The bond-slip behavior between I-shaped steel and shotcrete crucially influences the cooperative deformation and overall bearing capacity of tunnel initial support. To clarify the bond-slip mechanism between the steel section and shotcrete, this study conducted push-out tests on five groups of stud-reinforced specimens, investigating the effects of stud geometry and arrangement. The tests revealed two primary failure modes-tensile and expansion failure-governed by stud quantity and strength. The typical bond-slip curve comprises four stages: non-slip, ascending, descending, and residual. The quantitative results highlight that stud arrangement and diameter significantly impact bearing capacity. The quincuncial layout achieved an ultimate load of 372.4 kN, which is 16.8% and 54.9% higher than that of the double-row (318.9 kN) and single-row (240.5 kN) parallel arrangements, respectively. Increasing the stud diameter from 13 mm to 16 mm boosted the ultimate load by 16.7% (from 240.5 kN to 280.7 kN). The residual load was approximately 62-87% of the ultimate load. Based on these findings, a bond-slip constitutive model was developed, showing high agreement with experimental data. This study provides theoretical support for optimizing steel-shotcrete support systems in tunnels, though generalizability is limited by sample size and the exclusion of long-term load effects.

Sandy pebble soil particles, influenced by their generation environment, exhibit high strength, large permeability, and significant size variation, causing construction disturbances that alter their deformation and strength characteristics. This study examines the effect of moisture content on the initial modulus and peak strength of sandy pebble soil through large-scale triaxial tests. For the first time, the Duncan-Chang model is modified, incorporating moisture content as a disturbance factor, resulting in a revised D-C model for sandy pebble soil. This model is built using finite element software via secondary development to study the impact of moisture content on the soil's mechanical properties. The results show the following: (1) when the moisture content is constant, the peak stress and initial modulus of sandy pebble soil increase with the increase of the perimeter pressure, and when the perimeter pressure is constant, the peak stress and initial modulus decrease with the increase of the moisture content. Also, the effect of moisture content on the peak stress is much larger than that of the perimeter pressure. (2) Perturbation theory is used to establish a perturbation function for sandy pebble soil, leading to a modified D-C model. A comparison of the indoor test results, the modified D-C model, and the original D-C model reveals that the stress values from the modified D-C model align closely with those of the indoor tests. (3) Applied to numerical simulation software via the midpoint incremental method, the modified D-C model's experimental, calculated, and simulated values show strong agreement. The simulation also explores how moisture content affects mechanical properties, establishing relationship equations between internal friction angle, cohesion, and moisture content.(c) 2026 American Society of Civil Engineers.

Engineering Materials courses are characterized by dense conceptual content, cumulative knowledge structures, and heterogeneous student learning trajectories. Existing teaching reform studies often focus on isolated instructional techniques or digital tools, while paying limited attention to the systemic organization of learning activities, assessment, feedback, and instructional decision-making. This study proposes a system-oriented teaching framework for an undergraduate Engineering Materials course within an urban underground space engineering program. The framework conceptualizes course instruction as a closed-loop process driven by continuous learning evidence and feedback regulation. The framework was implemented in an undergraduate Engineering Materials course with 50 students over a 16-week semester using a learning management platform. Multiple sources of process data were collected, including platform access records, assignment submissions, weekly quiz performance, pre- and post-course concept assessments, instructor feedback logs, and instructional adjustment records. The results indicate that the proposed framework supported timely instructional regulation and adaptive responses to heterogeneous learning states. Observable improvements were found in student engagement patterns and assessment outcomes across the semester. Mean concept test scores increased from 55.7 to 72.2. Students with lower initial scores gained an average of 22.3 points, compared to 11.8 points for their higher-performing peers. A total of 312 feedback messages were delivered, with a median latency of three days. These improvements were observed in association with the implementation of the framework, although causal attribution is limited by the non-experimental, single-cohort design. The study provides an exploratory case showing that system-oriented teaching design may offer a coherent and practically feasible approach for enhancing engineering education in data-rich instructional environments, while also contributing to the application of systems thinking in teaching reform.

Sandy pebble soil particles, shaped by their generational environment, exhibit high strength, large permeability coefficients, and significant size variability. These characteristics can lead to soil disturbance during construction, affecting its deformation and strength properties. This paper investigates the impact of coarse fraction content on the initial modulus and peak strength of sandy pebble soil through large-scale triaxial tests conducted under varying confining pressures and distinct coarse fraction contents. Based on the experimental findings, a modified Duncan-Chang (D-C) model is presented by incorporating coarse fraction content as a disturbance factor within the framework of perturbation theory. A specific disturbance function is derived to quantify the effect of particle gradation on mechanical parameters. Results indicate that while peak stress and initial modulus increase with rising confining pressure, they decrease as coarse fraction content increases when confining pressure is kept constant. The impact of coarse fraction content on peak stress is shown to be more significant than that of confining pressure. Comparisons among laboratory tests, the modified D-C model, and the original D-C model demonstrate that the modified model achieves higher consistency with experimental results. Furthermore, numerical simulations of tunnel excavation implemented in Abaqus verify that the modified model predicts surface settlement and surrounding rock deformation with greater accuracy than the traditional model. Finally, quantitative relationships between shear strength parameters (internal friction angle and cohesion) and coarse fraction content are established.

Inadequate composite action between steel arch frameworks and shotcrete in tunnel support systems commonly leads to interface debonding and structural instability, particularly in complex geological conditions. This study introduces an improved support system that integrates circumferential stirrups with steel and shotcrete components to enhance their composite behavior. A comprehensive experimental program was conducted to investigate the axial compression performance through full‐scale specimens, with particular focus on stirrup spacing (50–200 mm) and extension range (0–60 mm). The experimental results revealed distinct failure mechanisms under different configurations: specimens with conventional bonding exhibited interface separation and concrete spalling, while the addition of circumferential stirrups transformed the failure mode to controlled crushing, indicating enhanced composite action. Quantitative analysis demonstrated that the optimized configuration (50 mm stirrup spacing, 60 mm extension) achieved a 35.57% increase in ultimate load capacity and a 147.15% improvement in ductility compared to conventional bonding. Notably, these specimens maintained 93.88% of their ultimate load capacity even at advanced loading stages, demonstrating exceptional structural stability. The enhanced performance was primarily attributed to the effective confinement of concrete by the stirrup system, which prevented premature interface debonding and enabled fuller utilization of material strengths. In addition, the error between the finite element results and the experimental results is 3%, which verifies the rationality of the selection of constitutive parameters and the definition of contact. Through parametric analysis, it is concluded that the expansion range of 45 mm stirrups is more reasonable to improve the ultimate bearing capacity of members. Based on the experimental observations, a theoretical model was developed to predict the axial compression capacity, achieving agreement with test results within 3% error. These findings provide quantitative guidance for optimizing tunnel support systems and extend current understanding of steel‐concrete composite behavior in tunnel engineering.

To improve the synergy between steel arches and shotcrete in tunnel support systems, a steel-concrete composite structure incorporating plum-shaped stud shear connectors and transverse stirrups with varying spacings was proposed. This study conducted small and large eccentric compression tests to investigate the structural behavior, strain development, and failure modes under different bonding and confinement conditions. The results show that under natural bonding, early slippage between steel and concrete led to poor strain coordination and reduced ductility. The addition of studs enhanced interface bonding, while stirrup confinement significantly improved the integrity of core concrete, delaying crack propagation and increasing load-bearing efficiency. Under large eccentric compression, the use of studs alone improved the ultimate bearing capacity (Nu) by 10.73 %. When combined with stirrups at 150 mm, 100 mm, and 50 mm spacing, the capacity increased by 16.07 %, 21.41 %, and 32.14 %, respectively. The corresponding ductility improvements were 36.54 %, 40.75 %, and 157.48 %, while lateral deflection was reduced by up to 31.83 %. Similar trends were observed under small eccentric compression, where the ultimate capacity improved by up to 31.55 %, ductility by 48.48 %, and deflection decreased by 37.72 %. Strain analysis showed that the plane section assumption failed at 0.3-0.5 Nu under natural bonding but remained valid up to Nu with combined confinement. A theoretical formula was developed based on this assumption, incorporating the effects of studs and stirrups. The model demonstrated good agreement with experimental results and provides valuable guidance for the design of tunnel support structures under eccentric loads.

To enhance the synergistic load-bearing capacity between tunnel support steel arches and shotcrete, it is proposed that a composite structure support be formed by arranging stud shear connectors on their contact interface. In response to the loading characteristics of tunnel supports, significant eccentric compression member tests were carried out to analyze the failure modes and load-bearing characteristics of the composite structure support, and a theoretical calculation expression for the ultimate load-bearing capacity of the tunnel steel-shotcrete composite structure was established. The research results show that when the steel and concrete contact interface is naturally bonded, the failure mode is characterized by separation and spalling, consistent with actual tunnel supports' large deformation failure mode. When stud shear connectors are arranged on the steel web, the failure mode only cracks and crushes, significantly enhancing its anti-slip and synergistic load-bearing capacity. The steel-concrete composite structure with stud shear connectors exhibits good ductility, load-bearing performance, and bending stiffness. Compared to the naturally bonded condition, the ultimate load-bearing capacity is increased by 14.83 %, and the lateral deflection is reduced by 24.27 %. Under natural bonding conditions, extensive eccentric loading greater than 0.4 times the ultimate load cannot satisfy the plane section assumption for the steel-concrete structure section. However, with stud shear connectors arranged on the web and loaded to 0.8 times the ultimate load, the plane section assumption is still well satisfied. At the same time, a theoretical calculation formula for the ultimate load-bearing capacity of the stud-reinforced steel-concrete support structure under significant eccentric compression was established and verified. The research results can provide theoretical support for the design of tunnel initial support.

The study is based on the combined advantages of PVA fibers and EPP materials, a new PVA fiber EPP concrete was prepared as a filler material for tunnel buffer layers. 10 groups of specimens with different working conditions were designed and prepared. The failure pattern, physical and mechanical parameters and energy absorption index of the material were analyzed by static mechanical test and Hopkinson pressure bar (SHPB) dynamic compression test. The results indicate that E0 specimen showed brittle failure in static tests and SHPB tests. When PVA fiber and EPP beads were added to the specimen, the failure mode of the specimen changed from brittle failure to ductile failure, and the specimen shows typical core-remaining failure under impact load. The static test results reveal that EPP volume content significantly influences the axial compressive strength, elastic modulus, and confined compressive strength of PVA fiber EPP concrete, while fiber content has the most pronounced impact on splitting tensile strength, Poisson ratio, and dynamic compressive strength. the confined uniaxial compression ontological relationship of PVA fiber EPP concrete under confined compression was established by confined uniaxial compression test, and the formula fitting was carried out. The fitting results were in good agreement with the test data. Based on the stress-strain curve of confined compression, the static energy absorption performance of PVA fiber EPP concrete was discussed. The results show that the energy absorption effect of E60-P18-1.2 concrete is the best; The results of SHPB test showed that comparing the energy absorption value and dissipation rate of each group of specimens under 0.06 MPa air pressure, it was found that the concrete of E50-P12-0.7 had the best energy absorption effect under dynamic compression. These studies provide a valuable theoretical basis for optimizing the design of tunnel buffer layers.

Creep stress is a detrimental stress generated by the surrounding rock during the operation of the secondary lining of the supporting structure used for high-stress soft rock tunnels in railways, highways and other projects. Therefore, the present study aims to investigate and provide solutions for damages such as cracking and deformation caused by creep stress. For this purpose, research methods used in the literature and experimental studies, as well as the theoretical, data and numerical simulation analyses, were used. Accordingly, the mix proportion design, specimen production and the tests of physical and mechanical properties of EPP foam concrete were carried out. Moreover, the EPP(polypropylene foam) concrete was used as the buffer layer of the supporting structure, the practical application of which was verified through numerical analyses. The findings of the study revealed the effective compression performance of the mix proportion design method. Furthermore, the EPP foam concrete was found to be able to absorb the energy generated by the creep of the surrounding rock, consequently reducing the surrounding rock pressure acting on the secondary lining structure, which, in turn, ensures the safety of the operation. The findings of the study can be used as a reference for designing similar projects.

Objective Affected by the occupation of existing buildings (structures) on the ground, the main retaining piles in shield receiving areas at both ends of some metro stations cannot be built. Therefore, it is necessary to study the pile-beam-arch (PBA)construction technology for expanding excavation of metro station undercrossing the parallel existing buildings or structures. Method With the project of Nijiaqiao Station on New Line 18 in Chengdu Metro undercrossing the existing structures as the research object, a finite element model is established to analyze the subsidence characteristics of the land and the existing structures according to the actual construction plan, and the results are verified by on-site monitoring data. Result & Conclusion PBA construction technologies including advanced large pipe shed, temporary column support system, staggering excavation of 7guiding holes and manual excavation cast-in-place pile are used, successfully implementing the station main retaining pile construction under the premise of effectively controlling the subsidence of land and the existing buildings. The construction steps that have the greatest impact on the above-mentioned subsidence are the excavation of guiding holes 1, 3, 5, 7. The subsidence of existing structures is obvious at guiding holes 1 and 2 with the maximum value of 9.62 mm, 1.5 times the simulated value. Both the on-site monitoring results and the simulated results meet the safety control requirements.

Stacked tunnel constructions adjacent to operating metro lines are frequently encountered in dense underground space, leading to undesired settlement and existing tunnel deformation. In this paper, ground movement and tunnel deformation were studied due to stacked shield tunnelling using field monitoring and numerical simulation, particularly the effect of adjacent moving train load on ground and tunnel responses was mainly investigated. Numerical model was implemented based one engineering project of the stacked shield tunnel in Tianjin, China. The results indicate that the ground vertical deformation is influenced by the position of new tunnel and existing tunnel, while the ground horizontal deformation occurs specifically at the top of the new tunnel. The train load contributes to an increase in both vertical and horizontal deformations of the ground and an intensified longitudinal settlement deformation in the existing tunnel. A ground settlement prediction was proposed that considers the stiffness of the existing tunnel and effect of train load. This study provides an in-depth investigation into the deformation of ground and existing tunnel and addressed the non-negligible effect of adjacent train load when evaluating safety of stacked shield tunnelling.

Objective It is aimed to elucidate the constitutive relationship of bond-slip at the interface between stud steel and shotcrete in the initial support of mining method tunnel. Method Four different working conditions are set by varying the length, diameter, and arrangement of the studs. Push-out tests are conducted on steel-shotcrete short columns with studs on web plate, analyzing failure modes, load-slip characteristics and bearing capacity. Result & Conclusion The failure modes of stud specimens are affected by the number and strength of studs, categorized into tensile splitting and bursting failure. The typical average bond strength-relative slip curve can be divided into four stages: no slip, ascending curve, descending curve, and horizontal residual stage. Laboratory tests demonstrate that the diameter and arrangement of the studs are primary factors affecting the bearing capacity. A bond-slip constitutive model for the interface between stud steel and shotcrete is established based on stress mechanism, validated through both laboratory tests and numerical simulations, showing high accuracy. The research results can provide theoretical support for the design of steel and shotcrete support structures of mining method tunnels.

The structure of sandy cobble soil is discrete, the particle size distribution is asymmetrical, and it has typical particle dispersion peculiarities. The macroscopic continuum mechanics theory method cannot accurately access the instability process and failure mode of sandy cobble surrounding rock of tunnel, which often induce instability collapse of surrounding rock of tunnel face, resulting in ground subsidence, deformation and collapse, which poses a serious threat to engineering safety. In this research, the particle discrete element theory and numerical simulation technology are utilized to conduct a fine analysis of the stability of the tunnel sandy cobble surrounding rock from the meson level. The paper focuses on the longitudinal instability failure mode of the tunnel face and failure characteristics of circumferential surrounding rock during tunnel excavation. The consequence display that after the excavation of the tunnel in sandy cobble stratum by the bench method, in the longitudinal space of the tunnel, the soil in front of the tunnel face is first destroyed, and the closer the distance is to the tunnel vault, the greater the soil deformation is, which is easy to cause surface subsidence. The stress relaxation area gradually spreads from the front of the working face to the upper right, which eventually provokes the instability of the excavation face. Correspondingly, the intrusion degree of surrounding rock and the height of vault collapse arch increase with the increment of water content in sandy cobble stratum. Meanwhile, intrusion size, collapse arch height, width and initial support effect of surrounding rock with different water content are calculated. The research results provide important reference and guidance for the design, construction and maintenance of sandy cobble stratum tunnel engineering.

The characteristics of expansive soil, such as overconsolidation, multi fissure and shrinkage cracking due to water expansion and water loss, are called "hidden disasters" by the geotechnical engineering community. Its damage mechanism has become an important technical problem that the underground space engineering must face and solve. The expansive soil is mainly distributed in the eastern region in Chengdu. According to the investigation, the soil collapse between the supporting piles often occurs in the construction of the deep foundation pit of the subway station in the eastern region, causing safety accidents such as personal injury or equipment damage. In this paper, taking the stability of soil between piles of deep foundation pit excavation and support piles of the East extension line station of phase II of Chengdu rail transit line 17 as the research object, the instability characteristics of soil between piles of deep foundation pit excavation and support piles of railway stations on expansive land in Chengdu area are systematically studied by means of field investigation, field measurement analysis, instability characteristics analysis and calculation and derivation of soil stability between piles, and the characteristics and causes of soil instability between piles of deep foundation pit excavation and support piles of railway stations on expansive land are proposed, and put forward prevention measures and suggestions.

The surrounding rock of layered rock mass tunnel is prone to engineering problems such as bedding slip and bending deformation. Based on the project of Yujiang diversion tunnel in Guangxi, this paper studies the deformation characteristics of surrounding rock and the mechanical properties of supporting structure of shallow layered tunnel under surface load by using block discrete element method. The results show that under the condition of no support, the deformation of surrounding rock is small under the condition of no load and anti-dip lateral load, and the deformation of surrounding rock is significant under the condition of bedding lateral load. The deformation of surrounding rock is characterized by the bending and breaking of the anti-dip side wall, the sliding deformation of the vault and the bedding side wall. Under the supporting condition, the supporting force and deformation of the bedding side load are significantly greater than that of the bedding side without load. The axial force of the bedding side support is greater than that of the anti-dip side under the bias load of the bedding side, and the other three loads are opposite. The bending of the supporting arch waist is greatly affected by the load distribution. When there is no load and anti-dip side load, the anti-dip side arch waist bends inward and the bedding side arch waist bends outward, while the other two loads are opposite. The unilateral load mainly affects the deformation of the same side support, and the full load has the greatest influence on the deformation of the tunnel bottom.

In order to study the influence of weathering degree on the shear strength characteristics such as shear strength and shear deformation of sawtooth structural planes with different undulating angles, four kinds of regular sawtooth structural planes with undulating angles of 15°, 25°, 35° and 45° were made. The rock samples with different weathering degrees were prepared by indoor weathering simulation test, and the direct shear test of indoor structural plane under different normal stresses was carried out to explore the variation law of shear strength and parameters of limestone sawtooth structural plane. The test results showed that shear stress-shear displacement curve of serrated structural plane showed peak shear type, which increased approximately linearly at first, then decreased after reaching the peak shear stress, and finally tended to be stable and maintained a certain residual shear strength. With the increase of weathering degree, the shear strength of limestone sawtooth structural plane showed a decreasing trend, and the shear strength parameters had different degrees of deterioration, and the deterioration degree of cohesion was greater than that of friction angle, while the fluctuation angle of structural plane was positively correlated with the shear strength. Based on the model test results, the shear strength estimation model of weathered sawtooth structural plane was established to reveal the quantitative relationship between shear strength and weathering degree and fluctuation angle.

研究目的:砂卵石围岩颗粒体系级配分布不均匀,颗粒间点对点接触,隧道施工过程中易引起围岩松散、失稳坍塌等突出问题.本文针对砂卵石围岩典型的颗粒物质特性,基于谷仓效应原理,采用颗粒物质离散元理论,探明砂卵石隧道围岩荷载计算方法,分析砂卵石土在不同细观组构下的细观力学行为,探究砂卵石颗粒级配对土体压力的影响特征,揭示隧道跨度对隧道围岩荷载的影响规律.研究结论:(1)提出了用于计算砂卵石土竖向压力的修正Janssen计算公式,并确定了公式中重要系数转向比;(2)揭示了砂卵石颗粒级配对土体竖向压力与侧压力的影响规律,得到了砂卵石土体底部压力和侧压力的计算公式;(3)通过不同跨度的隧道模型模拟试验,提出了竖向荷载修正系数,使用修正系数法的砂卵石围岩荷载计算值与模拟计算的结果相近,验证了该公式计算的准确性;(4)建立了基于Janssen模型的砂卵石围岩荷载计算方法,可为砂卵石地层隧道精细化设计提供理论基础.

近年来在我国发生的许多建设工程事故都是职业道德的缺失所引起的,造成许多工程悲剧.作为以后要从事于建筑工程这一行的主力军——土木工程专业的学生,对其在校期间进行工程职业道德建设更加重要.虽然我国近些年来土木工程专业教育有较大发展,但是许多高校只注重传授专业知识,对于工程职业道德教育没有足够的重视.新工科背景下,国家对于人才培养的要求更加严格,所以新工科背景下高校土木工程专业教学中职业道德教育的融入也变得十分重要.