Reliability Analysis Of Vertical Bearing Capacity Of Driven-cast-in-place Piles

In order to study the failure probability of the driven-cast-in-place piles, based on the static test data at the north bank of the Yangtze River in Nanjing and by estimating the vertical ultimate bearing capacity according to the curve of P ? Srelationship of the single pile, the reliability of the bearing capacity of the single pile is analyzed by the limit state equation of dimensionless random variables and the method of calibration. Under three different load combination forms, the reliability index is calculated through JC method in MATLAB language meanwhile the resistance partial coefficient can be determined. In addition, the influences of the general assurance coefficient, the loading effect ratio, different load compositions and the statistical parameters of random variables on the reliability index are investigated.Due to the lack of the static test data, in this study the vertical ultimate bearing capacity of the driven-cast-in-place piles is calculated by the numerical results according to the CPT curves at the north bank of the Yangtze River in Nanjing region. To consider the influence of the spatial variability on the reliability index of the driven-cast-in-place piles, the random field theory is applied to the reliability analysis. Based on the random field theory, the correlative distance is estimated through the recurrence space average method. Statistic feature of parameters in the limit state equation of the single pile is obtained. The reliability index is calculated by JC method with MATLAB language. Meanwhile the influence of the spatial variability of shaft resistance and tip resistance of soil layer, and the variability of the calculation models on the reliability index is investigated.It is indicated that the driven-cast-in-place piles have a high reliability index. This reflects the higher safe level of the single pile designed based on the current Specifications of Foundations. The reliability index increases as the assurance coefficient increases, and the effect is great. The reliability index decreases with the aggrandizement of the loading effect ratio. The statistical parameters of random variables also have some influences on the reliability index. The influence of different load compositions on the reliability index as well as on the resistance partial coefficient is not remarkable. The reliability index with the correlative distance is larger than those without the correlative distance. To the shaft resistance and the tip resistance, the more the parameters contribute to the bearing capacity, the larger the influence of the variability on the reliability index. The influence of the calculation model on the reliability index is remarkable. Finally, it is shown that the discrepancy of the reliability index of the ultimate bearing capacity calculated based on the static test data and the CPT curves is not great. Consequently, it can be implied that when the static test data is insufficient, the reliability analysis of the vertical ultimate bearing capacity by the CPT curves is feasible.