bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisotropic rock permeability evolution model based on wing crack propagation after dynamic load testing
Authors: Li Diyuan , Zhu Quanqi , Wang Wenjian 
Published: November 2020

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
Recent Advances in Nonlinear Fracturing Characteristics of the Hydraulic Fracture in the Deep Reservoir
Authors: Xing Yuekun , Zhang Guangqing , Huang Bingxiang 
Published: November 2020

Abstract
During hydraulic fracturing in the deep reservoir, the rock surrounding the hydraulic fracture (HF) presents three remarkable nonlinear mechanical behaviors: the fracture process zone (FPZ; microcrack zone) developing at the HF tip, the microcrack band surrounding the HF surface, and the plastic zone growing due to the opening compression of the HF. The above three mechanical behaviors constitute the HF nonlinear fracturing characteristics. However, understanding the HF nonlinear fracturing characteristics is challenging and crucial. In this work, we present our recent published advances in HF nonlinear fracturing. (1) We developed a characterization method for rock FPZ by utilizing and integrating fiber Bragg grating (FBG), digital imaging correlation, and acoustic emission (AE). The integrated measurements showed that FPZ softening followed a linear response. The relationship between FPZ length and crack tip opening displacement was linear, and the relationship between dissipated energy and FPZ length was quadratic. (2) Detailed analysis of the AE energy during cyclic fracturing tests of sandstone revealed that the FPZ propagation rate of subcritical fractures was related to the increasing rate of dissipated energy accumulated from all activated microcracks. Thus, a general law (Zhang’s law) of dl/dN = (1/2CG)l
−1(dG
D/dN) was proposed and validated. (3) The HF microcrack band of high-temperature (120 °C) granite was identified using AE waveform analyses. The fracture energy was reduced by approximately 75% adjacent to the wellbore (approximately 40% of the fracture length) in the microcrack band. The effective width of the microcrack band was reduced by 40%–56.4% at 120 °C, indicating that high temperatures decreased the effective stimulated volume of HF. (4) We proposed a thermoplastic constitutive model for high-temperature rocks (such as shale) in deep reservoirs. The constitutive relation depends on hydrostatic pressure, stress deviator, and temperature. Parameters characterizing effects of temperature on thermoplasticity were also proposed. The above research advances can provide bases for HF in the deep reservoir.
Experimental investigation on the effect of temperature on thermal conductivity of synthetic rock samples
Authors: Wang Zhuo 
Published: November 2020

Abstract
The effective thermal conductivity (ETC) plays an important role in many fields such as to solve basic geological problems, rock engineering, and utilization of heat energy; ETC is one of the most important thermo-physical properties of porous media. In this study, experiments on synthetic rock samples with different material mixture ratios under different operating temperatures are conducted to estimate the thermal conductivity property of the rock samples. The experiments were performed on synthetic samples with different ratios of gypsum, fine or medium sand, and water; 21 groups of tests were conducted under room temperature; another five groups of tests were conducted under different temperatures from 20 to 50 ° to assess the effect of temperature on thermal conductivity. According to existing studies and equations, thermal conductivity increases with an increase of sand content and a decrease in temperature. Moreover, based on our experiments, it is easy to identified a singularity on the general changing trend of thermal conductivity for each sample. Following our experimental results, we attempted to observe and interpret this alteration mechanism. According to the heat capacity theory in solid-state physics, this research provides new explanations for the above alteration.