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Dust pollution during shotcrete process in high-altitude tunnel based on numerical simulation

Particuology 2023年第4期75卷 82-95页

作者： Cong Li Zhongan Jiang Guoliang Zhang Xue Feng Fabin Zeng College of Civil and Resource Engineering University of Science and Technology BeijingBeijing100083China NHC Key Laboratory for Engineering Control of Dust Hazard University of Science and Technology BeijingBeijing100083China

The surrounding rock needs shotcrete support after drilling and blasting excavation in the tunnel;the high concentration of dust generated in the process will endanger workers'occupational ***,to ensure the cleanness and safety of the tunnel construction process,a full-scale model of the tunnel was established based on field data of a high-altitude tunnel of the Sichuan-Tibet *** dust production mechanism is summarized by combing the whole process of *** Computa-tional Fluid Dynamics(CFD)method was used to study the diffusion and transport of dust under different *** grey relational analysis was applied to investigate the correlation values of the influ-encing factors on dust diffusion in the shotcrete operation *** results show that the dust gener-ation mechanism of shotcrete includes the sudden change of particle velocity in the jet area leading to escape and particle impact dust generation,where fine dust is easily dispersed in the *** continuous dust production,the dust concentration is higher near the wet spraying machine and on the backflow side of the working *** the air supply volume and shortening the distance between the air duct and the working face is conducive to diluting the dust concentration in the *** the high-altitude environment,the dust concentration in the tunnel decreases,the diffusion distance be-comes smaller,the settlement proportion of dust particles increases,and the risk of secondary pollution *** simulation results and the field measurement data are consistent,which can provide theoretical support for the construction site dust control.

关键词： High-altitude tunnel shotcrete Dust diffusion Numerical simulation Ventilation system

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Numerical investigation on the tensile fracturing behavior of rock-shotcrete interface based on discrete element method

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International Journal of Mining Science and Technology 2020年第3期30卷 293-301页

作者： Jiadong Qiu Lin Luo Xibing Li Diyuan Li Ying Chen Yong Luo Shenzhen Key Laboratory of Deep Underground Engineering Sciences and Green Energy Shenzhen UniversityShenzhen 518060China Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring Ministry of EducationCentral South UniversityChangsha 410083China School of Resources and Safety Engineering Central South UniversityChangsha 410083China Center of Rock Mechanics and Geohazards Shaoxing UniversityShaoxing 312000China

Four groups of numerical models of Brazilian tests on rock-shotcrete interfaces were successfully conducted by PFC2D. The tensile strength and Young’s modulus of shotcrete were considered. Six different undulations of rock-shotcrete interface were set up. The influences of multiple parameters on the bearing characteristics of the rock-shotcrete interface were studied. The results showed that a better support performance can be obtained by increasing the Young’s modulus of shotcrete rather than the tensile strength of shotcrete. For different tensile strength and Young’s modulus, the increase of sawtooth height has different effects on the support performance. The failure mechanism of the rock-shotcrete interfaces was analysed in detail. The stress shielding effect and stress concentration effect caused by the shape characteristics of rock-shotcrete interface were observed. The influence of these parameters on the overall support performance should be fully considered in a reasonable support design.

关键词： Tensile strength PFC shotcrete Fracturing behavior Rock interface

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Porosity,Pore Size Distribution and Chloride Permeability of shotcrete Modified with Nano Particles at Early Age

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Journal of Wuhan University of Technology(Materials Science) 2016年第3期31卷 582-589页

作者：李贺东闫东明 CHEN Genda XU Shilang LIU Jintao HU Yanjia Department of Civil Engineering Zhejiang-UniversityHangzhou 310027China Dep-artment of Civil Architecture&Environment EngineeringMissouri University of Science and TechnologyRollaMissouri65401USA

Nano particles have been found to be effective in enhancing many properties of regular concretes. However, there is little information on the effect of nano particles on shotcrete. In fact, if similar positive effect of nano particles can also appear in shotcrete, they will greatly benefit the wide application of shotcrete in more and more repair and strengthening of structures in civil engineering, especially in corrosive environments. In this study, through experiments on 70 specimens, the effects of nano SiO2, CaCO3 and Al2O3 particles on the early-age porosity, pore size distribution, compressive strength and chloride permeability of shotcrete were *** results indicated that nano SiO2 particles significantly increased the compressive strength and chloride penetration resistance; nano Al2O3 and CaCO3 particles had slight enhancing effect on the compressive strength; nano CaCO3 particles were most effective in promoting the chloride penetration resistance of shotcrete. As a conclusion, nano SiO2 particles were recommended when both early age compressive strength and chloride penetration resistance were crucial, and nano CaCO3 particles were recommended when only chloride penetration resistance was concerned for their high cost-effectiveness.

关键词： shotcrete nanoparticles chloride penetration resistance compressive strength porosity

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Evaluation of earthquake impact on magnitude of the minimum principal stress along a shotcrete lined pressure tunnel in Nepal

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第5期11卷 920-934页

作者： Krishna Kanta Panthi Chhatra Bahadur Basnet Department of Ceoscience and Petroleum Norwegian University of Science and Technology

In situ stress condition in rock mass is influenced by both tectonic activity and geological environment such as faulting and shearing in the rock *** influence is of significance in the Himalayan region,where the tectonic movement is active,resulting in periodic dynamic *** large-scale earthquake causes both accumulation and sudden release of strain energy,instigating changes in the in situ stress environment in the rock *** paper first highlights the importance of the magnitude of the minimum principal stress in the design of unlined or shotcrete lined pressure tunnel as water conveyance system used for hydropower *** we evaluated the influence of local shear faults on the magnitude of the minimum principal stress along the shotcrete lined high pressure tunnel of Upper Tamakoshi Hydroelectric Project(UTHP)in Nepal.A detailed assessment of the in situ stress state is carried out using both measured data and three-dimensional(3D)numerical analyses with ***,analysis is carried out on the possible changes in the magnitude of the minimum principal stress in the rock mass caused by seismic movement(dynamic loading).A permanent change in the stress state at and nearby the area of shear zones along the tunnel alignment is found to be an eminent process.

关键词： shotcrete lined pressure tunnel The minimum principal stress Three-dimensional(3D)numerical model Geology Tectonic activity Himalaya

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Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第2期10卷 212-221页

作者： H.Yu L.Wu W.V.Liu Y.Pourrahimian School of Mining and Petroleum Engineering Department of Civil and Environmental Engineering University of Alberta

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

关键词： shotcrete Restrained expansion Fibers Calcium sulfoaluminate cement(CSA) Ordinary Portland cement(OPC) Calcium sulfate(CS)

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Preparation and Performance of a Fluorine-Free and Alkali-Free Liquid Accelerator for shotcrete

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Journal of Renewable Materials 2021年第11期9卷 2001-2013页

作者： Jianbing Zhang Rongjin Liu Siyuan Fu Tianyu Gao Zhongfei Zhang College of Material Science and Engineering Guilin University of TechnologyGuilin541004China Guangxi Engineering and Technology Center for Utilization of Industrial Waste Residue in Building Materials Guilin541004China Guangxi Beibu Gulf Engineering Research Center for Green Marine Materials Guilin541004China

Based on aluminum sulfate,a fluorine-free and alkali-free liquid accelerator(FF-AF-A)was prepared in this *** setting time and compressive strength of three cement types with different FF-AF-A dosages were fully *** compatibility of the FF-AF-A with the superplasticizers were also investigated,and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat,X-ray diffractometry(XRD),and scanning electron microscopy(SEM).Test results indicated that adding the FF-AF-A at 8 wt%of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting *** 1-day compressive strength of the cement mortar with 8 wt%of FF-AF-A reached 13.5 MPa,which represents an increase of 35%as compared to the strength of cement mortar without the FF-AF-A,and the 28-day compressive strength ratio was 119%.In addition,the FF-AF-A also showed good compatibility with different superplasticizer *** results show that,when the FF-AF-A was added to the cement paste,it promoted the formation of ettringite crystals due to the aluminum ions(Al^(3+))and sulfate ions(SO_(4)^(2-))reacted with gypsum in the cement,as well as promoted the hydration of tricalcium aluminate(C_(3)A)and tricalcium silicate(C3S)leading to the overall structure becomes more *** a consequence,the hydration heat rate of the cement sharply increased,the cement paste setting time is shortened,and the compressive strength of cement mortar is improved.

关键词： shotcrete alkali-free liquid accelerator setting time compressive strength mechanism

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Influence of New Compound Admixture on shotcrete Performance

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Journal of Wuhan University of Technology(Materials Science) 2017年第6期32卷 1392-1396页

作者：商岩冬郭艳培 ZHANG Wenquan ZHAO Wenbin TAN Yunzhen Department of Resources and Civil Engineering Shangdong University of Science and Technology Taian 271019 China State KeyLaboratory of Mining Disaster Prevention and Control Shangdong University of Science and Technology Qingdao 266590 China

To analyze the influence of new compound admixture on shotcrete performance, the ordinary Portland cement pr425 was used as matrix components. The optimum proportion of admixture was obtained by analyzing the influence of content on cement setting time and compressive strength. The microstructure of cement test block and the mechanism of reducing dust of composite macromolecule admixture were analyzed by scanning electron microscopy and infrared spectroscopy. It was shown that the ratio of polyacrylic acid was 0.02%. The ratio of J85 accelerator was 5%. The ratio of bentonite was 4.5% in composite admixture. The most optimal content of admixture in the slurry was 7%. The compound coagulant formed by additive together with C3A, C4AF which provided nucleation for hydration and crystallization of C3S and C3S, and played an active role to promote the activity of the mineral admixture in cement, and increased the elastic modulus of C-S-H gel and accelerated the hydration process of portland cement. Bentonite and polyacrylic acid promote the wettability, cohesiveness and workability of cement paste in the process of hydration. The formation of cement test block gel was even. The interface between the matrix phase and the aggregate phase was not obvious which ensured the matching between the matrix and the aggregate phase. The addition of bentonite formed hydrogen bonds in cement paste and improved the cohesiveness of the system. The J-85 accelerator promoted the combination of aluminate and gypsum which hindered the formation of calcium carbide around the cement particles which made cement rapid condensation. Polyacrylic acid mainly changed the strength of hydroxyl absorption peak in cement paste to improve the initial strength of cement test block. The addition of new admixtures promoted the process of cement hydration to be more thorough and affected the later strength development of concrete by affecting the formation of calcium carbonate stone.

关键词： shotcrete compound admixture optimum proportion microstructure hydration

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A Combined Experimental and Numerical Study of shotcrete Jets and Related Wet Spray Nozzles

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Fluid Dynamics & Materials Processing 2020年第5期16卷 947-960页

作者： Chang Su Qiangqiang Zheng Wukun Zhao State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines Huainan232001China School of Mechanical Engineering Anhui University of Science and TechnologyHuainan232001China School of Civil Engineering and Architecture Anhui University of Science and TechnologyHuainan232001China State Key Laboratory of Safety and Health for Metal Mines Maanshan243000China

In this research,the dynamics of wet spray nozzles with different geometries,used to accelerate shotcrete,are investigated on the basis of a suitable three-dimensional mathematical model and related numerical *** have been conducted in the frame of the SIMPLEC *** k-εturbulence model has been used to account for turbulent *** study shows that when the angle of the convergent section is less than 3°,it has a scarce effect on the dynamics of the jet of shotcrete;with the increase of the convergence angle,the shotcrete jet velocity decreases and the nozzle wear increases;when this angle is greater than 6°,the concrete outlet jet velocity is very small and the nozzle can easily be *** results are in good agreement with the outcomes of the numerical simulations,which indicates that the used approach is reliable.

关键词： shotcrete wet spraying nozzle turbulence flow convergence angle numerical simulation

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THE DESIGN AND ACCOMPLISHMENT OF shotcrete ROBOT

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Journal of Coal Science & Engineering(China) 1996年第2期2卷 86-91页

作者：李贻斌范永苏学成

The design and accomplishment of shotcrete robot is presented in this paper. This shotcrete robot is the first robot for underground coal mine in our country. It is a specific machine used for spraying concrete in underground coal mine. It has many advantages such as simple structure convenient operation and high reliability. The on-site experiments indicate that the sprayed layer is even, at the same time, the quantity of rebound and dust content decrease largely. The robot can satisfy the requirement of shotcrete process completely.

关键词： shotcrete robot coal mine concrete

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CALCULATION OF THE shotcrete UTILIZATION FOR LINING WITH INTEGRATED YIELDING ELEMENTS Paper No.262

CALCULATION OF THE SHOTCRETE UTILIZATION FOR LINING WITH INT...

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ISRM-Sponsored International Symposium on Rock Mechanics:"Rock Characterisation,Modelling and Engineering Design Methods"(SINOROCK2009)

作者： Nedim Radoni Wulf Schubert Institute for Rock Mechanics and Tunnelling Graz University of Technology

When dealing with tunnels in weak rock mass and with high overburden,the high displacements imposed on the lining dictate the application of ductile yielding elements with controllable stiffness and yield *** properties are chosen with two goals in mind:the time-dependent strength of the shotcrete shell must not be exceeded;however the support pressure must be kept reasonably high and *** attainable load-displacement lines of the ductile support elements are almost *** are almost countless possible combinations of their stiffness and yield load,thus enabling the development of custom-tailored support systems and leaving considerable room for adapting to the encountered ground conditions. Tunneling in weak ground should be accompanied by increased efforts on monitoring the system behavior,best by a dense pattern of absolute displacement measurements.A simple technique for calculating the shotcrete utilization ratio has been *** applies a Newton-Raphson root-finding algorithm to determine the interpolation parameters while obeying the requirements of force equilibrium and fitting the measured *** influence of nonsymmetrical displacement behavior caused by heterogeneity and anisotropy of the rock mass,on the lining loading can be quantified and used for support system optimization.

关键词： shotcrete yielding elements tunneling in weak ground squeezing conditions utilization ratio

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