Deep Dry Soil Mixingat

Thrandeston Bog

Client: Network RailM/C: Nuttall John Martin

Consultant: Mott MacDonald

Site Location – nr Colchester

Design Challenge

Design Challenge• Peats:

– Very soft to soft (cU = 5 to 10kPa)– Moisture contents up to 400%– Upper zone highly responsive to climatic

conditions• Clays:

– Soft to firm to stiff – Sandy bands

• Chalk:– Very soft at surface– Artesian water at depth

Binder is injected as mixing tool is extracted with reversed rotation

1 2

Rotating mixing tool penetrates to desired depth of treatment

3 4

Completed Column Completed Adjacent Columns

Ground Stabilisation Solution

Ground Stabilisation Solution

Ground Stabilisation Solution

Design Case: Rotational Slip

Ground Stabilisation Solution

Design Case: Consolidation Settlement

Ground Stabilisation Solution

Design Case: Soil Migration

Mix Design Considerations

• Laboratory testing undertaken on Borehole samples

• CEM I binder rates of 150 to 300kg/m3

• Column Strength Constraints:– Moisture Content – pH Level – Inclusions – Contamination

Laboratory Testing

• Testing indicated design strength only achievable with high binder dosage rate.

• This gave practical & commercial concerns

• Engineer revised design strength with no change in panel spacing or width

Site Trials & Validation

• In situ testing– Push-In Resistance Testing– Pull-Out Resistance Testing– Undrained & drained triaxial testing– CPT’s to assess early strength

• Additional SI - CPT’s to characterize site

• Environmental Monitoring

0

1

2

3

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8

0 25 50 75 100 125 150 175 200 225 250 275 300

Undrained Shear Strength (kPa)

Dep

th b

elow

hau

l roa

d (m

)

3 day testresults7 day testresults14 day testresults

Specifcation requirement 125 kPa

Approximate extent of working platform

Site Trials

Final Design binder dosage rates ranged between 175kg/m3 to 275kg/m3

Column Push in Test Results

Site Operations

•Stable Rig•Robust Platform Design•Restrained Mast•Embankment Monitored

Main Works

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2

4

6

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12

0 50 100 150 200

Dep

th (m

)

Binder Dosage (kg/m3) and RPM

Binder DosageTool RPM

0 100 200 300 400

Blade Rotation Number (BRN)

Stabilised Column

Soft Peatbetween

2.0m

• Scheme gave a saving of £6M to the client (50 –65% saving)

• First use of DDSM on UK infrastructure & in live transport environment

• 11,000 columns installed, 85,000 linear metres• Completed in 19 weeks (5 weeks early)• £90k saved through CPT site characterisation• The line stayed open for the entire project and is

now operating at 100mph• Ground Engineering Award for UK Project with a

Geotechnical Value over £1M

Summary

Completed profile

Total number of piles

Total length of piles (m)

Weight of steel (ton)

Embodied energy (GJ) Embodied CO2 (kg)

Tubular steel piles 1,200 18,329 7,331 256,585 17,594,400

Total number of columns

Total length of columns (m)

Weight of cement (ton)

Embodied energy (GJ) Embodied CO2 (kg)

Dry soil mixing 11,024 75,382 5,524 43,087 5,430,092

Sustainability Comparison