Soakaway Testing Report 1 - Borough of Great Yarmouth

A d i v i s io n o f Ha r r i so n G r o up E nv i ro n me n ta l L td .

Registered in England No. 1306165 Registered Office: Kimberley Street, Norwich, NR2 2RJ

5933 4031 5933

harrisongeotechnical

ENGNEERING

Harrison Geotechnical Engineering

Kimberley Street

Norwich NR2 2RJ

Tel: +44 (0)1603 613111

Fax: +44 (0)1603 618120

www.harrisongroupuk.com

email: [email protected]

7th

July 2014

Our Ref. GN18180_SA_RG

Persimmon Homes Limited (Anglia)

Colville Road Works

Oulton Broad

Lowestoft

NR33 9QS

For the attention of Laura Townes

Dear Sirs

Pointers East, Ormesby St. Margaret – Soakaway Testing - Infiltration Test Result Summary

The following investigation was carried out at the above location in accordance with our quotation dated 3rd

March 2014 and emailed instruction from the client on the 21st

May 2014. Initial background information for the

site indicated superficial deposits of Diamicton (clay) and sand of the Happisburgh Glacigenic Formation, with

a maximum permeability of high (sands) and a minimum permeability of low (Diamicton).

1. Site Works

The purpose of the investigation was to supply soakaway test data in general accordance with BRE document

365 (Soakaway Design) at three positions beneath a proposed residential development to be incorporated as

part of the surface water disposal system. We were requested to target the most permeable strata at each

location.

The test locations were selected in order to provide maximum coverage of the site and test all geological units

within the site boundary whilst minimising crop damage within the agricultural field. The appended drawing

(GN18180-DR002) illustrates the position of the test pits, which were excavated on 03/06/2014 to depths

between 1.6mbgl and 1.8mbgl (metres below ground level). The trial pits were installed with a monitoring

standpipe and filled with 1.0m of gravel to maintain the pit stability. Topsoil and arisings were used to backfill

the pits to ground level. Water was added to each pit up to three times by a tractor towable water bowser.

Falling water level readings were undertaken using manual electronic dip-meter readings by a geotechnical

engineer and technician.

Three fillings were achieved in trial pits TP2 and TP3, with full soakage to 25% test capacity (in line with BRE

365) achieved in each completed infilling. However, due to the slow fall in water level, only one infilling was

carried out in trial pit TP1 and soakage to 25% test capacity was not achieved. Following testing, the

monitoring pipes were removed.

A full record of the trial pit profiles is included in the appendix with a summary provided below.

A d i v i s io n o f Ha r r i so n G r o up E nv i ro n me n ta l L td .

Registered in England No. 1306165 Registered Office: Kimberley Street, Norwich, NR2 2RJ

5933 4031 5933

2. Findings

Soakaway Testing (TP1-3)

Trial pit logs and soil infiltration test result records can be found appended along with a summary of the

infiltration tests and drawing No. GN18180-DR002 showing the trial pit locations.

Topsoil of depths between 0.3m and 0.4m were found in pits TP1-3 consisting of a gravelly or slightly gravelly

clay. In TP1, this was found to be underlain by gravelly silty clay of the Happisburgh Glacigenic Formation

(diamicton), overlying a further layer of gravelly clayey sand from the same formation. The soakaway testing

targeted gravelly sandy clay (diamicton), found at depths of between 1.0mbgl to the base of the pit at

1.8mbgl.

In TP2, the topsoil was underlain by a sandy gravelly clay, with a clayey gravelly sand present from between

0.6mbgl and the base of the pit at 1.6mbgl. This material was targeted for the soakaway testing. Similar clayey

gravelly sand was found below the topsoil in TP3, underlain by silty very gravelly sand at depths of between

0.7mbgl and the base of the pit at 1.7mbgl. This material was also targeted for soakage testing.

Testing of the cohesive soils to the north east of the site (TP1) was not completed due to the slow fall in water

level, indicating very low infiltration rates and therefore this location is not generally considered suitable for

conventional depth soakaway drainage design. Deeper investigation for borehole soakaways could be

considered should soakaways be required in this area.

Testing of the generally clayey gravelly sand to the south of the site (TP2 and TP3) produced design infiltration

rates of 8.7x10-6

m/s and 1.0x10-4

m/s respectively (for soils below 0.7m depth). Both of these rates are

considered suitable for conventional surface water drainage design.

It is recommended that a site wide design infiltration rate of 9x10-6

m/s be considered for these granular soils

where found present. It should be noted that the entire site is likely to be underlain by the granular soils but

these may be present from significantly greater depths in places. It would be recommended that where

soakaways are planned further location specific investigation is undertaken to confirm the depth (below the

low permeability clay) from which the permeable sand unit is present.

Where the depth to the sand unit (below the clay) exceeds the use of conventional soakaways, it may be

prudent to consider use of borehole soakaways through location specific investigation. However, should these

be considered under consultation with the Environment Agency.

3. Attachments

Infiltration Test Result Summary

Soakaway Infiltration Test Results

Trial Pit Field Records (TP1-3)

Fieldwork Location Plan (GN18180-DR002)

Report Prepared By: R. Gregory Report Checked by: E. Orchin

Signature:

Signature:

Date: 24/06/2014 Date: 27/06/2014

Trial Pit

No

C

ol

u

m

Infilling 1 (m/s) Infilling 2 (m/s) Infilling 3 (m/s)

C

ol

u

m

Design Infiltration

Rate (m/s)

1.

00

Soil depth at which rate

applies (mbgl)Soil type at test depth

TP1 N/A N/A 1->1.8 Stiff gravelly sandy CLAY [DIAMICTON]

TP2 1.29E-05 9.62E-06 8.72E-06 8.7E-06 0.6->1.6 Slightly clayey gravelly SAND

TP3 1.27E-04 1.06E-04 1.29E-04 1.1E-04 0.7->1.7 Slightly silty very gravelly SAND

Client: Persimmon Homes (Anglia) LimitedDate: 03/06/2014

harrisongroup Infiltration Test Result Summary

Job Reference: GN18180 Location: Pointers East, Ormesby

Harrison Group Environmental Ltd.,

Kimberley Street, Norwich, Norfolk NR2 2RJ.

FM-Hn-R-3007 REV A

Minutes0.000.501.002.003.005.007.0010.0012.0014.0018.0021.0024.0027.00

60.61% full 32.0038.0044.0047.0054.0065.00108.00175.00307.00

Remarks:

282032403900648010500

1.0901.1001.1101.1401.1701.200

1.0601.0701.080

0.9700.9800.9901.000

1.050

Note: Estimated rate based on 75% Full to

60.61% full as test not completed to 25% full.

completed to 25% Full.

2640Infilling 1

Soil Infiltration Rate (f)

5.82E-07 m/s

18420

1.2101.2401.270

1.1501.1601.1701.1801.1901.200

End % for calculations:60.61% full

1.80

1.80

1.110

Start % for calculations:75% full

0.8100.8900.9100.9300.950

1.0901.100

Length

Width 0.50

Height of pipe above

ground level (if applicable)0.10

Depth

420300180

1.0101.0201.0301.040

Trial pit filled with gravel to prevent instability in pit walls?: Yes Void Space: 30%

1620

600720840108012601440

3060120

0 0.910

08:10

Date: 03/06/2014

Water level

(m) (mbgl)Seconds

1.1201.1301.140

0.9901.0101.0301.0501.0701.080

1.300

19202280

Engineer:

Client: Persimmon Homes Limited (Anglia) Test Pit No.:

SOIL INFILTRATION RATE TESTIn accordance with BRE Digest 365 (1991 with amendments in 2003 and 2007)

TP1

Job Number: GN18180

Job

Location:

RGR

Pit Dimensions (m)

Pointers East, Ormesby

Elapsed TimeDepth recorded

on dip meter

Time to fill pit:

(minutes)02:00 Time at start of test:

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Depth to water (m

bgl)

Time (seconds)

Water Level

75% full

60.61% full

Key:

Harrison Group, Kimberley Street, Norwich, Norfolk NR2 2RJ

FM-Hn-R-3007 REV A

Minutes0.000.501.002.003.005.008.0012.0018.0023.0031.0038.0048.0055.00

25% full 60.00

Remarks:

Engineer:



TP2

Job Number: GN18180

Job

Location:

RGR

Pit Dimensions (m)



on dip meter

Time to fill pit:

(minutes)02:00 Time at start of test: 08:37

Date: 03/06/2014

Water level

(m) (mbgl)Seconds

1.5901.6201.650

1.0601.1601.2101.2501.3201.380

3600

480300180

1.2401.2901.3201.350


3300

72010801380186022802880

3060120

0 0.980 0.6800.7600.8600.9100.950

1.4301.500

Length

Width 0.50



Depth

1.690

End % for calculations:25% full

1.60

1.80

1.540


1.390

1.0201.0801.1301.200

1.370

Note: Test completed between 75% full and 25%

full in accordance with BRE Digest 365

to 25% Full.

Infilling 1


1.29E-05 m/s

1.670

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 1000 2000 3000 4000 5000 6000 7000

Depth

to w

ate

r (m

bgl)

Time (seconds)

Water Level

75% full

25% full

Key:


FM-Hn-R-3007 REV A

Minutes0.001.003.006.0011.0071.0088.0092.0097.00101.00

25% full

Remarks:

to 25% Full.



Infilling 2

9.62E-06 m/s



6060 1.700 1.400


Depth 1.60660 1.280 0.9804260 1.600 1.300

1.360



5280 1.640 1.3405520 1.650 1.3505820 1.660

Length 1.800 0.760 0.46060 0.990 0.690

Width 0.50180 1.150 0.850360 1.210 0.910

Pit Dimensions (m)Elapsed Time

Depth recorded

on dip meterWater level

Seconds (m) (mbgl)

Client: Persimmon Homes Limited (Anglia) Test Pit No.: TP2 Date: 03/06/2014



Engineer: RGR Job Number: GN18180

Job

Location: Pointers East, Ormesby

Time to fill pit:


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 1000 2000 3000 4000 5000 6000 7000

Depth

to w

ate

r (m

bgl)

Time (seconds)

Water Level

75% full

25% full

Key:


FM-Hn-R-3007 REV A

Minutes0.001.003.004.006.009.0014.0022.0034.0049.0069.0099.00114.00

25% full

Remarks:

to 25% Full.



Infilling 3

8.72E-06 m/s



6840 1.670 1.370

2940 1.490 1.190


4140 1.560 1.2605940 1.630 1.330

Depth 1.60360 1.190 0.890540 1.230 0.930

1.120



840 1.280 0.9801320 1.350 1.0502040 1.420

Length 1.800 0.700 0.40060 0.960 0.660

Width 0.50180 1.120 0.820240 1.160 0.860


Depth recorded


Seconds (m) (mbgl)





Job


Time to fill pit:


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 1000 2000 3000 4000 5000 6000 7000

Depth

to w

ate

r (m

bgl)

Time (seconds)

Water Level

75% full

25% full

Key:


FM-Hn-R-3007 REV A

Minutes0.001.002.003.005.006.007.0010.0012.0013.0015.00

25% full

Remarks:

Engineer:



TP3

Job Number: GN18180

Job

Location:

RGR

Pit Dimensions (m)



on dip meter

Time to fill pit:


Date: 03/06/2014

Water level

(m) (mbgl)Seconds

1.700

1.1901.2701.3301.4301.4901.530420

360300

1.6701.700


600720780900

60120180

0 0.840 0.8401.1901.2701.3301.430

1.6201.630

Length

Width 0.50


ground level (if applicable)

Depth


1.70

1.80

1.670


1.4901.5301.6201.630



to 25% Full.

Infilling 1


1.27E-04 m/s

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 200 400 600 800 1000 1200

Depth

to w

ate

r (m

bgl)

Time (seconds)

Water Level

75% full

25% full

Key:


FM-Hn-R-3007 REV A

Minutes0.001.002.003.005.007.009.0011.0013.0015.0016.0017.00

25% full

Remarks:

to 25% Full.



Infilling 2

1.06E-04 m/s



900 1.670 1.670


960 1.690 1.6901020 1.700 1.700

Depth 1.70300 1.400 1.400420 1.490 1.490

1.650



540 1.560 1.560660 1.600 1.600780 1.650

Length 1.800 0.850 0.85060 1.200 1.200

Width 0.50120 1.270 1.270180 1.350 1.350


Depth recorded


Seconds (m) (mbgl)





Job


Time to fill pit:


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 200 400 600 800 1000 1200

Depth

to w

ate

r (m

bgl)

Time (seconds)

Water Level

75% full

25% full

Key:


FM-Hn-R-3007 REV A

Minutes0.001.002.003.004.005.007.009.0010.0012.0014.0016.0017.0019.00

25% full

Remarks:

to 25% Full.



Infilling 3

1.29E-04 m/s



1020 1.680 1.6801140 1.700 1.700

720 1.600 1.600


840 1.640 1.640960 1.670 1.670

Depth 1.70240 1.370 1.370300 1.420 1.420

1.560



420 1.480 1.480540 1.520 1.520600 1.560

Length 1.800 0.700 0.70060 1.150 1.150

Width 0.50120 1.260 1.260180 1.330 1.330


Depth recorded


Seconds (m) (mbgl)





Job


Time to fill pit:


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 200 400 600 800 1000 1200

Depth

to w

ate

r (m

bgl)

Time (seconds)

Water Level

75% full

25% full

Key:


Trial Pit Record

FM-Hn-R-3025-REV C

Contract No.

Location: Date:

Client: Plant: Ordnance Coordinates:

Description LegendRemarks

Depth O.D. Samples & Tests(m) Level Type Depth

Water Level Observations

Date Time WaterStrike (m)

StandingLevel (m)

Remarks:

Pit Dimensions: (L x D x W) Logged By:

KEYD

B

U

W

Disturbed Sample

Bulk Sample

Undisturbed Sample

Water Sample

Water Strike

Standing Water Level

(m) (m)

Environmental SampleES

HV

Checked By:

harrisongroup

Datum:

Results/WaterStrike

x x

Pocket PenetrometerPP

In-situ Hand Vane Test

Persimmon Homes (Anglia) Limited

1.80m

JCB 3CX

Pointers East, Ormesby StMargaret

Trial pit terminated at 1.80mbgl.1.2. Groundwater was not encountered.3. Backfill details: upon completion trial pit backfilled with

gravel to 0.80 and arisings to GL.

1.80m 0.50m

0.00

-

S. Kearney

GN18180

02/05/2014

651435E

313982N

E. Orchin

TP1

0.30

0.60

1.00

1.80

ES1

D1

D2

D3

D4

0.20

0.40

1.00

1.30

1.80

TOPSOIL (Brown gravelly CLAY. Gravel is fine to coarse subangular tosubrounded flint).

Soft grey mottled light brown slightly gravelly silty CLAY. Gravel isfine to coarse subangular flint. [HAPPISBURGH GLACIGENIC FORMATON -DIAMICTON]

Orangish brown gravelly very clayey SAND. Gravel is fine to coarsesubangular to subrounded flint. [HAPPISBURGH GLACIGENIC FORMATON -DIAMICTON]

Stiff orangish brown mottled grey slightly gravelly sandy CLAY. Gravelis fine to coarse subangular to subrounded flint. [DIAMICTON]

Trial Pit Complete at 1.80 m

Sheet 1 of 1

Trial Pit Record

FM-Hn-R-3025-REV C

Contract No.

Location: Date:






StandingLevel (m)

Remarks:


KEYD

B

U

W

Disturbed Sample

Bulk Sample

Undisturbed Sample

Water Sample

Water Strike


(m) (m)


HV

Checked By:

harrisongroup

Datum:

Results/WaterStrike

x x




1.80m

JCB 3CX




1.60m 0.50m

0.00

-

S. Kearney

GN18180

02/06/2014

651411E

313750N

E. Orchin

TP2

0.30

0.60

1.60

ES1

D1

B1

D2

0.20

0.50

1.30

1.60

TOPSOIL (Brown slightly gravelly CLAY. Gravel is fine to coarsesubangular to subrounded flint).

Firm brown slightly sandy slightly gravelly CLAY. Gravel is fine tocoarse subangular to subrounded flint. [DIAMICTON]

Light brown mottled yellow brown slightly clayey gravelly fine tocoarse SAND. Gravel is fine to coarse subangular to subrounded flint.Occasional yellowish brown clayey pockets. Becoming very clayey withdepth.[HAPPISBURGH GLACIGENIC FORMATON - SANDS]


Sheet 1 of 1

Trial Pit Record

FM-Hn-R-3025-REV C

Contract No.

Location: Date:






StandingLevel (m)

Remarks:


KEYD

B

U

W

Disturbed Sample

Bulk Sample

Undisturbed Sample

Water Sample

Water Strike


(m) (m)


HV

Checked By:

harrisongroup

Datum:

Results/WaterStrike

x x




1.80m

JCB 3CX




1.70m 0.50m

0.00

-

S. Kearney

GN18180

02/07/2014

651214E

313654N

E. Orchin

TP3

0.40

0.70

1.70

ES1

B1

B2

D1

0.20

0.70

1.20

1.70

TOPSOIL (Brown slightly sandy gravelly CLAY. Gravel is fine to coarsesubangular to subrounded flint).

Yellowish brown clayey gravelly fine to coarse SAND. Gravel is fine tocoarse subangular to subrounded flint. [HAPPISBURGH GLACIGENICFORMATON - SANDS]

Yellowish brown slightly silty very gravelly fine to coarse SAND.Gravel is fine to coarse subangular to subrounded flint. [HAPPISBURGHGLACIGENIC FORMATON - SANDS]


Sheet 1 of 1

Soakaway Testing Report 1 - Borough of Great Yarmouth

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