bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent Advances in Nonlinear Fracturing Characteristics of the Hydraulic Fracture in the Deep Reservoir
Authors: Xing Yuekun , Zhang Guangqing , Huang Bingxiang
Published: November 2020

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

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.
Movement Law of Overlying Strata with Loading Effect in the Large Space Structure of Deep Mines
Authors: Feng Cui , Zhaoyuan Lei , Tuanjie Li , Zhaohai Lv , Lei Li , shuai Dong
Published: November 2020

Under the action of high-stress field, overlying strata with load characteristics in large space structure formed by changes of working faces in deep mines intensifies the movement of the overlying strata on the working face, which may easily cause dynamic disasters at the working face. Considering the large space structure of deep mines and taking gob-side entry retaining as a breakthrough point, this study analyzes various types of overlying strata structures and their loading effects. The concept and differentiation method of deep “three layers” are introduced. The movement of the overlying strata with loading effect is analyzed by establishing a large-scale Flac3D numerical calculation model and on-site inspection. The results indicate that the “arch” structure formed by the working face shifts to the middle and rear parts of the working face under the influence of the large space structure, and the overlying strata continuously evolves upward during this process. Finally, the “arch” structures of the working face are integrated within the overlying strata to form a symmetrical structure. In the deep “three layers,” “Mk” provides the force source for normal weighing of the working face. “Mj” shifts the stress relief of the working face to the middle–rear position, which may easily cause strong strata pressure at the working face. The uniformly distributed load of “My” ensures the stress relief position at the working face. Through on-site monitoring, the disturbance range and stress of Working Face 418 with large mining height are greater than those of Working Face 416. The changes in pressure relief positions of the working face are as follows: ventilation roadway > middle > intake roadway.
Deformation monitoring of noncircular tunnels based on 3D laser scanning
Authors: Guo J F , Zong X , Xie X Y , Wang L , Zhai J L
Published: November 2020

Deformation plays an essential role in the safety control of tunnel construction, especially for tunnels with large deformation disasters. Consequently, tunneling professionals need practical ways to monitor tunnel deformation. However, traditional methods are not yet available for 3D monitoring. This study presents a technology for measuring tunnel deformation on using a 3D laser scanner. This technology includes an automatic noise removal algorithm based on spatial features and a measurement technology of absolute coordinates. For point clouds with different times of section with the same mileage, a point-to-point deformation analysis is performed based on the azimuth. Based on the standard grid of point clouds in the longitudinal and circumferential directions of the tunnel, an overall deformation cloud map of the noncircular tunnel is generated. The use of the proposed method in the construction of the Xinzai tunnel of the express connecting Jianshui and Yuanyang in Yunnan province allows engineers to obtain critical information about deformation. Compared with the traditional monitoring method, the proposed approach can meet engineering requirements well.
Field Tests and research of Large Deformation Control Measures for Soft Rock Tunnel with High Geostress
Authors: Sun Xiaoming , Zhang Bo , Zhang Yong , Qiao Xiaobing , Wang Zhijiao , Tao Zhigang
Published: November 2020

The Muzhailing highway extra-long tunnel is affected by high geostress, and during the construction, large deformation of soft rock frequently occurred. Taking this as the research background, the high-prestressed constant resistance and large deformation anchor cable support scheme was proposed. In the field test, the indicators of three support schemes were compared, including the convergence deformation of surrounding rock, the deep displacement of surrounding rock, the axial force of anchor cable and bolt, and the stress between primary support and surrounding rock. The field test results show that: under the support of bolts, the cumulative deformation of surrounding rock exceeded 1500 mm, and the primary support damage was serious; In the second scheme, under the support of 4 m and 5 m long constant resistance anchor cables, although the large deformation of surrounding rock was controlled, the cumulative deformation was about 600 mm; In the third scheme, under the support of 5 m and 10 m long constant resistance anchor cables, the cumulative maximum deformation of surrounding rock was reduced to 216 mm, and all the data of the field test were within the controllable range. Therefore, high prestressed constant resistance and large deformation anchor cable support measures can effectively control the large deformation of surrounding rock.
Stress-induced cracking performance of hard basalt in a large underground cavern based on multi-information observation
Authors: Jiang Quan , Xu Dingping , Zhao JinShuai , Li Shaojun , Wang Wei , Xu Jian
Published: November 2020

Overcoming the brittle cracking and the corresponding hard rock has become the key bottleneck challenge in the excavation of underground engineering with high geostress. To further understand the onsite cracking’s characteristics and the basic mechanism of hard rock, we carried out a detailed field monitoring action for basalt breaking behaviors in a large underground powerhouse by in situ investigation, digital borehole camera, multi-point deformation measurement, and real-time micro-seismic monitoring. On the basis of our observations, the inner cracking performances of surrounding rock embodied as discontinuous appearance and open of cracks during excavation, and these fractures were often parallel to the outline of the cavern and extended to the inner side because of the subsequent excavation disturbance. Corresponding numerical simulation indicated that the redistribution of rock stress induced local stress concentration and would result in the splitting break of basalt. Field complicated proof indicated that this stress-induced cracking of basalt belonged to the tensile break, and the macroscopic deformation of the surrounding was the result of the accumulation of abundant open deformation of discontinued cracks. This observed achievement can enrich our understanding of the cracking mechanism of hard rock and provide some key cures for optimization design for underground engineering construction under high geostress conditions.
Study on geotechnical engineering investigation method of strong karst deep backfill area in mountain area
Authors: Hao Liu , Maozhong Tian , Jinyang Liu
Published: November 2020

Guizhou Province is characterized as mountainous with few flat lands. It also features undulating terrains; widespread karst strata; large karst troughs; karst depressions and falling water caves; and well-developed underground karst caves, karst pipelines, and underground rivers. In such mountainous areas, large-scale construction of karst sites requires large-scale excavation and backfilling. The study site comprises several backfilled layers of 550 m thickness and features complex components and large thickness variations. The influence of the long-term seepage of surface water and groundwater is also apparent. However, the study site also exhibits an uneven settlement of deep backfilled layers and unstable karst foundation. The conventional survey method cannot identify effectively and comprehensively existing problems in engineering geology and hydrogeology according to the problems found in the investigation of large-scale building areas, municipal roads, urban rail transit, and university campuses. Through the combination of building engineering methods, such as new and old topographic and geomorphologic contrast methods, on-site geological surveys, karst hydrogeological surveys, borehole layout principle, drilling method, effective physical exploration test, field in-situ test, and indoor test, the scale and characteristics of karst development in the study site, changes in backfill thickness and material composition, and physical and mechanical properties of rock and soil mass are determined. The results provide comprehensive geotechnical data for the type selection, arrangement, and foundation scheme selection of structures. Through comprehensive analysis and summary, this work establishes a set of comprehensive geotechnical investigation methods for strong backfilled karst areas in mountainous regions. The results are expected to be applicable to other similar sites.
Spatial distribution characteristics of landslides in Xiluodu Reservoir Area
Authors: Pengcheng Su , Chun Ma , Jingjing Liu , Yong Li
Published: November 2020

There are many landslides in Xiluodu Reservoir Area. 161 landslides were interpreted to investigate. The key influential factors including the formation lithology, faults, rainfall, earthquake, reservoir water level and the Geodetecter methods was used to explore the relative impact of the factors and the interaction of the two factors on the spatial distribution of landslides. The results show that: (1) Due to the differences in the properties of different rock groups, the landslides show significant regional differences; (2) The landslides are mostly distributed in the range of 600~1200 m, 10°~40°, Ordovician-Silurian (O-S) strata, areas within 4 km of the fault, areas where the average annual rainfall is 800~900 mm and seismic peak ground acceleration of 0.15g; (3) There are 53 landslides affected by reservoir water. The effect is most obvious when the water level acts on the middle and front of the landslide. The effect time is gradually weakened with the annual deformation and stress adjustment; (4) Multi-factor interaction presents more clear relationship with the spatial distribution of landslides. The interaction of lithology and rainfall can explain 45.9 % of the spatial variation of landslides, which means that lithology and rainfall factors have the greatest influence on the spatial distribution of landslides. The results provide a certain basis for the prevention and control of landslides in Xiluodu Reservoir Area.
Integrated system of geophysical methods for shallow loose covering stratum exploration in the granite region in the northwest of Zhejiang Province, China
Authors: Fang Hao , Tong Bin , Du Xianxiang
Published: November 2020

The major triggering factor of the collapses, landslides, and debris flow in the northwest region of Zhejiang Province in China is the shallow loose covering stratum with a thickness of dozens of centimeters to dozens of meters generated by the intensive physical weathering process of granite. Therefore, accessing a three-dimensional model of the slope structure covering by the shallow loose stratum and quantifying its thickness and spatial distribution are very important in deepening one’s understanding of the failure mechanism and distribution features and improving the efficiency of geohazard prevention and mitigation. This study applies high-density electrical method, microtremor survey, artificial transient surface wave method, and ground-penetrating radar to explore the slope structure covered by the loose stratum. By validating and comparing the results obtained through engineering geological drilling, an integrated system of the geophysical methods for the shallow loose covering stratum is proposed herein with greater precision and suitability for the granite region in the northwest of Zhejiang Province. This integrated system of methods consists of geophysical exploration, followed by drilling for validation. Each individual method in the system can be applied with suitability evaluation and recommended parameters. The proposed system could also properly void shortage when only an individual method is used. The major conclusions obtained in this study are as follows: (1) the accuracy of the high-density electrical method in the dry condition could reach 85% or above, and in the rainy season, the test should be conducted 48 h after the rainfall; (2) the microtremor survey and artificial transient surface wave methods can achieve good results in the case of a complex climate condition or a large-area detection; (3) the ground-penetrating radar method can be used to discover the loose covering layer thickness with good precision (less than 5 m); and (4) the integrated method system is more applicable when the ground slope is less than 30°.
High-precision 3D real scene model construction method based on air-ground data combination
Authors: Yang Fei , Ma Chengrong , Zhang Bowen , Chen Xuannan , Cao Li , Li Changhong , Huang Yongliang
Published: November 2020

Due to low efficiency, low accuracy, and difficulty in intuitively realizing the real geological conditions for spatial data acquisition on mines and slopes, this study proposes the use of a 3D modeling method based on a combination of air and ground data. The method is based on Unmanned Air View (UAV) tilt photogrammetry data. In this article, 3D terrestrial laser scanning point cloud data is used as a supporting technique via control points to spatially fuse and improve the accuracy of the UAV tilt photogrammetry 3D model. This study uses the feature points to adjust the interior point coordinates of the UAV tilt photogrammetry 3D model. The application results show that the mining site model established by this method has high precision and processing efficiency. It can also display the overall characteristics of mines and provide a scientific basis for mining, exploration, measurement, and effective evaluation of slope stability.
Experimental study of blasting wave propagation in jointed rock mass and vibration reduction effect of barrier holes
Authors: Li Yashi , Zhao Rui , Zhu Jianbo
Published: November 2020

Blasting in underground rock opening could generate shock waves, propagating in surrounding rock mass and possibly leading to damage and instability of surrounding underground structures. Barrier holes are widely used in blasting vibration reduction. However, characteristics of blasting wave propagation in jointed rock masses have not been well determined, and the understanding of effect of barrier holes on vibration reduction is still at its infancy. To investigate the blast-induced wave propagation in jointed rock masses and vibration reduction effect of barrier holes, laboratory explosion tests were performed with the super dynamic strain test system and vibration monitor system. Results showed that the joint orientation has significant effects on the first-peak compressive strains in surrounding rock mass and adjacent opening. First-peak compressive strain of surrounding rock mass increases with decreasing scaled distance. The first-peak compressive strain on the wall of the adjacent underground opening is dependent on the characteristics of the adjacent underground opening. In addition, the dynamic responses of the surrounding rock mass are determined by the combined influence of the joint dip angle and location. The experimental results also indicated that barrier hole diameter has great effects on first-peak compressive strains of adjacent underground opening and the vibration-isolation rate of measuring points before and after barrier hole screen. With increasing barrier hole diameter, first-peak compressive strains and peak particle velocities (PPVs) significantly decrease and vibration-isolation rate of measuring points before and after barrier hole screen increases, indicating the vibration reduction effect of barrier hole increases. The findings in this paper could facilitate better understanding blasting wave propagation in jointed rock mass, and be helpful in vibration control of engineering explosions.
Coupled static and dynamic tensile property of granite
Authors: Man Ke , Liu Xiaoli
Published: November 2020

The principle of coupled static and dynamic loading is illuminated according to the basic principle of the SHPB, i.e., one-dimensional stress wave propagation and uniformity of the specimen. In the Tianhu area of Xinjiang Province, which is a preselected area for high-level radioactive waste geological disposal, a series of coupled static and dynamic loading was conducted in a borehole. The dynamic tensile strength could reach a maximum level when the axial tensile stress is about 50% of the static tensile strength. Meanwhile, as the axial tensile stress increases, the coupled static and dynamic tensile strength increases obviously, reaching about three times the static tensile stress and about 1.5 times the dynamic tensile strength. The failure model of the coupled test is a tensile failure pattern, which is the same as in the static tension and conventional dynamic loading test. Furthermore, through a series of coupled static and dynamic loadings, the strength of the rock specimen could be obtained under different kinds of axial tensile stress and dynamic loading. Thus, the critical value of the dynamic loading could be confirmed, which is useful for blasting excavation in deep geoengineering.
Shaking table test on the characteristics of seismic acceleration responses at the portal section of the loess tunnel
Authors: Zhao Tao , Liang Qingguo , Ma Xiaowen , Ai Shengjun , Zhou Wendi , Wang Lili
Published: November 2020

A large-scale shaking table test was conducted to study the dynamic response at the portal section of a tunnel based on the loess tunnel of the Baoji–Lanzhou high-speed railway as an engineering background. A wavelet packet transform method was applied to analyze seismic acceleration responses. The pattern of changes in energy in the loess tunnel under the seismic load was obtained. Results reveal that (1) the acceleration amplification factor of the slope surface increases with elevation, but a turn exists at the inverted arch of the tunnel because the stiffness of the tunnel is greater than that of the slope soil. As such, the tunnel elicits a certain protective effect on the slope soil below it. (2) The amplification effect of the internal slope soil decreases gradually outward, and the tunnel portal is affected by the amplification effect of the slope surface. The peak ground acceleration (PGA) of the tunnel vault is greater than that of the inverted arch of the tunnel. Thus, the vicinity of the tunnel vault should be the key seismic fortification area. (3) The loess layer causes an amplification effect on low-frequency-band seismic waves (0–12.51 Hz) and a filtering effect on the high-frequency-band seismic waves. The changes in the energy of the slope surface and the inside tunnel gradually stabilize as the seismic load increases. This study can provide a reference for the seismic fortification of the tunnel portal section of the loess slope–tunnel system under a seismic action.
Seismic analysis of a transition tunnel constructed with TBM and mining method
Authors: Yang Song , Li Ruozhou , Li Pengyuan , Wang Chao , Yu Fei , Yuan Yong , Yu Haitao
Published: November 2020

A transition tunnel is generally built to connect a TBM tunnel and a mining tunnel, given the different cross sections associated with each construction method. The transition tunnel may be sensitive to earthquake damage since the tunnel cross-section and stiffness change along the tunnel axis. Studying the seismic performance of the transition tunnel structure, a subtle 3D finite element model is carried out. Comparing with the calculation results of SHAKE91, a reasonable non-reflective boundary condition is used. The concrete adopts an elastoplastic damage constitutive model, and the surrounding rock mass uses an elastoplastic constitutive model based on the Drucker-Prager yield criterion. The effects of different ground motion magnitudes and different types of seismic waves are calculated and analyzed through dynamic time-history method. The calculation results show that the impact range of the construction method butted composite lining section on the tunnel structure of the mine tunnel and the TBM tunnel is about 10m, and the reinforcement of the inner lining will cause a sudden change in the stress of the outside TBM tunnel structure. Moreover, the compressive stress of the surrounding rock and tunnel structure is small, and the structural damage mainly occurs in the area of the arch shoulder and arch foot.
Method of S Wave Identification: Application to Measured blasting vibration signals
Authors: Yang Zhaowei , Hu Yinguo , Liu Meishan , Wu Xinxia , Zhao Gen
Published: November 2020

S wave identification is an indispensable step in the process of deriving the dynamic parameters of rock masses, which are highly significant in guiding the design and construction of hydraulic engineering projects. However, it is difficult to identify S waves accurately because of 1) the influence of overlapping within the P wave coda and 2) the incomplete separation between S and P waves owing to the characteristic short distances of blasting seismic wave propagation. This paper presents a modified method for accurately identifying S waves at the engineering scale using blasting vibration signals. The proposed method combines the application of the short-time average zero-over rate with polarization analysis. By using the short time average zero-over rate, it is possible to effectively reduce the computational time while improving the computational efficiency. Polarization analysis is used to improve the accuracy of the method. A comparison of numerical identification and theoretical results revealed that the improved method is clearly capable of S wave identification with errors of less than 2%. To demonstrate the capability and accuracy of the proposed method, measured vibration signals were introduced to the Fengning pumped-storage power station and the S wave velocities obtained from the first arrival times were compared to obtain an estimated S wave velocity.
A coal burst model based on roof vibration and coal slippage
Authors: Han J , Jia D , Cao C , Zhu Z , Li Y
Published: November 2020

Rock burst poses a serious threat to mining, and its mechanism still needs to be studied. Statistics show that more than 85% of rock bursts occur in mining roadways. The authors investigated the mechanism of rock burst in the roadways by creating a finite elastic long beam dynamic model in longwall mining based on the elastic foundation theory. In this study, the fracture failure of the basic roof and the related dynamic effects are analyzed. The results indicate that the occurrence of the free vibration of the basic roof is caused by fracturing during the first face advance. It is also found that the vibration frequency increases and the period decreases with the increase in roof thickness. Furthermore, the strength and elastic modulus increase with the increase in roof hardness. The effect of a thick, hard roof on the coal mass is mainly reflected in the vibration of the roof above the coal seam. During free vibration of the roof, the stress applied by the roof on the coal mass decreases. Under the action of horizontal stress, the coal mass slips along the interface between the roof and coal mass, which may result in rock burst. The mode of the basic roof vibration and the viscoelastic properties of the coal mass significantly influence the vibration–slippage impact. With the increase in the strength, thickness, and horizontal stress of the roof, the possibility of sliding between the coal seam and the roof also increases, which may potentially result in rock burst. This mechanism may explain the occurrence of rock burst in large-scale coal bodies that move out in the roadway, which could provide a reference for the prevention and control of such phenomena.
The effects of gas pressure and adsorption in coal permeability under uniaxial strain conditions
Authors: Zhu J , Zhang B , Tang J , Shao T S , Lin L
Published: November 2020

Coal permeability evolution related to gas pressure is important to coal mining and coalbed methane exploitation. To apply the exponential model of coal permeability, we simplified the stress of coal reservoirs to the uniaxial strain condition. To investigate the permeability of coal samples changed in gas pressure under strain-controlled conditions, we measured the strain and permeability of coal samples collected from 12-1# coal seam in Hongyang No. 3 Mine in Shenyang, China, during gas pressure reduction under strain-controlled and constant temperature conditions using the Gas seepage measurement system in State Key Laboratory of Coal Resources and Safe Mining of China University of Mining & Technology (Beijing). The permeability experiment was performed under uniaxial strain conditions using adsorptive gas (carbon dioxide) and non-adsorptive gas (helium). The experimental results show that with decrease in gas pressure, the permeability ratio, k/k
0, of coal samples with helium and carbon dioxide firstly changed slightly with gas pressure from 4.0 to 1.5 MPa and then increased sharply with a gas pressure of <1.5 MPa. Coal samples shrank with the reduction of gas pressure under the uniaxial strain condition. The gas pressure of 1.5 MPa can be considered as the turning point of the volumetric strain change. When gas pressure was <1.5 MPa, the volumetric strain of samples sharply changed because of carbon dioxide gas desorbed from coal when the outlet was open. As the gas pressure decreased, the radial stresses of coal samples with carbon dioxide were less than those of samples with helium. Therefore, coal matrix shrinkage because of gas desorption has an important influence on the radial stress of coal samples under the uniaxial strain condition.
Investigation of hydraulic fracturing mechanism by using a coupled continuous-discontinuous hydromechanical model
Authors: Zhao H J , Ma F S , Guo J
Published: November 2020

Fluid-induced fracture nucleation, propagation, and interaction are the essentials for a better understanding of the hydraulic fracturing process in unconventional reservoirs. In this study, a coupled continuous-discontinuous hydromechanical model was established to investigate the hydraulic fracturing propagation under varied conditions. The interactions between induced fractures and natural fractures are investigated and discussed by a series of hydraulic fracturing simulations. Also considered are the influences of bedding joints, in-situ stress ratios, and fluid injection rates on the patterns of hydraulic fractures and the stress field. It was found that hydraulic fracture propagation is controlled by both in-situ stress state and strength anisotropy of the reservoir rock. The simulations indicate that an increase in the fluid injection rate is favorable to the formation of a complex fracture network. More hydraulic fractures were developed when fracture fluids were injected into rock specimens with a faster pressurization rate than a quasi-static pressurization rate. However, higher fluid injection rates could result in higher breakdown pressures for fracture initiation and propagation. In addition, hydraulic fractures tend to extend along the direction of the maximum principal stress or approach this preferred path. Bedding joints are preferred locations and orientations for fracture initiation and propagation in laminated shale reservoirs.
Research on LiDAR technology in early identification of geo-hazards in alpine loess areas
Authors: Wang L C , Wang M , Hung X C , Feng Z
Published: November 2020

The early identification is a key topic in geo-hazards science in China. Methods including engineering geological analysis, optical RS, InSAR, field survey verification, have been used for early identification of geo-hazards. This paper presents the application of airborne LiDAR to data collection and landslide identification in alpine areas. High-resolution images and point clouds of several landslides were obtained. And the characteristics of landslides have been interpreted. The study of relationship between point clouds and vegetation removal model (VRM) showed that the density of point cloud had a great influence on VRM. The lusher the vegetation, the less point cloud could be collected, resulting in much less point cloud density and lower resolution of VRM. When the density of point cloud is greater than 15 points/m2, the hillshade map generated after vegetation removal was usable for landslide characteristics recognition. The boundaries, shape, zoning, and some micro-topography, such as cracks with a certain length and width, could be effectively identified. The hillshade map with different azimuth angles were able to visually display the micro-topography features from different orientations. The slope image and surface roughness image from airborne LiDAR provided quantitative topographic parameters for geo-hazards identification, boundaries delineation and volume assessment. In the end, this paper proposes a guidance of early identification of geo-hazards in alpine areas by using LiDAR Technology.
BIM-based Quantitative Assessment Method of Tunnel Collapse Risk in TBM Construction
Authors: Chengbin LI , Yadong XUE , Yongqiang FAN , Jiaxu WANG
Published: November 2020

Tunnel risk assessment plays an important role in tunnel design, construction and tunnel safety risk control. TBM method is more and more widely used because of its comprehensive advantages, especially in the diversion tunnel engineering. Because the geological conditions in the long tunnel are complex and changeable, TBM machines are extremely sensitive to the changing of geological conditions, various risks may occur during the TBM tunnel construction. But the risks are difficult to assess quantitatively. In this paper, an excavation model of diversion tunnel is established in ANSYS to analyze the deformation of surrounding rock, the instability probability of tunnel is obtained by Monte-Carlo method. Combined with BIM technology, the construction information model of TBM tunnel including personnel distribution, team cooperation, material transportation, structure layout and other engineering information is established. Based on combining surrounding rock information and TBM engineering information, the TBM tunnel is divided into several sections according to time and space by statistical method, the collapse risk of TBM tunnel during construction is quantitatively assessed by zoning to realize the visualization of risk class. The results can be used for TBM tunnel construction risk assessment, improving the efficiency of risk control.
Research on Critical Depth of Rock Burst in Coal Mines in China
Authors: Wen Jinglin , Li Husheng , Jiang Fuxing , Yu Zhengxing , Ma Haitao , Shu Couxian
Published: November 2020

With increasing coal mining depths in China, the number of mines experiencing rock burst is increasing. The conditions in which a mine can reach the critical impact-mining depth remain theoretically unknown, which hampers the determination of the depth at which rock burst prevention can begin in coal mines. Based on different mining boundary conditions of rock bursts occurring in coal mines, this study proposes the concepts and calculation methods of three critical depths of rock bursts in coal mining. The strength criterion for rock mass impact of medium–hard and hard coal is used to evaluate the failure strength and stress state of the coal rock mass under dynamic loading conditions. Then, the value of the dynamic stress coefficient of the coal rock mass is determined. The research team applied this method to numerous mines in China to test rock bursts under different types of working face conditions with a coincidence rate of 100%. Results verify the rationality of the calculation formula of the critical impact depth and the value of the dynamic stress coefficient. The findings of this research can provide a basis for evaluating rock bursts.
Study on the mechanism of crack formation and the behavior of crack propagation of directional tension blasting in deep and high stress coal mine
Authors: Xiaojie Yang , Di Yuan , Haojie Xue , Yubing Gao , Jindong Cao , Lin Hou
Published: November 2020

Roadway safety is related to the high productivity and efficiency of coal mining, roof cutting and pressure releasing technology is one of the effective measures for roadway stability control. Under deep mining conditions,the stress condition around the blasthole is complex, and the expansion of directional crack will be affected by high ground stress. In this paper, Based on the engineering background of the roof Cutting and Pressure Relief Technology of Non-pillar Automatic Roadway Formation in guotun coal mine, the crack propagation mechanism and propagation evolution of deep rock under directional tension blasting were investigated. Based on the stress model of blasthole under the deep condition, the mechanical conditions of crack propagation under the action of directional detonation wave and high surrounding rock binding force are obtained theoretically; The mechanical model of directional blasting under the condition of stress constraint is established by using LS-DYNA numerical calculation software, the evolution characteristics of effective stress and the law of crack growth are analyzed; Finally, through the drilling peep and other technical means, the field measurement of the presplitting effect is carried out, which verifies the previous research results and puts forward the appropriate roof presplitting scheme. The results show that when the deep roof strata of Guotun coal mine adopt four hole continuous blasting and per blasthole charge of 2800g, the roof strata can form a continuous seam, and the Roof presplitting effect is the best.
Effects of microwave irradiation on impact comminution and energy absorption of magnetite ore
Authors: Jiawang HAO , Qingwen LI , Lan QIAO , Naifu DENG
Published: November 2020

The severe mechanical wear and high-energy consumption in the comminution process of high hardness iron ore have always restricted the efficient and economic development of an enterprise. On the basis of the basic principle that microwave irradiation can induce rock damage, the magnetic ore specimens were subjected to microwave heating treatment with different heating paths and cooling paths; the uniaxial impact comminution test was conducted by the drop hammer impact equipment. This study analyzed the effect of the heating and cooling paths on the crack propagation process, dynamic mechanical strength, and energy consumption of magnetite ore. The results show that microwave irradiation causes obvious microwave-induced cracks in ore, and in the subsequent impact cracking process, the new cracks gradually penetrate the microwave-induced cracks and form the macroscopic fracture surface. With the increase of irradiation power and time, the ore dynamic strength decreased, and the absorption energy increased. Therefore, increasing the total output energy of microwave can effectively alleviate the mechanical wear and enhance the comminution effect of ores. Among the factors that affect the mechanical properties and absorption energy of ore, power has a higher priority than time. With the increase in the heat exchange rate between the ore and the external environment, the ore comminution becomes more intense, leading to the best comminution effect of ores. The research results have an important reference for the practical application of microwave irradiation technology in hard rock comminution.
Characteristics of stress and plastic zone of a deep shaft in a nonuniform stress field considering the bearing structure
Authors: Sun X M , Zhao C W , Zhang Y , Cui L , Wang J , Zhang S K , Shen Z H
Published: November 2020

The selection of support parameters for the shaft of a deep soft rock under a nonuniform stress field (NSF) is a technical challenge. In this study, the distribution characteristics of the maximum stress-bearing circle were investigated via a numerical simulation. Based on the characteristics of the shaft rock-bearing structure, the stress and plastic zone characteristics of deep shaft rock under NSF were investigated. The maximum stress-bearing circle expanded with depth and NSF coefficient under the no-support scheme, and the stress-bearing circle was circular when the NSF coefficient was 1. When the NSF coefficient was greater than 1, the stress-bearing circle began to show an elliptical nonuniform distribution characteristic along the long axis in the y-axis. As the NSF coefficient and depth further increased, the elliptical effect became more obvious. A constant resistance and large deformation (CRLD) cable was used to control the stability of the shaft under NSF. The stress-bearing circle and plastic zone under the CRLD cable-support scheme were smaller than those under the no-support scheme. Furthermore, the peak stress under the CRLD cable-support scheme was higher than that under the no-support scheme, which indicated that CRLD cable support could improve the bearing capability of the surrounding rock and reduce the plastic zone caused by the NSF coefficient. The findings of this study can provide reference for the supporting parameters for deep shafts.
Numerical Analysis of Anchor Bolt Pull-out Test by Cohesive Zone Model Combined with Finite Element Method
Authors: Li Erqiang , Feng Jili , Xie Hao , Zhang Hongchang
Published: November 2020

In this paper, to characterize the pull-out process of anchor in concrete, we combined the cohesive zone model and the finite element method. The embedding cohesive elements simulate the contact effect of the bolt interface. The results show that the numerical predictions are in good agreement with the experimental results. With the change of pull-out load, the shear stress of anchorage interface changes correspondingly until it is destroyed, which is consistent with the laboratory test. The strengths of the anchorage material and the concrete have a positive correlation with the bond strength of anchor bolt. The radial and lateral stresses acting along the bolt are similar. Therefore, in bolt anchorage, the bond strength increases as the radial (lateral) stresses increase.
New type of lightweight high-strength foamed concrete blocks
Authors: Zhou Bo , Zhao Yuhong , Li Zhe
Published: November 2020

Lightweight high-strength concrete materials have been paid increasing attention with the development of the civil engineering technology. This study tested the effects of the admixture ratio on the properties of lightweight high-strength foamed concrete (LWHSFC) samples in a laboratory. The results demonstrated that a type of foamed concrete with 1200 kg/m3 density and >15 MPa uniaxial compressive strength can be produced by chemical foaming and by adding three types of materials (i.e., silica fume, slag, and fly ash) to the cement–fine sand matrix at an optimized mix ratio. The laboratory tests also showed that the failure mechanism of the LWHSFC was similar to ordinary concrete (i.e., longitudinal splitting failure). The angle between the failure surface and the vertical load direction was 53°–76°, indicating the material’s brittleness. The decreasing order of the compressive strength of the LWHSFC with one type of mineral powder when tested 28 days after casting was: silica fume to slag to fly ash. Moreover, the decreasing order of the compressive strength of the LWHSFC with two types of mineral powder admixtures when tested 28 days after casting was silica fume + slag to silica fume + fly ash to slag + fly ash.
Influence of in-situ stress on rock fragmentation by TBM cutters and prediction of TBM performance for deep tunnels
Authors: Ma Hongsu , Yin Lijun , Gong Qiuming , Wang Ju , Chen Liang
Published: November 2020

In-situ stress is a significant factor influencing TBM tunneling for deep tunnels, especially for the construction of deep repository for radioactive waste disposal. Beishan area of Gansu Province is the first preferred area for high-level radioactive waste disposal repository in China, and the feasibility of using TBM technology in Beishan area is investigated in recent years. In this paper, six levels of in-situ stress related to different depths from ground to 500m at Beishan area were selected and the influence of in-situ stress on rock fragmentation was investigated by linear cutting test. The rock samples were collected from the Jijicao site in Beishan area, with uniaxial compressive strength of 105.6MPa. The test results show that: 1) there is a clear power function correlation between the penetration and the normal cutter force for each stressed condition, and the higher the confining stress, the smaller the gradient of the power function curve, which means slower increase of penetration rate under the same cutterhead thrust; 2) the required normal cutter force increases with the increase of overburden as the corresponding in-situ stress increases. Based on the laboratory testing, the Specific Rock Mass Boreability Index model was modified and further used in the prediction of TBM performance at different depths on Jijicao site. This paper helps better understanding of rock fragmentation mechanism in TBM tunneling in stressed ground, and also provides reference on parameter selection for TBM operation in deep tunnel tunnelling.
Numerical simulation on Time-dependent Behavior and Long-term Safety Analysis of Soft Rock Tunnel under Seepage Condition
Authors: Liu Shifan , Wang Wei , Gong Chuangen , Li Haifeng
Published: November 2020

This study investigates the time-dependent behavior of soft surrounding rocks of the Shanxi Panxiushan railroad tunnel. Based on the viscoelastic-plastic damage mechanics, the rheological problem, mechanical properties of degradation, and seepage problem of the soft rock tunnel are comprehensively considered. The time-dependent deformation and stress of the surrounding rock mass following excavation were simulated using the proposed model of finite-difference software FLAC3D. The stress distribution of the surrounding rock support and reinforcement after the excavation were obtained. The simulation results show that the rationality of the existing reinforcement scheme is verified and the final deformation stability time of the surrounding rock during the operational period is calculated. Furthermore, a novel damage-based long-term safety analysis method is proposed, providing theoretical guidance and technical support for the design and construction of soft rock tunnels. The factor of safety (FOS) of the surrounding rock during the excavation and operational period is analyzed using the proposed analysis method. These results could have reference value for the design and construction of similar soft rock tunnels.
Research on a visualized real-time monitoring system for the slurry chamber of a slurry shield
Authors: Li Dongli , Pu Xiaobo , Qi Baowei , Ma Lin
Published: November 2020

In this study, a visualized real-time monitoring system was established to monitor the working conditions of the slurry chamber and collect rotation situations of the cutter head, wear conditions of the disc cutters, image information of the excavated strata and flow characteristics of the slurry. The operating condition of the front-end equipment is shown on the upper computer, and the signal collected by the camera is transmitted to the video acquisition system in real-time. Hence, this paper presents solutions to the system with an emphasis on the system structure, hardware, and software design, and verification. The system verification was conducted through a field test in a project site, where the system could reliably monitor the slurry chamber.