砂填料桩承式路堤土拱效应模型试验

现有的桩承式路堤荷载传递计算方法主要依据3类土拱效应力学计算模型。由于宏观土拱形态观察的难度较大,现有计算方法普遍缺乏对不同填料与参数下拱效应传力机制以及宏观土拱拱形参数的深入探讨。采用自制的试验装置对砂填料桩承式路堤土拱效应模型进行探讨,进行了3组不同桩距比下3种填土高度的模型试验。模型试验装置配备了位移控制装置模拟与精确控制桩间土下沉,在下沉过程中连续、同步的采集土压力以及砂箱内部填料的照片,并通过摄影测量技术获取全场位移数据。通过对桩土应力比曲线特征以及曲线特征点所对应的填料颗粒位移图的综合分析,探讨了砂填料桩承式路堤拱效应传力机制,揭示了填料内部存在的初始三角形松动滑移面。基于此提出了初始三角拱力学计算模型,分析得到了滑移面角度随桩距比变化的规律,并利用滑移面夹角统计数据确定了拟合计算公式,通过力学推导建立了适用于砂填料桩承式路堤的桩土应力比计算方法。通过与Rogbeck法、BS8006法、Terzaghi法以及模型试验实测数据的对比,验证了计算方法的合理性。

Model tests on soil arching effects of piled embankments with sand fills

The load transfer methods for piled embankments are mostly based on 3 soil arching effect models. Most of these methods do not take into account changes of the arching effect mechanism under different fills and parameters for the difficulty of observing the macro soil arching. For each method, the same arch shape is always applied to all the situations. 3 groups of soil arching effect model tests with different pile spacings and sand-filling heights are done by using a model test apparatus. In the model tests, the settlement of soils is controlled by the displacement control device accurately. The soil pressures are measured and the pictures are collected during the settlement continuously and synchronously. Then, the photographic survey technique is used for measuring the overall displacement of the sand fills. The pile-soil pressure ratios are calculated and the feature point in the pile-soil pressure ratio curves are picked out. The force transfer mechanism of the piled embankment with sand fills is discussed. Triangular slide planes in the sand filling and the angles of slide planes’ change with the pile-spacing ratio are discovered. An initial triangular arching effect model is put forward based on these comprehensive analyses. A formula for the pile-soil pressure ratio is derived from the new arching effect model. The pile-soil pressure ratios under the model test situations are calculated by using the Rogbeck method, BS8006 method, Terzaghi method and a new method. The new triangular soil arching effect method is proved to best fit the actual measurements.