基于透明土技术的桩后土拱效应特征分析

为研究圆桩后土拱效应的特征及演化过程，从细观角度开展了基于透明土技术的桩土相互作用试验研究. 首先开展了透明土配比试验，获取物理力学性质适宜的土体；其次设计了试验系统并得到透明土与桩相互作用的散斑场图像；最后通过particle image velocimetry （PIV）技术分析得到位移矢量图，进一步分析得到透明土位移变化规律. 研究结果表明:通过位移矢量图可以得到圆桩作用下土体运动趋势及土颗粒的位移特征，并可进一步解译得到位移等值线构成的拱形结构，即桩后土拱结构，呈现出抛物线形，其范围与桩径、桩间距及深度有相关性；桩径越大，土拱区域越大，桩径30 mm时，土拱高达100 mm，桩土相互作用的影响范围越大；桩间距越大拱高最大值越大，桩间距80 mm时，土拱高也达100 mm；不同深度下土拱拱高在变化趋势上有较大的相似性，深度越深，土拱的最大拱高越小，深度50 mm时，拱高60 mm；通过拟合公式得到，土拱最大拱高沿桩身方向从桩顶至桩底呈逐渐减小趋势，同时随土体位移增加，表现出先增大，后趋于一稳定值的特征，其稳定值的大小与桩径呈正相关、桩间距呈正相关及深度呈负相关. 

Characteristics Analysis of Soil Arching Effect Behind Pile Based on Transparent Soil Technology

In order to study the characteristics and evolution process of soil arching effect behind a circular pile, an experimental study on pile-soil interaction based on the transparent soil technology was carried out from a microscopic perspective. Firstly, the tests as to transparent soil ratio were carried out to obtain the soil with desirable physical and mechanical properties. Secondly, the experimental system was designed and the speckle field image of the interaction between the transparent soil and pile was obtained. Finally, the displacement vector diagram was obtained through particle image velocimetry (PIV) technique, and the displacement variation rule of the transparent soil was further analyzed. The results show that the movement trend and displacement characteristics of soil particles under the action of the circular pile can be obtained through displacement vector, and the arch structure formed by displacement contour, namely, the soil arch structure behind the pile, can be further interpreted, as it presents a parabolic shape and its range is related to pile diameter, pile spacing and depth. The larger the pile diameter is, the larger the soil arch area is. When the pile diameter is 30 mm, the soil arch is up to 100 mm. Meanwhile, the pile-soil interaction affects larger region. The larger the pile spacing is, the larger the maximum arch height is. When the pile spacing is 80 mm, the soil arch height also reaches 100 mm. The soil arch height under different depths shows a similar trend. The deeper the depth is, the smaller the maximum arch height is. When the depth is 50 mm, the arch height is 60 mm. According to the fitting formula, the maximum arch height decreases gradually from the pile top to the bottom along the pile, and at the same time, it increases at first and then tends to stabilize with the increase of soil displacement. The stable value is correlated positively with pile diameter and pile spacing and negatively with depth.