A new method for predicting the ultimate shaft resistance of rock-socketed drilled shafts Available to Purchase

Data from 187 loading tests on rock-socketed shafts are used to develop a new relationship between the ultimate shaft resistance f_su and unconfined compressive strength σ_c of intact rock. The adhesion factor α_q of the shaft resistance for different types of rock and the relationship between α_q and the embedment ratio are discussed. Furthermore, because the shafts are socketed in the natural rock mass, as well as the aforementioned correlation with intact rock, three new relationships between f_su and the unconfined compressive strength σ_cm of the rock mass are proposed by considering the rock quality designation, which is related to discontinuity of the rock mass. Statistical methods are used to evaluate and verify the existing methods and newly proposed relationships. Results obtained using the new relationship based on σ_c are found to be more accurate than those obtained using existing methods, and when the rock quality designation is available, results obtained using σ_cm are closer to measured values than those based on σ_c. The value of α_q of the discussed rocks decreases with σ_c. Mudstone and shale have relatively high values of α_q with more dispersion, whereas α_q values for gneiss, basalt and granite are small overall with less dispersion.