20 August 2025, Volume 21 Issue 4
    

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  • Research on the Optimization of Pedestrian-Friendly Corner Spaces in Underground Commercial Streets
    Chen Xiaowei, He Yu, Tian Meixuan
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1105-1113. https://doi.org/10.20174/j.JUSE.2025.04.01
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    In the context of urban renewal, how to meet the public's demand for spatial quality in existing underground commercial streets has become an urgent problem to be solved. Corner space, as an important node in the pedestrian system of underground commercial streets, is a key area that affects spatial vitality, walking direction, pedestrian physiology, and psychology. Based on a pedestrian-friendly perspective, the impact of distance, constituent elements, and angles between different underground corners on pedestrian behavior is explored, and an adaptive corner space optimization strategy for (single building) underground commercial streets is proposed using spatial operation methods. The study aims to provide practical application value for optimizing the design of corner spaces in underground commercial streets. The results indicate that: Using obtuse corner angles, appropriate corner spacing, and increasing the boundary area at the corner can effectively enhance the overall vitality of the street and the attractiveness of shops.
  • Research on the Adaptive Reuse of Air-Raid Shelters in Chongqing Urban Area during the Anti-Japanese War
    Yang Yan
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1114-1125. https://doi.org/10.20174/j.JUSE.2025.04.02
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    Air-raid shelter is an important component of the underground space in Chongqing city. During the Anti-Japanese War period, they served as shelters for military and civilian production and life, enhancing the overall protection capacity of the city and providing effective protection for the war. Nowadays, there are problems with insufficient space utilization and unclear design concepts in the reuse of air raid shelters in the urban areas of Chongqing during the Anti-Japanese War. Therefore, specialized research on the adaptive reuse of air defense shelters in the urban areas of Chongqing during the Anti-Japanese War period is conducted. Based on relevant theories of adaptive reuse, firstly, by transforming and reusing the original functions and spaces of air defense shelters, the old functions is continued, the old functions is integrated with the new functions to expand the new functions. Secondly, the existing wartime air defense voids should be designed for adaptive reuse by expressing regional characteristics, optimizing internal spatial forms, showcasing ecological landscapes, upgrading functional efficiency, and enhancing safety performance, in order to improve and extend the efficiency and lifespan of wartime air defense voids. Finally, based on the unique regional characteristics of wartime air defense shelters, a diversified integration plan, a combination of civil defense functions and disaster prevention and rescue, and an adaptive reuse design strategy that integrates military and civilian functions are proposed, in order to better leverage the cultural and socio-economic benefits of air defense shelters in the Chongqing urban area during the Anti-Japanese War in the context of peace and war integration.
  • Rock Damage Model Considering Post-Peak Brittleness Characteristics
    Wei Anhui, Mou Qi, Tang Wei, LiJunrun, Zhao Haisong
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1126-1136. https://doi.org/10.20174/j.JUSE.2025.04.03
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    In response to the poor simulation performance of existing constitutive models for rock post-peak curves, a rock damage constitutive model that can reflect the brittle characteristics of rock post peak is proposed based on the assumption that the strength of rock microelements follows Weibull distribution and Drucker Prager failure criterion. The curve shape parameter β is introduced to modify the Young's modulus and damage factor of rock. Finally, the established constitutive model theoretical curve was compared and analyzed with the conventional triaxial stress-strain curves of three types of rocks (shale, marble, and granite), and combined with the analysis results of other similar models, the applicability and accuracy of the model proposed in this paper were confirmed. The results show that: The new model not only overcomes the defect of theoretical curves not reaching the origin, but also well describes the brittle characteristics of rocks after the peak and the influence of residual strength on the stress-strain behavior throughout the entire process. The model parameters is discussed . The larger the F value, the higher the peak strength, the larger the M value, the stronger the brittle characteristics before the peak, and the larger the β value, the stronger the ductility characteristics after the peak. The study results has certain reference value for the establishment of a comprehensive brittleness evaluation model for deep rock masses.
  • Study on the Creep of Surrounding Rock and Prestress Loss of Anchor Cable Based on Nishihara Model
    Song Ziyuan, Chen Qiang, Zhou Menglin, Peng Chuanyang, Wang Bo
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1137-1145. https://doi.org/10.20174/j.JUSE.2025.04.04
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    The influence of the surrounding rock creep of soft rock tunnel on the prestress of the anchor cable can not be ignored. In order to explore the relationship between rock mass and prestress loss under the creep coupling effect of prestressed anchor cable, this paper uses the theory of the component combination model and takes a soft rock highway tunnel in the west as the engineering background. The Nishihara model, with good applicability to describe the creep problem of soft rock, and the Hooke model describing the prestressed anchor cable are connected in parallel, and the Nishihara coupling model of anchor cable prestress changing with time under creep effect is established. The coupling model is used to calculate and analyze the initial stress between 15~30 MPa. The goodness of fit of the Xiyuan coupling model and the generalized Kelvin coupling model to the long-term monitoring value of the cable prestress. The results show that: The average goodness of fit of the Nishihara coupling model is 0.98, which is much higher than the average goodness of fit of 0.73 of the generalized Kelvin coupling model. It is proven that the calculation results of the Nishihara coupling model are better than the generalized Kelvin coupling model for the fitting of the monitoring data, and it is more suitable for simulating the prestress loss of the anchor cable under the long-term creep of the soft rock tunnel. The research results have certain guiding significance for the design and construction of prestressed support engineering.
  • Research on Seismic Active Earth Pressure of Inclined Rigid Retaining Wall Considering Principal Stress Rotation
    Zhang Jinwei, Zhou Yitao
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1146-1154. https://doi.org/10.20174/j.JUSE.2025.04.05
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    Considering the influence of principal stress rotation, time effect and wall back inclination, a new solution of seismic active failure angle is derived by using pseudo-dynamic method according to the total force balance of sliding soil. Through the horizontal differential layer method, a new differential equation of the normal seismic active earth pressure and its coefficient of the inclined rigid retaining wall under translation is obtained. Then, the Runge-Kutta method of ordinary differential equation is used to obtain the numerical solution, and the influence of parameters (i.e. vibration cycle time, wall back inclination, internal friction angle of backfill, wall soil friction angle, wall height, the amplitude of horizontal and vertical seismic acceleration coefficient) on the seismic active failure angle, as well as the seismic active earth pressure and its coefficient are discussed. In addition, the seismic active earth pressure and its coefficients calculated by the proposed method are compared with the existing pseudo-static and pseudo-dynamic methods. The results show that: The seismic active failure angle, the seismic active earth pressure and its coefficient change periodically with time, and the seismic active earth pressure distribution along the wall height is nonlinear. The seismic active earth pressure and its coefficient obtained by this method are larger than those obtained by the existing quasi-static method.
  • Modeling and Shear Characteristics of Pile-Soil Random Fluctuation Contact Surface
    Li Zhongbao, Wang Bo, Zong Yuanchun, Yuan Shuai
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1155-1160. https://doi.org/10.20174/j.JUSE.2025.04.06
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    Monte Carlo method is used to establish a random fluctuation surface model by considering the random ups and downs characteristics of the outer surface of the cast-in-place pile. Direct shear tests of the pile-soil random fluctuation surface under different normal stress and fluctuation height are carried out. The effects of normal stress and average fluctuation height on the shear behavior of the cast-in-place pile-soil random fluctuation interface are analyzed, such as shear strength, failure mode, shear stress-displacement relationship, etc. The results show that: Radial fluctuation of the outer side of the cast-in-place pile agrees with the Gaussian distribution, and the fluctuation height is mainly concentrated in the range of 0~8% of the pile diameter. With the increase of the fluctuating height, the number of soil particles embedded in the concave part of the pile-soil interface increases. The failure mode of the pile-soil random fluctuation interface gradually develops from pile-soil interface sliding shear failure to internal shear failure of the soil. The cohesion and internal friction angle of the pile-soil random fluctuation interface also increase, and the shear stress-strain curve of the random fluctuation pile-soil random fluctuation interface gradually approached to the shear stress-strain curve of soil.
  • The Flow Characteristics of Fractured Viscous Fluids in Dense Conglomerates
    Lu Caiwu, Luo Xintian, Zhang Sai, Jiang Song, Sun Yixiao
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1161-1172. https://doi.org/10.20174/j.JUSE.2025.04.07
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    The use of underground space to store oil is affected by fractures, which is simplified to a single-fracture seepage problem. Introducing the Reynolds number Re and using 3D printing technology, physical model tests are conducted to explore the influence of the hydrodynamic viscosity μ and the fracture aperture bi on the fluid flow characteristics and pressure gradient J under different injection flow rate gradients. The results show that: The fracture aperture bi affects the stabilization time of the seepage, while the hydrodynamic viscosity μ has a greater impact on the seepage pressure. After fitting the data, it is found that the fracture aperture bi has an exponential function relationship with the pressure gradient J, which shows a downward trend as bi increases. At the same time, the Reynolds number Re decreases, and the fluid flow capacity weakens; the hydrodynamic viscosity μ and the pressure gradient J show a downward trend. According to the relationship of the power function, J increases with the increase of μ, which reveals the evolution law of pressure gradient with hydrodynamic viscosity, indicating that the resistance of fluid flowing into the fracture increases and the inflow is more difficult. The fracture aperture and hydrodynamic viscosity have varying degrees of obstruction to fluid seepage in the fracture. Under the influence of multiple factors, the flow capacity is weakened, and blockage may occur. In a groundwater environment, oil can be stored at a certain height, indicating that it is possible to store petroleum-like viscous liquids in underground spaces containing tiny fractures without sealing measures.
  • Analysis of Energy Dissipation and Failure Law of Gabbro under Cyclic Dynamic Load
    Zhang Zhiyu, Chen Chengzhi
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1173-1182. https://doi.org/10.20174/j.JUSE.2025.04.08
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    In order to study the damage law and failure mode of pegmatite gabbro under cyclic loading, the Split Hopkinson Pressure Bar (SHPB) and PFC3D numerical simulation software were used to carry out cyclic impact tests of pegmatite gabbro at different impact velocities, and the damage characteristics and failure law were analyzed. The results show that: Under low impact velocity, the original cracks of the rock specimen are first compacted and then gradually destroyed with the increase of the number of cycles, and the dynamic compressive strength of the rock specimen increases first and then decreases gradually. With the increase of the number of cycles, the proportion of rock reflection energy and energy consumption density generally show an upward trend, and the proportion of transmission energy generally shows a downward trend. The damage variable of the rock specimen first shows a negative growth and then a steady growth, and the damage variable of the specimen increases rapidly before the macroscopic failure occurs. Under high impact velocity, the rock specimen will be destroyed in each cycle, the dynamic compressive strength of the specimen increases with the increase of the number of cycles, and the damage variable of the specimen also increases with the increase of the number of cycles. The failure process of the specimen under cyclic loading was simulated by PFC3D, and it was found that the rock specimen was always destroyed along the longitudinal plane under cyclic loading.
  • Numerical Simulation of Proppant Transportation and Distribution in the Nonplanar Fracture
    Chen Siyuan, Jin Yan, Wei Shiming
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1183-1193. https://doi.org/10.20174/j.JUSE.2025.04.09
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    Hydraulic fracturing of highly deviated wells is an effective means to develop ultra-deep oil and gas reservoirs. The transportation law of proppant becomes more complicated due to the complex nonplanar morphology formed by the distortion and extension of fractures in three-dimensional space. To investigate the transportation of proppant in nonplanar fracture, a fluid-solid coupling model of proppant transportation in the 3D nonplanar fracture was established and solved based on computational fluid dynamics (CFD) and discrete element method (DEM). The effects of displacement, proppant density, proppant size and fluid viscosity on proppant transportation and distribution were studied. The results show that: The shape of nonplanar fractures has a significant influence on proppant transportation. Compared with the flow form in planar fracture, the flow in nonplanar fracture appears eddy current. The collision frequency between proppant and fracture wall and other proppants increases, which increases the energy loss during sand-carrying fluid flow. By increasing the displacement, sand plugging in the near-wellbore area can be avoided and the length of sand bank in the fracture is increased. As proppant density and proppant size decrease, the length of the sand bank increases and the height decreases. High-viscosity fracturing fluid can effectively carry proppant for transportation and avoid proppant settlement near the wellbore to occur sand plugging. This study clarifies the laws of proppant transportation and distribution in the nonplanar fracture, and helps guide the design of proppant pumping construction parameters for ultra-deep highly deviated well fracturing.
  • Dynamic and Static Combined SHPB Experimental Study on the Mechanical Properties of Fractured Sandstone
    Ping Qi, Xu Yijie, Li Xiangyang, Wu Shiwei, Hu Jing
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1194-1201. https://doi.org/10.20174/j.JUSE.2025.04.10
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    To study the influence of fracture inclination angle on the dynamic mechanical properties of sandstone under dynamic and static combined loading conditions, impact compression tests were conducted on prefabricated fractured sandstone specimens with inclination angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90° using dynamic and static combined SHPB test device. The results show that: Under dynamic and static combined loading conditions, the dynamic stress-strain curves of prefabricated fractured sandstone specimens with different inclination angles are located below the complete sandstone specimen curve. As the inclination angle of fracture increases, the dynamic compressive strength, dynamic strain, dynamic elastic modulus, and average particle size of fragments all show a variation of first decreasing and then increasing, and the inflection point is located at fracture inclination angle of 45°. When the fracture inclination angle is 0°, the failure mode of the specimen is tensile failure along the loading direction, while failure mode is tensile-shear composite failure for fracture inclination angle of 15°~60° and shear failure for fracture inclination angle of 75°~90°. Moreover, the fragmentation degree of the specimen is largest at fracture inclination angle of 45° and is smallest at 0°.
  • Experimental Study of Grotto Sandstone Strength under Different pH Environments and Dry-Wet cycles
    Wang Chenglong, Guo Yue, Zhang Wengang, Jiang Siwei, Liu Dongsheng
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1202-1210. https://doi.org/10.20174/j.JUSE.2025.04.11
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    As an important outdoor cultural relic, the grotto temple is affected by the dry-wet cycles caused by rainfall, water seepage and other natural environment for a long time, As a result, the deterioration of physical and mechanical properties is induced, causing instability damage. In order to better protect grotto cultural relics, the sandstone of Dazu stone carving grottoes is selected as the research object. Experimental research on the strength deterioration characteristics of grotto sandstone under the action of dry-wet cycles is carried out through uniaxial compression test and Brazilian split test, and the influences of dry-wet cycles combined with immersion in solutions of different pH values are analysed. The results show that: (1) The uniaxial compressive and tensile strengths of sandstone after complete drying are improved compared to the natural state. (2) The mechanical properties of the sandstone deteriorate after several dry-wet cycles. With the increase of the number of cycles, the deterioration gradually increases. When the dry-wet cycle reaches a certain number, the impact on the strength of sandstone is weakened. (3) Different pH values also affect the degree of sandstone deterioration. The lower pH value will induce more serious deterioration of the sandstone mechanical properties. (4) After several dry-wet cycles using acidic solutions, the sandstone damage form changes compared to that in the natural state.
  • Experimental Study on the Optimization of Concrete Mix Ratio in Freeze-Thaw Environment
    Wei Ronghua, Zhang Kangjian, Zhang Zhiqiang
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1211-1218. https://doi.org/10.20174/j.JUSE.2025.04.12
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    In order to screen the good proportions of concrete under freeze-thaw environment, cement heat of hydration tests and uniaxial compression tests of concrete after freeze-thaw are carried out under different conditions to investigate the effects of admixture and water-cement ratio on the structural properties of concrete, to determine the good proportions of concrete in cold areas, and to establish the stress-strain prediction curve of the whole process after freeze-thaw. The results show that: (1) The total heat of hydration decreases with increasing mineral admixture content. However, a small dosage of silica fume can enhance early-age heat release. The reactivity of the materials at early ages follows the order: cement > silica fume > fly ash; (2) A small amount of fly ash and silica fume admixture into concrete can play the microaggregate and volcanic ash effect, improve the concrete compactness, and strengthen the structural frost resistance and mechanical properties; (3) Low admixture (0~10%) silica fume incorporation is beneficial to structural frost resistance, fly ash (0~20%) incorporation leads to first increase and then decrease in structural frost resistance, so there is an optimum value of fly ash incorporation, water-cement ratio leads to significant decrease in structural frost resistance, 15% fly ash—10% silica fume—0.36 water-cement ratio is an excellent concrete ratio applicable to cold regions; (4) The prediction curve of compressive stress-strain of concrete after freeze-thaw is proposed, which can be applied to the nonlinear analysis of concrete in cold regions.
  • Study on the Characteristics of Red Mud-Lime Solidified Cadmium and Lead Heavy Metal Contaminated Soil
    Li Lihua, Tang Zongzhen, Pei Yaoyao, Chen Xueling
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1219-1227. https://doi.org/10.20174/j.JUSE.2025.04.13
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    In order to realize the reuse of solid waste red mud and solve the problem of high lime emission, it is proposed to use red mud and lime to solidify/stabilize heavy metals, cadmium, and lead-polluted soil. The unconfined compressive strength, toxic leaching, scanning electron microscopy, and X-ray diffraction tests were carried out on cadmium and lead cured contaminated soil to explore the effects of different types of stabilizers, pollutant concentrations, and curing ages on the compressive strength and heavy metal leaching concentration in stabilized soil. The changes of microstructure and mineral composition were analyzed. The results show that: The addition of red mud-lime could significantly improve the compressive strength of contaminated soil and reduce the leaching rate of cadmium and lead. Under non-polluted conditions, the red mud-lime ratio of 4∶6 with a curing period of 28d resulted in the highest strength. The strength of solidified soil increased first and then decreased with the concentration of pollutants, and the addition of a small amount of pollutants could increase the strength. Brittle failure was more likely to occur after adding lime. The leaching concentration of cadmium decreased while that for lead initially decreased, then increased with an increase in lime content. The pH value of contaminated soil increased with the increase of the proportion of lime in the curing agent. The main product of red mud-lime solidification contaminated soil was C-S-H, which filled the soil pores to form a dense spatial structure. With the increase of lime content, the products increased significantly. The reaction was inhibited at high pollutant concentration, leading to fewer products being formed.
  • Effect of Fabric on Fracture Toughness and Crack Propagation Behavior of Gneiss
    Chen Lichao, Zhang Chaopeng, Yan Ruichang, Lü Shuaifeng, Xiao Yuhang
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1228-1235. https://doi.org/10.20174/j.JUSE.2025.04.14
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    The anisotropy of fracture behavior of gneiss is a key constraint to the fracturing of reservoir fracture network. The differences of fracture toughness, fracture energy and fracture morphology of gneiss in different directions are studied by selecting gneiss in Daqingshan of Inner Mongolia. The results show that: The fracture process of gneiss specimens under three-points bending loading includes four stages: pore compression, elastic compression deformation, fracture and rapid unloading. The brittleness of gneiss is significant, which is beneficial for volumetric fracturing. The fracture toughness of gneiss ranges from 0.93 to 1.28 MPa·m0.5, and the fracture performance of gneiss varies greatly in different orientations. The vertical bedding/vertical lineation > parallel bedding /vertical lineation > vertical bedding /parallel lineation > parallel bedding/parallel lineation has certain mechanical constraints on the selection of fracture propagation direction. In the vertical schistosity direction, the fracture propagation of gneiss is seriously affected by the weak plane. The shear and displacement of cracks occur at the schistosity face and form bedding-parallel fractures. In the later stage, the fractures turn to extend along the loading direction. In the parallel schistosity direction, the fractures of gneiss extend parallel to the maximum principal stress orientation. The fracture surface is flat, and the fracture tortuosity is small, which is not conducive to fracture network formation. The breaking energy consumption of samples in vertical bedding/vertical lineation, parallel bedding /vertical lineation, vertical bedding /parallel lineation, parallel bedding/parallel lineation direction is 0.47, 0.43, 0.37 and 0.25 J, respectively, and the energy consumption of fracture in each direction of gneiss varies greatly. In order to expand the reservoir volume fracturing coverage, it is recommended to drill horizontal wells parallel to gneiss lineation.
  • Mutual Feed Mechanism between Surrounding Rock Swelling and Supporting Structure in Water-Rich Argillaceous Slate Tunnel
    Zuo Qingjun, Chen Zhenming, Li Pan, Chen Fubang, Deng Maolin
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1236-1249. https://doi.org/10.20174/j.JUSE.2025.04.15
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    In order to characterize the relationship between the surrounding rock and support structure under the constraint system of swelling support structure, starting from the swelling problem of argillaceous slate, the swelling test, indoor tunnel scale-down physical model test and numerical simulation were utilized to analyze the interaction process between the surrounding rock and supporting structure in argillaceous slate tunnel in water-rich environment, and the mutual feeding model of the swelling and supporting structure of the surrounding rock of argillaceous slate tunnel in water-rich environment was constructed. The results show that: There is a strong positive correlation between the peak swelling stress, strain of argillaceous slate and the free saturated water absorption rate in the water-rich environment. Based on the relationship between the deformation of surrounding rock, supporting structure, tunnel displacement and swelling stress, the ultimate deformation of the tunnel is predicted according to the peak swelling force of the surrounding rock. The interaction between surrounding rock and supporting structure of swelling rock tunnel is a long-term “mutual feeding” process, which reflects the relationship of “promotion and inhibition” between surrounding rock and supporting structure. The swelling of surrounding rock promotes the deformation of the supporting structure, and the supporting structure in turn inhibits the deformation of the surrounding rock. The research results can provide reference for the design and construction of swelling rock tunnel.
  • Experimental Study on the Influence of Overlying Soil on Existing Shield Tunnels
    Huang Dawei, Chen Houhong, Zheng Mingxin, Hu Guangjing, Zhan Tao
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1250-1257. https://doi.org/10.20174/j.JUSE.2025.04.16
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    In response to the problem of shield tunneling prone to lateral elliptical deformation exceeding the limit under the action of overlying soil, a 1∶10 scale model shield tunnel is designed, the influence of overburden soil on the deformation of the existing shield tunnel is studied by experiment. The results show that: (1) As the thickness of the overlying soil layer increases, the maximum increase and change in soil pressure at the top of the tunnel, followed by the bottom, and the minimum on both sides. (2) Significant vertical soil pressure concentration occurs after the thickness of the overlying soil layer on the tunnel is greater than 0.4 m. As a result, the increase in vertical soil pressure is greater than vertical soil pressure concentration does not occur. (3) Under the action of soil cover on the tunnel, due to the vertical soil pressure being greater than the horizontal soil pressure, the tunnel undergoes transverse elliptical deformation. (4) At the location of the tunnel, the lateral soil pressure coefficient of the stratum gradually increases with the increasing thickness of the overlying soil layer. And after reaching a certain degree of thickness, the growth rate of lateral soil pressure coefficient significantly decreases. The results provide reference for the control of existing shield tunnels and the distribution of additional soil pressure around them.
  • Research on the Load Characteristics of TBM Cutterhead Based on Water Jet Slitting Assisted Rock-Breaking
    Tang Chongmao
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1258-1268. https://doi.org/10.20174/j.JUSE.2025.04.17
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    Tunnel boring machine (TBM) faces the problems of difficult rock breaking and high cutter loss when excavating hard rock, leading to low boring efficiency and high construction cost. In order to improve the rock-breaking performance of TBM cutterhead, various new auxiliary rock-breaking technologies have attracted much attention, among which water jet assisted rock-breaking has great potential. The disc cutter rock breaking experimental device with the function of water jet cutting slit is used to study the effects of single slit and double slit assisted cutter breaking. It is find that there exists the law of "critical spacing", and based on this law, the load models of single and double slit assisted cutter breaking have been established; A method of arranging water jet nozzles on TBM cutterhead is proposed. Based on this, the tilting moment, radial force, thrust force and torque calculation models of the cutter are established. The resluts show that: The load models based on the critical spacing ratio S/Smax can reflect the load reduction and change rule of cutter and cutterhead, and it can be used as a reference calculation method for the load of water jet slit-assisted rock breaking and water jet TBM cutterhead load.
  • Research on Load Characteristics of PDC Bit Rock-Breaking Cutting with Vibration Suppression
    Ren Haitao, Zhou Sheng, Zhou Chunxiao, Jia Xin, Yang Yingxin
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1269-1277. https://doi.org/10.20174/j.JUSE.2025.04.18
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    PDC drill bits often encounter frequent impact loads when drilling through formations containing gravel, alternating soft and hard formations, and performing directional drilling under complex operating conditions. These impact loads can lead to abnormal fatigue failures, such as tooth cracking, delamination of composite sheet, falling out of the teeth and broken teeth, greatly reducing the drill bit's service life and drilling efficiency. The concept of flexible rock cutting technology refers to the use of damping elements to reduce cutting stiffness, thereby limiting the magnitude of impact loads encountered during the cutting process within a certain range. The aim is to mitigate the fatigue damage of the cutter and extend the service life of the drill bit. By conducting experiments on flexible cutting units on limestone, the influence of factors such as cutting depth, rake angle, and the combination of damping units on the damping effect of flexible units are analyzed. The results show that: The flexible cutting can reduce the peak cutting load by 20% to 35%. The damping effect of the flexible unit shows a positive correlation with the combination stiffness of the damping units and the rake angle. The optimal combination for damping elements is a series connection of two A-type disc springs, and the optimal rake angle is 15°.
  • Influence Analysis of the Structural Characteristics of Whip-Tip Block on the Ultra-Low Friction Effect
    Li Liping, Li Qiuyu, Pan Yishan, Tang Lei
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1278-1285. https://doi.org/10.20174/j.JUSE.2025.04.19
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    The dynamic response of a deep rock body under mining disturbance is very similar to that of a high-rise building under seismic action, and the whip-tip structure is introduced into the study of the rock body's ultra-low friction effect. The model of the ultra-low friction effect of the whip-tip block is established, and the influence of its structural characteristics on the ultra-low friction effect is studied. The horizontal displacement size of the whipping block by changing the size, position, and aspect ratio of the whipping block was analyzed by using the self-developed experimental device of ultra-low friction effect, and the influence law of the structural characteristic parameters on the ultra-low friction effect was obtained. The results show that: The horizontal displacement time course curves of the whipping tip block under different working conditions are characterized by two stages; The whipping tip block size increases, the horizontal displacement decreases, and the ultra-low friction effect is weakened; Under the effect of vertical perturbation, the ultra-low friction effect of the whip-tip block tends to increase with its position away from the source of perturbation, and there is an interval of significant influence of the ultra-low friction effect on the height-to-width ratio.
  • Friction Performance Testing Study at Rock-Pipe Jacking Interface under Mixing Rock Debris with Slurry
    Liu Yu, Li Chao, Liu Xinrong, Zhong Zuliang, Zhao Yu
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1286-1298. https://doi.org/10.20174/j.JUSE.2025.04.20
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    To address the issues of pipe stuck and sudden increase in jacking force in ultra-long-distance and large-cross-section rock pipe jacking projects, this paper systematically investigates the complex friction characteristics between pipelines and rocks under different rock debris gradations and different mixing ratios of rock debris to slurry using direct shear tests. The results show that: When the total mass of debris is low and the proportion of large particles is dominant, the debris creates a furrow effect on the contact surface, with the friction coefficient primarily controlled by the roughness of the contact surface. Conversely, when the total mass of debris is high and the proportion of fine particles is dominant, the debris interlocks with each other, and the friction coefficient is mainly controlled by the void ratio. Then, an inverse analysis of the jacking force in the field based on the test results was carried out using the improved jacking force prediction model. The validity of this study was eventually confirmed by the results of the field monitoring. The presence of rock debris is very detrimental to jacking, and the inevitable formation of “cake bentonite” conditions at a later stage leads to a sharp increase in frictional resistance. Accordingly, the site should be cleared of debris from outside the pipe strings in a timely manner and consider regular and continuous injection of lower viscosity bentonite slurry. The study results can provide new research ideas and methods for solving problems in this field.
  • Study on Undrained Strength Indices for Resistant Heave Stability of Deep Excavations in Soft Clay
    Yang Zhou, Cheng Xiaohui, Guo Hongxian, Chen Haoran
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1299-1305. https://doi.org/10.20174/j.JUSE.2025.04.21
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    Deep excavations constructed rapidly in soft clay with poor drainage performance require resistant heave stability analysis under undrained conditions. Currently, total stress analysis with the total stress strength indices of conventional triaxial consolidated-undrained tests (Method C) is commonly used in domestic engineering community. In contrast, the academic and foreign engineering community recommend the effective stress analysis method based on effective stress strength indices (Method A) and the undrained strength analysis method based on undrained shear strength (Method B). Combining with real excavation cases, the applicability and rationality of the three methods for analyzing excavations are studied by the finite element limit analysis. The results show that: As the total stress path in excavation differs from that of the conventional triaxial compression test, Method C underestimates the true shear strength of unloaded soil, while CU tests overestimates the in-situ undrained shear strength. Therefore, the calculated safety factor by Method C is not reliable. Method A overestimates the undrained shear strength of shear-shrinkage clay and the safety factors. Method B is the most accurate theoretically.
  • Optimal Penetration Analysis of Disc Cutter under Different Cutter-Spacings Based on Characteristic Particle Size
    Zhai Shufang, Yue Qichao, Zhou Xiaoxiong, Song Yingjie, Gong Qiuming
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1306-1312. https://doi.org/10.20174/j.JUSE.2025.04.22
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    Tunnel boring machine (TBM) is widely used in tunnel construction. The boring efficiency is mainly affected by the cutter arrangement and construction parameters, in which the cutter spacing is designed to be reasonable and whether the penetration degree is set to be appropriate are the most important two aspects impacting the efficiency of rock breaking. As a direct product of rock breaking by cutter, rock ballast can provide comprehensive and intuitive feedback on the rock-breaking efficiency of TBM. The correlation mechanism between ballast particle size distribution and rock breaking efficiency is revealed by analyzing the rock chip morphology of granite cutting test. Based on the theory of characteristic particle size to predict the optimal penetration, it is verified by multiple working conditions that: The optimal penetration is 2.0 mm for cutter spacing of 60~70 mm, 2.5 mm for cutter spacing of 80 mm, and 3.0 mm for cutter spacing of 90~100 mm, and the characteristic particle size of the rock chips reaches the peak when the ratio of the cutter spacing to the penetration is in the range of 30~40, corresponding to the optimal efficiency of rock-breaking. It can dynamically optimize and adjust the combination of boring parameters according to the real-time monitoring of the characteristics of the rock chip particle size, and realize the scientific matching of the knife spacing and penetration.
  • Theoretical Research of the Reduction Law of Water Pressure Loaded outside the Lining of High-Water Pressure Karst Tunnel
    Zhang Zhien, Zhou Zongqing, Li Liping, Zheng Bo, Wang Lichuan
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1313-1319. https://doi.org/10.20174/j.JUSE.2025.04.23
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    In order to optimize the waterproof and drainage design of the lining of a high-water pressure karst tunnel, taking the New Yuanliangshan Tunnel as the research background, based on the differential equation of the plane radial stable seepage of pressurized water, considering the water pressure reduction effect of shotcrete, a calculation formula for the water pressure of the tunnel lining is derived. The influence of factors such as the drainage capacity of the drainage pipe, the thickness and impermeability of the grouting ring on the water pressure of the lining was analyzed. The results indicate that: The magnitude of water pressure on the lining varies exponentially with the tunnel drainage capacity, grouting ring thickness and permeability coefficient. The drainage capacity of the tunnel has the greatest impact on the water pressure of the lining. Once the drainage pipe is blocked, the water pressure reduction coefficient becomes 1, and the lining will withstand static water pressure. Increasing the thickness of the grouting ring is beneficial for reducing the water pressure loaded on the lining, but the reduction effect gradually weakens. Strictly controlling the quality of grouting operations, improving the homogeneity of the grouting circle, and reducing the permeability coefficient of local short plate grouting bodies can effectively improve the water pressure resistance of the grouting circle and reduce the permeability pressure of the lining.
  • Study on the Influence of External Water Pressure on the Stress and Deformation of Prestressed Double-Layer Lining
    Ma Xiaobin, Wang Ya, Liu Chang, Lin Weihao, Wang Shimin
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1320-1327. https://doi.org/10.20174/j.JUSE.2025.04.24
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    In order to investigate the influence of external water pressure changes on the mechanical characteristics of prestressed double-layer lining, a three-dimensional finite element model of the prestressed double-layer lining in a shield tunnel is established based on the Pearl River Delta Water Resources Allocation Project. The structural behavior and deformation of the double-layer lining during the prestressing construction and water flow operation stages are analyzed under different external water head heights (10 m, 20 m, 30 m, 40 m, 50 m). The results indicate the following: during the construction and operation stages, the overall shape of the double-layer lining exhibits an "elliptical" deformation pattern. When the external water head height decreases from 50 m to 10 m, the lateral deformation of the double-layer lining increases by 42.3%, the settlement at the crown decreases by 34.3%, and the uplift at the invert decreases by 42.4%. With the increase of external water pressure, the circumferential stress of the prestressed lining during the construction stage increases, and the tensile area of the segment lining during the operation stage decreases. The maximum circumferential tensile stress decreases by 54.05%. The prestressed double-layer lining tends to be in a hydrostatic pressure state, and the overall deformation pattern transitions from "elliptical deformation" to "overall contraction". This study contributes to the safety of the double-layer lining structure.
  • Research and Application of Large-Span Roof Support Technology for IV Grade Broken Rock Mass
    Long Gan, Wang Jun, Qiao Dengpan, Li Guangtao, Shi Renzhi
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1328-1343. https://doi.org/10.20174/j.JUSE.2025.04.25
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    To specifically address the support challenges posed by large-span roofs in Class IV fractured rock masses, a composite support scheme was proposed based on the principles of structural closure, arching effect, and span reduction. The scheme integrates a combination of anchor mesh, shotcrete, prestressed rock bolts, and prestressed anchor cables to achieve comprehensive reinforcement. A non-associated elasto-plastic analysis of the secondary stress field in the surrounding rock was performed based on the Mohr-Coulomb failure criterion. Considering the partitioned boundary conditions, analytical expressions were derived to determine the radii of the loosened zone and the plastic reinforcement zone. The calculated thicknesses of the loosened and plastic zones were 2.53 m and 2.83 m, respectively. Based on these results and relevant engineering standards, the support parameters for the roof were rationally designed. To verify the feasibility of the proposed scheme, a numerical model of Stope #9 was developed using FLAC3D software to simulate three scenarios: no support, the original support design, and the proposed support scheme. Simulation results indicated that the minimum principal stress in the supported roof area under the proposed scheme was reduced to 0~0.25 MPa, which is significantly lower than the tensile strength of the rock. The height of the plastic zone was reduced to 3.6 m, representing a 62.5% decrease compared to the original support design. An industrial-scale trial was subsequently carried out in Stope #9 based on the proposed design and simulation outcomes. During the excavation process, no roof collapse was observed, and the roof exhibited good integrity and stability. These results confirm the rationality and practical feasibility of the proposed support system and provide a valuable reference for similar underground mining projects.
  • Analysis and Optimization of Erosion Performance of Slurry Shield Cutterhead in High Viscosity Soil Layer
    Zhou Dongbo, Mei Yuan, Xu Wangyang, Gong Hang , Suo Fuzhong
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1344-1351. https://doi.org/10.20174/j.JUSE.2025.04.26
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    In order to reduce the risk of mud cake formation in large-diameter slurry shield tunneling cutterheads in high clay mineral formations, a three-dimensional numerical model of the shield cutterhead and scouring system is established using numerical simulation methods based on actual engineering. The distribution characteristics of the flow field near the cutterhead were studied, and the angle of the central scouring hole was optimized under multiple working conditions. The results show that: The overall mud flow rate in the center area of the static region ② was higher than that in the outer area. However, there is a significant decrease in the mud flow rate in some parts of the central area, and there is still a risk of the debris from the cutting tools gathering again on the back panel of the cutter head, forming large mud cakes that can block the cutter head; When the scouring angles of the central scouring holes ② and ③ are arranged at 45°, the scouring effect on the outer area is more thorough, and when they are arranged at 90°, the scouring effect on the outer area is the worst; According to the streamline performance factors of the four working conditions in the stationary region ②, rotating region, and stationary region ①, the priority order of erosion angle design can be determined as follows: working condition 2>working condition 3>working condition 1>working condition 4, that is, the order of erosion hole brushing angle is 45°>70°>20°>90°, the research results can serve as a theoretical basis for optimizing the design of the cutter head erosion system.
  • Study on Adaptability and Construction Technology of Compound TBM in Soil-Rock Mixture Backfill Area
    Wang Senjian, Wang Jiwen, Zhong Zuliang, Zhou Jihu, Duan Wanglong
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1352-1362. https://doi.org/10.20174/j.JUSE.2025.04.27
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    The section between Wangjiacheng Station and Shengjipu Station of Chongqing Line 4 needs to pass through 3 sections of newly filled soil-rock mixture. Due to the loose structure, poor uniformity, large voids, insufficient consolidation and low shear strength of the newly filled soil-rock mixture, tunnel construction is prone to cause significant ground settlement. The applicability and construction technology of compound TBM in soil-rock mixture backfill area are summarized in this paper. The results show that: Pre-reinforcement via surface sleeve-valve grouting (pressure: 0.1~0.3 MPa) enhances soil strength (unconfined compressive strength ≥1.2 MPa) and density (shear wave velocity ≥300 m/s); “Low penetration + high rotation” mode (advance rate ≤30 mm/min, cutterhead rotation 0.8~1.0 r/min) with strict control of muck discharge (72.46 m3/ring) and synchronous grouting volume (6.66~11.1 m3/ring) is adopted; Large boulders (≤300 mm) are fragmented by hydraulic splitting. Numerical analysis identified backfill depth and grouting range as dominant settlement factors and the area for surface pre-grouting reinforcement is suggested to expand to the sides of the arch rib by 1.0D. The measurement results show that this technology has controlled the surface subsidence to 24 mm (below the warning value of 30 mm), and the subsidence of the tunnel arch top and the net clearance convergence are below the design limits.
  • Normalized Analysis Method of Piled Raft Foundation Settlement in Layered Clay Foundation
    Luo Ruping, Li Zhidan, Zhu Bitang, Ding Wenyun
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1363-1372. https://doi.org/10.20174/j.JUSE.2025.04.28
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    In order to investigate the settlement characteristics of piled raft foundation in layered clayey ground, based on the practical analysis model of piled raft foundation considering the interactions of pile-raft-soil, the settlement of piled raft foundation in typical double-layer clayey ground is analyzed for an example. The influences of 11 different conditions, including the ultimate bearing capacity of the natural ground, the depth of upper and lower layers and the corresponding strength of the soil, the ultimate bearing capacity of the pile shaft and pile end, the size of the pile foundation and the configuration parameters on the settlement characteristics of the piled raft foundation are analyzed via MATLAB programs. Based on the parametric analysis results, a normalized settlement analysis model for piled raft foundation is proposed, which takes into account the influence of the safety factor of the piled raft foundation. By comparing and analyzing the on-site measured data with a series of pile raft foundation engineering examples, the reliability of the proposed normalized model for pile raft foundation was verified. As the design safety factor increases, the discreteness between the calculated results and values gradually decreases. The proposed normalized settlement model can provide a reference for the analysis of piled raft foundation for the engineers.
  • Calculation of Pile-Soil Stress Ratio of Cement-Soil Mixing Pile Composite Foundation and Cushion Optimization Design
    Liu Guangxiu, Dang Faning, Ma Xiaoli, Li Yugen
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1373-1383. https://doi.org/10.20174/j.JUSE.2025.04.29
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    The theoretical calculation method of pile-soil stress ratio of cement-soil mixing pile composite foundation with cushion under rigid foundation and the optimal design of cushion layer was studied. Firstly, based on the analysis of the mechanical deformation characteristics of cement-soil mixing pile composite foundation, the equivalent reinforcement area of single pile was taken as analysis unit, the distribution of pile side friction was simplified into a piecewise linear model, and the critical length of cement-soil mixing pile in composite foundation was defined from the perspective of bearing capacity. Then, based on the load transfer differential equation of the unit body, the pile-soil deformation coordination condition at the neutral plane depth, and the mechanical equilibrium relationship of the pile body at the critical pile length, a new method for calculating the pile-soil stress ratio of a cement-soil mixing pile composite foundation, considering negative friction, was established. The feasibility of the calculation method was verified by engineering examples, and the influence of cushion thickness, cushion modulus, pile diameter, pile spacing, pile-soil modulus and other factors on the pile-soil stress ratio were analyzed. The results show that: The pile-soil stress ratio decreases with the increase of cushion thickness and compression modulus of soil between piles, increases with the increase of cushion modulus, pile spacing and pile elastic modulus, and increases first and then decreases with the increase of pile diameter. The effect of pile-soil area replacement ratio on pile-soil stress ratio is not the only monotonic relationship, but is affected by the pile diameter and pile spacing. Finally, according to the design index of pile-soil stress ratio, the flexibility coefficient of cushion was obtained by inversion of this calculation method, and the thickness of cushion was optimized by combining with regional experience.
  • Field Test and Numercal Analysis of Bearing Characteristics of Super-Long Rock-Socketed Piles
    Tang Hong, Mao Binghong
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1384-1393. https://doi.org/10.20174/j.JUSE.2025.04.30
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    In order to study the influence of various factors on the bearing characteristics of super-long embedded rock piles, the bearing characteristics of ultra-long rock socketed piles is analyzed based on on-site static load tests. A three-dimensional finite element numerical model is established with FEA software and compared with the static load test to verify the feasibility of the numerical simulation; The influence of the factors, including pile length, pile diameter, embedded rock depth, pile-soil elastic modulus ratio and bedrock elastic modulus, on the bearing characteristics of the embedded rock piles is analyzed by changing the properties of the pile body and the soil body with the finite element software. The results show that: These five factors can improve the bearing capacity of super-long embedded rock piles to a certain extent, and the effects of embedded rock depth, pile-soil elastic modulus ratio, and bedrock elastic modulus on the bearing capacity of embedded rock piles should not be neglected except for the pile length and pile diameter.
  • Mechanical Behaviors of Cast-In-Place Pile in Loess Area upon Wetting Effect
    Luo Hongbo, He Xige, Miao Xiaoqin, Liu Yunlong, Jiang Shipeng
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1394-1404. https://doi.org/10.20174/j.JUSE.2025.04.31
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    In order to clarify the change mechanism of bearing properties of bored piles in wetted loess during rainfall infiltration, static load test and infiltration test of bored piles in wetted loess are carried out. The water content, cumulative wetting amount, axial force of the pile body and settlement of the top of the pile in the wetted loess around the piles were monitored in real time. The results show that: With the occurrence of wet subsidence of loess, the axial force distribution of the pile body is roughly in the shape of "D", and the location of neutral point also changes according to the different stages of wet subsidence. The increase of loess wetting deformation around the pile and the change of pile settlement at different stages during the infiltration process change the direction and size of pile-soil relative displacement, which leads to the change of bearing properties of the piles. Based on the principle of unsaturated soil mechanics, the change of matric suction is used as the key parameter to calculate the wet subsidence deformation of the soil around the pile. Considering the change of shear strength at the loess-perforated pile interface, a pile shaft friction load transfer curve model applicable to the loess-perforated pile interface is proposed. Also, the traditional load transfer method is simplified and corrected, so as to calculate the axial force and pile-side resistance change curve of the perforated piles. The experimental values are compared with the calculated values, which are in good agreement. The research results can support the design of bored piles and the evaluation of engineering properties in the region of collapsible loess under complex environmental loads.
  • Experiment and Numerical Simulation on Smoke Characteristics of Double-Fire Sources Tunnel
    Sun Jianchun, Zhang Min, Lu Xiaogang, Yang Shiyong, Zhang Xiaochun
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1405-1416. https://doi.org/10.20174/j.JUSE.2025.04.32
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    Based on the serious hazards of multiple-fire source accidents in tunnels, this paper investigates the characteristics of fire smoke in the case of double-fire source accidents in tunnels. By conducting a double-fire source scale-down test in the plain area, the effects of fire source spacing and longitudinal ventilation speed on the temperature in the tunnel vault of a double-fire source are investigated; By conducting a full-size numerical simulation with FDS software, the effects of altitude and longitudinal ventilation speed on the temperature evolution and critical velocity inside a double-fire source tunnel are investigated. The results show that: As the spacing of the double-fire source increases, the longitudinal decay of the smoke temperature rise downstream of the tunnel slows down, and the maximum temperature of the vault decreases, the longitudinal temperature decay model downstream of the double-fire source and the prediction model of the maximum temperature of the vault of the double-fire source are established. In the event of a fire at low or high altitude, longitudinal ventilation reduces the maximum temperature in the vault of a double-fire source. With the increase of altitude, the maximum temperature of the vault of the double-fire source increases, the critical wind speed of the double-fire source increases, while the maximum temperature at the characteristic height of the human eye of the double-fire source decreases. The empirical formula of the critical velocity of the double-fire source at different altitudes is established.
  • Model Experimental Study on the Dust Transport Characteristics of Construction Ventilation in Double-Track Railway Tunnel
    Zhang Wangqian
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1417-1424. https://doi.org/10.20174/j.JUSE.2025.04.33
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    Using similar proportional model test, the effects of different dust particle size, initial dust volume and return air rate on dust transport characteristics are explored based on the standard cross section of a long double-track railway tunnel. The results show that: With the increase of dust particle size, the peak dust concentration in the section shows a linear decrease, and the larger the dust diameter is, the more obvious the diffusion effect is driven by the wind flow field. The effect of initial dust concentration on dust transport mainly shows that with the increase of the concentration field. The peak concentration rises, the dust spreading rate decreases, and the diffusion effect by wind flow is relatively small. With the increase in longitudinal wind speed, the peak concentration in each monitoring section decreases, and the peak time appears earlier. Meanwhile, the reduction rate of section concentration is enhanced to a certain extent. The hysteresis effect of dolly on dust diffusion is positively correlated with the initial dust concentration of dust particle size, and negatively correlated with the longitudinal return wind speed; the peak dust concentration can be effectively reduced when the return wind speed of engineering operation section is 1.0 m/s.
  • Model Experimental Study on the Cooling Measures and Effects during Construction of High Geothermal Tunnel
    Liang Liang
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1425-1435. https://doi.org/10.20174/j.JUSE.2025.04.34
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    In order to study the cooling measures and effects in the construction environment of high geothermal tunnels and to explore their characteristics and determine the design parameters, a self-made model experimental platform was used, based on the Baoanying tunnel project in the Chengdu-Kunming railway. This platform deeply analyzed the influence of different tunnel return air velocities, fresh air initial temperatures, and different spray flows on the temperature field distribution in different cross-section positions in high ground temperature tunnels. The results show that wind speed mainly affects the initial cooling time of each tunnel section, while wind temperature mainly affects the cooling efficiency of the tunnel section. Both wind speed and wind temperature have a significant influence on the cooling rate. As the tunnel section is farther away from the tunnel face, the cooling rate and cooling efficiency will be greatly attenuated; The spray flow rate at different positions has different effects on the cooling rate, and the order of cooling efficiency from high to low is: part of tunnel basin behind nozzle > part of tunnel basin in front of air duct outlet > tunnel basin in between.
  • Research on the Influences of Train Vibration on the Segment of Shield Tunnel after Connecting Bolt Failure
    Mao Sheng
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1436-1444. https://doi.org/10.20174/j.JUSE.2025.04.35
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    Through the establishment of the three-dimensional tunnel-stratum-internal structure model, the effect of different bolt failures on the stress and deformation of the segment structure are analyzed. Furthermore, the sensitivity of the bolt failure to the ground conditions and lining type are discussed. The results show that: (1) The stress-displacement response of the tube segment is elastic under the train vibration load. The position of the vault is not synchronized with the waveforms of other parts. The principal stress fluctuation of the tube segment caused by train vibration is in the arch waist and arch. The bottom is most obvious. The maximum principal stress after superposition appears at the bottom of the arch. The displacement response of the segment occurs mainly in the vertical direction, and the maximum settlement occurs at the bottom of the arch under the influence of train vibration. (2)When single-layer lining is used under the domestic soft soil layer, bolt failure can reduce the stress of the segment, but it will increase the vertical settlement of the segment and the staggered opening of the segment. Considering that the segment stress is far from failure and the steel bars are often designed as over-reinforced, it is recommended to use connecting bolts in soft soil layers. (3) In the soft and hard composite soil layer, the segment stress and the deformation at the joints are reduced to a certain extent. The vertical deformation reduction effect on the segment is significant, and the influence of bolt failure is further weakened. The rationality of not using connecting bolts in shield tunnels with good geological conditions in Nordic and other regions during operation is verified. (4) The use of double-layer lining has little effect on the force of the segment, which can reduce the vertical deformation of the segment to a certain extent, but can greatly reduce the opening and staggering of the joint when the bolt fails. From the perspective of structural safety and stability, a inner lining can be applied to projects with higher safety requirements.
  • Study on the Instability Mechanism of Reinforced Concrete Pipes in Soft Soil Stratum
    Ji Fuquan, Feng Xin, Yang Zhao, Chen Peishuai, Cui Xuhui
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1445-1454. https://doi.org/10.20174/j.JUSE.2025.04.36
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    In order to explore the stability failure mechanism of reinforced concrete pipes during jacking in soft soil stratum and the influencing laws of various factors, a method for determining the pipe stability failure considering the pipe-soil contact state, pipe deflection, jacking force, buoyancy and slurry pressure is proposed through theoretical analysis. The applicability of this method was verified based on the field test data of the Tangxun Lake pipe jacking project in Wuhan. In addition, the influencing regularities of geological parameters, jacking force, pipe deflection angle and slurry pressure on the pipe stability failure were investigated through numerical simulation. The results show that: (1) The pipe-soil contact state and pipe deflection have a significant effect on the ultimate stress and additional stress of the soil around the pipes. (2) The stability failure of the pipe can be effectively determined by calculating the initial stress, additional stress and ultimate stress of the soil around the pipe. (3) The most obvious phenomenon of the pipe stability failure is the increase in the pipe displacement, and the pipe at the maximum axial deviation can be selected for stability failure analysis in actual construction. (4) In soft soil stratum, slurry pressure, buoyancy, pipe deflection, and jacking force are the main factors causing the stability failure of the pipe, and the above parameters should be monitored and controlled during construction.
  • Study on the Applicability of Coating Method to Prevent Crystallization of Tunnel Central Drainage Ditch
    Zhang Yonggang
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1455-1462. https://doi.org/10.20174/j.JUSE.2025.04.37
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    In recent years, the crystallization of drainage system has appeared in many highway tunnels around the world, which not only affects the drainage function of tunnels, but also threatens the operation safety of tunnels. In view of this problem, a lot of research has been carried out on its formation mechanism and main influencing factors by scholars. However, due to the concealment of the drainage system, effective prevention and control measures have not yet been formed. From the perspective of preventing crystallization, indoor experiments were carried out to simulate the crystallization rules of four coatings and one scale inhibitor under five working conditions. The results show that: The amount of crystallization on the surface of the blank control group is the most, and the rate of crystal formation is faster. Different types of coatings have a certain effect on preventing crystallization. The scale inhibition effect of the coatings is as follows: superhydrophobic coating > fluorocarbon coating > waterborne epoxy coating > oily epoxy coating. The superhydrophobic coating has the highest scale inhibition efficiency, up to 31.9%. The scale inhibitor has a significant effect on preventing crystallization in the early stage, but with the increase of the test cycle, the scale inhibition efficiency gradually decreases.
  • Enhancing the Spatial Visual Brightness of Multi-Stories Underground Space by Optical Material Integrated Daylighting Wells
    Bian Yu, Zhao Yonghui, Feng Liming, Pang Yuzhi, Yu Daxing
    Chinese Journal of Underground Space and Engineering. 2025, 21(4): 1463-1470. https://doi.org/10.20174/j.JUSE.2025.04.38
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    The purpose of this study is to solve the problems of underground space lighting, such as insufficient lighting in deep areas and the insufficient use of daylight, and to propose a new type of underground space daylighting wells integrating optical materials to optimize the distribution of daylight in the underground space, thereby enhancing the perceived brightness for users in underground levels. After theoretical analysis, an optical material with light deflection is designed. And the performance of three different daylighting well designs integrating this optical material was compared with conventional wells and optimized accordingly. The experiments were carried out in an artificial sky platform by means of a scaled-down physical model, using Lav,B40 (average luminance of horizontal band width 40° centered on the normal view height) as the evaluation index of spatial visual brightness, and comparing the light-gathering effects of different forms of daylighting wells with the spatial visual brightness data. The results show that: The integrated optical material improves the spatial visual brightness of underground space by 40%~60% compared with the through-well, in which the inverted cone daylighting wells in the first basement level have a better collection effect, and in the second and third basement levels away from the skylight, the closer the plane size of the daylighting wells is to the size of the skylight, the better the dispersion of the daylight is. It is concluded that: (1) daylighting wells integrating optical materials have significant lighting optimization effect in underground space, which can provide users with circadian rhythm sensation and reduce the energy consumption of artificial lighting; (2) the form of daylighting wells has a greater impact on the optimization of the light environment in underground space, that is preferable to adopt inverted cone form in the basement floor close to skylights, and it is preferable to use daylighting wells near skylight dimensions in the basement floor far away from skylights.
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