Scientific problems and research proposals for Sichuan–Tibet railway tunnel construction

Application of a micro-model for concrete to the simulation of crack propagation

Based on the upper limit theorem of limit analysis and the Hoek-Brown failure criterion and considering the adverse influence of the seepage force, we established a stability analysis method of analyzing the water-resistant rock mass of a karst tunnel face, developed a critical safety thickness criterion for water inrush caused by the instability of the tunnel face, and conducted a sensitivity analysis of the main influencing parameters. We defined the safety coefficient (k) of the tunnel face’s resistance to water-inrush instability during the tunnel excavation process and analyzed the dynamic evolution characteristics of the tunnel face’s stability during the tunnel construction according to the safety coefficient. We used the method introduced in this paper to calculate the safe thickness of the water-resistant rock mass of the Xiema tunnel face in the first horizontal line of the Chongqing Expressway where it is adjacent to karst cavity 268. We compared these results with the calculation results of a method that did not consider the adverse influence of the karst water seepage force. The results showed that the safety thickness of the water-resistant rock mass calculated using the method proposed in this paper more accurately conformed to the actual situation of the project, which can more effectively ensure the construction safety of the tunnel segment adjacent to the anterior, concealed, high-pressure, water-rich karst cavity. The results of this study hold great significance for improving the predictability and targeted prevention of water-inrush disasters in karst tunnels.

Upper limit analysis of stability of the water-resistant rock mass of a Karst tunnel face considering the seepage force

Tunnel excavation by cyclic blasting caused accumulative damages to the surrounding rocks, reducing the intactness of the rock mass. The blasting impact contributes to the formation of an excavation damaged zone (EDZ) around the tunnel, which may induce disasters such as surrounding rock failure and roof collapse, hazarding the construction safety. This study, in view of Lame’s equation and Hoek–Brown’s failure criterion, deduced the equation of the strength reduction coefficient and established a method to calculate cyclic blasting disturbance factor D based on the wave velocity decrease rate. After modifying Hoek–Brown criterion parameters mb and s based on the geological strength index, a method to calculate the thickness of the EDZ near the tunnel face was established, which quantified the EDZ range under the cyclic blasting disturbance. Subsequent theoretical calculations demonstrated a “three-stage” variation trend of the EDZ under cyclic blasting and revealed the EDZ thickness variation law with different excavation radii, initial stresses, rock strengths of surrounding rocks, disturbance factors, and lateral pressure coefficients. 

Thickness Calculation of Accumulative Damaged Zone by Rock Mass Blasting Based on Hoek–Brown Failure Criterion

Tunnel excavation by cyclic blasting caused accumulative damages to the surrounding rocks, reducing the intactness of the rock mass. The blasting impact contributes to the formation of an ...

Peridynamic micro-elastoplastic constitutive model and its application in the failure analysis of rock masses

The invention provides a lifting arm rack for a model test system and a working method, and relates to the field of model tests; the lifting arm rack comprises a first support and a second support; double-rocker mechanisms are hinged to the two sides of the first support respectively, and connecting rods corresponding to the two sets of double-rocker mechanisms are connected through a fixing plate; a loading mechanism is mounted on one side, facing the first support, of the fixing plate and is used for loading the test piece; the double-rocker mechanism is matched with a telescopic rod; one end of the telescopic rod is hinged to the double-rocker structure; the other end is hinged to the second support; the loading mechanism is connected with the support through a four-bar mechanism. The position of the loading mechanism is switched through swinging of the four-bar mechanism; when the test piece is installed, the loading mechanism withdraws from the path of the installation process ofthe test piece, after installation is completed, the loading mechanism restores to the original position to conduct loading operation, so automation of movement of the loading mechanism is achieved, the positioning precision of the working position is improved, and the test process is tightly connected.

Bai Songsong

Papers

Peridynamic micro-elastoplastic constitutive model and its application in the failure analysis of rock masses

Lifting arm rack for model test system and working method