Reliability Analysis And Design Of Pile Foundations For Serviceability Limit State

A great bearing capacity and a small settlement are two basic requirements for ensuring the safety of pile foundations. Due to a large number of uncertainties in pile foundation engineering, it is not reasonable to undertake safety analysis and design of pile foundations by the traditional safety factor method. Therefore, the reliability method should be adopted to cope with safety analysis and design of pile foundations. The essence of reliability-based analysis and design of pile foundations is the limit state analysis and design based on the probability theory. The limit states of pile foundations mainly include two types:ultimate limit state (ULS) and serviceability limit state (SLS). At present, less research results on the SLS reliability-based analysis and design of pile foundations have been published. On the basis of the present research of reliability-based analysis and design of pile foundations, this study systematically investigated the SLS reliability-based analysis and design of pile foundations, and the main work and findings are as follows:(1) Taking into account the uncertainties from the calculation model of bearing capacity and the load, with the reliability analysis method and the theory of probability and statistics, the calculation formulas of reliability indices for ULS and SLS of single piles were derived, respectively. Meanwhile, the linear relationship between reliability indices for ULS and SLS was presented. According to load test databases of single piles, the influence of soil conditions and pile types on the statistics of model factors for ULS and SLS of single piles was conducted. In addition, the influence of the uncertainties from the calculation model of bearing capacity, the load, and the limiting tolerable settlement on the reliability analysis for SLS was investigated.(2) In order to conduct the SLS reliability-based design of single piles, taking into account the uncertainties from the bearing capacity of single piles, the load, and the load-settlement model, the formula for computing the SLS reliability index was obtained using the mean value first order second moment (MVFOSM) method. Meanwhile, the limit state function for performing the SLS reliability analysis by the Monte Carlo simulation (MCS) method was established. Finally, the MVFOSM method and the MCS method were applied to develop an approach for the determination of the SLS target reliability index. Single pile load test databases collected were compiled to conduct reliability analysis. On the condition that both the safety factor and the limiting tolerable settlement were given, the target reliability indices were recommended based on the SLS reliability indices computed by the MVFOSM and MCS methods.(3) Based on the principle of the ULS reliability analysis and design of single piles, a novel reliability-based approach for the analysis and design of single piles by incorporating the SLS requirements was developed. Three methods for reliability analysis and resistance factor computation, namely the MVFOSM method, the advanced first order second moment (AFOSM) method, and the MCS method, were employed for comparison. The pile load test databases collected were compiled for illustration. The differences among the reliability indices and the resistances factors computed by the MVFOSM method, the AFOSM method, and the MCS method were analyzed considering the SLS requirements of single piles. Meanwhile, the influence of soil properties, pile types, and limiting tolerable settlement requirements on the differences among the reliability indices and the resistances factors was studied. The recommended resistance factors to use in the reliability-based design of single piles were presented based on the resistance factors computed by the AFOSM and MCS methods. Finally, the relationship between the reliability level with considering the SLS requirements and that without considering the SLS requirements was discussed.(4) The influence of different failure criteria and settlement control requirements on reliability analysis of single piles was studied. The bias factor defined with respect to the s-\gt failure criterion was introduced to each of seven failure criteria collected. With consideration of different failure criteria, model uncertainties, and settlement control requirements, the synthetic reliability analysis method was presented using the model factors for ULS and SLS. Finally, it was conducted that the impact of the randomness of limiting tolerable settlement on reliability analysis of single piles. The study recommended the combination of failure criterion and settlement control requirements for the comprehensive assessment of the safety of single piles.(5) Taking into account the uncertainties of models and parameters for ULS and SLS of piles, the linear relationship between reliability indices for ULS and SLS was described again using the reliability theory. With the combination of the ULS reliability method of pile groups, the approach for the assessment of the SLS reliability of pile groups was presented considering the correlation of pile group efficiency and system effect. Finally, the influence of the correlation between pile group efficiency and system effect, pile length-diameter ratio, and limiting tolerable settlement on the SLS reliability analysis of pile groups was studied utilizing pile load test databases.