The unique structural characteristics and special symmetry of columnar jointed rock mass result in its complex mechanical properties and strong anisotropy, which seriously affects the safety of engineering construction. To better simulate natural columnar jointed rock mass, a geometric model reconstruction method based on a single-random movement Voronoi diagram of uniform seed points using the feasible geological parameters of horizontal polygon density, irregular factor, dip angle, strike angle, transverse joint spacing, and transverse joint penetration rate is proposed in this paper. Based on this method, numerical simulation of CJRM models with varying strike angles, dip angles, and irregular factors under uniaxial compression were conducted. The results show that the uniaxial compression strengths versus strike angle and dip angle both decrease with the increase in the irregular factor, showing a U-shape and a gentle W-shape, respectively. The strength anisotropy of the strike angle decreases from 1.1057 to 1.0395 with the increase in the irregular factor, indicating relatively isotropy. With the increase int the irregular factor, the strength anisotropy of the dip angle increases from 4.3381 to 6.7953, indicating an increasing strong anisotropy at a high degree, and the effect of the irregular factor on strength behavior has the strongest and weakest impact at the dip angles of 60° and 90°, respectively.

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Study on the Anisotropy of Strength Properties of Columnar Jointed Rock Masses Using a Geometric Model Reconstruction Method Based on a Single-Random Movement Voronoi Diagram of Uniform Seed Points

Columnar jointed rock mass (CJRM) formed by intact rock divided by special symmetrical columnar joints is a special type of rock with poor mechanical properties, strong anisotropy, and weak self-supporting ability, severely affecting the excavation safety and stability of underground tunnels. In this study, taking the Baihetan hydropower station as the engineering background, CJRM geological numerical models with different dip angles that combined well with the natural CJRM were generated based on the geological statistical parameters of the engineering site and were verified to have high rationality and accuracy. Tunnel excavation and overloading tests were carried out on these numerical models, and the results showed that the stress and displacement distributions after excavation exhibited strong anisotropic characteristics under different dip angles, and the positions where engineering safety problems are most likely to occur are the side walls, which are prone to stress-structure-controlled failure mode. The self-supporting ability at different dip angles after excavation from weak to strong are 45°, 60°, 75°, 90°, 30°, 0°, and 15°. The safety factors assessed by overloading for CJRM with dip angles of 0–90° degrees were 2.5, 2.6, 2.6, 1.8, 2.1, and 2.2, respectively, providing a valuable reference for the construction safety and support measures of CJRM excavation.

A Case Study on Tunnel Excavation Stability of Columnar Jointed Rock Masses with Different Dip Angles in the Baihetan Diversion Tunnel

The Columnar Joint Landscape of Mesozoic Acidic Volcanic Rocks in China

Optimization of temperature coefficient of resistivity and magnetoresistance of La0.67Ca0.33Mn0.98Fe0.02O3: Ag ceramics by Ag adjustment

Optimization of Temperature Coefficient of Resistivity and Magnetoresistance of La0.67ca0.33mn0.98fe0.02o3: Ag X Ceramics by Ag Adjustment

Columnar joints are native rupture structures which are ordered columnar forms in basaltic lava. The cracks and joints inside them are well-developed which lead to the weak self-supporting ability after excavation. At present, loose and collapse of columnar rock mass are the main problem in the hydraulic diversion tunnel. Based on field observation and test, this paper studied the failure characteristics of columnar joints in the diversion tunnel and simulated the failure mechanism. Based on this discussion, optimized support measures have been taken to ensure the safe construction of the diversion tunnel.

Failure Characteristics and Support Optimal Design of Columnar Jointed Rock Mass at a Diversion Tunnel

Electrical properties and enhanced low-field magnetoresistance of Mn2O3-added La0.7Ca0.3MnO3 ceramics

In order to study the seepage failure mechanism of roadway filling medium consisting of cohesive soil under complex hydrogeological conditions, a large-scale triaxial stress-seepage test system was utilized to investigate the influence of kaolin content and seepage loading rate on the seepage characteristics of filling medium. Through the analysis on the variation rules of sand loss and particle size distribution, the seepage characteristics and whole process of seepage instability of filling medium were explored in depth. It is concluded that (1) The seepage instability process of filling medium can be categorized into three stages: the initiation loss of fine clay, the accelerating loss of soil, and the stable status of soil loss. (2) The seepage failure process rate is proportional to the seepage loading rate and inversely proportional to the content of kaolin. (3) The kaolin and sand content of remaining mixture presented initial>bottom>middle>top status. The research results have guidance value for exploring the instability evolution mechanism of filling medium in deep roadway.

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Xiang Dong Zhu

Papers

Failure Characteristics and Support Optimal Design of Columnar Jointed Rock Mass at a Diversion Tunnel

Electrical properties and enhanced low-field magnetoresistance of Mn2O3-added La0.7Ca0.3MnO3 ceramics

Experimental Study of Seepage Characteristics of Filling Structures in Deep Roadway

Enhancement of Temperature Coefficient of Resistance and Low-Field Magnetoresistance in La0.7ca0.3mno3:Mno2 Composite

Studying near room-temperature magnetoresistance of A-site Sr-doped into La_0.67Ca_0.33Mn_0.98Fe_0.02O_3: Ag_0.15 ceramics