Search Results (11)

The escalating disasters caused by the movement of shallow buried strata in China’s western mining areas are increasingly threatening operational safety. A critical issue in ensuring secure mining practices in these areas is the creep failure of weakly cemented soft rock under low-stress conditions. The unique particle contact mechanisms in weakly cemented mudstone, combined with the persistence of the cemented materials and the particulate matter they form, lead to mechanical responses that differ significantly from those of typical soft rocks during loading. Building on an existing multivariate linear regression equation for new similar materials, this study developed qualified weakly cemented medium similar materials, offering appropriate materials for long-term creep tests of weakly cemented formations. This was accomplished by employing orthogonal proportioning tests. The principal findings of our investigation are as follows: The new, similar material exhibits low strength and prominent creep characteristics, accurately simulating weakly cemented materials in western mining areas. The concentration of rosin–alcohol solution has a measurable impact on key parameters, such as σ_c, E, and γ in the weakly cemented similar material specimens. Furthermore, the creep characteristics of the specimens diminish progressively with an increase in the proportion of iron powder (I) and barite powder (B). The material was applied to a similar indoor model test simulating the weakly cemented material surrounding the auxiliary haulage roadway in Panel 20314 of the Gaojialiang Coal Mine, with speckle analysis employed for detailed examination. The experimental findings suggest that both the conventional mechanical properties and long-term creep characteristics of the material align with the required specifications, offering robust support for achieving optimal outcomes in the similar model test. Full article

The time-dependent deformation control of weakly cemented soft rock in deep underground engineering is a critical scientific issue that directly affects the long-term stability of roadways. Traditional Nishihsara models encounter limitations in accurately capturing the weakening effects of material parameters during rock creep failure and in describing the accelerated creep stage, making them insufficient for analyzing the creep failure mechanisms of weakly cemented surrounding rock. To address these limitations, this study integrates SEM and X-ray scanning results to reveal the microscopic degradation process during creep: under external forces, clay minerals, primarily bonded face-to-face or through cementation, gradually fracture, leading to continuous microcrack propagation and progressive parameter degradation. Based on damage theory, an enhanced Nishihara creep model is proposed, incorporating a time-dependent damage factor to characterize the attenuation of the elastic modulus and a nonlinear winding element connected in series to represent the accelerated creep stage. The corresponding three-dimensional constitutive equations are derived. Using the Levenberg–Marquardt (L-M) algorithm for parameter inversion, the model achieves over 98% fitting accuracy across the full creep stages of weakly cemented soft rock, validating its applicability to other rock types such as salt rock and anthracite. The damage creep model is numerically implemented through secondary development in FLAC3D 6.0, with simulation results showing less than 5% deviation from experimental data and the failure mode is similar. These findings provide a solid theoretical foundation for further understanding the creep behavior of weakly cemented soft rocks. Full article

In the western mining region, weakly cemented rock layers above the coal seams often lead to frequent catastrophic accidents during mining due to their instability. To address this, this paper analyzes the movement characteristics of surrounding rock in the recovery roadway and the effectiveness of from nearby large coal pillar roadways. A mechanical model for the failure of weakly cemented roadways was established, and numerical simulations were used to verify the feasibility of leaving small coal pillars along soft, thick coal seams. Additionally, existing measurements were used to evaluate the impact of leaving small coal pillars on the deformation of the surrounding rock in the recovery roadway. The results show that after changing the coal pillar retention to 5 m in the 130,205 working face of the Yangchangwan mining area, the roadway is in a low-stress zone, with minimal surrounding rock deformation, meeting safety requirements for production. Full article

Based on the engineering background of weakly cemented roadways and adjacent chambers in Western China, a numerical simulation method was used to examine the changes in stress distribution and increment in the surrounding rock of weakly cemented roadways adjacent to chambers. The results show that the surrounding rock stress of the weakly cemented roadway adjacent to the chambers increases by approximately 30%. The vertical stress of the surrounding rock mainly expands along the vertical direction, and the expansion range is 7–12 times that of the chamber height. The horizontal stress of the surrounding rock mainly expands along the horizontal direction, and the expansion range is 3–6 times that of the chamber width. Based on the support idea of “allowable deformation” + “relief pressure” + “maintaining roadway shape”, the support technology of weakly cemented roadways adjacent to chambers is established with “full section U-shaped steel shed + filling flexible materials between the steel shed and surrounding rock + patching the roof bolt + laying concrete on floor”. An engineering test based on the above support technology was carried out, and it was found that the deformation of the weakly cemented roadway adjacent to the chambers was 0 in 20 days. Full article

The Baishitou Tunnel of the Dali–Lincang railway project is a weakly cemented surrounding rock tunnel with geological bedding bias. The deformation of the surrounding rock on the side with the greatest stress is nearly 1 m, which seriously affects construction progress and significantly increases construction cost. In order to achieve the goal of safe, efficient, economic, and socially sustainable development in tunnel construction, it is necessary to study the large deformation of weakly cemented surrounding rock in the geological bedding bias tunnel. Engineering technicians first used field measurement methods to monitor the pressure and deformation of surrounding rock and studied the deformation law of surrounding rock pressure and deformation over time. Secondly, numerical simulation methods were used to study the stress distribution law, plastic failure depth, and initial support stress of tunnel-surrounding rock under different support schemes, and they independently designed a yielding anchor bolt with enhanced anchoring, which plays a key role in controlling the deformation of the surrounding rock. The main conclusions are as follows: (1) Through the analysis of the measured pressure data of the initial branch of the section and the displacement monitoring data of the measuring point, it is found that the deformation of the surrounding rock of the weakly cemented tunnel is large and fast. At the same time, the pressure and deformation of the surrounding rock of the tunnel are greatly affected by geological bedding bias. After the excavation of the inverted arch, the pressure and deformation of the surrounding rock at the right arch shoulder of the tunnel are the highest, reaching 0.832 MPa and 0.53 m, which are significantly greater than those on the left arch shoulder. (2) Using the numerical simulation software FLAC3D 5.0 and ANSYS 16.0, a three-dimensional numerical model of the roadway was established to simulate the stress distribution, plastic failure depth, and initial support stress of the tunnel’s surrounding rock under the influence of geological bedding bias. By comparing the support effects of different support schemes, it was concluded that under the support scheme of “I25 arch + yielding anchor bolt”, the surrounding rock failure depth was small, the stress concentration was weak, and the initial support deformation was controllable as a whole. (3) The self-designed yielding anchor bolt has good economic and applicable value, and it has received the expected support effect after field verification. (4) Various special support measures such as advanced grouting anchor rods, casing arches, or temporary cross supports are used to assist in controlling the large deformation of weakly cemented surrounding rock tunnels to a certain extent. Full article

This study examines frequent disasters, including large-scale deformation and collapse, caused by underground mining in weakly cemented strata in Western China. The weakly cemented rock’s unique characteristics, including low strength and easy disintegration, demonstrate a different damage pattern than that traditionally seen in the central and eastern regions. Using Fast Lagrangian Analysis of Continua-Particle Flow Code (FLAC2D-PFC2D) coupling, we model the strata, focusing on the 3-1 coal seam roadway at Hongqinghe mine. This study investigates the damage–rupture–destabilization progression in the peripheral rock under varying levels of moisture content. Our findings indicate that a water content of ω = 5.5% is the threshold for roadway damage, and moisture content <5.5% yields minimal rock deformation. However, moisture content >5.5% abruptly increases cracks and shifts the rock’s force chain, causing significant deformation and affecting the ceiling the most. Moreover, higher levels of moisture content weaken the anchor solid’s performance, with two primary failure modes: anchor interface slippage (comprising five stages: elasticity, elasticity–shear hardening, elasticity–shear hardening–decohesion, shear hardening–decohesion, and decohesion) and shear damage. These insights are vital for improving numerical simulations of underground mining, obtaining a more accurate understanding of mineral pressure disasters in weakly cemented strata mining regions in Western China, and developing a solid foundation for the better control of such strata. Full article

Maintaining the stability of the surrounding rock is an important prerequisite in ensuring the safe and efficient construction of underground mines—in particular, the surrounding rock of the cross-layer roadway, which is a combination of different media with different lithologies. Numerical models were established to investigate the effects of the different lateral pressure coefficients (λ), the angle (α) between the roadway and the maximum horizontal principal stress, and typical lithological combinations on the deformation of the surrounding rock of weakly cemented roadways. The main outcomes obtained from our research indicated the following: (1) under the action of tectonic stress, the focus should be on strengthening the roof of the roadway support of the slab, which is conducive to the stability of the surrounding rock; (2) roadway deformation and failure for the cases λ < 1.5 are approximately symmetrically distributed, whereas those for the cases λ > 1.5 are asymmetric; (3) roadway deformation and failure for the cases α < 45° are approximately symmetrically distributed, whereas those for the cases α > 45° are asymmetric; (4) tectonic stress has an important influence on stress redistribution, deformability, and damage in cross-layer roadways; and (5) when excavating cross-layer roadways under the action of tectonic stress, the concentrated stress around the end of the working face (especially the bottom corner) should be reduced. The research results provide insights for the roadway layout through coal seam and cross-layer excavation and deepen the understanding of the deformation mechanism of weakly cemented cross-layer roadway under tectonic stress. Full article

Aiming at the problems of large deformation, long duration, and difficult control of floor heave in gob-side entry driving in weakly cemented soft rock, this paper takes the weakly cemented soft rock mining area in Western China as the engineering background, and studies the characteristics and mechanism of floor heave in gob-side entry driving in weakly cemented soft rock by means of a field investigation, physical component analysis, mechanical property tests of the surrounding rock, and the stress monitoring of the surrounding rock. The classification control method of floor heave is put forward, and field tests are conducted. The results show that: (1) The floor heave characteristics of the dynamic change in the floor heave peak position of gob-side entry driving from the coal pillar side to the mining side are obtained through field observation. (2) Based on the analysis of field data and laboratory test data, it is concluded that the stability time of the overlying strata in gob-side entry driving is about 8 to 12 months. The main internal cause of roadway floor heave is the low load resistance of weakly cemented soft rock. High stress and strong disturbances are the main power sources of strong floor heave. The mechanism of floor heave affected by dynamic lateral abutment pressure is summarized, and the classification control method of floor heave is proposed. (3) The gob-side entry driving support technologies of “adjusting excavation deployment” and “surrounding rock pressure relief and improving support” are proposed. Through field tests, the floor heave can be effectively controlled. Full article

Weakly cemented rocks are characterized by low strength, loose structure, and easy disintegration. High-intensity mining activities can damage and rupture such rock bodies and induce damage, such as flaking and roofing on roadways. To reveal the mining intensity influence on the weakly cemented rocks’ deformation and damage, a numerical particle flow model of weakly cemented sandstone was established based on particle flow theory. Uniaxial compression simulation tests were conducted at four loading rates of 0.01, 0.1, 0.5, and 1 mm/min to study the weakly cemented sandstone’s stress–strain relationship, damage rupture, acoustic emission, and energy evolution. The results show that, with an increased loading rate, the uniaxial compressive strength of weakly cemented sandstone increases exponentially, and the rupture mode transforms from brittle damage to ductile damage; the greater the loading rate, the greater the degree of damage and crushing range of the rock. Further, with an increased loading rate, the peak hysteresis of rock acoustic emission events decreases, and the number of events increases; the energy accumulated in the rock increases, thus intensifying the degree of rock damage. Therefore, the possibility of engineering disasters should be considered when conducting high-speed underground mining activities. Full article

We used the 11,303 return air roadway of the Hongqingliang coal mine as the engineering background for a study exploring the impact of the structural morphology of the roadway on the stress distribution characteristics and the stability of a weakly cemented soft-rock mine roadway. This work studies the evolution law of stress and deformation, and the plastic zone of weakly cemented soft-rock roadways with retaining the top or bottom coal seams. The results show that when retaining the top coal is replaced by the bottom coal, the high-stress zone of the vertical stress is reduced, the peak stress is decreased, and the stress concentration coefficient is slightly reduced from 1.67 to 1.64. The peak value of the vertical displacement of the roof of the shaft which was 78.4% of that of the top coal also decreases significantly, while the peak value of the vertical displacement of the floor, which was 1.37 times that of the top coal, increases. The equal area method was used to change the aspect ratio of the roadway. When the aspect ratio decreased from 1.38 to 0.88, the high-stress zone of the vertical stress was reduced, the stress peak decreased, and the stress concentration coefficient decreased from 1.8 to 1.75. The vertical displacement of the roof increased by 27.7% from 10.91 mm to 13.93 mm, and the vertical displacement of the floor increased by 15.2% from 6.60 mm to 7.60 mm. The plastic failure range was significantly reduced, particularly at the bottom corners. These findings show that structural morphology has a great influence on the floor heave of weakly cemented soft rock. Reasonable retention of the top or bottom coal and the aspect ratio of the roadway can prevent the deformation and failure of the roadway in weakly cemented soft rock. Full article

Bond strength is one of the most important parameters and can affect the macroscopic mechanical properties and the damage state of rock to some degree. Coarse-grained sandstone was studied using the controlled variable method. The influence of parallel bond strength on the peak strength and failure mode of coarse-grained sandstone was simulated, and the evolution law of peak strength and the failure mode of bond strength were comprehensively analyzed. The results show that the peak strength of the rock was positively correlated with the bond strength; the difference in quantity between the tensile and shear cracks was negatively correlated with tensile bond strength and positively correlated with shear bond strength. With a tensile-shear bond strength ratio of less than 0.5, the peak strength of the rock was usually stable at the certain extreme value under a constant tensile bond strength. The tensile cracks were negatively correlated with the tensile-shear bond strength ratio, and the shear cracks were positively correlated with the tensile-shear bond strength ratio. The main failure mode of the coarse-grained sandstone in the weakly cemented stratum of the Hongqinghe coal mine is shear failure. The research results can be used to guide the ground control of other mine stopes or roadways with weak cementation lithology. Full article