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Geotechnical and environmental
considerations when redeveloping
deep-filled and former landfill sites
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Peter Witherington
Managing Director

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Introduction
Significant constraints:
 Social
 Economic
 Environmental
 Engineering
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BRE 424 Charles and Watts

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The problem of deep fill
Received little research attention
“…the heterogeneous nature of many waste fills makes characterisation and
analysis difficult, and it is easy to understand why the attention of geotechnical
engineers has usually focussed on more promising and better behaved natural
soils…”
BRE reaction:
 Monitoring of field performance
 Characterising fills on the basis of observed performance
 Assessing the effectiveness of various ground-treatment techniques
Dr J. A. Charles, 2008 Rankine Lecture, ‘The engineering behaviour of fill
materials: the use, misuse and disuse of case histories’
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Settlement mechanisms
Applied loading is rarely the problem…
However, we must address
 Self weight
 Change of groundwater level
 Collapse settlement
 Decomposition of biodegradable material
 Chemical decomposition
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How to investigate properties
Conventional investigation is of little use.
Difficulty of
 Drilling
 Sampling
 In situ testing
 Laboratory testing
Need for
 Long-term monitoring of
 surface settlement
 groundwater level
 Large and medium-size loading tests
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Treatment methods
“With non-engineered fills the unexpected is only too likely to occur. Ground
treatment before construction can mitigate or forestall the effects of the
unexpected.”
Consider
 Engineered backfilling
 Dynamic compaction
 Vibro compaction
 Pre-loading (surcharging)
 Pre-inundation
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Opportunity?
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Opportunity!
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Opportunity?
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Three centuries of mining
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Opportunity!
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Investigations: instrumentation
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Load tests
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Load tests
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Load tests
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And?
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How about other sites?
Research in 1980/90’s jointly with BRE into the performance and Stiffened
End Slabs (SES)
• Light and Heavy
• Types of Made Ground:
• Type A – Engineered Made Ground (any age)
• Type B - Cohesive Made Ground >50 years old or Granular >20 years old
• Type C – Cohesive Made Ground 20-50 years old of granular <20 years old
• Type D cohesive made ground <20 years old
• Methods of SI
• Specifications for Loading tests
• Skip tests
• Large Loading tests
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Former Gravel pit and Landfill on South
Coast
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A site in the South East
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