Static Load Test Imperfections Influence on Continuous Q-S Curves

Abstract

The static load test is the most reliable method of indicating the actual pile bearing capacity. Within the pile load increments, the settlement is measured and set of points Q-s (load – settlement) is plotted. The ways of executing the pile load test and their interpretation are far from optimal and have many different approaches. Usually, the pile test does not allow evaluating the bearing capacities within the measured range and extrapolation of the results within the Q-S curves is necessary. None of the present interpretation models includes the influence of imperfections in the pile load test. The paper presents the results of calculations with the model that takes into account the occurrence of imperfections during the test execution. The analysis is based on the modified Meyer-Kowalow curve model, proposed by Meyer and Wasiluk, and on the field test obtained on many construction sites for piles in different technologies, few of them loaded up to the failure. The model considered in the paper allows extracting statistical imperfections in the collected set of points. Imperfections should be understood as mechanical changes of the pile and pile-soil interaction. All phenomena are gathered within one imperfection. The imperfections are due to changing soil and pile skin when the soil body bends according to the Kirchhoff’s principle. Calculations indicate the influence of imperfections on the pile limit load and other parameters of the Q-s curves according to the basic model that exists. Performed analysis based on approximately 65 piles defines three main groups, first with a relatively small influence of imperfections, second with changes of the limit load for the entire pile and the pile toe without the large change of pile character (ratio of skin friction and pile toe resistance) and the third with a significant change in limit loads and pile bearing capacity components ratio (skin and toe). Values measured during the pile load test can be corrected within extract imperfections. Presented model in many cases determines more critical values for designers than basic models suggest.