Structure footprint part sand -part clay 1

[SLaryea]

Good day,

I've got a site that is partly on sand and partly on firm clay. The client wants to to use pads.

Just not certain what measures required and the associated allowable bearing pressures to control settlement to avoid differential settlement between the two materials?

Help most appreciated - in any form

 

[SlideRuleEra]

I had to handle a similar problem:
Ring footing for a large dome that was partly on:
1) Highly compacted soil under an abandoned railroad track
2) Never disturbed soil in a field
3) A wide, deep ditch full of "muck"

My solution:
Uniform, deep excavation for the entire footing and backfill / compaction of high quality material.
Twenty years later, no problems.

 

[geotechguy1]

Piles, ground improvements, or what slide rule said

 

[EireChch]

I think rushing to piles is too hasty.

Calculate the settlement beneath each portion.

Sand is purely elastic with some additional creep. Schmertmanns time factor is 1.54 so apply that your value calculated.

Calculate your consolidation settlement in CLAY, including secondary compression.

Work out the differential settlement between the pads. If its too much then you could over excavate some CLAY and replace with SAND to reduce the settlement to within tolerable limits. You could even replace with light weight polystyrene fill to reduce the net increase in stress. I have done this several times and its a good solution.

Might still not work even after doing this but run some numbers first.

If its a dense SAND and an over consolidated CLAY then settlements might in similar ball park.

SRE solution is also fine, but again you need to check the settlements.

 

[RGKVI]

If its a firm inorganic clay I wouldn't calculate for secondary compression, just primary consolidation.

 

[RGKVI]

If its a firm inorganic clay I wouldn't calculate for secondary compression, just primary consolidation.

 

[SLaryea]

Thanks a bunch.. Great info there