aggierockdoc
Petroleum
- May 11, 2020
- 1
I'm in the process of starting a new house build and I'm not getting a logical argument from my architect/engineer that explains his foundation design.
My question is whether i can pour my floor slab straight onto either bedrock or a thin layer of sand with an overlying DPC, or whether i have to excavate, put down a compacted soil then lay the slab. NB The slab will be supported on its edges by foundation "placas" of 0.8m x 0.25m.
To answer that, here are the details:
I live in a seismically active region and the property is to be built cut into a slope with a "basement" level containing the bedrooms and with the floor above on both the basement and on ground level higher up the slope, and as shown in the diagram.
My requirements are a foundation design that:
[ul]
[li]provides sensible engineering properties given the seismic design code[/li]
[li]avoids wasting money on unnecessary foundation excavation and refill[/li]
[li]protects the house from damp - particularly the basement level[/li]
[/ul]
We are building onto rock not soil. The rock is a rigid, but fairly soft marly limestone. The rock can be excavated without blasting using an excavator. I would estimate a UCS of 2 to 5MPa for the rock. It dips at around 30 degrees into the slope not away from it. The water table is around 40m below the site level(we are on a hill). Drainage around the basement level will be achieved using a drain pipe at foundation placa level ie below the floor by about 20cm.
We never have frost.
My architect proposes excavating under where the the floor slab goes then back-filling with an appropriate loose material and compacting.
I ask, why excavate then refill? Why not just lay the slab straight onto the bedrock? (possibly with a thin layer of sand to protect the DPC membrane).
The rock has already been cut flat. It is pretty uniform with layers of very similar physical and structural characteristics. I plan to cut trenches to lay 0.8m x 0.25m foundation "placas" to support the edges of the floor slab.
What are the hazards of pouring my floor slab onto either bedrock or a thin layer of sand with an overlying DPC? Suggested section shown here with cut as a blue line.
Any cogent advice appreciated.
Stephen
My question is whether i can pour my floor slab straight onto either bedrock or a thin layer of sand with an overlying DPC, or whether i have to excavate, put down a compacted soil then lay the slab. NB The slab will be supported on its edges by foundation "placas" of 0.8m x 0.25m.
To answer that, here are the details:
I live in a seismically active region and the property is to be built cut into a slope with a "basement" level containing the bedrooms and with the floor above on both the basement and on ground level higher up the slope, and as shown in the diagram.
My requirements are a foundation design that:
[ul]
[li]provides sensible engineering properties given the seismic design code[/li]
[li]avoids wasting money on unnecessary foundation excavation and refill[/li]
[li]protects the house from damp - particularly the basement level[/li]
[/ul]
We are building onto rock not soil. The rock is a rigid, but fairly soft marly limestone. The rock can be excavated without blasting using an excavator. I would estimate a UCS of 2 to 5MPa for the rock. It dips at around 30 degrees into the slope not away from it. The water table is around 40m below the site level(we are on a hill). Drainage around the basement level will be achieved using a drain pipe at foundation placa level ie below the floor by about 20cm.
We never have frost.
My architect proposes excavating under where the the floor slab goes then back-filling with an appropriate loose material and compacting.
I ask, why excavate then refill? Why not just lay the slab straight onto the bedrock? (possibly with a thin layer of sand to protect the DPC membrane).
The rock has already been cut flat. It is pretty uniform with layers of very similar physical and structural characteristics. I plan to cut trenches to lay 0.8m x 0.25m foundation "placas" to support the edges of the floor slab.
What are the hazards of pouring my floor slab onto either bedrock or a thin layer of sand with an overlying DPC? Suggested section shown here with cut as a blue line.
Any cogent advice appreciated.
Stephen
