| The second double route of Lan-xin Railway goes through a large area of the Gobi, mainly in the form of subgrade. One of the most important problems occurring in the construction refers to how to choose technically feasible, economically reasonable and environmentally friendly stuffing for the subgrade. With the subgrade test section of Lan-xin subway’s second double route as the research object, the thesis has made a research of the basic engineering properties and detection techniques of coarsely grained soil in the Gobi, with such technological means of combined laboratory test and field investigation. Main research contents are as follows:(1) Experimental investigations of the basic physical and mechanical properties of the coarsely grained soil in the Gobi region. Through the experiment of particle analysis of two typical coarsely grained soil, it has been concluded that:the coarsely grained soil at Chaiwopu working point belongs to fillet-like coarse and round gravel soil and it also is the stuffing of A group. The coarsely grained soil at Hongqicun working point belongs to gravelly sandy soil and it is the stuffing of the B group, with less coarse particles, and its composition is optimized through mixing it with30%Gobi aggregates. Particle composition has a great influence on the best water capacity and dry density of stuffing, and the larger the coarse particle amount is, the larger dry density after compaction is. As the coarse particle compositions are different, there is a great difference in the best water capacity of different stuffings.(2) Gobi area of coarse grained soil strength characteristics analysis. Chaiwopu site soil structure is obvious compacting-frame type, Hongqicun site soil structure is substantially suspended-dense type.Through direct shear test,we can find that the proption of thick and thin material in filler have great influence on shear strength characteristics. Particle composition is the main factor that determine filler’s shear strength, When the coarse grained soil structure types showed dense-frame type, its shear strength would be higher.(3) Gobi area of coarse grained soil compression property analysis. Through the indoor compression test, the elastic deformation is only a small part of deformation,and plastic deformation is the majority of deformation in two kinds of moisture state compression process. Under the same load compression deformation of saturated specimen is significantly larger than specimen compression deformation of the optimum moisture content. Compression modulus increases with the increase of the compacting factor, so to enhance compaction factor is beneficial to improve the compression index effect. Group A filler’s water stability is better than group B filler’s water stability.(4) The study of compaction quality test. The compaction effect of Chaiwopu site round gravel soil is better than Hongqicun site gravel sand, well graded soil is easier compacted than poorly graded soil. Combined with laboratory direct shear test and field trial found,under the same degree of compaction, friction angle increases with the increase of content of coarse particles,d value increases with the increase of the friction angle, and the distribution of Evd value is more discrete. So Hongqicun site Evd value is far less than Chaiwopu site Evd value. |
