Site Investigation – The Holistic Approach: A Case Study from

Providing Ground Solutions

Approach: A Case Study from Silvertown, London

Sarah Key, CEnv MIEnvSc , Principal EngineerNick Langdon, CEng FICE, Company Chairman

Introduction

Why a holistic approach?The developmentSite history and previous usageSite investigation 2013

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Site investigation 2013Remediation outcomesGeotechnical outcomesThe site today

Why a holistic approach?

A balancing act

The constraints• The professional team diktats • Client preferences

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• Client preferences

The drivers• Reduced disruption• Coordination of design thinking• Cost reduction

The site

38-acre site£1b+ to create 3300+ new homes, infrastructure, commercial and amenity facilities

Silvertown, London

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20,000m² of commercial space is to create around 20,000 jobsA new economic centre east of Canary Wharf, minutes from London City Airport and CrossrailCompleting 2019/20Silvertown Quays….starting 2018

Development summary

Silvertown, London

Oxley Holdings Limited A Singapore based developer

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Ballymore Properties Limited Founded in Ireland in 1982

Minoco Wharf + Crescent Wharf + Venesta Wharfs

Historical summary

1799: Marshland

Over 200 years of history

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Historical summary

1894: Industrial development

Over 200 years of history

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Goad Plans

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London’s Biggest Explosion

Friday, 19 January 1917 at 6.52 pm.Approximately 50 tons of TNT exploded.73 people killed and 400 injured.Debris was strewn for miles

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Debris was strewn for miles around damaging a gasholder on Greenwich peninsularBlew windows in the Savoy Hotel and almost overturned a taxi in Pall Mall.The fires could be seen in Maidstone and GuildfordThe blast was heard up to 100 miles (160 km) away

Historical summary

Rebuilt in the 1920’s

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Historical summary1940-41

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Historical summary

Post-war: Industrial evolution

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evolution

Historical summary

1999-2004Partial demolition and remediation for industrial re-use

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Current Site Investigation

Additional investigation required for 2012 consented schemeGeoenvironmental - large number of remaining

The Holistic Approach

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Geoenvironmental - large number of remaining sources needed investigationGeotechnical – limited site wide data for detailed designCombined investigation to provide comprehensive solution

Expected Geology

Made GroundAlluvium (including Peat layers)

London Basin sequence

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River Gravel DepositsLambeth GroupThanet SandsChalk at depth

Current Site Investigation

31 cable percussion boreholes • 15m or 28mbgl with in-situ testing and sampling• Gas and groundwater monitoring installations (some dual)

Scope of Works

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• Gas and groundwater monitoring installations (some dual)

157 window sampler boreholes• Maximum depth of 5mbgl• 56 monitoring installations

30 trial pits

Minoco WharfVenesta Wharf Crescent

Wharf

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Current Site Investigation

Not a bad place to be…

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Current Site Investigation

Dye WasteFree product

Encountered Contamination

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Current Site Investigation

River Wall

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Current Site Investigation

Concrete

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Current Site Investigation

Testing

SPTsGeotechnical testing

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• PSDs / sedimentation• Atterberg Limits• Moisture Content• Quick undrained triaxials• Sulphate and pH

Contamination testing• Standard soil suites• Asbestos screen/ID• Leachate suites• Groundwater analysis

Current Site Investigation

Monitoring

Ground gas/vapourGroundwater levels

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Groundwater samplingTidal monitoring

The Outcomes

Geological Cross-Section

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The Outcomes

Perched groundwater in Made Ground Shallow groundwater in KPG

Groundwater

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• In continuity with the River Thames

Deep groundwater • Under sub-artesian pressure

Tidal Variation

The Outcomes

Human health assessmentGround gas assessment• Range of Characteristic Situations (1 to 5) across the site

Contamination Assessment

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• Range of Characteristic Situations (1 to 5) across the site but generally, CS2

Groundwater assessment• soil contaminants leachable• underlying groundwater bodies affected

DQRA

Conceptual Site Model

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The Outcomes

Basement excavations proposed = mitigated majority of risks from soil sources Proposed permeable reactive barriers along River

Remediation Recommendations

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Proposed permeable reactive barriers along River edge and northern boundaryGround gas protection measures (vent layer, membrane and vent trench)Barrier layers in gardens and communal landscaping

The Outcomes

Geotechnical Assessment

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Shallow foundations for lightest structuresPiled foundations in to Kempton Park Gravel and Thanet Sands

Geotechnical outcomes

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The Outcomes

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Current Situation

Construction and remediationNew River wall

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E-Clay barrier wall

Current Situation

Construction and remediation

3.6%11%

10%

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16%

Thank You – Any Questions?

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