Analysis On Axial Bearing Behavior Of Large Diameter Piles

Compared with large-diameter pile and small-diameter pile,it has many advantages in using pile side friction,bearing capacity of pile end soil,rigidity of pile body,etc.At present,it is not practical to detect the ultimate state of large-diameter pile by static load test.Only through the incomplete Q-S curve,the load transfer law and ultimate bearing capacity of large-diameter piles can not be well understood.Therefore,it is necessary to use numerical simulation method to study the vertical bearing capacity of large-diameter piles.In this paper,based on FLAC^3D simulation software and relevant pile foundation design data of Paihe Extra-large Bridge Project in the 01 bid of He'an Expressway,the vertical bearing capacity of two kinds of large diameter piles is analyzed.The main research contents and results are as follows:?1?In order to verify the feasibility and accuracy of the numerical simulation,the convergence criteria of FLAC^3D software in the simulation process are analyzed and adjusted.Compared with 10^-5,10^-6,10^-7,and 10^-8 convergence criteria and relevant data,the convergence criteria of this simulation is 10^-6.The relevant data of the site test pile in the reconstruction and extension project of K94+920.9 channel bridge of Changping Expressway and the relevant data of the excavation method test pile ZJ1 in the reconstruction and extension of Zhongpai River Bridge are verified.The results show that the numerical simulation using FLAC^3D software has a good fitting effect.?2?By analyzing the effects of the aspect ratio,the properties of the soil layer at the end of the pile,the strength of the pile concrete and the necking,the vertical bearing capacity of large-diameter bored piles is analyzed and studied.The results show that the increase of the ratio of length to diameter of large diameter pile can effectively improve the vertical bearing capacity of single pile,and the compression value of pile body increases obviously with the increase of the ratio of length to diameter.The properties of soil layer at pile tip have obvious influence on the change form and vertical bearing capacity of Q-s curve in static load test.The soft Q-s curve of soil layer at pile tip shows steep change,while the hard Q-s curve shows slow change.The improvement of pile concrete strength has little effect on the vertical bearing capacity of single pile.The improvement of the concrete strength of pile body has little effect on the vertical bearing capacity of single pile,and the necking in the middle of pile body will obviously weaken the vertical bearing capacity of single pile,so the construction quality should be paid more attention to in the construction process.?3?The static load test simulation of four large-diameter hollow pipe piles with different wall thicknesses of 250mm,350mm,450mm,and 550mm are selected for analysis.The results show that when the wall thickness is small?250mm?,it will cause uneven settlement of the soil layer at the end of the pile in the ultimate state,but the ultimate bearing capacity of a single pile does not increase with the continuous increase of the wall thickness.For the large diameter hollow pipe pile with the simulated pile diameter of 1.5m,it is more economical to select the wall thickness of 350mm.?4?The load transfer law of two kinds of large-diameter piles in the process of loading shows that the side friction first reaches the limit,and then the increasing load increment is borne by the pile end resistance.In the process of loading,the plastic region of soil around the pile extends from top to bottom,and the soil at the pile end finally enters the plastic state.The effect of pile side friction of large-diameter hollow pipe is higher than that of large-diameter bored pile,and can effectively reduce the amount of concrete.Figure[60]table[22]reference[53]...