Research On The Influence Of Microstructure Of Red Beds Sandstone On Its Engineering Mechanical Properties In Longquan Mountain Area

Red beds are widely distributed in the southwest of China, it’s a common mass of civil engineering, and because of the low strength, soften by water, collapse after losing water, rheological characteristics it has been treated as special mass. In the area of reed beds, interbedded or interlayer phenomenon often appears between sandstone, siltstone and mudstone. In the layer of sandstone, two groups of conjugate joints often be found, it has a greater impact on the engineering properties. The main research object is red sandstone on Longquan Mountains, through the mineral composition and the characteristics micro-structural analysis and research on the difference of mechanical parameters and wave velocities, At the same time compared with the conglomerate, siltstone samples, and has yielded the following result:(1) Dissolution pores is often developed in the conglomerate; Scanning electron microscopy observation indicates that for sandstone the gray-green samples have a high cementation, and red-brown samples have more obvious pores, loose structure micro-fractures are developed.(2) In red beds sandstone and siltstone, there are significant differences between mechanics and wave velocity parameters of the vertical direction and the parallel direction, performance as:uniaxial compressive strength σc⊥>σc//, compaction segment displacement S2⊥> S2//, tangent modulus Eu⊥ Et//,the average of the longitudinal wave velocity Vp⊥< Vp//, but it does not show a clear consistency in shear wave velocity, the main reason for this difference is more micro cracks spread parallel with the bedding, but relatively less in the almost vertical direction.(3) The difference of mechanical parameters in red sandstone is mainly affected by the density of microstructures and the development degree of micro fracture, but has no clear relevance with particle size. Wave velocity and tangent modulus change with the uniaxial compressive strength varies in red sandstone and siltstone, while not in conglomerate and sandstone.(4) The uniaxial compressive strength in the red beds sandstone and siltstone is main between 24.6MPa to 70.5MPa, and their mechanical parameters change with the change of rock color. According to the double index classification of rock, conglomerate belongs to medium modulus ratio and low strength rock, Reddish brown sandstone and siltstone belong to low modulus ratio and low intensity rock, gray-green sandstone, Brown sandstone and siltstone belong to low modulus ratio medium intensity rock.(5) There are two groups of conjugate joints in red beds sandstone, it should be extensible fracture by inference. Statistical analysis shows, the size of the rock by joint cutting is mainly controlled by sandstone layers of thick and weathering degree. Joint development not only destroys the globality of engineering slope, but also provides abundant spaces for storage and seepage groundwater. So it has a great impact on the stability of slopes.