路堤荷载下坡脚处不同排距斜直组合桩工程特性试验研究

Experimental study on engineering characteristics of inclinedstraight composite piles with different row spacing at slope toe under embankment load

采用斜直组合桩加固坡脚软基,在此基础上,通过模型试验研究路堤循环加卸载下坡脚处不同排距斜直组合桩的工程特性。研究结果表明:桩侧土压力沿深度方向呈先增大、后减小的趋势,随荷载或者加载次数增大而增大。后排直桩桩侧土压力随排距增大而增大,在0.4L(L为桩长)处达到最大值;前排斜桩桩侧土压力随排距增大而减小,在0.6L处达到最大值。前排斜桩水平位移及其峰值随荷载和加载次数增大而增大,随排距增大而减小。上部位移增速大于下部位移增速,桩头位移增速最大。当排距为2.5d~4.0d(d为方桩边长)时,桩身水平位移峰值随排距增大而快速递减。桩身弯矩及其峰值随荷载或者加载次数增大而增大。后排直桩弯矩峰值出现在桩身中部,随排距增大而增大;前排斜桩弯矩峰值出现在桩头,随排距增大而减小。在均质砂土地基中,后排直桩将率先在桩身中部发生弯曲破坏,排距越大,破坏越早发生;前排斜桩将平移并绕桩底转动,最后在桩顶发生破坏。在工程实践中,建议排距取桩径或方桩边长的2.5倍,后排直桩的抗弯刚度取前排斜桩的2.5倍以上。

On the basis of the inclined-straight composite pile consolidating the soft foundation of slope foot,the engineering characteristics of the inclined-straight composite pile with different row spacing under cyclic loading and unloading of embankment were studied by model test.The results show that the soil pressure on the pile side increases firstly and then decreases along the depth,and increases with the increase of load or loading times.The soil pressure on the side of the back row straight pile increases with the increase of the row spacing,and has the maximum value at 0.4L(L represents the length of the pile).The soil pressure on the side of the front row inclined pile decreases with the increase of the row spacing,and has the maximum value at 0.6L.The horizontal displacement and its peak value of the front row inclined pile increase with the increase of load and loading times,and decrease with the increase of row spacing.The upper growth rate of displacement is larger than that of the lower part,and the maximum value occurs at the pile head.When the row distance is 2.5d~4.0d,the peak value of horizontal displacement of pile body decreases rapidly with the increase of the row spacing.The bending moment of the pile body and its peak value increase with the increase of load or loading times.The peak value of bending moment of the back row straight pile appears in the middle of pile body and increases with the increase of the row spacing.The peak value of the front row inclined pile appears in pile head and decreases with the increase of the row spacing.In homogeneous sandy soil foundation,the back row straight pile will take the lead in bending failure in the middle of the pile body.The larger the row spacing is,the earlier the damage is.The front row inclined pile will translate firstly and then rotate around the bottom,and finally is destroyed at the top of the pile.In engineering practice,it is recommended that the row spacing should be 2.5 times of the diameter or side length of the pile,and the bending stiffness of the back row straight pile should be more than 2.5 times of the front row inclined pile.