Estimation of the Load Bearing Capacity of Root Piles Partially Embedded in Rock Mass Rhyolite, Using Empirical and Semi-Empirical Methods-Paper

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The study evaluates methods for estimating the load-bearing capacity of root piles embedded partly in soil and partly in rhyolite-rich rock at the PetroquímicaSuape site in Pernambuco, Brazil. The heterogeneous rock mass included rhyolite, basalt, and intermediate material, with compressive strengths of approximately 30–110 MPa and varying degrees of weathering and fracturing.<br /><br />Three piles were assessed using static compression load tests. The tests reached twice the piles’ design working loads but produced only small settlements and did not cause failure. Failure loads were therefore extrapolated from load–settlement curves using the Van der Veen, Chin–Kondner, and Décourt methods. Chin–Kondner and Décourt estimates were the most consistent, yielding adopted failure loads of 3,863 kN, 3,012 kN, and 1,825 kN for piles E25, E100, and E110, respectively. The piles’ observed settlements were considered satisfactory.<br /><br />The researchers compared these estimates with bearing capacities calculated using empirical and semi-empirical methods, considering different combinations of soil shaft resistance, rock socket resistance, and pile-tip resistance. Including the soil contribution improved estimates. Combining soil resistance with the Horvath method for rock-side resistance produced estimates within −24% to +25% of the interpreted failure loads. When soil resistance, rock-side resistance, and pile-tip resistance were included using España’s method, estimates were conservative, differing by −30.5% to −8%.<br /><br />The findings suggest that soil resistance should not automatically be ignored when assessing piles partly embedded in rock. However, conclusions are limited by the small number of tests and the low settlements achieved, which likely did not fully mobilize pile-tip resistance.

Keywords

root piles

load-bearing capacity

static compression load tests

rhyolite-rich rock

settlement analysis

Van der Veen method

Chin-Kondner method

Décourt method

rock socket resistance

pile-tip resistance