Trenching Groundwater

[loukasse]

Good morning,
During trench excavation for a 16-inch pipeline, we encountered water at a depth of 1.5 meters b(200 meters length ), while the required trench depth is 2 meters.
Could you please suggest a suitable solution to proceed with the bedding and pipe lowering activities under these conditions?

 

[HTURKAK]

During trench excavation for a 16-inch pipeline, we encountered water at a depth of 1.5 meters b(200 meters length ), while the required trench depth is 2 meters.

If the total length of PL is 200 meters, you can collect the ground water at pits and pump it .
You can consider WELL POINT SYSTEM as an option if the PL is long .

 

[swazimatt]

based on depth i assume this is a gravity pipe (ww/sw) so cannot be made shallower - in addition to @HTURKAK comments if the insitu soil is saturated and unable to work on (some silts are highly sensitive to moisture and become liquefied) we often over excavate the trench to decent soils or a maximum of 300mm lay geofabric and build up the bedding using a mix of 20mm and 40mm drainage aggregate.

 

[LittleInch]

Basically either:
1) install the pipe at base level 1.5m and hence reduced depth of cover
2) pump out the trench continuously and put the pipe in and backfill quickly or install the pipe but use weights to stop it floating
3) Do some well point dewatering either side of the trench
4) install chilling pipes and freeze the ground below the water table
5) Wait for the dry period wherever you are and then install
6) sheet pile it and pump the water out
7) Inject grout either side of the trench then wait a day or two and then excavate

Silts and sands are prone to collapse if you pump out the water from the trench so a lot depends on the nature of the soil.