Unloading Rate Research Articles

Mechanical damage characteristics and acoustic emission characteristics of a bolt-slurry interface under cyclic pull-out loading

To consider the effects of various mining stresses in an actual project, a comprehensive laboratory pull-out study of the bolting system under different cyclic loads was carried out, a high stiffness MTS815.04 rock mechanics test system and an independently designed indirect pullout test device and an acoustic emission system was used for synchronous monitoring. Damage failure mechanism of bolt-slurry interface under cyclic loading revealed from macroscopic strength and deformation characteristics and microscopic damage in depth. The results are as follows.: (1) Compared with static pull-out loading, the bolting system under cyclic loading will enter the damage failure state earlier. (2) The greater the cyclic loading and unloading rate are, the greater the impact on the bolt-slurry interface, and the easier it is for sudden macroscopic damage to occur. (3) The greater the cyclic load stress amplitude is, the stronger the acoustic emission activity of the bolt-slurry interface, the greater the damage to the bolt-slurry interface, and the easier it is to fail and de-bond. (4) Finally, the acoustic emission energy, energy rate and count can be used to evaluate the damage characteristics of the anchor interface during cyclic drawing, and the analysis results are in good agreement with the macroscopic damage results. The research results can provide a reference for the support design and performance monitoring of full-length anchor bolts under different cyclic loads.

Experimental study on the effect of unloading rate on the damage of coal with boreholes

In coal mining, the gas pre-drainage boreholes in front of working faces are often repeated loading and unloading. Studying the failure characteristics of boreholes under cyclic loading has a guiding significance for clarifying the failure mechanism of gas pre-drainage boreholes. To simulate the influence of the advancing speed of the working face on the deformation instability of the borehole, a cyclic loading path under the influence of different unloading rates was designed. In this paper, the uniaxial cyclic loading test was conducted by the DYD-10 testing machine, and the variation law of mechanical strength characteristics with the unloading rate was obtained. Combined with digital image technology (XTDIC), the sample deformation characteristics were analyzed. The samples' compressive strength rose with the unloading rate. The sample was damaged in the tensile-shear composite form at different unloading rates. Crack opening displacement (COD) with the increase in the number of cycles shows a “stepwise” increase. Near the moment of destruction, COD suddenly increased. The number of surface fractures that could be seen reduced as the unloading rate increased, and reduced fragmentation when the sample failed. The various types of energy of the sample increase nonlinearly with the increase of the number of cycles, and the plastic damage energy drops as the unloading rate increases. When the external stress state enters the next stress state, the internal stress adjustment of the sample takes a particular time, which is manifested as lagging behind the change of the external stress state. The influence mechanism of stress adjustment lag on strength, crack evolution and damage under different unloading rates was proposed. The results of the study contribute to the research of destabilization control technology for gas pre-drainage boreholes.

A data assimilation method for blast load prediction

Blast load is a crucial parameter in blasting construction design and numerical simulation. However, it is characterized by dense energy, high loading rate and complex action process, which makes its accurate measurement difficult. In this study, based on experimental data-driven physical simulation, a data assimilation method for blast load prediction was proposed by integrating PFC2D software and Python language. The method can accurately measure the blast load, as it achieves an exact match between the numerical calculation results and the test far-field strain waves by automatically adjusting the peak blast pressure, rise/fall time and rock damping ratio. Furthermore, the effectiveness of the method was verified by performing rock blasting disturbance tests, and the superiority of the data assimilation algorithm was illustrated from two aspects, i.e., time-loading path and rock damping ratio. The following research results were obtained: 1) When the blast pressure is constant, the number of micro cracks within the rock decreases first and then increases with the rise of loading rate, while it always increases with the rise of unloading rate. Therefore, it is necessary to measure the time-loading path of blast pressure. 2) When the rock damping ratio deviates more notably from the true value, the error rate of the peak blast pressure by the assimilation method is greater correspondingly, indicating that the rock damping ratio is a prerequisite for accuracy of the assimilation method. 3) Superior to the traditional isentropic expansion theory, the assimilation algorithm not only accurately measures the peak blast pressure but also considers both the time-loading path and the rock damping ratio. The research results enrich rock dynamic tests and provide valuable references about blasting engineering.

Analisis Penentuan Tarif Bongkar Muat Peti Kemas Dengan Metode Activity Based Costing (Studi Kasus PT.Pelindo Terminal Petikemas New Makassar)

This study aims to analyze the determination of container loading and unloading rates using the activity-based costing method at PT PELINDO Terminal Petikemas New Makassar. The variable of this study is the determination of container loading and unloading rates measured using the activity-based costing method. The limits of this research are focused on domestic container loading and unloading rates. This is the case for data collection in the form of observations, interviews and documentation. Data analysis is done by quantitative descriptive analysis. The results of this study show that the calculation of container loading and unloading rates with the activity-based costing method is lower in full 20 feet containers of IDR 116,571.29, full 40 feet of IDR 228,808.74, empty 20 feet of IDR 197,415.69, and empty 40 feet of IDR 204,188.91. Compared with the results of the calculation of container loading and unloading rates carried out by the management of PT PELINDO Terminal Petikemas New Makassar. This is because container loading and unloading rates are calculated by the activity-based costing method based on the type of cost used and various cost drivers.

Numerical study of hydraulic characteristics of shale fractures during unloading-induced slipping: Effects of inclination angle and unloading rate

This study investigates the roles of inclination angle of fracture (θ) and unloading rate of confining pressure (Ur) on the hydraulic characteristics of shale fractures during the unloading-induced slipping process. A series of fluid flow simulations in the directions both parallel (x-directional) and perpendicular (y-directional) to the shear direction at different shear displacements (ds) were performed. The results show that the channeling effect is more pronounced in the y-direction than that in the x-direction. As ds increases, the fluid flow becomes less anisotropic, and the ratio of permeability in the y-direction (Ky) to that in the x-direction (Kx) gradually decreases first and then remains almost constant. Both Kx and Ky greatly increase with increasing in θ. The Ur significantly affects the permeability when ds increases to a certain value (i.e., 0.8 mm in this study). The efficiency of permeability enhancement represented by ΔK/Δds is evaluated. The mean ΔK/Δds during the slipping process for samples with θ = 50° is 4.73 times and 5.25 times larger than that for samples with θ = 30° in the x-direction and y-direction, respectively. With increasing Ur, the mean ΔK/Δds slightly increases first and then decreases. The occurrence of stick–slip events may control the ΔK/Δds.

Assessment of forces during side-posture adjustment with the use of a table-embedded force plate: Reference values for education.

Force-sensing treatment tables are becoming more commonly used by chiropractic educational institutions. However, when a table-embedded force platform is the sole measurement method, there is little information available about what force-time values instructors and students should expect for side-posture spinal manipulative thrusts. The purpose of this report is to provide force-time values recorded with such a system during side-posture manipulation with human recipients. Student volunteers were examined by and received lumbar or pelvic side-posture manipulation from experienced chiropractors who were diplomates of the Gonstead Clinical Studies Society. Forces were recorded using proprietary software of a Bertec force platform; force and time data were analyzed with a custom-programmed software tool in Excel. Seven doctors of chiropractic performed 24 thrusts on 23 student recipients. Preload forces, averaging 69.7 N, and thrust loading duration, averaging 167 milliseconds, were similar to previous studies of side-posture manipulation. Peak loads were higher than previous studies, averaging 1010.9 N. Other variables included prethrust liftoff force, times from thrust onset to peak force and peak load to resolution of thrust, and average rates of force loading and unloading. The values we found will be used for reference at our institution and may be useful to instructors at other chiropractic educational institutions, in the teaching of lumbar side-posture manipulation. A caveat is that the values of this study reflect multiple sources of applied force, not solely the force applied directly to the spine.

Investigation of the influence of model control parameters on fracture characteristics of GPU parallel FDEM

Surrounding rock mass fracture characteristics play a significant role in the understanding of the CO2 geological storage and utilization (CGSU) engineering practices in abandoned mines. The combined finite discrete element method (FDEM) shows advantages in simulating fracture and fragmentation of rock-like materials, however, many computational parameters and a lack of basis for accurate values affect the simulation results. For systematic explorations of the influence of the effect of model parameters with different time steps, this study conducted different loading rate specimen tests and unloading rate tests both in laboratory-scale tests and field-scale based on the CUDA-based GPU parallel FDEM program. In laboratory-scale uniaxial compressive strength (UCS) tests, a smaller loading rate ensures a quasi-static loading process and should be below 0.1 ms−1 for simulation. Then, continuous optimization and improvement of the GPU parallel FDEM in tunnel excavation were proposed, and the model parameters reflect the continuous improvement of the simulation results. In the process, the tunnel excavation simulation method with the reduction rate of the opening zone’s Young's modulus in the excavation was performed to investigate the unloading mode and rate by continuing to optimize the GPU parallel FDEM program and model parameters. Besides, the main factor in fracture mode and failure mechanism of the surrounding rock mass also was calibrated. The results indicate that the system kinetic energy of the model is maintained at a small level with the reasonable unloading mode and critical threshold set at a small value, the damping parameters, dissipation mechanism, and excavation fractures are clearer and reasonable, and the computational cost is significantly reduced with GPU parallel FDEM.

Safety of an express freight train running over a bridge in crosswind

Owing to the blunt car body and high design speed of express freight trains, the running safety is significantly affected by crosswinds when the train runs over a bridge; moreover, severe accidents, such as derailment or overturning may occur. Therefore, adequate measures should be adopted to avoid the occurrence of such accidents. In this study, a finite element model of the train, ballastless track, and parameterized 5-span simply supported girder bridge along with modal superposition method are adopted to establish the train-track-bridge coupling dynamic system. Numerical simulation of stochastic wind speed, wind tunnel tests, and computational fluid dynamics (CFD) simulation of vehicle-bridge scale model were conducted to calculate the wind load acting on the train and bridge. The dynamic responses of the bridge and train were evaluated to present the diagrams of wind and train speed limits for safe operation. The results indicated that the running safety of the vehicle declined with the wind and train speeds, and the wheel unloading rate was the most sensitive to wind speed. For safe operation, the train speed must be restricted if the mean wind speed is greater than 22.7 m/s, and an extreme scenario of derailment may occur for a mean wind speed of 34.0 m/s. In addition, the wind speed limit should be appropriately adjusted and improved according to the pier height of the bridge and terrain category. This research provides a theoretical basis and data support for the assessment of safety of express freight trains in actual operation.

Vertical compressive bearing performance and optimization design method of large-diameter manually-excavated rock-socketed cast-in-place piles

To study the vertical compressive bearing characteristics of large-diameter rock-socketed cast-in-place piles, eight manually-excavated rock-socketed cast-in-place piles were subjected to vertical compressive on-site load and pile stress tests. The test results showed that the load–displacement (Q-s) curves of the eight test piles were all slow-varying, and the settlement of the piles was less than 11 mm, which met the minimum engineering requirements. The unloading rebound rate was between 55 and 75%, and the elastic working properties of the piles were apparent. The pile axial force gradually decreased with depth, and the slope of the axial force distribution curve reached a minimum in the moderately weathered muddy siltstone layer while the pile side friction resistance reached its maximum value. Pile end friction increases with the increase of load. But the pile end resistance was inversely proportional to the single pile length-to-diameter (L/D) ratio and the depth of rock embedment for the pile. The percentage of pile side friction resistance under maximum load was 86%, indicating that these were characteristic friction piles. Based on the test results and the current Chinese code, the friction coefficient of the pile side soil layer η and the total resistance coefficient of the rock-socketed section ζ were introduced. A revision to the calculation equation for the vertical bearing capacity of the rock-socketed cast-in-place pile in the code was proposed, together with an optimization design method for large-diameter rock-socketed cast-in-place piles.

Train/track coupled dynamics model of long heavy haul train based on substructure and parallel computing

To consider the coupled effect on the running safety between elastic track and longitudinal impulse of Long Heavy Haul Train(LHHT), a train/track coupled dynamics model is established by using connection substructure theory. The ballasted track is divided into several segments called sub-tracks: a sub-track includes rail, sleepers and ballast. In the sub-track model, the sleepers and ballast are modelled as lumped mass. The rail is divided into the contact and connection rail. The contact rail is modelled as an Euler beam to reflect the wheel/rail interaction and the flexible vibration of the rail. The connection rail is modelled as a super element to reflect the interaction between adjacent contact rail. To increase the simulation speed, a new parallel computing method is proposed: a train/track coupled dynamics model is divided into different submodule, a submodule includes a sub-track and a vehicle on the sub-track. A submodule is calculated by a single computer core. The submodule is connected by connection rail, couplers and ballast. The advantage of this parallel method is that the load of each computer core is almost uniform. The simulation speed depends on the number of parallel computing cores instead of one core with a particularly large load. Finally, taking the 10,000-ton train as an example, the distribution of coupler force, the derailment coefficient and wheel unloading rate are given during the train braking on a curve, which shows the application and necessity of the train/track coupled dynamics model based on substructure and parallel computing.

Modeling on magnetization behavior of ferromagnetic material during cyclic deformation

In this paper, a nonlinear magneto-mechanical coupling constitutive model is established to describe the magnetization behavior of ferromagnetic materials under cyclic elastoplastic deformation. The critical state is introduced into the hysteretic magneto-mechanical model. In the critical state, the magnetization rates of loading and unloading are different. A new nonlinear plastic effective magnetic field is proposed by considering the effect of pinning sites caused by cross slip dislocation to describe the magnetization behavior under asymmetric cyclic loading. The softening factor and activation condition of plastic modulus parameter are introduced based on the cyclic plastic constitutive model to describe the decrease of plastic modulus. A new magnetization model for ferromagnetic materials under cyclic plastic deformation is established by combining the magneto-mechanical coupling model with the cyclic plastic constitutive model. Compared with the experiments and existing models, it is shown that the proposed model can capture the deformation and magnetization behavior well under cyclic loading.

Effect of liquid sloshing in lateral and longitudinal directions on railway tank cars based on an improved equivalent model

Additional slosh forces and moments are generated owing to the movement of the liquid inside a partly filled tank car. The loads may have a great influence on the structure reliability and dynamic performance of the vehicle. An improved equivalent model of liquid sloshing is put forward to obtain the forces and moments of sloshing liquid acting on the tank during the lateral and longitudinal sloshing processes. An improved method is proposed to obtain the equivalent masses and stiffness for the improved equivalent model. The equivalent model is integrated into the multi-body dynamic model of a railway tank car with 68 degrees of freedom. Furthermore, the equivalent liquid-vehicle model is used to investigate the effects of fluid sloshing on dynamic characteristics. The influence of the filling ratio on the dynamic response of the tank car is discussed based on the forces and the corresponding moments between the tank car body and the liquid in different layers. The railway tank car is obviously influenced by the liquid sloshing during passing the curved and sloped tracks. The influence of liquid sloshing on the pitching motion of the tank is heavy if the tank is about half filled. The derailment coefficient and the wheel unloading rate are slightly influenced by the filling ratio of tank cars on curved tracks while the indices of the tank cars on sloped tracks are the greatest if the filling ratio is 40%.

Theoretical study on dynamic stress redistribution around circular tunnel with different unloading paths

This study presents a solution for stress redistribution induced by dynamic excavation of a rock tunnel in hydrostatic and non-hydrostatic stress states. Considering rock as an elastic medium, the analytical solution of dynamic excavation unloading was derived in the Laplace transform space utilizing the wave function expansion method and mode decomposition, and transformed into the time domain using the approximate numerical inversion method. The effects of the unloading path (linear, cosine, and exponential), unloading rate, and initial stress state on stress redistribution were analyzed. The analytical results indicated that a high unloading rate led to a high stress concentration and oscillations around the tunnel, and instantaneous dynamic unloading caused 20–30% stress concentration. When dynamic unloading is complete, the stress state around the tunnel converges to the Kirsch solution. The 3D numerical results indicated that deformation of the tunnel boring face increased as the initial stress increased. Moreover, the accumulation and release of strain energy and stress state change paths were analyzed and discussed. The results of this study provide a theoretical basis for understanding the stress adjustment and failure of surrounding rock induced by excavation of deep-buried openings in hydrostatic and non-hydrostatic stress states.

Experimental and DEM Simulation Study on the Mechanical Characteristic and Strain Energy Evolution of Longmaxi Shale under a Confining Pressure Unloading Path

Drilling vertical and horizontal wellbores in the shale reservoir may trigger the in-situ stress release around the wellbore walls and change the original stress equilibrium state, leading the wellbores to instability. This stress change in the wellbore corresponds to the stress paths of confining pressure unloading and axial stress loading under laboratory conditions. In this paper, according to the conventional triaxial compression test results, laboratory experiments and DEM simulations by PFC2D were conducted to deeply study the strength, failure, strain energy evolution, and micro-crack damage mechanism of shale specimens under confining pressure unloading conditions. The shale specimens at different bedding inclinations were tested under different initial axial stress levels and confining pressure unloading rates, with fixed initial unloading confining pressure. This research revealed that confining pressure unloading induces greater plastic deformation, more micro-crack damage and strain energy dissipation, and a more complex failure pattern. The strain energy dissipation and dilatation under confining pressure unloading conditions are mainly induced by the generation and accumulation of tensile cracks. Moreover, the unloading rate has a significant effect on the mechanical properties, and the high unloading rate enhances the failure strength and induces more strain energy dissipation and micro tensile cracks. For the wellbore drilling in shale formations, when the buried depth and vertical stress are fixed, the lower the lateral stress is, the easier it is to form tensile failure around the wellbore wall in the drilling process, and the more induced fractures will be generated in the formation around the wellbore.

Drained instability of coarse oil sand tailings

Lateral stress relief and effective stress reduction have been recognised as the culprits in flow failures of several mine tailings dams. This research examines the instability of coarse oil sand tailings (CSTs) subjected to such a stress path through a series of monotonic direct simple shear tests. To investigate the impact of tailings fabric, laboratory specimens were reconstituted by moist-tamping, air pluviation and slurry deposition techniques. Loose, medium-dense and dense specimens were prepared and consolidated to target vertical and initial shear stresses. The vertical stress was subsequently unloaded while maintaining a constant initial shear stress under a drained condition. The occurrence of instability coincided with the volumetric collapse of the specimens followed by a sharp rise in shear strain. The effects of consolidation stress, bitumen, void ratio, initial shear stress and unloading rate on the drained instability of CST specimens were also investigated.

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths.

To investigate the strength and failure characteristics of silty mudstone using different stress paths, silt-like mudstone specimens were subjected to triaxial unloading tests. The results indicate the following. (1) When subjected to equivalent initial deviator stress levels and differing confining pressures, the peak stress, residual stress, and elastic modulus, exhibited during unloading, increased concordantly with greater initial confining pressure. Both the peak strain and residual strain increased with rising initial confining pressure. The increase in peak strain and residual strain initially decelerated, then noticeably increased, before ultimately decreasing again. Additionally, the unloading failure time and strain rate demonstrated a negative correlation as the confining pressure increased. (2) Under different initial deviatoric stress conditions, the peak stress, residual stress, and residual strain, under unloading confining pressure conditions, decreased as the initial deviatoric stress levels elevated. Conversely, the peak strain and elastic modulus initially increased, then decreased under increasing initial deviatoric stress conditions. The unloading failure time and strain rate were both observed to decrease as the initial deviatoric stress levels increased. (3) Utilizing the Mohr stress circle enabled the characterization of the shear strength variation in the specimens during the unloading process. The cohesion and internal friction angle remained relatively consistent across the different unloading stress paths appraised, with cohesion being greater in path I versus path II, whereas the internal friction angle exhibited an inverse relationship. (4) The specimen failed during unloading due to lateral expansion caused by unloading confining pressure and collapse failure. The failure fracture surfaces predominantly manifested shear failure morphologies.

Deformation and acoustic emission characteristics of hard rock under different unloading rates

In this paper, triaxial loading and unloading tests under different conditions were carried out to explore the deformation and failure characteristics of hard rock marble, and the acoustic emission information of the test process was monitored synchronously to obtain the acoustic emission distribution characteristics. The test results show that: (1) when the confining pressure unloading rate is low, the rock yielding is more obvious, the damage peak is higher, and the Poisson effect is more obvious under loading and unloading, while when the unloading rate is high, it shows multi-stage damage; (2) there is a linear relationship between strain deviatoric stress flexibility and unloading rate, as the unloading rate accelerates, the circumferential and volumetric flexibility increases and the axial flexibility decreases; (3) the lower the unloading rate, the higher the confining pressure, and the main shear surface of the rock gathers a large number of tensile microcracks to form a shear zone, while the higher the unloading rate, the lower the confining pressure, and the main shear surface is thoroughly penetrated and ruptured; (4) acoustic emission can characterize the damage degree of marble in the process of loading and unloading, when the confining pressure is low, acoustic emission at the peak damage point appears sharp phenomenon, the overall damage increases with the accelerated rate of unloading, when the confining pressure is high, acoustic emission grows progressively, the overall damage decreases with the accelerated rate of unloading, the overall damage of the rock will appear “ pre-peak to post-peak ” hysteresis effect.

Phase transition of sulfur during continuous impact loading-unloading process

Raman spectra of sulfur at a rapid unloading rate were obtained through a continuous impact loading-unloading process. In the process, we find that the values of the relative area ratios Av1, v2/Av3 (v1 is the peak at 156 cm−1, v2 at 217 cm−1 and v3 at 475 cm−1) are discontinuous with increasing pressure. The breakpoint is around 1.41 GPa, showing that a phase transition is likely to occur around this pressure. At the same time, when the pressure is higher to 5.45 GPa, the amortization of sulfur was detected, accompanied by a spectrum with the light absorption characteristic. This phenomenon is thought to be a unique amorphization phenomenon under impact loading.

Crack instability in deep coal seam induced by the coupling of mining unloading and gas driving and transformation of failure mode

Coal and gas outburst is a violent mechanical instability of gas-containing coal, and its mechanism is crucial for prevention of gas dynamic disasters. The macroscopic instability of gas-containing coal is the result of the expansion and connection of micro cracks driven by unloading induced tensile stress and gas pressure. This study is aimed at solving the problem of crack instability of gas-containing coal during mining unloading. To this end, first, the governing equations of unloading-induced tensile stress and gas pressure evolutions in cracks were built, and the dynamic evolutions and main controlling factors of tensile stress and gas pressure were revealed. Furthermore, the evaluation indexes of crack stability under tensile stress and shear stress were established, and the variation of crack stability during unloading was investigated. Finally, the phase diagram of crack failure mode was drawn, and the transformation of crack failure mode was analyzed. The results show that unloading-induced tensile stress is generated when θ > 54.73°, and it rises gradually with the increase of original stress, unloading rate, unloading time and crack size and dip angle. Overall, gas pressure in cracks increases first and then decreases during unloading. It increases gradually with the increase of initial gas pressure, gas desorption rate and original stress, while it decreases as the unloading rate gets higher (k from 10−4 to 10−2 s−1) and the dip angle gets larger (θ from 50 to 90°). With the increase of unloading ratio, the crack stability declines slowly first and then plunges rapidly until the crack finally becomes unstable. In addition, burial depth of coal seam, unloading rate, gas desorption rate and mechanical strength of coal have significant effects on this process. Different factors have important influences on the crack failure mode. With the increase of burial depth from 100 to 2000 m, the crack failure mode gradually transforms from tensile failure to shear failure, and the higher the unloading rate is, the more easily tensile failure occurs. With the increase of cohesion (0.1–2 MPa), the scope of the shear failure zone shrinks gradually, and the crack is less prone to shear failure. The desorption rate has a notable effect on the scope of the non-failure zone. Under a higher gas desorption rate, the scope of the non-failure zone becomes smaller, which is due to the greater gas pressure in crack for a given time. The research in this paper has certain reference value for further grasping of the instability failure of gas-containing coal and the mechanism of coal and gas outburst.

The Deformation Behavior and Failure Modes of Surrounding Rock after Excavation: A Experimental Study

The deformation and failure of the surrounding rock during roadway excavation often determine the choice of supporting methods. To study the deformation behavior and failure modes of the surrounding rock after excavation under unloading stress, structural model tests were carried out with a novel experimental device. The present structural model test using partial hollow thick-walled cylinder cement mortar specimen φ200 mm × 280 mm with a horizontal central circular hole of 60 mm diameter and the hollow height of 160 mm was conducted to investigate the deformation, failure characteristics, and AE response of a whole testing process from excavation to postunloading state. Experimental results revealed that the amount of deformation behind the surface is significantly higher than that in front of the surface, and the radial strain increases with the increase of the distance from the surface within the range affected by unloading. Furthermore, the unloading rate has a little effect on the radial deformation of the surrounding rock in front of the surface, but has a substantial effect on the radial deformation behind the excavation surface. The peak value of the strain rate at the unloading rate of 2 MPa/s is much higher than that at the unloading rate of 0.1 MPa/s. According to AE results and the failure of opening the boundary, the increase of unloading rate triggers and exacerbates the damage of the specimen under high in situ stress conditions. The surrounding rock expanded to the inner hollow, accompanied by large dilation and volume changes, and it resulted in the shrinkage of the hole diameter. A large number of rock slices are generated at the opening curved free surface and then fell off, whose morphology is similar to the rock blocks that fell off after caving failure and rock burst in situ field. The results show that the system can accurately simulate the mechanical response and acoustic emission response of the excavated surrounding rock, which provides a new experimental method for further study of the unloading response of the surrounding rock.