Hi All.
I’ve provided a foundation design for a proposed two storey domestic dwelling in the UK. The house is located on a site where some tree have been removed and some trees remain. A tree report has been produced and some of the remaining/removed trees are within the zone of influence of the dwelling (when analysing the NHBC guidelines in the UK).
The existing strata consists of clay above rock. The rock is approximately 1000mm below ground. Therefore, I have used un-reinforced mass concrete deep trench foundations which are to bear onto the rock strata to avoid bearing onto the clay which could shrink/swell.
As some significant trees have been removed from the site, I’ve taken the precaution to allow for heave within the soil and so have placed compressible material below the suspended slab and to the inner faces of the deep trench foundations (as per the NHBC guidelines for heave). See attached sketch for typical foundation section.
My question is – do I need to allow for the compressible material below the GF slab? Once the foundations have been installed (down to the rock) and the GF slab is cast, as I see it the soil below the slab is effectively sealed off and no ground/rain water can get to the soil causing it to swell.
For the same reason would I need to install the compressible material to the inner faces of the deep trench foundations? I’ve always thought that the compressible material should go on the outer face of the foundation anyway?
Regards,
Martin.
I’ve provided a foundation design for a proposed two storey domestic dwelling in the UK. The house is located on a site where some tree have been removed and some trees remain. A tree report has been produced and some of the remaining/removed trees are within the zone of influence of the dwelling (when analysing the NHBC guidelines in the UK).
The existing strata consists of clay above rock. The rock is approximately 1000mm below ground. Therefore, I have used un-reinforced mass concrete deep trench foundations which are to bear onto the rock strata to avoid bearing onto the clay which could shrink/swell.
As some significant trees have been removed from the site, I’ve taken the precaution to allow for heave within the soil and so have placed compressible material below the suspended slab and to the inner faces of the deep trench foundations (as per the NHBC guidelines for heave). See attached sketch for typical foundation section.
My question is – do I need to allow for the compressible material below the GF slab? Once the foundations have been installed (down to the rock) and the GF slab is cast, as I see it the soil below the slab is effectively sealed off and no ground/rain water can get to the soil causing it to swell.
For the same reason would I need to install the compressible material to the inner faces of the deep trench foundations? I’ve always thought that the compressible material should go on the outer face of the foundation anyway?
Regards,
Martin.
