Bearing Capacity vs. SPT

[jim57]

Are there any good books or sources that can relate the two. i would like to obtain soil beairng capaicy in chart form

 

[ashjun]

There is a book "Practical Foundation Engineering Handbook" by Robert W Brown.
A section in the book sumaries all the SPT methods used to analyse the SBC (including terzaghi, Bowles, etc.) method. He has also made a comparison between all the methods.

Rgds

 

[BigH]

While you ask for SPT vs Soil Bearing Capacity - as we have discussed on many occasions in other threads - it is the settlements that will govern most foundation designs. Few structures fail due to bearing at working loads unless on very soft to soft clays. With SPT, you estimate the phi angle for sands or the undrained shear strength for clays in order to go to your formulas (basically for clays, allowable bearing pressure due to shear is 2xUndrained shear strength). But many books give ways to estimate settlements with the SPT values in cohesionless soils. Ground Engineering magazine years ago had a nice state of the art paper on this.

 

[iandig]

If you track down "Foundation Design and Construction" by Tomlinson, there are several ways in which you can use the SPT to assess an initial allowable bearing pressure for both cohesive and granualr soils, but there definatley is a sequence to go through.
In general this is broken down into:
1. Obtain an initial allowable bearig pressure based on SPT N Value. From the general relationships, the allowable bearing pressure based on this assumption should 'typically' provide settlements of less than 25mm but they need to be checked once a more detailed design is known.
2. Undertake an initial design using the initial estimate of allowable bearing pressure
3. Check the detailed design against failure by settlement, differential settlement etc...
4. Undertake a re-design as required, based on the previous findings.
If you are going to use 'generic' values to identify an initial allowable bearing pressure, make sure you state the properties associated with it, i.e. 150kN/m² is not sufficient, it should be 150kN/m² based on a foundation width of 2.00m founded at 1.00m bgl. As you change the size of the foundation, you change the allowable bearing pressure.

 

[BigH]

iandig - on bringing to the fore one of the best foundation books available (at least before he went to the EuroCode).