青藏铁路多年冻土区路基变形裂缝发生机理及其防治

MECHANISM AND PREVENTION OF DEFORMATION CRACKS OF EMBANKMENTS IN THE PERMAFROST REGION ALONG QINGHAI-XIZANG RAILWAY

青藏铁路多年冻土区路基工程的修建 ,改变了路基基底多年冻土的热量平衡状态。通过对青藏铁路多年冻土区试验工程和已经施工的路基工程所发生的变形裂缝的调查和分析 ,认为多年冻土区路基几何尺寸不对称和路基边坡坡向不同导致的路基人为上限形态不同 ,是造成多年冻土区路基温度场不对称以及基底土体冻结融化过程不同步的主要原因 ,也是造成路基变形裂缝的主要原因。文章在此基础上提出了减少或消除路基温度场不对称 ,从而减少或消除这类变形裂缝的主要工程结构形式和工程措施 ,作者的看法和结论已经在2 0 0 3年青藏铁路冻土区路基工程设计和成形路基补强工程措施设计中得到广泛应用。

In the first two frost-thaw cycles after construction of embankments in the permafrost region along Qinghai-Xizang railway, part of testing embankments and part of the construction′s embankments show different degrees of secondary engineering diseases (deformation cracks on the slope and top of embankments ) caused by cryogenic process of permafrost. For investigating deformations and cracks derived from deformations of permafrost embankments, we study and analyze the temperature sub-area of permafrost, the ice content in frozen soils and shape of embankments′ structures. We find that the deformation of embankments actually is composed of compress deformation of soil under embankments and the embankments itself, deformation of thaw settlement during frost-thaw cycles and deformation of frost heaving. Thaw settlement, frost heaving deformation of embankments and the surface change caused by these deformations, as deformation cracks, are results of cryogenic process or cryogenic phenomenon of permafrost from essence of engineering geocryology. There are two kinds of deformation of railway embankments, transverse cracks and longitudinal cracks. Geometry asymmetry and difference of slope direction cause the difference of temperature, shape asymmetry of permafrost table and variation of thaw-frost pace under railway embankment. This is the direct reason of deformation cracks on railway embankments. Therefore, we put ripped-stone and gravel protection slope structures in order to reduce heat passing into ground. At the same time, using the different effect of diverting heat and hiving cold to different size of ripped-stones and gravels, we correct asymmetry of temperature fields and variation of thaw-frost pace so as to control the development of the cracks. These engineering measurments have been widely used in the design and construction of the embankment in the permafrost area along the Qinghai-Xizang railway.