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Raft Foundation in a construction site near a River.

We have a construction site with clayey soil for a very large depth(20 mts.) near a river where a G+7 structure is going to be constructed. The undrained shear strength is around 3 KN/m2. The subgrade modulus of soil is around 1200 KN/m3. The water table is at a depth of 3 m and the SPT value ranges from 10 to 20 with depth. I wanted to inquire if Raft foundation of thickness 0.6 metres would be suitable for such a soil condition(0.6 metre depth value has been found on designing but I am a little skeptical with the results because the water table is very high in the area). Pile foundation may be used for this kind of soil but choosing Raft foundation shall be more economical. Is a 0.6 metre thick Raft foundation a convincing foundation for this conditions.

Replies

  • Kaustubh Katdare
    Kaustubh Katdare
    Thread moved to Civil/Structural engineering section.
  • Anil Jain
    Anil Jain
    In no condition I would suggest you to go for Raft foundation with water table at a depth of 3m and with the other specifications you had given. That can be a disastrous decision.

    As you yourself had identified Pile foundation can be an option.

    -CB
  • Ravi Agarwal
    Ravi Agarwal
    Considering that the depth of the Raft foundation is being planned to be kept low(2.5 metres) and seeing that uplift pressure wont be encountered to the base of the Raft Foundation at this depth, does not water table remains not an issue to our foundation any more. Also, during construction, wouldn't surrounding the Raft Foundation with diaphragm walls eliminate the problem of interference due to the water during construction.
  • Anil Jain
    Anil Jain
    Even if you plan to keep raft foundation at 2.5 meters, and considering water table at 3 mt. Soil strata would be comparatively softer, and you may face settlement issues.

    Just my 2 cents.

    -CB
  • Ravi Agarwal
    Ravi Agarwal
    Proper compaction of soil has been planned. If required, filling of the base may also be done. Should settlement still remain an issue?
  • Anil Jain
    Anil Jain
    If you are so keen to lay a raft foundation design only.
    You can opt for safety measures.

    However I am assuming this is still on papers (design) where no body would hurt in person. In actual I would not suggest to lay that for a residential apartment.

    -CB

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