A Review of Rock Socket Skin Friction for Cast In-situ Bored Piles based on Instrumented Pile Load Tests

Abstract

With rapid societal development, there is an increasing trend of communities establishing settlements near townships to meet socio-economic needs. However, due to the scarcity of available lands for infrastructure and community development, low-lying marshy lands are often encroached upon. Constructing structures on these compressible, weak soil layers leads to excessive settlement, potential bearing failure, and stability issues. To mitigate these challenges, deep foundations with rock socketing are employed, transferring loads to a strong substratum. In deep foundations, upper weak soil layers contribute minimally to load-bearing capacity, while rock socket shaft friction and end-bearing resistance play a significant role. Estimating these capacities is complex, requiring consideration of rock properties, fracture conditions, weathering, and intact rock mass characteristics. Even though, various empirical and semi-empirical methods have been developed, making it challenging for designers to select the most suitable approach. Accordingly, this study assessed different methods for estimating the bearing capacity of rock-socketed piles in fractured gneissic rock to establish an optimized foundation design approach. Instrumented Pile Load Test (IPLT) data, obtained using vibrating wire strain gauges, were compared with empirical and semi-empirical equations to verify the reliability. This study conclusively demonstrates that currently available predictive models fail to provide accurate estimates of rock socket skin resistance for bored piles constructed in Sri Lankan gneissic rock. The proposed linear model, which incorporates a 45% reduction factor for bentonite effects, yielded predictions that closely matched the measured resistance values, indicating its suitability for local design applications.