Loose sand and fill: low bearing capacity and settlement
Loose natural sands and uncontrolled fills compress under load. Structures built on them can settle more than they tolerate, and settle unevenly.
How it is recognised
- Low SPT blow counts or low CPT cone resistance in granular layers.
- Fill of unknown origin, placed without controlled compaction.
- Variable thickness of loose material across the site.
Why it matters
The main risks are excessive total settlement and differential settlement between parts of a structure, which cracks slabs, tilts tanks and misaligns equipment.
Methods usually considered
-
DC
Dynamic Compaction
Deep loose layers over large, open areas.
-
RIC
Rapid Impact Compaction
Shallow-to-moderate depths, or work closer to existing assets.
-
HEIC
High Energy Impact Compaction
Near-surface layers and large fill platforms.
-
VC
Vibro Compaction
Clean sands at depth, including hydraulic fill.
Which method fits depends on the site investigation and the performance requirement. More than one may be combined.
How the choice is made
- Thickness and depth of the loose layer.
- Fines content and groundwater level.
- Size of the area and distance to neighbouring structures.
- Required bearing pressure and allowable settlement.
How the result is verified
Densification is verified by comparing in-situ tests before and after treatment, with surface stiffness checked where slabs or pavements are planned.
Tests typically used
Other ground problems
Have this ground problem on your site?
Share the site investigation report and the performance requirement.