Estimating Earth Pressure during Tunneling in Gravel-cobble Stratum by Considering Sensor-particle Size Effect

摘要

When tunneling in gravel-cobble stratum with earth balanced shield, the ratio between the diameters of the pressure sensor embodied in muck chamber and cut gravels is generally small. The small sensor-particle size ratio leads to considerable difference between the measured and actual earth pressure. This makes the configuration of earth pressure a difficult task and furtherly affects tunneling efficiency and safety. This work characterizes the variation of stress measurement error in a granular packing with consideration of the sensor-particle size ratio, the particle size distribution as well as the contact force distribution. The probability density function of stress measurement error is built according to a general probability distribution of inter-particle contact force. After then, a probability-based regressive procedure is proposed to estimate the applied stress with the measured stress. For stress samples with a same target stress but different biases, the stress estimated by the probability-based procedure has a minor variation and thus is more reliable than the arithmetic mean stress. Finally, the probability-based procedure is adopted to estimate the actual earth pressure of a well-tunneled section in Chengdu gravel-cobble stratum, according to which the lateral pressure coefficient of Chengdu gravel-cobble stratum is suggested as 0.20 - 0.28.