Laboratory Study On Mechanical Properties And Improvement Of Red Sandstone In Lanzhou Area

With the continuous development of China's infrastructure construction,large-scale engineering construction in the northwest region is developing rapidly.With more and more deep excavation,how to deal with a large amount of earthwork excavated not only involves local environmental protection issues,but also directly affects project cost.A large number of red sandstones were excavated during the construction of several subway stations on Line 1 of Lanzhou Metro.If they are used as backfill after proper treatment,they will produce good economic and environmental benefits.Relying on the Dongfanghong Square Station Project of Lanzhou Metro Line 1,taking the red sandstone in Lanzhou area as the research object.Through a lot of laboratory tests,field tests and numerical simulation,the physical and mechanical properties of undisturbed red sandstone and modified red sandstone soil in this area are studied,and the effects of different modifiers on their physical and mechanical properties are analyzed.The main work and conclusions are as follows:(1)Firstly,the gradation of undisturbed red sandstone is studied by particle analysis test.Secondly,the microstructure and element composition of the red sandstone are analyzed by scanning electron microscopy.Then the cohesion,internal friction angle and compression modulus of undisturbed red sandstone are determined by direct shear test and consolidation test.The test results show that the physical and mechanical parameters of red sandstone in Lanzhou area are quite different from the empirical values.(2)The compaction test of red sandstone remolded soil with single modifier is carried out to determine the maximum dry density of red sandstone remolded samples under different modifiers.The direct shear and consolidation tests of red sandstone remolded soil under the maximum dry density are carried out,and the results of the improved remolded sample test and the original sample are compared.The results show that the physical and mechanical properties of the red sandstone remolded soil have been improved by adding a single modifier.(3)Taking cohesion and internal friction angle as evaluation indexes,orthogonal tests are carried out to determine the optimum mix ratio of red sandstone remolded soil with various modifiers,and the effects of different additives on shear strength parameters of red sandstone remolded soil are analyzed according to the test results.The test results show that the compressive modulus and cohesion of the remolded samples are greatly increased by cement,and the internal friction angle is partly increased by loess.(4)The direct shear and consolidation tests of red sandstone remolded soil under the optimum mix ratio show that its physical and mechanical properties have been greatly improved.At the same time,the results of water immersion test on the remolded samples showed that the water stability is good,indicating that the loess did not significantly affect the remolding samples after immersion.(5)Direct shear and consolidation tests of undisturbed red sandstone and red sandstone remolded soil with optimum mix ratio are simulated by PFC software.The results show that on the basis of improving the shear strength of red sandstone remolded soil,loess and cement have a great influence on the failure mode of red sandstone,and greatly improve the compressive modulus of red sandstone,which also improves its deformation resistance.