bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation analysis of the shear tests on cemented surface between bedrock and concrete
Authors: Wu C J , Lai Y J , Yu J
Published: November 2020

Based on anchorage foundation of Ganjiang Highway Bridge situated on weakly weathered argillaceous siltstone, numerical simulation analysis of shear tests were carried out to investigate the shear strength of cemented surface, which is between anchorage foundation concrete and bedrock surface. In order to evaluate the effect on shear strength effectively due to the cemented surface roughness, random distribution of parameters is firstly introduced to quantify the roughness and the Monte-Carlo method is employed to simulate the morphology of cemented surface. Secondly, numerical simulation analysis on shear tests is implemented to study the effect of different cemented surface roughness on shear strength. At last, a new evaluation method of cemented surface shear strength is put forward based on the numerical simulation with random contact interface. In addition, the results from numerical simulation method are compared with the field direct shear test, and it is validated that the results are highly consistent.
Numerical simulation study of the support system by gob-side entry retaining by roof cutting
Authors: Li Wei Tao , Guo Zhi Biao
Published: November 2020

Gob-side entry retaining by roof cutting (GERRC) is an innovative, long-wall mining method that has been widely used in China as a new mining revolution. However, current research on the influence of this technology on the support system remains limited. To understand the response of each supporting structure after cutting the roof, this study uses the cable element and beam element built in the finite difference software FLAC3D to simulate the bolt, anchor cable, steel beam, and single hydraulic props based on the engineering geological conditions of the Lvtang Coal Mine in Guizhou Province, China. Then, the force and displacement changes of each supporting structure between the GERRC and traditional coal pillar mining are compared and analyzed. Simulation results reveal that during the process of conventional mining, the force and deformation of anchor cable behind the working face is relatively large; furthermore, even yield and breaking of the cable occurs. Meanwhile, the serious deformation of a single hydraulic prop occurs, which affects the normal use of the roadway. When the GERRC is adopted, the force of each supporting structure is reduced by 17.6% on average and the deformation is not obvious. Moreover, using the GERRC decreases the stress of the supporting and reduces the displacement of solid coal in the roadway by 33.3%. Finally, the concentration degree of stress becomes lower, and the environment of retaining roadway is more optimized.
Influence of rainfall on transient seepage field of deep landslides: A case study of area II of Jinpingzi landslide
Authors: Jing Fu , Ling Huang Shu , Xiuli Ding , Jinlong Wang
Published: November 2020

Rainfall is one of the primary factors that induce landslides. Rainfall infiltration forms a transient seepage field in slopes, thereby leading to an increase in water content, a decrease in matric suction, and an increase in the volume weight of slopes. The increase in water content in rock and soil leads to the degradation of the mechanical properties of the slope medium and reduces the shear strength, thus causing slope instability. In this study, a large-scale accumulation landslide is taken as the research object. The front edge of the landslide is high and is not eroded by river water. Hence, rainfall is regarded as the main external factor that changes the groundwater and seepage field of the landslide. According to the landslide’s topography, geological data, local rainfall, and hydrological monitoring results, the saturated–unsaturated seepage theory of rock and soil and the finite difference method are used to analyze the impact of rainfall on the landslide’s seepage field and groundwater. The evolution law of the transient seepage field of the landslide under the condition of rainfall duration is studied. The results provide a basis for the analysis of landslide deformation and stability.
Casing Deformation Caused by Hydraulic Fracturing-Induced Fault Slip in Sichuan Basin and Optimization of Treatment Parameters
Authors: Huang Rui , Chen Zhaowei , Zeng Bo , Song Yi , Zhou Xiaojin
Published: November 2020

Casing deformation is a key issue that restricts the efficient development of shale gas in the Sichuan Basin. In this study, the H pad of shale gas wells in this area is used to determine correlations among the casing deformation and ant-tracking faults, microseismic events, and treatment pressure. The results show that the deformation might have been caused by fault slip induced by hydraulic fracturing. Moreover, three-dimensional seismic and well log data are used to establish fracture and in situ stress models based on discrete fracture network and finite element methods, respectively. The relationship between treatment parameters and fault activation is established by hydraulic fracturing simulation, from which the parameter sensitivity is evaluated. The results show that when the fluid volume is reduced by 20%, the length of the activated fault and the number of activated fractures decrease by 9% and 23%, respectively. In contrast, when the pumping rate is reduced by 20%, these parameters decrease by 25% and 38%, respectively. These results indicate that reducing the pumping rate is more effective than reducing the fluid volume for mitigating fault activation. In summary, arranging the fracture stages adjacent to the fracture zones should reduce the pumping rate to some extent. This method can be used to mitigate fault activation during hydraulic fracturing, which in turn can prevent casing deformation.
Dynamic Stress Field Evolution of the Shale Oil Reservoirs: Development and Optimization of Well Patterns
Authors: Wang Shiguo , Jin Yan , Wei Shiming , Xia Yang
Published: November 2020

Research on shale oil has gained considerable attention with regard to global unconventional oil exploration, which is of the strategic significance in the field of energy. Considering the characteristics of continental shale reservoirs, a three-dimensional fluid–solid coupling model of a multistage fracturing horizontal well was established based on the poroelasticity theory. The difference in stress sensitivity among different layers was also considered in this model. The evolution of pore pressure and stress field during the production process was analyzed through numerical simulation. A comparison of the planar well pattern and stereo well pattern revealed that the latter has less interwell-flow interference and smaller alteration angle of the minimum principal stress; thus, in the latter pattern, intersection with existing hydrofractures during refracturing can be avoided. It is more advantageous to refracturing in the middle of the outside horizontal section, but with increase in production time, the optimal fracturing section shrinks. Considering the maximum recovery factor and interwell interference, well-spacing optimization is recommended from 200 m to 300 m.
Simulation and Analysis on the Mechanical Properties of a New Slide-in Joint for Shield Tunnel Segment
Authors: Rundong ZHANG , Yadong XUE , Lin LIAO
Published: November 2020

There are many joint forms of shield tunnel lining segments. The new types of joints mainly include plug-in type and slide-in type where few researches concerning whose mechanical properties. This paper aims to construct a full-size numerical simulation model of the selected slide-in quick coupling joint and accomplish a fine prefabricated model. Given the complexity of the mechanics on the joint, loading and constraints are designed into the simulation model which achieves a successful simulation on various working conditions. The numerical results show that joint deformation can be reduced by optimizing the connectors’ position; A strengthening on the structure of C-type embedded groove can improve the overall bearing capacity of segment joint; Axial force can significantly reduce the deformation of the joint. Therefore, this research will help facilitate the effective design of the new type of shield tunnel joint.
Study on Water/mud Inrush of Tunnel Inclined Shaft Based on Material Point Method
Authors: Jiaxuan Wang , Yadong Xue , Mingliang Zhou , Bo Lv , Ping Li
Published: November 2020

Water/mud inrush is a serious threat to the safety of tunnel construction. It is very important to set up a certain thickness of aquifuge to prevent water/mud inrush and eliminate the catastrophe causing object when there exists potential risk of water inrush in front of the tunnel face. Taking the water inrush accident of No.1 ventilation inclined shaft at K21+693 in Yingpanshan Tunnel as an example, the cause of water inrush is analysed from angle of the geological and hydrological conditions. Then, a minimum aquifuge thickness of the tunnel face valuing 8.6m is obtained based on the thin elastic plate theory model. In order to explore the mechanism of water/mud inrush near the water-bearing fault, the numerical models of the aquifuge with a thickness of 10m/5m/1m were established based on the material point method. The results show that it is reasonable to take 10m as the construction safety thickness, and the water/mud inrush mechanism varies with the aquifuge thickness. The overall extrusion failure occurs when the aquifuge is thicker, and the middle fracture failure occurs when the thickness is thinner. The material point method has advantages in studying large deformation problems including water/mud inrush. The results provide references for strengthening aquifer, eliminating catastrophe causing object and ensuring construction safety.
Discrete element numerical simulation on the accumulation of wave-induced excess pore pressure in silty seabed sediments
Authors: Li Y S , Liu X L , Liu C , Hu C , Tian H Q , Chu X J
Published: November 2020

Marine geological disasters, such as seabed liquefactions, submarine landslides, debris flows and turbidity currents, are all closely related to the accumulation of wave-induced excess pore pressure in the seabed. Due to the limitations of physical model experiment and in-situ observations, numerical analysis has become an important method to explore the microscopic mechanism of the accumulation of excess pore pressure. Based on the discrete element porous density flow method, we simulated the changing process of excess pore pressure in seabed sediment in this study, comparing with laboratory flume experiment. The simulation results reproduce the changing process of excess pore pressure in the laboratory flume experiment. The excess pore pressure occurs in the surface of seabed and gradually transfers to the deep layer, tending to a stable value. Thus, the discrete element porous density flow method is well suitable for simulating the accumulation of wave-induced excess pore pressure. Furthermore, the method constitutes a promising tool to study the microscopic mechanism of seabed liquefaction.
Time-dependent deformation analysis of the surrounding rock mass around a tunnel
Authors: Fu Teng-Fei , Xu Tao , Nara Yoshitaka , Xue Yan-Chao , Heng Zhen , Yuan Yang
Published: November 2020

A numerical time-dependent model is established by incorporating the stress corrosion model into the three-dimensional discrete element grain-based model (3DEC-GBM) to analyze the fracture evolution and instability mechanism of the surrounding rock mass around a circular tunnel. The surrounding rock of the tunnel is assumed to be made from intact Yunnan sandstone formation, whose material properties were found using laboratory experiments (ignoring scale effects). The mesoscale mechanical stress corrosion parameters in the model are calibrated to reproduce the time-independent and -dependent deformation and failure of Yunnan sandstone observed in a laboratory. The model is validated against laboratory data and then further applied to analyze the time-independent and -dependent deformation of the surrounding rock of the tunnel. The fracture evolution around the tunnel instability is numerically visualized. The failure zone around the tunnel gradually extends deeper into the surrounding rock with time, and the location of failure at the roof and floor of the circular tunnel becomes more evident as the lateral pressure coefficient increases. We conclude that the model is not only able to simulate the location of the concentrated tensile and shear stress around the tunnel but also has important theoretical guidance and practical significance for the long-term stability study of tunnels.
Study on construction mechanics of in-situ expansion of ultra-large flat tunnel in collapse section of an existing tunnel
Authors: Song Yang , Bo-ran Shi , Hui Liu , Zhi-guo Ma , Bin He , Yong Yuan , Hai-tao Yu
Published: November 2020

To meet the needs of the transportation, a tunnel in Fujian Province was expanded in situ to form an ultra-large flat tunnel. In some sections, a large-scale collapse has occurred during the original tunnel construction, which brings a huge risk for the expansion construction. Based on the above background, the theoretical formula is used to calculate the spatial distribution of the collapse, and the dynamic construction mechanical characteristics of the CRD method are studied through numerical analysis and field tests. The results show that: (1) curves of the surface settlement are presented small in both ends while big in the middle, and the settlement center appears above the left side of the tunnel centerline, and the surface settlement caused by the excavation of the upper bench is the largest; (2) the surrounding rock disturbance range is 0.5 times of the tunnel diameter in front and rear of the tunnel. The deformation of the left spandrel of the tunnel is the largest; (3) there are two "V" shaped shear plastic areas in the arch of the tunnel, which is deep into the surrounding rock. During the tunnel construction, the monitoring results of surface settlement, surrounding rock, and support system deformation are in good agreement with the numerical simulation results, which verifies the reliability of the numerical simulation. The research results can provide a reference for the further study of the stability of surrounding rock during the expansion construction of the ultra-flat section tunnel and provide some reference for similar projects in the future.
A Nonlinear Damage Creep Model with Time-varying Viscoelasticity Based on Fractional Theory for Rock Materials
Authors: Liu Xiaolin , Li Dejian
Published: November 2020

This study is aimed at introducing a nonlinear damage creep model with time-varying viscoelasticity, which is based on the Caputo fractional derivative with respect to the Mittag-Leffler (M-L) and damage functions. First, the M-L function was applied to the Caputo fractional calculus to describe the nonlinear creep behavior. A series of creep experiments of sandstone were performed and the mechanical behavior of the accelerating creep was depicted in detail. Second, the experimental data of sandstone and experimental data of salt rock and mudstone achieved from previous classical studies were used to confirm the reasonability and applicability of the proposed damage creep model. Finally, the proposed damage creep model was reported to be in excellent agreement with the obtained experimental creep data, and the accuracy between predicted data and measured data is analyzed.
Study on the unloading damage constitutive model of sandstone based on hydro-pressure cycle
Authors: Yongcheng GUO , Yan SIMA , Jianlin LI , Zuogui CHEN , Qinglin XIAO , Bin YAN
Published: November 2020

The periodic rise and fall of reservoir water level under hydro-pressure cycle leads to the deterioration of physical and mechanical properties of rock and seriously triggers the instability of the reservoir slope. From the laboratory data and characteristics of the stress–strain curve under different hydraulic cycles, combined with the generalized Hooke’s law, the Weibull distribution theory, and the Hoek–Brown strength criterion, the energy dissipation in the unloading process is assumed as the damage variable, and the unloading damage constitutive model of saturated sandstone under hydro-pressure cycle is established. Under hydro-pressure cycle, the parameters m and F of the constitutive model are gradually decreasing, and the sandstone brittleness and macroscopic strength are gradually weakened. In addition, the scattered energy increases, while plastic deformation slowly plays a dominant role. The comparative analysis shows that the constitutive model fits well with the experimental curves. The damage constitutive equation can be expressed under hydro-pressure cycle. This research can help in the stability analysis of rock slope under the reservoir water in the field.
Transmission and Frequency Characteristics of Stress Waves through the Cemented Joint of Rock Mass
Authors: Cui Chunyang , Qi Qingxin , Li Haitao , Sun Zhongxue
Published: November 2020

During the process of rock dynamic fracture, the rock mass releases a huge amount of fracture energy, which primarily transforms into a strong stress wave; the stress wave can cause serious damage to the neighboring zones when passing through the structural rock medium. In this study, the transmission and frequency features of the stress wave through cemented joints are investigated. The polyurethane (PU) is chosen as the cementing material to glue the cut faces of the rock sample. The bonding stiffness of joints is adjusted by the mixing proportion of the polyurethane diluent. By conducting the Split Hopkinson Pressure Bar (SHPB) test, the effect of the stiffness and thickness of the PU adhesive layer is studied by monitoring the coefficients of reflection, transmission, and dissipation, as well as the frequency components. The testing results indicate that the transmission effect increases significantly, whereas the dissipation decreases with the growth of the bonding stiffness. The increasing impact energy results in a higher degree of body fracture and crack density. The low-pass filtering (LPF) effect of the stress wave is observed evidently in low bonding stiffness.
Quantitative description of the joint surface roughness considering the influence of shear direction
Authors: Song Y , Liu B , Ren D , Yu M
Published: November 2020

The joint surface roughness in consideration of the influence of shear direction is quantitatively described. A natural joint produced by Brazilian splitting test is scanned, a digital elevation model that represents the morphological features of the joint is established. The two-dimensional roughness of joint profiles along the shear direction is analysed according to the parameters of root mean square (Z2), joint roughness coefficient (JRC) and the statistical characteristics of dip angles, respectively. It is proved that the standard deviation of dip angles is linearly correlated with the value of JRC2D. Further, the probability distribution of apparent dip angles along the shear direction is introduced to describe the shear-related three-dimensional joint roughness. Based on the scanning images of the joint morphology, the probability distribution of apparent dip angle varies with different shear directions.
Static and coupled dynamic testing of granite for geological disposal of high-level waste
Authors: Man Ke , Liu Xiaoli
Published: November 2020

The Tianhu area of Xinjiang Province has been pre-selected for the geological disposal of high-level radioactive waste. To engineer the design of the disposal site, one must understand the static and dynamic properties of the granite in the borehole. In the present study, rock was sampled at the same depth in the same borehole, and its tensile and uniaxial-compression strengths were evaluated. Both strengths were steady and representative. The dynamic tensile and dynamic compression strengths increased with loading rate, confirming the loading rate effect on the brittle material. A coupled static-and-dynamic tension test was then carried out. Under increasing axial static stress, the dynamic tensile strength first increased and then decreased in a stable manner. The dynamic tensile strength was maximized when the static axial pre-pressure reached approximately 50% of the static-tensile strength. Meanwhile, the coupled static-and-dynamic strength increased under increasing axial static pressure, reaching approximately three times the static tension strength, and 1.5 times the dynamic tension strength. The failure model in the dynamic test was mainly tension failure, consistent with the static tension test. Therefore, the rock in this area is mechanically stable and putatively suitable for the geo-disposal of high-level waste (HLW). For a complete assessment, the rock should be tested by other methods such as seepage and in situ stress testing. After a detailed analysis of the rock in this area, the testing results and theoretical knowledge will become available for deep geo-engineering blasting and excavation, and HLW geo-disposal.
Model experimental test and numerical analysis of the influence of a strike-slip fault on a tunnel project
Authors: Wang T Q , Cui Z , Sheng Q , Ning B K , Ma Y L N , Zhou G X
Published: November 2020

Many active faults exist in the west of China, especially strike-slip faults; thus, passing through active faults is inevitable during tunnel construction, and the stability problem of tunnels becomes an important research topic. To investigate pivotal issues caused by active faults, such as the failure modes of tunnels, considering Xianglushan tunnel as a backing project, this study examined the response law of a tunnel under a strike-slip fault in virtue of model experimental test and numerical analysis, which is a comprehensive method. On the basis of the prototype tunnel, a numerical analysis model was established to acquire the failure mode of deformation, the distribution of stress, and the internal force of lining under the dislocation of the strike-slip fault. Meanwhile, a model experimental test was performed under the strike-slip fault to monitor tunnel deformation and failure, strain distribution, ground deformation, and crack caused by the fault. First, the results of the model test were in good agreement with the numerical analysis, indicating that the liner maintains high stress state near the fracture surface but low stress state in its ends. The west haunch of the hanging wall and the east haunch of the footwall presented a tensile failure. Moreover, the east haunch of the hanging wall and the west haunch of the footwall reaching fault trace suffered in press condition lightly. According to the result of the numerical analysis, the tensioned zone of the lining was distributed along the longitudinal direction of the tunnel, which mainly focused on the longitudinal position of the wall on both sides of the tunnel in the range from 0.5 D (D is the diameter of the tunnel) to 2 D away from the fracture surface in the footwall and in the same range in the hanging wall. Second, the wrinkling range of ground was from -2.4 D to 1.3 D in the model size according to the model test. Furthermore, the failure form of lining under the strike-slip fault is a kind of combined failure, including tensile failure and direct shear failure, but shear failure is the main failure form. Last, the affected zone of lining was wider within the hanging wall than the footwall. Therefore, the footwall under the fault dislocation is the control point to resist such dislocation. This research provides a reference for the fortified range of the tunnel crossing a strike-slip fault with certain practical significance.
Experimental Investigation on Permeability Evolution of Granite Samples Containing a Grout Infilled Fracture under Triaxial Compression
Authors: Zhou Dong , Zhao Zhihong , Ding Wenqi
Published: November 2020

Grouting has been widely used in rock engineering to improve the stability and strength of fractured rock mass, as well as to decrease the permeability of fractured rock mass. Fractures infilled with grout may endure different in-situ stress conditions during the construction and operation life of tunnels and other underground spaces in fractured rocks. To study the stress induced changes in permeability of fractures infilled with grout, we carried out triaxial compression tests on the fractured rock samples infilled with grout, during which the permeability of fractured rock samples was measured. Both planar and rough fractures with different apertures were tested. The results showed that the permeability of infilled fracture samples increases with increasing grout width, but the strength of infilled fracture samples decreases with increasing grout width. The evolution of permeability is highly related with the volumetric strain. The permeability decreases slightly with increasing deviatoric stress from 0 to crack damage stress, followed by drastic enhancement in permeability with further increasing deviatoric stress. The sample’s permeability is enhanced by about 5~10 times at the peak deviatoric stress compared with the initial value at 5MPa deviatoric stress.
Temperature-dependent factors on hydraulic fracturing of hot dry rock (HDR): An experimental investigation
Authors: Yin Tubing , Zhuang Dengdeng , Li Qiang , Tan Xiaosong , Wu You
Published: November 2020

Hot dry rock (HDR) is rich in geothermal energy and renewable and does not cause pollution; therefore, it has attracted considerable research attention. Previous studies have extensively discussed the process of HDR hydraulic fracturing based on the crack initiation mechanism, initiation pressure, and crack propagation law. However, the temperature-dependent factors (thermal damage and thermal shock) affecting the HDR hydraulic fracturing process have not been specifically discussed. Therefore, HDR hydraulic fracturing tests with different sample temperatures and injection rates were designed in this study. Further, various factors affecting the hydraulic fracturing related to temperature, including the thermal damage, thermal shock, and injection rate, were analyzed. The test results indicate that under the condition of variable temperature parameters, thermal damage and thermal shock caused the initiation pressure of the reservoir to decrease with the increasing temperature. The degree of weakening increased with the increasing temperature. After fracturing, the initial fracture in HDR continued to expand under the action of thermal shock and residual pressure, and the fracture expansion scale increased with the increasing temperature. Under the condition of variable fracturing parameters, microfractures with large areas were more likely to form when fracturing occurred at a lower injection rate, which is beneficial to improve the heat exchange efficiency of the reservoir and avoid short circuits. These research results provide a scientific explanation for the influencing factors of HDR hydraulic fracturing and offer geological and engineering guidance for optimizing the hydraulic fracturing in an enhanced geothermal system.
Analysis of the AE signal parameters during granite compression process based on the K-means clustering method
Authors: Xu Feng , Xiang Jiaming , Li Yao , Wen Huibo , Liu Zhongshuai , Ma Xiaofei , Yang Guangqing
Published: November 2020

The average frequency (AF), rise-time divided by amplitude (RA), and peak frequency of acoustic emission (AE) generated during the granite uniaxial and triaxial compression failure process are taken as the main factors of the type of sample crack. Further, AE signals can be characterized based on the K-means clustering method. Results show that there is a large difference between the AE signals generated by uniaxial and triaxial compression. The former has more diversity in the category, e.g., better clustering effect and uniaxial or triaxial compression. AE signal parameters can be divided into four categories based on the K-means clustering method. Acoustic signals A, B, C, D in the two compression modes are substantially similar and uniaxial compression mainly generates tensile crack before the peak stress, and shear crack appears after the peak stress. During the triaxial compression process, tensile and shear cracks are both generated before the peak stress, but shear crack is no longer present after the peak stress.
Toppling mechanical characterization based on rheological test of the cantilever beam
Authors: Zheng D , Wang X
Published: November 2020

This study aims to explain the time-sensitive deformation of rock mass toppling and analyze its mechanical characteristics. A mechanical model of the toppling rock beam is abstracted by performing a force analysis of the countertendency layered slope, and the bending rheological test of the cantilever beam is carried out. The flexural rheological model and constitutive equation of the rock cantilever are identified from the experimental results. The strain (ε = 0) at the ultimate depth of development of the toppling deformation and the strain acceleration (a ≥ a2) during rock beam dumping bending are selected to obtain the development depth LF
and bending depth LZ
of the toppling deformation, and LF
≥ LZ,LF
> 0,LZ
> 0 is used to obtain the development conditions of the toppling deformation. The time-sensitive characteristics of toppling differ from those of other types of slope deformation. This study could serve as a reference for elucidating the mechanical mechanism and evaluating the stability of the toppling deformation.
Anisotropic rock permeability evolution model based on wing crack propagation after dynamic load testing
Authors: Li Diyuan , Zhu Quanqi , Wang Wenjian
Published: November 2020

The permeability evolution of rock is essential in geotechnical engineering, which is related to seepage. A permeability evolution model, which is based on the wing crack propagation model and Darcy’s law, is created for rock after dynamic load testing with confining pressures. It is assumed that permeability has two types: isotropic initial permeability and anisotropic microcrack-induced permeability. In this model, the wing crack length is associated with the absorption energy per unit volume of the rock specimen under dynamic loads, in accordance with the surface energy theory. Assuming that the initial crack families are evenly distributed, the contribution of each crack family to permeability in different directions is investigated. In this study, an expression of permeability, which is related to axial stress, confining pressure, and absorbed energy per unit volume, is obtained. Two groups of dynamic load testing with confining pressures of sandstone are conducted using a modified split Hopkinson pressure bar technique. In group A, the incident energy is a variable, whereas in group B, the confining pressure is a variable. After the dynamic load testing, the permeability of the sandstone specimens is measured using the pulse decay method on MTS 815. Owing to the limitations on the test equipment, only the permeability in the direction of the dynamic load is measured. The permeability obtained from the dynamic load testing is in good agreement with the permeability calculated by the model. In this model, the anisotropy of rock permeability is theoretically studied. The minimum microcrack-induced permeability in all directions is about 0.65 of the maximum permeability value. In summary, the model discussed here enables the prediction of the permeability of the rocks under dynamic impact and establishes the relationship between macro-mechanical parameters and micro-mechanical parameters. In addition, it provides a new idea for the research on the anisotropy of rock permeability.
Latest Progress of Research on Rockburst Experiment Mechanism and Its Control
Authors: He Manchao , Li Jieyu , Liu Dongqiao , Sun Jie
Published: November 2020

Rockburst experimental research is an important method to understand rockburst and its mechanism. This paper proposes a rockburst classification method, which can be divided into strain burst and impact rockburst. Independently developed three true triaxial rockburst experimental systems, including the first-generation strain burst experimental system, the second-generation strain burst experimental system, and the impact rockburst experimental system. Successfully reproduced different types of rockbursts in experiments, including: single-face unloading strain burst, two-face unloading strain burst, three-face unloading strain burst, four-face unloading strain burst, impact rockburst, and rockburst of jointed rock mass induced by impact. Macro NPR anchors and micro NPR anchors with negative Poisson’s ratio effect have been developed, and field rockburst simulation experiments have been performed. The anchor has good rockburst resistance. The rockburst experimental simulation and NPR anchor in this paper can provide reference for the study of rockburst mechanism and its control.
Tunnel damage identification method based on relative entropy of wavelet packet energy: An experimental verification
Authors: Zhang Y L , Xie X Y , Li H Q , Zhou B
Published: November 2020

Ineffective methods used to detect damage in subway tunnels can result in severe safety risk. Traditional detection methods use laser scanning, image recognition, and inspection to identify damages in the inner lining of a tunnel after the subway is out of service; these methods have low efficiency and accuracy. In this study, a new method is proposed to analyze the vibration signal of a moving train based on the relative entropy of the wavelet packet energy, which can quickly identify and evaluate the damage of the subway tunnel and its auxiliary structure in real time. The test model includes a three-dimensional printed tunnel and a moving vehicle to simulate the train running in the tunnel. Wireless acceleration sensors are installed inside the vehicle and at the top of the tunnel to record the vibration signals of the car and the tunnel lining. After obtaining the acceleration signal of the vehicle, the relative entropy of energy is calculated using wavelet packet transform, in which sudden changes in entropy reflect damages. The model test results show that the vertical acceleration of the vehicle is sensitive to tunnel damage and the signal energy is mainly concentrated at 30–80 Hz and 200–400 Hz. By comparing the energy of the relative entropy between healthy and damaged signals, the location and degree of damage can be identified.
Non-coaxial Deformation Characteristics of Fine Sand under Principal Stress Rotation
Authors: yue TENG , ping HU
Published: November 2020

A series of pure principal stress rotation tests with dynamic hollow cylinder apparatus were conducted on saturated fine sand. The elastic torsional shear strain was reported to account for a large proportion of the total torsional shear strain, which could not be ignored. On this basis, the non-coaxial angle is redefined and the non-coaxial deformation characteristics and influencing factors of saturated fine sand are studied. The results show that the principal stress rotation will cause obvious plastic deformation of the fine sand and that the initial shear stress has a more significant influence on the non-coaxial deformation characteristics of the sand compared to the intermediate principal stress coefficient.
Particle breakage characteristics of coarse-grained soil under point-point contact
Authors: Li L , Zhao C , Zhang Y W , Ouyang G B , Yu S C , Zhou J
Published: November 2020

As an excellent building material, the coarse-grained soil is widely used in various construction engineering. The breakage of coarse-grained soils has a great influence on the overall quality of the engineering. Therefore, it is very important to study the breaking characteristics of coarse-grained soils. In this study, limestone was used to simulate coarse-grained soil. Point-point contact experiments of different particle sizes and loading conditions were carried out to study the breakage characteristics of soil particles. The effect of particle size and loading conditions on breakage characteristics was investigated through analyzing the breakage processes, failure modes, force-displacement curves and cone core sizes. The results indicated that the spherical limestone particles break locally at the contact point with the increase of normal force in the normal loading experiments. And with the contact area expanding, the particles finally split into several fragments. The diameter and the depth of the cone core are proportional to the particle size. Whether particles broke completely depended on the loading lever of normal force under complex load conditions. The critical loading level of normal force of limestone with a diameter of 5cm was 70%. The horizontal angles of crack are proportional to the loading lever of the normal force. The diameter of the cone core is affected by both normal force and tangential force, and its depth is mainly affected by the magnitude of the normal force.
Experimental research on mechanical property of granite under erosion by seawater
Authors: Zhang C H , Zhang Q , Liu J , Tian L G , Dai G L
Published: November 2020

When offshore rock-socketed foundations are constructed, seawater will deteriorate the mechanical properties of fresh granite at the excavation surface of the foundation, thereby reducing the bedrock bearing capacity of the granite. In this paper, elastic P-wave velocity, uniaxial compressive strength, and slake durability tests are used to study the deterioration of the mechanical properties of granite due to seawater. The time effect is also considered by using different immersion durations (3, 7, and 15 days). The results indicate that the mechanical properties of granite deteriorate with an increase in erosion time. After being eroded in seawater for 15 days, dried samples have an elastic P-wave velocity of 4.274 km/s, saturated samples have a uniaxial compressive strength of 68.196 MPa, and the slake durability index is 84.24%. An evident decline is seen in the mechanical properties of granite under the effect of seawater erosion compared with the initial values of each index parameter. Thus, the influence of seawater erosion on rock-socketed foundations needs to be considered.
Experimental investigation on the SAGD dilation start-up in shallow heavy oil reservoirs
Authors: Wang Xiaohua , Zhang Fengshou , Sun Jun , Xu Bin
Published: November 2020

There are few related researches focused on the steam assisted gravity drainage (SAGD) dilation start-up technology (termed as dilation start-up in this paper), especially with physical modelling experiments. Therefore, in order to better understand the dilation start-up process, several large-scale experiments of SAGD start-up with dual horizontal wells were carried out by using the oil sands from Xinjiang oilfield, northwest China. The dilation process characterized by temperature changes at different positions inside the experimental samples was monitored in real time. The performance differences between dilation start-up and conventional start-up were discussed in detail, and the effects of dilation pressure and dilation time on the dilation process were also studied. The experimental research indicated that dilation start-up can significantly enhance the range of dilation zone and improve the uniformity of dilation zone along the horizontal wellbores. Moreover, it was found that dilation pressure is an essential factor influencing the dilation effect, in that the size and distribution of dilation zone are largely dependent on dilation pressure. The evolution of dilation zone with time shows that a long-time dilation prompts the uniform propagation of dilation zone along the horizontal wellbores.
Influence of end effect under loading in the intermediate principal stress direction on strainburst behaviors of Beishan granite
Authors: Zhao Xingguang , Wang Ju , Cai Ming , Su Guosao
Published: November 2020

In this study, strainburst tests on Beishan granite under different intermediate principal stress (σ
2) loadings were performed using a true-triaxial rockburst system. Rectangular prism specimens were prepared and divided into two groups. For the first group, the specimens were in direct contact with platens. For the second group, the specimen surfaces loaded by σ
2 were daubed with a layer of lubricant to reduce the end friction of the platens. A loading mode, which kept one specimen surface free and applied loads on the other five surfaces of the specimen, was used to simulate the stress state of a rock element on the excavation boundary. A high-speed video camera was then used to capture the failure process of the specimens. The experimental results indicated that as σ
2 increased, the degree of violence of the specimens during failure increases. However, the σ
2-dependent strength and energy release characteristics of the lubricated specimens were significantly different from those of the non-lubricated specimens. The strength of the lubricated specimens was lower than that of the non-lubricated specimens under a given σ
2, and the strength difference between them increased as σ
2 increased. Moreover, the kinetic energy difference of the rock fragments between the non-lubricated and lubricated specimens increased with increasing σ
2.
Research on acoustic emission characteristics of marble damaged by pre-peak unloading
Authors: Zhu Zihan , Yu Liyuan , Li Jinglong , Su Haijian , Zhang Zhanqun , Zhang Jing
Published: November 2020

Excavation of the tunnel in high geo-stress environment induces strong stress redistribution, resulting in unloading damage of surrounding rock. The damaged surrounding rock is the main load bearing body for the tunnel in the running period. Therefore, it is necessary to study the acoustic emission (AE) characteristics during the reloading of damaged rock. The marble was chosen to manufacture specimens in this paper, and we designed pre-peak unloading tests. Confining pressure of pre-peak unloading test is 15MPa and three types of unloading point (70MPa, 80MPa and 90MPa). The laboratory tests are made for studying AE characteristics of damaged marble samples by using MTS816 and acoustic emission instrument AE21C. The test results showed that as the unloading point increases, the peak strength of the rock decreases with increased corresponding peak strain. Rock failure mode gradually changed from brittle failure to quasi-brittle failure; Accumulated AE count is negatively correlated with the unloading point, and the AE quiet period is positively correlated with the unloading point. The evolution of b-value is divided into three phases: slow increase, sharp increase and rapid decrease. The findings of this research can provide the significance for selecting mechanical parameters of the surrounding rock and optimizing support scheme.
Quantification of statistical uncertainties of rock strength parameters using Bayesian-based Markov Chain Monte Carlo method
Authors: Han Liang , Wang Lin , Zhang Wengang
Published: November 2020

Although unconfined compressive strength (UCS) plays an important role in geotechnical design and analysis involving rock materials, how to quantify the statistical uncertainties underlying rock strength parameters is rarely reported. Based on a site investigation report in Bukit Timah Granite (BTG) formation in Singapore, this paper presents a set of database about UCS from four sites in BTG formation. Subsequently, Markov Chain Monte Carlo (MCMC) algorithm was applied to quantitatively evaluate the uncertainties of statistical parameters including the mean value, variance, and autocorrelation distance of UCS of BTG rocks making use of the available test data under the Bayesian framework. It was proven that the Bayesian-based MCMC method can effectively quantify the uncertainty of geo-mechanical parameters via a series of equivalent samples. The results indicate that the uncertainties of statistical parameters of UCS of BTG rocks are significant, and the magnitude to some extent relies on the selection of basic parameter in Bayesian framework. In terms of the basic parameters, the sensitive degree of uncertainties of three statistical parameters is different from each other.
Physical and mechanical characteristics of saturated tuff under the freeze–thaw cycle
Authors: Jiang Jianliang , Tang Bin , Guan Renqiu , Wang Huajun , Huang Man
Published: November 2020

The freeze–thaw cycle of rocks is a research hotspot in the field of geotechnical engineering, and it significantly affects the eastern part of the Zhejiang Province in China. In this study, we test 40 occurrences of freeze–thaw cycles on tuff from the Ningbo area and investigate the variation of the physical and mechanical properties. The results show that only a small amount of debris falls off the saturated tuff samples during the freeze–thaw cycle. The overall quality of the rock sample gradually decreases with the increase in the number of freeze–thaw cycles. However, the average loss rate of the quality is extremely low, accounting for only 0.07% of the rock sample quality. The wave velocity of the rock sample gradually decreases, and the extent of reduction decreases when the number of cycles increases. In the uniaxial compression test, a failure surface appears for the rock samples with low freeze-thaw cycles. The complete failure surface of the samples gradually disappears. Moreover, the compressive strength of the samples progressively decreases with the increase of the number of freeze–thaw cycles.
Experimental Study of Time-Frequency Characteristics of Acoustic Emission Key Signals during Diorite Fracture
Authors: Jiaxu Wang , Yadong Xue , Yongfa Guo
Published: November 2020

High in-situ stress and rock burst have been important issues for risk assessment of deep tunnelling. The issue of prediction and control of rock burst remains to be solved, though various researches have been done. Based on the Lhasa-Linzhi tunnel project of the Sichuan-Tibet railway, the laboratory test of acoustic emission for diorite was carried out in this study. The uniaxial compression test was developed on the diorite specimens collected in the field, and the acoustic emission signals was recorded. Decision tree model was used to filter and classify key signals. Based on the feature parameters, time-frequency characteristics, rupture scale and rupture mechanism of each sort of key signal were analysed. The result shows that the decision tree model has good classification effect and key signals was divided into four groups. Signal A contains high energy, which indicates macro crack propagation and linked up. Signal B and C are continuous signal, which appear before the inflection point of load curve and are helpful for early warning. A simple early warning model was established based on signals distribution, which divides the risk into four levels and provides measures for each stage.
Influence of water content on mechanical behavior of basalt in Baihetan Hydropower Station, China
Authors: Sha Song , Li Bowen , Chen Wenfu , Tan Yaosheng , Rong Guan
Published: November 2020

Water content is a critical factor affecting rock strength in numerous geotechnical engineering applications. This study experimentally investigates the influence of water content on the mechanical behavior of basalt in the Baihetan Hydropower Station. Uniaxial compression tests were performed on basalt specimens at five moisture content levels. The strength evolution of shale and sandstone specimens with different water content levels were also analyzed through an extensive literature review. The results show that an increase in water content can exacerbate the initial damage to the basalt specimens, increasing the nonlinearity in the initial deformation stage of the stress-strain curve. As the water content increases, both uniaxial compressive strength and Young’s modulus gradually decrease, but Poisson’s ratio remains almost constant. Splitting failure is the dominant mode for all tested specimens. Because of the differences in pore structures and mineral compositions, the mechanism of water-weakening on the compressive strength of shale, sandstone, and basalt is different. The negative exponential function provides a good representation of the compressive strength versus water content of shale and sandstone, but unsuitable for describing that of basalt.