ᐅ Excavation work has not started yet – is the ground too wet?

Hello everyone,

I couldn't find a specific subforum for groundworks / foundation, so I’m posting it here:

We are about to build our house in the Elbe marshland (approximately 1km distance from the dike) and are therefore dealing with problems related to high groundwater levels and damp soil. Our plot needs to be raised entirely by 60cm (24 inches). According to the geotechnical report, the groundwater level before the fill is approximately 0.5m (20 inches). In addition, due to the soil conditions, the recommendation is to pour a rigid concrete slab foundation.

We have contractually agreed on the following groundworks with our general contractor: stripping the topsoil to a depth of 40cm (16 inches) and compactly laying a sand base with a thickness of 1m (39 inches).

The soil layers are as follows:
up to 0.4m (16 inches): silty sand, humus; designation: topsoil
up to 0.8m (31 inches): silty sand; designation: sand
up to 2.5m (8 feet 2 inches): medium sand, coarse-grained, slightly fine-grained; designation: sand
up to 3.0m (9 feet 10 inches): silty clay, humus, slightly sandy; designation: clay
Based on this, the recommendation is to pour a rigid concrete slab.

Now to the problem:
Due to the heavy rainfall in February, standing water was present on the site about two weeks ago. The earthworks contractor then decided not to begin the groundworks because they saw no way to install the sand properly.
Since the weather has improved, the top 10cm (4 inches) is now “dry” enough. Nevertheless, yesterday the statement was made again that construction cannot start yet and at least two more dry and sunny weeks are needed.

Therefore, I have the following questions:

• Is it generally impossible or not advisable to install sand if the bottom 30cm (12 inches) cannot be compacted dry?
• Would it possibly be an option to skip stripping the topsoil and only install a 60cm (24 inches) thick sand layer? I suppose the geotechnical engineer would have to answer that, right?
• Are there any other possible solutions without extensive groundwater lowering or similar measures?

Thanks in advance!

Best regards,
Mirco

sn4tch schrieb:

2. Would it possibly be feasible to skip removing the topsoil and instead just install a 60cm (24 inches) sand slab? I guess the geotechnical engineer would need to answer that, right?

I think this question is actually obsolete. At this point, I want to dismiss the idea of skipping the removal of the topsoil.

Hello Mirco,

sn4tch schrieb:

Now to the problem:
Due to the heavy rainfall in February, standing water was on the property about two weeks ago. The earthworker then refrained from starting the groundworks because he saw no way to install the sand.

What the users of this forum consider _possible_ or not won't help you, as in the worst case they have no warranty obligation toward you.

I can well imagine that it’s frustrating for you to watch time pass without any progress on your property. BUT – your foundation contractor is also responsible for ensuring that the foundation permanently supports the load of your single-family house. Therefore, trust him; in my opinion, he knows what he is doing or refraining from doing.

See it as a “trial phase” for the later drying time of the screed; during this time you can do nothing but wait.

Best regards, Bauexperte

When I imagine compacting completely soaked sand... splish splash. Better to wait.