neilquane
Civil/Environmental
- Mar 7, 2016
- 3
Good evening,
I am seeking to undertake the IStructE membership examination and I have began to review some previous examination papers as well as reading through guidance provided on the institution CD-ROM.
The query I have relates to the derivation of allowable bearing pressures and settlement of structures in relation to cohesive soils.
Generally the input parameters on the exam are for the un-drained state with the description of strata (stiff etc) apparent cohesion and internal angle of friction.
I have read that settlement calculations are not required for the exam however reference to settlement criteria is required.
In the un-drained state I would propose calculation of the ultimate bearing pressure using Terzaghi followed by application of an appropriate FOS to develop a allowable bearing pressure which would cater for construction stage settlements.
An alternative approach within the IStructE CD notes is; soil bearing capacity = 4 . apparent cohesion (Bell & Packshaw); although I haven't been able to locate this reference. I assume this value would also have a FOS applied??
As there are generally no input parameters for the drained state, is it fair to state that as part of detailed design further soil investigation is required to establish the internal angle of friction in the drained state and thus allow the development of the allowable bearing pressure and the sub-structure should be reviewed in accordance with the findings?
The IStructE notes state that as the drained angle of friction is not provided then calculation cannot be undertaken, however in Reynold's RC designers handbook it is possible to relate the angle of friction with apparent cohesion and description of clay strata thus making calculation possible.
Kind Regards
Neil
I am seeking to undertake the IStructE membership examination and I have began to review some previous examination papers as well as reading through guidance provided on the institution CD-ROM.
The query I have relates to the derivation of allowable bearing pressures and settlement of structures in relation to cohesive soils.
Generally the input parameters on the exam are for the un-drained state with the description of strata (stiff etc) apparent cohesion and internal angle of friction.
I have read that settlement calculations are not required for the exam however reference to settlement criteria is required.
In the un-drained state I would propose calculation of the ultimate bearing pressure using Terzaghi followed by application of an appropriate FOS to develop a allowable bearing pressure which would cater for construction stage settlements.
An alternative approach within the IStructE CD notes is; soil bearing capacity = 4 . apparent cohesion (Bell & Packshaw); although I haven't been able to locate this reference. I assume this value would also have a FOS applied??
As there are generally no input parameters for the drained state, is it fair to state that as part of detailed design further soil investigation is required to establish the internal angle of friction in the drained state and thus allow the development of the allowable bearing pressure and the sub-structure should be reviewed in accordance with the findings?
The IStructE notes state that as the drained angle of friction is not provided then calculation cannot be undertaken, however in Reynold's RC designers handbook it is possible to relate the angle of friction with apparent cohesion and description of clay strata thus making calculation possible.
Kind Regards
Neil
