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.

Roof-cutting and roadway retaining (RCRR) technology refers to the process of mining a coal mine face without retaining protective coal pillars. By cutting the roof, the previous section of the transportation roadway is retained as the track roadway for the next section, which has the advantages of good economic value and fast construction speed. The most important factor of RCRR effectiveness lies in the stability of the retained roadway roof, especially in areas with complex geological conditions. Due to high ground stress, ground water pressure and weak surrounding rock, the roof stabilizing and bearing mechanism is complex, restricting the promotion of RCRR. In response to above difficulties, the fiber reinforced polymer (FRP) anchoring cable is introduced for the roof stability control owing to its high strength and low costs. In this paper, the calculation formula of the bearing strength of the Fiber reinforced polymer anchoring cable in the top cutting and retaining roadway is derived. We have also discussed the effects of various strength properties of the FRP anchoring cable, including cohesion, internal friction angle, and preload, as well as layout parameters such as cable spacing, length, and diameter. The results indicate that as the strength parameters, preload, length, and diameter of FRP anchoring cable increase, so does the bearing strength of the FRP anchoring cable in the roadway. Therefore, using high-strength and high preload FRP anchoring cables with grouting reinforcement can effectively ensure the stability of the retained roadway roof. The research results can provide theoretical and practical experience for relevant engineering cases.

To investigate the mechanism of anchor-grouting support in the construction of roadway roof cut-off, this study focuses on a typical deep roadway with fractured surrounding rock. This research employs a combined methodological approach. Theoretical analysis and physical model experiments were integrated to investigate anchor-grouting reinforcement mechanisms. Specifically, we quantify how this technique enhances support efficiency in surrounding rock strata. Furthermore, an analytical model is established to characterize the comprehensive mechanical properties of the rock mass reinforced by anchor-grouting. This study investigates the influence mechanisms of four key parameters (namely cohesion, internal friction angle, cable preload, and layout spacing) on the mechanical properties of the anchorage grouting complex. Building upon the roof evolution mechanism of roof-cutting roadways, theoretical formulas for calculating the required support strength in both the influence area of coal seam and the stability area of coal seam are established and validated through large-scale geomechanical model tests. The results demonstrate that the combined anchor-grouting support technology effectively reduces both horizontal stress and displacement in the surrounding rock strata, confirming its engineering applicability for deep soft rock roof-cutting projects. These findings provide valuable technical references for the design and construction of similar mining engineering projects.

This study proposes an eco-efficient soil stabilization approach to resolve subgrade engineering difficulties encountered in Jibin Intercity Railway project, includes structural instability, gradation deficiencies, and low bearing capacity of loess soils, which can also improve the ecological sustainability and minimize cement consumption during construction. Through comprehensive analysis of the gradation properties of silt, unconfined compressive strength, and compaction characteristics, a novel geopolymer binder was developed by synergistically combining waste basalt powder with slag. Employing orthogonal experimental design, the alkali activator components (type, concentration, modulus) and slag proportion were optimized and validated, ultimately formulating a 20 % basalt-enhanced cementitious material, and the 7-day unconfined compressive strength of this material is 2.74 MPa, which is 10.96 times that of the Chinese regulatory requirements. Integrated shear strength evaluation and XRD/SEM characterization demonstrated that alkaline-activated basalt-slag composites can produce dual aluminosilicate gels that cohesively bind soil particles, supported by theoretical models clarifying the stabilization mechanisms. This methodology advances sustainable soft subgrade treatment for high-speed rail systems, delivering both technical innovations and actionable protocols for geopolymer implementation in transportation engineering.

As more and more TBM tunnels are constructed under complex conditions such as high stress and fault fracture zones, large deformation disasters of squeezing soft surrounding rocks occur frequently. However, TBM method shows poor adaptability to major engineering challenges. Equipment damage, track deviation and support structures failure are widely observed. It is important to propose an effective support scheme and to fully clarifying the mechanical properties of the support structures in TBM tunnel. In this case, this paper aims to conduct laboratory and numerical tests considering steel–concrete interface bond-slip behavior so as to verify the effectiveness of the proposed support scheme. Thus, the quantitative relationship between arch type, arch spacing, longitudinal connection strength, concrete strength, steel fiber content, and tunnel surrounding rock deformation can be obtained. The research results show that the support scheme proposed in this paper shows good applicability for deformation control of TBM tunnels under squeezing soft rock conditions, which provides a reference for TBM tunnel support under squeezing soft rock conditions.

In order to determine the damaging effect of different fire temperatures on a segment, experimental research was carried out on the structural performance of segments subjected to different fire temperatures. A temperature plateau occurred when the temperature reached 100 degrees C. There were two temperature layers across the 300 mm thickness of the segment due to heating on one side only, and the temperature gradient within 0-50 mm was much more significant than that within 50-300 mm. The concrete spalling and the cracking initiated on the fired surface of the segment were severe; the maximum depth of concrete spalling on the fired surface of the segment at different fire temperatures was 600 degrees C: 15 mm; 800 degrees C: 45 mm; and 1,000 degrees C: 67 mm; further, the main reinforcement was exposed or even softened. Cracking was also initiated on the unfired surface, and even penetrating cracks developed on the side surface. The damage at both ends of the segment was more severe than that in the center. The fire temperatures were 600 degrees C, 800 degrees C, and 1,000 degrees C, the maximum midspan deflections were 5.27, 7.83, and 11.79 mm, the maximum midspan axial forces were 65.58, 208.41, and 333.63 kN, and the maximum reinforcement stresses were 22.49, 35.08, and 52.63 MPa, respectively. The mechanical parameters of the segment increased during the firing process and recovered during the cooling process, which is equivalent to a loading and unloading cycle for the segment. This study advances the understanding of the structural performance of shield tunnel segments subjected to different fire temperatures.

To investigate the deformation and failure characteristics and bearing mechanism of composite concretefilled steel tube support structure, pure bending indoor tests and refined numerical simulation are carried out for support structures, taking into account the arch frame-concrete bond-slip characteristics on the basis of typical failure mode of support structures. An in-depth analysis is conducted on the mechanical response of the specimens under the action of bending moment, so as to clarify the impact pattern of different parameters, such as arch frame installation position, shotcrete strength, steel mesh diameter and protective layer thickness, on the structural bearing capacity. The results show that the concrete-filled steel tube specimens without steel mesh（SRCS-FW） are weaker in strength, the concrete cracks rapidly and then slips with the arch frame, while the concrete-filled steel tube specimens with double-layer steel mesh（SRCS-FS） are better in terms of deformation effect and display better bearing characteristics later. Besides, the SRCS-FS specimen has a higher strength of critical slip failure and its ultimate bending moment is 40.9% higher than that of the SRCS-FW specimen. Furthermore, the synergistic effect of the arch frame, the steel mesh and the concrete is significant in the elastic deformation phase of the component. The tensile force of the specimen in the cracking phase is mainly shared by the tensile-side steel mesh and the arch frame,while the pressure is shared by the arch frame and the concrete under compression. It is suggested that the parameter design for the support structure should take into account its load-bearing performance, economy and engineering experience, and construction convenience.

This study was proposed to solve the problems of low efficiency and poor safety of tunnel arch installation under complex conditions. Based on the difficulties of traditional arch construction, this paper develops mechanized equipment such as high degree of freedom arch main installation machine and auxiliary installation machine and assembly supporting devices suitable for mechanized construction and forms the mechanized construction technology of assembly arch. The results show that the fabricated construction method is of great significance in improving the initial strength of the arch frame; the rapid formation of the arch frame bearing system is the key to ensuring the effective control of the elastic-plastic deformation of the surrounding rock. Based on the above research, the results have been preliminarily applied in the reconstruction and expansion of Magongci tunnel of Binlai expressway, the construction efficiency has been significantly improved, and the surrounding rock deformation has been effectively controlled.

Multi-layer composite support structure is widely applied in tunnel excavation but shows complicated failure behavior under rock pressure. Local joint broken, out-of-plane instability and arch-shotcrete interface slip widely exist and highly weaken the overall strength of support structure, which is inconsistent with the ideal assumption, leading to sever engineering disaster. Based on above situation, this paper adopts laboratory and numerical methods to investigate the bearing mechanism and failure behavior of arch joint, arch frame and arch-shotcrete composite lining. Then, a modified safety evaluation method of arch is proposed based on convergence-confinement method. The research results proved that, component strength and arch critical instability strength check are necessary in arch design. On the other hand, compared with thin-walled steel arch, the concrete-filled steel tube arch shows higher critical instability strength and better ductility, effective for controlling large deformation of soft rock. The research conclusions can provide reference for related tunnel design and construction.

This paper aims to propose a probabilistic approach to evaluate tunnel safety considering anchoring-grouting effect and arch failure mechanism based on mechanical analysis, machine learning and reliability calculation. Cohesion and internal friction angle of rock mass influenced by grouting, bolt preload and bolt layout are deduced based on Mohr–Coulomb criterion. Test inversion analysis has achieved promising results. Hence, the coupling model of reinforced and unreinforced rock mass is constructed to obtain the ground reaction curve. The support characteristic curve of different kinds of supporting arches are investigated based on numerical simulation which highlights the influence of structural buckling. Thereafter, a case study based on a deep tunnel in loosening rock mass is investigated to study the rock-support interaction and to evaluate engineering reliability. The research results provide insights into the design of tunnel support schemes through the viewpoint of convergence-confinement method and statistical analysis, which provides basis for safety design in tunnel excavation.

A tunnel primary lining structure is consist of sprayed shotcrete and encased steel arch exhibiting inherent steel–concrete bond-slip failure. This paper aims to quantify the impact of interface slippage on tunnel safety. Firstly, a four-point flexural laboratory test and numerical simulation are conducted on different types of lining structures to study the mechanical properties of lining. Secondly, mechanical deduction of composite linings is carried out and verified by experimental results; validation results show promising consistency. The support characteristic curve (SCC) of primary lining is modified accordingly to interact with ground reaction curve (GRC) based on convergence-confinement method, representing the relationship between bond-slip properties and tunnel safety index, which is also trained by a support vector machine (SVM) learning model. Thereafter, a reliability-based tunnel safety evaluation approach considering lining failure mechanism using SVM is proposed. Research results revealed that bond-slip failure has a significant effect on the strength, stiffness, and ductility of tunnel lining, which is also proved to be important to tunnel safety control. The research results can provide reference for related engineering.

Studying the bearing mechanism of concrete-filled steel tubular (CFST) arch components and constructing the quantitative design method of the CFST arch is an important subject in underground support. In order to clarify the bending and compression properties of CFST arch joints, considering different structural parameters of the joint, bending and compression tests of square CFST components without joints, with tubular joints and with flange joints were carried out. The mechanical properties and failure modes of the bending and compression combinations of each component were analyzed, and the influence of structural parameters of joints on their bearing capacity was clarified. The results show that (1) the failure mode of the component without a joint and the component with a tubular joint present uniform curve deformation, and the flange joint presents typical brittle failure and broken line failure; (2) compared to the specimens without a joint and with a flange joint, the tubular joint has higher yielding strength and ultimate strength due to the strengthening effect of the tubular joint, while the bending bearing capacity is 623.639 KN; (3) the tubular length and flange thickness are the key structural parameters of the two types of joints, which have a significant influence on the bending capacity of the specimens; (4) the tubular joint has a simple structure and high bearing capacity, so it should be used as the preferred joint connection form of the concrete-filled steel tubular support arch in deep mine roadways with complex conditions.

Steel reinforced shotcrete lining (SRSL) support is the primary structure to maintain the stability and mobilize the self-bearing capacity of surrounding rock. However, the structural design of SRSL in underground excavation still relies on experience-based method and lack of quantitative mechanical analysis. This paper aims to propose a modified analytical model of support characteristic curve (SCC) that represents the mechanical behavior of SRSL structures in underground construction, through which the interface bond-slip behavior between steel arch and shotcrete layer is taken into consideration. Four-point bending test of SRSL composite beam was carried out to study the bearing mechanism and failure performance. Test results show that the shotcrete-steel interface is prone to slip failure which significantly reduces the overall strength of SRSL. The laboratory test is complemented by non-liner finite element parametric studies considering the bond-slip properties to clarify the design principles and to obtain the flexural stiffness of tunnel primary lining structures. Based on above studies, the simplified formulas for the SCC of SRSL is constructed. The research results provide a theoretical basis for the design and application of SRSL structure in related projects.

The quantitative design of fabricated joint is a key issue to realize the effective mechanized assembly of tunnel steel set. However, there is no reported research on the failure mechanism and quantitative design method of fabricated joint for underground support structures. Taking a type of fabricated joint used for concrete-filled steel tubular (CFST) set as research object, the refined finite element model is constructed in this paper considering the complex nonlinear characteristics of joints. The simulation scheme is verified and validated based on four-point flexural and eccentric compression experiments. Failure modes and bearing mechanism of fabricated joint are obtained through above methods. Research results prove that there are two primary failure modes: the destruction of joint components and the tearing fracture at joint-CFST junction, the latter of which might lead to overall brittle failure of tunnel support structures. Parametric studies of joint specimen are carried out accordingly to establish an analytical model for fabricated joint design. The research results could provide basis for the design and application of mechanized assembly construction in tunnel excavation.

In the process of underground excavation with weak and broken surrounding rock, high-strength arch support is the primary bearing structure to resist rock pressure, especially after shotcrete layer cracks. Field destruction in underground excavation indicates that, with high ground pressure, the primary failure mode of arch is instability failure, which might lead to sudden loss of strength. Therefore, a quantitative analysis of arch instability in tunnel support design is necessary to avoid insufficient support strength so as to ensure the safety of underground engineering. The research method in this paper is based on the application of convergence-confinement method in underground arch support. The modified assumption of support characteristic curve (SCC) is proposed considering the instability failure of arch. The SCC of I-shaped arch and concrete-filled steel tubular (CFST) arch is constructed, respectively, based on mechanical analysis and verified by numerical simulation. A parametric analysis is also carried out to provide reference for arch design. Ground reaction curves (GRCs) of tunnel surrounding rocks with different lithology and ground stress considering arch failure mode are obtained to study the rock–arch interaction mechanism. The research results provide a theoretical reference for the design and application of arch support in related projects.

The large section tunnel support is facing tremendous challenges. They are large in span and poor in self-stability of surrounding rocks. Traditional I-steel arches are easily subject to buckling failure. As a result, safety accidents always occur, such as the failure of supporting system and the collapse of tunnels. To solve the problems, a new support technology of confined concrete and corresponding arches are invented. With high strength and rigidity, it can effectively control the deformation of surrounding rocks on large section tunnels. To clarify the bearing capacity and failure mechanism of the new arch, a mechanical testing system for the combined arches in large section tunnels is developed. Comparative tests were carried out on the mechanical mechanism of the combined arches of confined concrete and traditional I-steel. The tests took Longding Tunnel, one of the largest city road tunnels in China, as engineering background. In the test, the following results were found. The in-plane flexural buckling occurred on the vault of the combined I-steel arch first, and then out-plane flexural-torsional buckling occurred on the hance and bottom of the arch. It resulted in the overall loss of its bearing capacity and the entire arch being flattened. In the other hand, the confined concrete combined arch showed no severe deformation; its bearing capacity was 2.63 times that of the I-steel arch; and its average rigidity at the coordinated bearing stage is 2.51 times that of the I-steel arch. It is superior in bearing capacity and stability to the I-steel arch. Based on the experimental research conclusions, the engineering suggestions are put forward for the application of the confined concrete support technology in tunnels and the field application was carried out. The control effect is excellent on surrounding rocks. The results can provide a reference for the future research and design in this field.

方钢约束混凝土支护体系以其强度高、施工方便的优点,在深部软岩巷道中的应用日益增多.节点作为拱架连接的关键构件,是进行支护结构合理设计的前提,对拱架内力分布及承载力发挥具有重要影响.但目前约束混凝土拱架节点设计大多基于工程类比,针对其力学特性的深入研究较少.本文以典型深部软岩矿井——巨野矿区万福煤矿为工程背景,对约束混凝土拱架常用的法兰节点及套管节点进行对比分析.开展方钢约束混凝土无节点构件、法兰节点构件及套管节点构件的纯弯室内试验和数值试验,对比各构件的变形过程及破坏形态;基于M-θ曲线,综合分析各参数对无节点构件、法兰节点及套管节点力学性能影响规律,提出依托工程方钢约束混凝土拱架节点设计建议.基于上述研究结果,进行方钢约束混凝土拱架的现场应用.试验结果表明,依托工程现场采用方钢约束混凝土支护体系,围岩变形得到很好控制.套管节点传力明确、承载力高,极大地缩短了施工难度,降低了经济成本,应作为方钢约束混凝土拱架优选的节点形式.

Concrete filled steel tubular (CFST) arch has broad application prospects as a high-strength support form in underground excavations, especially in weak and broken surrounding rock. However, the structural design of CFST arch in underground excavation still relies on experience-based method and lack of quantitative mechanical analysis. This paper presents a detailed analysis on the mechanical behavior of CFST arch and proposed an analytical model to construct support characteristic curves (SCC) according to convergence-confinement method. Experimental tests of jointless CFST component and joint component under pure bending condition and compression-bending condition are carried out to obtain the stiffness and strength of different arch sections. Casing joint, which is the most commonly used form of connection joint in CFST arch, shows different mechanical properties with jointless components. Numerical and analytical studies of casing joint are conducted to establish a quantitative design method of joint stiffness. Based on above research results, a mechanical model of CFST arch is proposed in order to construct the SCC for support design. The research results could provide a theoretical basis for the design and application of CFST arch support in related projects.

为解决约束混凝土现场应用过程中套管节点设计保守、施工困难等难题,采用室内试验与数值试验相结合的方式,综合考虑不同套管节点构造参数及不同偏心率加载,分析套管节点试件压弯组合力学性能及破坏形态,开展套管节点参数影响规律研究.结果表明:1)节点试件压弯组合作用下呈现典型两阶段工作模式及变形破坏模式;2)节点与拱架接触部位发生明显的应力集中现象,试件呈折线形破坏;3)荷载-位移曲线表现为典型的弹性、弹塑性和塑性3阶段特性,轴压承载力与无套管试件相比降低19.4％左右;4)得到了不同套管节点参数的M-N曲线,提出了节点经济性指标β1,β2,量化了套管节点强度与经济成本之间的关系,提出了工程设计建议,为相关工程设计应用提供借鉴.

Uniaxial compressive strength (UCS) is an important index for classification of the surrounding rock and determination of the supporting parameters in underground engineering. The commonly used standard UCS tests are expensive, time-consuming and difficult to quantitatively evaluate the UCS of fragmented rocks because these rocks cannot be effectively cored. To solve the above problems, a method for predicting UCS of rock mass based on digital drilling test technology is introduced in this paper. The key to implementing this method is to establish a quantitative and universal relationship between the drilling parameters and the UCS. Therefore, the digital drilling tests and standard UCS tests of rock specimens with different strength values are carried out based on the laboratory rock mass digital drilling test system developed by the authors. A relational model between the drilling parameters and the UCS is established by support vector machine (SVM). The drilling parameters as model input parameters include the rotation speed N, drilling rate V, torque M and thrust F measured by the sensors, and the unit cutting energy eta(c) deduced from energy analysis by the authors as well. The research shows that the UCS predicted by the relational model in validation set is close to the UCS measured by the uniaxial compression test, the coefficient of determination R-2 is 0.977, and the mean absolute error (MAE) is 3.037 MPa. These results indicate that the relational model between the drilling parameters and the UCS based on SVM method is successful in the rock UCS prediction, and the digital drilling test technology could realize the effective prediction of UCS of rock mass.