# HOW TO CALCULATE PILE LOAD CAPACITY IN WEATHERED ROCK OR SOFT ROCK?

## Calculation of Pile Load Capacity in Weathering or Soft Rock

This method of calculating pile load capacity was suggested by Cole & Stroud. Cole & Stroud used the ‘n’ value, or the results of standard penetration tests, to determine the allowable load capacity of piles in weathered rocks.

The formula suggested by Cole & Stroud is given below. in formula, 1scheduled tribe Term end gives bearing resistance and 2Ra The term gives the socketed bond strength between the rock and the pile.

Where,

Whya = Allowable load capacity of the pile, kN. In

CU1 = shear strength of the rock below the base of the pile, kN/m. In2, (This is shown in Figure-1 below)

CU 2 = Average shear strength of the rock over the socketed length of the pile, kN/m. In2, (This is shown in Figure-1 below)

nC = bearing capacity factor 9. taken as

Fs = factor of safety usually 3 . is taken as

α = adhesion factor, (recommended value is 0.9)

B = Minimum width of pile shaft (or diameter in case of circular pile) in metres.

L = socket length of the pile, m . In

#### notes to remember

• A rock is considered a weathering rock or soft rock when the SPT value or N value is greater than 60. If less then it is considered clay.
• If N values ​​are greater than 200, the pile load capacity should be calculated on the basis of shear strength or rock.

### Reference

IS: 2911-Part-1-Sec-2

Er. Mukesh Kumar

Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.