Decrease In Effective Stress Research Articles

Structure and formation of mud volcanoes in the South Caspian Basin according to seismic data

The South Caspian Basin (SCB) constitutes a classic province to study mud volcanoes and their associated processes. Approximately 280 active mud volcanoes have been documented in the offshore and the onshore areas of Azerbaijan, emitting water, hydrocarbons (oil and mainly methane), and fluidized muds that transport solid fragments from deep sedimentary sequences. Seismic characteristics of mud volcano systems in the Azerbaijan area of the SCB are used to address (1) the nature of the mud volcano source layer; (2) the internal geometry of the feeder systems; and (3) the processes associated with shale mobilization and extrusion. We confirm that the source layer is mainly the Maykop Suite (Oligocene-Lower Miocene), which is a thick (≤3 km) and deep (>10 km) clayey sequence rich in organic matter. This layer was quickly buried due to basin subsidence and the rapid deposition (since the Middle Miocene) of thick fluvio-lacustrine sediments of the Productive Series (PS) (Upper Miocene-Upper Pliocene), which contributed to the creation of high pore pressures and the transformation of organic matter into methane (through thermal cracking). Since the Middle Miocene and more important, during the Upper Pliocene, the Maykop shales mobilized due to an increase in shear stresses and pore pressures, which promoted a decrease in effective stresses and, as a consequence, facilitated the achievement of critical state conditions in the shales that began to flow. This process, repeated over time, allowed multiple pulses of shale mobilization to originate (as in a loading piston system). Shale piercing transporting deep-sourced fluids (and hydrocarbons) was carried out through fractures in the outer arc of anticlines, forming subvertical feeder systems. The mobilized hydrocarbons and fluids also recharged some of the younger and more permeable layers of the PS, creating shallower reservoirs in the vicinities of the mud volcano structures.

Research on Stability of Tower Crane based on ANSYS Software

In order to strengthen the safety management of tower cranes on construction sites and prevent accidents caused by the deformation of the standard section of tower cranes during the construction process, in response to the stability of the WA6013-6A tower crane operation process, the static analysis of the standard section structure and attachment method during the lifting process of tower cranes was carried out using Ansys software, and the maximum displacement and stress-strain situation of tower cranes with different tower crane heights and attachment distances were obtained. The results show that the more attached the tower crane is, the higher the standard section stress dispersion and the continuous decrease in effective stress; The smaller the distance between connecting walls, the more connecting components there are, the smaller the standard deformation rate of tower cranes, and the better the stability of tower cranes.

Effect of groundwater dynamics in rain-induced landslides: centrifuge and numerical study

Landslides are a multifaceted phenomenon triggered by rainfall infiltration as a consequence of the decrease in effective stress upon the development of porewater pressure. Although many studies concentrated only on rainfall infiltration as the source of the primary hydrological regime, the impact of groundwater dynamics has been relatively underexplored owing to its elusive nature. Field investigations after the landslide incidents provide insight into the influence of groundwater dynamics and speculate its effect as a secondary hydrological regime is immense. Therefore, this paper uses centrifuge modeling and numerical simulations to study groundwater dynamics in rain-induced landslides. Instrumented model slopes made of silty sand were tested to examine the hypothesis of pre-existing groundwater flow levels and surcharged groundwater flow conditions in rain-induced landslides. It was observed that swiftly rising porewater pressure along the soil–bedrock interface triggered landslides more rapidly under high groundwater flow and immediate surcharged groundwater flow conditions. Deformation analysis confirmed that a voluminous landslide could be expected if the role of groundwater dynamics is higher. A two–dimensional coupled hydromechanical finite element simulation was performed to back–analyze the experimental results and to discuss the failure mechanism. Upon validation, numerical simulation emphasized how the failure was accelerated under low-intensity rainfall if high groundwater flow exists. Furthermore, the study identified that surcharged flow profoundly affects landslide initiation if the slope has a low pre-existing groundwater flow. The outcomes highlighted that groundwater dynamics should be an integral part of the temporal predictability of landslides as they can also govern the magnitude of landslides.

Collaborative multi‐scale optimization of molding processes for thermosetting/quartz fiber composites based on balancing between efficiencies and mechanical properties

AbstractIn terms of the interplay between manufacturing cost and quality during the molding of fiber reinforced thermosetting composites, this study proposes a multi‐scale collaborative optimization strategy aimed at shortening molding time and reducing the diminishing defects generated during the process. Macro‐scale thermochemical and micro‐scale thermomechanical calculations are conducted on the composite molding to analyze the origins of temperature gradients and residual stresses. Then, the curing cycle, temperature gradient in the macro‐scale model, and residual stresses in the micro‐scale model are optimized by combining finite element analysis with the Non‐dominated Sorting Genetic Algorithm II. Several curing processes within the Pareto front were selected, and their impact on compressive performance was assessed through experimental analysis. Compared to the standard curing process (SCP), the optimal curing process exhibited a 41.4% reduction in maximum temperature gradient (∆Tmax), a 25.2% decrease in effective residual stress , and a 20.0% increase in compressive strength. Multi‐scale collaborative optimization strategies are integral to the advancement of production and application of fiber‐reinforced thermoset composites. Multi‐scale collaborative optimization strategies are integral to the advancement of production and application of fiber‐reinforced thermoset composites.Highlights Investigated of interactions among components in composites molding. Optimization of composite molding process with Non‐dominated Sorting Genetic Algorithm II and finite element. Examined the impact of composite molding process on compressive performance.

Energy-Based Assessment of Liquefaction Behavior of a Non-Plastic Silt Based on Cyclic Triaxial Tests

Earthquakes cause cyclic shear deformations in soil and build-up of excessive pore water pressure as a result of undrained loading, accompanied with rearrangement of soil particles and degradation in stiffness of the soil due to decrease in effective stresses. During loading, the onset of soil liquefaction is defined as a stress state in which the excess pore water pressure is equalized to the total stress. From this point of view, assessment of the pore water pressure development pattern under cyclic loading has been one of the most salient research topics in geotechnical and earthquake engineering. In this study, results of a series of cyclic triaxial tests on non-plastic silt specimens consolidated under 100 kPa effective isotropic consolidation pressure were used to question the modelling ability of pore pressure development models previously proposed for sands. Tests were performed on specimens of 6 different initial relative densities (Dr) ranging between 30-80% and 10 different cyclic stress ratios (CSR). The key parameters of pore water pressure development and shear deformation in the energy-based model used are relative density, cyclic stress ratio and number of cycles. The results revealed that, these energy-based models have a strong potential in evaluation of pore water pressure development pattern of non-plastic silts. Test results also show that the increase in relative density and decrease in CSR causes a ladderlike behavior among pore water pressure and cyclic shear strain, which is relevantly rendered by energy-based models.

Adding N to enhance low-cycle fatigue properties of high-Mn austenitic steel

This study comparatively investigated the low-cycle fatigue properties and microstructure of two high-Mn austenitic steels, Fe−18.5Mn–7Cr−0.6C and Fe−18.5Mn–7Cr−0.6C−0.21 N. The results revealed that adding N promoted the dislocation planar slip during cyclic deformation in high-Mn austenitic steel, due to the presence of Cr–N short-range ordering (SRO) and the decrease of stacking fault energy (SFE). With an increased number of cycles, the planar slip characteristics of the N-containing high-Mn austenitic steel led to a rapid decrease in effective stress, which promoted cyclic softening. Moreover, adding N increased the fatigue life of high-Mn austenitic steel, by enhancing the fatigue strength, reducing the plastic damage accumulation, and inhibiting the fatigue crack propagation. This study provided a valuable reference for the practical applications of N-alloyed high-Mn austenitic steel.

Seismic performance improvement of liquid storage tank based on base-isolation and pendulum tuned mass damper

It is necessary to ensure the safety of liquid storage tanks under earthquakes, but the damage probability of the non-damping liquid storage tanks is higher under earthquakes. Based on the damping principle of tuned mass damper (TMD) and the characteristics of the liquid storage tank, a new pendulum TMD (PTMD) system is proposed. Considering the material nonlinearity, the fluid–structure interaction and liquid sloshing characteristics, the three-dimensional numerical calculation models of the non-damping, PTMD, base-isolation (BI) and BI-PTMD liquid storage tanks are established, respectively. The seismic responses of different types of liquid storage tanks under the action of near-field pulse-like earthquakes are investigated, the damping performance of the hybrid control system with the isolation and the PTMD is analyzed, and the influence laws of the mass ratio of PTMD-structure and base-isolation period on the dynamic responses of the liquid storage tanks are discussed. The results show that the BI-PTMD hybrid control system has a significant damping effect on the seismic responses of the liquid storage tank. The damping rate of the base shear is the largest, reaching 86.0%, and the control rate of the PTMD on the displacement of the isolation layer is about 20.0%. The hoop stress, effective stress, liquid pressure and displacement of isolation layer decrease with the increase of the mass ratio of PTMD to structure. With the increase of base-isolation period, the hoop stress, axial compressive stress, effective stress and liquid pressure decrease, and the control effect of PTMD on the liquid storage tank is weakened.

Implications for fault reactivation and seismicity induced by hydraulic fracturing

Evaluating the physical mechanisms that link hydraulic fracturing (HF) operations to induced earthquakes and the anticipated form of the resulting events is significant in informing subsurface fluid injection operations. Current understanding supports the overriding role of the effective stress magnitude in triggering earthquakes, while the impact of change rate of effective stress has not been systematically addressed. In this work, a modified critical stiffness was brought up to investigate the likelihood, impact, and mitigation of induced seismicity during and after hydraulic fracturing by developing a poroelastic model based on rate-and-state fraction law and linear stability analysis. In the new criterion, the change rate of effective stress was considered a key variable to explore the evolution of this criterion and hence the likelihood of instability slip of fault. A coupled fluid flow–deformation model was used to represent the entire hydraulic fracturing process in COMSOL Multiphysics. The possibility of triggering an earthquake throughout the entire hydraulic fracturing process, from fracturing to cessation, was investigated considering different fault locations, orientations, and positions along the fault. The competition between the effects of the magnitude and change rate of effective stress was notable at each fracturing stage. The effective stress magnitude is a significant controlling factor during fracturing events, with the change rate dominating when fracturing is suddenly started or stopped. Instability dominates when the magnitude of the effective stress increases (constant injection at each fracturing stage) and the change rate of effective stress decreases (the injection process is suddenly stopped). Fracturing with a high injection rate, a fault adjacent to the hydraulic fracturing location and the position of the junction between the reservoir and fault are important to reduce the Coulomb failure stress (CFS) and enhance the critical stiffness as the significant disturbance of stresses at these positions in the coupled process. Therefore, notable attention should be given to the injection rate during fracturing, fault position, and position along faults as important considerations to help reduce the potential for induced seismicity. Our model was verified and confirmed using the case of the Longmaxi Formation in the Sichuan Basin, China, in which the reported microseismic data were correlated with high critical stiffness values. This work supplies new thoughts of the seismic risk associated with HF engineering.

Water–rock two-phase flow model for water inrush and instability of fault rocks during mine tunnelling

Water inrush hazard is one of the major threats in mining tunnel construction. Rock particle migration in the seepage process is the main cause of water inrush pathway and rock instability. In this paper, a radial water–rock mixture flow model is established to study the evolution laws of water inrush and rock instability. The reliability of the proposed model is verified by the experimental data from a previous study. Through the mixture flow model, temporal-spatial evolution laws of different hydraulic and mechanical properties are analysed. And the proposed model’s applicability and limitations are discussed by comparing it with the existing water inrush model. The result shows that this model has high accuracy both in temporal evolution and spatial distribution. The accuracy of the model is related to the fluctuation caused by particle migration and the deviation of the set value. During the seepage, the porosity, permeability, volume discharge rate and volume concentration of the fluidized particle increase rapidly due to the particle migration, and this phenomenon is significant near the fluid outlet. As the seepage progresses, the volume concentration at the outlet decreases rapidly after reaching the peak, which leads to a decrease in the growth rate of permeability and porosity, and finally a stable seepage state can be maintained. In addition, the pore pressure is not fixed during radial particle migration and decreases with particle migration. Under the effect of particle migration, the downward radial displacement and decrease in effective radial stress are observed. In addition, both cohesion and shear stress of the rock material decreased, and the rock instability eventually occurred at the outlet.

Numerical investigation of soil dynamic response during high-frequency vibratory pile driving in saturated soil

The high-frequency vibratory pile driving has been gradually applied for pile installation in central urban areas. However, its adverse impact on the surrounding environment is still uncertain. This paper develops a refined three-dimensional numerical model based on the hydro-mechanical coupling method to investigate soil dynamic responses produced by high-frequency vibratory pile driving in saturated soil. The soil vibration velocity, pore water pressure, and mean effective stress are analyzed. Additionally, parametric analyses of excitation frequency and excitation force are conducted to examine soil responses under different installation parameters. The results show that the peak particle velocity (PPV) of soil reaches its maximum at the depth of the pile tip, with greater vertical PPV below the ground surface than radial PPV. Pore water pressure around the pile increases significantly, leading to a noticeable reduction in effective stress. The changes in pore water pressure and effective stress decrease as the distance from the pile increases. The parametric analysis results indicate that increasing the excitation frequency can significantly decrease the vertical PPV of soil at the depth of the pile tip and reduce the stress disturbance range in the surrounding soil. The pressing force mainly affects the efficiency of pile sinking, while the centrifugal force primarily affects the stress state evolution of soil around the pile shaft.

The study of newly established approaches to control soil liquefaction: An overview

As a result, continuous decrease in effective stress and increase in pore water pressure, liquefaction that is triggered by earthquakes can harm the foundation of existing building and other structures and cause large financial losses. Numerous earlier studies looked into ways to control sand liquefaction while lowering costs, negative effects on the ecology, and other related problems. Recent advances in Materials science and interdisciplinary methods have made novel materials readily available that can be used to increase liquefaction resistance and enable other liquefaction prevention techniques. studies into the recently studies into the recently technologies are examined in this work in order to bring up some crucial issues and inspire additional study and discussion. To have a firm understanding of the development of liquefaction resistance, The review first looked at and discussed the qualities of the recently created approaches, the efficiency of the mitigation mechanism, potential control difficulties. The relevance and homogeneity in soil together varying sizes, as well as potential disruption to surrounding structures, are then explored. Additionally, a brief description of the probable cost and length of the site construction mitigation measures is provided. The reader will thoroughly comprehend the liquefaction mitigation research trend after reading this review; they will also be able to further investigate new approaches and techniques that may be efficient, simple to implement on-site, inexpensive, environmentally amiable, and extremely durable. This research suggests long-term in-depth studies on quantitative cost evaluation, length time, and mitigation effectiveness.

The Effect of High Pore Water Pressure on Liquefaction Potential in Sidoarjo Mud Volcanoes (LUSI)

LUSI until now is still active and holds the potential for subsequent disasters due to the influence of high pore water pressure in the affected area. The presence of high pore water pressure will cause a decrease in effective stress and decrease in soil / rock strength. This type of subsequent disaster is closely related to the process of liquefaction which has the potential to occur with the addition of earthquake events. Analysis of liquefaction potential with empirical analysis on standard penetration test (SPT) based evaluation, with input of soil properties parameters, seismicity, and groundwater level parameters. The groundwater level parameter in the calculation will show a normal pore water pressure value in accordance with the depth of the water-saturated layer. Input of high pore water pressure parameters so far has not been done. CPT-u measurement data for pore pressure value input consists of 13 points of measurements was on the northern embankment, with the lowest level of stability. The input of these parameters will provide variations in the differences in the level of potential liquefaction in the study area. The result is changes occur in the decrease in the safety factor value ranging from 0.1-0.4 and the change in the liquefaction potential index (LPI) value from originally low to high, and originally high to very high. The anomaly input of pore pressure in CPT-u measurement results ranges from 40%-70% higher than normal pore pressure in the sand layer. Analysis of the potential for liquefaction in the study area showed that the results of the high-very high liquefaction potential in the northern and eastern research areas, and the low Liquefaction potential was in the southern and western areas.

Investigation of Heat Extraction in an Enhanced Geothermal System Embedded with Fracture Networks Using the Thermal–Hydraulic–Mechanical Coupling Model

This paper presents a numerical study on thermal energy mining from hot dry rock (HDR) using an enhanced geothermal system (EGS). In these simulations, the thermal–hydraulic–mechanical (THM) coupling model is employed on the basis of the embedded discrete fracture model. The evolution of physical fields of the fractured reservoir, including temperature field, pressure field, and stress field is studied over time, and the effects of different controllable factors, such as fracture morphology, fluid injection rate, and the distances between the injection well and producing well on the heat recovery capacity are investigated. The results show that the fracture morphology significantly influences heat extraction performance. The working fluid mainly flows along with the fracture networks, which causes locally low temperatures and low mean effective stress near fractures. The porosity and permeability increase due to the decrease in mean effective stress. For reservoir models with inclined fractures, there will be a significant decrease in the extraction temperature. In the 30th year, the decline in the heat recovery rate is 46.6%, which is much higher than the model without inclined fractures. Moreover, the increasing injection temperature barely influences the production temperature, while it significantly decreases the heat recovery of the EGS. When the injection and production well spacing is small, increasing the well spacing is an effective way to improve the thermal extraction performance of the EGS. In the model in the paper, the heat production increases up to 13.7% when the injection-production well spacing is increased from 150 m to 450 m. The results of this work could provide guidance for the optimization and operation of EGS.

Physical Modelling of Rainfall-Induced Sandy and Clay-Like Slope Failures

Small-scale slope modelling was performed to evaluate the failure process of a landslide triggered by artificial rainfall. The model platform 2.3 m long, 1.0 m wide, and 0.5 m deep was used to build small-scale slope models with the same geometric conditions but different soil types/materials, including sand and two sand-kaolin mixtures with the same slope angle. The hydraulic response of the slope models under simulated rainfall conditions was monitored using volumetric water content, pore water pressure, and matric suction sensors installed at different depths and along different profiles. Slope surface deformation and failure development was also monitored. This paper discusses the factors affecting landslide initiation and propagation, and their relationship to the slope material, infiltration process, and overall soil resistance in a slope related to soil strength, effective stress, and matric suction contribution in the unsaturated part of the slope. Rainfall infiltration caused increase of volumetric water content, dissipation of suction in initially partially saturated materials of the small-scale slope models, resulting in a decrease in effective stresses and shear strength, which in turn led to the occurrence of movements and initiation of slope failures. The main observations arising from the results of the conducted tests relate to initiation and development of the observed instabilities of sandy and clay-like slopes. The test results have shown that within the slopes built from clean sand failure occurs due to groundwater level rising at the slope foot and further retrogressive failure towards the top of the slope, while in the slopes built from sand-kaolin mixtures, instabilities occur in the form of cracks in unsaturated conditions and are the result of matric suction dissipation due to rainfall infiltration.

The 2022 Luding, Sichuan, China, M 6.8 earthquake: A fluid-related earthquake?

We determine a detailed 3-D crustal S-wave velocity structure in and around the Xianshuihe (XSH) fault zone using the direct ambient-noise surface-wave tomography. The continuous waveform data recorded at 22 portable seismic stations of our newly deployed around the XSH fault zone and 13 Chinese provincial stations are used in the data collection during September to December 2020. Our results show obvious low-velocity (low-V) anomalies under the Sichuan basin and high-velocity (high-V) anomalies under the Songpan-Ganzi block at 5–10 km depths but high-V anomalies under the Sichuan basin and low-V anomalies under the Chuandian block at 20–40 km depths. The XSH faut zone shows a clear boundary of low-V and high-V anomalies. Furthermore, there is a clear relationship between velocity structure and Luding mainshock. The Luding mainshock and its aftershocks occurred at the boundary of high-V anomalies in the upper crust but underlain by low-V anomalies in the mid-lower crust. These low-V anomalies indicate that the fluids have reached in the source area. These results suggest that fluids might reduce the friction force due to the decrease of both frictional coefficient and effective normal stress on the fault planes and trigger the strike-slip movement of the fault zone and the occurrence of the Luding earthquake. These fluids could be contained in the hot and wet mantle upwelling flow in the big mantle wedge caused by the deep subduction of the India slab down to the mantle transition zone, in addition to the crustal channel flow due to the Indo-Eurasian collision.

Effects of Climate Change on Geotechnical Infrastructures — state of the art

Geotechnical infrastructures, like slopes and embankments, retaining walls, foundations, engineered landfills, overburden dumps, and pavements, get continuously exposed to various environmental factors which are climate dependent. Fate/stability of these infrastructures due to extreme and abrupt change in precipitation, temperatures, humidity, and wind/airflow is quite questionable. Some of the issues related to climate change on soils include increase in infiltration rate, high pore-water pressure, decrease in effective stress, soil liquefaction, seepage failures, frost heaving, changes in soil suction potential, swelling and shrinkage in fine-grained soils, differential settlement, and damage to vegetation cover and thereby causing slope failures, waterlogged conditions, floods, soil erosion and/or internal erosion of fines, damage to landfill liners and soil covers, desertification, desiccation cracks on the ground surface, and groundwater table pollution due to contaminant migration. Therefore, studies on the impact of climate change on geotechnical infrastructures have gained attention of many researchers in the recent times. In present study, an up-to-date review of the works related to the influence of various climatic factors on geotechnical properties and thereby on geotechnical projects is carried out. Topics related to climate data downscaling using global climate models (GCM), climate change-induced slope instability, acid rains, desiccation cracking in soils with changing temperatures, impacts of dry-wet cycles and freeze-thaw cycles, and vegetation effects on soils are emphasized in this paper. Furthermore, to address the challenges, need-based research related to resilient infrastructures, thermo-hydro-mechanical models, bioremediation methods, innovative sustainable composite materials, and incorporation of climatic factors in design is highlighted and discussed.

Liquefaction potential in the governor's office of West Sulawesi after the 2021 Mamuju-Majene earthquake

The Governor's Office of West Sulawesi Province is close to an active fault, which triggers its vulnerability to seismic activity. The Mamuju Majene Earthquake destroyed the Governor's office building with a magnitude of Mw 6.2 in 2021. The geological conditions at the site are alluvial deposit formations. In addition to the geotechnical conditions, it has the characteristics of sandy soil with fine to medium gradations. Liquefaction causes a loss of soil strength and an increased pore water pressure caused by vibrations on the earth's surface in the form of seismic waves. It causes a decrease in effective stress, ground settlement, and lateral spreading. This study aims to determine the potential for liquefaction in The Governor's Office of West Sulawesi using a simplified procedure method with a Standard Penetration Test (SPT). The Peak Ground Acceleration (PGA) value is determined using the RSA Human Settlements. The Liquefaction Potential Index (LPI) produces five zones of liquefaction potential levels. The analysis showed that The Governor's Office of West Sulawesi experienced liquefaction at a depth of 12-18 meters with a moderate to very high level.

Pore-water pressure accumulation during closely spaced earthquakes: Fundão Tailings Dam

ABSTRACT This paper focuses on pore-water pressure accumulation in loose sandy tailings during three (3) earthquakes within four minutes and the accompanying decrease in effective stress to assess the dynamic stability of the Fundão Tailings Dam, which failed on 5 November 2015. Results of laboratory cyclic direct simple shear tests are used to illustrate the accumulation of pore-water pressures with closely spaced low-level cyclic events. The seismically-induced pore-water pressures in the loose sands below the left abutment downstream slope and setback area are used to estimate the decrease in factor of safety with time until failure occurred within 20–30 minutes of the earthquakes. Field cone penetration and standard penetration test conducted prior to the failure are used to calculate the factor of safety against liquefaction to estimate pore-water pressures generated during the fore, main, and aftershocks in the sandy tailings. The effective stress stability analyses utilise a liquefied shear strength ratio for the sand tailings below the left abutment downstream slope and toe of the plateau because the sand tailings reached the critical state condition due to a reduction in the effective stress. SITE LOCATION: 20.206500°S, 43.467111°W

Fracture characteristics of iron ore under uncoupled blast loading

A blasting experiment was conducted on iron ore samples by considering multiple coupling charge coefficients. The resulting internal fracture and damage characteristics were quantitatively analyzed via computerized tomography (CT), scanning, and three-dimensional (3D) model reconstruction. The results show that the iron ore primarily displayed radial and circumferential cracks along the blast hole under an explosive load. When the decoupling coefficient was small, the crack surface was dominated by transgranular fractures in the form of intracrystalline fractures. As the uncoupling coefficient increased, the crack surface exhibited transgranular and intergranular coupled fracture modes. Using fractal theory to analyze crack distribution characteristics, as the decoupled coefficient increased, the body fractal dimension tended to decrease, and the degree of damage gradually decreased. The degree of damage reached a turning point when the decoupling charge coefficient was approximately 1.33. A numerical simulation suggested that the explosion energy transmitted to the iron ore and the effective stress decrease sharply when the decoupling coefficient exceeds 1.33. In some optimal uncoupling coefficient range, excessive fragmentation of the ore body is prevented, thereby allowing full use of the explosive energy.

Experimental Investigation on the Effect of Loading and Unloading on Coal Permeability with Different Sediment Beddings

Abstract The sediment bedding direction and loading-unloading have significant effect on permeability of coal sample. The coal samples taken from Zhangcun Coal Mine in Shanxi were used to measure coal permeability with different sediment beddings under the effect of loading and unloading by the triaxial coal-rock seepage experimental apparatus. The influence of gas pressure, loading-unloading, and sediment bedding direction on the permeability of coal samples was analyzed, and the functional relationship among these parameters was recovered by fitting. The results show that the permeability of all vertical, dip, and horizontal bedding coal samples decreases exponentially with the increase of effective stress during stress loading, while the permeability of three kinds of bedding coal samples increases exponentially with the decrease of effective stress during stress unloading. Under the same gas pressure, the fracture space of coal samples with vertical and dip bedding is more likely to be compressed and closed at the initial stage of loading, resulting in great decrease of the permeability. In the initial stage of unloading, the microcracks and natural beddings in coals gradually expand and connect. Due to the well development of fractures, the permeability of vertical bedding coal samples increases greatly, while the permeability of dip and horizontal bedding coal samples increases slightly. In the loading process, the permeability of coal sample is vertical bedding > dip bedding > horizontal bedding in order. For the tested samples, the permeability of vertical bedding coal samples is 1.3 to 2.8 times that of dip or horizontal bedding coal samples. In the unloading process, the permeability of the vertical bedding coal samples was 2.8 to 3.3 times that of the dip or horizontal bedding coal samples.