Liquefaction risk in loose, saturated sands
During an earthquake, loose saturated sand can lose its strength as pore-water pressure rises. The ground then behaves like a liquid, and foundations settle or tilt.
How it is recognised
- Loose, clean-to-silty sand below the groundwater table.
- A liquefaction assessment in the geotechnical report showing a low factor of safety.
- Reclaimed land and hydraulic fill.
Why it matters
Liquefaction causes sudden settlement, loss of bearing capacity and lateral spreading towards free faces such as quay walls and slopes.
Methods usually considered
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VC
Vibro Compaction
Clean sands: densifies the sand so it is less likely to liquefy.
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VR
Vibro Replacement (Stone Columns)
Silty sands: stone columns reinforce the ground and help pore pressure dissipate.
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DC
Dynamic Compaction
Granular soils over large open areas, within its depth range.
Which method fits depends on the site investigation and the performance requirement. More than one may be combined.
How the choice is made
- Fines content of the sand.
- Depth and thickness of the liquefiable layer.
- The design earthquake and the required factor of safety.
- Site constraints and neighbouring structures.
How the result is verified
The target is usually a minimum cone resistance with depth, derived from the liquefaction assessment and checked by CPT after treatment.
Tests typically used
Other ground problems
Have this ground problem on your site?
Share the site investigation report and the performance requirement.