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Quick Search     Advanced Search MODERN TUNNELLING TECHNOLOGY   2017 Vol.54 Issue.5 Published 2017-10-25 Article 1 Tunnels and Underground Works for Hydropower Projects Einar Broch During the last decades there has, on a worldwide scale, been considerable development in tunnelling technology and an increase in the use of the underground for various purposes. This has had an important influence not least on the hydropower industry. The paper describes the design of the cost saving unlined high pressure tunnels and shafts. Also the technology behind the unlined air cushion replacing the surge chamber is described and the potential for applying this technology for underground gas storage is shown. The use of heavy rock anchors for roof stabilization in underground powerhouses is discussed based on theoretical studies and real cases. Selected examples of stability problems in tunnels caused by slaking basalts, friable sandstones and swelling shales are described. The concluding remarks demonstrate that with a good understanding of rock masses and their behaviour,there are considerable advantages in using the underground for hydropower projects as well as for other projects.Structures should be made safe enough for their purpose, but overly conservative support should be avoided as this adds unnecessary costs to the projects. 2017 Vol. 54 (5): 1-12 [Abstract] ( 1807 ) [HTML 1KB] [ PDF 6276KB] ( 2960 ) 13 Suggestions for Revision of Some Clauses of Structure Calculations in the“JTG D70-2004 Code for Design of Road Tunnels TIAN Zhiyu1 LIN Guojin1 WU Qingfa2 WANG Bo3 ZHANG Zhaojie Based on experience with the design and construction of highway tunnels, this paper discusses some problems in relevant clauses of the“JTG D70-2004 Code for Design of Road Tunnels”, especially the load calculation method for open-cut tunnels, the load calculation method for shallow-buried tunnels, and the reinforcement cal?culation method for flexural and compressive reinforced concrete members. Corresponding suggestions are proposed for specification preparation and revision. 2017 Vol. 54 (5): 13-17 [Abstract] ( 1626 ) [HTML 1KB] [ PDF 1045KB] ( 2980 ) 18 Challenges during Construction of Railway Gas Tunnels—Case Study of Gas Burst in the Tianping Tunnel YANG Kun In order to solve some key challenges in the construction of railway gas tunnels, especially tunnels with gas bursts, a comparative study on the problems related to the existing specification, design, construction and man? agement is conducted based on the construction practice of a gas burst section of the Tianping tunnel on the Chongq? ing-Guizhou railway and experience with similar coal mining projects. Suggestions such as optimization of grading for gas tunnels, establishing observational evaluation systems and organization and management modes are proposed. 2017 Vol. 54 (5): 18-23 [Abstract] ( 1246 ) [HTML 1KB] [ PDF 1094KB] ( 1587 ) 24 Unified Solutions for an External Load on a Frozen Soil Wall in an Unloaded State CAO Xueye1 ZHAO Junhai1 ZHANG Changguang1 LI Yan2 Based on unified strength theory and a mechanical model of the interaction between a frozen soil wall and the surrounding soil mass in an unloaded state, the stress and displacement fields of the elastic zone and plastic zone, as well as the unified solutions of the elastic limit external load, plastic limit external load and external load in the elastic-plastic state, are derived considering the intermediate principal stress. The laws of how the stress field and displacement field vary with the radius and the parameters of strength theory are analyzed. The effects of the radius ratio, the parameters of unified strength theory and the calculation depth of the frozen soil wall on the unified solutions are discussed. The results show that:1) the radius and parameter of the unified strength theory have certain influence on the stress and displacement fields, and the calculation results are more accurate when they take the intermediate principal stress into consideration ; 2) the elastic limit external load and the plastic limit external load increase with an increase of the radius ratio and the parameters of the unified strength theory; 3) the external load in the elastic-plastic state decreases with an increase of the depth of the frozen soil wall and increases with an increase of the parameters of the unified strength theory; and 4) the external load on the frozen soil wall is lower than the original horizontal stress because of the interaction between the frozen soil wall and the surrounding soil mass in an unloaded state. 2017 Vol. 54 (5): 24-29 [Abstract] ( 1165 ) [HTML 1KB] [ PDF 1603KB] ( 2176 ) 30 Complex Variable Function-Based Elastic Stress Analysis Solution for a Deeply-Buried Cavern with a Circular Lining YUAN Wei1,2 FU Helin1 ZHANG Jiabing1 HUANG Zhen1 Aiming at the stress contact issue of a deeply-buried cavern with a circular lining, an expression for the stress components of the surrounding rock and lining is derived by means of a power-series solution of complex variable function from the perspectives of the boundary and contact conditions. It is verified by solving the generalized solution formula of the axisymmetric stress of the elastic mechanics, and the same exact solution is obtained for elasticity, which verifies the accuracy of this complex variable function and provides new considerations for the solution of stress on the surrounding rock and lining under irregular loading by using a complex variable function. 2017 Vol. 54 (5): 30-35 [Abstract] ( 1126 ) [HTML 1KB] [ PDF 849KB] ( 1950 ) 36 Estimation Method for Geostress Based on a Modified Shoerey Model PEI Qitao1 DING Xiuli1 HUANG Shuling1 ZHANG Yuting1 LUO Chaowen2 Geostress is one of the basic loads of underground works, and the vertical stress of a rock mass can be calculated using the overburden pressure while the horizontal stress is difficult to determine. The elasto-static thermal stress model established by Shoerey is widely accepted, but the model does not take the tectonic movement induced by regional differences into consideration, and the distribution rules of the horizontal maximum principal stress and minimum principal stress haven′t been obtained. In this paper, Shoerey′s model is modified by introducing the correction factors of regional tectonic stress based on elasticity theory, and an estimation method for horizontal stress in an elastic rock mass is proposed. An in-situ stress and rock mass modulus measurement are carried out for the Meihuashan tunnel, and a comparison between the calculated results and the measured geostress data are conducted. The results show that the prediction error caused by the local geological structure and rock mass homogeneousness is small and within the allowed scope, meeting the precision requirements for engineering. 2017 Vol. 54 (5): 36-43 [Abstract] ( 1108 ) [HTML 1KB] [ PDF 1625KB] ( 2064 ) 44 Seismic Response Law of a Tunnel in a Stratified Rock Mass HU Hongyun1,2 ZHOU Xiaojun1,2 LIU Jianguo1,2 CHEN Tao3 The seismic response law of tunnels in stratified rock masses is studied considering the characteristics of the transverse isotropy of a stratified rock mass. An aseismic calculation formula for a tunnel in a stratified rock mass is derived based on the free-field deformation method and results of research on phase velocity in a three-dimensional transversely isotropic medium. A large number of numerical calculations are conducted based on the physical parameters of certain stratified rock masses and the variables of incident angle of the seismic wave, dip angle and ratio of the elastic moduli parallel and perpendicular to the rock stratum. The law of the tunnel′s seismic response and the working conditions corresponding to the maximum strain are obtained by comparing the results of the analysis and calculations. 2017 Vol. 54 (5): 44-53 [Abstract] ( 1087 ) [HTML 1KB] [ PDF 3974KB] ( 1903 ) 54 Back Analysis of Tunnel Displacements Based on the IAF-SVM Algorithm HU Jun1 CAO Jinhai1 GE Kaihua2 WANG Kaikai In light of the defects of overtraining a sample of a BP neural network and the low precision of a small sample, a SVM-based back analysis method for tunnel elastic-plastic displacement is proposed using the generalization ability of a support vector machine(SVM). Considering that the performance of the support vector machine (SVM) largely depends on the selection of parameters, the efficient global search ability of the improved artificial fish (IAF) is adopted to get the optimal parameters of the SVM to avoid randomness in parameter selection. A tunnel is analyzed using FLAC3D and the inversion of the elastic-plastic displacements is conducted based on the calculated displacements of measured points. The results show that the convergence rate and inversion precision of this method are better than that of the BP neural network regarding small samples. 2017 Vol. 54 (5): 54-60 [Abstract] ( 1042 ) [HTML 1KB] [ PDF 938KB] ( 1881 ) 61 Soil Mass Deformation Induced by Shield Tunnel Construction XIE Dongwu1 GE Shiping2,3,4 DING Wenqi2, 3 OUYANG Wenbiao5 Based on the Mindlin solution in a semi-infinite elastic space, the composition of a settlement trough is studied by analyzing the influence of lateral pressure on the ground settlement trough, and a systematic sensitivity study on the influential parameters for the surface displacement of a single tube tunnel is conducted. Changes to the elastic modulus, Poisson′s ratio, the buried depth and the stress release coefficient will affect ground loss, while changes to Poisson′s ratio, the buried depth and the lateral pressure coefficient will affect the width parameters of the settlement trough. The parameters for ground loss and settlement trough width affected by tunnel construction at different stratum depths are analyzed. Compared with the horizontal surface displacement, the horizontal displacement in the stratum decreases significantly due to different confinement conditions. 2017 Vol. 54 (5): 61-69 [Abstract] ( 1027 ) [HTML 1KB] [ PDF 4782KB] ( 2173 ) 70 Soil Mass Stability at the Working Face of a Rectangular Pipe-Jacking Tunnel with a Large Section XU Youjun1 LIANG Weizhen1 LIU Xinmei2 CUI Guangqin1 BAI Xueguang3 Based on an underpass project at the Inner Mongolia University of Science and Technology, which was constructed with an earth pressure balance rectangular pipe-jacking machine, the active and passive failure laws of the excavation face of the rectangular jacking pipe in sand and gravel are studied using theoretical analysis, numerical simulations, and site monitoring. The following conclusions are determined: 1) in light of the characteristics of rectangular sections, a trapezoidal wedge calculation model is set up, a calculation formula for extreme support stress during active failure of the tunnel face is derived and applied in a practical project, and the limited support pressure calculated by the above formula is determined to be very close to that of the numerical simulation, so the two methods are verified; 2) the form of the ground surface settlement trough simulated by FLAC3D is similar to the measured ground settlement trough, which approximately complies with a normal distribution and is very close to the ground settlement value; 3) with a decrease of the support stress ratio, the plastic zone of the excavation face develops from the front of the face to the inclined top. When support stress ratio is 0.165, the soil horizontal displacement in front of the excavation face suddenly increases, the plastic zone extends to the ground surface and active failure occurs with a loss of overall stability. The development pattern of the plastic zone at the surface after excavation face failure resembles a trapezoidal wedge shape, so the rationality of the calculation model is verified; and 4) with an increase of the support stress ratio, the plastic zone in front of the excavation face develops from the face top to the inclined top and reaches the ground surface, resulting in instability of the soil mass with passive failure occur? ring when the support stress ratio is 3.0, and the plastic zone is much smaller than that of active failure. 2017 Vol. 54 (5): 70-77 [Abstract] ( 1177 ) [HTML 1KB] [ PDF 3308KB] ( 2688 ) 78 Environmental Effects Caused by Construction of Rectangular Jacking Pipes with Large Section, Small Space and Shallow Overburden WU Yong1 XU Riqing1 DUAN Jinchuan2 XU Xin3 ZHU Yihong1 A rectangular pipe jacking machine is adopted in construction of the underground passages between North Huaqiang Station and Huaxin Station in Shenzhen, which are characterized by a large section, small spacing,a shallow overburden, parallel construction of several jacking pipes, and passage over a metro tunnel and under underground pipelines. A numerical model is established and the simulation method for the grouting pressure and the function of the pipe jacking machine head is discussed and improved, and the effect of pipe jacking construction on the surrounding environment is analyzed. The results show that: the surface settlement trough caused by rectangular pipe jacking construction complies with the Peck Formula, and ground loss plays a leading role in the formation of stratum displacement; with serial construction of several jacking pipes, the shape of the surface settlement trough changes from a "V" to a "W" and the vertical displacement of the shield tunnel superimposes continuously; and pipe roof support effectively decreases the deformation of ground surface and underground pipelines. 2017 Vol. 54 (5): 78-85 [Abstract] ( 1116 ) [HTML 1KB] [ PDF 2984KB] ( 2001 ) 86 Dynamic Response Characteristics and Reasonable Design Parameters for Railway Tunnel Floor Structures under Heavy Loading LIN Yuexiang1 PENG Limin1 SHI Chenghua1 LEI Mingfeng1 FU Xiaokang2 A numerical model coupling a heavy-haul railway tunnel structure and its surrounding rock is estab? lished using the excitation function and based on the theory of dynamic finite element. The influence of different rise-span ratios and the thicknesses of the filling layer and invert on the characteristics of the dynamic response in a heavy-haul railway tunnel structure are analyzed. The results show that dynamic response of the whole floor structure of a heavy-haul railway tunnel is larger than that of normal railway tunnel and it is unfavorable for the stability of tunnel structure. The maximum response values of different mechanical indexes for a tunnel floor structure under heavy load and corresponding positions are obtained. Reasonable design parameters for the floor structure of a double-track railway tunnel under a heavy load are discussed; for the floor structure of a heavy-haul double-track railway tunnel, a reasonable rise-span ratio and thickness of the filling layer and invert are 1/10~1/11, 1.2~1.3 m and 40~50 cm, respectively. These parameters could effectively improve the dynamic response and stress state of these structures. 2017 Vol. 54 (5): 86-92 [Abstract] ( 1024 ) [HTML 1KB] [ PDF 2567KB] ( 1901 ) 93 Analysis of the Vibration Responses of High-Speed Railway Tunnels Based on Damage Theory HUANG Juan1 PENG Limin1 DING Zude2 LEI Mingfeng1 Based on the known Mazars and Loland damage models, an elastic-plastic damage constitutive model for concrete is developed by introducing a damage variable to the Drucker-Prager yield function. Using the interface of the finite-difference software FLAC5.0, secondary development is carried out to program the proposed damage constitutive model. The dynamic vibration response of a high-speed railway tunnel on the Wuhan-Guangzhou Passenger Dedicated Line is calculated using the secondary developed damage model, which quantifies the damage of tunnel linings and lays a foundation for the analysis of fatigue lifetime prediction and a durability evaluation of highspeed railway tunnel structures. The results show that:1) the settlements at the tunnel floor and the peripheral deformations induced by the vibration load of the train are less than 4 mm; 2) the main adverse effect caused by train loading is an increase of tensile stress of the tunnel lining; 3) the maximum damage to the tunnel appears on the invert facing the surrounding soils; and 4) a vibration-induced stress wave attenuates very quickly in the tunnel lining structure and vibrations caused by train loading influence local parts of the tunnel floor. 2017 Vol. 54 (5): 93-100 [Abstract] ( 1075 ) [HTML 1KB] [ PDF 2744KB] ( 1898 ) 101 Matlab-Based BP Neural Network Applied to the Prediction of TBM Advance Rate XIONG Fan1 HU Zhiping1,2 REN Xiang1 ZHANG Peng Driving efficiency of a TBM is closely related to the characteristics of the surrounding rock and machine performance, which are the two factors that need to be considered for predicting the TBM advance rate. Because of the uncertainty of geological factors, the statistical distribution of UCS and RQD are simulated using a normal distribution and an exponential distribution, and the corresponding random input parameters are generated with the Monte Carlo algorithm. When considering the factors of machine performance, the differences caused by the influence of various TBM performance factors are eliminated with the ratio of the net thrust and cutterhead diameter.Based on the inputs of both the surrounding rock and machine performance parameters, a BP neural network model to predict TBM penetration is set up in Matlab. Practical cases verify that the predicted results are close to the measured ones. 2017 Vol. 54 (5): 101-107 [Abstract] ( 1096 ) [HTML 1KB] [ PDF 1542KB] ( 1973 ) 108 Method for Evaluating the Driving Performance of a Cutterhead System of a Shield Machine WU Li1 LI Xinxin1 GUAN Tianmin1 QU Fuzheng2 ZHANG Jiayuan Research on the method for evaluating the driving performance of cutterhead systems is helpful to obtain optimal cutterhead design, which is significant for improving the efficiency of shield tunneling, reducing construction costs and improving construction safety. Combining simulation analysis with the fuzzy evaluation method, a fuzzy comprehensive evaluation method is proposed based on the driving performance of the cutterhead to determine optimal cutterhead design. The performance index of the cutterhead driving system is presented. A discrete-element simulation model of the cutterhead system and the method to obtain the driving performance index are established. Five driving performance indexes of cutterhead systems are selected as the evaluation factors and the importance degrees of the five factors are determined by the Delphi method. The grade index and the evaluation matrix of the evaluation factors are determined by simulation and data analysis. The driving performance of the cutterhead is evaluated by the generalized fuzzy synthesis algorithm. Using the shield construction of the Beijing Metro in a sandy pebble stratum as an example, it is proved by the fuzzy comprehensive evaluation method that the driving performance of a spoke-type cutterhead is better than the board-type cutterhead. 2017 Vol. 54 (5): 108-114 [Abstract] ( 1342 ) [HTML 1KB] [ PDF 1710KB] ( 2680 ) 115 Dynamic Response of the Tethers of a Submerged Floating Tunnel Caused by Road Undulation Excitation LIU Bin LIU Zuoqiu WU Zhiwen In order to analyze the dynamic characteristics of the tethers of a submerged floating tunnel subjected to road undulation excitation, a non-linear vibration equation of tethers was set up by taking the sag of the tether into account. The vibration response of the frequency-domain and time-history analysis of the tethers was obtained by applying the pseudo-excitation method and the Runge-Kutta method. Effects of the damping ratio and the initial tension of the tethers, track power spectrum and vehicle speed on the vibration response of the tethers were analyzed. It may be concluded that the larger the damping ratio and initial tension of the tethers the smaller the displacement power spectrum density of the tethers; the displacement at the middle position of the tethers increases gradually as the vehicle speed increases; and due to the influence of the equivalent linearization, the displacement root mean square obtained by the frequency-domain analysis is smaller than that of the time-domain analysis. 2017 Vol. 54 (5): 115-121 [Abstract] ( 966 ) [HTML 1KB] [ PDF 2145KB] ( 1844 ) 122 Analysis of the Mechanical Behaviors of Shallow-Buried Large-Span Tunnels under Expressways CAO Chengyong1 SHI Chenghua1, 2 PENG Limin1, 2 LEI Mingfeng1, 3 TAN Yong4 The construction of the Hongmianlu Tunnel in soft rock is difficult and high risk due to its shallow bur? ied depth (about 6 m), large span(about 16 m) and long distance under the Jihe Expressway, which has a large traffic volume and strong dynamic load. To study mechanical behaviors during tunnel excavation, the dynamic variation laws of ground settlement, crown settlement, extrusion displacement of the tunnel face, steel arch stress in the primary support and the stress in the secondary lining were obtained by numerical calculations and field tests. The results show that the influential scope of the antecedent deformation is 1~1.5 times the tunnel span. By anchoring and shotcreting at the tunnel face, the extrusion displacement of the tunnel face decreases significantly. To guarantee successful construction under the Jihe expressway, it is necessary to determine a reasonable support time, optimize the construction procedure, decrease the closure time of the tunnel section and improve site monitoring. 2017 Vol. 54 (5): 122-129 [Abstract] ( 979 ) [HTML 1KB] [ PDF 5014KB] ( 2169 ) 130 Law of Ground Surface Settlement Caused by Shield Tunnel Construction in Sand/Clay Compound Strata GUO Le Based on the Bao′ an- Bihai shield tunnel of Shenzhen metro line 11, the law of ground settlement caused by shield tunnel construction in sand/clay compound strata is studied by field tests and the finite element method. By fitting the field-measured data of ground surface settlement at the cross section with the Gaussian Peak Function, the key parameters for the coefficient of the settlement trough width, maximum settlement and ground loss ratio--which represent the characteristics of settlements at the cross section--are obtained. The coefficient of the settlement width in the sand/clay compound stratum is smaller than that in soft soil strata and larger than that in sand and cobble strata. The influence of the tunnel's buried depth, the conditions of the overlying strata and the strata conditions of the main tunnel on ground surface settlement are studied by numerical simulations and field-measured data, with results indicating that ground surface settlement is influenced significantly by the overlying strata conditions and closely related to the properties of the strata approaching the ground surface. 2017 Vol. 54 (5): 130-137 [Abstract] ( 1016 ) [HTML 1KB] [ PDF 3256KB] ( 2374 ) 138 Failure Characteristics and Mechanical Mechanism of Deeply-Buried Tunnels with High External Water Pressure for Drill &Blast and TBM Methods JI Feng1 ZHANG Qianqi1 LI Hongming1 ZHOU Chunhong2 GAO Jishun1 Drill&blast and TBMs are two main methods for excavating underground works, and both have a signifi? cant impacts on the disturbance degree and reinforcement measures of surrounding rock. Based on four large parallel tunnels adopting the TBM and drill&blast methods, the influence of the excavation method on surrounding rock damage is studied. Through statistical processing of geological data and mechanical analysis, the failure modes of the tunnel′s surrounding rock are summarizedand common features of the effects of the two construction methods on the surrounding rock are concluded. In addition, a comparison of the effects of the two construction methods on the surrounding rock are conducted, and it is determined that the secondary failure range by TBM is larger than that of the drill & blast method and a TBM is inclined to produce rock bursts and stress failure, while structural plane failure is more likely to occur when the drill& blast method is adopted. Furthermore, mechanical mechanisms of various failures are analyzed based on the above 2017 Vol. 54 (5): 138-145 [Abstract] ( 1011 ) [HTML 1KB] [ PDF 2602KB] ( 2169 ) 146 ailure Mechanism and Excavation Method for Soft-Rock Tunnels with Large Deformation under Complex Geological Conditions XU Guowen1 HE Chuan1 DAI Cong1 WANG Yao2 By analyzing the large deformation events that occurred in the Zhegushan tunnel of the WenchuanMaerkang expressway, the rock failures are divided into three categories: plastic flow of soft rock, bending deforma? tion of the plate girder and slipping of the structural surface. A comparison of the two-step excavation method and three-step excavation methodwas performed for a 50-meter-long test section with a typical rock mass. The results show that for the two-step excavation method, the advance rate and construction space between the left and right side of the lower bench have a significant effect on tunnel stability. Based on a comparison of the tunnel′s peripheral displacement, contact pressure between the surrounding rock and the initial support (as well as the internal force of the steel arch) for the two-step and three-step construction methods, it is found that for the two-step excavation method, the tunnel′s peripheral deformation, the pressure between surrounding rock and the initial support are relatively large since the one-pass excavation section is very large and the pressure of the rock mass increases too quickly, and the safety reverse of the steel arch is not enough. For tunnels in complex regions or environments, the re? served deformation volume of the rock mass should be adjusted for the actual situation at the site, a reasonable construction method and tunnel advance rate should be chosen and the three-step construction method can effectively control the occurrence of large deformation in cases of unfavourable rock masses. 2017 Vol. 54 (5): 146-154 [Abstract] ( 1040 ) [HTML 1KB] [ PDF 5608KB] ( 2400 ) 155 Deformation Mechanism of Tunnel Surrounding Rock Based on an Anisotropic Test of the Wudang Group Schist ZOU Hao CHEN Jinguo The deformation and failure events that occurred in the Tongsheng tunnel resulted in longitudinal crack? ing in the crown and steel arch breaking at the spandrel. Considering the anisotropic characteristics of the Wudang group schist, the characteristics of the stress-strain curve and the failure pattern of samples of the Wudang group schist are analyzed based on the surrounding rock deformation properties, the numerical simulation, the wave velocity test, the uniaxial compression test and the triaxial compression test. A corresponding relationship between the elastic modulus, Poisson′s ratio and compressive strength versus the schistosity angle changing from 0° to 45° and 90° is established, the failure mode of the tunnel surrounding rock is presented and the deformation mechanism of the tunnel′s surrounding rock is summarized. The results show that the anisotropy of the Wudang group schist plays a controlling role in the process of deformation and failure of the tunnel′s surrounding rock; the asymmetric mode is the main failure mode of the tunnel′s surrounding rock; and when the spatial relationship between the maximum shear stress of the tunnel′ s surrounding rock and the schistosity is unfavorable, the surrounding rock will shear along the schistosity plane. 2017 Vol. 54 (5): 155-163 [Abstract] ( 1098 ) [HTML 1KB] [ PDF 4536KB] ( 1789 ) 164 Particle Vibration Velocity in the Surrounding Rock of Arched Tunnels with Straight Walls during Blasting JIN Xiaobo1,2 SUN Jinshan1 LI Zhengchuan3 LIU Guiying3 ZHOU Bin3 For two parallel arched tunnels with straight walls, the distribution law of the particle vibration velocity of the tunnel′s surrounding rock mass, which is induced by the blasting excavation of an adjacent tunnel, is analyzed based on in-situ monitoring data. The scaling effect of the particle vibration velocity of the adjacent tunnel′s surrounding rock under the function of a P wave and its influence factors are studied using numerical simulation,and the differences between the scaling effect of the vibration velocity and the concentration effect of dynamic stress are compared and analyzed. The calculation results show that when the P wave passes through an arched tunnel with a straight wall, the particle vibration velocity of the rock mass at one side of the tunnel wall near the vibration source is faster than that at the vibration source, while it is slower at the other side of the tunnel wall. In the zones of the surrounding rock mass where the dynamic stress concentration factor is higher, the rock mass particle vibration velocity is lower, and the rock mass particle vibration velocity is higher in the zones where the dynamic stress concentration factor is lower. 2017 Vol. 54 (5): 164-154 [Abstract] ( 996 ) [HTML 1KB] [ PDF 2182KB] ( 1920 ) 171 Three-Dimensional Model Test of Surrounding Rock Deformation of a New Tunnel Approaching an Existing Tunnel LIU Xinrong1, 2 WANG Jiming1, 2 LI Dongliang1, 2 GUO Zihong1, 2 In order to analyze the effects of the approaching distance of an existing tunnel on rock mass deforma? tion during construction of a new adjacent tunnel, a similarity model test and numerical simulation study are conducted based on the approaching section of the Chongqing Liangjiang tunnel. The results show that: 1) the approaching distance between the two tunnel tubes is inversely proportional to the crown settlement and convergence of the left and right tunnel haunches of the new tunnel; 2) the change tendency of the crown settlement complies with that of the convergence of the left and right tunnel haunches during construction of the new tunnel, and it can be summarized as the three phases of rapid increase, slow increase and stabilization; and 3) the tunnel crown settlement is larger than the sum of the haunch convergence, so the designed upper limit of rock mass deformation should be mainly based on the crown settlement for this type of tunnel. A relationship expression regarding the tunnel deformation H(mm)and tunnel approaching distance L(m) is established by means of data fitting, with the correlation coefficients all being more than 0.995, which provides a reference for the design of reserved deformation and the construction of similar projects. 2017 Vol. 54 (5): 171-179 [Abstract] ( 1030 ) [HTML 1KB] [ PDF 4731KB] ( 1924 ) 180 Mechanical Characteristics of a Multi-Arch Tunnel Support Structure in Loess LAI Jinxing YU Deqiang FENG Zhihua QIU Junling FAN Haobo To understand the mechanical characteristics of a multi-arch tunnel support structure in loess, the pres? sure on the surrounding rock, the axial force of the anchor bolt, the internal force of the steel arch and the force on the secondary lining are tested using steel-wire transducers. The test results indicate that: 1) the pressure of the surrounding rock fluctuates a lot at the juncture between the top of the mid-wall and the arch and the joint between the bottom of the wall and the invert, with maximum pressures of 195 kPa and 115 kPa, respectively. The pressure of the tunnel invert center at a rock transition section is relatively large, with a maximum pressure of 267 kPa and shaped like a large heaving floor, with the pressure of the rock mass distributing in a "double-saddle" shape; 2) the measured vertical pressure of a rock mass at a deep buried depth is close to the result calculated based on a half span of a multiple-arch tunnel specified in the“Code for Road Tunnels.”The pressures on rock masses calculated by different formulas are larger than the ones measured at the shallow-buried section, while the pressures obtained by the Terzaghi formula are relatively close to the measured ones; 3) the proportions of load sharing between the initial support and the secondary lining of this loess tunnel are 47.66% and 52.34%, which shows the secondary lining is in a load-bearing state; 4) the axial force of an anchor bolt is relatively small and distributed in a“fish-maw” shape, with the load largely borne by the steel arch and the anchor bolt playing a limited function due to the strong support of the steel arch; and 5) it proves that there is a longitudinal effect on the loess tunnel because of the existence of middle wall torque, and attention should be paid to this during construction and design. 2017 Vol. 54 (5): 180-191 [Abstract] ( 1033 ) [HTML 1KB] [ PDF 6968KB] ( 1927 ) 192 Mechanical Property Test for Reactive Powder Concrete Columns under Eccentric Compression SHI Chenghua1,2 MA Hui1 LONG Guangcheng1,2 LEI Mingfeng1,2 Long Min1 To discuss the feasibility of reactive powder concrete (RPC) materials used for shield tunnel segments, the bearing features of RPC columns with and without steel fibers are determined for different section dimensions,reinforcement ratios and compressive strengths by performing a large eccentric compression test of 22 RPC columns.The distribution characteristics of the strain of the section over the test columns are obtained under various loading conditions. The results indicate that the section strain behavior of test columns under eccentric compression is coincident with the plane-section assumption and the thickness of a shield tunnel segment can be decreased significantly if RPC material is used; section thickness has the most significant influence on the bearing capacity of the RPC column; as the compressive and tensile strength of the RPC column increases, the action of the steel bar’s bearing capacity is weakened and the reinforcement can be appropriately reduced in an RPC column under eccentric com? pression. 2017 Vol. 54 (5): 192-199 [Abstract] ( 890 ) [HTML 1KB] [ PDF 3002KB] ( 1950 ) 200 Optimization for Excavation Spacing of Two Lower Tunnel Tubes at Overlapped Section with a Minimum Clear Distance WANG Weiming1 WANG Chong1 QIN Zhibin2 CAO Zhenglong3 SUN Jiecheng1 Aimed at addressing the complex force conditions, challenges to blasting and support in overlapping tun? nels with a minimum clear distance, a numerical simulation is carried out for lower tunnel tubes regarding five kinds of excavation spacing. The distribution features of the surface and crown settlements of two lower tunnel tubes for different excavation spacings are analyzed based on the Zaoshanlu-Lichun running tunnel project of the Qingdao metro, and the stability of the rock mass and construction costs for different excavation spacings are studied by numerical calculations and theoretical analysis. The results show that the surface settlement, vault settlement and volume of the plastic zone will decrease gradually with an increase of the excavation space between the parallel tunnel tubes, along with the extension of construction period and the increasing of expenses; so a reasonable excavation spacing between the left and right tube is 25~35 m determined by the multi-index comprehensive assessment meth? od. 2017 Vol. 54 (5): 200-208 [Abstract] ( 990 ) [HTML 1KB] [ PDF 3586KB] ( 1864 ) 209 Optimization and Application of the Shallow-Buried Construction Method for an Urban Underground Road Tunnel WANG Wei PAN Wenshuo BIAN Jiasheng GAO Lingtao Taking an urban underground bored road tunnel as an example, a three-dimensional numerical simula? tion of dynamic excavation using the CRD and cross diaphragm with step methods is conducted based on the finiteelement theory. A contrastive analysis of the deformation and force characteristics of the rock mass and support structure of the tunnel constructed by the above two methods is carried out and an optimization of the cross diaphragm with step method is performed based on the results of numerical calculations. A comparison between the two construction methods is performed in terms of the advantages and disadvantages regarding construction safety, quality, progress and cost. The research and practice indicate that the two construction methods can both meet the requirements for rock mass and support structure stability, but the cross diaphragm with step method is superior to the CRD method in respect to construction progress and cost and produces better economic benefits in practice. 2017 Vol. 54 (5): 209-216 [Abstract] ( 1010 ) [HTML 1KB] [ PDF 3461KB] ( 2197 ) 217 New Techniques for Bridgehead Deformation Control for Expressways Passed by Approaching Metro Running Tunnels WANG Guofu1,2 LU Linhai1 LI Qiang1,2 When a metro running tunnel passes through an approaching bridgehead area of an existing expressway, it will increase uneven settlement of the bridge slope section and is liable to cause a serious vehicle bump at the bridgehead. Based on a running tunnel of Jinan metro line R1 underneath the existing Beijingjing-Fuzhou expressway bridge, the deformation law of an expressway bridgehead during shield tunnel construction is analyzed by a numerical model regarding the original reinforcement scheme, which only considers reducing the effects of shield construction on the pile foundation and ignores controlling the bridgehead deformation. The results show that adopting the construction sequences of the left line and then the right line is more favorable for reducing the deformation of the expressway bridgehead than the original reinforcement scheme, but it would cause 26.5 mm differential settlement at the bridgehead and can′t effectively prevent a vehicle bump at the bridgehead. In this context, a new technique is proposed that takes a cement mixing pile as an isolation pile and uses a deep concrete bridging slab to control bridgehead deformation. With this new technique, the maximum differential settlement at the bridgehead is 4.0 mm, the maximum longitudinal gradient variation is 0.4‰ and the maximum subgrade settlement is 6.5 mm, meet? ing the requirements specified. 2017 Vol. 54 (5): 217-223 [Abstract] ( 1090 ) [HTML 1KB] [ PDF 3239KB] ( 2000 ) 224 Application of the Grouting Technique in a Fractured Rock Mass in the Qingdao Metro ZHANG Yaguo The joints and fissures of a rock mass easily form passages for water inflow and endanger metro con? struction. Based on the Jingjia section of Qingdao Metro Line 13, a water-rich zone, the scope and means of the ground water supply are determined by geological radar detection. Targeted grouting is conducted; that is to say annular grouting is carried out at the upper end of the water seepage area to seal the upstream water inflow. Radial grouting to the group holes is adopted to effectively prevent grout leaking and improve grouting efficiency regarding water inflow in fractured rock masses in deep strata, and filled grouting is implemented at the back of the initial support and the area with shallow fractures to cut off the hydraulic connection and improve the impermeability of the primary support. Practice indicates that good results are obtained by systematic grouting, which insures that shallow fissure grouting goes after deep fracture grouting in order to control water inflow from surrounding rock. 2017 Vol. 54 (5): 224-228 [Abstract] ( 1077 ) [HTML 1KB] [ PDF 1829KB] ( 2051 ) 229 Construction Techniques for a Shield Running Tunnel Passing through the Anchor Cables of an Adjacent Foundation Pit in Soft Strata YOU Jie1 YAN Yue2 The shield running tunnel of the Guangzhou-Foshan rail transit project passes through many anchor ca? bles of an adjacent foundation pit. The advantages and disadvantages of the common treatment schemes for this problem are analyzed in terms of the construction period, construction cost, etc., and a construction scheme combining ground rotary drilling and cutting with shield driving is proposed based on reasonable driving parameters, which eliminate the anchor cable effect on the shield construction and avoid the influence of large-area excavation on the surrounding environment. 2017 Vol. 54 (5): 229-235 [Abstract] ( 880 ) [HTML 1KB] [ PDF 3156KB] ( 2258 )

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