A large air shaft engineered between the Olympic Sports Center Station and Century Avenue Station of the Lanzhou Metro Line one, China, occurred in strong permeable sandy gravel complex strata. The short distance between the Yellow River and the pit (shaft) resulted in many challenges during construction. These challenges mainly included the quick recovery of the water level and the difficulty of plugging the water. Some measures for monitoring the structural safety and response of the surrounding environment were taken. As the data showed, the design combined a bottom-up method with a top-down method using a peripheral cut-off wall for anti-seepage treatment, the underground diaphragm wall and the concrete bracing had a large rigidity, good impermeability and little influence on the surrounding environment in the process of dewatering and excavation, the external plastic concrete cut-off wall could contribute to the groundwater drawdown inside the pit and reduce the soil pressure on the retaining structure of the pit.

Performance of a deep excavation in Lanzhou strong permeable sandy gravel strata

Stability Evaluation Method and Support Structure Optimization of Weak and Fractured Slate Tunnel

This study investigates the distribution of pore water on the basis of the measured mass moisture content after soaking the tunnel insulation material. This study also analyzes the influence of the distribution of pore water on the thermal conductivity of the material on the basis of this mass moisture content. Scanning images of phenolic and polyurethane insulation boards are obtained by computer tomography (CT). The gray volume moisture content (Gv) is deduced based on the CT scanning images, to determine the distribution of pore water (Gv is the ratio of the volume of the water sample (represented by the gray value) to the volume of the saturated water sample (represented by the gray value) which is the gray volume moisture content of the sample). The correlation between gray volume moisture content and mass moisture content is determined by comparing different algorithms of gray volume moisture content and volume moisture content. The relationship between mass moisture content and thermal conductivity can be determined using a self-made quasi-steady-state tester, whereas the relationship between gray volume moisture content and thermal conductivity can be derived indirectly. Related experimental research can predict the thermal conductivity of thermal insulation materials by using a new perspective and shows the influence of pore water distribution on the thermal conductivity of materials.

https://downloads.hindawi.com/journals/amse/2020/9345615.pdf

Thermal Conductivity Characteristics of Thermal Insulation Materials Immersed in Water for Cold-Region Tunnels

The layered rock showed the characteristics in Mountain tunnel, Yunnan. A series of uniaxial compression tests and variable angle shear tests were carried out, and the aim was to investigate the effect of the bedding on its mechanical parameters and failure modes. The test results show that the uniaxial compressive strength, elastic modulus, and Poisson's ratio of layered rock present a U-shaped distribution with the increase in bedding orientation from 0° to 90°. All of them have a maximum when the bedding orientation is 0° and a minimum when the bedding orientation is 45°. The failure modes of layered rock can be summarized into three types: the fracture tensile failure parallel to the weak plane of bedding; the shear slip failure along bedding weak plane; and tension-shear composite failure between bedding weak plane and matrix. Based on the testing data and analysis results, it can be concluded that the layered rock specimen with different bedding orientations is an important reason for the anisotropy of mechanical parameters and failure modes.

/pdf/bedding-plane-effects-on-mechanical-behavior-of-surrounding-2gsd3ykd09.pdf

Bedding Plane Effects on Mechanical Behavior of Surrounding Rock in Mountain Tunneling

Water Content and Bedding Angle Effects on the Mechanical Properties and Micro-/Macro-Failure Mechanism of Phyllite

In order to provide guidance for Muzhailin tunnel design and construction, in this study, five groups of slate specimens with different bedding angles (β, angle between bedding plane and vertical a...

Effect of bedding angle on tunnel slate failure behavior under indirect tension

A combination of Hoek–Brown strength criterion and geological strength index (GSI) rock mass classification is a common method to determine rock mass strength. However, the conventional method invo...

Strength anisotropy of jointed rock slope considering mining damage: a numerical analysis method

The spatiotemporal variability of rock mass strength for jointed rock mass is crucial for the stability of open-pit mine slopes. The Dagushan Open-pit Iron Mine was taken as the background to systematically study the unloading damage and energy evolution of high slope jointed rock mass. Through a field survey of mixed rock slope and fuzzy C-means clustering optimization analysis, the random distribution parameters of two dominant joint sets of rock mass were determined, and a three-dimensional joint network of rock mass was reconstructed. Additionally, a numerical analysis method is proposed for the energy evolution of jointed rock mass considering the spatiotemporal variation of strength, and the variation trends of gravity potential energy, elastic strain energy, and dissipation energy of jointed rock slope were analyzed. Moreover, based on the cusp catastrophe theory, an energy criterion was established for jointed rock mass slope instability. Furthermore, the energy evolution mechanism of deformation and failure of jointed rock slope under mining was elucidated. The slope safety factor obtained from the energy cusp catastrophe dissipation energy cusp catastrophe is the same as that obtained from the limit equilibrium Janbu method.

Energy Catastrophe of Jointed Rock Slope Considering Spatiotemporal Variability of Strength


 In this study, the carbonaceous slate of Muzhailing tunnel was selected to explore the deformation and failure mechanism of tunnel layered slate under direct shear conditions. Five sets of direct shear tests were carried out on slate with different bedding dip angles (β: 0°, 30°, 45°, 60°, and 90°). The strength parameters, failure mode, fracture topography, dissipated energy, and acoustic emission (AE) characteristics were analyzed in detail to study the bedding effect of slate failure. The results show that the cohesion and internal friction angle of slate increases and decreases linearly with β from 0° to 90°, respectively, and the shear strength of bedding plane is lower than that of matrix. Additionally, the relative roughness (δ) of gray-scale image was defined, and the linear relationship between δ and root-mean-square height (Sq) was established to improve the efficiency of evolution of fracture topography. Furthermore, the shear energy consumption per unit area (us) was calculated, less sensitive to the variation of β. Moreover, a larger AE count and energy release rate were observed when the shear stress decreased, and a relative quiet period was observed before the peak loading. Additionally, both the count and energy release rate linearly decreased with the increase in β, and the proportion of tensile microcracks for vertical bedding is slightly higher than that for horizontal bedding. The main frequency of vertical bedding slate is smaller than that of horizontal bedding, i.e., the size of microcracks of slate with β of 90° is relatively larger. Generally, the frequency bandwidth of slate became narrower when β was varied from 30° to 60°, and the main frequency increased, indicating that the degree of shear failure of matrix is weakened. In contrast, the degree of cracking along the bedding plane increased.

Fuqiang Ren

Papers

Effect of bedding angle on tunnel slate failure behavior under indirect tension

Strength anisotropy of jointed rock slope considering mining damage: a numerical analysis method

Energy Catastrophe of Jointed Rock Slope Considering Spatiotemporal Variability of Strength

Bedding Effect of Carbonaceous Slate Failure Behavior at Direct Shear Tests