Piling & Contaminated Land

Dr Derek Egan

Technical Director Keller Ltd

The FPS began in 1963 with 5 companies.

Now we have 18 members accounting for circa £500M of

specialist geotechnical contracting per annum.

Membership by rigorous registration.

Three sub committees

Health, Safety & Training

Plant

Commercial

Technical

FEDERATION OF PILING SPECIALISTS

Aims

The FPS...... • Promoting Best Practice in safety, innovation, technical

excellence, value engineering & quality management;

• Independently audited membership.

Past initiatives include:-

•safety of temporary working platforms,

•working adjacent to railway lines,

•ICE Piling & Embedded Retaining Wall Specification,

•publication of a range of guidance notes relevant to piling

www.fps.org.uk

What governs the choice of foundation solution?

Structure Size/weight

Form

Geology &

Groundwater

Economy Time, Cost

Sustainability

Environment Noise

Vibration

Logistics

Access

Weight Limits

Performance Load-settlement

Durability

Considerations when encountering contaminated land

Durability Ground

&

Ground water

Flow Paths Temporary

Permanent

Transport Pushing contaminated

Soil down/sideways

Health Chemical

Particulate

Considerations when encountering contaminated land

Replacement

• Continuous Flight

• Auger (CFA)

• Rotary Bored

Displacement

• Driven PC Piles

• Driven Cast In-situ

• Steel Tubes

• Sheet piles

Piling

• High capacity

• Low noise & vib.

• In-situ concrete

• Creates spoil

• Moderate capacity

• No spoil

• Noise & vib.

(but less so these days)

Cast In-situ Displacement Piling

Driven cast in-situ piling

Olympic Stadium

Old car plant

Daganham

Cast In-situ Displacement Piling

Vibro concrete columns

Olympic Stadium

Other Cast Insitu Piling

Rotary Displacement

Continuous Flight

Auger

Pre-formed Displacement Piles

Replacement

• Continuous Flight

• Auger (CFA)

• Rotary Bored

Displacement

• Driven PC Piles

• Driven Cast In-situ

• Steel Tubes

• Sheet piles

• Soil Mixing

• In-situ/ex-situ

• Dynamic Compaction

• Vibro Stone Columns

• Vibro Compaction

Piling Ground

Treatment

• High capacity

• Low noise & vib.

• In-situ concrete

• Creates spoil

• Moderate capacity

• No spoil

• Noise & vib.

(but less so these days)

• Lower capacity

• No spoil

• Potential for pathways

Cast in-situ Pre-formed

Ground Improvement Techniques include – vibro stone columns, vibro compaction, dynamic

compaction, deep soil mixing (wet & dry), grouting (jet grouting,

compaction grouting, in-fill grouting etc)

Process

Decide if

site/groundwater

is contaminated EC7 Desk study & GI

No more action

required

No

Consider the need/do

a Foundation Works Risk

Assessment Report

Consider potential adverse

impacts using

Source-Pathway-Receptor approach

Yes

Mitigate risk

Consider 6 Scenarios

(Westcott et al)

The 6 Scenarios

The Six Scenarios Pollution Scenario 1

Creation of preferential Pathways through an aquitard to allow potential contamination of an aquifer.

Contaminated Layer

Aquitard

Aquifer

Driven pile, VCC,

Stone Column

Contamination

of Aquifer

Source

Pathway

Receptor

• Driven piles – no open void

- cast in-situ enhanced

sealing with the ground

• CFA – OK but opportunity for

temporary pathway

• VSC – open pores – unless

special measures taken

Use of QC/QA to ensure installation is correctly recorded

Pollution Scenario 2

Creation of preferential Pathways through a low permeability surface layer, allowing migration of landfill gas, soil gas or contaminant vapours to the surface.

Low Permeability Cap

Gassing material/soil

Founding stratum

Pile, VCC, Stone Column

Gas

Source

Pathway

Receptor

• Driven piles – no open void

- cast in-situ enhanced

sealing with the ground

• CFA – OK but opportunity for

temporary pathway

• VSC – open pores – unless

special measures taken

Contaminated Layer

Aquitard

Aquifer

Contamination

of Aquifer

Source

Pathway

Receptor

The dilemma:-

• VSCs need to be ‘flexible’ to interact with the ground upon loading

• VSCs may need sealing to prevent a pathway

• Cementitious grout/concrete does not fulfil the flexibility criterion

Innovation - ESCs

Innovation - ESCs

The solution - development of a flexible non-setting grout:-

• low permeability (k = 10-8 m/s)

• does not ‘set’ leading to hard spot

• allows standard column construction

Dartford, Powdermill Road

Strip Footing

qw=125kPa

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 20 40 60 80 100 120 140 160 180 200

Bearing Pressure (kPa)

Set

tlem

ent

(mm

)

Pollution Scenario 3

Direct contact of site workers and others with contaminated soil arisings that have been brought to the surface.

Isolation Layer/Cap

Waste/contaminated material

Founding stratum

Replacement

Pile

Receptor

(Poisoned worker)

Contaminated

Spoil

Source

Pathway

• ‘Rotating’ replacement

piles CFA, rotary bored (lesser extend rotary

displacement)

• Displacement systems – no

spoil

Pollution Scenario 4

Direct contact with contaminated soil or leachate causing degradation of materials - durability

Contaminated/aggressive

Soil

Founding stratum

Pile, VCC, Stone Column

Attack Attack Source Pathway

Receptor

• Mainly concerns concrete

• Use BRE SD1 (2005)

Pollution Scenario 5

The pushing of solid contaminants down into an aquifer during pile driving.

Contaminated Layer

Aquitard

Aquifer

Pile, VCC,

Stone Column

Contaminated Soil

• Effects displacement piles

only - but not that critical.

• Solid piles – drag down max. 3d – pointed shoes help – but

not really necessary?

• H piles – trapped soil risk

• Tubular piles – soil plugging

Pollution Scenario 6

Contamination of groundwater and subsequently, surface waters by wet concrete, cement paste or grout

Fractured/permeable soil

Pile/VCC

Groundwater

contamination

• Natural soil + very open structure

& flowing water

• Services/drainage/voids –

greater risk?

• Only affects cast in-situ

Foundation Works Risk Assessment Report

1. Geology/SI

2. Selection of preferred piling

method – considering geology,

structural, noise, vibration etc.

3. Adverse impacts due to

preferred method

4. Site specific assessment of

magnitude & consequence of

risk

5. Changes/special measures

required

6. QA/QC measures

7. Final selected method –

considering geotechnical,

financial, environmental

considerations.

To be undertaken by the scheme designer.

A Note on Ground Investigation

Poor quality geotechnical investigations still rife.

FPS Survey 2006

• ~20% of all contracts in the UK in a 3 month period (of all sizes)

• 30% of projects had Poor SI

• 55% thought between geotechnical & environmental elements wrong

NHBC Survey 2010

•60% of respondents – insufficient SI undertaken for low rise developments;

• most strongly felt by foundation designers compared to house builders and developers (but are they at the front line of taking the risk?).

• On 16% of projects no BH location plan

• On 73% of projects BHs not levelled (83% not

coordinated)

• In 59% of cases inadequate topographical

information

• Boreholes too shallow (at least 5m below pile

toe, may need to be more for large rafts)?;

• Insufficient insitu and/or laboratory geotechnical

testing (e.g. SPTs every 1m to 2m).

Some common failings

Summary

Contaminated land:-

• presents an added, but surmountable, additional complexity;

• the 6 scenario approach provides a systematic assessment

framework;

• knowledge of different piling & ground improvement options informs

the choice;

• mitigation don’t be afraid to demand high levels of QA/QC from

contractors.

Thank you for listening.