大直径嵌岩灌注桩承载特性试验与有限元模拟

Test and Finite Element Simulation of Bearing Characteristics ofLarge Diameter Rock-Socketed Cast-in-Place Pile

基于青岛某工程的4根大直径嵌岩灌注桩,在现场开展了单桩竖向抗压静载试验和桩身完整性测试,以明确大直径嵌岩灌注桩在竖向荷载下的承载特征,拟揭示不同荷载水平下嵌岩灌注桩的承载力发挥机制。结合不同嵌岩深度的单桩承载性能有限元模拟,重点分析了单桩在不同嵌岩深度下的竖向抗压承载特性和桩土位移分布特征。研究表明:在笔者试验条件下,大直径嵌岩灌注桩单桩竖向抗压承载力具有一定离散性,桩头部位的损坏会极大影响单桩承载力的有效发挥;加载完成后,数值模拟得到的桩顶沉降量为31.56 mm,约为现场实测值的1.1倍,模拟结果与实测结果较为吻合;通过不同嵌岩比的模拟结果对比发现,嵌岩深度越大桩端阻力占桩顶荷载的比例越小,且桩端阻力占比的变化速率随着嵌岩比的增加逐渐减缓;嵌岩深度取2.5倍桩径为宜。

Based on four large-diameter rock-socketed cast-in-place piles in a project in Qingdao,the vertical compressive static load test for single pile and the pile body integrity test were carried out on site,to clarify the bearing characteristics of large-diameter rock-socketed cast-in-place piles under vertical loads and reveal the bearing capacity mechanism of rock socketed cast-in-place piles under different load levels.Combined with the finite element simulation of the bearing capacity of a single pile with different rock-socketed depths,the vertical compressive bearing characteristics and pile-soil displacement distribution characteristics of a single pile at different rock-socketed depths were mainly analyzed.The research results show that under the test condition of the writer,the vertical compressive capacity of single large diameter rock-socketed cast-in-place pile is discrete,and the damage of pile head will greatly affect the effective performance of the bearing capacity of single pile.After loading,the settlement of pile top obtained by the numerical simulation is 31.56mm,which is about 1.1 times of the measured value on site.The simulated results are in good agreement with the measured results.By comparing the simulation results of different rock-socketed ratios,it is found that the larger the rock-socketed depth,the smaller the ratio of pile tip resistance to pile top load,and the change rate of pile tip resistance ratio gradually slows down with the increase of rock-socketed ratio.It is advisable to take 2.5 times the pile diameter for the rock-socketed depth.