Determination of ultimate bearing capacity of uplift piles using intact and non-intact load-displacement curve

Based on the field destructive test of six rock-socketed piles with shallow overburden, three prediction models are used to quantitatively analyze and predict the intact load-displacement curve. The predicted values of ultimate uplift capacity were further determined by four methods (displacement controlling method (DCM), reduction coefficient method (RCM), maximum curvature method (MCM), and critical stiffness method (CSM)) and compared with the measured value. Through the analysis of the relationship between the change rate of pullout stiffness and displacement, a method used to determine the ultimate uplift capacity via non-intact load-displacement curve was proposed. The results show that the predicted value determined by DCM is more conservative, while the predicted value determined by MCM is larger than the measured value. This suggests that RCM and CSM in engineering applications can be preferentially applied. Moreover, the development law of the change rate of pullout stiffness with displacement agrees well with the attenuation form of power function. The theoretical predicted results of ultimate uplift capacity based on the change rate of pullout stiffness will not be affected by the integrity of the curve. The method is simple and applicable for the piles that are not loaded to failure state, and thus provides new insights into ultimate uplift capacity determination of test piles.