Research Of The Mechanical Characteristics Of Red-bed Of Drinking Water Project In Middle Part Of Yunnan Province And The Primary Classification Of The Tunnel Wall Rocks

Drinking water project in middle part of Yunnan Province is a livelihood project of which the length is252.650km. Tunnels take up86.50%of its total line and cross a numbers of regions full of red-bed soft rock including the Jurassic and Cretaceous mudstone, argillaceous siltstone, siltstone (including marlite) and sandstone etc.Based on field investigation of the red beds and examination of the Drinking water project in middle of Yunnan Province, the engineering characteristics of red-bed soft rocks are revealed and primary classification of wall rocks has been conducted combining with regional and engineering geological environment and the result has been proved reasonable by numerical simulation. Conclusions achieved are the follows:(1) According to the research on the mechanical properties of red-bed soft rocks, the compressive strength and shear strength are not high. The rock strength increases as the sandy ingredients increase and the loss of it is20%-30%when water-saturated. On the other hand, the rock strength decreases as the argillaceous portion increases and the loss of it is40%-50%when water-saturated.(2) The red-bed soft rock in middle part of Yunnan Province reveals the characteristics of disintegration and swellability. As for the same kind of rock, the anti-disintegration is better when the completeness is better. As for different kinds of rocks, the anti-disintegration gets worse when the argillaceous portion increases, and which has no direct relationsip with the dry-wet cycling times. However, the swellability is proportional to the clay mineral content in the agillaceous components of the rocks.(3) Research on the rheology and fracture properties show that: Creep deformation occurs when the external load is relatively small and the long-term strength is small which is less than60%of the instantaneous strength; the fracture toughness is low, which in every soft-rock layer is less than1MPa·m and will easily expand when forced.(4) Wall rocks classification according to BQ as combined with geological data and laboratory tests of red layer soft rock, shows that wall rocks in study area has been obviously controlled by its lithology and rock mass integrity, wall rock is mostly made of type Ⅳ. Combined with the classification, numerical simulation of the Liujiacun tunnel unstable wall rocks in different lithology combinations is done and the result shows that the deformation of wall rock gets bigger when the mechanical property is worse and the bed thickness is small, which corresponds to the BQ classification standard.