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[Anjan7601]

I have basement wall on raft foundation.
The height of basement wall is 2.1 m below ground level so there will be an lateral earth pressure for 2.1 m height of soil.

i. Now what will be the load and moment on the base of raft foundation for basement wall?

ii. Do I need to provide any foundation beam on raft for basement wall?

iii. How can I apply those load and moment on raft in staad foundation or safe 2016.
Please provide in detail explanation. Thank you 😊

[vikram.jeet]

Basement wall :-

Though not expert on computer software applications,, I think In modelling in staad,  lateral pressures due to eath pr plus LL surcharge ( plus any hydrostatic pressure as result of rise of subsoil  ) are to be modelled in Loading inputs.

Software will take care of wall load,, Moments transferred in overall model.

However most important is construction phase when raft is cast plus retaining wall 2.1 m constructed and back fill done causing wall to behave as Cantilever ret wall transferring full moment to raft.  To avoid this situation,, drgs must be provided with boxed notes regarding timing of backfilling  Or level of backfilling to limit the base moment from wall.

In case backfill is permitted after construction of basement roof slab, beams,, the bare moment will be low.
But contractors tend to backfill first,, and to avoid heavy bade moments, backfill can be permitted upto  1.0 to 1.2 m only.

Another angle is rise lof subsoil water which may cause upliftment of raft and need protection till two /three floors are constructed depending on water table. Protection of raft is in form of continuous pumping of area which is very costly and chances of stoppage of pumping can not be ruled out.
Other way to protect is to provide temporary holes at few locations in ret wall to be plugged later when upper two / three storeys constructed. In this case upliftment of raft is saved,, but subsoil water is allowed to enter raft to balance uplift force.

Long post,  kindly pardon