Vertical Load Under The Pile Of Work Performance

Based on theories of predecessors, bearing capacity, settlement of vertically loaded single pile and pile groups and dynamic feature of single pile were discussed and researched in this paper. The following results and conclusions are obtained:1. According to the feature of load-settlement curve, determination methods of failure load, ultimate load, yield load and elastic limit load named as "characteristic loads" were discussed. These methods were used to determine "characteristic loads" of 12 examples which were published in publication and the statistic relations between each characteristic load were gotten. In addition, it is founded that the ultimate load, yield load, elastic limit load of pile which is carried out one static load test are higher than the original pile, so the preloading method can be extended in pile engineering.2. On the base of analysis of calculating ultimate base resistance by static method, the formulas of ultimate base resistance under undrained condition using different static methods were derived by using L.Hospital law.According to engineering example, the static method, national code and the SPT method calculating ultimate base resistance and ultimate shaft resistance were tested. The results indicate that the a method andλmethod can give a higher accuracy than the national code and the static method, national code and the SPT method give a much higher ultimate base resistance value than the test value, the reason of which is that there is false dense soil under the pile tip because of construction. So the ultimate base resistance should be reduced according to construction level and past experience.3. For undrained condition, the velocity field was firstly tested by calculating the upper bound analytical solution of shallow strip foundation. Then the upper bound analytical solutions of bearing capacity of single circular pile were derived, according to correcting to the deep strip foundation and 3D analysis. On the basis of theories of predecessor, the lower bound analytical solution of bearing capacity of single circular pile was developed.4. The shape feature of pile side friction was interpreted by load-transfer method. On the basis of modified load-transfer method, the more exact method was proposed.5. The result of Poulos' elastic theory method used in friction pile (or floating pile) was proved by ANSYS FEM analysis. The parameter in elastic theory was analyzed by ANSYS. The results indicate that the main difference between them is that the settlement increases with the poisson ratio by elastic theory method, but it increases with the poisson ratio firstly and reaches the max value and then decreases by ANSYS analysis. For the condition that the soil is elastic, the axisymmetric analysis applied initial stress field can model condition of pile-soil not sliding and pile-soil sliding very successfully. For the condition that the soil is elastic and plastic, the 3D analysis applied initial stress field can model condition of pile-soil not sliding and very successfully.6. The feature of wave shape measured by case method was interpreted by Smith model. The formula of static bearing capacity and the assumptions in calculation were introduced. The errors induced by assumptions were analyzed and the formula of total ultimate resistance and the formula of static bearing capacity when the pile tip is not free were deduced. The result indicates that the total ultimate resistance when the tip is not free is same to that when the tip is free, and the difference between static bearing capacity when the tip is not free and that when the tip is free is small. Although there are many assumptions in case method, the result is permissible to engineering if the driving hammer with rather large energy and long buffering time is selected. Large damp coefficient should be chosen for long pile and small damp coefficient should be chosen for short pile in order to reduce the error.7. The two-pile interaction factor was analyzed by ANSYS using axisymmetric model and the results indicate the difference between the interaction factor value, the interaction factor value changing rule with two piles space increasing calculated by ANSYS and that by Poulos' elastic theory method is little. The two-pile interaction factor which is calculated considering "reinforcement effect" and the factor that is calculated without considering "reinforcement effect" was analyzed by ANSYS using 3D model and the results indicate the difference between two is little.