The intersection points of coal mine roadways, as key nodes in the mining transportation system, directly determine the overall safety and service life of the roadway. This paper classifies the roof rock beam at deep roadway intersections into three regions-namely, the pure suspended roof beam area, the equivalent suspended roof beam area, and the middle rock pillar supported roof beam area-based on the intersection structure and the failure characteristics of different regions. Based on structural mechanics and the Rayleigh-Ritz energy method, mechanical models for the three roof rock beam regions were established, and deflection calculation formulas for the roof rock beam in different regions were derived. The results indicate that the beam span (L) is the most important factor affecting the deflection of the roof rock beam, followed by the beam thickness (D) and the equivalent support stiffness (k(eq)). A stability criterion based on the span effect coefficient and the support stiffness coefficient is proposed. When the span effect coefficient lambda >lambda(cr), the rock beam undergoes instability and failure, and the pure suspended roof beam area enters a failure state. When the support stiffness coefficient kappa < 1, the middle rock pillar becomes unstable, and the middle rock pillar transitions into the equivalent suspended roof beam area. When the support stiffness coefficient kappa >= 1, the middle rock pillar meets the required strength, and the middle rock pillar transitions into the stable region of the middle rock pillar supported roof beam area. For the different failure characteristics of each region, three types of fundamental support structures were designed: concrete-filled steel tube (CFST) composite supports, CFST pier column, and two-way opposite anchor cable. Bearing capacity tests and numerical simulations were conducted for CFST pier column, verifying the load-bearing performance advantages of CFST pier column, and stability criteria for the support performance of the CFST pier column and composite support were derived. Engineering applications were further carried out at Yangcheng Coal Mine and Qingshuiying Coal Mine. After implementation of the support schemes, the deformation of the intersection roof and surrounding rock was controlled to within 100 mm, satisfying service requirements and providing a useful reference for deep roadway intersection support.

This study presents a comprehensive investigation into the deformation mechanisms of existing metro stations subjected to the simultaneous construction of adjacent foundation pits and underground tunnels. A refined three-dimensional numerical modeling framework is developed to simulate the entire construction process, capturing the complex interactions between excavation activities and station structures. The modeling encompasses deep excavation, side-crossing, and overcrossing passage construction, and the staged installation of support systems. Six construction schemes, varying in excavation sequence, interlayer thickness (clear distance), and passageway layout, are systematically analyzed. Field monitoring data are incorporated to validate the numerical models, enhancing the reliability of the results. The analysis identifies the construction sequence as the primary factor influencing station deformation. Specifically, the strategy of constructing passageways first, followed by excavation of the interchange hall, effectively reduces both vertical and horizontal displacements by leveraging the early-stage portal-frame reinforcement effect. Increasing the clear distance between new structures and the existing station helps mitigate construction-induced deformation, although the benefits plateau beyond a certain threshold. Sensitivity analysis shows that overcrossing passages are most sensitive to variations in clear distance, followed by foundation pits and side-crossing tunnels. Additionally, the spatial positioning of passageways significantly impacts deformation magnitude and propagation. Passageways near expansion joints cause the greatest uplift, while those placed at mid-span experience minimal disturbance due to enhanced structural stiffness. This research provides a quantitative understanding of metro station deformation under concurrent construction activities and offers practical insights for optimizing excavation sequences, structural layouts, and interlayer spacing. The findings contribute to ensuring structural safety and minimizing risks in densely built urban metro environments.

The smooth blasting of hard granite tunnel will have problems such as poor fragmentation of the tunnel face. To address these issues, this study investigates the mechanism of empty hole blasting. According to the blasting theory, by deducing the formula of the equivalent damage zone radius of the group hole, and a criterion for defining the blasting effect is proposed. The rationality is verified by numerical simulation and field test. The results show that the empty hole can change the stress distribution of the group hole blasting, and has the effect of directional to crack. With the increase of empty hole-group hole spacing, the peak stress decreases gradually. Aiming at the damage change, the damage feature transformation coefficient m is proposed to define the blasting effect and m = 0.6 is determined as the damage feature transformation threshold. With the increase of distance, the propagation speed and length of rock cracks gradually weaken, and the regional penetration effect gradually deteriorates. The relationship between damage threshold and vibration velocity is constructed. It is concluded that when the space is greater than the damage threshold, the maximum vibration velocity fluctuation interval gradually increases, and the stress wave propagation velocity gradually weakens. The Sadovsky formula of spacing and vibration velocity peak is constructed to characterize the change law. It provides a reference for the optimization of smooth blasting parameters in hard granite tunnels.

The proximity of a tunnel to an existing station renders it susceptible to settlement. Jack lifting is a common method for mitigating the settlement at such stations during tunnel construction. This study investigates the mechanical responses of structures subjected to jack lifting based on case studies, numerical simulations, and theoretical analyses. These findings indicate that jack lifting significantly elevates the station structure. However, upon removing the lifting load, the station experienced resettlement. A lower initial support stiffness was correlated with increased settlement. Settlement control was achieved using a combination of active jacking and passive support. Effective jack lifting relies on addressing both advanced. A large jack load reduces the settlement of an existing structure; however, excessive loading can cause structural uplift. Therefore, the relationship between lifting load and displacement must be considered during jack lifting. Utilizing the elastic foundation beam theory, a correlation between the settlement of the existing structure and the jack-lifting load was derived, thus facilitating bidirectional control of force and displacement during the jacking process. The results offer valuable insights into the control of jack lifting in existing structures beneath tunnels.

Under the action of disturbance load,the rheological rock mass in the"sensitive neighborhood"is prone to de-formation and failure.In order to study the influence of confining pressure on the range of disturbance"sensitive neighbor-hood",the red sandstone is taken as the research object,and the RRTS-Ⅳ rock rheological disturbance effect test system is used to carry out the disturbance impact test on the rheological rock mass under different confining pressures and axial pressures.The change rule of axial disturbance strain with axial pressure is observed,and the change of"sensitive neigh-borhood"under different confining pressure conditions is analyzed.The nuclear magnetic resonance analysis system is used to compare and analyze the rheological rock mass under different confining pressure conditions.The variation of porosity,T2 spectrum curve,spectral peak area and pore size distribution of rheological rock mass in sensitive and non-sensitive areas before and after disturbance.The results show that:When the confining pressure remains constant,the axi-al disturbance strain value shows a nonlinear trend of decreasing first and then increasing with the increase of axial pres-sure,and when the axial pressure applied to the rheological rock mass is closer to the long-term strength under the confin-ing pressure condition,the axial disturbance strain value generated by the dynamic disturbance is larger.There is a sensit-ive transition point(σm)in rheological rock mass under different confining pressure conditions,which determines the sens-itivity of rheological rock mass to dynamic disturbance.When σ1＜σm,the sensitivity of rheological rock mass decreases with the increase of axial pressure.When σ1 ≥ σm,the sensitivity of rheological rock mass increases with the increase of axial pressure.According to the sensitivity of rheological rock mass,three sensitive areas are divided:R1 non-sensitive area,R2 sensitive area and R3 creep failure area.It is determined that the range of sensitive neighborhood(Δσ)should be between long-term strength(σp)and sensitive transition point strength(σm).By calculating the change of"sensitive do-main ratio"under different confining pressure conditions,it is found that the inhibition of confining pressure on crack propagation in rock mass and the increase of damage threshold do not increase nonlinearly,but show a trend of decelera-tion growth.When the rheological rock mass is in the sensitive area,the external disturbance impact will lead to the gener-ation of new micro-pores inside the rock mass,and under the action of disturbance impact,the micro-pores inside the rock mass will gradually penetrate and expand into new large-aperture pores,which makes the number of pores inside the rock mass increase.At the same time,the influence of external disturbance impact on the development of pores inside the rock mass will gradually decrease with the increase of confining pressure.When the rheological rock mass is in the non-sensit-ive area,the external disturbance impact will make the large pores in the rock mass close,resulting in a decrease in the total number of pores in the rock mass.At the same time,the formation rate of new micro pores and the closure rate of large pores in the rock mass will gradually decrease with the increase of confining pressure.The research results have im-portant practical significance for enriching the theory of rheological disturbance effect of triaxial rock.

As a part of the research on the countermeasures of prefabricated steel structure residences under rarely occurred earthquakes,the concept of realizing rapid replaceable resilient function of peripheral wall panel system under rarely occurred earthquakes was put forward,based on the traditional connection tech-nique between wallboard and main structure was optimized and improved,and an L-shaped joint with angle steel perpendicular to light wall panel was proposed,six specimens of autoclaved aerated concrete wall panels(ALC)were designed.Through the quasi-static load test,the deformation behavior of the new connection and the failure mode of ALC were studied.The effects of thickness of angle steels at connections and restraint at the lower end of wall panels on the hysteretic characteristics,deformation capacity,stiffness degradation,angle steel strain and energy dissipation capacity of peripheral wall panels were discussed.The test results showed that the smaller thickness of angle steel of L-shaped joints,the greater the deformation,the better the energy consumption and the less the damage of wall panels;the lower end restraint of the wall panels was strengthened,the overall stiffness and bearing capacity of the peripheral wall panels were increased,small re-sidual deformation;when the drift reached 2％,the L-shaped node had sufficient stability and the wall panel had no obvious damage;when the drift exceeded 2％,the L-shaped joint showed a good deformation perform-ance,which could make the peripheral wall plate adapt to large structural deformation.

This study targets at asymmetric deformation of narrow coal pillar in gob-side entry driving.We put forward the bidirectional reinforcement of narrow pillar with opposite-crossing anchor cable.Specifically, we designed two types of anchor cable structure: the byelongation type and the expansion lock type, and carried out the pull-out test of opposite-crossing anchor cable, the test shows that both anchor cable structures could meet the tensile requirements.We conducted comparative analysis on the morphology of anchor cable failure, construction convenience and the economic aspect of material selection, where the expansion lock type crossed anchor was selected for narrow coal pillar bidirectional reinforcement.Furthermore, we investigated the bearing deformation patterns of coal pillars and the stress characteristics of anchor cables under different reinforcement methods through similar model tests and numerical simulation.Results show a 96.04% increase of peak load in the specimen reinforced by the double-row tight opposite-crossing anchor cable compared with that of the not reinforced specimen, and higher stability of the narrow pillar reinforced by the double-row tight opposite-crossing anchor cable as the rows of the anchor cable increases in number.The expansion lock anchor type crossed cable improved the energy storage and the critical failure point before the coal pillar was destroyed.Finally, the engineering test of expansive lock type crossed anchor cable to reinforcing narrow coal pillar was carried out in the transportation roadway of 123 lower 04 working face of Jining No.3 Coal Mine.The monitoring show that the anchoring force of the anchor cable exceeded 220kN, with 70& reduction of the coal pillar in the reinforcement area and good overall stability of the narrow coal pillar.It proves the feasibility of the bidirectional reinforcement technology of narrow pillar and provides new technical way for gob-side entry driving.

Concrete-filled steel tubular (CFST) composite supports have a high bearing capacity and are suitable for the support of roadway intersections with complex cross-sections and stress concentrations, especially for cross-point intersections. According to the cross-sectional shape and support frame combination, CFST composite supports are divided into three types: circular arc concrete-filled steel tubular composite support (CCS), rectangular concrete-filled steel tubular composite support (RCS), and circular arc + rectangular concrete-filled steel tubular composite support (CRCS). Through engineering practice and literature review, the top component of portal support frame is the key bearing structure of CFST composite support. Taking the top component of portal support frame as a key component, the bearing performance tests of the circular arch and straight beam were conducted. The bearing performance variation of key component influenced by the diameter of steel pipe, wall thickness of steel pipe, beam to span ratio and bending strengthening parameters were analyzed, providing guidance on the structural optimization of portal support frame. Numerical investigation of these three types of composite supports was carried out. The findings demonstrate that while the maximum deformations of the composite support under the constrained surrounding rock load exhibit the order CCS support frame structure optimization, the ultimate bearing capacities of the composite supports exhibit the order CCS > RCS > CRCS. The simulation found that the portal support frame is the key bearing structure of the composite support. Taking the top arch section of the portal support frame as a typical component, bearing capacity testing of the CFST straight beam and the arch was performed. The difference in the circular arch bearing performance was analyzed based on changes in the steel pipe diameter, steel pipe wall thickness, rise-span ratio, and anti-flexural strengthening, and the results provide a basis for portal support frame structure optimization. Three roadway intersections in practice were used to evaluate the performance of the three types of composite supports. After structural optimization, the composite supports meet practical requirements and generally produce good results, making them a suitable reference for other roadway intersections.

Single Recovery Roadway (SRR) is a novel retraction technology in the non-pillars mining innovation system. In previous support withdrawing, single recovery roadway was usually replaced by a dual-recovery roadway or cut the coal wall before the support. This study is set against the background of the longwall panel at Duanshi Coal Mine, where a mechanical model based on the stress characteristics of a composite cantilever beam was constructed to analyze the failure of the main roof in a single recovery roadway. Through numerical analysis, the relationship between deformation failure of the recovery roadway and interlayer slippage structures was explored, as well as how mining-induced stress distribution and the evolution of key strata fractures impact the stability of the roadway. The results indicate that after the connection of the longwall panel and the recovery roadway, the overlying composite interlayered rock strata are affected by the interlayer slippage structures, leading to significant asymmetric deformation in the surrounding rocks. Additionally, borehole observation data support the theoretical calculations of the cantilever beam model. These research results enhance the understanding of the interlayer slip instability mechanism and provide important guidance for mine design under similar geological conditions.

The existing Beijing Pingguoyuan Subway Station was extended through a extension project. The excavation for the extension was located directly above the existing station. Complex interactions exist between the existing structure and the retaining pile wall of the excavation. Based on this project, three-dimensional finite element models were established to investigate the mechanical characteristics of the embedded and non-embedded retaining pile walls. A parametric analysis was performed for both types of pile walls. The stress and deformation characteristics of the retaining pile walls and existing structures were analyzed. The results show that when the bottom of the non-embedded retaining pile walls are connected to the existing structure, the uplift of the existing structure is essentially constant; however, the maximum displacement of the pile is increased by approximately 2.7 times, and the bending moment of the pile is reduced to 57.1% of the connection condition. As the distance between the embedded retaining pile wall and the existing station increases, the uplift of the existing station increases linearly, whereas the soil between the pile and the station exhibits a non-linear increasing trend. The displacement of the embedded retaining pile wall increases as the inner force decreases. When the distance is greater than 4.7 m, the displacement and force of the pile remains essentially unchanged. The effect of the pile embedded depth on the force and deformation of the pile is mainly observed in the lower part of the pile. As the embedded depth increases, the maximum displacement decreases by approximately 16.9%, the maximum bending moment decreases, and the maximum negative bending moment increases. The key contribution of this research is to provide a prediction method for the mechanical behaviors of a expansion project. The findings from the study also provide industry practitioners with a comprehensive guide regarding the specific applications of the construction technology of a deep excavation structure overlying an existing subway station.

Long-term waterproofing and water leakage treatment of existing underground structures have become prominent issues in the operation and maintenance of underground structures. The use of single organic or inorganic materials for water leakage treatment is not effective for solving practical engineering problems. Considering the properties of organic and inorganic materials, a novel composite material mixing the waterborne epoxy resin and superfine ordinary Portland cement-sulphoaluminate cement was presented, which was studied as a polymer-modified cementitious composite for waterproofing and plugging. This study investigated the primary physical properties of the raw materials of the polymer-modified cementitious composite. Experimental tests were performed to investigate the effects of waterborne epoxy resin on the impermeability, interface adhesion, and tensile deformation performances of the superfine cementitious waterproof material. The results showed that the average water penetration height of the waterborne epoxy resin-modified material was only 52.2% that of the cementitious materials, indicating better impermeability performance. When 3% waterborne epoxy resin was mixed, the bending bond strength of the polymer-modified composite material was 10.6% higher than that of the cementitious material. The direct tensile bond strength of the polymer-modified composite material with various waterborne epoxy resin content significantly improved, demonstrating a maximum increase of 72.6%. Compared with the original cementitious material, the toughness, tensile deformation capacity, and tensile strength of the polymer-modified superfine cementitious composite material were improved. The maximum tensile amount increased by 48.3% when an appropriate amount of waterborne epoxy resin was mixed, which is the primary performance in long-term waterproofing. Moreover, the bearing capacity increased by 335.2% compared with the cementitious materials when 7% waterborne epoxy resin was mixed. The key contribution of this research is to propose a high performance and effective polymer-modified composite material for the treatment of waterproofing and plugging. The findings from the study also provide industry practitioners with a comprehensive guide regarding the mechanical and impermeability performances of the polymer-modified superfine cementitious composite material.

The pipe roof is an effective means to control the surface settlement during the construction of the super-shallow buried subway station. The transverse pipe roof method can not only reduce the construction work surface, but also improve the construction efficiency by multi-stage flow construction. Based on the transfer station project of the Olympic Sports Center of Jinan Rail Transit Line 3, the ground settlement law caused by the excavation of ultra-shallow buried subway station under the action of transverse pipe roof is analyzed through field measurement. The mechanism of pipe roof controlling ground settlement and the influence of steel pipe spacing and steel pipe length on the bearing mechanism of pipe roof are analyzed by numerical simulation. The following conclusions are drawn. 1) The surface settlement curve caused by the excavation of the small pilot tunnel in the lateral direction of the station is a wavy U-shaped, and the surface settlement curve becomes a smooth U-shaped after the soil is broken. In the longitudinal direction of the station, the surface settlement is jagged, and the surface settlement above the pipe roof is less than the surface settlement between the pipe roofs. 2) After soil excavation, pipe roof can bear the load of surrounding rock and restrain the settlement of soil above, and soil arch effect is formed between pipes to restrain the relaxation of soil between pipes. With the increase of the spacing of the steel pipe, the height of the soil arch increases. After exceeding a certain spacing, the micro-soil arching effect disappears and the surface settlement increases. 3) The length and stiffness of pipe roof will affect the bearing capacity of pipe roof and there is an upper limit. When it exceeds the upper limit, increasing the length or stiffness of pipe roof has little effect on the control effect of ground settlement. The research can provide reference for shallow buried excavation station and other projects.

In this study, an open-cut approach using steel-sheet piles and jet grouting piles for waterproofing was proposed to resolve the problem that ordinary pipe-jacking equipment cannot cross areas with existing anchor cables in soft stratum. The case history of a pipe-jacking project of a sewage treatment plant in the Jinan East Railway Station area was investigated. The mechanical properties of steel-sheet piles, horizontal displacement of piles, and ground surface settlement in the anchor-cable crossing area were investigated based on in situ observations. Numerical investigations were performed using the finite element method (FEM). The effects of existing anchor cables on the mechanical behaviors of retaining structures, deformation variation of the ground, and stability of the excavation were studied. The results indicate that the composite supporting structures of steel-sheet piles and jet grouting piles have a positive effect on waterproofing and deformation control in areas with existing anchor cables. When the steel-sheet pile touched the anchor cable during pile jacking, the compressive stress at the pile cap increased rapidly until it reached 62.8 MPa (the maximum pressure provided by the pile-pressing machine), which is twice the pressure under ordinary conditions. The maximum horizontal displacement of the retaining pile, δv, increased linearly with the excavation depth He. Existing anchor structures behind the excavation can restrain the deformation of the ground and retain the structure to a certain extent. The δv value of the pile with existing anchor structures behind is 6.5 mm or approximately 0.01% of the He value, which is 70% of that of the retaining pile without existing anchor structures. “Groove type” ground surface settlements are found on both sides of the excavation. The maximum ground settlements δh are 0.29% He and 0.05% He, respectively. The plastic zone at both sides of the excavation bottom extends to the ground surface with an angle of about 45°. When an excavation fails, the plastic zone range in the ground with existing anchor cables is significantly larger than it is in the ground without anchor cables. The key contribution of this research is to provide an effective and low-budget treatment for pipe-jacking crossing through an anchor-cable group region. The findings from this study also provide industry practitioners with a comprehensive guide regarding the specific applications and mechanical performance of the crossing excavation for obstacle treatment.

Due to the complex environment and ground stress at depth, and the various cross-sectional shapes and sizes, the damage types of deep roadways are diversified. The maximum ground stress, maximum compressive strength, and the corresponding support methods are compared by systematically analyzing the influence of high stress and dynamic pressure on the deep weak surrounding rock of roadways. And the stress intensity ratio is proposed to evaluate the support difficulty of surrounding rock of roadways. Then, the concept of active-passive full space collaborative control is proposed, and the core of the concept is to control the deformation of the roadway through active support methods such as destressing, grouting and bolt-cable to bring the self-supporting capacity of the surrounding rock of roadway into play, forming an active support body, and restoring its partial bearing capacity. Using passive support methods such as concrete-filled steel tube sets and U-shaped steel sets with high support resistance to form a passive support ring to assist or mobilize the bearing capacity of the rock surrounding roadways. Additionally, the mechanical mechanism of the collaborative support for concrete-filled steel tube sets and bolt-cable were analyzed, and the active-passive full space collaborative control technology and construction technique were developed and applied in the field. The study shows that the bolt-cable can reduce the bending moment and shear force of the concrete-filled steel tube sets, while reducing the axial force of the support and protecting the steel tube and the core concrete with poor tensile properties. The active-passive full space cooperative control technology has been successfully applied in deep roadway subjected to dynamic pressure and weak rock roadway in Jincheng Hudi Coal Mine and Yangquan Xinyuan Coal Mine, which has further developed the theory and technology of equal-strength support in deep roadway.

The Tashan coal mine is selected as a case study to determine the deformation and damage mechanisms of the lower roadway in a close-range residual coal pillar area. Roof drilling peephole technology is applied to detect the damage to the roadway roof surrounding rock. A boundary invisibility equation is derived for the plastic zone of a circular hole based on the theory of a butterfly plastic zone in a non-uniform stress field in which the principal stress occurs at an arbitrary angle to the vertical. Maple mathematical drawing software is combined with FLAC 3D numerical simulations to investigate the influence of the principal stress ratio and direction on the roadway plastic zone. The results indicate that the plastic zone of the roadway surrounding rock assumes a butterfly shape when the bidirectional stress ratio is large, and the direction of the butterfly-shaped failure of the roadway is related to the principal stress direction. Field test images are combined to show that the asymmetric damage pattern of the lower roadway in a close-range residual coal pillar area is influenced by the presence of the roadway in a non-uniform stress field in which the main stress direction is deflected.

With increases in the mining depth and area in the Ordos coal field, the failure law of the super thick sandstone in the Zhidan group leads to frequent disasters, such as rock bursts and mine earthquakes, which have become a significant issue, restricting large-scale continuous mining. To adequately understand the movement mechanism of the super-thick and weakly cemented overburden, and to promote the large-scale mining of the coal resources under it, this study analyzes the physical and mechanical properties, along with the microstructural characteristics, of the weakly cemented overburden of the Yingpanhao Coal Mine through mechanics tests, scanning electron microscope tests (SEM) and hydrolysis experiments. A two-dimensional discrete element model of the survey region is then built to explore the temporal and spatial evolution laws of the overburden failure. The results show that, even though poorly cemented strata such as the Cretaceous Zhidan group sandstone and the Zhiluo group sandstone are weak in lithology, their unique mineral composition and microstructural characteristics give them a greater rigidity when their thickness reaches a certain value. The surface subsidence exhibits a sudden increase, and the dynamic disaster range of the overlying strata is wide when deep multi-face mining was carried out under the super-thick and weakly cemented overburden. The temporal and spatial evolution laws of the strata subsidence and influence boundary are closely related to their depth, and their relationships evolve into the Boltzmann function and Boltzmann–parabolic function, respectively. The failure mode of the super-thick and weakly cemented overburden is ‘beam–arch shell–half arch shell’, and the failure boundary exhibits arch fractures.

In this study, a mountain tunnel of the Qianjiang-Zhangjiajie-Changde Railway, which passes through a giant karst cave at a high position, was investigated as a case study. The cave cavity height below the tunnel track is approximately 30-55 m, and the collapse accumulation thickness at the cave bottom is approximately 37-66 m. After solution comparison analysis, a superthick backfill subgrade solution was selected by filling the karst cave with a cave ballast backfill + upper grouting. In connection with railway operation, large vibrations and dynamic settlements may occur under train loads, and the safety of train operations can be compromised. To investigate the vibration response of a superthick backfill subgrade in a giant karst cave, 12 dynamically scaled model tests with a scale ratio of 1 : 5 were performed with a high-speed railway subgrade dynamic test platform. The subgrade slab thickness and running speed of the train were investigated as the variable parameters. The working state of each part of the subgrade was studied while the train passed, and the time-history variation and long-term development trend of the dynamic properties were analyzed. The attenuation behaviors of vibration displacement, dynamic stress, and acceleration in the superthick backfill subgrade were analyzed using the three-dimensional finite element method. The results showed that as the thickness of the subgrade slab increased, the dynamic response of the train decreased rapidly. At a running speed of 200 km/h, the average acceleration decreased by 75.2% at the bottom of the subgrade slab when the thickness of the slab decreased from 60 to 20 cm at the initial passage. Under a long-term load, acceleration at the same depth below the subgrade slab of thickness 60 cm decreased by 69.5% compared to that of thickness 20 cm. The superthick backfill subgrade with a 3-m-thick RC subgrade slab avoided evident dynamic settlement induced by the running load. When the tunnel was opened to traffic, tunnel structure settlement was monitored. Furthermore, the settlement of the tunnel invert was <1 mm within 1 year, which was consistent with the test results. The results proved that the design parameters and solution selection were reasonable and reliable and could serve as a reference for the development of similar projects and researches. The key contribution of this research is to propose an effective and low-budget treatment for the construction of railways that pass through giant caves. In addition, the findings from the study on superthick backfill subgrades provide industry practitioners with a comprehensive guide regarding the specific applications and mechanical performance of superthick backfill subgrades, which can serve as a stepping stone to facilitate the development of construction technology in the transportation industry. (C) 2022 American Society of Civil Engineers.

Distribution of joints and fissures under hydraulic coupling condition is particularly critical to the stability of surrounding rock masses in underground engineering construction. In this paper, DDARF (Discontinuous Deformation Analysis for Rock Failure) and RFPA (Rock Failure Process Analysis) are compared and analyzed firstly based on laboratory tests. Then using preferred software RFPA, the failure process, stress state, acoustic emission characteristics and energy dissipation laws of rock masses with different joint locations are analyzed under the hydraulic coupling condition. Results show that a large tensile stress region is generated on both ends of the original joint with the micro-cracks’ propagation, water pressure in cracks promotes the generation of tensile stress to a certain extent, damage effect angle increases gradually from the rock specimen with the middle joint to that with the marginal joint; the same water pressure has a certain auxiliary effect on the main crack failure when the joint is close to the middle part of the specimen, and has a dominant effect on the local crack failure when the joint is far away from the middle; the maximum water pressure shows the “U” shaped distribution. At low initial water pressure, stresses of specimens with symmetrical joint locations have similar evolution trends, while at high initial water pressure, the water pressure in cracks has significant dissipation and thus the maximum water pressure in the system does not exceed the initial value. The length of the main crack path is positively proportional to the number of acoustic emissions and the energy accumulation capacity, and evolution of the damage variable basically shows a development trend of steady growth-rapid growth-steady growth.