| With the continuous growth of the population,the human demand for space is constantly increasing,and more and more high-rise and super-high-rise buildings have been built.At the same time,ultra-deep foundation pit and multi-level basement are widely used in modern construction engineering,but anti-floating and anti-overturning problems also come.Compared with traditional equal-section pile,variable-section pile has the advantages of high bearing capacity and high unit material utilization.Therefore,using variable-section pile as uplift pile has inherent advantages.However,due to insufficient research on its bearing mechanism and failure mode in variable-section uplift pile,the application of this pile is limited.Based on the research of variable-section uplift pile by relevant scholars,this paper uses semi-model tests combined with numerical simulation to change the setting position of the expanding plates.The bearing characteristics and dynamic deformation process of variable-section uplift pile with two plates in dry sand foundation are studied.The conclusions obtained from the study are as follows:(1)Through the model tests,it is feasible to observe the dynamic deformation process of the foundation using the research method of laying the logo layer in the semi-model test.The influence of the logo layer on the bearing characteristics of the model pile can be ignored.The inherent advantage of the variable-section uplift pile on bearing capacity is verified.Compared with the equal-section uplift pile under the same condition,the ultimate pullout capacity is increased by 35.7%,but the required displacement of the variable-section pile is larger.(2)In the model test,the position of the expanding plates have a great influence on the bearing characteristics of the variable-section uplift pile.As the distance between the plates increases,the supporting forces by the two expanding plates and the friction on the pile side play a coordinated role when subjected to the pull-up load.The working order is frictional resistance,upper plate,lower plate.The ultimate pullout bearing capacity reaches its maximum when the plate spacing is 8 times the pile diameter,and then gradually decreases.When the buried depth of the upper expanding plate is less than 8 times the pile diameter,the overlying soil is destroyed first,and the supporting force provided by the upper plate begins smaller,leading to the reduction of ultimate bearing capacity.(3)By observing the dynamic deformation process of the foundation,the damage range of the soil near the expanding plate is spindle-shaped,with a horizontal influence range of about 4 times the pile diameter and a vertical range of 4 to 5 times the pile diameter.At the same time,it was found that when the distance between the plates is less than 2 times the pile diameter,a linear shear failure occurred in the soil between the two plates along the edge of the plates.With the increase of the distance between the plates,the damage pattern gradually changes from a gourd-shaped connected damage near the two plates to a separate destruction form.When the upper plate gets closer to the surface of the foundation,the influence range of the upper plate on the surrounding soil gradually increases.When the buried depth is 8 times of the pile diameter,the damage surface is connected with the surface,indicating that the upper plate can no longer work effectively.(4)The numerical simulation results of the representative groups show that the overall law of pile stress,model foundation stress and displacement is basically consistent with the model test.In conclusion,in the design of variable-section pile with two plates,it is suggested that the spacing between the two plates should be kept at 8 times the pile diameter to obtain a higher ultimate bearing capacity,and the buried depth of the upper plate should be greater than 8 times the pile diameter to avoid the soil near the upper plate being preferentially damaged and losing its support. |
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