Search

The excavation of the tunnel on the expressway in northwest Yunnan province induced landslide and a series problem such as ground surface cracks of the slope, sliding of the slope, and cracks in the tunnel lining. This research aims to reveal the interaction relationship between the tunnel and the landslide from the prospective of field monitoring and numerical simulation. Firstly, the engineering geological conditions of the slope where the tunnel was located were obtained by field investigation. The "landslide traction segment-tunnel longitudinal tensile failure" mode was put forward based on the spatial relationship between the tunnel and the landslide. Secondly, field monitoring methods were adopted to monitor the surface displacement of the slope, the deep-seated displacement of the landslide, and the propagation of cracks in the tunnel lining. Finally, three-dimensional numerical models were established to investigate the stability of the slope and the tunnel under natural conditions, tunnel excavation conditions, and rainfall conditions. The field investigation results, field monitoring results, and numerical simulation results illustrated that: (1) The tunnel traversed the traction segment of the landslide body in parallel, and tensile failure or shear dislocation failure would occur at different stages of the interaction between the tunnel and the landslide. (2) Two sliding layers were discovered in the landslide, the shallow creep sliding layer and the deep creep sliding layer, which corresponded to the tensile failure and shear dislocation failure modes proposed in the "landslide traction segment-tunnel longitudinal tensile failure" mode, respectively. (3) The slope was in an unstable state under natural conditions. The tunnel excavation disrupted the initial stress equilibrium of the slope, resulting in stress release of the surrounding rock mass. Both excavation and rainfall would exacerbate the deformation of the landslide and the tunnel. Eventually, control measures based on the control grouting technology of the steel floral tubes were suggested to counter with landslide-tunnel deformation problems. [ABSTRACT FROM AUTHOR]

The distribution of cracks around a perforation, as the initial condition for hydraulic fracturing, has a non-negligible influence on the fracturing process. This work presents a perforating experiment to investigate the crack distribution around the perforation tunnel. The distribution of the number of cracks on samples was statistically analyzed. Then, a 2D cross-section was selected as the research target for numerical simulation. And a numerical model was introduced to describe the rock cracking in the cross-section during perforation based on FEPG (Finite Element Program Generator) software. The meso-mechanical parameters were set to be randomly distributed to ensure a random distribution of cracks. The tensile failure criterion, Mohr-Coulomb criterion, and the fracture toughness criterion were used as the failure criterion. The modulus reduction method was applied to show element cracking. The simulation results show that the damage zone can be divided into four parts after perforation. According to the main causes of cracked elements, the four zones were named as the central crushed zone, the compression-shear damage zone, the tensile damage concentration zone, and the tensile damage propagation zone. The variations of the distribution of cracks under different perforating charge sizes and confining pressures have been analyzed. The reliability of the numerical model was verified by comparing the results of the numerical simulation to the physical experiments. [ABSTRACT FROM AUTHOR]

The complicated process of coal and gas outburst hinders the exploration of gas outburst mechanism. In order to better quantitatively evaluate gas outburst instability of reverse fault and normal fault combination using the RFPA2D numerical simulation software to study the coal face through fault from downthrown side to uplifted side and from uplifted side to downthrown side, the results showed that the outburst process can be divided into four stages, namely, stress concentration stage, coal-rock fracturing and splitting induced by the combinations of gas pressure and in situ stress, cracks propagation driven by gas pressure and the abrupt ejection of coal and gas; Wu 9-10-20090 belt transporter tunnel outburst occurs near the fault by the tensile failure, coal seam pressure shear failure occur, due to the fault sealing formation pressure gradient, under the influence of ground stress and gas pressure, fault and broken coal outburst risk; − 320 east outstanding is due to the fault sealing effect in coal roadway, gas pressure, coal shear failure occurs, breakage of coal is relatively serious, to highlight the accident when exposed fault; face from fault plate to increase plate driving is more likely to happen to highlight the phenomenon is determined by the conditions of gas release. [ABSTRACT FROM AUTHOR]

The extensive bedding and cleats have a great influence on the mechanical properties of coal. The previous research mainly focused on the bedding effect, and few studies took the influence of both bedding and cleats into consideration. The scanning electron microscopy (SEM), uniaxial compression experiments, and acoustic emission (AE) monitoring were conducted on one hard coal specimen with different bedding and cleat angles. The experimental results show that for the bedding dip of 0° and face and butt cleat dip of 90°, the properties of coal specimens were characterized by the highest peak strength, the drastic failure process, the post-peak brittle behavior, the long initial quiet stage, and the short violent booming stage of AE hits number. For the bedding and face cleat dip of 45°, and the butt cleat dip of 90°, the properties of coal specimens were characterized by the lowest peak strength, the slip failure mode, the step-like drops of the post-peak stress-strain curve, and the several peaks of AE hits number. On the other hand, for the bedding and butt cleat dip of 90°, and the face cleat dip of 0°, the properties of coal specimens were presented as tensile failure mode with plate cracks, the short non-linear stage and the slight step-like drops of stress-strain curve, the short initial quiet stage of AE hits number, and the large value of elastic modulus. Then, a theoretical model of coal containing bedding and cleats was established in this paper. The simulation results of peak strength and failure mode verified the proposed model. The simulation of coal strength shows that bedding had the decisive influence on the uniaxial compressive strength of coal, while the weakening effect of cleats was non-negligible. When bedding and cleats were taken into consideration together, the minimum peak strength was reduced and the bedding dip related to the minimum peak strength changed. [ABSTRACT FROM AUTHOR]

A large-scale shaking table test and a series of numerical simulations were performed to clarify the seismic response of the slope reinforced by frame beam and anchor cable by applying Wenchuan-Qingping and El Centro seismic records. The horizontal acceleration responses and response spectrum characteristics of slope, the axial force of anchor cable, and the displacement of frame beam were mainly studied by shaking table test. The influence of the excitation direction of seismic waves was investigated in numerical simulation. The results show that the amplification effects of acceleration and response spectrum along the slope height are independent of the type of earthquake, while the amplification effects of acceleration and response spectrum with excitation amplitude are related to the type of earthquake. There are obvious differences in the acceleration responses between the lower and upper weak sliding layers, and a stronger nonlinear behavior occurs in the upper weak sliding layer, which is explained by the time-frequency spectrum calculated by synchrosqueezing wavelet transform (SWT). The axial force of anchor cable and the peak displacement of frame beam increase with the increases of slope height and excitation amplitude. The dynamic response and damage range of the slope under bi-directional earthquake excitation are significantly larger than that under one-directional earthquake excitation. [ABSTRACT FROM AUTHOR]

To improve the cutting efficiency in the deep hole blasting of rock roadways, a straight hole cutting blasting technique with supplemental blasting of the central hole was developed. First, the blasting mechanisms of the traditional and novel cutting methods were analysed theoretically. For the novel cutting method, the upper uncharged part of the central hole still acted as empty hole. Cutting hole blasting could eject most of the rock mass in the cutting cavity and hence produce a new free face to weaken the clamping effect of central hole blasting. Then, the residual rock mass could be fully removed after central hole blasting. Second, simulation of the new cutting mode was conducted, which visualized the stress wave forming process. Simulation results showed that the rock mass at the bottom of the cutting cavity could be predamaged by the stress wave caused by cutting hole blasting, and the high-intensity stress field generated by central hole blasting would lead to further damage to the residual rock mass. Thus, the residual rock mass could be thrown out readily. Finally, the auxiliary roadway of an iron mine was selected for the blasting experiments. After statistical analysis, due to the supplemental blasting of the central hole, the average blasting footage was increased by 0.35 m, and the average specific charge was reduced by 0.43 kg·m−3, which validated the predominance of the novel cutting method in the deep hole blasting of rock roadways. [ABSTRACT FROM AUTHOR]

Hasdrubal is a naturally fractured carbonate reservoir field located in offshore Tunisia. Over the last decade, the field has manifested serious integrity and water coning production issues. The extended network of discontinuities in addition to the impact of reservoir depletion renders the stability of the reservoir a major concern for the field operator. An integrity study of the field was necessary to accurately determine the ever-changing stress settings (magnitudes and orientation of stresses tensors) in order to accordingly adjust the design of well trajectory while properly assimilate their impact on the production trend. An elaborated workflow was initiated to fine-tune mechanical properties of rock basing on geological information, drilling event, and field logs. The one-dimensional mechanical earth model (MEM) was then built to validate wellbore failure and explain drilling incidences reported. The stress regime was also confirmed and matches the geological history of the area with an alteration between normal faulting and strike-slip regimes. The mechanical earth model was in position to explain the drilling events for all the vertical wells and so providing reasonable guide design for the wells under development. The shear stability of faults encountered by horizontal well Hasdrubal-A1 was also appraised using the Fracture Stability Advisor software. The results show that at initial reservoir pressures, the fractures in Hasdrubal field are stable and do not exceed the failure criterion. Previous interpretation is applicable to any major discrete discontinuity that is present in the same stress field and depicts similar rock-related properties strength. A predictive and robust three-dimensional model to represent the complex environment of reservoir is necessary to explain production profile induced from pressure depletion, especially alteration at fractures and faults network, and so improving well planning and long-term field development. The mechanical earth model described herewith has represented an indispensable foundation of the three-dimensional model that has been built to address the classical 1D-MEM limitations and so to properly assimilate the presence of fractures and their impacts on the geomechanical behaviour of the field. [ABSTRACT FROM AUTHOR]

Under the influence of mining, a lot of cracks and deformation were developed on the back edge of the Jianshanying landslide. Through monitoring data analysis and numerical simulation of dangerous rock collapse after coal mining, the landslide deformation mechanism is analyzed. Results show that in the landslide after coal seam mining, the stress redistribution formed "increased stress area" and "stress weakened zone." The deformation of the landslide is intensive, and the strongest deformation occurred in the goaf roof and boundary. Overlying strata moved forwards to goaf area, and thus, tensile stress concentrated in goaf boundary, producing amounts of tensile fractures. Tensile fractures further expanded by the influence of air surface. The formation mechanism of the Jianshanying landslide can be summarized as "tensile crack–creep–shear slip" failure in the mechanical model. The monitoring results provide fundamental data for evaluating the long-term performance of displacement change and for assessing deformation mechanism of the Jianshanying landslide under the effect of mining activity. [ABSTRACT FROM AUTHOR]

Gob-side entry retaining is a common method in underground coal mining. Conventional gob-side entry retaining (CGER) always causes stress concentration and large deformation around roadways under the condition of thick and hard sandstone roofs. Thus, an innovative method of no pillar gob-side entry retaining (NPGER) in longwall mining is proposed in this paper. First, a physical model was established to explore the mechanism of the new method. The modeling results indicate that the progressive caving of the strata in the middle of the stope is consistent with CGER. The major difference between NPGER and CGER is that CGER collapsed with a structure of a long arm beam, but NPGER collapsed with a structure of a short arm beam near the roadway. In the end, a new roadway with a gangue rib was formed when the immediate roof and main roof slipped along the pre-cutting plane. Subsequently, the numerical simulation software Universal Distinct Element Code (UDEC) was adopted to establish the numerical model of the 8501 working face in Tangshangou coal mine. The NPGER process is simulated. The evolution of the roof structure and stress characteristics were clearly demonstrated. The results showed that the roof structure noticeably changed from a long beam to a short beam after roof fracturing. The retained roadway was under low stress conditions, and the stress was transferred to the deep rock. In the end, the NPGER method was applied in the field, and the results showed that the retained roadway could meet the requirements of the next working face, which may provide guidance for longwall mining with thick and hard roofs. [ABSTRACT FROM AUTHOR]

The evolution law of surrounding rock pressure in deep mining is explored in this paper by analyzing the stress, displacement, and failure progress of surrounding rock in the deep mining of Beiminghe Iron Mine by in situ monitoring and FLAC3D numerical simulation. The evolution characteristics of surrounding rock deformation of different layer roadways during the entire excavation and mining process are observed, with results showing that movable support pressure exists in the excavation and mining process of the roadways. In the process of roadway excavation, vertical stress increases at the pillars, while horizontal stress increases at the roof and floor of the roadway. When the roadways are mined, the stress relaxed area is 0–4 m from the mining face, the stress increase area is 4–60 m from the mining face, and the original rock stress area is 60 m from the mining face. During the mining period, the horizontal convergence displacement of two sides of the roadway is lateral expansion caused by vertical stress, while vertical deformation of the roof and floor of the roadway is predominately caused by horizontal stress extrusion. The mining of upper layer roadways has a certain influence on lower layer roadways, and the mining of the same layer roadways only has a significant impact on adjacent roadways. With the increase of mining depth, the stress concentration becomes more obvious, and the convergence of vertical displacement and horizontal displacement of rock strata increases. In addition, shear failure occurs in overburden strata and shear tension failure occurs in the floor of the roadway. [ABSTRACT FROM AUTHOR]

In this study, a trigon-based numerical manifold method is developed to study the mechanical properties, including the crack propagation and coalescence process as well as peak compressive line loads of the pre-cracked Brazilian disks. An assemblage of trigon loops is adopted to approximate the microstructure of the rock-like specimens, based on which a modified cohesive contact model considering cohesion and tensile strength is used to interpret the fracturing behaviors of the cemented interfaces as well as the interactions between the initiated cracks. Firstly, numerical uniaxial compression test is carried out to calibrate the micro-mechanical parameters of the model. With the calibrated parameters, a series of numerical Brazilian splitting tests are conducted on the pre-crack disks including both single-cracked and double-cracked disks with varying crack inclination angles. Comparisons between the numerical simulations and laboratory results indicate that the mechanical behaviors of the pre-cracked specimens can be well predicted by the trigon-based NMM models. [ABSTRACT FROM AUTHOR]

A systematic approach to numerically simulating an island longwall panel operation is proposed: it aims to investigate the evolution of overlying strata, static stress and displacement response and dynamic load arising from roof fracturing and fault slip. The results show that due to a small gob width (70 m) on both sides, the evolution height of overlying strata is limited, i.e. the heights of the cave-in zone and fracture zone are 30.98 and 66.91 m, respectively. The numerical model matches the theoretical analysis and field observations. Dynamic analysis reveals that the envelope of mine tremors confirms the good correlation with the evolution of the fracture zone. As the mining panel is far from the fault, fault slip does not occur; at this time, the dynamic load mainly comes from roof fracturing. When mining activities approach the fault, the calculation of the dynamic response of fault slip is performed over the area where the increase of relative shear displacement during dynamic analysis exceeds 0.05 m and where the shear stress along the fault decreases. It is shown that during the initial stage of the mining process, and in a square mining panel, fault slip is more likely to occur, leading to strong tremors and rock bursts, which become more notable in the later stages of the mining of the island panel. [ABSTRACT FROM AUTHOR]

In view of the fact that rib spalling of coalfaces seriously affects normal production in a large-cutting-height panel, the mechanical model of the "coalface–support-roof" is established to analyze the main factors affecting coalface stability, and a real panel, no. 8101, is used as an example. Using the main influence factors with different levels, orthogonal experimental design is used to determine the numerical simulation scenarios. The coalface failure conditions for different simulated scenarios are studied using DEM method. The orthogonal experiment method was used to analyze the simulation results in this study. The coalface is strengthened using the "manila+ grouting" reinforcement technique. The results show that the factors affecting coalface stability are the cutting height, support capacity, coal cohesion, coal friction, and upward-inclined angle. The larger the cutting height is, the larger the roof pressure is on the coalface. The larger the support capacity is, the smaller the roof pressure is on the coalface. The larger the coal cohesion and friction values are, the larger the roof pressure is that the coalface can bear. The sensitivities of cutting height, support capacity, coal cohesion, coal friction, and an upward-inclined angle with respect to coalface stability are 14.60, 2.29, 38.63, 1.19, and 1.95, respectively. In descending order of influence, the factors are coal cohesion ˃ cutting height ˃ support capacity ˃ upward-inclined angle ˃ coal friction. The "manila+ grouting" reinforcement technology effectively controls coalface failure, yields a 30~40% saving in costs, and reduces incidents of coalface failure by 70~80%. The research results provide new insights for the evaluation and control of coalface stability. [ABSTRACT FROM AUTHOR]

Coalfields in Northwest China are mostly thick or extra-thick coal seams with low strength. During the tunneling of deep full-coal roadway, "roof-shock" may appear to the surrounding coal rock due to distortion and fracture caused by mining, which results in such accidents as roof caving and collapse. This study, taking the ingate connecting roadway of Yili No.1 Coal Mine as an example, discusses the roof-shock phenomenon during excavation. Firstly, the inducing factors of roof-shock are obtained by field monitoring and coal rock burst proneness tests. Next, FLAC3D simulation is employed on the failure characteristics of roof-shock, and on the pressure relief schemes of layered excavation. The modeling results show that the roof-shock aggravates the stress concentration and the damage of surrounding rock in the ingate connecting roadway. Stress distribution can be improved by adopting the layered excavation of the roadway and taking pressure relief and vibration-adsorption support measures. Further, the study creatively puts forward a "four-step" scheme to prevent roof-shock in the deep full-coal roadway, and applies it in the field test of ingate connecting roadway in Yili No.1 Coal Mine. The field monitoring results show that the support measures can effectively control the roof-shock, and the "four-step" scheme is proved a way to solve this problem in deep, extra-thick, and full-coal roadways. [ABSTRACT FROM AUTHOR]