Drilled Shaft Load Tests to Investigate Side Friction Development along Drilled Shafts in Very Weak Porous Limestone: Fid-Bau Portal

Drilled Shaft Load Tests to Investigate Side Friction Development along Drilled Shafts in Very Weak Porous Limestone

Ramírez, José R. / Frediani, Matias R. / Pando, Miguel A.

This paper presents the results of two load tests on instrumented drilled shafts in very weak limestone performed to investigate the ultimate side friction that can be developed in this type of rock. The test site is located in NW Puerto Rico and involved a very weak porous limestone with a representative unconfined compressive strength of 2.7 MPa, and an average rock quality designation (RQD) of 34%, corresponding to a highly weathered state. The paper also evaluated the predictive performance of 10 commonly used empirical correlations of the maximum unit side friction based on the unconfined compressive strength. The range of the predictions of the ultimate side friction was found to be very large, highlighting the importance of improving our capability of predicting this parameter for design purposes. Furthermore, the measured ultimate side friction values were found to be above the upper bound of the range of predicted values using the selected static methods. The higher measured values are attributed to the medium to high surface roughness of the rock socket walls. The authors recommend the development of improved correlations that incorporate important design aspects such as rock socket roughness and stiffness ratios of the surrounding rock and drilled shaft.