A Tentative Discussion on the Genetic Mechanism of the Cleavable Zone along the Yunnan-Tibet Border Sector of the Yunnan-Tibet Railway Line and an Analysis of its Engineering Effect
滇藏铁路沿线滇藏交界段劈理化带成因探讨及工程效应分析

The newly discovered cleavable zone along the Yunnan-Tibet border sector of the Yunnan-Tibet railway line is a transitional tectonic type with close-spaced fractures between the cleavage type and the joint type, which is closely related to the river slope in the gorge area between high mountains. Based on relatively comprehensive survey, mapping and statistic analysis, the authors have reached the conclusion that the cleavable zone is distrib-uted in the discontinuous banded form, with its scale in relation to the river slope scale, so there exist large-sized zones along the Jinsha River and the Lancang River, and that the cleavable zone is in connection with the local micro-landform. In addition, the "cleavage" in the zone is characterized by steep dip angle and uneven interval, with its strike usually paralleled to the local river orientation. The zone was generated by the interaction between the endokinetic process and the exogenous process. This means that the cleavable zone could be generated by the endokinetic process, and that on the basis of the endokinetic process, the cleavable zone along rivers could also be formed by the exogenous process. Furthermore, the cleavable zone could be altered by later endokinetic or ex-ogenous process. The scheduled Yunnan-Tibet Railway will pass through many cleavable zones, and there might oc-cur serious deformation of railway foundation, tunnel and bridge, collapse over tunnel, percolation around tunnel, and geohazards such as landslide, collapse and debris flow. It is suggested that we should take appropriate control meas-ures to tackle these problems in the construction and operation processes of the railway and other projects.