Numerical Simulation of Rock Mass Structure Effect on Tunnel Smooth Blasting Quality: A Case Study

Taking the Zigaojian tunnel, Hangzhou–Huangshan high-speed railway, China, as background, the rock mass structure effect on smooth blasting quality was studied. Four rock mass structures were determined on the basis of the information collected on the tunnel site. Smooth blasting finite element models were established using LS-DYNA. The accuracy of the numerical calculation model was verified by comparing the overbreak and underbreak between the numerical simulation and monitoring. Orthogonal numerical test was used to study the rock mass structure effect through single factor and main effect analysis methods. With the decrease in rock mass integrity, the smooth blasting overbreak of tunnels with massive integrity structure, massive structure, layered structure, and cataclastic structure increased. For massive integrity structure and cataclastic structure, the peripheral hole spacing should be emphatically considered. Meanwhile, in massive structure and layered structure, the included angle and spacing of structural planes had a great influence on the smooth blasting quality. The research results could provide a reference to improve the quality of similar tunnel smooth blasting.

Numerical Simulation of Crack Evolution Mechanism and Subsidence Characteristics Effected by Rock Mass Structure in Block Caving Mining

In the block caving mining, the significant rock mass deformation and surface subsidence will be formed with the continuous extraction of ore. However, the internal crack evolution mechanisms in rock mass and associated subsidence characteristics present one of the key issues in rock mining engineering. Although block caving method has been used for many years, current knowledge of the crack evolution mechanisms, the subsidence characteristics under the influence of rock mass structure and subsidence prediction capabilities are limited. Based on the rock mechanics model provided by CEMI, crack evolution mechanisms and subsidence characteristics effected by the rock mass structure in block caving are numerically investigated using RFPA 2D, a numerical code based on FEM. Crack formation, propagation and coalescence in the overlying strata and the stress-balancing arch evolution in the stress field are represented visually during the whole process of extraction. The numerically obtained crack evolution shows that the stress-balancing arch has a significant influence on the fracture development of rock mass, and directly determines the slump form and rate of the rock mass. After understanding of the crack evolution mechanism in rock mass, the characteristics of surface subsidence are analyzed. Numerical experiments emphasize the geometrical configuration of joints and faults about mechanisms of subsidence development, including joints orientation, faults location and inclination, which can provide significantly meaningful guides for investigation of subsidence mechanisms and implementation of remedial measures.

Evolution Pattern and Matching Mode of Precursor Information about Water Inrush in a Karst Tunnel

The water inrush of the Shangjiawan karst tunnel is used to study the evolution pattern of precursor water inrush information in water-filled caves and to further reveal the matching mode of the information. The three-dimensional numerical method FLAC3D was used to simulate the evolution process of water inrush after damage to a water-blocking rock mass structure in a water-filled cave and to obtain the evolution pattern of precursor water-inrush information caused by the damage. The results show that the multifield response to the characteristic precursor information of the water-inrush pattern after the fracture of the water-blocking rock mass follows the order of stress-field displacement-field seepage-field. Further, the matching pattern of the information shows that the stress field increased first and then decreased, the displacement field always increased, and the seepage field increased first and then decreased.

Experimental Study on Sand Inrush Hazard of Water-Sand Two-Phase Flow in Broken Rock Mass

In the western region of China, coal mining activities are prone to induce water and sand inrush disasters, which seriously threaten the safe production of the coal resources. In this paper, an experimental device was designed to simulate the process of water and sand inrush, and then, the control factors of the disasters in the broken rock mass in the goaf were investigated. Also, the seepage fracture channels in the broken rock mass were simplified by using the 3D printing technology, and the effects of fracture aperture and angle on the seepage characteristics of water-sand mixtures were analyzed. The experimental results showed that the porosity and skeleton structure of the broken rock mass were the key factors to control the water and sand inrush disasters. The smaller the initial porosity of the broken rock mass, the weaker its permeability, and the less probable to form a dominant channel for the water and sand inrush disasters. Conversely, the broken rock mass structure with larger size gradation was more likely to form the permeable channels, and the quality of the sand inrush was greater. In addition, it was also found that the angle of the fractures within the broken rock mass affected the seepage characteristics of water-sand mixture, and the permeability showed an exponential relationship with the fracture angle. Meanwhile, as the fracture aperture increased, the fracture angle generated greater influence on the permeability. Finally, we proposed the water and sand inrush prevention and control technology based on the experiment results. The results of this study can provide a reference for the control of water and sand inrush disasters in western China.

Case Study of Roadway Deformation Failure Mechanisms: Field Investigation and Numerical Simulation

The safety of underground roadways is a major issue in mining engineering, with economic impacts and potential threats to the lives of workers. Elucidating the deformation failure mechanisms is necessary to solve these problems. The deformation failure modes and characteristics of roadways buried at various depths were investigated using a detailed field survey in the Jinchuan nickel mine. At greater depths, roadway deformation was more serious, the creep phenomena were more prominent, and support structures were more prone to failure. Numerical simulations were performed on the roadways under various geo-stresses and rock mass structures, which indicated that the roadway deformation mode was mainly controlled by a rock mass structure in a lower stress environment and the control effect was weakened with the gradual increase of ground stress. Six deformation failure types were proposed to examine roadway deformation failure mechanisms. Field representation of each failure type was characterized under natural or induced conditions. The findings provide a reference for stability evaluation and support the design of roadway engineering under similar geological conditions.

Geomechanical Model Experiment Study on Deformation and Failure Mechanism of the Mountain Tunnel in Layered Jointed Rock Mass

The Minxian tunnel is a key engineering of the Weiyuan-Wudu expressway that is excavated in layered jointed carbonaceous slate rock mass. During the construction process, the surrounding rocks of the tunnel encountered serious large deformations and failure, which brought about great difficulties to the safety and cost of the tunnel. In order to study the deformation and failure mechanism of the surrounding rocks, a physical model test was conducted, and integrated methods including strain gauges, a digital camera, and noncontact full-field digital imaging correlation technique were used to record the response information of the surrounding rocks. The evolution process of surrounding rocks failure was simulated successfully in the model test, and the deformation characteristics were basically consistent with the actual engineering. The modelling results show that concentrated stresses in the surrounding rocks were very uneven due to developed stratified and jointed rock mass structure. The maximum and minimum concentrated stresses appeared at the vault of the tunnel and left of inverted arc area, and concentration factors were 3.11 and 1.98, respectively. The main forms of surrounding rocks deformation and failure were large area spalling of surface, severe circumferential fractures, serious bending deformations of thin rock layers, and collapse of overlying strata. The maximum displacements occurred at left sidewall and right shoulder of the tunnel and the corresponding actual displacements were 460 mm to 500 mm. Caving and failure took place firstly at several key positions with maximum concentrated stresses or displacements and subsequently gave rise to massive collapse of surrounding rocks.

Geotechnical prerequisites for safe and efficient accessing and mining of thick coal seam in highlands

Bel-Alma deposit is located in the Batken region in Kyrgyzstan. Orographycally, the deposit occurs on the south shoulder of the Kichik–Alai ridge, 1–1.5 km away from the cognominal river. The local relief is high-mountain, rocky and heavily broken. Geologically, the deposit is composed of the Upper Paleozoic rocks, which underlay the stratified Meso-Cenozoic deposits, and amorphous loose overburden. The productive strata is the bottom range of the Sogul series of the Jurassic system. The total thickness of the series in the cross-section is 102.7 m. The Sogul series rocks feature erosion and distinct structural unconformity in the Paleozoic residuum. The overlying strata are represented by red conglomerates and sandstone of the Upper Cretaceous age. The geotechnical estimation of the properties of rocks composing the study area in Bel-Alma deposit is performed. The rock mass structure is determined using geological exploration cores. The parameters of stable pit wall and benches are preliminarily optimized and will be included in the ultimate pit limit design.