Uncertainty Analysis Of Vertical Compressive Bearing Capacity Of Single Pile By Static Load Test

In this paper,theoretical simulation and statistical analysis are combined to evaluate the uncertainty of the ultimate bearing capacity of single pile in static load test and the prediction models.The main contents and conclusions are as follows:（1）The uncertainty caused by jack and pile foundation settlement was analyzed using GUM method,and the uncertainty of the load was synthesized from the two uncertainty component.The results show that the uncertainty of parallel jacks is about the algebraic sum of the uncertainty of the jacks.Load and pile type have little effect on the uncertainty caused by the settlement of the pile,and the load deviation distributes normally.When the test load is large,the relative uncertainty of the load is small.When the test load is small,the relative uncertainty of the load is large.When the bearing capacity of the test pile is small,it is recommended to use a load cell to measure the load.（2）The elastic simulation method based on Mindilin’s solution and Boussinesq’s solution was used to carry out the theoretical simulation of the static load test of the heap method and the uncertainty of the settlement was evaluated based on the measurement data.The results show that when the distance between the reference pile and the pier and the distance between the reference pile and the test pile is equal,the distance between the reference pile,the test pile and the pier has little effect on the static load test results.If the size of the pier is too large,the error of the static load test result will become larger,so the size of the pier should not be too large.The load size and pile type have little effect on the uncertainty of static load test settlement.When calculating the settlement of the pile foundation using the elastic theory method,E_s=5～6E_1-2 can be taken.The elastic modulus of the soil has a greater influence on the static load test results.The larger the elastic modulus,the smaller the error of the static load test results.（3）Comparative analysis of slow maintenance load method and rapid maintenance load method was carried out from the aspects of Q-S curve characteristics,settlement distribution law and the difference in settlement.The uncertainty of the ultimate bearing capacity of single pile was evaluated by Monte Carlo method.The results show that there is no difference in curve characteristics between slow maintenance load method and rapid maintenance load method.The settlement values of the slow maintenance method and the fast maintenance method in the site are normally distributed in any load.The difference between the settlement of the slow maintenance method and the fast maintenance method is related to the size of the load.With the increase of the test load,the deviation of the settlement of the slow maintenance method and the fast maintenance method increases first and then decreases.The maximum value is reached when the test load is 0.8 times the maximum load.When the test load is greater than5000k N,the relative uncertainty of the ultimate bearing capacity is small and relatively stable.When the test load is less than 5000k N,the smaller the test load,the greater the relative uncertainty of the ultimate bearing capacity.The load maintenance time and the type of pile foundation failure have a great influence on the uncertainty of the ultimate bearing capacity.Among them,the uncertainty of the ultimate bearing capacity of the progressive failure pile by fast maintenance load method is the largest.The uncertainty of the ultimate bearing capacity of the progressive failure pile by slow maintenance load method is the smallest.The uncertainty of the ultimate bearing capacity of the abrupt failure pile by slow maintenance load method is the same as that of the abrupt failure pile by fast maintenance load method.（4）The applicability and limitations of several prediction models are analyzed,and complete exponential model and gray theory model are optimized.A method for judging whether the complete exponential model can be used to predict the ultimate bearing capacity,which based on the slope change of the Q-S curve is given.Monte Carlo method was used to evaluate the uncertainty of the prediction model of the ultimate bearing capacity.The rseults show that complete exponential model has the highest prediction accuracy,which is suitable for the prediction of the ultimate bearing capacity of progressive failure piles and abrupt failure piles.The gray GM（1,1）model is suitable for the prediction of the ultimate bearing capacity of progressive failure piles,but cannot predict the ultimate bearing capacity of abrupt failure piles.The adjusted hyperbolic model is suitable for the prediction of the ultimate bearing capacity of progressive failure piles.But the prediction results of the ultimate bearing capacity of abrupt failure piles are poor.The prediction results of the hyperbolic model are more discrete,and are not suitable for the prediction of the ultimate bearing capacity of of progressive failure piles and abrupt failure piles.The uncertainty of the prediction results of the adrupt failure pile by fast maintenance load method and the adrupt failure pile by slow maintenance load method is the same and the largest.The uncertainty of the prediction result of the progressive failure pile by slow maintenance load method is the smallest.