Fast Lagrangian Analysis Of Continua Research Articles

A numerical investigation into the equivalent parameters of a compressible soil treated by stone columns

A series of triaxial test simulations are adopted to estimate the equivalent strength parameters for compressible soil samples reinforced with stone columns. The simulations utilize the finite difference code, Fast Lagrangian Analysis of Continua in three dimensions FLAC3D. An elasto-plastic model is applied to utilize a Mohr-Coulomb yield criterion. The equivalent strength parameters are estimated using newly proposed formulas for geo-composite materials. The researchers compare the obtained results to the analytical formulas proposed in the literature. Additionally, the equivalent parameters are used in equivalent area models. This study investigates the effect of the replacement area ratio. This study offers two applications. Firstly, it evaluates the safety factor of embankments constructed on compressible soil improved with stone columns. Secondly, it estimates the bearing capacity of strip footings on compressible soil treated with stone columns. In all applications, both individual column and equivalent area models are considered. The proposed equations for the equivalent elastic parameters (E, ν) and the mechanical properties, equivalent cohesion, and internal frictional angle (c and φ) give results that agree with the solutions reported in the existing literature.

Numerical investigation of granular column-improved soils using the direct shear test

The granular columns treatment is widely used in the weak soils. The present paper focuses on the numerical modeling of a direct shear test on granular columns in soils. The finite difference code Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was used in this research work, to evaluate the equivalent properties of granular column-improved soils with different diameters of the columns, and different plan configurations. The results of these numerical tests are discussed in terms of increases the shear load-strength and decreases the horizontal displacement due to the variation of arrangements, Young's modulus and the friction angle of the granular columns. Different types of failures observed in the granular columns. Bending failure mode is the main in the granular column with large values of Young's modulus and the friction angle when subjected a lateral load.

The pioneer of intelligent and sustainable construction in tunnel shotcrete applications: a comprehensive experimental and numerical study on a self-sensing and self-heating green cement-based composite

In this study, a self-sensing and self-heating natural fibre-reinforced cementitious composite for the shotcrete technique was developed using Kenaf fibres. For this purpose, a series of Kenaf fibre concentrations were subjected to initial chemical treatment, followed by integration into the cement-based composite containing hybrid carbon nanotubes (CNT) and graphene nanoplatelets (GNP). The investigation encompassed an examination of mechanical, microstructural, sensing, and joule heating performances of the environmentally friendly shotcrete mixture, with subsequent comparisons drawn against a counterpart blend featuring a conventionally synthesized polypropylene (PP) fibre. Following the experimental phase, a comprehensive 3D nonlinear finite difference (3D NLFD) model of an urban twin road tunnel, completed with all relevant components, was meticulously formulated using the FLAC3D (fast lagrangian analysis of continua in 3 dimensions) code. This model was subjected to rigorous validation procedures. The performances of this green shotcrete mixture as the lining of the inner shell of the tunnel were assessed comparatively using this 3D numerical model under static and dynamic loading. The twin tunnel was subjected to a harmonic seismic load as a dynamic load with a duration of 15 s. The laboratory findings showed a reduction in the composite sensing and heating potentials in both cases of Kenaf and PP fibre reinforcement. Incorporating a specific quantity of fibre yields a substantial enhancement in both the mechanical characteristics and microstructural attributes of the composite. An analysis of digital image correlation demonstrated that Kenaf fibres were highly effective in controlling cracks in cement-based composites. Furthermore, based on the static and dynamic 3DNLFD analysis, this green cement-based composite demonstrated its potential for shotcrete applications as the lining of the inner shell of the tunnel. This study opens an appropriate perspective on the extensive and competent contribution of natural fibres for multifunctional sustainable, reliable and affordable cement-based composite developments for today’s world.

Seismic Structure-Soil-Structure Interaction (SSSI) between piled neighboring bridges: Influence of height ratio

Abstract This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interaction (SSSI) for three adjacent bridges with varying superstructure masses (Mst = 350, 1050, 350 t) through 3D numerical simulations. A comprehensive series of numerical analyses has been conducted across different height ratios (R = 1, 1.1, 1.15, 1.2, 1.25, 1.5, 2, and 3) to assess their influence on superstructure acceleration and the internal forces within the foundation piles. The bridges under investigation are supported by groups of piles embedded in nonlinear clay. The numerical simulations were executed using fast Lagrangian analysis of continua in three dimensions (FLAC 3D), a three-dimensional finite differences modeling software. The findings revealed that variations in mass ratios significantly impact the SSSI effects on superstructure acceleration and pile internal forces. Notably, adverse effects were more pronounced for mass ratios of R = 1.1 and 1.2, leading to an increase in bending moment, shear force, and superstructure acceleration by up to 237.8%, 291.4%, and 70.33%, respectively. In contrast, a mass ratio of R = 3 resulted in a decrease in bending moment, shear force, and superstructure acceleration by up to 72%, 82.14%, and 81.13%, respectively. This implies that a careful arrangement of adjacent structures with different masses can be employed effectively to manage the (SSSI) effects.

Excavation compensation and bolt support for a deep mine drift

To overcome large deformation of deep phosphate rock roadways and pillar damage, a new type of constant-resistance large-deformation negative Poisson's ratio (NPR) bolt that can withstand a high pre-stress of at least 130 KN was developed. In the conducted tests, the amount of deformation was 200–2000 mm, the breaking force reached 350 KN, and a high constant-resistance pre-stress was maintained during the deformation process. A stress compensation theory of phosphate rock excavation based on NPR bolts is proposed together with a balance system for bolt compensation of the time-space effect and high NPR pre-stress. Traditional split-set rock bolts are unable to maintain the stability of roadway roofs and pillars. To verify the support effect of the proposed bolt, field tests were conducted using both the proposed NPR bolts and split-set rock bolts as support systems on the same mining face. In addition, the stress compensation mechanism of roadway mining was simulated using the particle flow code in three dimensions (PFC3D)-fast Lagrangian analysis of continua (FLAC3D) particle-flow coupling numerical model. On-site monitoring and numerical simulations showed that the NPR excavation compensation support scheme effectively improves the stress state of the bolts and reduces the deformation of the surrounding rock. Compared to the original support scheme, the final deformation of the surrounding rock was reduced by approximately 70%. These results significantly contribute to domestic and foreign research on phosphate-rock NPR compensation support technology, theoretical systems, and engineering practices, and further promote technological innovation in the phosphate rock mining industry.

Effect of Multiple Factors for the Roadway Excavation Process Stability in FLAC3D

Abstract Appropriate simulation set parameters are the precondition to obtain accurate results; while the simulation results are affected by multiple factors, it is thus crucial to investigate the sensibility of different factors. This paper first analyses the application situation of numerical simulation software in the field of geotechnical engineering and finds that Fast Lagrangian analysis of continua in three dimensions (FLAC3D) has been widely used on roadways or tunnels. Then, taking the roadway excavation process as the engineering background, FLAC3D was used to create 171 schemes of different simulation parameters and analyze the influence of different factors on the simulation results. The findings show that there is a considerable difference in the degree of effect of different parameters on the simulation results. Most of the factors have a remarkable effect on the numerical simulation results (displacement and stress), and only some factors (parameter uniformity and density) have almost no effect on the results. Meanwhile, the trend of displacement and stress is opposite in most cases. In addition, some neglected factors can also have a considerable effect on the simulation results, such as the zone amount; therefore, it is necessary to avoid the variation of nonstudy factors as possible when carrying out the numerical simulation. This study may significantly assist concerned engineers and technicians in developing a more organized and thorough grasp of the impacts of various parameters on simulation outcomes.

Assessment of stability of earth dams based on construction pace by fuzzy inference logic

This study aims to evaluate the earth dam stability fuzzy model based on the pace of construction by way of influential parameters, including the dam construction time (embankment consolidation time) in the stability analysis of earth dams. A fuzzy inference system based on the Sugeno inference engine was developed, and 620 if-then rules in plane strain and axial symmetry (Plaxis) were used to train the fuzzy system. The input parameters included the dam height, crest width, dam slope, cohesion, friction angle, elasticity modulus, Poisson’s ratio, unsaturated unit weight, consolidation (construction) time and permeability coefficient, with the factor of safety output. To develop the fuzzy inference system, a triangular membership function was employed, calculating the influential parameters over five periods in Matrix laboratory (Matlab) software. The fuzzy model results were compared with the results of numerical Plaxis and fast Lagrangian analysis of continua models. High coefficients of determination (R2) suggest good agreement between the fuzzy and numerical models, and it can be assumed that the proposed fuzzy model is efficient and effective for the stability analysis, and hence assessment of factors of safety, of earth dams.

Scaling factors for 1-D ground response amplification in a soft soil basin

Basin presence is believed to affect the ground surface response due to earthquakes, particularly in areas around the basin edge. Previous studies showed that 1-D and 2-D wave propagation analyses resulted in significant differences in amplification at the basin edge. However, the link between 1-D and 2-D responses has not been studied for engineering practices. In practical application, seismic studies were commonly performed using 1-D analysis, for example, to develop a city micro-zonation map. Based on practical considerations, it is necessary to estimate the scaling factor for the 1-D analysis by considering the basin presence, particularly for one containing soft soil. There are three stages carried out in this study. The first stage: collecting data on some basin geometries for the 2-D modeling references and then defining selected site class and input motions. The second stage: modeling 1-D and 2-D wave propagation using D-MOD and Fast Lagrangian Analysis of Continua (FLAC), respectively. The third stage: comparing spectral acceleration resulting from the 1-D and 2-D analyses to obtain the scaling factors. This research studied and reported the relationship between PGA values varied as 0.2 g, 0.3 g, 0.4 g, and 0.5 g, basin geometry (e.g., the angle was set to 5°, 10°, 15°, 30°, and 45°, with depth and width variations of 0.0125, 0.025, 0.05, 0.075, 0.1, 0.2, and 0.4, while the basin width was adjusted to 500 m, 1 km, 2 km, and 4 km), and the spectral acceleration in several observation points on the ground surface. Based on this evaluation, a series of scaling factors are proposed. These factors can be used for spectral acceleration from available hazard maps, commonly developed based on 1-D analysis. The application example of this scaling factor is presented in this study, using the Bandung Basin case.

A method for determining the optimum supporting opportunity of roadway based on energy dissipation

The time and space of the support structure applying is related to the overall stability of the roadway after excavation directly. Designed twenty-four groups of roadway support schemes with time and space dimensions, and studied the stability characteristics of roadway in different schemes by using Fast Lagrangian Analysis of Continua in Three Dimensions. The main conclusions are as follows: the influence of energy dissipation (time) and support position (space) on the stability of the roadway is not a linear relationship, and supporting at the appropriate opportunity can be beneficial. Established the "displacement-dissipation energy" curve, founding that there is an obvious "jump" phenomenon in the dissipation energy of surrounding rock during the process of gradually increasing displacement. A novel method for determining the optimum supporting opportunity of roadway based on energy dissipation was proposed, based on the above finding. This study can provide an original idea for the determination of roadway supporting opportunity.

Sliding behaviors of the trapezoidal roof rock block under a lateral dynamic disturbance

The surrounding rock of underground space is always affected by external dynamic disturbance from the side position, such as blasting vibration from a stope at the same level or seismic waves from adjacent strata. A series of laboratory tests, numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance. Firstly, the experiments on trapezoidal key block under various clamping loads and disturbance were conducted, followed by numerical simulations using the fast Lagrangian analysis of continua (FLAC3D). Then, based on the conventional wave propagation model and the classical shear-slip constitutive model, a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block. The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide (without instability). Meanwhile, when the key block was disturbed to fall, two types of instability process may appear as immediate type or delayed type. In addition, the propagation of stress waves in the block system exhibited obvious low-velocity and low-frequency characteristics, resulting in the friction reduction effect appearing at the contact interface, which is the essential reason for the sliding of rock blocks. The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rock-falling disasters.

Thermo-hydro-mechanical (THM) coupled simulation of the land subsidence due to aquifer thermal energy storage (ATES) system in soft soils

Aquifer thermal energy storage (ATES) system has received attention for heating or cooling buildings. However, it is well known that land subsidence becomes a major environmental concern for ATES projects. Yet, the effect of temperature on land subsidence has received practically no attention in the past. This paper presents a thermo-hydro-mechanical (THM) coupled numerical study on an ATES system in Shanghai, China. Four water wells were installed for seasonal heating and cooling of an agriculture greenhouse. The target aquifer at a depth of 74–104.5 m consisted of alternating layers of sand and silty sand and was covered with clay. Groundwater level, temperature, and land subsidence data from 2015 to 2017 were collected using field monitoring instruments. Constrained by data, we constructed a field scale three-dimensional (3D) model using TOUGH (Transport of Unsaturated Groundwater and Heat) and FLAC3D (Fast Lagrangian Analysis of Continua) equipped with a thermo-elastoplastic constitutive model. The effectiveness of the numerical model was validated by field data. The model was used to reproduce groundwater flow, heat transfer, and mechanical responses in porous media over three years and capture the thermo- and pressure-induced land subsidence. The results show that the maximum thermo-induced land subsidence accounts for about 60% of the total subsidence. The thermo-induced subsidence is slightly greater in winter than that in summer, and more pronounced near the cold well area than the hot well area. This study provides some valuable guidelines for controlling land subsidence caused by ATES systems installed in soft soils.

Numerical Study on Optimization of Piled Raft Foundation on Stratified Soil under Static Load

Piled raft foundation (PRF) is a combination of pile and raft that provides adequate bearing capacity under the allowable settlement. This research aims to optimize the PRF design for a 48-story Commercial Bank headquarters building in Addis Ababa, Ethiopia, by conducting parametric study on various pile configuration using FLAC3D (Fast Lagrangian Analysis of Continua in three Dimensions) software. We analyzed 28 piled raft configurations and found that increasing the distance between piles increases the raft load sharing distribution by 11.5% while reducing settlement. Despite variations in pile length and diameter, a close load sharing between the pile and raft is accomplished at a separation of seven times the pile diameter (7D). The largest settlement decrease achieved was 9% for a 2-m pile diameter by doubling the pile length from 10 to 20 m, indicating that increasing pile length is ineffective for settlement reduction. We also proposed two new pile configurations that share load equally among pile and raft, and slightly increase total settlement below 10-cm limit. The results show that the first configuration exceeds differential settlement limit, but the second configuration reduces it by 95% and saves 40% of piles. This study provides a useful reference for designing PRF for high-rise buildings in similar soil conditions.

Pattern of Influence of the Mining Direction of the Protective Seam on the Stress of the Surrounding Rock

The maximum principal stress of the original rock has obvious directionality, and the pressure relief effect is different when the protective seam is mined along different directions. In this paper, the Fast Lagrangian Analysis of Continua (FLAC3D 6.0) numerical simulation software was used to establish a numerical calculation model according to the actual stratum conditions of the Pingdingshan No. 8 Coal Mine. The distribution and evolutionary characteristics of three-dimensional stress and three-dimensional displacement of the stope are studied under the condition that the mining direction of the protective seam is parallel to or vertical to the maximum principal stress direction of the original rock; the pattern of influence of the mining direction on the pressure relief and outburst prevention effect of the protective seam mining is analyzed. For the protective seam, the maximum principal stress in the coal in front of the protective seam cut–hole is significantly reduced, and the outburst potential is reduced in parallel mining. However, in vertical mining, the maximum principal stress in the coal in front of the protective seam cut–hole increases significantly, and the outburst potential increases. For the protective seam and surrounding rock, parallel mining can more fully reduce the maximum principal stress of the protective seam, reduce the difference in the three-dimensional stress, and effectively reduce the outburst potential of the protective seam. Therefore, parallel mining can not only improve the safety of the protective seam but also improve the pressure relief and outburst prevention effect of the protective seam. This conclusion is verified by the outburst prevention effect of the parallel mining of the remote upper protective seam in the Pingdingshan No. 8 Coal Mine. The research results are helpful for optimizing mine outburst potential prevention and control work from the aspect of mining layout. Through parallel mining, the outburst potential of the mine can be effectively reduced overall.

Impact of Soil Properties’ Spatial Correlation Lengths and Inclination on Permanent Slope Displacements Due to Earthquake Excitation

Natural disasters, when and where they occur, often cause serious social and economic consequences, which require an urgent solution to the problem. In particular, Greece, which is characterized by a complex geological structure and intense tectonic stress, has suffered and continues to suffer the consequences of such catastrophic phenomena. Among the various destructive phenomena recorded on the Earth’s surface, two of the most important problems are landslides and land subsidence. The above phenomena may cause, in addition to the serious case of loss of human life, a threat to the social and economic fabric affecting sustainability in general, i.e., the quality of life of an area (destruction of property, filling of reservoirs, blockage of streams and rivers, etc.). In fact, landslides are a phenomenon with enormous social and economic consequences, since apart from the financial burden due to the collapse of a technical project or the interruption of transportation, they are accompanied by the loss of human life. This research examines the stochastic characteristics of a slopes’ stability to investigate the variation range of permanent earthquake movements. More specifically, the influence of inclination as well as the lengths of the spatial correlation of ground are investigated. The method in the present study follows the development of arbitrary fields of soil properties, which follow the Gaussian distribution characterized by autocorrelation lengths lx and ly in the horizontal and vertical directions, respectively, mean value μ, standard deviation σ, and cross-correlation coefficients ρij. The estimation of permanent displacements is performed by the combination of the Local Average Subdivision algorithm and the FLAC software (Fast Lagrangian Analysis of Continua) used in the parametric investigation of this work. The results of this research showed that the spatial correlation of the properties has an important impact on the permanent displacements of slopes caused by strong earthquake excitations.

Three-dimensional strength reduction and two-dimensional limit equilibrium methods of slope stability analysis

Landslides caused tremendous damage to the life and properties of society. In this study, cut slopes were analyzed using the two-dimensional (2D) limit equilibrium method (LEM) by slope/w software and a three-dimensional (3D) strength reduction method (SRM) by using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D), which is a finite difference method (FDM) numerical software. Analysis of the slope is done by representative soil samples collected and transported to the laboratory to determine input parameters like unit weight (γ), shear strength parameters (c,φ), and the water level position. Strength parameters were determined from direct shear tests for cohesionless soil and consolidated undrained (CU) triaxial tests for cohesive soils. For 2D analysis, the factor of safety (FOS) was calculated for the condition of dry and maximum water levels using Morgenstern-price methods, and the analysis gave FOS 0.743 and 0.614 for the dry and maximum water level conditions, respectively; for SRM, the input parameters of bulk and shear modulus (B, G) which were determined from the empirical equation using modulus of elasticity(E) and Poisson's ratio(ʋ).Moreover, ʋ were adjusted according to the principle of φ-v inequality. For 2D analysis, FOS were 0.743 and 0.614 for dry and maximum water levels using Morgenstern-price methods, whereas 3D analysis gave FOS 0.34 and 0.31 for dry and maximum water levels, respectively. From the analysis, it is concluded that 2D LEM is given higher FOS than 3D FDM. Moreover, the 3D analysis showed that velocity and displacement in the lateral Y direction were minimal and maximum in the horizontal X direction. The maximum horizontal velocity for the respective dry and maximum water level conditions gave 6.64*10−4 m/step and 6.04*10−4 m/step and maximum horizontal displacement 7.36 m and 6.06 m for dry and maximum water levels, respectively.

Slope Stability and Effectiveness of Treatment Measures during Earthquake

Slopes are prone to instability during earthquakes, which will cause geological disasters such as landslides and pose a great threat to people’s lives and property. Therefore, it is necessary to analyze the stability of slopes and the effectiveness of treatment measures during earthquakes. In this study, an actual slope in the creeping slide stage was selected and located in an area where earthquakes occur frequently. Once the slope experiences instability, it will produce great damage. Therefore, a finite difference program, Fast Lagrangian Analysis of Continua in Two Dimensions (FLAC2D), was employed in the numerical simulation to explore the stability of the slope before and after treatment under earthquake action. Different from previous studies, this study explores the effectiveness of various treatment measures on slope stability during earthquake. The computed results show that the stability of the slope is greatly influenced by earthquakes, and the slope displacement under seismic conditions is far larger than that under natural conditions. Three treatment measures, including excavation, anti-slide piles, and anchor cables, can significantly reduce slope displacement and the internal force on anti-slide piles, and improve the stability of a slope during an earthquake. This will provide a valuable reference for the strengthening strategies of unstable slopes. The analysis technique as well as the derived insights are of significance for slope stability and the effectiveness of treatment measures.

A preliminary analysis of the mining-induced rock movement characteristics in the Xinli deposit of the Sanshandao gold mine

Commensurate with economic globalization, the demand for mineral resources is increasing. With increased mining activity, problems related to ground subsidence and rock movement are becoming increasingly prominent, even affecting mining production activities. However, the physical mechanisms behind the ground subsidence phenomenon have been poorly studied, especially for metal mines with a steep dip. This paper applies the Interferometric Synthetic Aperture Radar (InSAR) technique and the numerical simulation method to deduce the characteristics of rock movement in the Xinli deposit of the steeply inclined Sanshandao gold mine. The InSAR results indicate that more subsidence has occurred in the southern part of the Xinli Village coastline area than in the northern part. This is also supported by the numerical simulation results obtained by the fast Lagrangian analysis of continua in three dimensions (FLAC3D). Notably, the range of ground subsidence obtained by numerical simulation shows an obvious asymmetry. The monitoring data of the No. 55 prospecting profile offer a plausible explanation for this, as the surrounding rock of the fault’s hanging wall has a wider range of rock movements. Furthermore, the sublevels of the No. 55 prospecting profile at different depths show different rock movement characteristics, and a logistic function can be well applied to the right part of the settlement curve; the parameter “a” in the function formula is very close to the maximum subsidence value for each sublevel. We defined the ratio “r” to measure the difference between the maximum subsidence value and the corresponding parameter “a” and found this value to be positively correlated with the fractal dimension value of deeper sublevels (−320 m, −400 m, −480 m, and −600 m) and negatively correlated with the fractal dimension value of lower sublevels (−200 m and −240 m).

Analysis of the damage mechanism of strainbursts by a global-local modeling approach

Strainburst is the most common type of rockbursts. The research of strainburst damage mechanisms is helpful to improve and optimize the rock support design in the burst-prone ground. In this study, an improved global-local modeling approach was first adopted to study strainburst damage mechanisms. The extracted stresses induced by multiple excavations from a three-dimensional (3D) global model established by fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) are used as boundary conditions for a two-dimensional (2D) local model of a deep roadway built by universal distinct element code (UDEC) to simulate realistic stress loading paths and conduct a detailed analysis of rockburst damage from both micro and macro perspectives. The results suggest that the deformation and damage level of the roadway gradually increase with the growth of surrounding rock stress caused by the superposition of mining- or excavation-induced stresses of the panel and nearby roadways. The significant increase of surrounding rock stresses will result in more accumulated strain energy in two sidewalls, providing a necessary condition for the strainburst occurrence in the dynamic stage. The strainburst damage mechanism for the study site combines three types of damage: rock ejection, rock bulking, and rockfall. During the strainburst, initiation, propagation, and development of tensile cracks play a crucial role in controlling macroscopic failure of surrounding rock masses, although the shear crack always accounts for the main proportion of damage levels. The deformation and damage level of the roadway during a strainburst positively correlate with the increasing peak particle velocities (PPVs). The yielding steel arch might not dissipate kinetic energy and mitigate strainburst damage effectively due to the limited energy absorption capacity. The principles to control and mitigate strainburst damage are proposed in this paper. This study presents a systematic framework to investigate strainburst damage mechanisms using the global-local modeling approach.

Study of the Evolution Characteristics of Microseismic Events during the Excavation of Underground Caverns under High Geostress

A microseismic (MS) monitoring system was established, and numerical modeling was performed using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) to examine the evolution characteristics of MS events during the excavation of underground caverns under high geostress. Specifically, the spatial and temporal damage characteristics of the rock mass, the dynamic relationship between the evolution of MS events, the site construction conditions, and the geological structures under high geostress were also analyzed. In addition, a three-dimensional numerical model of underground caverns was built to demonstrate the deformation characteristics of the rock mass. As a result, the characteristics of a large number of MS events, multiple concentration zones of MS events, and long periods of stress adjustment were discovered in underground caverns under high geostress. It was found that the primary cause of MS events was site blasting construction. In particular, the distribution of the MS events was strongly correlated with the location of the site blasting construction, and the frequency of the MS events was positively correlated with it. The structural plane is a discontinuous plane with very low or no tensile strength, and its presence also increased the number of MS events and raised the possibility of the surrounding rock becoming unstable. Moreover, the MS monitoring data agreed with the numerical modeling results, which can be useful in estimating damage to underground caverns under high geostress and predicting disasters.

Influence of the Preexisting Fracture Network on the Mechanical Properties of Rock Mass and the Secondary Crack Propagation

Preexisting fracture network (PFN) is ubiquitous in natural rock mass and is one of the key factors affecting the mechanical properties of rock mass. This research employed a combined approach of theoretical analysis and finite element numerical simulation to investigate the mechanical behavior of PFN-containing rock mass. Based on the sliding crack model and fracture mechanics theory, the initiation mechanism of closed and open cracks driven by compressive and shear stress was theoretically analyzed. Rock mass models with different inclination angles (β) of PFN were built in Fast Lagrangian Analysis of Continua in 3 Dimensions. The complete stress–strain curves of rock mass and the secondary crack propagation were obtained. Results indicated that the increase of β reduced the strength and elastic modulus of rock mass. When β is less than 45°, this influence is more prominent. Based on the load-bearing capacity of PFN-containing rock mass, the stress–strain curves can be classified into two types: type I curve has multipeak and is strain-softening in the postpeak stage when β is 15°, 30°, 45°, 60°, and 90°; type II curve is unimodal and with brittle failure when β is 60° and 75°. Secondary crack propagation can be classified into four main types: type I is the coplanar crack, type II is the wing crack around PFN, type III is the near-field wing crack, and type IV is the macroscopic shear crack.