Marine Clays
Marine Clays
(OP)
Hi peoples,
I have a problem im trying to solve.
We are the structural engineer for a residential building (3 storey timber framed slab on ground) which has been built on a fill platform which is for flood protection and is average 1.5m deep.
It's still in construction and the builder noticed that the slab has settled 60mm. Up to 8m of marine clay (normally consolidated) wasn't identified as underlying the fill platform.
The settlement is occurring level across the slab (a stiff waffle slab) so that's good and the builder is willing to allow it to settle. Preliminary discussions suggest it could end up being 200mm.
Im interested to hear from anyone who is aware of any systems or processes that can speed up the consolidation process, conventional wick drains are difficult due to site constraints, additional pre-loading can be placed in some areas but not everywhere.
Has anyone used the vacuum consolidation method on a small scale project?
And one last question has anyone used injection grouting or any other similar method to stabilise/arrest the consolidation process in a soil mass. Bearing in mind we need to get under the slab which is 11m wide x 35m long.
Its a tricky problem but that's what we as Engineers are good at. I'm hoping someone out there might have an idea that we haven't thought of.
Cheers
I have a problem im trying to solve.
We are the structural engineer for a residential building (3 storey timber framed slab on ground) which has been built on a fill platform which is for flood protection and is average 1.5m deep.
It's still in construction and the builder noticed that the slab has settled 60mm. Up to 8m of marine clay (normally consolidated) wasn't identified as underlying the fill platform.
The settlement is occurring level across the slab (a stiff waffle slab) so that's good and the builder is willing to allow it to settle. Preliminary discussions suggest it could end up being 200mm.
Im interested to hear from anyone who is aware of any systems or processes that can speed up the consolidation process, conventional wick drains are difficult due to site constraints, additional pre-loading can be placed in some areas but not everywhere.
Has anyone used the vacuum consolidation method on a small scale project?
And one last question has anyone used injection grouting or any other similar method to stabilise/arrest the consolidation process in a soil mass. Bearing in mind we need to get under the slab which is 11m wide x 35m long.
Its a tricky problem but that's what we as Engineers are good at. I'm hoping someone out there might have an idea that we haven't thought of.
Cheers
Talk To Other Members
RE: Marine Clays
RE: Marine Clays
Marine clays can't be grouted (too many fines). Yous vould think of a rigid inclusions array using driven ductile iron piles, micropiles or compaction grouting columns (with cement in the mortar) or jet grouting columns. This way you will transfer the loads to a deeper layer.
A proper site invistigation might prove useful to go further (this is generally how to avoid tricky problems !)
RE: Marine Clays
RE: Marine Clays
Underpinning with piling is a last option at this stage.
Thanks for any ideas guys.
RE: Marine Clays
CPTu is helpful to estimate the yield stress and coefficient of horizontal consolidation, but not enough to get the compression ratio (CR) and strain rate of creep (C_alfa/1+e0) for consolidation settlement and creep estimate. You need to run oedometer tests on high quality undisturbed samples to get CR and C_alfa/1+e0 if you want more accurate estimate of settlement.
For rigid inclusions, suggest you talk to Menard for CMC advice.
RE: Marine Clays
Can you please explain what CMC stands for
RE: Marine Clays
RE: Marine Clays
If it is possible to remove a couple meter of soft marine clays to reduce the negative skin friction and replaced by compacted cohesionless soils. Otherwise the pile capacity will be reduced by the negative skin friction.
RE: Marine Clays
Perhaps you could preload the foundation with an earth surcharge. If you extend the surcharge well past the edges of the slab, you may be able to keep the settlement reasonably uniform, especially if you increase the surcharge height near the perimeter to achieve uniform pressure increase across the slab.
Preloading with anchors might be feasible if the underlying hard layer is strong enough. You could lay some beams across the slab to distribute the anchor loads. Keep adjusting the anchors to force the settlements to be equal. Calculate the moments in the slab to avoid overstressing it.
You could core holes in the slab and install micropiles to support it, but the soil will settle away, so you need to address lateral stability and corrosion protection, not to mention utility settlement.