foundation on soft soil
foundation on soft soil
(OP)
I need to build a segmental wall on soft soil having N value of ZERO from 0 till 10 m deep near a monsoon drain . How to have a foundation of 100KN/M2 by replacing the soft soil with crusher rock & how deep to replace ?
I have suggested to client to replace 1.2m of soft soil
A) with bottom layer 0.6m of 200mm size crush rock wrap with membrane
B) Also with top layer 0.6m of 50mm crush rock on top wrap with membrane .
Any suggestion & calculation formula to convince my client ?
I have suggested to client to replace 1.2m of soft soil
A) with bottom layer 0.6m of 200mm size crush rock wrap with membrane
B) Also with top layer 0.6m of 50mm crush rock on top wrap with membrane .
Any suggestion & calculation formula to convince my client ?





RE: foundation on soft soil
Then your application is a wall. For a building one surely soon would go with piles to competent layers, maybe piled mats or even vessel foundations, or foundations balanced with the weights. But for a significant wall (not merely a 1 m tall thing, in which the problem would be the same but less untreatable) a floating foundation itself doesn't make sense if the wall itself is not buttressed against anything to be stable and inmobile enough as to provide the demanded serviceability. Hence, the vertical stabilization by flotation if used would surely need horizontal (and/or vertical) supplement by piles to competent soil able to sustain the whole horizontal forces. I would (gladly!) consider any contribution of the standing ground layers as long I would find them truly of use by my technical interpretation.
RE: foundation on soft soil
RE: foundation on soft soil
100 KN/m2 = 100 kPa ~ 1 tsf
You can't have a "net zero load" foundation - the applied load is too high for the depth in question. I suspect the answer may be wick drains or stone columns to improve the site - or a pile foundation to provide support. Please describe the soil (type, water content, other properties, thicknesses) so that we can give you some better suggestions and comments -
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: foundation on soft soil
RE: foundation on soft soil
Question ; WHAT IS A WICK DRAIN DRAIN & HOW IT CAN BUILD UP THE SHEAR STRENGTH ?
Appreciate your precious infor
RE: foundation on soft soil
RE: foundation on soft soil
RE: foundation on soft soil
This is a actuall case:
I have a chance to visit a site which is in the same condition like yours, 11 m of weak OH soil, about 4m of surcharge by well compacted sand. Fence (by clay brick) is supported by shallow foundation placed directly on the soil. The fence high is 2.3m as initial design. one and half year later, the fence is only 1.3 m high, 1 m already disappeared.
In this site, main & heavy structures are supported by pile foundation but the others are just supported by shallow foundation with some small woodden pile (the length is about 5 m, meaningless). Probably, the designer though fence is just miscellaneous simple structure. At the present this site still settle down, and the owner is calling for bid to treat this consolidation settlement.
After the experience getting from this site, the other sites neighbour to it applied wick drain or piled foundation for almost structure (fence, small building etc). of course the cost is increased.
RE: foundation on soft soil
Wick drains are prefabricated vertical drains (of similar operation to the older sand drains). You can install these units quickly using a crane-mounted "stitcher". What you are doing is using vertical drains to reduce the drainage path of "escaping" water during consolidation.
As for increasing the undrained shear strength, as soil is compressed by loading (hopefully preloading), water in the soil is forced out to the vertical drains. As the void ratio is thus decreased, there is an increase in the undrained shear strength accordingly.
You can check out the US Army manual on settlements. Also, check out Terzaghi, Peck and Mesri (p323); Coduto (Geotechnical Engineering) (p672, Tchebotarioff; Bowles (Focht3 - I tried not to reference this - I really did). You can also do a search on "wick drains" under www.rediff.com or other search engines. There is a lot of reference out there on the net.
RE: foundation on soft soil
Yeah, right!
mary787:
Strength and moisture content are inversely related (in a general sense) - as moisture content decreases the shear strength increases. The soil's density will also increase as the moisture content decreases - as BigH indicated. You should expect the ground to settle as the drainage occurs -
Do you have a geotechnical engineer for your project?
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: foundation on soft soil
I think for areas like this that surely are inhabited to such extent as to require public works treatment precisely by the richness brought by the seasonal rains, any modern policy must demand the usefulness of what built to stand for some time, and this demands the use of technologies able to cope with the recurrent monsoons. Hence anything to be dissolved each year should be more or less dismissed. Floating structures, anchors between them, piling for most works of reasonable value and cost of replacement plus bridging between these and the others, is in my view the way to go.
RE: foundation on soft soil
mary787
I wish to thank all of you who have provided very good informations with regards to my question on soft soil foudation .
Thank You
GOD BLESS YOU
RE: foundation on soft soil
I understand your concern for "things washing away" in monsoon areas. But sometimes it is cheaper to rebuild (several times) than it is to use a structural approach (to do things "right") in constructing 'minor' structures.
I would not expect a wall bearing on improved soil to simply melt away. Done properly, it will last for many years - perhaps decades. But I do understand and appreciate your concerns -
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.