bluuebunny/crossref_metadata_2025 huggingface dataset:
Method for calculating the shear strength of rock masses with different combined structural planes based on the 3D printing technology
Authors: Feng Wenkai , Yin Yibo , Dong Shan , Dai Hongchuan , Hu Rui
Published: November 2020

The mechanical behavior of rock masses with different combined structural planes is poorly understood because of the difficulties associated with the performance of rock observations and analyses from the surface, collection of samples during field investigations, specimen preparation, and laboratory tests. The combination of rock mass structural planes has a significant effect on the rock mass mechanical properties. The three-dimensional (3D) printing technology can conveniently create 3D entities with complex structures, thereby providing an unprecedented opportunity to break through this bottleneck. In this study, model samples of structural surface models with different combinations are printed using the 3D printing technology, and a cement slurry with 3:1 water–cement ratio is used as the structural body to produce rock masses with different combined structural planes. The method replicates well the morphological features of natural joints. Moreover, the shear properties and the failure characteristics are stable and consistent. Direct shear tests are also performed on the rock masses of different combined structural planes from the intersection line parallel and perpendicular to the structural planes to obtain the relevant mechanical parameters and rock mass failure modes. The results prove the feasibility of the 3D printing technology in the experimental study of rock mass mechanics and show that the strength and failure modes of rock masses with different combined structural planes are different. A calculation method for the shear strength of rock masses with different combined structural planes is proposed herein based on the experimental data and the Mohr–Coulomb theory, and the method’s feasibility is verified by several examples.
Physical Characteristics of the Compressibility of Saturated Cohesive Soil
Authors: Xian-bin LIAO , Xin-jie ZHAO
Published: November 2020

Water content and liquid limit are basic physical properties in saturated cohesive soils. Through the statistical analysis of compression index and these two physical properties, trends showed that compression index increases with increasing water content and liquid limit. Very loose and soft saturated cohesive soils with high water content have high compressibility; however, very stiff and hard saturated cohesive soils have low compressibility. Based on these tests, the correlations of compression index and physical properties were established for soils in China. These correlations provide a good approach to predict compression index based on physical properties and can be used for geotechnical parameter analysis.
Applied research on slope reinforcement with cement mixing pile in deep soft soil foundation pit
Authors: Zhong yi WEN , Zi cong FAN , Li juan ZHANG , Zhao bin WANG
Published: November 2020

Deep Quaternary soft soil layer with poor mechanical properties are widely distributed in the Pearl River Delta. In this paper, based on engineering examples, a numerical simulation method was used to study the action mechanism of new reinforcing techniques of grading slope combined with cement mixing piles. The effect of construction conditions, the thickness of the cement mixing piles, and reinforcement of the passive zone on the deformation and overall stability of a foundation pit were analyzed. Finally, the simulation results and the actual monitoring data were compared and analyzed to further verify the rationality of the model. The research reveals that the step-slope combined with cement mixing pile reinforcement has significant effects on limiting the deformation of deep foundation pit and ensuring the stability of the pit. The findings of this study can serve as a reference for similar researches[1].
Mechanical properties of organic-rich shales based on nanoindentation: A case study of deep shale gas reservoirs in Zigong area, Sichuan Basin
Authors: Jia Lichun , Deng Hu , Liu Dianchen
Published: November 2020

The deep shale gas in the Zigong area of the Sichuan Basin has a wide distribution and has good prospects for exploration, which has become an important replacement area for shale gas exploration and development. In this area, the burial depth of Longmaxi Formation Shale is generally >3500 m. One of the most challenging tasks in the development of this type of reservoir is the accurate prediction of the mechanical properties of organic-rich shale. The application of the mechanical properties of shale is important to the success in multiple aspects of drilling, hydraulic fracturing, and production. Methods such as unconfined/triaxial compression tests with the use of core plugs and logging data interpretation are commonly used to obtain mechanical properties. However, these methods have their own limitations. Thus, to address the difficulty in the measurement of the mechanical properties of shale, the advanced nanoindentation test is introduced and used. Nanoindentation is a technique based on a hard tip, which is pressed into the surface of a sample. The advantage of this test is the use of a sample with a small volume, such as drill cuttings or fragments, which are easily obtained during drilling. The mechanical properties at the nanoscale level, including the hardness, Young’s modulus, and fracture toughness, are measured in the nanoindentation. Moreover, this technique can be used to evaluate the creep behavior of shale. In this study, grid nanoindentation is used to investigate the mechanical properties of drill cutting samples from the Longmaxi Formation Shale in Zigong area, Sichuan Basin. Subsequently, these mechanical parameters are used to evaluate the heterogeneous properties of shale at the nanoscale level. The results can help in analyzing the correlation between rock mechanical properties and shale constituents. This suggests that the nanoindentation test is a useful approach of estimating the elastic and mechanical properties of shale in situations where conventional rock mechanics test data cannot be measured.
Study on Rock Burst Behavior and Tendency Identification of Surrounding Rocks in Hard and Brittle Formations of Deep and Ultra-deep Wells
Authors: Zeng Yijin , Chen Junhai , Li Dandan , Li Xin
Published: November 2020

The phenomenon of the continuous collapse or the instantaneous block-falling incidents during the drilling of deep wells cannot be sufficiently explained by traditional wellbore instability theory. This phenomenon is similar to rock bursts that often occur during tunnel excavations and other engineering projects. This paper focuses on hard/brittle formations such as limestone, dolomite, and shale, which represent the most frequently collapsed formations while drilling a borehole. Based on rock burst theory and the results of the rock mechanics experiments, combined with rock failure model and other intuitive conditions, rock bursts are divided into three categories: weak, medium, and strong bursts. We establish the calculation models of strength brittleness index R and elastic energy index W based on rock uniaxial compressive strength and determine the interval values of these indexes for rock burst identification. We also propose a set of comprehensive identification methods for rock burst tendency and the classification of surrounding rocks in hard and brittle formations during the drilling of deep wells. The findings of this work provide a solid foundation for the research of wellbore instability prevention and control based on the classification of hard/brittle formations.
Experimental investigation of rock cuttability based on rock indentation tests by a conical pick
Authors: Wang Shaofeng , Tang Yu , Li Xibing , Wang Shanyong
Published: November 2020

Stress conditions and rock properties significantly influence rock breakage. The rock indentation tests by a conical pick were conducted to investigate the rock cuttability corelated to confining stress conditions and rock strengths. Based on the test results, the regression analyses were used to find the relationship among rock cuttability, uniaxial confining stress applied to rock, uniaxial compressive strength (UCS) and tensile strength of rock material. It was found that the regression models can accurately reflect the variation law of rock cuttability, which presents decreases followed by increases with increases in uniaxial confining stress and the negative correlation to UCS and tensile strength of rock material. The established models are suitable for guiding the rock cutting by conical pick and will provide useful information for mechanized mining in deep hard rock.
Evaluation and optimization of existing force prediction models for TBM disc cutters based on full-scale rotary cutting tests
Authors: Tang Miaoyuan , Huang Xin , Zhuang Qianwei , Zhang Chi , Wang Shuaifeng
Published: November 2020

A variety of theoretical or semi-empirical models have been proposed to predict the forces acting on the disc cutter and the wearing degree during TBM tunnelling. These models were developed based on different cutting scenarios with specified assumptions, which unavoidably have limitations. A series of full-scale rotary cutting tests on a circular specimen with an outer diameter of 3.3 m assembled from granite blocks collected from site were conducted in a multi-functional disc cutting platform. Different cutting parameters were considered, including different penetrations, rotatory speeds, and cutting radiuses. Variation of three orthogonal axial forces acting on the disc cutter during the experiments was obtained. The topology of cutting grooves was measured using the laser vision sensors, from which the information of specific energy was derived. The effectiveness of different theoretical models in predicting disc cutting behaviour was assessed by comparing the predicted force values with experimental data.
Construction and application of a PCC energy pile model test system
Authors: Gao Lei , Gong Yunhao , Zhou Hui , Li Ping
Published: November 2020

PCC energy piles represent a new type of energy pile technology. At present, research on the bearing characteristics of PCC energy piles is relatively limited. This study designs and builds a PCC energy pile model test system, including a model pile, optical fiber sensors, and heat transfer, loading, and data acquisition devises. The system is used to study the bearing characteristics of PCC energy piles under different temperatures. Results show that the temperature of the pile is transferred to the soil along the radial direction under the action of a circulating temperature and the moisture in the soil around the pile migrates along the direction of heat transfer. The migration speed increases when the temperature gradient is large. At the end of circulation, the displacement of the pile top increases by 0.6% D, the resistance at the pile end increases by 1.28 times, and the maximum strain point of the pile body is 70%L from the pile top. The PCC energy pile test system proposed in this work is feasible and applicable.
Offshore Cone Penetration Test and Its Application in Full Water-Depth Geological Surveys
Authors: Lu Y , Duan Z , Zheng J , Zhang H , Liu X , Luo S
Published: November 2020

Characterizing seabed sediments is one of the most important processes in marine engineering surveys. Marine sediments, which are characterized by low strength, typically consist of soft fine-grained sediments (either clay, or in some regions, carbonate muds and silts) that have been deposited relatively slowly. Sampling these soft sediments is extremely difficult, and in situ testing is preferable. Cone penetration test (CPT) is widely used due to its prominent advantages in accurately determining the physical-mechanical properties and types of seabed sediments. Due to the world’s escalating demand for energy, combined with the continued depletion of oil and gas reserves in shallow waters, offshore engineering has moved beyond the immediate continental shelf into deeper waters and untested environments, thus posing a challenge to the operating water depth of CPT. The paper presents an overview of recent developments and applications in CPT technology associated with different water depths, including the cone penetration equipment suitable for the beach/shallow sea, the areas with normal water depth, and the extremely deep sea. Furthermore, the nature of CPT design has changed radically partly due to the types of engineering and partly because of the specific nature of the seabed sediments. Thus, the CPTs with multiple functions are also reviewed.
Anelastic strain recovery in situ stress measurement method and its application prospect in underground mines
Authors: Sun Dongsheng , Chen Qunce , Li A-wei , Yang Yuehui
Published: November 2020

Current stress state data are important in underground mine construction, analysis the of tunnel stability, the forecasting of coal and gas rock bursts in underground mines. At present, the hollow inclusion gauge is primarily used for in situ stress measurement in underground mines. However, the sensors of these gauges often fail to fully adhere to the borehole wall, which can reduce the reliability of the measurement results. In this study, the anelastic strain recovery (ASR) in situ stress measurement method based on oriented cores is introduced. The effectiveness of this technique is analyzed by comparing the test results with those obtained by the hydraulic fracturing method. In addition, the reliability of the ASR method is evaluated by repeatability testing. The ASR results indicate a horizontal minimum principal stress error of less than 10% compared with those obtained by the hydraulic fracturing method. The repeatability test results show good consistency in the in situ stress measurement results of two back-to-back test samples. The ASR method is a safe and highly efficient technique that is not limited by the depth and measurement environment. Therefore, it is expected to have broad application for underground mine in situ stress measurement.
Experimental Study on Dynamic Evolution Mechanism during Coal and Gas Outburst
Authors: Geng Jiabo , Nie Wen , Yang Shun , Li Qihang , Xu Jiang
Published: November 2020

Coal and gas outburst is one of the most serious disasters in coal mining. To research the outburst evolution mechanism, we used the multi-field coupled coal mine dynamic disaster large-scale test system for simulating coal and gas outburst. In the present study, the evolution characteristics of gas pressure, temperature, and coal body stress during the outburst process were explored. Experiment results show that (1) the coal seam gas pressure decreased faster where the position is closer to the outburst, and the spherical shell-shaped outburst wave front formed in the coal seam propagated rapidly from the outburst outlet to the inside; (2) during the process of coal and gas outburst, the elastic energy of coal body released instantly, which slightly increased the temperature and then the gas desorption absorbed the heat, thereby slowly dropping the temperature; (3) after the outburst, coal and gas released the pressure, and the stress inside of the coal body decreased. The reduction of stress around the outburst hole was the most obvious.
Characteristic analysis of the Nayong rock avalanche based on the seismic signal
Authors: Luo Hao , Yin Yueping , Xing Aiguo , Jin Kaiping , Xu Shimin , Zhuang Yu
Published: November 2020

A rock avalanche that destroyed 23 houses and killed 35 people occurred on August 28, 2017 in Nayong, southwest China. A discrete element model, MatDEM, was combined with the dynamic parameters of seismic signal inversion to determine the kinematic behavior of rock avalanches. The best fitting parameters were identified by comparing the velocity evolution process of numerical simulation with that of seismic signal inversion. The dynamic process obtained by modeling was compared with the frequency distribution spectrum of the nearest seismometer, with results revealing that the dynamic process agrees with the parameters inverted from the seismic signals. The simulation results further indicate that the movement process lasted for nearly 40 s, with a maximum speed of 40 m/s. The selected models and parameters can help provide a more accurate explanation of the dynamic processes of similar rock avalanches and are significant to hazard prediction in karst areas.
Study on the integrated planning of deep mining considering rock burst prediction
Authors: Chen L , Wu S , Guo L J
Published: November 2020

Deep mining is an inevitable future trend involving resource acquisition. However, as mining depth increases, the high geostress and severe mining disturbance lead to prominent rock burst disasters. At present, the design of deep mines is mainly based on the engineering experiences based on shallow mining. To date, no integrated planning has been implemented for deep mining in domestic mines. Moreover, during the deep mining process, most problems are handled and solved only after the disaster happens due to the lack of understanding of deep disaster problem. In this paper, a large-scale 3D numerical model was established by Map3D software by considering the high geostress environment, the physical and mechanical parameters of rocks, the constitutive model, and preliminary design parameters Based on this model, the disturbance coefficient and energy accumulation state of stopes was predicted, and the rock burst risk was evaluated. According to the analysis results, the medium-deep hole sublevel open stopping method was chosen to reduce the rock burst risk during deep mining. Through the integrated planning of deep mining, the risk of rock burst disasters can be evaluated ahead of time, thus facilitating the use of a more scientific and reasonable mining method in the field of mining engineering. Integrated planning provides a new method for deep mining and can also and can help reduce or even control fundamentally the magnitude and frequency of rock burst disasters. Thus, it has great security and economic significance for mining engineering.
Overall Design and Optimization of Mining Sequence in High-Stress Environment of Thick Orebody
Authors: Shan WU , Xiaocong YANG , Lijie Guo , Lu CHEN
Published: November 2020

After entering deep mining, the stress concentration level because of engineering excavation is considerably greater than the strength of the engineering rock mass. Here, we consider the engineering impact of a high stress environment in the deep mine plan, integrate the high-stress environment and its evolution with the mining process into the mining plan, and realize the balance of improving the stress state and getting the maximum net present value. Using Map3d boundary element simulation software, we planned two vertical and four horizontal mining sequences for deep and thick orebody backfill mining, respectively, and then analyzed the changes in stress and rock mass energy because of mining disturbance. The results show that the surrounding mining sequence can effectively improve the mining stress environment and increase production capacity. Using large-spaced dispersion and mining sequence from the middle to both ends can gradually redistribute the stress to adjacent areas, thus reducing the degree of stress concentration.
Study of the frequency response of the block–rock mass with bimodulus characteristics
Authors: Jiang Kuan , Qi Cheng-zhi , Zhu Shou-dong , Jin Tian-wei
Published: November 2020

The pendulum-type wave phenomenon is a unique mechanical phenomenon in deep rock mass. It propagates at low frequencies and low speeds in the rock mass, and can cause deep rock engineering disasters such as rockbursts. For determining the low-frequency characteristics of a pendulum-type wave, the frequency response of the pendulum-type wave in block-rock mass with bimodulus characteristics is studied under a half-sine impact load. The dynamic pendulum-type wave model in a block–rock mass is used to determine the low frequency characteristics of the wave. The improved central difference method is applied, and the influence of the modulus ratio on frequency response is analyzed. Furthermore, the natural frequency of the system is inverted, through the frequency response of the block, and its correctness is verified. The results show that a decrease in the modulus ratio causes an obvious increase in the number of frequency response peaks of the block. The amplitude of the frequency response peaks decreases and the position of peaks moves to a low frequency range. The low-frequency characteristics of the pendulum-type wave in the block–rock mass with bimodulus characteristics are more obvious. The natural frequency of the system can be inverted by the fact that it corresponds to the peak frequencies of the frequency response. This approach provides a new method for the determination and measurement of the natural frequency of nonlinear systems.
Characteristics of Roof Movement and Ground Pressure Behavior of Gob-side Entry Retaining by Roof Cutting in Continuous Mining
Authors: Li Minzu , Ma Zimin , Wang Haohao , Zhang Yong , Jia Fayuan
Published: November 2020

Gob-side entry retaining by roof cutting (GERRC) technology has been widely used in China, but application research of the entry-retaining technology in continuous mining is relatively scarce. Based on the analysis of the technology of continuous mining and GERRC, this study adopted the methods of theoretical analysis and in-field monitoring of ground pressure and behavior to obtain the roof movement characteristics and ground pressure distribution law during the entire process of roof directional pre-splitting, entry retaining, and entry reusing. Using the engineering geological conditions and analysis of field data of Dianping coal mine in Shanxi Province, the principal design parameters and technological process of GERRC in continuous mining were obtained. The structure model of the retained roadway roof in continuous mining was constructed to study roof movement patterns and the mechanism of stability control of the retained roadway. The movement regularity of the overlying strata in the mining and entry-retaining stage was obtained, enriching the theory of roof structure evolution and stress transfer under the condition of continuous mining with GERRC. The research results provide significant support for further popularization and application of the technology of GERRC.
Stress characteristics and control of coal and rock in steeply dipping coal seam mining under the goaf of a close coal seam group: a case study
Authors: Fu Qiang , Yang Ke , Liu Qinjie , Chi Xiaolou
Published: November 2020

Steeply dipping coal seams, which are widespread in western China, are considered to have complex mining conditions. The development of such a seam plays an important role in regional economic development. Some steeply dipping coal seams are distributed at close distances. For closely located coal seam groups, China generally adopts the downward mining method for mining. Aiming at the problems of the appearance of ground pressure such as coal wall spalling and roadway squeezing deformation of a fully inclined working face under a goaf in a close coal seam group, the mining of the 5th and 4th coal at the steeply dipping coal seam in Panbei Mine was established as the engineering background. The mechanical model of the coal zone plastic area in front of the 12124 working face under the goaf and the distribution characteristics of abutment pressure in front of the coal wall were obtained. The working surface layout and coal rock physical and mechanical parameters were derived based on field observation records and indoor rock mechanics experiments. A numerical analysis model based on the fast Lagrangian analysis of Continua 3D software was constructed, and the surrounding rock mechanics during the 12124 working face mining process was simulated. The stress distribution characteristics of the front and back of the 12124 working face under the goaf were obtained, magnitude and location of the stress peak were determined, and superposition mechanism of the support pressure evolution of the fully mechanized thick seam under the goaf was revealed. Through field measurement of the distribution of the working resistance of the supports, the maximum working resistance, position of the supports, and accuracy of the theoretical calculation and numerical simulation were verified within the error range. Furthermore, stability control technology of the surrounding rock of the stope, roof falling, and roadway under this condition was proposed and implemented. Good economic and technical effects were obtained, which ensured safe mining at these working faces.
Anisotropic Failure in Foliated Rock Tunnels: Comparison between Deformational Behavior and Confined Pressure
Authors: Peng SHA , Shuyu GAO , Yiwen ZHAO , Mossa A S
Published: November 2020

Foliated rock mass, such as slate, schist, and phyllite, is widely distributed in Northwest China. During tunnel excavation, some geotechnical problems are encountered in the surrounding rock, such as excessive over break and intense deformation by asymmetric squeezing, because of low strength, poor self-stationary, and intense anisotropy of structural strength. The large deformation results in intense damage of the primary support and splitting of the secondary support, which can significantly influence the construction and security of tunnels. Anisotropic failure in foliated rock tunnels under high stress conditions has become an engineering challenge. The deformational anisotropy of both rock and underground structures has drawn increasing attention in the field. The relative orientation of foliation plays an essential role on the deformational behavior of layered surrounding rocks by laboratory experiments and numerical simulations. Meanwhile, the symmetrical rigid support structure cannot effectively resist the asymmetric deformation exhibited by the excavation in foliated rock mass. Consequently, the excessive confined pressure generated between surrounding rock and support is essential for anisotropic failure in tunnels. In-situ monitoring tests of deformation and contact pressure were conducted in different positions of sections within a deep-buried tunnel in the Lanzhou–Chongqing railway. The comparison results indicated that the contact pressure of the support system showed irregular space distribution, which agreed with the concentrated deformation position of the surrounding rock. However, the monitoring data showed that the occurrence of failure obviously lagged behind the stabilization of convergence deformation. The internal confined pressure could last for a long time period than the deformation monitored outside. The failure of the support takes place in the weak axis plane because of its small lateral anti-bending rigidity. The authors believe that the proposed findings will be a step further in supporting the design of tunnels passing through foliated rock mass under high in-situ stress conditions.
Predicting the settlement of Urumqi subway based on wavelet denoising and BP neural network
Authors: Zhang J Q , Qin Y J , Xie L F
Published: November 2020

In this study, we propose a model to accurately predict the ground subsidence caused by subway excavation using the wavelet denoising model and BP neural network. First, we develop an optimal denoising model by comparing and analyzing the denoising effect of different wavelet denoising parameters. The model is used to reduce the noise of the monitoring data. Then, we utilize BP neural network to develop a prediction model in which the proposed denoising model is used. Finally, we apply the proposed model to Urumqi subway. The results demonstrate the rationality and accuracy of the proposed model.
Analysis of TBM disc cutter wear: a case study of a water conveyance tunnel project in Xinjiang, China
Authors: Ban Chao , Gong Qiuming , Zhou Xiaoxiong , Li Shuyuan
Published: November 2020

Disc cutter is one of the most significant tools for TBM excavation and it is also a part that is most likely to consume. Its high cost and complicated maintenance process often bring great troubles to a project. Exploring the wear law of disc cutter can not only promote TBM excavation efficiency but also effectively save the cost. In this paper, the wear data of 671 disc cutters over a 3688-meter-long advancing distance was collected from a water conveyance tunnel project in Xinjiang, China, and the wear law of disc cutter as well as the influence of interactions among cutters on disc cutter wear were analysed. It was found that the wear velocity of one single cutter was high in the initial stage, and then it gradually decreased as the cutter constantly wore. The wear velocity of cutter increases greatly when it’s turned from outer area into front area due to its unbalanced wear while serving in outer area. The wear of a cutter increases with the increase of its installation radius, however, this phenomenon is not obvious in outer area, which is mainly because of interactions among cutters, the weaker the interaction among cutters are, the severer the wear of the cutters will be. This study can provide a useful guidance for cutter replacing process and cutterhead layout design in TBM tunnelling projects.
Study on Underpinning Scheme of Viaduct Pile Foundation Crossed by Shield Tunnel
Authors: Liangliang Zhang
Published: November 2020

Rapid developments in domestic metro construction could inevitably result in cross-engineering conflicts between metro lines and existing bridge pile foundations. Pile underpinning technology has been successfully applied to such projects to ensure the operating safety of viaducts and synchronous construction of metro lines. One section tunnel of Jinan Metro Line R2 is selected as the research object in this study. First, the processes of pile underpinning and tunnel crossing construction are numerically simulated using finite element software. Next, the deformation law of underpinning structures is studied and the engineering risk points are determined. Finally, the design scheme of pile underpinning is proven to be correct and reasonable. The results are as follows: (1) The underpinning structure presents a trend of overall settlement. The horizontal displacement of the pile body occurs in the form of a bow. Maximum deformation occurs at the underpinning beam and top of the pile. (2) The influence area of the soil surface is approximately 4 m outside the underpinning beam, and the deformation values of the underpinning system meet construction requirements. (3) The following construction steps are recommended. Step 1: Pre-jacking constructing. Step 2: Pile cutting. Step 3: Jack removal and underpinning beam and pile cap construction. Step 4: Road surface backfilling and repair. The shield machine should then be allowed to pass. (4) This paper provides targeted risk management measures. For example, isolation piles should be set on both sides of the tunnel.
Analytical solutions for the internal forces of lining structure in shallow double-arched tunnel subject to unsymmetrical loads
Authors: Li Xiaochang , Yang Song , Dai Rui , Ai Zubin , Zhang Chao , Huang Xin
Published: November 2020

This paper presents analytical solutions for the internal forces of lining structure in shallow double-arched tunnel subjected to unsymmetrical loads, mainly for the section of arch rings. The force method is employed during the derivation. The internal forces obtained from the analytical solutions are compared with that from the numerical simulation by FEM model utilizing the load-structure-method. It is found that the largest positive bending moment appears at the arch crown, while larger negative bending moment is located at both haunches of arch rings. The axial forces of both ends of arch rings are larger than that at the arch crown, which indicates that the side and middle walls are in larger compression than the arch crown. The larger shear forces of arch rings appear at the cross section approaching the top of side walls, which may be caused by the application of elastic resistance to the side wall. The comparison results and variation trend verify the applicability of presented analytical solutions for the double-arched tunnel subjected to unsymmetrical loads.
Research on the Mechanism and Treatment Technique of Invert Floor Heave After the Penetration of Large Cross-section Tunnel in Slight Inclined Stratum
Authors: Ma Kaimeng , Li Wuhong , Li Jianjun , Wang Haijun , Zheng Jieyuan , Zhang Junru
Published: November 2020

The newly built Chengdu–Guiyang Railway Gaopo Tunnel crosses through an interstratified rock mass of slightly inclined mud-sand. Sometime between the completion of the main structure and the construction of the monolithic ballast-less track, some sections began to bulge or even crack with a maximum deformation of up to 46 mm. At the same time, the vault jet concrete began to peel, causing significant risks in and challenges to the construction of the ballast-less track and the succeeding operations. In this study, the mechanism of and treatment techniques for invert floor heave following penetration of a large-cross-section tunnel into a slightly inclined stratum were investigated. In the study, the in-situ stress values and physical and mechanical parameters of the surrounding rock were obtained through field testing, and the extracted parameters were used in theoretical analysis based on discrete element numerical calculation to determine the applicable mechanism of invert floor heave. Finally, the implementation effects of different treatment techniques were compared and analyzed using the control variable method to identify final treatment measures. The results of this study reveal the following. (1) The heaving section of the invert floor in the tunnel area primarily comprised thin to medium-thick or interbedded mudstone and sandstone with argillaceous cement and was, in general, gently inclined. The joints of the rock mass were relatively well developed and broken. The effects of tectonic stress were not strong, and vertical stress was dominant. The swelling of the surrounding rock was weak. (2) The rock layer cracked as a result of the bending deformation of the layered surrounding rock in the unfavorable force direction. The argillaceous cement was lost or diluted in the presence of water. The weakening of the interlayer connection up to and including failure was an important contributory factor to the invert floor heave. (3) In treating the invert floor heave problems induced by joint surface weakening, the control effect of deepening the inversion was determined to be superior to those obtained by increasing the bolt length or strengthening the support stiffness. Based on these conclusions, a comprehensive management method involving the construction of a circular cavern using double linings and a 12-m long bolt was selected as a replacement treatment to effectively control the deformation. These results provide a reference for the design and construction of similar projects in the future.
Formation process of paste HDN slurry in gravel stratum
Authors: Shuyi Luo , Weiran Huang , Jinsheng Mi
Published: November 2020

At present, due to the complex geological conditions and long-distance drive, scheduled and unscheduled cutter head intervention maintenance during shield tunneling has become a major innovation in shield engineering in China. Therefore, paste HDN has been successfully applied to cutter head intervention under pressure, but corresponding research work on its film-forming mechanism and process is lacking. Film-forming experiments and theoretical analysis of the paste indicated that the film-forming process of the paste during gravel-stratum formation can be divided into two stages: Seepage blocking of the forming pore diameter and forming of a mud cake on the excavation surface. The seepage process was completed almost instantaneously, and the forming process of a 5–10 cm mud cake required 1–2 days. In addition, a mud diffusion model was established for investigating the mud infiltration process. The results of the aforementioned experiments were applied to the cutter head intervention of Guangzhou Metro and Lanzhou Metro, and this application ensured the efficient and safe completion of the intervention task.
Study on Design of Tunnel Lining Reinforced by Combination of PCM Shotcrete and FRP Grid Technique
Authors: Han Wei , Jiang Yujing , Gao Yuan , Koga Dairiku
Published: November 2020

The purpose of this paper is to investigate the reinforcing effect of the fiber-reinforced plastic (FRP)-polymer shotcrete mortar (PCM) technique on degraded tunnel lining based on the finite difference method. One adverse condition that cavities exist between the lining and rock masses was concerned, and another adverse condition was considered, namely, that due to the existence of the cavity, the rock mass located above the cavity underwent large deformation that may have exerted excessive pressure on the lining. This pressure was defined as loosening pressure; In addition, the degree of deterioration was defined to represent the degraded level of the lining concrete compared to the original strength of the concrete. The limit state design method of the Moment-Axial force (M-N) performance curve was proposed to determine whether the structure is in a safe state. The results show that when the lining deterioration degree is 0% and 50%, the location of (M, N) is all distributed inside the corresponding M-N performance curves, which indicates that the reinforcing measures can meet the safety requirement, while when the lining deterioration degree is 80%, ten sets of cases (four cases for ground class DI and six cases for ground class DII) where the M-N values of several strengthening measures distributed outside the corresponding M-N performance curves were summarized, and these cases should be avoided in the corresponding engineering. The results of this investigation can provide a valuable reference for study on the reinforcing behavior with the FRP-PCM technique.
Reasonable Width of Narrow Coal Pillars Along Gob-side Driving Entries in Gas Outburst Coal Seams: Simulation and Experiment
Authors: Hao LIU , Yu-jun ZUO , Wen-ji-bin SUN , Zhong-hu WU , Lu-jing ZHENG
Published: November 2020

In gob-side entry driving, the coal pillar width determines the stability of the surrounding rock and the pillar itself. Thus, to improve the stability of gas outburst coal seams, the reasonably narrow width of the coal pillars of the 40403 working face of the Shengyuan coal mine 4# was theoretically determined. Through two-dimensional simulations, the surrounding rock stability for a roadway with different coal pillar widths was evaluated. The mechanism of the surrounding rock displacement and stress distribution with the increase of the coal pillar width was also defined; for pillar widths of 2–4, 4–6, and 6–10 m, the vertical stress distribution was approximately triangular, trapezoidal, and parabolic, respectively. The coal pillar displacement was significantly greater on the goaf side than on to the roadway side. As the width of the coal pillar was incremented, its displacement on the goaf side increased, while that on the roadway side remained relatively small. The combination of the simulation results with on-site measurements finally revealed that 5 m is a reasonably narrow coal pillar width. Then, the findings were successfully applied to the 40403 working face of the Shengyuan coal mine 4#, achieving good outburst prevention and cost reduction.
A Review on Seismic Response and Aseismic Measures of Fault-crossing Tunnels
Authors: Zhang L F , Li R H , Liu H , Fang Z B , Wang H B , Y Yuan , Yu H T
Published: November 2020

Several earthquakes have challenged the traditional view that the seismic performance of tunnels is excellent. The seismic damage of these tunnels has led scholars and engineers to study the seismic response of tunnels and underground facilities. Many earthquake damage investigations of mountain tunnels reveal that fault or fracture zone is one of the most critical factors leading to tunnel damage. In this paper, the mechanisms of seismic damages and the main factors that influencing the seismic response of fault-crossing tunnels have been explained. Based on two different aseismic philosophies, different aseismic measures of fault-crossing tunnels including buffer layer, fiber concrete, flexible joint, grouting and enlarging tunnel across have been review, and the advantages and disadvantages of different aseismic measures as well as their application scope have been assessed. The ideal aseismic design of fault-crossing tunnels is as follows: verify the fault activity, accurately estimate the possible displacement and the earthquake intensity of the fault area, and then combine the advantages of different aseismic measures, set up composite aseismic measures at the place where the tunnel crosses the fault zone. It is believed that the present study will help in a better understanding of the seismic response of fault-crossing tunnels and have some guidance of aseismic design of fault-crossing tunnels in engineering practice.
Study on the optimum grouting materials and their performance in the TBM tunnel collapse reinforcement project
Authors: Weiwei HAN , Xiaoguo WANG , Lujia HAN
Published: November 2020

Considering the water inrush and collapse accident involving a tunnel boring machine (TBM) in a tunnel of the Qingdao Metro Line 1, the difficulties in grouting reinforcement in the collapse area were analyzed in order to avoid the adverse effects of grouting on the TBM equipment. The zoning governance method was chosen to solve these problems. The performance requirements of grouting materials for different areas were analyzed, after which the key properties of the materials were tested and the optimum was determined. For the water gushing area, polyurethane material was the common option, whereas for the shield area, a new high-expansion grouting material with low-strength was chosen. For the cutter head area, cement silicate grout modified by adding bentonite and quick-setting additives was tested, with the resulting material showing low strength and a quick-setting property. For the tunnel vault area, cement silicate grout and polymer-modified material were deemed suitable. After testing its viscosity change, we found that the polymer-modified material had a viscosity stabilization period. Thus, it was subsequently used at the key area. The selection of materials could reduce the consolidation risk of cutter disc and shield shell in the TBM. The research findings provide useful reference for similar projects.
Progressive Deformation Failure Characteristics of Highway Tunnel Working Face in Sand Pebble Stratum
Authors: Lu Junfu , Zhu Yi , Luo Aolei
Published: November 2020

The sand pebble stratum is typically unstable with discrete particles. The most important constituent elements are sand and pebbles. The surrounding rock of tunnels in the sand and pebble stratum has prominent engineering problems, such as being loose, easy to collapse, and unstable when exposed to water. Therefore, it is critical to ensure the safety of tunnel construction in this stratum. This paper studies the failure modes of surrounding rock on sand and pebble tunnel working face of different excavation footage, and the formation of subsidence law starting from the micro-mechanical and motion characteristics of particulate matter. This study is based on the Bai Heqiao tunnel of the Wudu expressway in Gansu Province. The results show that the instability failure of the surrounding rock mainly occurs in the upper part and sliding area in front of the tunnel working face. The sliding area is a curved body after the failure of the tunnel working face. The deformation and failure of the surrounding rock in the lower half of the tunnel working face are relatively small, and are gradually transferred from the vault to the surface, resulting in the subsidence of the surface and collapse. The deformation degree of the surrounding rock in the region closer to the tunnel vault is more obvious. After the formation is stabilized, the maximum subsidence deformation occurs above the tunnel vault. The final settlement amount of the stratum is also different with different footage. The smaller the excavation footage, the smaller the stratum settlement amount. Therefore, the appropriate excavation footage is selected as the principal safety control index during the excavation with the short-step method. The research results provide the necessary reference for the fine design and construction of tunnel engineering in the sand pebble stratum.
A fast automatic extraction method for rock mass discontinuity orientation using fast k-means++ and fast silhouette based on 3D point cloud
Authors: Wu Wei , Zhang Keshen , Zhu Hehua
Published: November 2020

In this paper, a fast automatic extraction method for rock discontinuity orientation using fast k-means++ and fast silhouette based on three-dimensional (3D) point cloud is proposed. The main contributions of the proposed method include: (1) a concept of base vector is proposed, (2) a fast k-means++ algorithm and a fast clustering validity index of silhouette are proposed and combined to automatically achieve a fast optimal grouping of discontinuities, and (3) the generation and optimization of independent discontinuity based on a double-clustering algorithm. The proposed method consists of three steps : (1) point cloud preprocessing, (2) optimal grouping of discontinuities, and (3) discontinuity generation and optimization. Several cases, including two polyhedral models under laboratory conditions and two rock slope models, are adopted to verify the accuracy and efficiency of the proposed method. A sensitivity analysis is performed to determine the optimal parameters. The results show that the proposed method can automatically achieve a fast and effective extraction of discontinuity orientations compared with the classical method, Slob (2010), Riquelme et al. (2014) and Li et al. (2016), and the efficiency is significantly improved compared with Rousseeuw (1987), Arthur and vassilvitskii (2007) and Li et al. (2016).
Research on the deformation and failure mode of rock slope with multiple locking segment failure characteristics
Authors: Hongnan QIN , Haitao MA , Zhengxing YU
Published: November 2020

Landslides are the most critical types of geological disasters in China, seriously threatening the safety of life and property of the inhabitants in the surrounding areas. Most landslides in China are large and giant rock landslide slope failures of large and giant rocks. Brittle failure of multiple locking sections usually accompanies rock slope failure. The locked section is significant for the early identification of rock slopes, slope deformation control, and slope failure prevention. This study uses the ground-based synthetic aperture radar technology to obtain the surface deformation data of the entire process of slope failure. By analyzing the development law of slope surface deformation before landslide failure, the dynamic process and evolution model of the time–space evolution of slope deformation and failure are proposed. The finding of the research shows that the deformation time-series curve of slope failure with multiple locking sections completely differs from the typical three-stage theory of slope failure deformation with creep characteristics. The failure process of each locking segment before the failure of the critical locking segment is accompanied by the transverse expansion of the shear failure of the sliding surface and the pulling failure of the trailing edge. After the failure of the last key-locking section, the final landslide failure will be formed. The entire process is a process of energy accumulation and downward movement, manifested by the stage displacement of the sliding mass, the mixed deformation characteristics of oscillation, and rising trend of the monitoring curve. Based on the characteristics of the entire surface deformation data in the landslide failure process, the research results prove the typical failure mode of rock slope with three sliding-tension cracking-shearing sections. The research results are critical in identifying the failure mode, analyzing slope stability, predicting landslide failure, and judging the scale of the landslide.