20 June 2025, Volume 21 Issue 3
    

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  • Zhou Zhicai
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 739-747. https://doi.org/10.20174/j.JUSE.2025.03.01
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    The construction of utility tunnel plays a significant role in improving the resilience of urban lifelines and intensively utilizing urban three-dimensional space. It is an important infrastructure that serves the city's high-quality development. Based on the practical needs of urban utility tunnel planning and construction, the analytic hierarchy process and expert consultation method were used to clarify the assignment rules and weights of 15 key influencing factors, and build a suitability evaluation system for urban utility tunnel planning and construction. With the help of the spatial analysis and statistical functions of GIS, the suitability of the utility tunnel in the study area was evaluated more scientifically and objectively. The construction scale was optimized using the construction rate of the utility tunnel and the density of the urban utility tunnel construction indicators, reaching a balance of the coverage of the utility tunnel construction with the expenditure on infrastructure construction. This study provides support for regional utility tunnel planning schemes.
  • Tang Yao, Fan Jiancai
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 748-758. https://doi.org/10.20174/j.JUSE.2025.03.02
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    The development of underground transportation based on TOD mode drives the process of underground development of surrounding commercial space, and the connectivity between underground transportation and commercial space has become a link that cannot be ignored. Based on the place theory, this study highly summarizes the spatial composition of the two connected Spaces of Shanghai People's Square Station and Xujiahui Station. Considering the spatial structure and place spirit, field investigation and questionnaire distribution are conducted. Moreover, exploratory factor analysis and SPSS algorithm software are used to find out the strongly related reasons affecting the connectivity quality. By quantifying the subjective factors of pedestrians, five influencing factors are summarized, namely, central place and direction, regional division and shaping, spatial theme culture, spatial interaction, public safety and management, and corresponding optimization method are proposed to provide some reference for the design of underground connected space.
  • Zou Jinfeng, Wu Qinhua
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 759-773. https://doi.org/10.20174/j.JUSE.2025.03.03
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    In order to investigate the mechanical state of pre-stressed anchors for tunnel support under water-rich ground conditions, an elastoplastic analysis of the tunnel surrounding rock was carried out based on the three-dimensional Hoek-Brown failure criterion, considering the effects of hydraulic coupling and strain softening of the surrounding rock, and considering the pre-stressed anchors as a passive anchor model with anchor pads and non-zero strain at both ends. The numerical calculation method of shear stress distribution and end prestress of prestressing anchor was established by using bond-slip theory. Through the comparison and analysis of the calculation results of relevant engineering cases, the rationality of the calculation method in this study is verified. At the same time, parametric analysis is carried out on the change law of surrounding rock stress and displacement under the influence of different factors by relying on the actual project. The results show that: The maximum values of anchor shaft force, tunnel surface force, and anchor neutral point are well-fitted with the monitoring values of the selected engineering cases. When the anchor shear stress reaches the peak stress of the tunnel wall, the decoupling phenomenon occurs between the anchor and the surrounding rock near the tunnel wall. The actual project reflects that the method of this study can effectively solve the design calculation problem of pre-stressed anchors in the deep tunnel, and the pre-stressed anchors can effectively reduce the surrounding rock deformation after installation. Compared with the passive anchor, its support effect is better. The study results can theoretical guidance for the design of the deep tunnel support under similar engineering geological conditions.
  • Wu Zusong, Zeng Qiang
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 774-779. https://doi.org/10.20174/j.JUSE.2025.03.04
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    Aiming at the existing blasting seismic wave stress calculation formula mainly considers the source parameters and ignores the influence of the propagation medium, using the method of magnitude analysis, the blasting seismic wave stress equation of the rock body is deduced, and the theoretical calculation model of the critical vibration velocity of the rock body yielding is established by combining with the DP yielding criterion. The results show that: The magnitude of positive stress is positively correlated with the vibration velocity and the mechanical parameters of the medium. When the vibration velocity is certain, the smaller the elastic modulus is, the more obvious the change of positive stress in the medium is; when the elastic modulus is certain, the larger the vibration velocity is, the more obvious the change of positive stress in the medium is; compared with the empirical formulas, the theoretical model of the positive stress in blast seismic wave has a wider scope of application, and it can simulate the propagation of seismic waves in different medium materials and seismic wave conditions more accurately; based on the DP yield criterion, the blast seismic wave stress equation is adopted Based on the DP yield criterion, the blasting seismic wave stress equation is used to accurately predict the critical vibration velocity of different media materials when they reach yield.
  • Zhou Xiangyun, Hu Shixiang, Zhuo Weiding, Sun De'an, Xu Xun
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 780-791. https://doi.org/10.20174/j.JUSE.2025.03.05
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    The spatiotemporal distribution of temperature fields serves as a critical basis for the thermal design and safety assessment of high-level radioactive waste repositories. Based on the multi-barrier concept of disposal systems, a two-dimensional axisymmetric three-layer thermal model was developed. The governing heat transfer equations were solved using the Laplace transform, Fourier transform, and their corresponding inverse transforms, yielding semi-analytical expressions for temperature distributions in the bentonite block layer, pellet layer, and host rock. Comparative analyses with numerical simulations and two-layer analytical solutions demonstrated the validity and superior capability of the three-layer model in addressing complex heat conduction phenomena. Utilizing the derived semi-analytical solutions, parametric studies were conducted to investigate the influence of geometric and thermal properties on buffer layer temperature maxima. Furthermore, the model was applied to determine optimal disposal container spacing for various nuclear waste types and to simulate the thermal response in Sweden's prototype repository. The results indicate: (1) inclusion of the bentonite pellet layer increases buffer peak temperature by 14.84 ℃ compared to its exclusion; (2) pellet layer thickness significantly affects temperature maxima due to its relatively low thermal conductivity; (3) buffer temperature variations become negligible when container spacing exceeds 20 m; (4) the proposed solution accurately predicts thermal behavior in prototype repository heating experiments.
  • Li Tao, Zhang Xinghua
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 792-799. https://doi.org/10.20174/j.JUSE.2025.03.06
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    The macro and microscopic properties of methane hydrate-bearing soils (MHBS) subjected to hydrate dissociation control the reservoir stability in methane hydrate exploration engineering. By randomly filling hydrate particles into the silty skeleton and installing bond contact model at silt-hydrate and hydrate-hydrate contacts, a discrete element model for MHBS was established. In the DEM model, van der Waals forces between fine particles and the effect of temperature-back pressure condition on the bond strength are considered. Considering the influence of temperature-back pressure parameter on the rate of hydrate dissociation. Simulation of hydrate dissociation using depressurization under one-dimensional stress condition is carried out. The results show that: The skeleton void ratio gradually decreases while the deviator strain gradually increases under hydrate dissociation, with some deformation recovered in the stress recovery stage. In terms of fabric, the degree of anisotropy of the contact normal of silt-silt contacts gradually decreases while those of silt-hydrate and hydrate-hydrate contacts increase throughout hydrate dissociation. In terms of stress-bearing, the hydrate is efficient to bear the mean stress rather than the deviator stress. When the hydrate saturation degree decreases to 4%~6%, the hydrate bearing ratio on the mean stress is about 16%, while the hydrate bearing ratio on the deviator stress is about 1%, indicating different effects of hydrate dissociation on the soil shear strength and the soil volumetric yielding.
  • Liu Hangyu, Gu Xiaoqiang, Hu Jing
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 800-804. https://doi.org/10.20174/j.JUSE.2025.03.07
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    The hardening strain model with small strain (HSS) can reflect the high nonlinearity of soil modulus at small strain range, which has been widely applied in deformation calculations during pit excavations under complex geological conditions. The appropriate values of model parameters have a significant impact on the computational results. However, the current recommended parameter values have a large range of fluctuations, which brings inconvenience to engineering applications. Therefore, further research is needed on the parameter values of the model. This study analyzes the data characteristics of existing HSS model parameters and introduces the artificial neural network method (ANN). The empirical relationships between the modulus parameters of the HSS model for Shanghai soils and factors such as the initial pore ratio (e) and oedometer modulus (Es1-2) are established. This allows for the rapid determination of HSS model modulus parameters based on survey reports. Compared with the recommended values, the proposed method for determining the HSS model modulus parameters is closer to the measured value. The study results can provide references for projects in Shanghai.
  • Ye Youlin ,Qian Zijie, Lu Zhiwang, Shang Shijian, Niu Ben
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 805-815. https://doi.org/10.20174/j.JUSE.2025.03.08
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    In order to better evaluate the passive instability failure mode of shallow shield tunnel face in sandy soil stratum, the existing three-dimensional calculation model is improved to make the failure area closer to the real soil failure contour. Considering the friction between the upper and lower blocks, the limit support pressure calculation formula is established by using the limit equilibrium method. The finite difference software FLAC3D is used to construct the numerical model, and the variation law and failure mode of the passive failure support force of the tunnel face are analyzed. The limit support pressure solution obtained by the theoretical model is compared with the solution obtained by numerical simulation and the existing passive failure theoretical model to verify the reliability of the model. The results show that: The proposed theoretical calculation model can meet the limit calculation of passive instability of the tunnel face. The limit equilibrium method is used to calculate the friction between the upper and lower blocks of the model, and it is more reasonable to consider the static friction force. The optimal solution of the logarithmic spiral angle is affected by the internal friction angle. When the internal friction angle increases, the optimal solution of α will become smaller. The passive limit support pressure of the tunnel face of the shallow shield tunnel increases with the increase of the internal friction angle of the soil and decreases with the increase of the tunnel diameter.
  • Ye Junneng, Ban Yongting, Ye Xiaowei, Zhang Xiaolong, Song Ke
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 816-823. https://doi.org/10.20174/j.JUSE.2025.03.09
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    Shield tunneling method is widely used in subway tunnel construction because of its advantages such as not affecting ground traffic, high mechanization degree and short construction period. However, the problems of cracking and damage caused by uneven rising of segments are often encountered in the construction process of shield method, which affects the normal use of tunnel. However, the research on the mechanism and theoretical calculation of shield tunnel segment floating is relatively rare. In this paper, the floating mechanism of segments in the initial floating stage of shield tunnel is analyzed deeply, and the corresponding theoretical calculation formulas of upward buoyancy/anti-buoyancy and buoyancy are proposed. The theoretical calculation results are compared and analyzed with engineering examples. The results show that: The initial floating of the segment can be divided into two stages: rapid rising and slow rising, in which the rising amount of the rapid rising stage accounts for about 80%~90% of the total rising amount. The theoretical calculation value of the total floating amount is greater than the monitoring value, but the calculation error of the floating amount per ring is relatively stable, the theoretical calculation formula presented in this paper can provide reference for the calculation of the floating amount of the actual segment.
  • Wang Yunxiao, Liu Yuanxue, Bai Yunshan, Yao Weilai, Mu Rui
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 824-834. https://doi.org/10.20174/j.JUSE.2025.03.10
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    To enhance the resilient protection of underground engineering, real-time monitoring of cracks in the whole engineering is of great significance. In the present paper, a real-time localization method for structural cracking is proposed. Through the method of transfer learning, the picking model of structural cracking direct acoustic wave and reflected acoustic wave was established after training the deep learning model of seismic phase-pick with 1 847 sets of training data. Automatic recognition and extraction of cracking acoustic signals is realized in this way. To solve the problem that the localization accuracy of broadband multi-signal classification (MUSIC) algorithm is reduced due to spatial aliasing, the equation between the direction of sound source and inter channel phase difference is established through the relationship of time delay in spatial and frequency domain. The narrow bands with two specified positive phase differences are used to calculate spatial spectral in localization after further analysis of the relationship between phase difference and spatial aliasing. The in-situ lining cracking simulation test verifies that the improved algorithm effectively reduces the spatial aliasing and improves the positioning accuracy. The average error distance between the estimated cracking point and the actual cracking point is 0.05 m. The monitoring of the extending direction and length of crack can be realized after connecting each cracking point, which can meet the engineering needs.
  • Zai Penghui, Dong Zhuo, Wu Junjie, Yuan Ruifu, Liu Jinrong
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 835-844. https://doi.org/10.20174/j.JUSE.2025.03.11
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    Taking green medium sandstone as the research object, indoor experiment, numerical simulation and theoretical analysis methods were comprehensively used to study the initiation and propagation laws of single-hole and multi-hole prefabricated cracks in rocks under mechanical expansion cracking. The results show that: The crack initiation pressure is reduced by more than 53% compared with that of the unprepared crack specimens, and the theoretical model coincides well with the results of numerical simulation and indoor tests; the penetration pressure of cracks under multi-hole conditions increases with the increase of hole spacing and peripheral pressure, and its reduction rate gradually decreases with the increase of peripheral pressure while it is not affected by the hole spacing; the crack initiation pressure gradually rises with the increase of peripheral pressure, and the hole spacing has no effect on it. The multi-hole mechanical expansion crack extension process can be divided into three basic stages: crack initiation, crack propagation and penetration, and the above expansion process is caused by mutual interference of peak tensile stresses generated by neighboring boreholes. The results of the study are of guiding significance to the engineering of hydraulic fracturing, expansion agent fracturing and directional blasting fracturing of hard roof slabs in coal mines.
  • Zhang Jiafan, Che Hubin, Zhang Huimei, Yuan Chao, Liu Xiaoyu
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 845-853. https://doi.org/10.20174/j.JUSE.2025.03.12
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    Different fracture penetrations exist widely in rock mass, but the research on penetration is rare at present. In order to study the deformation and failure behavior of rock mass with different fracture penetrations, triaxial compression tests were carried out on red sandstone with fracture penetrations of P=0%, 25%, 50%, 75%, and 100%, and PFC numerical simulation was conducted. The results show that: The greater the degree of fracture penetration, the smaller the strength of the rock sample, and the more obvious the plastic deformation section of the stress-strain curve. For intact rock samples, confining pressure will change the failure mode of rock samples, from tensile failure to shear failure. For fractured rock samples, the greater the penetration, the more complex the crack when the rock sample is destroyed. Under different confining pressures, the cracks of the same fractured rock sample are different when they are destroyed, but the overall failure type is unchanged. PFC3D shows that when the complete rock sample is destroyed, the tensile crack first appears at the loading point, while the fractured rock sample first appears at the loading point and the prefabricated crack. Acoustic emission ringing count has a stationary period, a slow increase period, and a surge period. The macroscopic failure of the rock sample will occur in the strain-softening stage. The results in this paper can provide a basis for studying the fracture evolution law of rock mass in engineering.
  • Lei Jiang, Chen Weizhong, Yu Hongdan, Li Fanfan, He Linkai
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 854-861. https://doi.org/10.20174/j.JUSE.2025.03.13
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    Taking clay rock as the research object, scanning electron microscope tests have been carried out under the conditions of resaturation and in-situ stress, and three-dimensional porosity was used to quantitatively analyze the structural changes. The microstructure characteristics and macro and micro mechanism of self-sealing were studied. The results show that: Under the condition of no external force, the self-sealing is mainly characterized by hydration-swelling and anisotropy. The vertical bedding and parallel bedding are mainly characterized by granular unit disintegration and lamellar structure spalling, respectively. Clay particles are constantly swelling, spalling, caving and stacking to fill the void in a loose state. The degree of self-sealing is positively correlated with the resaturation time. Under the action of stress and heating, the self-sealing is dominated by compression and compaction, the particles are fine, and the structure changes from loose to agglomeration state. The mechanism of self-sealing is related to hydrochemistry and volume strain. The content of expansive clay minerals and long resaturation time are conducive to the self-sealing of fractures. Stress, heating and long-term creep lead to volume compression, structure becomes dense and promotes the self-sealing of fractures, whereas volume expansion inhibits it. The research results can provide surpport for geological site selection and safety assessment of clay rock high-level radioactive waste.
  • Wei Li, Chang Xinxin, Chai Shouxi, Wei Xuetao
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 862-870. https://doi.org/10.20174/j.JUSE.2025.03.14
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    Salt crystallization causes a decrease in compressive performance and microstructral damage of lime cured sulfate soil. A series of tests, including unconfined compressive strength test, SEM observation, and EDS test, were conducted on lime stabilized soil with a salt content of 0.3% to 5% to study the relationships between salt content, compressive strength, and microstructure indicators. The results show that: (1) The compressive strength of the soil first increases and then decreases with the increase of salt content, and the strength of stabilized soil with salt content of 1.5% reaches its maximum. (2) When the salt content is less than 1.5%, the shape of soil particles tends to be an ellipse, and the soil structure becomes compact. After the salt content is more than 1.5%, the shape of soil particles tends to be a circle, leading to the instability of the soil structure. (3) For soil with low salt content, some salt particles fill the soil pores and play a role as soil skeleton, improving the strength of the soil. But the salt content is more than 1.5%, and salt swelling plays a dominant role, weakening the structural stability of the soil. Therefore, lime can be used to stabilize the soil with a salt content less than 1.5% to meet the requirements of oil and gas pipeline foundation engineering. Saline soil with a salt content above 1.5% cannot be directly used in engineering, and special research should be conducted.
  • Wang Shengfu, Zhang Xiangrong, Liu Guangyan, Ji Xiaolei, Li Xianghui
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 871-881. https://doi.org/10.20174/j.JUSE.2025.03.15
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    In the pursuit of understanding the shear strength variations of red clay in three states, i.e., normal, frozen, and freeze-thaw, during the implementation of the artificial permafrost method, a low-temperature MTS triaxial testing system is utilized. Triaxial shear experiments on remolded red clay are conducted under varying initial moisture levels, freezing temperatures, and confining pressures. The aim is to explore the triaxial shear strength characteristics of red clay in different freeze-thaw states and elucidate the variations in shear strength throughout the entire artificial freeze-thaw process under diverse conditions. The results show that: (1) In the frozen state, stress-strain curves of red clay consistently exhibit strain hardening. With increased confining pressure at normal temperature and post freeze-thaw cycles, stress-strain curves transition from strain softening to strain hardening, particularly evident under a high confining pressure of 800 kPa. (2) In the frozen state, the shear strength, cohesion, and internal friction angle of red clay exhibit an initial increase followed by a decrease with rising moisture content, reaching a peak at 30%. Throughout the process from normal temperature to freezing and then to freeze-thaw, the shear strength of red clay in the frozen state average increase is 10.5 times, while post freeze-thaw shear strength is lower than that at normal temperature. (3) Lower freezing temperatures correspond to higher shear strength in the frozen state of red clay. After freeze-thaw, cohesion, internal friction angle, and shear strength of red clay decrease with decreasing freezing temperatures. The study results can provide theoretical and technical insights for the construction of artificial permafrost in red clay formations.
  • Wang Sui, Fang Yuanming, Zhou Zidong, Zhao Peng, Pan Shilei
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 882-890. https://doi.org/10.20174/j.JUSE.2025.03.16
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    Based on the GDS dynamic triaxial test system, a series of dynamic characteristic tests were conducted on remolded sand-mixed soft clay with varying sand contents to systematically investigate the influence of loading frequency and sand content on plastic cumulative deformation, dynamic shear modulus, and damping ratio. The results indicate that: The development of plastic cumulative deformation exhibits a rapid initial phase followed by a decelerating phase. As the number of vibrations increases, the densification of the soil skeleton inhibits the rate of plastic deformation, while higher sand content significantly amplifies the cumulative deformation. Regardless of whether the loading frequency was below or above 1.0 Hz, the dynamic shear modulus displayed a decreasing trend with increasing sand content. For every 10% increase in sand content, the modulus reduction reached 12%~18%. During vibration, the pore pressure coefficient A continuously increased, intensifying the shear contraction effect and deteriorating soil stability. Higher sand content exacerbated this phenomenon, resulting in distinct inflection points in the dynamic shear modulus and damping ratio curves (critical sand content approximately 20%). In summary, sand content significantly influences the dynamic response mechanisms of sand-mixed soft clay by altering the soil skeleton structure and drainage pathways, providing critical insights for constructing dynamic constitutive models and guiding seismic engineering design.
  • He Jia, Qu Siyuan, Gao Yufeng, Ji Jiafeng
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 891-899. https://doi.org/10.20174/j.JUSE.2025.03.17
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    Soybean-urease induced calcium carbonate precipitation (SICP) is an effective and environmentally friendly method for soil solidification. However, multiple treatments are required to achieve the desired strength, resulting in low treatment efficiency and long time consuption. The sand column samples were treated once by adding additives such as non-fat powdered milk and magnesium chloride based on the SICP treatment technique. The unconfined compressive strength (UCS) in the saturated state, calcium carbonate content and conversion rate of the samples were tested. The results showed that: Adding non-fat powdered milk had the best effect. Under saturated state, the maximum strength after one treatment could reach about 0.6 MPa, which was about 70% higher than the SICP treatment without additives (0.35 MPa). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed that: More spherical calcite crystals could be formed after adding non-fat powdered milk. Organic matter such as non-fat powdered milk would remain on the surface of the crystal particles, further improving the bonding and bridging between sand particles.
  • Ma Lina, Luo Wei, Hu Junqing, Ding Xiaogang, Guo Jinran
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 900-909. https://doi.org/10.20174/j.JUSE.2025.03.18
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    Modifying the expansion characteristics of mudstone filler is a feasible way to reduce the arch deformation on mudstone roadbeds. Through the free expansion rate test, no-load and loaded expansion rate test on the modified mudstone filler with NaCl solution, the response rule between the expansion rate of mudstone filler and the concentration of NaCl solution and the mixing ratio of NaCl solution was investigated, and the microstructure of mudstone filler before and after the modification was analyzed by nuclear magnetic resonance (NMR) test. The results show that: (1) The modified mudstone filler with NaCl solution concentration of 12% and doping ratio of 14%, the unloaded expansion rate and loaded expansion rate decreased by 10.651% and 75.439%, respectively, compared with that of the unimproved mudstone filler; (2) With the increase of NaCl solution concentration, the percentage of small pores of mudstone filler showed a tendency of increasing and then decreasing; (3) Under the same NaCl solution concentration, the percentage of small pores of mudstone filler also showed a tendency of increasing and then decreasing with the increase of NaCl solution mixing ratio; (4) NaCl solution concentration and small pores of mudstone filler jointly affect the intergranular stress of mudstone filler and thus change its expansion.
  • Guo Yongcheng, Wang Shunan, Li Jianlin, Hu Peng, Wang Xingxia
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 910-916. https://doi.org/10.20174/j.JUSE.2025.03.19
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    Rock mass in the water-level fluctuation zone of bank slope of the Three Gorges Reservoir area has been saturated for a long time during the process of water level rise and fall. In order to study the deformation characteristics of the internal rock mass, the rock mass on bank slope of the reservoir is selected, standard rock samples are made according to relevant regulations, and TOP INDUSTRIE multi-functional rock triaxial test system is used. Creep test of saturated sandstone has been carried out under three states: no water pressure, with water pressure and circulating water pressure. The results show that: (1) The creep deformation of saturated sandstone is the largest in the state of circulating water pressure, the next in the state of water pressure, and the smallest in the state of no water pressure. (2) There is a positive correlation between steady state creep rate and creep deformation of saturated sandstone. (3) The influence of circulating water pressure on the circumferential deformation of saturated sandstone is greater than that on the axial deformation. In the stage of failure stress grade, the effect of circulating water pressure on the circumferential deformation of saturated sandstone is obvious. (4) The cyclic water pressure greatly reduces the long-term strength of saturated sandstone, and the saturated sandstone under the cyclic water pressure is the first to be destroyed.
  • Zhang Jiabing, Yang Zongquan, Du Ronghuan, Xiang Xu, Chen Yiling
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 917-928. https://doi.org/10.20174/j.JUSE.2025.03.20
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    To study the influence of transverse isotropic creep characteristics of layered phyllite on the deformation characteristics of tunnel lining structures, uniaxial compression creep tests were conducted to analyze the creep characteristics of phyllite with different bedding angles. Based on existing viscoelastic plastic damage creep models, a transverse isotropic creep damage constitutive model of phyllite was constructed. Then, the creep damage constitutive model was embedded into the FLAC3D numerical model to analyze the deformation characteristics of tunnel surrounding rock and support structures with different bedding angles. The results indicate that: As the dip angle of the bedding increases, the cumulative creep deformation and creep time during the stable creep stage of layered phyllite show a trend of first decreasing and then increasing. When the dip angle of the bedding is 0°, the maximum horizontal displacement of the surrounding rock occurs at the arch foot, exhibiting an approximately symmetrical deformation characteristic; When the bedding angle is 22.5°, 45°, and 67.5°, as the bedding angle increases, the maximum horizontal displacement position of the surrounding rock gradually deviates from the left and right walls, and the deviation direction is parallel or perpendicular to the bedding plane; The vertical creep deformation of the surrounding rock is basically consistent with the dip angle direction of the bedding, and there is a settlement trend above the surrounding rock along the dip angle direction of the bedding, while there is a uplift trend below. When the dip angle of the bedding is 90°, the maximum horizontal displacement of the surrounding rock reaches its maximum value at the arch foot, approximately 77 mm; The maximum vertical settlement and uplift positions of the surrounding rock are located at the arch crown and inverted arch, respectively, at 184 mm and 159 mm. The deformation of the surrounding rock support structure shows significant transverse isotropic changes.
  • You Zexi, Zhao Dazhou
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 929-939. https://doi.org/10.20174/j.JUSE.2025.03.21
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    Through the establishment of a nonlinear Nishihara rheological model reflecting the whole process of rock creep, the effects of changes in stress conditions and internal water pressure on the long-term mechanical characteristics of segment lining in a pressure water conveyance tunnel project located in soft rock were studied. The results show that: (1) The radial deformation of segment lining caused by the rheology of surrounding rock increases gradually with the increase of tunnel buried depth. The greater the difference between the initial horizontal and vertical stress values in surrounding rock, the greater the extreme value of radial deformation of segment lining caused by the rheology of surrounding rock. The greater the stress release rate of the surrounding rock, the greater the radial deformation of segment lining caused by the rheology of the surrounding rock. (2) After considering the rheological effect of surrounding rock, the distribution pattern of lining internal force along the ring circumference is basically similar to that of the initial stage, but the values are all changed from the initial stage, among which, the values of axial force are all increased from the initial stage, and after 100 years of project operation, the axial force growth rates of the segment lining for each scheme are between 25.6% and 112.4%, and the average annual growth of the average value of the axial force is between 50 kN/a and 82 kN/a, the extreme value of bending moment is also increased from the initial stage, and its average annual growth is positively correlated with the tunnel buried depth, and the closer the lateral pressure coefficient of surrounding rock is to 1.0, the smaller the average annual increase in bending moment extreme value is. (3) After considering the rheological effect of surrounding rock, the interaction force between segment lining and surrounding rock increases with time, but the extent of increase decreases year by year, and the stress on the lining structure also tends to stabilize gradually. The average annual increase of the interaction force between segment lining and surrounding rock increases with the tunnel buried depth, lateral pressure coefficient, or stress release rate. (4) The differences in the effects of surrounding rock rheology on the long-term stress of segment lining at different internal water pressures are not significant.
  • Sun Guowen, Huang Gun, Huang Xinyu, Liang Qinming, Lu Yu
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 940-949. https://doi.org/10.20174/j.JUSE.2025.03.22
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    The strength of fractured rock significantly affects the safety and stability of underground engineering construction projects. To gain a deeper understanding of the strength and energy evolution characteristics of fractured rock, this paper carries out an experimental study on the strength of sandstones with different inclination angles under true triaxial stress conditions. The experimental results show that: With the change of the fissure inclination angle (α), the initiation stress has a small change under the condition of α of 15°~45°, and shows a rapid increase under the condition of α greater than 45° (60°,75°,90°). The damage stress and peak stress in general show a trend of first decrease and then increase. According to the calculation results of the energy theory: With the increase of α, the total strain energy, elastic strain energy and dissipative strain energy of the specimen at the time of damage show a trend of decreasing and then increasing, which has a good correspondence with the peak strength of the specimen. The research results can provide theoretical reference for the stability assessment of fissured rock engineering.
  • Feng Jie, Zhong Zhibin, Lü Lei, Wei Xingcan, Chen Xu
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 950-958. https://doi.org/10.20174/j.JUSE.2025.03.23
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    Understanding the deformation characteristics of soft and fractured rock masses is crucial for the rational design and safe construction of underground engineering projects. Based on the diversion tunnel project of the Guzhen Hydropower Station, where undisturbed rock samples were collected to conduct passive triaxial compression tests. Deformation curves of the soft fractured rock mass in the tunnel site area under graded loading were obtained. The study analyzed the time-dependent deformation characteristics using both empirical rheological models and the viscoelastic rheological model proposed by Sun Guangzhong. The results indicate that: (1) Under passive triaxial compression, the soft fractured rock mass exhibits three-stage deformation characteristics, including initial significant compaction deformation during the loading stage, relatively elastic deformation in the middle stage, and significant plastic deformation after yielding. The stable pressure stage shows accelerated deformation under relatively small axial stresses. (2) Both rheological models can effectively describe the stable pressure deformation process of the soft fractured rock samples. The parameters of the viscoelastic rheological model vary with axial loading pressure, revealing differences in time-dependent deformation characteristics during the closure-compaction stages of internal fissures within the sample.
  • Wang Chenglong, Liu Dongsheng, Li Rongjia, Jiang Siwei, Zhang Wengang
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 959-958. https://doi.org/10.20174/j.JUSE.2025.03.24
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    Grotto temples are important historical relics, and their protection and utilization are becoming increasingly important. However, under the effect of cooling and heating for a long time, the physical and mechanical properties of the grotto rock mass will change in a certain. In this paper, the sandstone of Dazu grottoes in Chongqing was taken as the research object, and the deterioration properties of the grotto sandstone were studied through the mass, longitudinal wave velocity test, CT scanning, X-ray diffraction (XRD), X-ray fluorescence (XRF) analysis. The experimental process involves multiple conditions such as different heating-cooling cycle times, different durations of high and low temperatures, and different cooling methods. These test conditions are designed to analyze the effects of different temperature changes on the quality, longitudinal wave velocity, fracture development, mineral element composition, and internal pores of grotto sandstone. The results show that: (1) The longitudinal wave velocity of sandstone decreased after multiple heating-cooling cycles. The degree of reduction was influenced by the number cycles and the cooling methods. (2) As water cooling method was used during the experiment, soluble salt minerals in sandstone would gradually lose, which leaded to an increase in pore size of the rock sample and the formation of cracks.
  • Huang Zhi, Xia Ming, Xu Yiyong, Shi Xiaoyang, Zhang Zhiqiang
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 968-976. https://doi.org/10.20174/j.JUSE.2025.03.25
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    The clay shock method is gradually introduced as auxiliary construction in the shield tunnel that crosses the existing structures. The rheological properties of the clay shock slurry have an important influence on the backfilling injection construction of mid-shield. The hydration mechanismand rheological properties of the slurry are investigated based on the analysis of the material composition of the clay shock slurry. The RVDV-1T rotational viscometer with stepless speed regulation was used to carry out the rheological test. The applicability of the commonly used shear-thinning rheological model to characterize the rheological properties of the clay shock slurries was studied. The effects of stirring time, stirring rate, hydration time, and water-powder ratio on the rheological properties of the clay shock slurries were analyzed. The permeability and diffusion of the clay slurry in the stratum were investigated based on the actual project. The research results are as follows. (1) The Bingham model is more suitable for characterizing the rheological properties of the clay shock slurries. (2) The apparent viscosity and yield stress of clay shock slurry initially increase and then decrease with increasing stirring time and stirring rate. They also increase with increasing hydration time and decrease with increasing water-powder ratio of component A. (3) The soil in the infiltration zone is affected by the injection of the clay slurry, resulting in cohesive effect and an increase in strength. (4) The penetration diffusion distance of the slurry in the sand and round gravel strata is between 5 and 10 cm. The apparent viscosity and the yield stress of the slurry have a strong negative correlation with the diffusion distance. The permeability coefficient and the porosity of the stratum correlate positively with the diffusion distance. The research results provide reference for the engineering application of the clay shock method.
  • Chang Suling, Wang Zaiquan, Cong Yu, Wang Xiaoshan, Chao Wenwen
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 977-985. https://doi.org/10.20174/j.JUSE.2025.03.26
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    In order to study the effect of impact load on straight-wall arch cavern and surrounding rock, large-scale steel fiber reinforced concrete specimens were prepared, and a self-developed pendulum impacting system with biaxial stresses was used to carry out impact tests. A super-dynamic information acquisition system was used to record the impact force and internal strain, and digital image correlation technology was used to characterize the surface strain field. 0.6 MPa stress was applied vertically, and the height of 2 000 kg pendulum was raised to 150 mm. The results show that: The shock wave with amplitude attenuation was a typical low-frequency shock wave. Four cracks appeared in the spandrel and foot of the straight wall arch specimen, and the cracks at the spandrel were connected by a circumferential crack on the vault of the cavern. The internal peak strain and plastic strain are mainly tensile strain, compressive strain distributed near the left foot of the tunnel. The peak strain was larger in the circumferential direction, smaller in the radial and axial direction. And the plastic strain in the left spandrel was the largest. And the vault was prone to plastic deformation which can not be recovered through peak or plastic strain, but the ratios of plastic strain to peak strain in the vault were all larger. DIC strain cloud map showed that within less than 200 μs, the four cracks of spinner and foot of the sample were formed and connected, and the vertical strain changed the most, the vertical strain concentration area was consistent with the fracture morphology, the horizontal strain concentration area mainly appeared at the spinner position, and the shear strain concentration area was mainly distributed at the bend of each crack.
  • Li Mei, Han Yafeng, Luo Weibang, Liang Ninghui, Zou Huiqiong
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 986-993. https://doi.org/10.20174/j.JUSE.2025.03.27
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    To study the influence of dip angle of layered strata on the bearing characteristics and stability of tunnel-type anchorage, the geological model of tunnel-type anchorage under typical dip layered strata is generalized through case analysis. The influence of dip angle of strata on the displacement of plug body, the development of deformation and plastic zone of surrounding rock, the stress distribution of interface between the plug body and rock mass are systematically discussed by numerical analysis method. The results show that: The axial displacement of the plug body and the plastic zone of surrounding rock after failure are the largest when the rock stratum inclination is 30°, which has the greatest influence on the bearing stability of the tunnel-type anchorage. When the dip angle of rock stratum is 70°, the tunnel-type anchorage tends to rotate counterclockwise under the design load, which will lead to the existence of unconfined area on the crown of the back face of the plug body. Simultaneously, the normal stress of the interface is zero. The greater the dip angle of rock strata, the greater the fluctuation of the isoline of principal stress of surrounding rock due to the dislocation resistance between rock strata. When the dip angle of rock strata is greater than the dip angle of plug body, there will be no concentrated compression ring of plug body. The research results can provide reference for the construction design and stability control of tunnel-type anchorages in layered strata.
  • Shi Hongyan, Yang Desen, Tu Binhong
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 994-1000. https://doi.org/10.20174/j.JUSE.2025.03.28
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    Pile-anchor (-strut) retaining structure is widely used in deep foundation pit, and the elastic foundation beam method is a common method to simulate and analyze the deformation and stress changes in the construction process of this kind of support of foundation pit. However, when applying this method for analysis, it is necessary to first divide a soldier pile into several segments at the braces for each construction stage, and then re-derive the corresponding undetermined parameter equations by using the continuous conditions of displacement and force balance conditions at the junction of the segments, resulting in difficulty to form a unified calculation formula and complication in the analysis method. In order to solve the above problems, by using δ-function to represent the concentrated force of brace on the soldier pile and re-solving the deflection equation of the soldier pile, a unified calculation formula is derived which applies to pit with strutted or anchored retaining structures, arbitrary number braces and case of excavation or brace setting. The new method not only avoids the subdivision of the soldier pile, but also forms a simple and unified calculation method. The numerical results of the method proposed in this article have only slight differences from the segmented method, indicating that the method is feasible.
  • Li Zhenya, Zhao Chiheng, Zhang Cun, He Xianbin, Xi Yuqian
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1001-1010. https://doi.org/10.20174/j.JUSE.2025.03.29
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    Based on the plane strain model, the torsional vibration of a belled pile is theoretically investigated considering the construction disturbance effect. First, in view of the cross-sectional characteristics of the belled pile and the radial inhomogeneity of the surrounding soil caused by construction disturbance, the belled pile is divided into finite sections along the longitudinal direction, and the surrounding soil is divided into finite annular zones along the radial direction. The pile and soil vibration governing equations are established, respectively. Then, the soil governing equations of each zone are solved one by one through the shear complex stiffness transfer model to obtain the shear complex stiffness at the pile-soil interface, which is substituted into the governing equation of the pile. The displacement impedance function at the belled pile head is obtained in the frequency domain by virtue of the Laplace transform and impedance function transfer method, and further the amplitude-frequency response function of the twist angle at the belled pile head is obtained. Finally, the influence of bottom-expanding section parameters and construction disturbance effect on the complex impedance and amplitude-frequency of the twist angle at the pile head are analyzed in the low frequency range utilizing parametric analysis.
  • Zhang Yin, Zhang Jiping, Yang Jianjun, Yin Lidong, Su Shijie
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1011-1020. https://doi.org/10.20174/j.JUSE.2025.03.30
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    Mechanical reaming and pressure-relief can accurately reduce the stress concentration of shallow surrounding rock mass, which is of great significance to effectively solve the problem of decreasing stability of roadway surrounding rock caused by dense large-diameter drilling and pressure relief. Based on the engineering practice of the 3106 working face of a mine, ABAQUS finite element simulation software was used to compare and analyze the changes of vertical stress, displacement, and plastic zone of surrounding rock after pressure relief by large-diameter drilling and mechanical reaming, and study the mechanism of pressure relief by mechanical reaming. The results show that: After mechanical reaming, the peak stress of the surrounding rock decreases by 14.89%, the stress of the relief section decreases by 13% on average, and the peak stress shifts back by 1.25 m. The displacement at the roof of the roadway decreases by 28.67%, and the average displacement at the top, middle, and bottom of the roadway slope decreases by 98.71%, 97.27%, and 90.63%, respectively. The proportion of plastic strain zone is reduced to 12.92%, and the plastic zone between the adjacent holes around the mechanical reaming is connected to play a coupling pressure relief role. After field application, the mechanical reaming reduces the maximum microseismic energy by 63.11%, the pressure relief effect is good, and the impact risk of the working face in the test range is eliminated.
  • Xu Bingnan, Wang Quansheng, Bai Zhongkun, Wang Shutai
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1021-1029. https://doi.org/10.20174/j.JUSE.2025.03.31
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    U-shaped shield is the mobile mechanical supporting structure for foundation pit construction in China. In order to rationally design the U-shaped shield and determine the timing of reverse force demolition, the formula and method for calculating the thrust force and the timing of reverse forces removal of the U-shaped shield are analyzed and determined according to the shield construction process and its force mode. The results show that: (1) The earth pressure on both sides of the U-shaped shield is in accordance with the Rankine active Earth pressure theory, and the rationality of the hypothesis is proved by the back analysis of the field thrust test results. (2) The estimating formula for the thrust and the reverse force demolition time of the U-shaped shield design is presented. (3) Combined with concrete engineering, the paper analyzes the reasons for the deviation of the design and the measured value, in order to ensure the redundancy and simplified calculation, it is suggested that the calculation of the active earth pressure and the lateral frictional resistance should be unified according to the 1.3~ 1.5 times, and the maximum thrust force according to the calculated value 1.5 times the design, the equipment capacity is relatively economical. (4) In determining the timing of the reverse force demolition, the U-shaped shield design of the maximum thrust and pipe section and the surrounding friction resistance of the preliminary estimate, and based on the actual thrust of the correction after the determination. (5) The calculation and analysis results can be used as reference for the optimization design and construction of the U-shaped shield in the future.
  • Li Yajie, Bao Tai
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1030-1037. https://doi.org/10.20174/j.JUSE.2025.03.32
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    When slurry-assisted soil-pressure balance shield construction is used to penetrate the existing line in the karst strong development area, the poor control of shield tunneling parameters will cause large disturbance to the existing line under the coupling effect of train load and cavern, resulting in excessive settlement or uplift bulge, which seriously threatens the safety of the existing structure. The influences of karst cave and train load on stratum deformation are analyzed by numerical simulation combined with field measurement, based on the project of building a comprehensive pipe gallery under a subway line in a city. Meanwhile, the effects of different slurry-assisted shield tunnelling parameters on the ground surface and the subsidence of the existing operating subway lines are studied under the coupling of the karst cave and train load. Combined with the ground surface monitoring results show that: Under the coupling effect of train load and karst cave, increasing the synchronous grouting pressure and the face grouting pressure appropriately can effectively control the deformation of the formation. The conclusion of the study can provide a reference for the future slurry-assisted shield structure under the existing line in karst area.
  • Xiao Shihui, Cao Xiong, Li Weipeng, Lin Binbin, Li Xiaogang
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1038-1049. https://doi.org/10.20174/j.JUSE.2025.03.33
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    For large-section tunnels crossing fault fracture zones, indoor experiments were conducted to study the mechanical and permeability characteristics of the rock specimen. Based on the correlation between rock integrity index and physical and mechanical indicators, the parameters of surrounding rock under different degrees of fragmentation were quantified. Considering the permeability of surrounding rock changes with confining pressure, a three-dimensional numerical model was established to analyze the impact of the engineering characteristics of fractured zone surrounding rock on the tunnel deformation. Through on-site monitoring, the deformation of the tunnel and the stress changes of the support structure are mastered. The results show that: (1) The mechanical properties of the rock specimen in the fractured zone are greatly affected by the water-rock interaction, and the peak stress of the rock specimen in the saturated state is significantly reduced compared to the dry state. (2) The permeability of the rock specimen in the fractured zone decreases in a logarithmic relationship with the increase of confining pressure. When the confining pressure exceeds the crack closure stress, the penetration water pressure of the rock sample approaches. (3) As the integrity index Kv of the rock mass in the fault fracture zone decreases, the maximum settlement of the tunnel arch increases in a logarithmic relationship, and the adverse effect of seepage on tunnel deformation increases. (4) By taking reasonable strengthening support measures and parameters, the tunnel can safely pass through the mileage section of the fault fracture zone, which can be used as a reference for engineering applications.
  • Hu Yu, Wang Genzhong, Zhou Min, Gao Wenxue, Zhang Xiaojun
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1050-1056. https://doi.org/10.20174/j.JUSE.2025.03.34
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    To reduce the vibration intensity of wedge-shape excavation blasting in tunnel, the precisely controlled delay time technology of tunnel V-cut blasting was proposed based on the Mohr-Coulomb strength criterion, the maximum tensile stress, and Anderson superposition theory. Firstly, the mechanism of segmental blasting of V-cut is revealed through theoretical analysis. Secondly, the function of blasting vibration waves was obtained by fitting the Gauss function. Finally, the precise delay time of reducing blasting vibration was obtained by superimposing different delay times with Matlab. The results show that: The stepped V-cut blasting improves the free surface conditions of blasting, and weakens the vibration propagation energy by reducing the amount of blasting charge in a single stage. Based on the Qi Jiazhuang tunnel of National Highway 109, the vibration strength of V-cut blasting was reduced by about 60% when the delay time was 13 ms. The engineering practice showed that the relative error between the theory and the field monitoring data was 13.9%, which verified the validity of the technology.
  • Shi Jiangwei, Wang Jinpu
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1057-1065. https://doi.org/10.20174/j.JUSE.2025.03.35
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    Improper control of supporting face pressure of shield tunnel may induce excessive ground movements, which may threaten the serviceably and safety of adjacent underground pipelines. Currently, extensive studies have been conducted to investigate pipeline responses due to tunnelling under various volume loss, effects of active face instability on deformation characteristics of existing pipelines are rarely explored. Physical model tests are conducted to investigate the effects of tunnel cover to diameter ratio (C/D) and normalized horizontal distance (H/D) between tunnel face and existing pipeline on three-dimensional pipeline deformation mechanisms. The results show that: When the pipeline is located 0.1D away from the tunnel face (i.e., H/D = 0.1), active face instability induced pipeline settlement reaches the maximum value. By increasing H/D ratio from 0.1 to 0.5, the maximum settlement and bending strain of pipelines are reduced by up to 64.8% and 51.6%, respectively, while the respective maximum reductions in the pipeline settlement and bending strain are only 14.9% and 7.3% as the C/D ratio from 1.0 to 1.5. It is indicated that H/D ratio is the key parameter to control pipeline settlement. Based on systematic numerical parametric analyses, calculation charts for estimating pipeline settlements due to tunnel active face instability are established by using two dimensionless groups of pipeline settlement ratio and relative pipeline-soil stiffness. The validity of the proposed calculation charts is verified by the physical test results, and the calculation charts can provide a rapid evaluation of pipeline safety and adjustment of supporting face pressure during tunnel construction.
  • Hu Mengling, Xu Wenhao, Zhang Xiaolong, Wang Zhiwen, Chen Hao
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1066-1075. https://doi.org/10.20174/j.JUSE.2025.03.36
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    Loess cave dwellings is a residential building with local characteristics in northwest China. In order to explore the influence of loess rainfall infiltration on the water migration law and stability of cave dwellings, the loess of an abandoned cave dwelling in the suburbs of Yan'an was selected as the research object, and indoor experiments were carried out to obtain the soil-water characteristics and unsaturated shear strength of loess. The COMSOL finite element software was used to establish the cave dwelling model, analyze the water migration law and stability changes of the cave dwelling under rainfall conditions, and explore the effects of factors such as rainfall duration, rainfall intensity and rainfall type on the moisture field and stability of cave dwelling. The results show that: Rainfall infiltration leads to a sharp increase in the water content of the soil covering the cave dwelling, moisture continues to accumulate around and the arch of cave dwelling which result in a continuous decrease in the safety factor of the cave dwelling. The greater the duration and intensity of rainfall, the greater the decrease of safety factor. Compared with long-term weak rainfall, short-term heavy rainfall had a greater impact on the moisture distribution of deep soil in cave dwelling, and the stability of cave dwelling decreased sharply in a short time. The change of safety factor of the cave dwelling lags behind the rainfall process. The vertical displacement generated by the forward type rainfall is the largest, and the decrease in the safety factor of the cave dwelling is also the largest. But the safety factor of the peak rainfall after the rainfall is the smallest, which is the most unfavorable to the stability of the cave dwelling.
  • Li Zhao, Luo Zujiang, Lu Jiansheng, Zhang Yingying
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1076-1084. https://doi.org/10.20174/j.JUSE.2025.03.37
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    In order to study the influence of the water insulation property of the horizontal bottom sealing curtain on the environment around the foundation pit. Firstly, a field test is carried out to reveal the characteristics of groundwater seepage in highly permeable aquifers and the mechanism of land subsidence. Secondly, based on the groundwater seepage theory and the principle of effective stress, a three-dimensional fluid-solid coupling numerical model is established. Finally, the drawdown of groundwater and land subsidence caused by dewatering is simulated when the diaphragm wall is expended by 4 m, 8 m, and 12 m and the permeability of bottom sealing curtains is reduced to 2%, 5%, 10%, 15%, and 20% of the original stratum, respectively. And the impact of the bottom sealing dewatering on the foundation pit surrounding environment is revealed. The results show that: The bottom sealing can effectively control the land subsidence which is reduced by 68.48%~76.37%. When the permeability of bottom sealing curtains is reduced to less than 10% of the original stratum, the control effect of land subsidence is significant. Significant increasing the length of the diaphragm wall could also have a good effect on land subsidence control. However, it is necessary to analyze the feasibility of construction difficulty and cost.
  • Zheng Yuchao, Liu Guolei, Cui Yu, Wang Zedong, Qu Xiaocheng
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1085-1093. https://doi.org/10.20174/j.JUSE.2025.03.38
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    Low permeability coal seam is characterized by broken coal body, high gas content inside the coal seam, high pressure, and difficult to escape, leading to problems such as imperfect monitoring and warning system of protruding danger and single warning index. This paper puts forward the theoretical assumption of the disaster caused by the protruding center body in digging face based on the theory of comprehensive role hypothesis and the principle of superposition of dynamic and static loads, and accordingly constructs a prediction model of the protruding center body, and researches the multi-parameter monitoring and early-warning technology. Taking the main and secondary roadway excavation in the north third mining area of the north wing of the 8# coal seam in a mine in Yangquan mining area as the engineering background, a study on the relationship between the prediction of protruding danger of the center body of the excavation face and the response of multi-parameter monitoring was carried out by using the methods of on-site test and theoretical analysis, and the results show that: The breeding and development of the outburst center body in the structural area of the North Three Lane are significant. The changing trend of microseismic energy response and K1 value during excavation is similar, which verifies the feasibility of using microseismic to predict the outburst danger of the center body. The microseismic event, bolt stress, excavation speed and K1 value are positively correlated with the outburst risk of the center body. The research results are of great significance in revealing the disaster mechanism of coal and gas outburst in low permeability coal seam and to improve the effectiveness of disaster monitoring and prevention.
  • Shen Huitao
    Chinese Journal of Underground Space and Engineering. 2025, 21(3): 1094-1104. https://doi.org/10.20174/j.JUSE.2025.03.39
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    Excavating tunnels within the influence range of goaf area poses significant technical challenges commonly encountered in underground construction projects. Considering the Baiyunshan Tunnel as the project backdrop, FLAC3D was utilized to analyze the stability of the tunnel under conditions that if the goaf area was filled with water or not. Then optimize the original support plan to suit different conditions. The results show that: Excavating the tunnel without grouting in diverse engineering conditions presented significant safety hazards. Stress concentration occurred at the left end of the goaf, resulting in a wide range of plastic zone above the tunnel and extensive damage to the tunnel. The vertical displacement of the tunnel floor was expected to surpass the prescribed control value that outlined in the pertinent guidelines. The presence of water in the goaf exacerbated the rock softening and damage. High pore water pressure posed a significant risk of water inflow into the tunnel's crown. For the tunnel that underpassed dry goaf area, grouting was carried out within a range of 140° when the distance between the goaf and the tunnel was less than 4.5 meters. Grouting was applied to the entire surrounding area when the distance between the goaf and the tunnel was within the range of 4.5~9 meters. If the distance exceeded 9 meters, grouting was not required to meet safety regulations. During the construction of the tunnel underpassing water-bearing goaf area, it was necessary to extend the grouting range to cover a distance of 4.5~10 meters from the goaf to the tunnel. Other parts of the tunnel could be supported in the same way as the tunnel that underpassed dry goaf area. The field monitoring results indicated that the stability of the tunnel had been ensured.