铁路路基下膨胀土地基浸水响应现场试验

Field tests on soaking response of expansive soil foundation under railway subgrade

在工程建设中,膨胀土大都属于非饱和土范畴。对高速铁路无砟轨道路基而言,膨胀土的胀缩变形可能加剧线路的不平顺性,影响高速铁路的正常运营。为研究铁路路基荷载下非饱和膨胀土土层在人工浸水后的变形特征,结合云桂铁路建设,设计并开展了铁路原型路基荷载下膨胀土地基现场浸水试验,并监测了从路基填筑开始到人工浸水结束时膨胀土地基与路基本体变形及浅层土水分的时程变化。试验结果揭示了膨胀土地基浸水饱和后的极限相对膨胀量、膨胀变形沿路基横向与地基深度的分布规律以及地基表面膨胀变形沿路基本体的衰减特征。基于试验成果,初步提出了以路基表面膨胀变形为0作为控制标准确定路基临界填高的设计思路。现场试验的设计原则与实施方法也可为今后研究铁路路基下膨胀土地基胀缩特性提供参考。

The expansive soil is classified as the unsaturated one in engineering construction. The swelling and shrinkage deformation of the expansive soil may cause intensified line harshness for the ballastless track on high-speed railway subgrade, affecting the normal operation of high-speed railway. To study the deformation characteristics of unsaturated expansive soil layer under lining of railway subgrade after artificial soaking, considering the construction of Kunming-Nanning Railway, field soaking tests on expansive soil foundation under railway subgrade are designed and carried out. Meanwhile, the time histories of deformations of expansive soil foundation and subgrade body, and moisture migration of shallow clay are measured from the beginning of subgrade filling to the end of artificial soaking. The test results reveal the ultimate deformation of relative expansion of expansive soil foundation after being soaked and saturated, distribution of swelling deformation along the cross section of subgrade and the depth of foundation as well as decay characteristics of swelling deformation of ground surface along the subgrade body. Based on the test results, the objective of the subgrade surface without swelling deformation control, which is used to determine the critical height of subgrade, is initially derived. The design principles and implementation methods of field tests can be used as a reference method for studying the swelling and shrinkage characteristics of expansive soil foundation under railway subgrade.