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# Soil spring stiffness

## Soil spring stiffness

(OP)
Hi,

"If you look at Bowles Table 9-1, modulus subgrade, kv (kN/m3)
approx equal to 240 Cu (kPa).
Allowable bearing pressure, qa (kPa) = Nc Cu / SF = (5.14 /3) Cu..."

Bowles Table 9-1 shows ks (not kv), and there is no Cu there...
Also, where is the 5.14 value coming from?

Thanks.

### RE: Soil spring stiffness

Nc is bearing capacity factor of 5.14. This is for phi = 0

### RE: Soil spring stiffness

(OP)
Thanks, EireChch - where could I find a reference for this?

So for phi=0 (cohesive soils) use Nc=5.14, but what if c=0 or for c-phi soil types?

### RE: Soil spring stiffness

Any soil mechanics/ foundation book (bowles) that has a section on bearing capacity shows Nc values for phi = 0 to phi = 40+. Its a row of tables.

c is typically taken as 0 in c-phi soils as it is conservative (generally).

When c = 0 the first part of the bearing capacity equation is ignored. The second and third parts, which includes Ngamma and Nq are used to calculate bearing capacity.

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