Table of Contents

**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, 1^{scheduled tribe} Term end gives bearing resistance and 2^{Ra} The term gives the socketed bond strength between the rock and the pile.

Where,

Why_{a} = Allowable load capacity of the pile, kN. In

C_{U1} = shear strength of the rock below the base of the pile, kN/m. In^{2}, (This is shown in Figure-1 below)

C_{U 2} = Average shear strength of the rock over the socketed length of the pile, kN/m. In^{2}, (This is shown in Figure-1 below)

n_{C} = bearing capacity factor 9. taken as

F_{s} = 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

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