Search Results (663)

The aim of this work was to investigate the evolution of the mechanical integrity of the selected offshore oil reservoir during its life cycle. The geomechanical stability of the reservoir formation, including the caprock and base rock, was investigated from the exploitation phase through waterflooding production to the final phase of enhanced oil recovery (EOR) with CO₂ injection. In this study, non-isothermal flow simulations were performed during the process of cold water and CO₂ injection into the oil reservoir as part of the secondary EOR method. The analysis of in situ stress was performed to improve quality of the geomechanical model. The continuous changes in elastic and thermal properties were taken into account. The stress–strain tensor was calculated to efficiently describe and analyze the geomechanical phenomena occurring in the reservoir as well as in the caprock and base rock. The integrity of the reservoir formation was then analyzed in detail with regard to potential reactivation or failure associated with plastic deformation. The consideration of poroelastic and thermoelastic effects made it possible to verify the development method of the selected oil reservoir with regard to water and CO₂ injection. The numerical method that was applied to describe the evolution of an offshore oil reservoir in the context of evaluating the geomechanical state has demonstrated its usefulness and effectiveness. Thermally induced stresses have been found to play a dominant role over poroelastic stresses in securing the geomechanical stability of the reservoir and the caprock during oil recovery enhanced by water and CO₂ injection. It was found that the injection of cold water or CO₂ in a supercritical state mostly affected horizontal stress components, and the change in vertical stress was negligible. The transition from the initial strike-slip regime to the normal faulting due to formation cooling was closely related to the observed failure zones in hybrid and tensile modes. It has been estimated that changes in the geomechanical state of the oil reservoir can increase the formation permeability by sixteen times (fracture reactivation) to as much as thirty-five times (tensile failure). Despite these events, the integrity of the overburden was maintained in the simulations, demonstrating the safety of enhanced oil recovery with CO₂ injection (EOR-CO₂) in the selected offshore oil reservoir. Full article

Tunnel anchorages are critical components in long-span suspension bridges, transferring immense cable forces into the surrounding rock mass. Although previous studies have advanced the understanding of their pullout behavior through field tests, laboratory models, numerical simulations, and theoretical analyses, significant challenges remain in predicting their performance in complex geological conditions. This study investigates the pullout failure mechanism and bearing behavior of tunnel anchorages situated in heterogeneous conglomerate rock, with application to the Wujiagang Yangtze River Bridge in China to employ a tunnel anchorage in such strata. An integrated research methodology is adopted, combining in situ and laboratory geotechnical testing, a highly instrumented 1:12 scaled field model test, and detailed three-dimensional numerical modeling. The experimental program characterizes the strength and deformation properties of the rock, while the field test captures the mechanical response under design, overload, and ultimate failure conditions. Numerical models, calibrated against experimental results, are employed to analyze the influence of key parameters such as burial depth, inclination, and overburden strength. Furthermore, the long-term stability and creep behavior of the anchorage are evaluated. The results reveal the deformation characteristics, failure mode, and ultimate pullout capacity specific to weakly cemented and stratified rock. The study provides novel insights into the rock–anchorage interaction mechanism under these challenging conditions and validates the feasibility of tunnel anchorages in complex geology. The findings offer practical guidance for the design and construction of future tunnel anchorages in similar settings, ensuring both safety and economic efficiency. Full article

During the construction of deep underground soft rock strata, the adverse effects of high geostress, unfavorable geological conditions, and excavation disturbances are significant, easily triggering Material-Stress-Induced (MSI) large deformation disasters, leading to the failure of support structures or even collapse, thus posing great challenges to the safe construction of this type of underground engineering. Based on this, this study first classifies the large deformations, analyzes the instability mechanism of material-stress-induced large deformation in soft rock, and identifies the influencing factors of this type of large deformation from three aspects. Subsequently, a numerical investigation (FLAC3D 6.00) is utilized to examine the surrounding rock deformation characteristics under different material factors (uniaxial compressive strength and elastic modulus), stress factors (burial depth and lateral pressure coefficient), and construction factors (excavation method, support pattern, and timing of initial support installation). On this basis, a multi-factor sensitivity comparison analysis is conducted, which clarifies the differences and prioritization of parameter influences on large deformation, and reveals the dominant role of controlling factors such as elastic modulus. The analysis demonstrates a strong negative correlation between the examined material factors (uniaxial compressive strength and elastic modulus) and the magnitude of surrounding rock displacement, with both values eventually converging. A significant positive correlation between the examined stress factors and the magnitude of surrounding rock displacement was observed. A pronounced positive correlation was observed between stress factors and surrounding rock deformation. These factors distinctly have different effects on the peak displacement of different surrounding rock parts. Vault settlement demonstrates the most pronounced displacement, while arch bottom deformation is the least apparent. The three excavation methods exhibit relatively low sensitivity to surrounding rock displacement. Similarly, the support patterns demonstrate limited influence on surrounding rock deformation. The material factor of soft surrounding rock is the main controlling factor of the large deformation of soft surrounding rock in deep underground engineering. The elastic modulus has the strongest influence on the displacement of the surrounding rock. When the elastic modulus is less than 2 GPa, the sensitivity coefficient is much higher than the stress factors. The research results can provide some reference and guidance for similar underground projects. Full article

The advancing speed of the coal mining face has a significant impact on the mining-induced stress and energy accumulation of the surrounding rock. To explain the influence mechanism from a mesoscopic perspective, this study conducted a uniaxial compression test on the coal–rock combination body under different quasi-static loading rates, and analyzed their mechanical properties, failure characteristics, acoustic emission characteristics and energy evolution characteristics. The main findings are as follows: The uniaxial compressive strength and elastic modulus of the coal–rock combination body show a variation law of first increasing and then decreasing with the increase in loading rate, while the degree of impact failure significantly increases gradually as the loading rate rises. With the increase in loading rate, there is a tendency that the AE parameters concentrate from the first two stages to the latter two stages. The post-peak residual elastic energy density of the coal–rock combination body increases gradually with the increase in loading rate. The formation of the advancing speed effect of mining-induced stress concentration and elastic energy accumulation in coal–rock masses is caused by the “competitive” interaction between fracture propagation and coal matrix damage when the coal component in the coal–rock combination is deformed under stress. Full article

Investigating the pore structure and understanding the relationship between pore characteristics and mechanical properties are crucial to research in the study of cement mortar. At present, the segmentation of large-scale concrete pores is mainly conducted using traditional algorithms or software, which are time-consuming and operate in a semi-automated manner. However, the application of these methods faces challenges when analyzing large-scale rock pores due to factors such as a lack of data, artifacts, and inconsistent contrast. In this study, six series of cement mortars were subjected to real-time CT scanning under uniaxial loading (RT-CT) to collect real-time three-dimensional data on the evolution of pore structures during loading. To address issues such as artifacts and inconsistent contrast, a new augmentation method was proposed to overcome artifacts and enhance contrast consistency. Finally, the augmented dataset was utilized for training, and the Fast R-CNN algorithm served as the framework for developing the pore recognition model. The results indicate that the improved algorithm demonstrates enhanced convergence and greater accuracy in pore segmentation. A mathematical model is developed to relate uniaxial compressive strength (UCS) to pore fractal dimension and porosity, based on pore segmentation analysis. The fractal dimensions evolution of each specimen is consistent with the progressive failure indicated by the strain-stress curve. Under uniaxial loading, specimens with a 4:1 cement–sand ratio exhibited peak strength. The incorporation of fractals improved particle contact, thereby facilitating the formation of the skeletal structure. These efforts contribute to improving the identification of the deformation of cement mortars. Full article

To alleviate strong strata-pressure bursts during ultra-thick coal extraction, we selected the 26 m number five seam of the Chenjiagou Coal Mine as a full-scale prototype. Three objectives were pursued: (1) elucidate the initiation mechanism of high-energy roof failures under top-coal caving (TCC); (2) quantitatively link the failure sequence of key strata to burst intensity; and (3) deliver field-oriented prevention criteria. A 1:300 physical similarity model and UDEC plane-strain simulations were combined to monitor roof deformation, stress evolution and dynamic response during extraction. Results demonstrate that pressure bursts are driven by abrupt kinematics of the overburden, triggered by sequential breakage of key horizons: the secondary key stratum collapsed at 130 m face advance, followed by the main-key stratum at 360 m. Their combined rupture generated a violent energy release, with roof displacement accelerating markedly after the main horizon failed. We therefore propose two dimensionless indices—the dynamic load factor (DLF) and stress concentration factor (SCF)—to characterize burst severity; peak values reached 1.62 and 2.43, respectively, while pronounced stress accumulation was localized 6–15 m ahead of the face. These metrics furnish a theoretical basis for early warning systems and control strategies aimed at intense rock burst. Full article

Addressing the core issue of rock mass failure and deformation induced by local water-induced uneven expansion in expansive soft rock tunnels, this study systematically analyzes the stress–displacement response of the rock mass under various working conditions. This analysis integrates physical model testing with FLAC3D 6.0 numerical simulation and covers four typical expansion zone configurations (vault, spandrel, haunch, invert) as well as multiple stages of stress loading. Leveraging the mathematical analogy between heat conduction and fluid seepage and combining it with a thermo-hydraulic coupling approach, the FLAC3D temperature field module precisely simulates the moisture-induced stress field. This overcomes the limitations of traditional tools for direct moisture field simulation and enables quantitative assessment of how localized expansion impacts tunnel lining failure. The study reveals that horizontal expansion zones significantly increase the risk of shear failure in tunnel structures. Expansion zones at the tunnel crown and base (invert) pose critical challenges to overall safety and exhibit a pronounced nonlinear relationship between stress loading and displacement. This research deepens the theoretical understanding of the interaction between localized non-uniform expansion and the surrounding rock mass and provides crucial technical guidance for optimizing tunnel support systems and improving disaster monitoring and prevention measures. Full article

In rock slopes with a three-section landslide, the locking section is the key control factor. This study conducted double-sided freeze–thaw tests on a scale model of a rock slope with a three-section landslide in a cold region. We monitored the changes in frost heave force, strain, and fracture during the water–ice phase change and investigated the effect of the trailing edge tensile crack length on the frost heave fracture of the locking section. A crack frost heave model was proposed based on rock and fracture mechanics to explore the mechanism of slope crack freeze–thaw weathering. According to the results, the slope shoulder froze first, with the freezing front progressing from the slope shoulder to the interior of the rock mass. The fracture failure in the three-section rock slopes was mostly caused by the frost heave of the trailing-edge tensile cracks. The largest frost heave force and locking section deformation occurred when the temperature of the top of the trailing edge tensile crack decreased from −3.5 °C to −6 °C (whereas that of the bottom of the crack dropped from 0 °C to −2.6 °C). Additionally, the results demonstrate that the frost heave force is positively correlated with the length of the trailing edge tension crack, and shear marks are virtually absent on the tensile fracture surface. Full article

When constructing subway tunnels in composite strata consisting of overlying soil and underlying rock, placing the tunnel within the overburden rock strata and setting a certain thickness of safety cover rock on top is an effective way to ensure the safety of tunnel construction and the stability of the surrounding rock. However, there is currently no unified understanding or standard regarding the safe overburden thickness of the tunnel and its general rules. To investigate the effect of changes in the roof overlying rock thickness on the surrounding rock stability of subway tunnels, this study is based on the typical soil–rock strata of an underground tunnel section of Jinan Metro Line 4 in China. A total of 4 different conditions for the thickness of the overlying soil layer were considered, and 48 comparison schemes were designed. A systematic study of numerical simulation comparisons of tunnel excavation under different cover rock thicknesses was conducted. The deformation and plastic zone evolution characteristics of the surrounding rock were revealed under different cover rock thicknesses, and the existence of an optimal cover rock thickness range for tunnel crowns in soil–rock strata was identified. Based on this, a theoretical analysis model for the failure of the tunnel roof overlying rock was constructed. Using the upper-bound approach limit analysis method, the theoretical formula for the critical overburden thickness of the tunnel crown was derived. The influence of different rock mechanical parameters and tunnel design parameters on the critical overburden thickness was analyzed. The results were compared with numerical simulation results to verify the effectiveness of the proposed method. The research findings provide theoretical references for selecting reasonable buried depths and support designs for mining-bored tunnels in soil–rock composite strata. Full article

The estimation of the area susceptible to rock failure and the prediction of its movement process are pivotal for hazard mitigation, yet they are also challenging. In this study, we proposed a novel integrated method combining field investigation, remote sensing, and three-dimensional discrete element method (DEM) simulation to achieve our goal. The field investigation and remote sensing analysis are used for the purpose of ascertaining the deformation phenomenon and the structure of the rock slope, identifying the potential failure position and area of the slope. Subsequently, a three-dimensional DEM simulation is employed to quantitatively assess the potential rock failure-affected area and movement process, based on the above potential failure information. The simulation results demonstrate that potential rock failure persists for approximately 30 s, and its movement process can be categorized into two distinct stages: acceleration and deceleration. The initial acceleration stage is characterized by a duration of 10 s, culminating in a peak average velocity of 13 m/s. The subsequent deceleration stage extends for a duration of 20 s. Notably, the maximum attainable velocity for the segment of rock mass under consideration is estimated to be 50 m/s. Furthermore, the model demonstrates the variation in fracture energy, friction energy, and kinetic energy over time. The potential affected area is 140,000 m², and approximately 8000 m² of residential construction will be destroyed if a rock failure occurs. It is imperative to implement measures aimed at the prevention of rock failure in order to mitigate the risk of such an occurrence. Full article

Based on the high strength and superior deformation control capabilities of rock strata, a novel cantilever anti-floating ledge has been proposed to resist the floating of underground structures in rock strata. To explore the actual anti-floating effect and working performance of the structure, laboratory shear tests were designed based on the actual project. The shear characteristics and failure evolution process were then discussed using the Particle Flow Code (PFC) numerical simulation. The main conclusions are as follows. The shear stress–shear displacement curve of the cantilever anti-floating ledge can be described as six stages according to the different states of stress and deformation. With the increase in groundwater buoyancy, the damage to the cantilever anti-floating ledge occurs successively from the ledge, the concrete–rock interface, the connection between the ledge and the side wall, and the connection between the ledge and the bottom plate. Local damage and delamination of the interface do not affect the structural strength, but structural cracks should be prevented from continuing to form and connect. It is necessary to pay attention to the stress and deformation state of the crack-prone area mentioned above, improve the reinforcement ratio in the crack-prone area, and strengthen the bond between the concrete and the rock. Full article

When excavating roadways in underground mines, stress redistribution within the surrounding rock mass leads to stress concentration and release. Should the concentrated stresses exceed the rock mass’s tensile or shear strength, rock deformation and failure occur. Thus, a knowledge of stress distribution around the roadway is of great significance for revealing the roadway instability mechanism and design support methods. In this work, the powerful complex variable function theory was used to solve the surrounding rock stress around the triple-arched roadway and the analytical results were verified with the on-site stress state. The results show that the tensile stress occurs on the roadway roof and floor under low lateral stress coefficients, while concentrated compressive stress emerges on the two sidewalls. However, the surrounding stress distribution exhibits an opposite characteristic under high stress levels. Beyond five times the roadway radius, the stress in the surrounding rock is unaffected by the roadway and approaches the in-situ stress. For the +1890 m level trackless transport roadway in Kunyang No. 2 phosphate mine, it is further calculated that the minimum stress concentration factor in the rib area of the roadway within the stress relief zone is 0.34, while the maximum stress concentration factor in the concentrated stress zone of the roof, floor, and sidewalls of the roadway is 5.87. The measured stress values of two monitoring points in the surrounding rock of this roadway are fairly consistent with the analytical values, suggesting the complex variable method for solving excavation-induced stresses are effective and reliable. Full article

When jointed rock masses are in a high-stress environment, the roughness of the joints is the key factor controlling their shear strength. Their loading behavior is also different from the constant normal load (CNL) conditions controlled in conventional laboratories; rather, they follow the constant normal stiffness (CNS) conditions. To investigate the effects of normal stiffness and roughness on the shear mechanical properties of unfilled joint surfaces, shear tests were simulated using PFC3D (5.0) software under CNS conditions. The effects of normal stiffness of 0 (constant normal stress of 4 MPa), 0.028 GPa/m (low normal stiffness), 0.28 GPa/m (medium normal stiffness), and 2.8 GPa/m (high normal stiffness), and joint roughness coefficients (JRC) of 2~4 (low roughness), 10~12 (medium roughness), and 18~20 (high roughness) on the shear stress, normal stress, normal deformation, surface resistance index, and block failure characteristics of the joint surface were obtained. The results indicate that for different combinations of normal stiffness—JRC—the shear simulation process primarily exhibits three deformation stages: linear stage, yield stage, and post-peak stage. Shear stress increases initially and then decreases as shear displacement increases. When normal stiffness is no less than 0.28 GPa/m, both normal stress and JRC increase gradually with increasing JRC and normal stiffness. When the normal stiffness is no greater than 0.028 GPa/m, the normal stress shows no significant change. The normal displacement changes from “shear contraction” to “shear expansion” with increasing shear displacement and from positive to negative values while the displacement gradually increases; the maximum normal displacement decreases with increasing normal stiffness and increases with increasing JRC. The peak SRI value increases with increasing JRC and decreases with increasing normal stiffness. As normal stiffness increases, the number of tensile cracks for JRC 2~4 first decreases and then increases, while the number of shear cracks gradually increases; for JRC 10~12 and 18~20, both the number of shear cracks and tensile cracks increase with increasing normal stiffness. This paper simulates the actual mechanical environment of deep underground joints to expound the influence of normal stiffness and joint roughness on the stability of deep rock masses. The research results can provide certain theoretical references for predicting the stability of deep surrounding rocks and the stress of support structures. Full article

This study addresses the issue of coordinated development of coal, oil, and gas resources in the Yulin-Shenmu Coalfield. Taking the 132,201 working face of the Xiaobaodang No. 1 Coal Mine as a case study, the study combines FLAC^3D numerical simulation with on-site monitoring to analyze the impact of mining activities on the stability of gas well casings. Simulation results indicate that mining activities cause stress redistribution in the surrounding rock, with a maximum shear stress of 5.8 MPa, which is far below the shear strength of the casing. The maximum horizontal displacement of the wellbore is only 23 mm, with uniform overall deformation and no shear failure. On-site monitoring showed that the airtightness was intact, and the wellbore diameter test did not detect any destructive damage such as deformation or cracks. Concurrently, fiber optic strain monitoring of the inner and outer casings aligns with simulation results, confirming no significant instability caused by mining activities. The conclusion is that mining activities have a negligible impact on the stability of the gas well casing-concrete composite structure. The dual casing-cement ring structure effectively coordinates deformation to ensure safety. This finding provides a reliable technical basis for the coordinated exploitation of coal, oil and gas resources at the Xiaobaodang No. 1 Coal Mine and similar mines. Full article

To address the stability control challenges of narrow coal pillar roadways along goaf-sides affected by thick coal seam secondary mining, this study investigates the 51507 track gateway in Liuyuanzi Coal Mine through theoretical analysis, numerical simulation, and field testing. The research focuses on stress evolution and energy distribution characteristics during secondary mining extraction. Key findings include the following: (1) Under the superimposed influence of goaf-side abutment pressure and secondary mining front abutment pressure, roadway surrounding rock exhibits regional asymmetric characteristics in energy dissipation. (2) Within 10 m ahead of the secondary mining face, the coal pillar experiences intense energy dissipation and plastic zone penetration, leading to bearing structure failure. (3) The energy mechanism reveals that asymmetric dissipative energy distribution drives plastic zone expansion. Accordingly, an integrated control strategy combining differentiated support (bolts/cables + tension-type opposite anchor cables + hydraulic props) with coal pillar grouting modification was developed. Field implementation demonstrated effective control of surrounding rock deformation within 200 mm. This study provides theoretical foundations and technical references for roadway stability control under similar mining conditions. Full article