Characteristic GSF LSF

c-phi soil (σ-ε test)

Low strain < 5% High strain 10-20%

φ > 360 < 280

N ≥ 30 ≤ 5

e < 0.55 > 0.75

ID > 70% 35-70 (as per IS 6403, ID < 20)

Soil Low compressibility (dense to stiff)

High compressibility (soft to medium dense). For purely cohesive soil UCS ≤ 100 kPa

PSF

1. Loose sand

2. Footings

located at considerable depth

3. ID < 35; e > 0.75

Above are just a few guidelines to assist in making an appropriate decision while selecting analysis as GSF or LSF or PSF.

Expected modes of failure of footings in sand