bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation and Analysis of Cave Penetration by Hydraulic Fractures
Authors: Kao Jiawei , Wang Wenzhi , Jin Yan , Liu Hailong 
Published: November 2020

Abstract
The cavernous carbonate reservoir in the Tahe oilfield in northwestern China has high development potential. Fluid is distributed in caves due to low matrix permeability, and recombination acid fracturing is a primary development method. The effects of fracturing depend on the number of caves connected by fractures. An estimate of whether a hydraulic fracture can penetrate a cave and continue propagation is therefore important for production safety and efficiency. We developed a numerical model using COMSOL Multiphysics to calculate the fluid-solid coupling stress distribution after fractures connect with caves and determine whether the fractures can continue to expand. We first developed an analysis group based on parameters from fracturing experiments in which caves were placed in man-made samples. A comparison of the calculation and experimental results verifies that the model is reasonable. The penetration ability of hydraulic fractures and influencing factors under different conditions were analyzed in combination with characteristics of the cavernous carbonate reservoir in the Tahe oilfield. The results show that when holding fixed certain working parameters, such as displacement and fluid viscosity during fracturing, the hydraulic fractures more easily penetrate smaller caves, the in-situ stress ratio increases, and the distance between the well and caves that would lead to a higher penetration ability decreases. If the fractures of a given cave are connected but not penetrated, several methods can be applied to effectively increase the hydraulic pressure in the cave, such as increased fracturing injection fluid displacement or replacing low-viscosity fracturing fluid. This can form new fractures in the wall that continue to expand and connect more caves. We calculated the fluid-solid coupling stress distribution after the fractures had connected caves to determine whether hydraulic fractures could also achieve penetration. The main influencing factors and optimization methods affecting the ability of fracture penetration are clarified, which provide an important reference for fracturing design in the Tahe cavernous carbonate reservoir.
Fluid solid coupling analysis of hard rock wall structure in over kilometer deep shaft
Authors: Li Cheng , Xingquan Liu , Mingde Zhu , Kuikui Hou 
Published: November 2020

Abstract
Taking the auxiliary shaft proposed by Ruihai Mining Co., Ltd. as the research object, in order to study the load law of shaft lining and ingate under high stress fluid solid coupling in deep bedrock and the influence of different permeability coefficient on the stability of shaft lining and ingate surrounding rock, Midas software was used for numerical simulation analysis, and the results show that:( 1) After the shaft excavation, the pore water pressure of surrounding rock around the shaft wall and ingate decreases gradually, which is the main permeable area. After the support, the pore water pressure is obviously raised, and the water isolation effect of the supporting layer is obvious. (2) After the shaft excavation, the area near the arc surface of shaft wall tangent to Y direction shows high compressive stress, and the maximum principal stress at - 1277.5m depth is more than 150MPa. When the polar angle increases from 0 to 180 °, the maximum principal stress increases first and then decreases. (3) After the excavation of ingate, the bottom corner and arch top are stress concentration areas before and after support. ( 4) Under the action of three different permeability coefficients, the influence of permeability coefficient on pore water pressure and maximum principal stress can be ignored after supporting measures are taken. The research results provide important theoretical basis for auxiliary shaft construction design.
Phase field modeling of hydraulic fracture propagation in spatially variable rock masses
Authors: Chen F Y , Zhou S W , Zhuang X Y , Zhang W G 
Published: November 2020

Abstract
Due to differences in mineral compositions, sedimentary conditions, stress history, and geological processes, the spatial variability of the mechanical properties of rock masses is usually considerable. Therefore, the influence of the spatial variability of rock mass parameters on the irregular propagation of hydraulic fractures should be studied. In this work, an efficient approach is proposed for studying the irregular propagation of hydraulic fractures considering the spatial variability of rock mass parameters; this approach is based on the phase field method and random field theory. Combined with random field theory, the phase field method is adopted to simulate the fracture propagation in a spatially variable rock mass. Random fields of the Young’s modulus are generated using the Cholesky decomposition method and then embedded into the phase field model. The influences of different scales of fluctuation of the rock mass parameters’ random fields on the fracture shape under fluid-driven conditions are investigated in this study. The results indicate that the spatial variability of the Young’s modulus has a significant influence on the propagation of hydraulic fractures.
Two-Dimensional Representation and Connectivity Analysis of Nature Fracture in Fractured Reservoir
Authors: Zhao Huan , Li Wei , Li Siqi 
Published: November 2020

Abstract
The mechanism of hydraulic fracturing in fractured reservoirs is complex. To understand the complex distribution characteristics of natural fractures and the mechanism of hydraulic fracture propagation in fractured reservoirs, the natural fracture characterization of a two-dimensional model was established based on the fractal method and topology principle. Furthermore, based on this model, the hydraulic fracture propagation dynamic fluid-structure interaction model was built using the global embedded cohesive element method. The influence of natural fracture connectivity on hydraulic fracture morphology was analyzed. The results show that multi-fracture development can effectively reduce the influence of stress anisotropy on the fracture propagation direction and improve the natural fracture connectivity of the reservoir. Moreover, the reservoir connectivity reached 35.87% after fracturing.
Spectral Correlation Between the Non-uniform Input Ground Motion and the Dynamic Response of the Surrounding Rocks of a Long Tunnel
Authors: Zhou Yongqiang , Sheng Qian , Li Nana , Fu Xiaodong 
Published: November 2020

Abstract
To generate several different time-history curves of ground motion, which have the ability to reflect local site effects, such as the traveling-wave effect and attenuation effect, for long circular tunnels, a random method for the synthesis of ground motion is employed. The dynamic response of the surrounding rocks of a long tunnel under the uniform and non-uniform input ground motions is analyzed using the vertical input method. Based on this, the spectral correlation between the input ground motion and the dynamic response of the surrounding rocks is investigated through the coherence function. Unlike the results under the uniform input ground motion, the transmission coefficient of the surrounding rock monitoring points of each section along the axial direction of the tunnel under the non-uniform input ground motion varies in the main frequency band. In addition, at the same frequency, the transmission coefficient of the monitoring points gradually increases along the tunnel’s axial direction, but the increasing magnitude is variable. The correlation function of each monitoring point along the tunnel axis under the non-uniform input ground motion generally decreases with frequency. Moreover, the further the distance from the tunnel entrance, the faster the attenuation of correlation. The maximum coherence coefficient and the axial distance of the tunnel are basically in conformity with the quadratic polynomial relationship. However, the maximum coherence coefficient of the non-uniform input ground motion is considerably greater than that of the uniform input ground motion. The gap increases with the distance, and the maximum gap is about 0.15.
Coupling DDA and 4D-LSM through contact theory for rock cutting
Authors: Zhao Gao-Feng , Li Yiming , Jiang Baoyuan 
Published: November 2020

Abstract
In this work, the rock cutting is modelled through coupling of 4D-LSM with DDA. The rock cutter and its 3D motion were simulated by using DDA with triangular surface mesh, and the rock is modelled by using 4D-LSM with multi-body failure criterion. The dynamic contact treatment between the cutter and the rock specimen was further handled by using Dr. Shi’s contact theory where the entrance block of the cutter between spherical particles was used to calculate the contact forces. Then, the 4D-LSM and DDA were coupled through an explicit-implicit mixed solving scheme. Finally, the coupled model is used to model rock cutting problems and compared with exist numerical approach to highlight its advantages.
Influence of Ground Water on Blasting Construction of Adjacent Tunnel
Authors: Peizhe Shi , Yadong Xue , Mingliang Zhou , Yongyi Wang , Lining Wang 
Published: November 2020

Abstract
During the construction of a mountain tunnel, water-rich strata are often encountered. Current research on the influence of groundwater on the blasting construction of the adjacent tunnel is not in-depth enough. Based on the Yingpanshan tunnel project of Huali Expressway in Yunnan Province, China, this paper analyzes multi-factor couplings such as blasting dynamic load, large-section excavation, groundwater and adjacent construction. An adjacent construction model with a size of 80×80×50m is established by COMSOL Multiphysics software. Considering the change of permeability and elastic modulus of the model, the influence of blasting construction on the adjacent construction is reflected by the vibration velocity of the existing tunnel lining. The results show that the impact of groundwater on the safety of the adjacent structure is mainly related to the permeability, and its influence degree increases with the water pressure. In the water-rich stratum with high permeability of rock mass, it is necessary to pay attention to the influence of groundwater on the safety of adjacent blasting construction.
An empirical strength criterion for deep rock incorporating the effect of fracture intensity using distinct element method
Authors: Jiang Mingjing , Liu Asen , Wang Huaning , Lu Guowen , Li Lei 
Published: November 2020

Abstract
Deep rock strength is one of the most important research areas in rock mechanics and engineering which is closely related to bearing capacity and stability of underground structures. Due to high ground stress, the mechanical behaviours of deep rock are different from those of shallow rock. In order to characterize deep rock strength precisely, a great number of rock strength criterions have been proposed over the past few decades to quantitatively describe the relationship between complex stress state and rock strength parameters. Some microscopic characteristics like fracture intensity(P32
) have received some attention. They are thought to have significant influences on the strength of deep rock. Currently, most of the constitutive models and strength criterions focused on the shallow rock and macro mechanical parameters, and they can not directly explain the relationship between the microscopic fracture characteristics and the strength of deep rock. In this research, the effects of fracture characteristics and confining pressure on deep rock strength were investigated using distinct element method(DEM). Firstly, an improved bond contact model incorporating rolling and twisting resistances was implemented in the rock numerical specimens, and the Smooth-Joint contact model was used for simulating fractures of rocks. The fracture length distributions in specimens were characterised by an exponent parameter a. Then numerical simulation of triaxial compression tests were carried out on numerical rock specimens under different confining pressures and P32
. The results show an approximate linear relationship between the maximum principal stress and P32
. Rock strength decreases with the increase of P32
, and it decreases rapidly at a higher confining pressure. Based on the results, a new empirical strength criterion is proposed. The criterion considers the nonlinear relationship between maximum principal stress and confining pressure of deep rock, additionally reveals the correlation between microscopic fracture characteristics and rock strength. In principle stress space, the corresponding failure envelopes projected onto the π-Plane showed a good agreement with DEM simulation results, which indicates a good applicability for the prediction of deep rock strength.
Micro-crack propagation and coalescence during time-dependent deformation of granite based on numerical manifold method
Authors: Yu Xian-yang , Xu Tao , Heap Michael J. , Baud Patrick , Heng Zhen 
Published: November 2020

Abstract
An understanding of influence of micro-cracks on time-dependent deformation in granite is of fundamental importance in many situations, such as nuclear waste storage facilities or the exploitation of geothermal resources. Time-dependent cracking is considered to be the main mechanism of brittle creep in granite. Creep strain rates are strongly influenced by the density of pre-existing defects that also exert a significant influence on rock physical properties. We introduce a new model that combines the subcritical crack growth (SCG) theory and the numerical manifold method (NMM) to link the local damage (using an exponential material softening law) caused by micro-crack propagation and the macroscopic creep deformation typically observed in granite specimens. In this model, each element contains a virtual micro-crack that can propagate sub-critically following Charles’ law. Once the virtual micro-crack length reaches a given value, it will convert to a real micro-crack, which can cut through adjacent elements, open, and slide according to the principle of NMM. We also investigated the influence of virtual micro-crack length, confining pressure and differential stress on creep behaviour. The fact that numerical simulations are in good agreement with experimental results shows that the NMM combined with the SCG theory is a suitable method for modelling the creep behaviour of rocks.
Impact of Mode I and Mode II Fractures on Fracture-Gas Permeability in Shale: An Experimental Study
Authors: Lu Yunhu , Chen Guanglei , Yang Shuai , Jin Yan , Li Ji , Xie Quan 
Published: November 2020

AbstractThe natural-fracture network and a large part of hydraulic fractures are poorly supported, and the conductivity of the natural-fracture network is highly sensitive to stress and strain during the production stage. In this work, we aimed to understand the impact of mode I (tensile) and mode II (shear) fractures on fracture-gas permeability as a function of effective stress in Long Ma Xi shale in the Dragon Horse Creek Group in Western China. Experimental results showed that the two-mode fracture tortuosity and width of shale were opposite those of sandstone. Our results implied that in Long Ma Xi shale, mode I fractures likely contributed significantly to early-stage high well productivity, with low effective stress, and mode II fractures may contribute to well productivity after the initial stage of gas production, with relatively high effective stress.
Effects of normal stiffness on the shear behaviors and acoustic emissions of rock joints
Authors: Wang Changsheng , Jiang Yujing , Luan Hengjie , Zhang Sunhao , Han Wei 
Published: November 2020

Abstract
In this study, direct shear tests were conducted on plaster joints under various boundary conditions. During shearing, the acoustic emission (AE) was measured by the PAC AE system. The damage of the asperities was evaluated based on the AE signals. The effects of the normal stiffness on the shear behavior and asperity damage were studied, and the corresponding AE characteristics were analyzed. The results show that the peak shear stress for rock joints under constant normal load boundary conditions is larger than that under the CNS boundary conditions. The shear dilation decreases as the normal stiffness increases. The AE signals are more active in the post-peak stage for the rock joints sheared under higher normal stiffness conditions. Both the AE count and AE energy rate increase with an increase in the normal stiffness. Thus, the total AE events increase with increasing normal stiffness.
Influence of stress amplitude on the dynamic characteristics of phyllite samples under triaxial multi-stage cyclic loading
Authors: Bie P F , Liu H X 
Published: November 2020

Abstract
The generation of a rockslide in an earthquake event is strongly dependent on the dynamic characteristics of the rock materials constituting the rock slope. In this study, phyllite samples were extracted from the Donghekou landslide area of Qingchuan County. The landslide occurred during the 2008 Wenchuan earthquake and the samples were made to undergo multi-stage cyclic loading and unloading tests under triaxial compression conditions. The confining pressure during the tests was 10 MPa, the loading frequency was 2 Hz, the loading waveform was sine wave, and 60 loading cycles were carried out at each level of stress. From the dynamic axial stress–strain curves, the effect of stress amplitude on the hysteresis loop area, the dynamic elastic modulus, the dynamic damping ratio, and the damping coefficient of the phyllite samples was analyzed. The results are as follows. (1) The strain–stress hysteresis loop area experienced a rapid increase as the stress amplitude exceeded a certain value, indicating that the rock samples have entered an accelerating crack propagation stage under high levels of cyclic loading. (2) As the stress amplitude increases, the dynamic elastic modulus, the dynamic damping ratio, and the damping coefficient of the rock sample followed a similar two-phase evolution law. There was a rapid reduction in the three parameters relative to the initial value in Phase I. Moreover, there was a minor change in Phase II. (3) The effect of the number of loading cycles number on dynamic elastic modulus and damping parameters was much more obvious under the lower levels of cyclic loading than under the higher levels.
Influence of Drying–Wetting Cycle of Acid Solution on the Mechanical Properties of Sandstone
Authors: Chen Z H , Chen W F , Tan Y S , Rong G 
Published: November 2020

Abstract
Ensuring the stability of reservoir slopes requires a comprehensive understanding of the mechanical properties of rocks after the drying–wetting cycles under acidic conditions. In this work, sandstone samples were selected and subjected to cyclic drying–wetting treatments with aqueous solutions of pH 7.0, 6.0, 4.0, and 2.0. The uniaxial compression tests and P-wave velocity measurement were carried out to evaluate the variations in the physico-mechanical properties of sandstones with different treatments. The results revealed that the internal structure of sandstones is softened by the drying–wetting cycles, which deteriorate their physico-mechanical properties. As the acidity of the aqueous solution increases, porosity and Poisson’s ratio show an increasing trend, while the strength characteristics, Young’s modulus, and P-wave velocity of sandstones present a decreasing trend. The physico-mechanical properties of sandstones significantly deteriorate from neutral to weakly acidic solutions; however, the deterioration becomes slower as the acidity continues to increase. Moreover, the physico-mechanical properties of sandstones are markedly reduced under strong acidic conditions.
Experimental research on the anisotropic properties of sandy slate
Authors: Wang Lehua , Tang Kaiyu , Li Jianlin , Xu Xiaoliang 
Published: November 2020

Abstract
In this study, the effect of joint on the anisotropy of a homogeneous, stiff, and intact sandy slate from a typical hydropower station is investigated by selecting and making jointed rock samples with jointed angles of 0°, 30°, 45°, 60°, and 90°. Accordingly, an acoustic measurement and a triaxial compression test are conducted on these jointed rock samples. The research results show that the joint angle significantly influences the rock mass anisotropy. In other words, the average value of the longitudinal wave velocity of the jointed rock samples is smaller than that of the intact rock. Furthermore, the value of the longitudinal wave velocity increases with the increase of the joint angle and is the largest when its spreading direction is in line with the joint inclination. The stress–strain curve, elastic modulus, peak strength, and failure mode of the joint rock samples are found to have anisotropic features. The failure stage occurs in samples with joint angles of 0°, 30°, and 90°. The stress–strain curve of the samples with joint angles of 45° and 60° tends to be horizontal. Meanwhile, the elastic modulus and the compression strength displayed a U-shaped distribution with an increase of the joint angle and the smallest value that belongs to samples with joint angles of 30° and 60°. The peak value ratio of the elastic modulus and the compression strength gradually decrease when the confining pressure increases, indicating that the anisotropy of the samples has weakened (i.e., the increase of the confining pressure decreases the anisotropy of the sandy slate strength). The failure mode of the samples with different joint angles is presented as follows: the samples with a 0° joint angle exhibit a tensile splitting damage; the samples with a 90° joint angle exhibit compression–shear damage; the samples with a 30°joint angle exhibit the combination of slide and compression–shear damage; and the samples with 45° and 60°joint angles exhibit slide damage along the joint surface.
Distributed monitoring of deformation of PCC pile under horizontal load using OFDR technology
Authors: Gao Lei , Cao Yang , Liu Han Long , Kong Gang Qiang , Cheng Xing , Zhang Xiao Lei 
Published: November 2020

Abstract
To study the horizontal bearing behavior of cast-in-place concrete (PCC) pipes, a horizontal static load model test is conducted based on the optical frequency domain reflectometry (OFDR) technology. The deformation distribution in the pile is studied. Results show that the pile moment increases with the horizontal load, whereas the position of the maximum point of moment is roughly unchanged. Moreover, the calculated and measured values of horizontal displacement at the pile top are compared; results show that the values are in agreement, which demonstrates that the deformation of a PCC pile can be successfully measured using the OFDR technology.