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The excess pore-water pressures (u) induced by piezocone penetration and their dissipation around the cone have been investigated by laboratory model tests and theoretical–numerical analyses. Based on the test results, a method for predicting cone penetration–induced distribution of u has been proposed. By numerical analysis using the predicted initial distribution of u it has been demonstrated that dissipation of the pore-water pressure measured at the shoulder of the cone (u2-type cone) is a two-dimensional (horizontal radial and vertical) process. A back-fitted coefficient of consolidation in the horizontal direction (ch) can be obtained by comparing the simulated and laboratory-measured two-dimensional dissipation curves. It has also been shown that a published method for estimating ch from measured nonstandard dissipation curves (in which u2 increases initially and then decreases) results in values of ch that agree well with values of ch deduced from the two-dimensional analysis.

ABSTRACT:The disc cutter failures during shield machine tunnelling in mixed-face ground were summarised by classifying the wear data gathered from the construction of Guangzhou Metro Line 7. The stress state of disc cutter and different effective factors in mixed-face ground condition were analysed. A prediction model for disc cutter wear in mixed-face ground was proposed taking the working status of TBM and the characteristics of geological conditions into consideration. The TBM parameters and geological characteristics of the north tunnel in Guangzhou Metro Line 7 was used to determine the prediction model. With the prediction model, the disc cutter wear of the south tunnel was predicted. The effectiveness of the prediction model was verified by comparing the predicted value and the actual value of the south tunnel.

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