OPTIMIZATION OF PILE SOCKET DESIGN IN SRI LANKAN METAMORPHIC BEDROCK BY LABORATORY EXPERIMENTS AND PILES’ PERFORMANCE

Ayodya Bulathsinhala, Anurudda Puswewala

Abstract: Socketing into bedrock is widely practiced in Sri Lanka, yet existing design standards continue to adopt conservative assumptions derived from sedimentary rock conditions. Consequently, rock-socketed bored piles in crystalline metamorphic formations are frequently overdesigned, leading to excessive construction costs. This study evaluates performance-based optimization of skin friction in metamorphic rock sockets by combining theoretical estimation, field load test interpretation, and laboratory-derived shear strength models. Skin friction values were computed for fifteen instrumented load test piles and compared against theoretical predictions adjusted for bentonite filter cake effects. Mobilized skin friction frequently exceeded theoretical design assumptions by factors of 2–7, even in weathered rock. Laboratory results further validated the significantly higher interface shear capacities achievable in crystalline formations. Based on these findings, a revised design approach with a reduced safety factor of 2.5 is proposed, enabling substantial decreases in socket length without compromising safety.

Keywords: Pile socket design, Skin friction, Metamorphic rocks, Borehole load testing, Bentonite filter cake, Foundation optimization

DOI: 10.24874/PES08.02B.013

Recieved: 19.12.2025  Revised: 08.02.2026  Accepted: 07.04.2026  
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