analytical geotechnics limited

Dear Giri,

Roundhill School, Beeston.

We attach copies of the exploratory hole logs and test results in connection with a ground

investigation carried out at the above site. A sketch plan showing the approximate location

of the exploratory holes is also attached.

The purpose of the investigation was to establish the ground conditions present beneath the

site, to reveal the existing foundation and establish the ground bearing pressure, soluble

sulphate content, pH, clay plasticity, moisture content, particle size distribution and

contamination. This was achieved by sinking three boreholes to a maximum depth of

about 3.6m. b.g.l. using a window sample drilling rig. Prior to drilling, the holes were hand

excavated to 1m. b.g.l. as a precautionary check for underground services. In addition, one

trial hole was excavated by hand to expose the foundation of the existing building.

The geological map for the area indicates the site to be underlain by the Beeston Sand and

Gravel overlying the Nottingham Castle Sandstone of Permian age.

The ground conditions encountered during the investigation comprised soil and made

ground overlying clayey sand and gravel and sandstone with bands of mudstone.

Fill comprising soil to about 0.2 m. to 0.3m. overlying further soil with varying amounts of

sand, clay and gravel was encountered in all the holes to depths ranging from about 0.75m.

to about 1.2m. bgl..

Underlying the made ground, the holes encountered an initially loose and very loose,

brown, orange-brown and reddish-brown, gravely sand/sand and gravel containing

variable amounts of clay. Recorded thicknesses ranged from just over 1m. in BH3 to

around 2m. in BH2

The gravely sand tended to grade downwards into very weakly cemented, reddish-brown

and yellow-brown, slightly gravely sandstone containing bands of red-brown mudstone.

All three boreholes were terminated within this horizon at depths of between about 2.8m.

and 3.6m. bgl.

Nottinghamshire County Council,

Property Services Design Group,

Trent Bridge House,

Fox Road,

West Bridgford,

Nottingham,

NG2 6BJ.

FAO: Giri Kanagasabai

Ref: brs/1402

11th

February, 2014

ANALYTICAL GEOTECHNICS LIMITED Geological, Geotechnical & Environmental Investigations

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Groundwater was encountered in all the boreholes at depths ranging from about 2.6m. bgl

to about 3m. bgl. The water was noted to be under slight sub-artesian pressure, rising

approximately 0.15m. to 0.4m. following the initial strike. As groundwater levels can vary

seasonally, long term monitoring would be necessary to more accurately establish the

depth of the permanent water table.

The trial pit excavated down the wall of the adjacent building was abandoned at a depth of

about 1.2m. bgl without encountering the foundation.

Standard penetration tests carried out within the boreholes indicated N values to range

from 2 to 6 at a depth of 1m. bgl. When adjusted for effective overburden pressure, these

may be increased to approximately 3 to 9. Using an average value of 6, an allowable

bearing pressure in the region of about 60kN/m² would be indicated. A marked increase in

strength was noted at about 2m. bgl, with N values ranging from 23 to 50. Corrected N

values are anticipated to be between about 30 and 65. Based on the lowest result, an

allowable bearing pressure of approximately 300kN/m² would be expected. However,

there is evidence that foundations constructed at this depth may be at or close to the

groundwater table and the bearing pressure should therefore be halved. Standard

penetration tests carried out within the weathered bedrock all exceeded 50 suggesting the

presumed bearing value to exceed 500kN/m². The bedrock is likely to exhibit variable

degrees of weathering and could also contain less competent, cohesive horizons. It would

therefore be advisable to limit the allowable bearing pressure to around 200kN/m². It is

important that foundation excavations are inspected and if necessary re-tested to confirm

the bearing capacity in advance of construction. Should less dense, more highly weathered

horizons or deleterious material be revealed, then deeper excavation or alternative

foundations may be required. As the sand and gravels were noted to contain a variable

amount of clay, then it is feasible that excessive differential settlements may occur if

foundations bear upon strata having significantly differing properties. As mentioned

above, prior inspection of foundation excavations is recommended to assess the suitability

of the selected bearing stratum.

Tests have been carried out to ascertain the plasticity of three samples of clay, with results

suggesting the samples to have a low volume change potential. Moisture contents were

above the plastic limit in all cases and would not be indicative of any significant degree of

desiccation.

One soluble sulphate analysis was carried out on a sample of clayey sand and gravel using

a 2:1 water:soil extract. The result indicates the sample to be within Class DS-1 of BRE

Special Digest 1. No special precautions to protect subsurface concrete from sulphate

attack should therefore be required. pH values were essentially slightly alkaline and

conditions aggressive to concrete would not be expected.

Two samples of fill taken from BH1 and BH2 were subject to analyses to determine the

concentration of the following potential contaminants: arsenic, cadmium, chromium,

copper, cyanide, lead, mercury, nickel, PAHs, pH, phenols, selenium, sulphate, TPHs and

zinc. In addition, the sample from BH2 was examined for the presence of asbestos fibres.

Results of the tests are appended and indicate all values to be below the CLEA limit for a

residential garden end use. Where CLEA guidelines are not available, the results have

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been compared with CIEH/LQM limits for a similar end use. Apart from PAH

concentrations in the sample from BH1, none of the results exceed these latter limits.

The benzo(a)pyrene concentration of 5.63mg/kg recorded from the fill in BH1 at 0.5m. bgl

exceeds the guideline value of 1.0mg/kg (based on a soil organic matter of 6%). In

addition, the concentration of 4.4mg/kg recorded for indeno(1,2,3-cd)pyrene marginally

exceeded the threshold value of 4.2mg/kg. Typical source material could include partially

combusted organic matter and tarmac fragments.

Leachate analyses were undertaken on a sample of the made ground obtained from TP1 to

assess the solubility of a similar suite of contaminants. All results were below the leachate

quality threshold values recommended by the Environment Agency.

The test results have also been compared with WRAS guidelines for the installation of

water supply pipes. The only result to exceed these thresholds was the PAH concentration

in BH1. Pipe construction suitable for ground containing organic contaminants may be

necessary.

Shallow excavations, to about 2m. bgl, would be expected to be predominantly dry

although sides may require support. Deeper excavations may require dewatering.

Excavations should be inspected prior to entry to assess their stability and those taken

below 1.2m. b.g.l. must be adequately supported.

In summary, the results of the investigation indicate that foundations may bear within the

medium dense to dense sand and gravel horizon suggested to be present below about 2m.

bgl. The allowable bearing pressure should not exceed about 150kN/m². Greater bearing

pressures may be accommodated within the underlying weathered bedrock. The

laboratory test results indicate levels of benzo(a)pyrene to exceed available guidelines

within the made ground around BH1. It is recommended that affected material is either

removed or adequately covered to ensure there is no risk to end users. WRAS guidelines

indicate that metallic or PE/AL/PE pipe may be required for water supplies. The leachate

analyses carried out would not suggest there to be any risk to controlled waters. The clay

deposits are indicated to have a low volume change potential. In the absence of tree roots,

no special precautions should be required to protect the proposed building from clay heave

or shrinkage. No additional precautions to protect subsurface concrete from sulphate or

acidic ground conditions are likely to be necessary. Shallow excavations would generally

be expected to be dry, however those taken below about 2m. bgl may require dewatering.

We must point out that the comments provided in this letter are based on the results of a

limited ground investigation which has only examined a very small part of the subsurface

conditions present beneath the site. No liability can therefore be accepted for changes in

ground conditions which were not revealed by this investigation. The exploratory hole logs

provide a description of materials revealed at each hole location. The insitu and laboratory

tests carried out may only be applicable to the samples/locations tested. All comments,

conclusions and recommendations which are based on information/results provided by

third parties are given in good faith on the assumption that such information/results are

true and correctly reported. Comment on the presence of ground gas or intrusive

vegetation on or in the vicinity of the site was outside the scope of this investigation. In the

event of any omission or lack of care or due diligence in carrying out the specified work,

the extent of any liability shall be limited to the re-performance of the service by

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Analytical Geotechnics Limited up to the total paid by the client. If the results of the

investigation are to be included in tender documents, then it should be made clear to

tenderers that they shall make their own interpretation and obtain confirmation of the

factual data by additional ground investigation and laboratory testing. The use of this

report, whether in its entirety or in any part, is expressly prohibited unless payment

is received by Analytical Geotechnics Limited within the specified credit period.

Yours sincerely,

J. Davies MSc, BSc.

For Analytical Geotechnics Limited

Fairfield House, 1 Fairfield Street, Bingham, Nottinghamshire, NG13 8FB

Tel: 01949 877062 e-mail: [email protected]

For Data Protection

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ANALYTICAL

GEOTECHNICS BOREHOLE : BH1

BOREHOLE LOG

Location: Roundhill School,

Beeston.

Method : Dynamic Investigation Rig Date : 24.01.2013

Level :

Sample/Test Description

Legend Depth

(m). Type Depth SPT

Water Notes

FILL – topsoil.

FILL – soil with sand, gravel and

slight clay.

Very loose becoming medium

dense and dense, brown and orange

brown clayey, gravely SAND with

bands of soft sandy clay.

Grading to very weak red-brown

and yellow SANDSTONE with

MUDSTONE.

XXXX

XXXX

XXXX

XXXX

XXXX

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~::::o:::

o:::::::::

~~:~~::

00.00

00.25

00.90

02.80

J1

S1,J2

J3

S2,J4

S3,J5

0.50

1.00

1.50

2.00

2.60

N=2

N=37

N=*

Rose to

2.45m.

_�_

2.60m.

*50 blows 85mm

Backfilled on completion.

KEY B – bulk sample D – disturbed sample U – undisturbed tube sample J - jar sample

V – hand shear vane S – standard penetration test C – SPT with solid cone W – water sample

REMARKS 1. Hole completed at 2.8m. bgl.

2. Hand excavated to 1.0m. bgl.

Page 1 of 1 pages

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ANALYTICAL


BOREHOLE LOG


Beeston.


Level :


Legend Depth

(m). Type Depth SPT

Water Notes

FILL – topsoil.


slight clay.

Loose becoming medium dense,

brown and orange brown clayey,

gravely SAND with bands of silty

and sandy clay.

Grading to very weak red-brown

SANDSTONE & MUDSTONE.

XXXX

XXXX

XXXX

XXXX

XXXX

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:~x~:~::

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:o::::::::

~~x~~x

::::::::::::

00.00

00.20

00.75

03.20

J1

S1,J2

J3

S2,J4

S3,J5

0.20

1.00

1.50

2.00

3.00

N=6

N=23

N=*

Rose to

2.6m.

_�_

3.00m.

*50 blows 150mm


KEY B – bulk sample D – disturbed sample U – undisturbed tube sample J - jar sample V – hand shear vane S – standard penetration test C – SPT with solid cone W – water sample



Page 1 of 1 pages

�

ANALYTICAL


BOREHOLE LOG


Beeston.


Level :


Legend Depth

(m). Type Depth SPT

Water Notes

FILL – topsoil.


slight clay.

Loose becoming medium dense

and dense, brown and red- brown

clayey SAND and GRAVEL.

With bands of weakly cemented

occasionally gravely sandstone

below about 2.3m.

XXXX

XXXX

XXXX

XXXX

XXXX

XXXX

::o:~:o:

o:~o::o:

~:o:o:~:

o:~:o:o:

:o:o::~o

:~o:~:o:

:o:::::::::

::::::::::o

::~o:o::

o::::::::::

::o~o:o:

:o:o:o:o:

::o::::::::

00.00

00.30

01.20

03.60

J1

S1,J2

J3

S2,J4

S3,J5

S4

0.50

1.00

1.50

2.00

3.00

3.50

N=3

N=50

N=*

N=*

**

2.90m.

** seepage

*50 blows/200mm

*50 blows/95mm


KEY B – bulk sample D – disturbed sample U – undisturbed tube sample J - jar sample

V – hand shear vane S – standard penetration test C – SPT with solid cone W – water sample



Page 1 of 1 pages

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For Data Protection

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ANALYTICAL GEOTECHNICS LTD

LABORATORY TEST RESULTS – CHEMICAL ANALYSES CLIENT: Nottinghamshire County Council DATE: 30.01.2014

SITE: Roundhill School, Beeston

HOLE

No.

REF

DEPTH (m)

SO4 2:1 extract

(g/l)

SO4 (%)

SO4 (water) (mg/l)

CHLORIDE CONTENT

(%)

High Alumina Cement

(1)

pH

BH3 J3 1.50 0.08 7.6

NOTES:

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ANALYTICAL GEOTECHNICS LTD

LABORATORY TEST RESULTS - CLASSIFICATION CLIENT: Nottinghamshire County Council DATE: 30.01.2014

SITE: Roundhill School, Beeston

HOLE

No.

REF

DEPTH

(m)

LIQUID LIMIT (%)

PLASTIC LIMIT (%)

PLASTIC INDEX

(%)

WATER CONTENT

(%)

<425µm

(%)

MODIFIED PLASTIC

INDEX (I'P) (%)

BH1 J2 1.00 27.5 14.7 12.8 17.0 55 9.4

BH2 J4 2.00 35.6 18.1 17.5 17.8 61 10.7

BH3 J3 1.50 23.2 13.3 9.9 16.3 47 4.7

NOTES:

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ROUNDHILL SCHOOL, BEESTON

APPROXIMATE LOCATION OF EXPLORATORY HOLES

analytical geotechnics limited

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