bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

AbstractHot 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

Abstract
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

Abstract
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.