砂填料桩承式路堤宏观土拱形态与演化模型

 基于目前研究很少关注土拱效应模型的适用条件和演化规律的现状，采用自制平面应变模型对砂填料桩承式路堤在不同桩间距下的宏观土拱形态，以及宏观土拱在桩间土下移过程中可能出现的演化现象进行探讨。模型试验将桩与土相互作用简化为桩间土挡板下移这一位移边界条件，配备可精确控制桩间土下移量的位移控制装置与摄影测量设备。每下移0.02 mm采集一张图片，采用图像分析软件追踪桩间土下移过程中路堤颗粒位移，实现全场位移量测。共进行3种填土高度下3种不同桩间距的模型试验。通过对9组试验填料内部滑移面的分析，揭示桩间土下移过程中均首先出现对称的三角形滑移面，即初始三角拱模型，之后继续增加桩间土下移量，初始三角拱模型存在2种不同的演化模式：在填土高度与桩距比＜1.8情况下，随桩间土下移量的增加滑移面逐级张开，称为三角多拱模型；在填土高度与桩距比≥1.8情况下，滑移面则逐级上移，演化为塔形多拱模型。最后，统计各模型的关键参数，为下一步土拱演化条件下的力学分析计算提供依据。

MACROSCOPIC SOIL ARCH SHAPE AND EVOLUTION MODEL OF SAND FILLING PILED EMBANKMENT

At present，there are few studies of applicable conditions of models and evolution laws of soil arching effect. To solve this issue，a new plane strain model test apparatus is developed to discover macroscopic soil arch shape under different pile spacings and the evolution process of soil arching during the settlement of soil between the piles. Soil and piles are simplified into removable plates and rigid plates，and the pile-soil interaction is simplified into relative settlement on the pile top，which could be simulated by moving the removable plates in a precise way. Photographic survey is applied to the model test. Every 0.02 mm when the plates settle，a photo is taken. Then whole field displacements of the embankment can be measured by tracing the particles. Nine groups of piled embankment model tests with 3 different filling heights and 3 different pile spacings are carried out with the new apparatus. A couple of symmetrical triangular sliding surfaces appear initially in all the 9 tests，which is called initial triangular arch model. Following two different evolution modes for the initial triangular arch model will be revealed with further moving the removable plates：in the case of H/(s?a)＜1.8，the initial triangular arch model will turn to be triangular multi-arch model with the increased settlement of soil between piles；in the other case of H/(s?a)≥1.8，the initial triangular arch model will evolve into pagoda-shaped multi-arch model with the increased settlement of soil between piles. Key parameters of different stages of the models are summarized，which will provide reference for the next mechanical analysis in soil arching development condition.