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The excavation by earth pressure balance (EPB) shield could cause stress fields varied, which is harmful to adjacent existing structures. Thus the effect of excavation clearance of the EPB shield on the settlement of existing structures should be taken into account. The transit tunnel from Meicun to Shangmeilin of Shenzhen Metro Line 9 constructed by the EPB shield with mid-shield-grouting was investigated. The deformation of existing tunnel is analysed by three-dimensional (3D) finite element methods (FEM). It is found that the settlement of overburden soil is obviously influenced by the structure of the existing tunnels through the plastic development of the soil. The rate of settlement is remarkable when the shield effect zone approaches the existing tunnels so that timely mid-shield grouting is an efficient method of controlling the settlement induced by the excavation clearance. However, the grout used in this method should be with the properties of short hardening time, large elastic modulus and low shear strength. Different standards of settlement control should be employed with respect to different underground tunnels, in which minimum elastic modulus of the filler that is usually determined by fitting function. This can be taken as a guide rule of the selection of material parameters in the project. The simulation results are in good agreement with the settlements measured for the existing tunnels and the ground surface. The parameter sensitivity analysis by means of the Spearman’s correlation coefficients shows that the elastic modulus of filling material significantly influences on the settlement of the existing tunnels and the ground surface. [ABSTRACT FROM AUTHOR]

This paper focuses on the influence of particle size distribution, test time, and moisture content on the Laboratoire Central des Ponts et Chaussées (LCPC) abrasivity coefficient (LAC). Image analysis and X-ray diffraction were used to analyze the particle shape characteristics and equivalent quartz content (EQC) of a sandy stratum. The test results show no significant differences in the shape characteristics and EQC of particles with different diameters obtained from the same sandy stratum. For the same EQC, the main factors affecting the LAC are particle size distribution, test time, and moisture content. An optimized effective size (ESop) index was established to represent different particle size distributions. The test results showed that the ESop index is more accurate than other indices in determining the LAC of soil samples, and the LAC had a linear relationship with the ESop index. Soil samples with moisture content less than the saturated moisture content have an LAC larger than that of a dry soil sample, and soil samples with moisture content greater than the saturated moisture content have an LAC similar to that of a dry soil sample. The influence of test time on the LAC of the soil samples could be divided into two stages, where the first and second stages are represented by a quadratic function and a linear function, respectively. [ABSTRACT FROM AUTHOR]