| At present, China’s urban railway transit construction is in full swing, which has widespread geographical distribution and various geological conditions. Due to properties of strength, deformation and fracture of expansive soil, underground structures of urban railway transit could be affected by the special strata, few relevant research results of underground structures of urban railway transit are found in expansive soil stratum area, studies of which have important implications.Design theory and key technology of underground structures of urban railway transit,including shield tunnel, shallow buried tunnel and deep foundation pit, are studied by theoretical derivation, data research, numerical simulation and field test, combined Hefei railway transit. The following conclusions are obtained:Expansive soil factors on underground structures of urban railway transit are identified,including reduction of expansive soil strength and additional expansive stress field caused by surface rainfall, groundwater level changes and construction. Logarithm of c, φ are negative linear correlation with the moisture content. Expansion force or expansion deformation and moisture content is approximately linear. The scope and distribution of stratum water content are gained, which caused by the three factors. The additional expansive stress field can be simulated by using equivalent thermal stress field and key parameter of which is proposed.Based on elastic theory, the analytical solution of ground displacement and stress caused by deep buried circular tunnel excavation in general stratum is deduced. By refering displacement potential function, the analytical solution of ground displacement and stress caused by additional expansive stress field is deduced. Superposition of two above parts is the analytical solution caused by deep buried circular tunnel excavation in expansive soil stratum. Based on image method, the analytical solution of ground displacement and stress caused by shallow buried circular tunnel excavation is deduced in general stratum. The analytical solution of ground displacement and stress caused by additional expansive stress field is deduced reversely. Superposition of two above parts is the analytical solution caused by shallow buried circular tunnel excavation in expansive soil stratum. By comparing additional stress and displacement of deep tunnel and shallow tunnel, additional expansive stress field has greater impact on shallow tunnel. Ground displacement and stress can provide the basis for tunnel design in expansive soil stratum area.Based on Terzaghi relaxation pressure formula, correction of vault load calculation method of shield tunnel is gained by analyzing reduction of expansive soil strength caused by the three factors. Regulation of earth pressure on shield tunnel segment caused by additional expansive stress field is gained by numerical simulation, which values are proposed. Superposition of two above parts is correction of earth pressure method of shield tunnel in expansive soil stratum. Integrated resistance coefficient of grouting layer-ground is deduced. And design method of shield tunnel segment in expansive soil stratum is proposed,which rationality is verified through field test. A 3D numerical simulation method reflecting the characteristic of the whole tunneling process in expansive soil stratum is established,ground disturbance caused by shield tunnelling in Hefei expansive soil stratum by using the method.Based on Xiejaiixao pressure formula, correction of vault load calculation method of shallow buried tunnel is gained by analyzing reduction of expansive soil strength caused by the three factors. Regulation of earth pressure on shallow buried tunnel caused by additional expansive stress field is gained by numerical simulation, which values are proposed.Superposition of two above parts is correction of earth pressure method of shallow buried tunnel in expansive soil stratum, which rationality is verified through field test. Baded on limit equilibrium theory, boundary of deep tunnel and shallow tunnel in Hefei area is gained.Reasonable parameters are proposed by analyzing construction parameters of shallow buried tunnel in Hefei expansive soil stratum.Regulation of earth pressure of deep foundation pit is gained by analyzing different displacement mode with effect of moisture content changement and rainfall. Correction of calculation method of earth pressure of deep foundation pit is proposed based on Rankine pressure formula. No-changing-strut method in Hefei expansive soil stratum is proposed by compared with normal change support method, and which rationality is verified through field test of Wanghucheng station in Hefei railway transit line 1. |
