CLIENT



Sheet 1 of 1

Scale 1 : 25

result

Depth

EW

95

TP01 0.35 79 79

TP01 0.75 74 74

TP02 0.30 79 79

TP02 0.80 82 82

TP03 0.40 44 44

TP03 0.90 70 70

TP03 1.60 82 82

TP04 0.30 82 82

TP04 0.65 77 77

TP05 0.20 74 74

TP05 0.70 82 82

TP06 0.30 77 77

TP06 0.80 83 83

CONTRACT

SITE KINGSWOOD PLAYING FIELD

borehole

27979

depth(m)

CHECKED

remarks

*Average pocket penetrometer results reported as undrained shear strength.

averagepocket

penetrometer(kPa)*

CLIENT

no.

general remarks:

/trial pit



averagehand vaneremoulded

(kPa)

hand vaneremoulded

(kPa)

averagehand vane

peak(kPa)

hand vanepeak(kPa)

IN-SITU HAND VANE/POCKET PENETROMETER

Hand vane test results reported as undrained shear strength.

pocketpenetrometer

(kg/cm2)


/trial pit

general remarks:

no.

borehole


27979


CLIENT

SITE

CONTRACT CHECKED

EW

Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/6/1

3

96

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

0 100 200 300

scalereading(mm)

CBR(%)

4.1

5.7

5.3

4.6

3.5

2.5

4.8

7.2

10.5

13.1

15.1

13.4

10.7

15.1

13.8

28.0

22.9

25.2

24.0

21.8

69.8

55.1

33.5

29.6

29.6

21.8

26.5

22.9

31.5

94.6

302.0

DCP(mm/blow)

59

43

46

53

69

93

50

35

24

20

17

19

24

17

19

10

12

11

11

12

4

5

8

9

9

12

10

12

9

3

1

depth bgl(m)

penetrationincrement

(mm)

59

85

92

105

137

185

100

69

48

39

34

38

47

34

37

19

23

21

22

24

8

10

16

18

18

24

20

23

17

6

1

64

149

241

346

483

668

768

837

885

924

958

996

1043

1077

1114

1133

1156

1177

1199

1223

1231

1241

1257

1275

1293

1317

1337

1360

1377

1383

1384

Remarks:

no. ofblows

Dep

th (

m)

Test carried out in accordance with operating instructions for the dynamic cone penetrometer Model A2465 byCNS Farnell Ltd.CBR correlation based on the relationship Log10 (CBR) = 2.48 - 1.057 * Log10 (mm/blow) developed by TRLtaken from The Highways Agency Interim Advice Note 73/06 - Design Guidance for Road Pavement Foundations(2009)

Initial scale reading (mm) 0

1

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

1

CBR (%)

DYNAMIC CONE PENETROMETER TESTING

Datum bgl (mm)5

0.06

0.14

0.24

0.34

0.48

0.66

0.76

0.83

0.88

0.92

0.95

0.99

1.04

1.07

1.11

1.13

1.15

1.17

1.19

1.22

1.23

1.24

1.25

1.27

1.29

1.31

1.33

1.36

1.37

1.38

1.38


CONTRACT CHECKED

DCP01CLIENT


DATE 29 April 2013

27979 EW


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/6/1

3

97

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

0 20 40 60 80 100

scalereading(mm)

CBR(%)

55.1

10.1

12.7

12.7

12.7

10.1

7.1

9.3

7.3

7.8

8.6

8.9

8.6

9.3

10.5

10.1

8.3

10.1

8.3

8.3

8.0

20.1

16.1

13.4

6.0

4.6

6.3

7.5

7.1

6.0

7.1

7.8

55.1

26.5

94.6

DCP(mm/blow)

5

25

20

20

20

25

35

27

34

32

29

28

29

27

24

25

30

25

30

30

31

13

16

19

41

52

39

33

35

41

35

32

5

10

3

depth bgl(m)


(mm)

5

25

20

20

20

25

35

27

34

32

29

28

29

27

24

25

30

25

30

30

31

13

16

19

41

52

39

33

35

41

35

32

5

10

3

60

85

105

125

145

170

205

232

266

298

327

355

384

411

435

460

490

515

545

575

606

619

635

654

695

747

786

819

854

895

930

962

967

977

980

Remarks:

no. ofblows

Dep

th (

m)



1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

CBR (%)


Datum bgl (mm)55

0.01

0.03

0.05

0.07

0.09

0.12

0.15

0.18

0.21

0.24

0.27

0.30

0.33

0.36

0.38

0.41

0.44

0.46

0.49

0.52

0.55

0.56

0.58

0.60

0.64

0.69

0.73

0.76

0.80

0.84

0.88

0.91

0.91

0.92

0.93


CONTRACT CHECKED

DCP02CLIENT


DATE 29 April 2013

27979 EW


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/6/1

3

98

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

0 50 100 150

scalereading(mm)

CBR(%)

5.1

9.5

3.9

3.2

4.8

9.1

7.6

15.1

20.1

12.7

12.7

7.9

12.1

15.6

10.7

10.1

15.1

20.1

35.9

38.6

33.5

20.9

20.9

80.3

45.5

49.8

29.6

33.5

80.3

145.2

DCP(mm/blow)

48

27

61

74

50

28

33

17

13

20

20

32

21

17

24

25

17

13

8

7

8

13

13

4

6

6

9

8

4

2

depth bgl(m)


(mm)

48

53

122

147

100

55

65

34

26

40

40

63

42

33

47

50

34

26

15

14

16

25

25

7

12

11

18

16

7

2

53

106

228

375

475

530

595

629

655

695

735

798

840

873

920

970

1004

1030

1045

1059

1075

1100

1125

1132

1144

1155

1173

1189

1196

1198

Remarks:

no. ofblows

Dep

th (

m)



1

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

1

CBR (%)


Datum bgl (mm)5

0.05

0.10

0.22

0.37

0.47

0.53

0.59

0.62

0.65

0.69

0.73

0.79

0.84

0.87

0.92

0.97

1.00

1.03

1.04

1.05

1.07

1.10

1.12

1.13

1.14

1.15

1.17

1.18

1.19

1.19


CONTRACT CHECKED

DCP03CLIENT


DATE 29 April 2013

27979 EW


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/6/1

3

99

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0 20 40 60

scalereading(mm)

CBR(%)

5.3

5.3

7.1

7.5

7.1

5.4

5.2

5.7

6.1

6.5

6.6

8.3

8.0

7.3

8.3

9.7

10.5

9.7

29.6

26.5

14.2

15.1

10.1

26.5

17.3

17.3

12.7

55.1

55.1

55.1

DCP(mm/blow)

46

46

35

33

35

45

47

43

40

38

37

30

31

34

30

26

24

26

9

10

18

17

25

10

15

15

20

5

5

5

depth bgl(m)


(mm)

46

46

35

33

35

45

47

43

40

38

37

30

31

34

30

26

24

26

9

10

18

17

25

10

15

15

20

5

5

5

81

127

162

195

230

275

322

365

405

443

480

510

541

575

605

631

655

681

690

700

718

735

760

770

785

800

820

825

830

835

Remarks:

no. ofblows

Dep

th (

m)



1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

CBR (%)


Datum bgl (mm)35

0.05

0.09

0.13

0.16

0.20

0.24

0.29

0.33

0.37

0.41

0.45

0.48

0.51

0.54

0.57

0.60

0.62

0.65

0.66

0.67

0.68

0.70

0.73

0.74

0.75

0.77

0.79

0.79

0.80

0.80


CONTRACT CHECKED

DCP04CLIENT


DATE 29 April 2013

27979 EW


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/6/1

3

100

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 50 100 150

scalereading(mm)

CBR(%)

8.3

3.6

4.8

7.3

9.1

11.5

12.4

13.1

16.7

17.3

16.7

26.5

29.6

31.5

45.5

20.1

17.9

16.7

19.3

22.9

24.0

38.6

28.0

26.5

26.5

29.6

45.5

55.1

94.6

45.5

94.6

94.6

145.2

DCP(mm/blow)

30

66

51

34

28

22

21

20

16

15

16

10

9

9

6

13

15

16

14

12

11

7

10

10

10

9

6

5

3

6

3

3

2

depth bgl(m)


(mm)

30

132

101

68

55

44

41

39

31

30

31

20

18

17

12

26

29

31

27

23

22

14

19

20

20

18

12

10

6

12

6

6

2

30

162

263

331

386

430

471

510

541

571

602

622

640

657

669

695

724

755

782

805

827

841

860

880

900

918

930

940

946

958

964

970

972

Remarks:

no. ofblows

Dep

th (

m)



1

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

1

CBR (%)


Datum bgl (mm)0

0.03

0.16

0.26

0.33

0.39

0.43

0.47

0.51

0.54

0.57

0.60

0.62

0.64

0.66

0.67

0.70

0.72

0.76

0.78

0.81

0.83

0.84

0.86

0.88

0.90

0.92

0.93

0.94

0.95

0.96

0.96

0.97

0.97


CONTRACT CHECKED

DCP05CLIENT


DATE 29 April 2013

27979 EW


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

RIA

LJH

.GP

J G

EO

TE

CH

.GLB

18

/6/1

3

101

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

0 50 100 150 200

scalereading(mm)

CBR(%)

2.9

5.7

6.4

6.5

6.4

7.4

8.9

8.9

8.9

8.6

8.0

11.8

94.6

145.2

114.7

196.7

80.3

55.1

35.9

26.5

12.7

12.7

49.8

49.8

45.5

49.8

20.9

9.1

94.6

DCP(mm/blow)

81

43

39

38

39

34

28

28

28

29

31

22

3

2

3

2

4

5

8

10

20

20

6

6

6

6

13

28

3

depth bgl(m)


(mm)

81

86

77

76

77

67

56

56

56

58

62

43

6

4

5

3

7

10

15

20

40

40

11

11

12

11

25

55

3

81

167

244

320

397

464

520

576

632

690

752

795

801

805

810

813

820

830

845

865

905

945

956

967

979

990

1015

1070

1073

Remarks:

no. ofblows

Dep

th (

m)



1

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

1

CBR (%)


Datum bgl (mm)0

0.08

0.17

0.24

0.32

0.40

0.46

0.52

0.58

0.63

0.69

0.75

0.80

0.80

0.81

0.81

0.81

0.82

0.83

0.85

0.87

0.91

0.95

0.96

0.97

0.98

0.99

1.02

1.07

1.07


CONTRACT CHECKED

DCP06CLIENT


DATE 29 April 2013

27979 EW


Geo

tech

nica

l Eng

inee

ring

Ltd,

Tel

. 014

52 5

2774

3

27

979.

GP

J T

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.GP

J G

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CH

.GLB

18

/6/1

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102

LABORATORY TESTING

2797

9Geotechnical Engineering Limited

APPENDIX B

103

2718

GEOTECHNICAL ENGINEERING LTD

For the attention of Sophie Collins Date of IssuePage Number 1 of 6

PROJECT/SITE Kingswood Playing Field Samples received 08/05/2013GEL REPORT NUMBER 27979 Schedule received 08/05/2013Your ref/PO: Testing commenced 19/05/2013

QUANTITY ACCREDITEDTEST

22 YES6 YES2 YES2 YES

29 May 2013

TEST REPORT

SUMMARY OF RESULTS ATTACHED

TEST METHOD & DESCRIPTION

BS1377: Part 2: 1990:3.2, Moisture ContentBS1377: Part 2: 1990:4.2‐4.4&5.2‐5.4, Liquid & Plastic LimitsBS1377: Part 2: 1990:9.2, Particle Size Distribution ‐ Wet SieveBS1377 Part 2 1990 9 4 Particle Si e Distrib tion Pipette 2 YES

Remarks Approved Signatories:The report should not be reproduced except in full without R Ewens (Laboratory Business Manager) R Pratt (Client Manager)

written permission from this laboratory. W Jones (Laboratory Supervisor) J Hanson (Director) C Thomas (Consultant)

Doc TR01 Rev No. 5 Revision date 22/03/13 DC:JH

Geotechnical Engineering Ltd www.geoeng.co.ukCenturion House [email protected] Park, Quedgeley TEL: 01452 527743Gloucester GL2 4NF Fax: 01452 729314

Registered number: 00700739 Payments: Geotechnical Engineering Limited

VAT Number: 682 5857 89 Sort code: 30‐15‐99 Bank account: 00072116

BS1377: Part 2: 1990:9.4, Particle Size Distribution ‐ Pipette

104

TP01 1D* 0.15 0.15 46 E Brown slightly sandy CLAY with a little f-mgravel and rare rootlets

TP01 2B 0.30 0.30 39 BXE 2 78 29 49 Brown mottled orange-brown slightlysandy CLAY with a little fine gravel andrare rootlets

TP01 3B 1.00 1.00 27 BXE 12 67 23 44 Grey-brown slightly sandy CLAY with alittle f-m gravel

TP01 4B 1.80 1.80 28 BXE 5 71 29 42 Grey slightly sandy CLAY with a little f-mgravel

TP02 1D* 0.15 0.15 47 E Brown slightly sandy CLAY with rarerootlets

TP02 2B 0.30 0.30 39 BXE 3 90 33 57 Brown mottled orange-brown slightlysandy CLAY

TP02 3B 0.60 0.60 20 BXE 9 52 21 31 Light grey slightly sandy CLAY with a littlef-m gravel

TP02 4B 1.00 1.00 29 BXE 7 72 23 49 Grey-brown slightly sandy CLAY with alittle f-m gravel

TP03 1D* 0.25 0.25 35 E Brown slightly sandy silty CLAY with alittle f-m gravel and rare rootlets

TP03 2B 0.30 0.30 26 E Brown slightly sandy silty CLAY with alittle fine gravel

TP03 3B 1.50 1.50 35 E Grey mottled orange-brown slightly sandyCLAY

TP04 1D* 0.15 0.15 59 E Brown slightly sandy CLAY with frequentrootlets

TP04 2B 0.30 0.30 39 E Brown mottled orange-brown and greyslightly sandy CLAY with a little finegravel

TP04 3B 1.00 1.00 25 E Light grey mottled brown slightly sandyCLAY with a little fine gravel

TP05 1D* 0.15 0.15 40 E Brown slightly sandy CLAY with a little f-mgravel and rare rootlets

TP05 2B 0.30 0.30 38 E Brown slightly sandy CLAY with rarerootlets

TP05 3B 1.30 1.30 27 E Brown mottled grey slightly sandy CLAYwith a little fine gravel

TP05 4B 1.50 1.50 25 E Grey mottled orange-brown slightly sandyCLAY with a little f-m gravel

limit

(%)

moisture preparation

X - cone penetrometer (test 4.3)test method:

A - as receivedB - washed on 0.425mm sieve

specimen preparation:

BS.1377 : Part 2 : 1990 : 4 and 5

Z - Casagrande apparatus (test 4.5)Y - one point cone penetrometer (test 4.4)

C - air dried

NP denotes non-plastic

E - oven dried (105°C)F - not known

natural moisture content determined in accordance with BS1377 : Part 2 : 1990 : 3.2 (unless specified)

# denotes sample tested is smaller than that which is recommended in accordance with BS1377

D - oven dried (60°C)

LIQUID AND PLASTIC LIMITS

plastic

limit

(%)

plasticity

index

(%)

specimen

and

test method

natural

content

(%)

fraction

>0.425

mm

(%)

description and remarks

liquid

CLIENT


SITE

CONTRACT CHECKED

general remarks:


27979


borehole

/trial pit

no. no./typedepth(m)

specimen

depth

(m)

sample

WJ

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Par

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L2 4

NF

. T

el. 0

1452

527

743

279

79.G

PJ

29/0

5/20

13 1

6:20

:27

105

TP06 1D* 0.15 0.15 47 E Brown slightly sandy CLAY with rarerootlets

TP06 2B 0.30 0.30 34 E Light brown mottled orange-brown slightlysandy CLAY with a little fine gravel

TP06 3B 0.60 0.60 27 E Light brown slightly sandy CLAY with alittle fine gravel

TP06 4B 1.40 1.40 31 E Grey mottled brown slightly sandy CLAYwith a little fine gravel

limit

(%)

moisture preparation

X - cone penetrometer (test 4.3)test method:

A - as receivedB - washed on 0.425mm sieve

specimen preparation:

BS.1377 : Part 2 : 1990 : 4 and 5

Z - Casagrande apparatus (test 4.5)Y - one point cone penetrometer (test 4.4)

C - air dried

NP denotes non-plastic

E - oven dried (105°C)F - not known

natural moisture content determined in accordance with BS1377 : Part 2 : 1990 : 3.2 (unless specified)


D - oven dried (60°C)

LIQUID AND PLASTIC LIMITS

plastic

limit

(%)

plasticity

index

(%)

specimen

and

test method

natural

content

(%)

fraction

>0.425

mm

(%)

description and remarks

liquid

CLIENT


SITE

CONTRACT CHECKED

general remarks:


27979


borehole

/trial pit

no. no./typedepth(m)

specimen

depth

(m)

sample

WJ

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Ltd,

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turio

n H

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, O

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L2 4

NF

. T

el. 0

1452

527

743

279

79.G

PJ

29/0

5/20

13 1

6:20

:28

106

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100 110

49

44

42

57

31

49

remarks

CH

liquid limit - LL (%)

plas

ticity

inde

x -

PI (

%)

MV

0.30

1.00

1.80

0.30

0.60

1.00

MEMH

CE

ML MI

BH/TP No. PI

TP01

TP01

TP01

TP02

TP02

TP02

78

67

71

90

52

72

depth (m) PL

CV

LL

ATTERBERG LINE PLOT

CL CI

29

23

29

33

21

23




CLIENT

SITE

CHECKEDCONTRACT

27979 WJ

Geo

tech

nica

l Eng

inee

ring

Ltd,

Cen

turio

n H

ouse

, O

lym

pus

Par

k, Q

uedg

eley

, G

louc

este

r. G

L2 4

NF

. T

el. 0

1452

527

743

279

79.G

PJ

29/0

5/20

13 1

6:20

:33

107

0

10

20

30

40

50

60

70

80

90

100

SPECIMEN DEPTH (m) 0.30

remarks:

20

6

2

89

76

63


5

2

1.18

0.6

0.425

0.212

0.15

0.063

100

97

97

96

96

93

20

5

0.02 0.2

medium

test method(s)

passing

Brown mottled orange-brown slightly sandy CLAY

150

75

63

50

37.5

20

10

6.3

(mm)

%

passingsoil type

102

CLAY

37.5

SILT

% fraction

BS test sieve (mm)

63

coarse

0.063

20

SAND

6.3

BS test sieve

0.425

9.2 & 9.4

CLAY

SILT

SILT & CLAY

SAND

GRAVEL

COBBLE & BOULDER

test method:

9.2 - wet sieving

9.3 - dry sieving

9.4 - sedimentation by pipette

9.5 - sedimentation by hydrometer

coarse fine medium

( m)

BS.1377 : Part 2 : 1990 : 9

%

finer

BS test sieve

(mm)

0.6

mm 0.0063 0.063 0.63 6.3

0.15

1.18

particle size

fine medium coarse

0.002

50

63

PARTICLE SIZE DISTRIBUTION

75

%

GRAVELCOBBLE

DESCRIPTION

BOULDERfine

% p

assi

ng

2 200

0.212

63

30

93

7

0

0

SAMPLE DEPTH (m)

SAMPLE No./TYPE


BH/TP No. TP02KINGSWOOD PARISH COUNCILCLIENT

CHECKEDCONTRACT

27979 WJ

SITE KINGSWOOD PLAYING FIELD2B

0.30

Geo

tech

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Ltd,

Cen

turio

n H

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Par

k, Q

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r. G

L2 4

NF

. T

el. 0

1452

527

743

279

79.G

PJ

29/0

5/20

13 1

6:20

:40

108

0

10

20

30

40

50

60

70

80

90

100

SPECIMEN DEPTH (m) 0.30

remarks:

20

6

2

89

58

46


5

2

1.18

0.6

0.425

0.212

0.15

0.063

100

99

99

98

98

97

97

96

20

5

0.02 0.2

medium

test method(s)

passing

Brown slightly sandy silty CLAY with a little fine gravel

150

75

63

50

37.5

20

10

6.3

(mm)

%

passingsoil type

102

CLAY

37.5

SILT

% fraction

BS test sieve (mm)

63

coarse

0.063

20

SAND

6.3

BS test sieve

0.425

9.2 & 9.4

CLAY

SILT

SILT & CLAY

SAND

GRAVEL

COBBLE & BOULDER

test method:

9.2 - wet sieving

9.3 - dry sieving

9.4 - sedimentation by pipette

9.5 - sedimentation by hydrometer

coarse fine medium

( m)

BS.1377 : Part 2 : 1990 : 9

%

finer

BS test sieve

(mm)

0.6

mm 0.0063 0.063 0.63 6.3

0.15

1.18

particle size

fine medium coarse

0.002

50

63

PARTICLE SIZE DISTRIBUTION

75

%

GRAVELCOBBLE

DESCRIPTION

BOULDERfine

% p

assi

ng

2 200

0.212

46

50

96

3

1

0

SAMPLE DEPTH (m)

SAMPLE No./TYPE


BH/TP No. TP03KINGSWOOD PARISH COUNCILCLIENT

CHECKEDCONTRACT

27979 WJ

SITE KINGSWOOD PLAYING FIELD2B

0.30

Geo

tech

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inee

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Ltd,

Cen

turio

n H

ouse

, O

lym

pus

Par

k, Q

uedg

eley

, G

louc

este

r. G

L2 4

NF

. T

el. 0

1452

527

743

279

79.G

PJ

29/0

5/20

13 1

6:20

:41

109

GEOTECHNICAL DATA

2797

9Geotechnical Engineering Limited

APPENDIX C

110

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25 30 35 40 45 50 55 60

27979



Dep

th (

m)

Moisture Content (%)


CLIENT

SITE

CONTRACT CHECKED

MOISTURE CONTENT PLOT

TP01

TP02

TP03

TP04

TP05

TP06

EW

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52 5

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111

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 0.2 0.4 0.6 0.8 1.0


CLIENT


27979

SITE

CONTRACT CHECKED

Dep

th (

m)

Moisture Content/Liquid Limit

TP01

TP02


MOISTURE CONTENT/LIQUID LIMIT PLOT

EW

Geo

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Ltd,

Tel

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52 5

2774

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112

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0 20 40 60 80 100


27979

KINGSWOOD PARISH COUNCILde

pth

(m)

STRENGTH v DEPTH PLOT

cohesion (kPa)


CLIENT

SITE

CONTRACT CHECKEDdenotes cohesion determined from triaxial test results

denotes cohesion determined from hand shear vane test results

denotes a cohesion determined from SPT results using a factor of 5kPa (Stroud,1974)

EW

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52 5

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113

Appendix 12

Peer Review of Flood Risk Assessment

114

!

!

Peer review of Flood Risk Assessment and Drainage

Assessment

Document: 1 Version: Draft

Professional advice Re S.11/1839/FUL, Land at Chestnut Park, Kingswood

Stroud District Council

October / 21 / 2011

!

!!

!!

!!!

115

!

!

!

Authors!

!

Andy!McConkey!–!Principal!urban!water!consultant!

!

Rebecca!Bailey!"!Hydrologist

116

!

!

Halcrow Group Limited

Burderop Park, Swindon, Wiltshire SN4 0QD

tel 01793 812479 fax 01793 812089

halcrow.com

Halcrow Group Limited has prepared this report in accordance with

the instructions of client Stroud District Council for the client’s sole and specific use.

Any other persons who use any information contained herein do so at their own risk.

© Halcrow Group Limited 2011

!

Peer review of Flood Risk Assessment and Drainage

Assessment

Professional advice Re S.11/1839/FUL, Land at Chestnut Park, Kingswood

Stroud District Council

October / 21 / 2011

!

117

Peer review of Flood Risk Assessment and Drainage Assessment

!

!

Contents

1 Scope of review 51.1 Introduction 5

1.2 Scope 5

1.3 Site location 3

1.4 Ground conditions 6

1.5 Site assessment – sources, mechanisms and pathways of flooding 6

1.6 Surface water drainage strategy 7

1.7 Foul water drainage strategy 11

2 Conclusions and recommendations 12

!

!

!

118


!

5!

1 Scope of review

1.1 Introduction

Halcrow!Group!Limited!have!been!commissioned!by!Stroud!District!Council!to!

review!the!Flood!Risk!Assessment!and!drainage!strategies!submitted!in!support!of!

Planning!Application!S.11/0812/FUL!for!27!houses!at!Chestnut!Park.!

The!review!has!been!requested!to!consider!5!key!questions:!

1.!Is!the!application!sufficiently!detailed?!

(a)!If!not,!what!additional!information!is!required?!

2.!Are!the!mitigation!measures!appropriate?!

3.!What,!if!any,!impact!would!the!proposed!development!have!on!flooding!both!on!

the!site!and!the!surrounding!area/displacement?!!

4.!Will!the!development!preserve!the!greenfield!run!off!values!of!the!existing!field?!

5.!Are!there!any!maintenance!concerns!or!arduous!regimes!required!to!ensure!the!

longevity!of!the!proposals?!

1.2 Scope

This!review!has!been!prepared!using!the!following!documents:!

Planning!Policy!Statement!25:!development!and!flood!risk;!March!2010!!

Planning!Policy!Statement!25:!development!and!flood!risk;!December!2009!

Sewers!for!Adoption!6th!Edition;!2006!

Flood!and!Water!Management!Act;!2010!

Environment!Agency!representation!13!October!2011!

Flood!Risk!Assessment,!Chestnut!Park,!BWB!consulting!for!Taylor!Wimpey,!

September!2011.!!!

Interpretive!Report!on!site!investigation,!Structural!Soils!Limited!for!Taylor!Wimpey,!

July!2010.!

Code!for!Sustainable!Homes!Version!2;!May!2009!

Code!for!Sustainable!Homes!Technical!Guide;!November!2010!

!

!

!

!

!

!

119


!

6!

1.3 Review of ground conditions

The!bedrock!geology!is!Jurassic,!Lower!Lias!Mudstones.!!There!are!no!superficial!

deposits.!(Source:!http://www.bgs.ac.uk/GeoIndex/)!

Bedrock!Aquifer!designation!=!Secondary!undifferentiated!(This!has!been!assigned!in!

cases!where!it!has!not!been!possible!to!attribute!either!category!A!or!B!to!a!rock!type.!!

In!most!cases,!this!means!that!the!layer!in!question!has!previously!been!designated!as!

both!minor!and!non"aquifer!in!different!locations!due!to!the!variable!characteristics!of!

the!rock!type).!

Ground!investigations!are!detailed!in!the!interpretative!report!on!site!conditions.!!

These!confirm!that!the!soil!is!primarily!clay!with!intervening!limestone!strata,!and!

support!the!application!of!soil!type!WRAP!4!for!modelling!purposes.!!!

A!soakaway!test!was!undertaken!in!one!trial!pit!(TP7)!and!after!3!hours,!no!drop!in!

water!level!was!observed.!!The!report!concludes!that!no!infiltration!rate!could!be!

calculated!and!soakaways!are!unlikely!to!be!suitable!for!this!site.!!!

We!consider!that!this!conclusion!is!acceptable.!

1.4 Review of site assessment – sources, mechanisms and pathways of flooding

Fluvial!flood!risk!(flood!risk!from!rivers):!!The!FRA!and!drainage!strategy!concludes!

that!the!site!has!a!low!probability!of!flooding!from!river!(less!than!0.1%).!!We!have!

reviewed!the!Environment!Agency!Flood!Maps!and!used!our!local!knowledge!from!

preparing!the!Stroud!District!Council!Strategic!Flood!Risk!Assessment;!September!

2008!and!agree!with!this!assessment.!!!

We!find!no!fault!with!the!calculations!assessing!the!risk!of!flooding!from!the!

unnamed!drainage!ditch!on!the!north!west!boundary!of!the!site,!and!concur!that!the!

drainage!ditch!has!capacity!for!the!peak!flow!deriving!from!its!calculated!upstream!

catchment.!!This!is!subject!to!the!drainage!ditch!being!maintained!and!regularly!

cleared!such!that!there!are!no!obstructions!to!flow1.!!!!

Tidal!flood!risk:!(flood!risk!from!the!coast!or!tidal!waters)!–!The!FRA!and!drainage!

strategy!concludes!that!the!site!has!a!low!probability!of!flooding!from!coastal!or!tidal!

waters.!!We!have!reviewed!the!Environment!Agency!Flood!Maps!and!used!our!local!

knowledge!from!preparing!the!Stroud!District!Council!Strategic!Flood!Risk!

Assessment;!September!2008!and!agree!with!this!assessment.!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!

!

!

!

1!The!modelling!has!assumed!that!the!roughness!of!the!ditch! is!equivalent!to!rough!

grass.!!This!assumption!is!only!correct!if!the!bankside!vegetation!is!low"level!scrub!or!

uncut!grass.!!!!See!section!1.5.6!!for!more!information.!

120


!

7!

Pluvial!flood!risk:!!Modelling!has!been!undertaken!to!assess!the!implications!of!

pluvial!flood!risk!and!mitigation!has!been!identified!to!manage!this!risk.!!We!agree!

that!the!site!is!at!risk!of!pluvial!flooding,!and!our!assessment!of!the!proposed!

mitigation!follows!in!section!1.5.6!

Groundwater!flooding:!Given!the!geological!characteristics,!the!risk!of!flooding!from!

groundwater!is!considered!low.!!This!agrees!with!the!assessment!made!in!section!2.1!

of!the!report.!!

Sewer!flooding:!!Flood!risk!to!the!site!from!surface!water!sewer!flooding!should!be!

prevented!through!good!design!of!the!drainage!system.!!!Our!comments!on!this!

follow!in!section!1.5.3.!

Foul!water:!!!Subject!to!foul!drainage!meeting!the!requirements!of!Sewers!for!

Adoption!6th!volume,!there!should!be!no!foul!flood!risk!to!the!site.!!!

No!assessment!has!been!made!of!the!impact!of!development!on!downstream!foul!

sewer!flooding.!!However!the!wastewater!and!sewerage!company!(Wessex!Water)!

have!implied!that!they!have!no!objections!to!the!development!in!their!letter!dated!30th!

September.!!!For!the!sake!of!completeness,!it!is!recommended!that!the!developer!seek!

a!letter!from!Wessex!Water!confirming!that!they!have!no!objections!to!the!

development,!and!confirming!that!they!have!capacity!in!their!foul!water!network!for!

this!development,!without!development!increasing!the!risk!of!downstream!foul!

flooding!or!overflows!from!combined!sewers.!

Surface!water.!!Subject!to!surface!water!drainage!meeting!the!requirements!of!PPS25,!

there!should!be!no!surface!water!sewer!flood!risk!to!the!site.!!Good!design!of!this!

system!should!prevent!any!change!in!risk!of!flooding!from!the!downstream!system.!!

We!consider!the!drainage!system!design!in!section!1.5.3.!

1.5 Review of surface water drainage strategy

1.5.1 Hierarchy of drainage

PPS25!and!the!SUDS!manual!require!developers!to!consider!the!following!hierarchy!

of!destination!of!surface!water:!

! Infiltration!

! Above!ground!river!system!

! Surface!water!sewer!

! Combined!sewer!

The!FRA!has!confirmed!that!infiltration!to!ground!is!not!suitable,!and!has!proposed!

that!a!conventional!below!ground!drainage!system!be!constructed!to!intercept!surface!

water!and!store!it!on!site,!with!a!controlled!discharge!via!the!existing!surface!water!

sewer!system!to!the!Ozleworth!Stream.!!!!!

There!is!a!more!proximate!drainage!ditch,!referenced!throughout!the!FRA,!that!has!

not!been!assessed!as!a!possible!destination!for!drainage!for!the!development.!!It!

would!be!expected!that!the!developer!should!confirm!that!that!ditch!is!unsuitable!for!

drainage!before!determining!to!discharge!into!an!existing!surface!water!sewer.!!

However,!in!general!terms,!the!philosophy!of!the!destination!of!drainage!hierarchy!

has!been!followed.!!!!

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1.5.2 Greenfield runoff calculations

Peak!flow!discharge!rates!have!been!provided!based!on!Greenfield!runoff!

calculations!undertaken!in!WinDES.!!!The!ADAS!345!methodology!has!been!used!to!

determine!Greenfield!rates.!!Defra/EA!guidance!specifies!that!IH124,!not!ADAS!345!

should!be!used!to!determine!Greenfield!rates.!!There!is!merit!in!the!FRA!choosing!to!

use!ADAS!345!as!it!is!the!only!accepted!methodology!that!includes!a!gradient!factor.!!

In!the!case!of!this!development,!the!upstream!gradient!is!a!factor!for!concern.!!!!

However,!in!light!of!the!DEFRA/EA!guidance!that!specifies!IH124,!we!would!expect!

the!FRA!to!use!both!methodologies!and!provide!the!results!for!both!methodologies.!!

We!would!then!expect!the!FRA!to!conclude!which!method!they!were!using!and!how!

the!design!approach!put!forward!allows!or!mitigates!for!the!uncertainty!between!the!

two!methodologies.!!

Notwithstanding!the!above,!the!calculations!of!the!peak!flow!for!the!entire!fluvial!

catchment!(Table!3.1)!are!considered!acceptable.!!!

Notwithstanding!the!first!paragraph!above,!calculations!of!peak!flow!at!the!location!

of!the!proposed!highway!for!passage!of!water!through!the!culvert!are!considered!

acceptable.!!

Calculations!of!peak!flow!for!the!site!area!(Table!3.2)!are!considered!acceptable.!!!

1.5.3 Proposed drainage strategy

A!range!of!attenuation!storage!based!on!the!calculated!Greenfield!rates!have!been!

provided!(Table!4.2),!but!no!value!has!been!selected!for!use!in!the!drainage!system.!!

The!conclusion!that!a!positive!drainage!system!below!ground!is!required!partly!

because!of!the!number!of!trees!that!need!to!be!retained!seems!reasonable!and!fair.!!It!

is!noted!that!the!applicant!has!significant!holdings!of!land!outside!the!application!red!

line!boundary.!!However,!this!is!upgradient!of!the!application!site!therefore!not!

suitable!for!above!ground!SUDS!features!development.!!Therefore!the!philosophy!of!

providing!attenuation!storage!below!ground!is!acceptable.!!

The!volume!of!attenuation!storage!to!be!provided!has!not!been!confirmed.!!!The!

calculated!storage!provided!in!table!4.2!is!based!on!1!hour!storage!of!peak!flow!in!a!

range!of!return!period!rainfall!events.!!!Further!modelling!will!be!required!to!

determine!the!volume!of!storage!required.!!!!

This!additional!modelling!will!also!need!to!determine!the!long!term!storage!

requirement!that!will!be!required!to!mitigate!for!the!additional!volume!of!runoff!

being!generated!that!cannot!be!infiltrated.!!!

The!Code!for!Sustainable!Homes!technical!guide!(November!2010)!has!a!mandatory!

requirement!that!the!drainage!strategy!must!ensure!‘the!additional!predicted!volume!of!

runoff!for!the!100!year!6!hour!event!must!be!prevented!from!leaving!the!site!by!using!

infiltration!or!other!SuDS!techniques.’!(see!Figure!1_2!below).!The!applicant!has!shown!

that,!in!general,!infiltration!is!not!possible.!!They!have!also!identified!small!scale!

SUDS!features.!!However,!some!of!these!SUDS!features!are!deliberately!designed!to!

prevent!infiltration,!and!no!information!has!been!provided!to!quantify!or!manage!this!

additional!predicted!volume.!!!!It!is!essential!that!the!applicant!provide!further!detail!

regarding!the!long!term!storage!that!will!be!required,!and!how!the!volume!and!rate!

of!this!long!term!storage!will!be!managed!in!accordance!with!the!Code!for!

Sustainable!Homes!(see!Figure!1_2!below).!

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With!respect!to!runoff!from!the!impermeable!area!of!the!site,!the!applicant!has!stated!

that!the!new!impermeable!area!will!generate!between!75l/s!and!100l/s!of!surface!

water!runoff!but!has!not!provided!any!modelling!evidence!or!calculations!to!support!

this!statement.!!We!consider!that!the!values!are!realistic,!but!for!the!sake!of!

completeness!an!FRA!would!be!expected!to!include!this!evidence.!The!applicant!has!

proposed!controlling!the!rate!of!discharge!from!the!new!development!impermeable!

area!(to!mitigate!for!the!75!–!100l/s)!at!the!point!of!discharge!downstream!of!the!

existing!development!to!68l/s!(which!includes!the!Greenfield!rate!of!the!existing!

development!and!the!Greenfield!rate!of!the!new!development.!!!This!in!principle!is!

acceptable.!!However,!it!is!unclear!if!a!flow!control!device!will!be!constructed!at!the!

downstream!end!of!the!new!development!drainage.!!!We!consider!that!flow!control!at!

this!point!is!required!to!ensure!that!Greenfield!rates!are!to!be!maintained.!!We!

therefore!would!recommend!that!a!staged!flow!control!device,!controlling!to!the!1!in!

5,!1!in!30!and!1!in!100!rates!is!constructed!at!the!point!marked!‘proposed!storm!water!

flow!control!manhole!in!drawing!number!02"100"01.!!!!

We!note!that!Drawing!02"21"01!suggests!a!flow!control!device!of!57l/s!will!be!applied!

at!this!point,!which!is!significantly!greater!than!the!Greenfield!1!in!100!year!rate!of!

39.8l/s.!!!!!

The!applicant!has!stated!several!times!that!the!downstream!surface!water!drainage!

system!was!designed!to!accommodate!predicted!flows!from!both!the!existing!and!

proposed!development,!but!has!not!provided!any!evidence!to!support!this!statement.!!

We!recommend!at!further!evidence!be!provided!to!support!this!statement.!

The!applicant!has!stated!that!the!flow!controlling!device!at!the!downstream!point!of!

discharge!into!the!Ozleworth!Stream!will!need!to!be!increased!to!allow!for!the!

additional!Greenfield!runoff!rate!from!the!proposed!development.!!This!change!will!

need!a!land!drainage!consent!from!the!EA,!and!we!recommend!that!any!permission!is!

conditional!on!this!consent!being!granted.!

No!allowance!appears!to!have!been!made!for!the!drainage!of!undeveloped!or!

permeable!areas!of!the!site.!!Runoff!from!permeable!areas!will!occur,!especially!

because!the!developer!has!advised!that!the!soil!type!is!generally!impermeable!clay!

like!materials.!!If!land!use!in!these!areas!is!not!changing,!then!the!runoff!rate!and!

volume!will!not!change!significantly!from!the!existing!Greenfield,!and!this!should!not!

affect!the!volume!of!storage!or!the!peak!rate!of!runoff!control.!!However,!any!

drainage!system!draining!the!site!must!be!able!to!drain!the!total!area!of!the!site!

effectually,!not!just!the!developed!area.!!The!developer!must!clarify!that!the!drainage!

system!proposed!has!capacity!for!100%!of!the!1.470ha!site!area!in!a!100year!+!climate!

change!rainfall!event.!

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Figure 1-1 Extract for Code for Sustainable Homes Technical Guide November 2010

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1.5.4 Drainage system adoption

The!FRA!and!drainage!strategy!has!proposed!that!the!positive!drainage!system!will!

be!adopted!by!Wessex!Water.!!!The!system!as!proposed!appears!to!have!been!

designed!to!meet!Wessex!Water!adoption!criteria!as!stated!in!their!latter!on!30th!

September.!

1.5.5 Drainage system failure

No!consideration!has!been!given!to!the!risk!of!flooding!following!failure!of!flow!

control!devices.!!It!is!expected!that!a!failure!mechanism!would!be!provided!to!ensure!

that!property!flooding!does!not!occur!even!following!failure!of!the!device.!!

1.5.6 Pluvial flooding mitigation

It!is!agreed!that!the!localised!topography!at!the!southern!boundary!currently!suggests!

that!the!natural!flow!path!of!runoff!would!be!through!the!site!rather!than!in!to!the!

pond!and!ditch!system!(section!3.11).!!!

The!construction!of!a!land!bund!along!the!southern!border!will!provide!protection!

from!fluvial!flooding!if!designed!correctly.!!!

In!its!current!location,!we!consider!that!the!bund!will!only!protect!plots!18!and!24!and!

those!downslope!of!these.!!Given!the!levels!presented!in!the!site!survey!drawing,!the!

bund!is!considered!to!provide!no!protection!to!the!properties!to!the!east!of!the!site,!

namely,!25,!26,!27,!1,!2,!3,!and!4.!!!

The!profile!of!the!ground!behind!the!bund!needs!to!be!such!that!the!water!drains!

towards!the!pond.!!The!topographic!survey!does!not!provide!enough!evidence!that!

this!will!occur!if!current!levels!are!maintained.!!!

The!calculations!for!the!capacity!of!the!drainage!ditch!are!acceptable,!subject!to!the!

ditch!being!kept!in!a!clear!and!well!maintained!state.!!The!modelling!of!the!ditch!has!

assumed!that!the!ditch!is!‘rough!grass’.!!If!the!state!of!the!ditch!is!overgrown,!or!

blocked!with!debris,!the!carrying!capacity!of!the!ditch!will!be!less!than!modelled,!and!

there!may!be!a!residual!risk!of!flooding!from!this!ditch.!

1.6 Review of foul water drainage strategy

Wessex!Water!has!stated!that!they!have!no!objection!to!the!proposal!subject!to!a!

separate!system!being!installed,!no!land!drainage!being!connected!to!the!system,!and!

no!surface!water!being!connected!to!the!surface!water!system.!!The!system!as!

designed!appears!to!comply!with!these!stipulations.!!

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2 Conclusions and recommendations

2.1 Is the application sufficiently detailed, and if not, what additional information is required?

Further!information!would!be!expected!in!support!of!this!application.!!!If!the!

authority!is!minded!to!grant!permission,!we!would!recommend!conditional!

agreement!based!on!the!additional!information!below!being!provided,!and!a!detailed!

drainage!masterplan!being!agreed!with!the!planning!authority,!prior!to!construction.!!!

Critical:!!!!

Volume!of!attenuation!required!to!mitigate!to!Greenfield!rate!and!volume.!!Insufficient!

evidence!has!been!provided!regarding!the!volume!of!storage!that!will!be!provided.!!

Further!detail!regarding!the!volume!or!storage!provided,!including!the!need!to!

control!both!volume!and!rate!of!long!term!storage!must!be!provided.!!

No!allowance!appears!to!have!been!made!for!the!drainage!of!undeveloped!or!

permeable!areas!of!the!site.!!The!developer!must!clarify!that!the!drainage!system!

proposed!has!capacity!for!100%!of!the!1.470ha!site!area!in!a!100year!+!climate!change!

rainfall!event.!

Drainage!system!failure:!No!consideration!has!been!given!to!the!risk!of!flooding!

following!failure!of!flow!control!devices.!!It!is!expected!that!a!failure!mechanism!

would!be!provided!to!ensure!that!property!flooding!does!not!occur!even!following!

failure!of!the!device.!!

Pluvial!runoff!protection!bund:!!It!is!not!clear!from!information!provided!in!the!FRA!

that!the!bund!would!protect!all!properties!that!may!be!at!risk!of!pluvial!flooding.!!

The!applicant!needs!to!demonstrate!through!detailed!design!that!all!properties!at!risk!

are!protected,!and!that!the!profile!of!the!ground!behind!the!bund!ensures!water!

drains!towards!the!pond.!!!

Downstream!system!design:!The!applicant!has!stated!several!times!that!the!downstream!

surface!water!drainage!system!was!designed!to!accommodate!predicted!flows!from!

both!the!existing!and!proposed!development,!but!has!not!provided!any!evidence!to!

support!this!statement.!!We!recommend!further!evidence!be!provided!to!support!this!

statement.!

For!completeness:!!!

Foul!water:!For!the!sake!of!completeness,!it!is!recommended!that!the!developer!seek!a!

letter!from!Wessex!Water!confirming!that!they!have!no!objections!to!the!

development,!and!confirming!that!they!have!capacity!in!their!foul!water!network!for!

this!development,!without!development!increasing!the!risk!of!downstream!foul!

flooding!or!overflows!from!combined!sewers.!

Greenfield!runoff!calculations:!!The!assessment!is!not!fully!compliant!with!the!Defra/EA!

guidance.!Although!there!are!sound!technical!reasons!why!the!approach!chosen!has!

been!applied!in!light!of!the!variation!from!the!prescribed!approach,!we!would!expect!

the!FRA!to!use!both!methodologies!and!provide!the!results!for!both!methodologies.!!

We!would!then!expect!the!FRA!to!conclude!which!method!they!were!using!and!how!

the!design!approach!put!forward!allows!or!mitigates!for!the!uncertainty!between!the!

two!methodologies.!

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2.2 Are the mitigation measures appropriate?

In!principle!yes,!subject!to!the!further!information!identified!above!being!provided!

and!agreed.!

2.3 What, if any, impact would the proposed development have on flooding both on the site and the surrounding area/displacement?

Mitigation!measures!appear!to!have!been!considered!in!principle.!!Subject!to!further!

information!required!being!provided!and!agreed!with!the!authority,!these!principles!

should!ensure!there!is!no!impact!on!flooding!on!the!site!or!surrounding!

area/displacement.!

The!calculations!for!the!capacity!of!the!drainage!ditch!are!acceptable!for!the!

conveyance!of!upstream!pluvial!runoff,!subject!to!the!ditch!being!kept!in!a!clear!and!

well!maintained!state.!!!If!the!state!of!the!ditch!is!overgrown,!or!blocked!with!debris,!

the!carrying!capacity!of!the!ditch!will!be!less!than!modelled,!and!there!may!be!a!risk!

of!flooding!from!this!ditch.!

2.4 Will the development preserve the greenfield run off values of the existing field?

In!principle!yes,!subject!to!the!further!information!identified!above!being!provided!

and!agreed.!

2.5 Are there any maintenance concerns or arduous regimes required to ensure the longevity of the proposals?

The!positive!drainage!system!has!been!designed!in!principle!to!meet!Wessex!Water’s!

adoptions!requirements.!

The!pluvial!runoff!mitigation!and!protection!system!will!require!maintenance.!!We!

recommend!that!the!developer!be!required!to!consider!the!operational,!management!

and!funding!requirements!to!ensure!that!maintenance!of!the!bund!and!ensure!the!

maintenance!and!regular!clearance!of!the!pond!and!drainage!ditch!from!debris!and!

plant!growth.!!!

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For details of your nearest Halcrow office, visit our website halcrow.com

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