| Precast pipe piles are widely used with the characteristics of convenient construction and low cost.However,in the later stage of service,in addition to bearing the permanent weight of the upper load,it is also subject to the action of the ring load,and the timeliness of its bearing capacity is constantly decreasing.In this thesis,field tests,indoor model pile longitudinal load tests and finite element numerical simulations will be carried out to study the force bearing characteristics of pipe piles under different circumstances,and the conclusions are as follows.1.The ultimate bearing capacity of the test pile measured in the static load field in-situ test is 8100 k N,and the ultimate bearing capacity of the test engineering pile calculated in the high strain test is 7520 k N,the vertical bearing capacity of the foundation pile measured by the high strain test is about 7.2% lower than the vertical bearing capacity obtained from the monopile vertical compressive static load test,and the ultimate bearing capacity of the large diameter PHC pile obtained from the compressive static load test and the high strain test is about 7.2% lower than the vertical bearing capacity obtained from the monopile vertical compressive static load test.The ultimate bearing capacity of large diameter PHC piles obtained from compressive static load test and high stress variable test meet the design requirements of bearing capacity and have good vertical bearing performance.The accuracy of the ultimate bearing capacity of single pile obtained from high stress variable test meets the requirements of engineering site testing and can be used to replace or verify the static load test results.2.The experimental study of model pipe pile pile power in silt soil has obtained the following conclusions:（1）When the number of vibrations is fixed,the frequency of high sedimentation value is faster and more stable,the sedimentation value accumulates rapidly,and when it reaches 600 times,the sedimentation value tends to be stable,when the frequency is certain,the high vibration amplitude sedimentation value is faster and more stable,the vibration amplitude is certain,and the cumulative sedimentation value will increase with the increase of the vibration frequency.（2）As the number of vibrations increases,the axial force of the pile also increases.An increase in load amplitude and vibration frequency causes an increase in the axial force of the pile body.The distribution law of side friction resistance is that the resistance value of side friction will increase with the increase of burial depth in the early stage,and even if the burial depth continues to increase in the later stage,the resistance value of side friction will slowly begin to become smaller.3.The results of the vertical compressive static load test of the indoor single pile in the silt soil show that the pile top displacement will continue to increase with the application of the load.Before the applied load value reaches 45% of the limit bearing capacity value,the bearing capacity of the open model pipe pile P1 is mainly borne by the side friction resistance,and if the load continues to increase,the proportion of pile end resistance gradually increases.The ultimate load carrying capacity in the silt of the open model pipe pile is 8 k N.4.The results of the finite element numerical simulation show the following conclusions:（1）Under the periodic vibration,the vertical displacement development speed of the open pipe pile gradually decreases until it is stable.The lateral pressure of the outer side of the open pipe pile will increase with the increase of the burial depth,the lateral pressure of the upper part of the open pipe pile will gradually decrease with the increase of the number of vibrations,and there will be almost no change after the number of vibrations is 10 times,and the lateral pressure in the middle of the open pipe pile will gradually increase under the increasing number of vibrations,and the lateral pressure at the bottom of the open pipe pile will basically not change.（2）Under the action of the cycle,the change law of the outer friction resistance of the open pipe pile with the increase of the burial depth is basically the same,that is,with the increase of the burial depth,the friction resistance of the outer side of the open pipe pile fluctuates greatly along the burial depth,but overall,with the increase of the burial depth,the outer friction resistance shows a gradual increase trend.The maximum friction resistance on the outside of the open pipe pile is in the middle and lower part of the pile,and the greater the vibration amplitude,the greater the maximum friction resistance on the outside of the open pipe pile.（3）The curve of strain at the position closer to the top of the pile hardly changed,with a small increase in the first 10 times,followed by a stabilization.The deepest strains were positively correlated with the number of vibrations and did not show a stable trend.The strain at the top of the pile is the largest at different numbers of vibrations,and the strain along the pile gradually decreases from top to bottom,with the same pattern at different cyclic load ratios.Under the shear effect of cyclic load,the pile side hole pressure value increases rapidly at the beginning of the cycle,and then gradually decreases and stabilizes after reaching the peak.（4）The parameter analysis of different cyclic load ratios under cyclic load shows that the sedimentation value gradually increases with the increase of the number of cycles,and the sedimentation value increases significantly in the early stage of cyclic loading,and then the growth trend weakens.When the number of cycles is the same,the greater the cycle load ratio,the greater the final value of the cumulative settling amount.The average friction resistance on the inside and outside of the circulating pile gradually decreases with the increase of the number of vibrations,the greater the circulating load ratio,the more obvious the decrease in the average friction resistance on the outside,and the average friction resistance on the outside shows a weakening trend,and eventually stabilizes.（5）The parameter analysis of different cycle periods under cyclic load shows that the vertical displacement development rate of the open pipe pile gradually decreases until it is stable.The inner friction resistance of the open pipe pile is the largest,and the inner friction resistance of the open pipe pile will gradually increase with the increase of the burial depth,and the greater the circulating load ratio,the greater the maximum friction resistance of the open pipe pile. |
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