bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear seismic responses of the soft rock site for nuclear power plants
Authors: Li Furong , Chen Guoxing 
Published: November 2020

Abstract
With the development of the nuclear power industry, high-quality bedrock nuclear power stations have become scarce. Thus, it is inevitable that nuclear power stations will be built on soft rock sites. This involves the issue of the seismic safety of soft rocks as sites for nuclear power plants. Based on the soft rock site involved in the site selection for nuclear power plants, this paper uses ground motions with different spectral characteristics. Using the DEEPSOIL software for soil layer analysis and the Abaqus finite element software, one-dimensional equivalent linear and nonlinear methods are employed to compare and analyze the characteristics of the nonlinear seismic response of the soft rock site for nuclear power plants. The soft rock site has a significant amplification effect on the input ground motion. The equivalent linear and nonlinear methods have different levels of influence on the acceleration response of the soft rock site. Under the action of far-field earthquakes, surface acceleration and its response spectrum, which were calculated using the abovementioned methods, are relatively close. As the input ground motion intensity increases, the nonlinearity of the soft rock increases, and the amplification effect of the soft rock site weakens. However, the peak ground acceleration of the surface obtained using the two methods gradually differs. Moreover, the nonlinearity is greater than the equivalent linear. Therefore, the nonlinear characteristics of soft rocks should be considered in the site selection and seismic analysis of nuclear power plants.
Characterization and mesosimulation of the triaxial compression failure of rock-like materials
Authors: Wang G , Li X P , Luo Y , Liu T T , Liu X Q , Qu D X 
Published: November 2020

Abstract
The laboratory tests and the numerical simulation of the particle flow code of triaxial compression are conducted to analyze the fractal dimensions of fracture surface, strength properties, energy dissipation, damage patterns, and crack evolution. The following results are obtained. (1) Under low confining pressure, the fracture surface of a brittle specimen is rough, and the angle relative to the maximum principal stress is small. The specimen eventually exhibits a local tensile–shear failure mode. As the confining pressure increases, the strength of the specimen increases, and the yield platform for the stress–strain curve is more obvious. The main fracture surface flattens, and the fracture angle increases as the confining pressure increases. The specimen macroscopically exhibits a shear failure mode. (2) As the confining pressure increases, the trend of transgranular shear failure becomes obvious, and the microfracture surface has a smaller fractal dimension. (3) In the triaxial compression test, energy is stored, dissipated, and released. When the storage limit is reached, the internal elastic strain energy becomes released sharply, and the damage variable increases rapidly. (4) As the confining pressure increases, the number of tensile and shear cracks accumulates in an “S” shape, and the proportion of shear cracks increases gradually.
Pile—soil interactions in frozen soil foundations based on frost heave rate and soil stiffness variations
Authors: Zhou Yalong , Wang Xu , Liu Deren , He Fei , Niu Fujun 
Published: November 2020

Abstract
The frost heave rate and stiffness of soil in frozen soil foundations varies remarkably with the freezing depth under the influence of the freezing-end temperature, temperature gradient, and overburden stress. The stress level of frozen soil increases with increasing frost penetration, leading to greater stiffness and a smaller frost heave rate. In this work, the freezing-end temperature and temperature gradient are introduced to the traditional Takashi model via the frost heave layering method and the overburden stress is modified to establish an empirical prediction model of frost heave rate and stiffness. Analytical solutions of load transfer differential equation of single pile considering stiffness increase and frost heave rate decrease along the frost penetration are derived on the basis of the mechanism of pile–soil interactions. The calculation results are in good agreement with measured values, thus confirming the correctness of the analytical solution. Variations in frost heave rate and soil stiffness with increasing depth are then combined to form four models, and changes in axial force and tangential frost heave force as a function of frost penetration are calculated and analyzed on the basis of these models. Results show that calculation of the frost heave rate and stiffness of soil along the frost penetration depth according to normal values will significantly underestimate the axial force of on the pile.
Deformation Failure Mechanism and Motion Laws of Near-horizontal Thick-layer with Thin-layer Columnar Dangerous Rock Mass in the Chishui Red Bed Area
Authors: Xie J , Yang G L , Qin Y G , Xu X T 
Published: November 2020

Abstract
The collapse of dangerous rock masses, either due to natural causes (such as weathering by rain) or anthropogenic factors (such as engineering construction in the rock area), poses a threat to both life and property. Therefore, investigating deformation failure mechanisms and determining the movement characteristics of the rock masses after collapse can provide practical guidance for conducting linear projects while taking adequate measures to prevent the collapse. In this study, a dangerous rock mass on the right side of the Yuanhou Toll Station of the Rongzun Expressway was used to study the deformation and failure mechanism of near-horizontal and thick layer with thin-layer columnar dangerous rock masses in the Chishui red bed area. A high-definition 3D-surface model was generated by using unmanned aerial vehicle (UAV) tilt photography technology to obtain an aerial image of dangerous rock masses with spatial coordinates in the research area. The three-point method was used to interpret the structural surface of the dangerous rock mass based on the 3D model. A model for the deformation and failure of dangerous rock masses was developed via an engineering geological analysis. We simulated and analyzed the cause of deformation and failure of dangerous rock masses using FLAC3D software. In addition, the motions of rock fall were studied by performing simulations using Rockfall software. From the interpretation of the 3D model of the UAV, the dangerous rock mass developed two sets of dominant structural planes that were nearly vertical and perpendicular to the stratum level, cutting the rock mass into cuboids. Based on the analysis of a stereographic projection, the dangerous rock mass was in an unstable state. The results showed that the dangerous rock mass had a high stress concentration in the middle and lower soft rock, which is likely due to dumping collapse under self-weight and differential weathering. Moreover, rock fall has a 60% probability of causing damage to the road below the rock mass if it collapses, threatening the safety of passing vehicles and people’s lives and property.
Drillability characteristics of formation and evaluation of bit selection for the Zhongtaishan structural strata in Sichuan Basin, China
Authors: Jie Chen , Feiyun Huang , Bin Xiang , Xiangchao Shi , Bo Liu 
Published: November 2020

Abstract
Selecting a suitable bit for a specific formation is very important in increasing the rate of penetration (ROP) and reducing the drilling cost during the drilling process. Drillability and rock mechanical parameters are frequently used to evaluate the resistance of strata to drilling engineering. Based on the drilling well history data for the Zhongtaishan structural strata in the Sichuan Basin, it can be observed that the slow ROP and high drilling cost have become critical factors in restricting the efficient development of tight gas in this tectonic region. Furthermore, a new model for the rock drillability index was established based on the experimental rock drillability data under simulated bottom-hole conditions. Part of the drillability test data was used to verify the accuracy of the model, which can accurately describe the effect of wellbore pressure on drillability. Well history and logging data were also used to calculate the rock mechanics parameters and rock drillability index. In the Xujiahe Formation, characterized by high uniaxial compressive strength (UCS) and drillability index, the Poisson’s ratio of the formation rock was approximately 0.21–0.24, the elastic modulus was 80 GPa–110 GPa, the average value of the internal friction angle increased from 40° to 45°, and cohesive increased from 18 MPa to 36 MPa. The formation drillability index without wellbore pressure ranged from 5–7, whereas that under wellbore pressure conditions ranged from 8–9 with a high Cerchar abrasion index (CAI). Mechanical specific energy (MSE) models were used to optimize the bit quantitatively, and the results demonstrated that the SH633, HJ537GK, I437, and KPMD1642DRT combined drill bits were more suitable for the Da’anzhai, Zhenzhuchong member of Ziliujing Formation, and the 6th, 3rd, and 2nd variables of the Xujiahe Formation respectively.
Relationship between wellbore instability and rock mechanics when drilling in the fault area of Shunbei Formation
Authors: Liu Jingtao , Yu Yang , Ren Pengju , Zhou Zhou 
Published: November 2020

Abstract
The Tarim Basin is one of the most important oil formations in China, and it is prospected to exceed 110 billion barrels. Recently, some fault areas were drilled to achieve high potential oil reservoirs in the Tarim Basin. However, during drilling, wellbore stability is difficult to ensure in the fault areas. Wellbore collapse and lost circulation may unexpectedly occur. Therefore, analysis of wellbore stability according to the formation characteristics of the fault zone is necessary. On the basis of the formation mechanism of the fault zone, the stratigraphic characteristics corresponding to the internal structure of different fault zones were analyzed in this work. As a result of the formation characteristics, the corresponding logging identification methods of the induced fracture zone and sliding crushing zone formed, and the differences in wellbore instability in different internal structures were compared. The formation characteristics and mechanical properties of the sliding crushing zone were characterized by XRD, SEM, linear expansion rate test, rolling recovery test, and other physical experiments. Logging calculations were also conducted to assess the phenomenon of collapse that often occurs in the sliding crushing zone, and the collapse mechanism was analyzed accordingly. In view of the leakage phenomenon in the induced fracture zone, the complex mechanism of the leakage was analyzed, and the traditional minimum principal stress model was modified to obtain the leakage pressure calculation model suitable for the fault zone. Finally, taking the F1 fault zone in Shunbei area as an example, the internal structure of the fault zone was divided by using the summarized logging identification method. The wellbore instability of the different internal structures was compared, and the newly established loss pressure model was applied in the SHBX1 well, thereby proving that the model has a good application effect. The study in this paper provided some mechanisms of wellbore instability based on formation property and rock mechanics in the fault area. In addition, a loss pressure model based on the special formation characteristics was proposed to guide drilling in the fault zone.
Effect of heat exposure on anisotropic mechanical properties of host rock in the Tamusu pre-selected area for high-level radioactive waste disposal in China
Authors: Zhang Haiyang , Liu Jian , Liu Feiyang , Ma Hongsu , Wang Chunping , Zhao Xingguang , Chen Liang 
Published: November 2020

Abstract
As a typical sedimentary rock, clay rock with bedding structure shows clear anisotropy in its mineral composition and mechanical properties. When the clay rock is selected as the host rock for a high-level radioactive waste (HLW) geological repository, its temperature rises because of the continuous release of heat by the HLW. To examine the influence of temperature on the anisotropic mechanical properties of clay rock in the Tamusu pre-selected area for HLW repository in China, a series of direct shear tests in different directions were conducted on the Tamusu clay rock exposed to a range of temperatures. The microstructural characteristics were observed by scanning electron microscopy, and the morphology of the shear failure surfaces was analyzed with the help of 3D laser scanning. The results show that the shear strength parameters of specimens sheared perpendicular to the bedding plane were significantly higher than those of specimens sheared parallel to the bedding plane, and the former specimens exhibited a more rugged failure surface. Strength of both types of specimens increased with the increase in temperature from 30°C to 200°C because of water evaporation and mineral expansion. The mechanical anisotropy was also enhanced by heat exposure. These findings provide key information for the site characterization of the HLW repository, and a reference for the design and construction of underground engineering structures in layered clay rock.
Experimental investigation of the mechanical properties of basalt in the Baihetan hydropower station region in China
Authors: Liu N , Liu Z J , Chen P Z 
Published: November 2020

Abstract
The Baihetan hydropower station is mainly situated in the basalt formations of Mount Emei (Sichuan Province, China). During the excavation process, basalt has shown some special mechanical characteristics. In this study, the deformation and failure characteristics of basalt are investigated via laboratory tests (uniaxial and triaxial compression tests on blocky basalt samples) and field deformation tests (rigid bearing plates applied in situ to columnar jointed basalt). The information gathered is then analyzed to reveal the mechanisms responsible for the failure of basalt. Results show that (1) the stress–strain curves of cryptocrystalline basalt are essentially linear in the pre-peak region and the stress drops rapidly in the post-peak region. The failure mode of the rock changes from being fragmentation-dominated under low–medium confining pressure to fragmentation–shear composite failure under high confining pressure. (2) In the post-peak region, amygdaloidal basalt exhibits brittle mechanical behavior under low confining pressure and ductile behavior under high confining pressure. In terms of failure mode, the basalt transforms from splitting failure under low confining pressure to shear failure under medium–high confining pressure. (3) The deformation moduli measured during field tests with rigid bearing plates are spread over a large range and are influenced by various factors (including column nature, lumpiness, loading direction, unloading-induced relaxation, and stress state). (4) The deformation moduli of the rock masses of Classes II, III1, and III2 successively decrease and exhibit significant anisotropy.
Stability analysis of an expansive soil-embankment slope with a soft interlayer
Authors: Shi Zhenming , Zhao Siyi , Qiao Yafei , He Manchao 
Published: November 2020

Abstract
The soft interlayer in the foundation is one of the most important factors that induce landslide in the expansive soil-embankment slope. The existence of large soft layers significantly reduces the overall stability of the slope, and they have the tendency to further develop into a sliding surface. To investigate the influence of the soft interlayer on expansive soil slopes, taking the high-fill embankment slope with a soft interlayer in the Baoshan area of Yunnan Province as an example, the causes and strength effects of the soft interlayer are analyzed via landslide investigation, laboratory test, and numerical simulation, and the stability and instability mode of the slope are studied. Results indicate the following: ① The soft interlayer is located at the bottom of the weathering layer within the depth of the atmosphere. Its strength is less than that of the expansive soil on both sides. ② The overall stability of the slope and the shape of the sliding surface are controlled by weak interlayers, and its strength greatly impacts the damage scope of the slope. When the strength is high, it appears as a collapse of the fill area, and when the strength is extremely low, it appears as the overall sliding of the slope. Using the residual strength as the calculation parameter of the weak layer reflects well the actual stability and failure mode of the slope. ③ Results of soil layer parameter sensitivity analysis indicate that the internal friction angle of the soft interlayers has the most significant effect on slope stability. Using the lightweight embankment fill can effectively improve the stability factor of embankments.
Strain localization in hydraulic fracturing of granite specimens based on DIC method
Authors: Xing J Q , Zhao C , Zhou Y M 
Published: November 2020

Abstract
Hydraulic fracturing is a crucial and widely-used technology in shale gas exploitation and enhanced geothermal systems, while the fundamental mechanisms of hydraulic fracturing are not comprehensively understood. This paper aims to promote the understanding of strain localization in hydraulic fracturing of granite specimens based on digital image correlation (DIC) method. Through a specially designed pressure enclosure, the hydraulic fracturing processes were captured by a high-speed camera. The strain localization phenomenon, evolution, and coalescence of SLZs in hydraulic fracturing were analyzed. Results show that obvious strain localization occurs before the specimen failure, which gradually develops into a continuous strain localization zone. With the evolution of SLZs, the specimen will be unable to bear the liquid pressure, and macro cracks occur at SLZs. The statistical data in the query region shows that the strain localization in hydraulic fracturing occurs earlier than previously thought, and the evolution of SLZs can be divided into steady, soaring, and fracture stages according to the changing trend. The coalescence of the patchy distribution SLZs occurs frequently throughout the evolution process of SLZs, and the coalescence of SLZs may be the cause of the increasing speed of evolution.
Analysis and test on stress-strain of cement sheath in shale gas wells with hydraulic fracturing
Authors: Liu K , Ding S D , Zhou S M , Tao Q , Liu R G , Gao Y 
Published: November 2020

Abstract
The sealing failure of cement sheath which caused annulus pressure in shale gas wells have significantly affected the safe and efficient development of shale gas. In view of the integrity of cement sheath which is affected by the high fluid pressure in casing during the hydraulic fracturing treatment, an experimental device for testing the integrity of cement sheath is established. In addition, the analytical model for calculating the stress and strain of the well system is established based on parameters of the experimental device. The analytical model for calculating the circumferential strain at outer wall of the steel cylinder is achieved. The error of stress-strain between analytical calculated results and the experimental results is very small. In sensitivity analysis, the parameters which affect the stress on cement sheath interface is discussed. This study has a certain reference value for the design of experiment device and the analysis of sealing ability of cement sheath in shale gas wells.
Influence of water content and maceral composition on the properties of outburst-prone coal: laboratory experiment
Authors: Gong Shuang , Wang Zhen , Zhang Guoqiang , Zhou Lei , Wang Wen , Zhao Yixin 
Published: November 2020

Abstract
We conducted laboratory experiments to investigate the influence of water content and maceral composition on the properties of outburst-prone coal using X-ray diffraction and optical electron microscope. For comparison, two groups of experiments were completed on contrasting coals, namely, outburst-prone and outburst-resistant coals. The complete stress–strain behavior, uniaxial compressive strength, Young’s modulus, and acoustic compressional velocity were measured and correlated with water content. Test results showed that the microhardness and microembrittlement of the outburst-prone coal were higher than those of the outburst resistant coal. When the water content increased to 4%, the uniaxial compressive strengths of the outburst prone and outburst resistant coals decreased by 82.4% and 85.1%, respectively; and their elastic moduli decreased by 90.3% and 86.6%, respectively. The difference between the maximum reflectance and the minimum reflectance of vitrinite was smaller for the outburst resistant coal than for the outburst prone coal. The distribution of maceral composition in the outburst resistant coal was simple, and the primary damage was minimal.
Influence of sidewall size on spalling in deep D-shaped tunnels: An experimental simulation
Authors: Luo Yong , Gong Fengqiang 
Published: November 2020

Abstract
A series of true triaxial compression tests was performed herein on cubic red sandstone samples containing a D-shaped hole with three sidewall sizes to study the influence of sidewall size on spalling in D-shaped tunnels. The initial horizontal stress of the tests refers to the in-situ stress at 500 m depth. The hole axis was arranged along the direction of the maximum horizontal principal stress. The vertical stress was increased to simulate the increasing surrounding rock stress after tunnel excavation. During the test, a self-made monitoring device was used to monitor and record the failure process of the tunnel models in real time. Furthermore, the spalling process of the D-shaped tunnels with different sidewall sizes was reproduced indoors. The failure process and the stress and fracture characteristics of the tunnel models with three different sidewall sizes were then analyzed and summarized. The effect of the sidewall size on spalling in D-shaped tunnels will be discussed in this paper. The results show that the failure of the tunnel models with different sidewall sizes first occurred on the sidewall near the corner then gradually developed upward and axial along the sidewall with the increase of the vertical stress. The width and the depth of the failure zone gradually increased, and a V-shaped notch was finally formed on the sidewall. No failure occurred on the roof and the floor of the tunnel models. The dominant failure modes were tensile failure. The failure forms were mainly spalling occasionally accompanied by slab ejection. The slabs were shaped in thin plates. The vertical stress that caused the initial failure of the tunnel models gradually decreased with the increasing sidewall size. Furthermore, the ability of the surrounding rock to store elastic strain energy decreased. The tensile characteristics became more prominent, and the size of the plate-shaped slabs increased. In the same stress environment, the greater the sidewall size, the larger the failure width and depth on the sidewall, and the more visible the V-shaped failure zone. The stability of deep D-shaped tunnels can be improved, and spalling can be mitigated by reducing the sidewall size. However, the risk of a rockburst will increase. This finding has an important engineering significance for the optimization design of a tunneling cross-section and the prevention of spalling and rockburst in D-shaped tunnels.