Chuanyong Qu

Experimental Analysis on Deformation Evolution and Crack Propagation of Rock Under Cyclic Indentation

Indentation-induced cracking may have many implications in rock drilling and cutting processes. In the present work, cyclic indentation tests have been conducted on Yunnan sandstones to investigate the deformation and failure process. Deformation fields on the sample surface have been obtained via the digital image correlation (DIC) technique. It has been found that the macroscopic force–indentation curve exhibits hysteresis and the residual displacements increase during the loading–unloading cycles. Furthermore, a median crack has been observed to nucleate, running almost parallel to the loading axis when the indentation force amounts to a critical value. Such a crack always results in the final failure of the sandstone samples. Experimental analysis reveals the deformation and failure mechanism of sandstone during cyclic indentation. By the DIC technique, the displacement distribution along the crack surface can be easily calculated and, hence, the fracture parameters, such as crack opening displacement and fracture toughness.

Modeling Specific Energy for Shield Machine by Non-linear Multiple Regression Method and Mechanical Analysis

The specific energy, defined as the energy consumption to complete the excavation of unit volume of the soil, can well describe the working efficiency of a shield machine. An identification model of the specific energy is established in this paper by introducing the mechanical analysis of the shield excavating process into the nonlinear multiple regression of the on-site data. The mechanical analysis of the shield-soil system helps to decouple the nonlinear multi-parameter problem and the regression process is conducted based on a group of on-site data of subway project in China. Fairly good consistency between the model results and the on-site recorded datum can be achieved. This work provides a useful tool for the analysis of the energy consumption of shield machines.

Mechanical model for operational loads prediction on shield cutter head during excavation

This paper presents a mechanical model to predict the operational loads acting on the cutter head of shield tunnel machine during excavation based on contact mechanics theory, in which the cutter head is considered as a rigid cylinder punch and the soil to be excavated is simplified as an elastic half-space. Then the estimation formulae of the operational loads are obtained and the influence of some key factors including the geological parameters, the radius of the cutter head and especially the excavation penetration can be analyzed based on the proposed model. The results show that the operational loads increase linearly when the machine works with a deeper excavation penetration. The prediction presented in this paper agrees with experimental results given by other researcher. It also can be seen that the geological condition affects both the quantity and the changing rate of loads with the excavation penetration. The proposed model may be a possible and feasible way to predict loads of shield tunnel machine.