Abstract: It is essential to determine the mechanical properties of soils effectively during shield tunneling in the water-rich sandy pebble strata, which can be used to dynamically adjust the shield tunneling parameters. Since the conventional geological exploration cannot provide accurate strata parameters, the big data statistical analysis of stratum distributions and soil properties in Chengdu is conducted in combination with laboratory shear test and penetration test to explore the interaction between the mechanical properties of water-rich sandy pebble soils and the main parameters such as fines content, moisture content and water pressure. Test results show that with the increase in water content, the internal friction angle first decreases and then increases, while the interlocking force increases first and then decreases. The values of C and φ  decrease to a certain extent as the fines content increases from 1% to 6%. The formulae for describing the relations of two strength indices of soils (C and φ ) with the fines content and moisture content, as well as the equation for describing the relation between fines content and saturated moisture content, are derived. The feasibility of the proposed formulae is verified by fitting to the actual data. It is concluded that the failure pattern of the sandy pebble strata is piping type and the permeability of the sandy pebble strata declines as the fines content increases. Finally, the mechanism of the influences of tunneling parameters’ dynamic adjustment and the muck improvement process on construction is investigated by analyzing the characteristics of the excavated layers. The research results can provide a reference for the selection of the shear strength parameters of the water-rich sandy pebble soil layer used in empirical formula, value selection in numerical simulation, key tunneling technologies and construction plans in Chengdu area.

Key words: sandy pebble soil, shear strength, permeability, particle gradation, fines content, moisture content