Deep excavations next to structures and below groundwater
A deep excavation removes the support of the ground beside it. Next to buildings and roads, or below the water table, the sides must be retained and the water controlled.
How it is recognised
- Basements, shafts or pump stations deeper than the ground can stand unsupported.
- Neighbouring buildings, roads or services close to the excavation edge.
- Groundwater above the planned formation level.
Why it matters
Without support, the sides can fail or move enough to damage neighbouring structures. Uncontrolled groundwater floods the excavation and can loosen the base.
Methods usually considered
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Secant & Contiguous Piles
Embedded walls next to structures; secant walls where water must be cut off.
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Soil Nailing & Rock Anchoring
Stable ground above the water table; anchors to tie back pile walls.
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Shotcrete
Facing for nailed faces and temporary protection of cut slopes.
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Dewatering
Lowering groundwater below the formation with wellpoints or deep wells.
Which method fits depends on the site investigation and the performance requirement. More than one may be combined.
How the choice is made
- Excavation depth and available space.
- Soil and groundwater conditions.
- Allowable movement of neighbouring structures.
- Whether the wall is temporary or part of the permanent structure.
How the result is verified
Wall and ground movements are monitored against trigger levels during excavation, and groundwater levels are confirmed below formation before digging proceeds.
Tests typically used
Other ground problems
Have this ground problem on your site?
Share the site investigation report and the performance requirement.