Study Of Vertical Bearing Capacity And Reliability On Manual-excavated Pile

The vertical bearing capacity and the checking method of bearing capacity transforming from permissible stress method to probability limit condition design method of manual-excavated pile are problems urgently needed to be solved. Combinating the analysis of test data, theoretical study and example calculation, some problems of manual-excavated pile were studied in some aspects of increase coefficients of subgrade bearing capacity, reliability index on serviceability limit state and ultimate limit state in local foundation basic code in Liaoning Province, reliability direct design method, Sub-coefficient Design Method and so on.The influences of soil groups of sustaining layer, bottom diameter of pier foundation, relative embedment depth and soil compactness on the increase coefficients of subgrade bearing capacity in pier foundation is discussed. Then the empirical formulas about increase coefficients of subgrade bearing capacity in manual-excavated pile and pier foundation were obtained. It was also found that designing manual-excavated pile with the smaller relative embedment depth according to code would lead to a relatively bigger calculation result, which is not safe in engineering application.The calculating formulae were derived according to random field theory and variance propagation law for the mean values, standard deviations and coefficients of variation of the Vertical Bearing Capacity of manual-excavated pile considering the self-correlation of the number of DPTs, with the statistical parameter of pile end diameter given. A numerical example showed that the heavy-duty DPT data are suitable to the calculation of correlated distance for the foundations of sand soil and gravelly soil.The target indexes of reliability in the local Specification of Foundations were calculated by the method of calibration, and the calculation equation and calculation steps of reliability direct design method were gived. It was shown that the resistance of manual-excavated piles follows the lognormal distribution, the influence of loading effect ratio and different load compositions on the reliability index is remarkable, the influence of distribution types of resistance on the reliability index is to a certain extent, whereas the target index of reliability of resistance is different with different load compositions.The reliability analysis of single pile was made by using the limit state equation of dimensionless random variables on ultimate limit state and the reliability index is calculated by the JC method. The target index of reliability and the resistance partial coefficient in the local Specification of Foundations were got. It was shown that the influence of loading effect ratio and different load compositions on the reliability index is to a certain extent, the influence of distribution types of resistance on the reliability index is remarkable, whereas the influence of different load compositions and loading effect ratio on the resistance partial coefficient is weak.