Development and Use of Axial Load Test Databases for Analysis and Design of Soft Rock Sockets

In this paper, a total number of 363 rock-socket load tests are compiled into a database – DUT/PileROC/363 and analyzed in a consistent manner. This database is used to evaluate the variability of predictions of mobilized resistances (fs and qb), loads Qa at settlements w = 5–20 mm and 0.5%–2% of socket diameter, and Q-w curves. For fs, qb and Qa, the results are characterized as the mean and coefficient of variation (COV) of the ratio of measured over predicted values. It is observed that (1) both shaft shearing and end bearing can be mobilized at small displacements when good construction and inspection procedures are followed, (2) the majority of empirical models for fs and qb are too simplistic and the resulting predictions are highly dispersive (COV > 0.6), (3) the prediction quality does not necessarily improve with an increased level of model sophistication, (4) rock mass modulus Em is crucial for predicting Qa and Q-w curves, (5) predictions of Qa by one nonlinear and two side-slip design methods are of medium dispersion (COV = 0.3–0.6), and (6) only the nonlinear design method produces Q-w curves that resemble the shape of measured curves in load tests.