Marine Clays 1

• Feb 24, 2017

• #2

HENRYZAU

Geotechnical

Feb 12, 2017

94

AU

You will be in luck if in its design life only 200mm settlement occurs. First you need to hire a geotechnical engineer who has local experience on embankment over soft marine clay, do a proper SI and assess how much the foundation is expected to settle and what differential settlement is expected. The latter could be more damaging. Goog luck!

 

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• Feb 24, 2017

• #3

BigHarvey

Geotechnical

Jan 7, 2003

403

FR

Vacuum consolidation is associated with both horizontal and vertical drains. It's a different way of loading the soil.
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 !)

 

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• Feb 25, 2017

• #4

dik

Structural

Apr 13, 2001

26,128

CA

Some marine clays are unstable and sensitive to loading

 

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• Feb 26, 2017

• Thread starter
• #5

thechud

Structural

Feb 15, 2012

3

AU

We are getting some CPT's to confirm the Marine Clay depth then we will be able to establish the expected settlements. I still want to look into options for accelerating the settlement through the primary range and then stabilising the soil mass from future creep settlement if possible.
Underpinning with piling is a last option at this stage.
Thanks for any ideas guys.

 

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• Feb 27, 2017

1
• #6

HENRYZAU

Geotechnical

Feb 12, 2017

94

AU

thechud,

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.

 

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• Feb 27, 2017

• Thread starter
• #7

thechud

Structural

Feb 15, 2012

3

AU

Thanks Henryzau,
Can you please explain what CMC stands for

 

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• Feb 27, 2017

• #8

HENRYZAU

Geotechnical

Feb 12, 2017

94

AU

Controlled Modulus Column

 

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• Mar 14, 2017

• #9

L0k

Geotechnical

Dec 11, 2014

96

NZ

Hi thechud, the fastest way is using driven piles seating in the hard layer. A pile loading test may be required to estimate the pile capacity. So, you may distribute the pile evenly within the area of 11m x 35m.
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.

 

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• Mar 20, 2017

• #10

aeoliantexan

Geotechnical

Dec 21, 2006

350

US

I agree that you need a good geotechnical investigation to evaluate any approach.

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.

 

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