刚性桩复合地基支承路堤稳定破坏机理的离心模型试验

对上软下硬成层土地基中刚性桩复合地基支承路堤,进行了单排桩和群桩条件下路堤稳定破坏机理的离心模型试验,研究了不同桩体抗弯刚度和强度,不同桩体加固位置,不同桩间距和桩端嵌入硬土层深度条件下桩体的受力与变形性状,破坏模式以及路堤的失稳破坏机理.离心机试验结果表明,不论是在单排桩还是群桩条件下,桩身最大弯矩作用点均产生于软硬土层交界面附近;在群桩条件下,桩体越靠近路堤中心桩身弯矩越小;当桩身抗弯刚度与强度较高,桩距较大且桩下端嵌入较硬土层足够深度时,可产生桩间土体沿桩的绕流甚至因产生绕流而导致路堤失稳破坏;当桩身抗弯刚度与强度较低时,在单排桩条件下,桩体会首先在软硬土层交界面处发生弯曲破坏,并可在路堤失稳前在桩身上部发生第二次弯曲破坏,而在群桩条件下,坡脚附近部分桩体首先在软硬土层交界面附近发生弯曲破坏,并可能伴随桩体受拉破坏而使桩断为上下两段,最后由于部分桩体发生整体倾覆破坏或者再次发生弯曲破坏而导致路堤发生失稳破坏;针对路堤具体的破坏情况有针对性地增大桩身抗弯强度,减小桩间距或增加桩端嵌入硬土层深度均可提高路堤的稳定性.

Centrifugal model tests on failure mechanisms of embankments on soft ground reinforced by rigid piles

Centrifuge tests are carried out to study the embankment supported on the rigid pile composite ground. For all the test models, the upper layer of the ground is soft clay and the lower layer is stiff sand. The cases of using single-row piles and group piles are considered. The deformation behavior, load transfer and failure mechanisms of the piles and embankment are investigated with different pile bending stiffnesses and strengths, piles locations, pile spacings and embedded depth of pile toe into stiff stratum. The centrifuge tests show that in all the cases, the maximum bending moment of piles is located near the interface of soft and stiff strata. For the embankment on group piles, the closer to the embankment center the pile is, the smaller the bending moment is. When the piles have a high bending stiffness and strength, a large spacing, and a sufficient embedded depth into stiff stratum, soil may flow around the piles, which will lead to the overall failure of embankment. In contrast, for the single-row piles with a low bending stiffness and strength, the piles will fail firstly by bending failure mode at the interface of the soft and stiff strata, and then the secondary bending failure may occur at the upper part of the pile before the embankment failure. For the group piles with a low bending stiffness and strength, some piles near the embankment toe would also fail firstly by bending failure mode at the interface of the soft and stiff strata. Besides, the tensile failure may break the pile into two parts. In the final stage, the collapse failure or the secondary bending failure of the pile upper part will lead to the overall failure of embankment. According to the failure mechanisms of embankment, the embankment stability may be enhanced by the measures of increasing pile bending strength, decreasing pile spacing or increasing the embedded depth of pile toe into stiff stratum.