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The terminal joints of the steel support system play a critical role in controlling the deformation and stability of the foundation pit. However, accidents caused by issues with these terminal joints have been frequently observed. This paper introduces the Mold-bag Concrete Clamped Joint (MCCJ) as an innovative joint for enhancing the performance of terminal joints in the steel support system of subway station foundation pit projects. Design principles of MCCJ in the steel support system of the subway station foundation pit project are presented. It provides a detailed explanation of its structural characteristics and working principle, as well as elucidates its stress situation and force transmission mechanism. Three MCCJ specimens were designed and processed for indoor compression load tests, further their load-displacement curves, load-strain curves, and failure modes were obtained and analyzed to explore the load-bearing performance and mechanical characteristics in a more professional and academic manner. The test results demonstrate a designed bearing capacity of over 4000kN, exceeding the axial design bearing capacity of Φ609/630 steel support and meeting strong joint design requirements. Meanwhile, a refined numerical model of MCCJ was established using Abaqus, validated by comparing numerical and experimental results. Parameter analysis reveals the significant influence of steel tube wall thickness and connecting flange thickness on load-bearing performance, while the mold-bag concrete strength grade enhances MCCJ load-bearing capacity within a certain range. Furthermore, to fulfill the compatibility between MCCJ and existing steel supports, and achieve joint strength and high performance, the parameter optimization directions for MCCJ were proposed. • A novel joint, namely Mold-bag Concrete Clamped Joint (MCCJ) was proposed. • Three MCCJ specimens were designed and processed for indoor compression load tests to study bearing performance. • Load-displacement/strain curves and failure modes were analyzed to explore the load-bearing performance. • A numerical model of the MCCJ was established, and the parameter analysis was conducted by nonlinear numerical simulations. • Parameter optimization directions for MCCJ are proposed. [ABSTRACT FROM AUTHOR]

The rational structural design and compositional merits as well as the synergistic coupling effect can break the properties of single material and broaden the microwave absorption band. Herein, the unique lightweight Fe-doped MnO 2 @C hollow nanocubes are rationally designed and successfully synthesized via a scalable wet chemical process and polydopamine coating followed by high-temperature calcination. By virtue of the unique structure and compositional merits, the as-obtained Fe-doped MnO 2 @C hollow nanocubes (Fe–MnO 2 @C-HNBs) displayed notable microwave absorption performance (MAP), simultaneously achieving ultra-broad absorption bandwidth and strong absorption characteristics at a low thickness of 2.3 mm (the reflection loss of −41.02 dB and the effective absorption bandwidth of 5.86 GHz). Surprisingly, the effective absorption bandwidth (RL < −10 dB) could reach up to 8.08 GHz and the minimum reflection loss (RLmin) was −38.20 dB at the thickness of 2.7 mm. The results further confirmed that the excellent microwave attenuation ability of the as-prepared Fe–MnO 2 @C-HNBs composites benefitted from the special "air@core-shell" structure and multiple heterointerfaces as well as multi-component recombination. These results demonstrated that the as-obtained Fe–MnO 2 @C-HNBs composites could be attractive candidates for broadband microwave absorption materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A type of bolt fasten wedge (BFW) active joint is developed. • Loading tests are conducted on four full-scale specimens. • Load-displacement curves, load–strain curves, moment-rotation curves and failure modes of BFW joints are obtained. • The field test is carried out and compared with the commonly used steel wedge active joint. In this paper, the bearing capacities and failure behaviors of bolt-fastened wedge active joints used in prestressed internal supports are studied. A thorough exploration of the design of the bolt-fastened wedge active joint is elaborated, and an overview, working mechanism, stiffness analysis, parameters, and strength checking are provided. Then, loading tests are conducted on four full-scale specimens. One test is an axial compression test, while the other three tests are performed to analyze the long-axis (Y-axis) eccentricity, short-axis (X-axis) eccentricity, and biaxial (XY-axis) eccentricity. The load–displacement curve, load–strain curve, bending moment-rotation curve, and failure mode of each specimen are obtained. The experimental results show that the samples have good compressive properties and bending resistance. The impact of the X-axis and Y-axis eccentricities on the compressive ultimate bearing capacity is investigated, revealing a significant reduction in the former, while the latter has a minimal effect. Under bidirectional eccentricity, the weakening of the axial bending performance is most apparent. Bidirectional eccentric loads lead to a reduction in the yield load and initial compression stiffness to approximately 90% of those observed under unidirectional eccentricity. Finally, a field test is carried out to compare the constructability and load-holding performances of bolt-fastened wedge active joints with those of commonly used steel wedge active joints. It is demonstrated that the bolt-fastened wedge active joint effectively maintains prestress through bolt fastening, substantially enhancing the safety of foundation pit excavation construction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bending stiffness of Y-joint of the station built by enlarging tunnels were studied. • A bending mechanical model of the segmental joint was proposed. • Theoretical equations were derived for the joint's bending stiffness. • Bending experiments on full-scale models of the joints were carried out. • Calculated values were in good agreement with the experiment result when l c was 0.5. Based on the characteristics of the Y-shaped joint of a subway station built by enlarging two parallel shield tunnels, a bending mechanical model of the segmental joint was proposed. The model was used to characterize the cracking and crushing of concrete, the yielding of the bolt, and the damage of the segmental joint. Theoretical equations were derived for the bending stiffness of the joint under various forms of joint opening. Bending experiments were conducted on full-scale models of the joints under different structural configurations. The results demonstrated that the nonlinear properties of the joint structure were evident under loading and that the bending stiffness of the joint initially increased and then decreased. The computed values were in good agreement with the experimental results for the pre-embedded connector joint when l c was 0.5 times the height of the compression zone, where l c was the effect depth of the compressive deformation of the outer edge of the concrete. The axial force had a great influence on the bending stiffness. The mechanical performance of the joint was influenced not only by the change in the stress–strain curve of the concrete from the rising stage to the descending stage but also by the structural morphology of the rotational angle of the joint. [ABSTRACT FROM AUTHOR]

A method of constructing a double-deck subway station by combining two parallel shield tunnels and the cavern–pile method is presented. Taking the practical engineering of the Beijing subway as the background, numerical simulations were carried out to study enlarging construction. Mechanical and deformed performances for opening segments, important nodes, and main components of the station structure were investigated. Subsequently, a comparative analysis was performed to investigate the effects of side piles. Finally, an economic investigation was conducted to validate the practicability of the present method. This paper systematically demonstrates the applicability of the proposed method through a three-dimensional numerical simulation. The results show that it is safe and feasible to create a double-deck subway station by enlarging two parallel shield tunnels using the cavern–pile method. [ABSTRACT FROM AUTHOR]

• The influence of dilatancy angle on the limit support pressure and the failure zone is analyzed. • A 3D theoretical model in cohesive–frictional soils is proposed. • The accuracy of the proposed model is validated by comparing with other approaches. This paper aims at analyzing the influence of non-associated flow rule on face instability of a circular tunnel in cohesive–frictional soils. A series of three-dimensional numerical simulations are performed to analyze the influence of dilatation angle on the limit support pressures and the failure zones. The dilatation angle significantly influences the limit support pressure and the failure zone. Then, a three-dimensional failure mechanism that consists of the ellipsoid and the multi-block is proposed based on the upper-bound theorem. Finally, the limit support pressures and failure zones obtained from the new mechanism are compared with those given by existing approaches of limit analyses, numerical simulation and centrifuge tests. The results indicate that the presented model is more effective in analyzing the face stability of tunnels. [ABSTRACT FROM AUTHOR]

• Y-shape joints between segment and wall column of subway station built by enlarging tunnels were proposed. • Experiments of low frequency cyclic load of full scale joint models were carried out. • The pre-embedded steel plate joint have advantages in terms of energy dissipation capacity. • Both of the joints could meet the performance requirement of strong joint and weak component. To improve the seismic performance of subway stations built by enlarging two parallel shield tunnels, joints of special structures between prefabricated open-loop segments and cast-in-site main station structures were proposed. Experiments on the low-frequency cyclic loading of full-scale models of joints under different structural configurations were carried out. The seismic performance, such as the load–displacement hysteresis curves, skeleton curves, structural ductility, strength degradation, energy dissipation, strain of the cable-stayed bars and failure modes, were studied. The results showed that compared with the pre-embedded connector joint, the pre-embedded steel plate joint had advantages in terms of the mechanical stability, intensity, stiffness, energy dissipation capacity and ductility performance. However, the relative displacement between the segment and wall column of the pre-embedded steel plate joint was larger than that of the pre-embedded connector joint. Both types of joints had a full hysteretic circle, good ductility nature, energy dissipation ability, and stable elastic and elastic–plastic deformation. The cable-stayed bars did not yield in the stretch area when the joints failed. Both of the joints could meet the performance requirements of strong joints and weak components. [ABSTRACT FROM AUTHOR]

Considering the shortcomings of traditional tunnel support methods like shotcrete, including large rebound, poor water retention, and dust pollution, this paper proposes an innovative method to use mold-bag concrete (MBC) for initial tunnel support. Through macroscopic mechanical tests and microscopic structural characterization, a high-fluidity mix ratio of MBC suitable for actual construction conditions has been developed. To clarify the mechanical properties of MBC, compressive tests were conducted, leading to important conclusions: 1) Mold-bags can significantly enhance the compressive strength and ductility of MBC. The specimens of mold-bag concrete of PP (MBC-PP) fail first but have good ductility, while specimens of mold-bag concrete of SNG-PET (MBC-SPET) have the best compressive performance but poor ductility; 2) Without pressurized drainage, mold-bags can increase the compressive strength of MBC due to the water permeability characteristics, with MBC-SPET having the largest increase in compressive strength, 69.1 %; 3) MBC-SPET tests show that increasing pressure has a better effect than increasing drainage time, with 90 s and 20 kg pressurized drainage being the best increase effect. These findings highlight the potential of MBC in addressing the limitations of traditional methods, providing strength enhancement, environmental benefits, and practical feasibility for tunnel support. ● An innovative approach to utilize mold-bag concrete for the initial support of tunnels is proposed. ● A high-fluidity mold-bag concrete mix and corresponding testing protocols have been formulated to meet on-site construction requirements. ● The impact of different mold-bag material and weight on concrete at 3, 7, and 28 days is investigated under identical drainage conditions. ● The impact of pressurized drainage on the compressive strength of concrete is investigated under consistent mold-bag conditions. [ABSTRACT FROM AUTHOR]

This paper focuses on the mechanical properties of bolt-fastened wedge (BFW) joints utilized in prestressed internal support under eccentric loading. The validated finite element model was established based on the full-scale test results of BFW joints subjected to eccentric loads. A series of numerical simulations were conducted to systematically investigate the bearing capacity and bending performance of the BFW joint under eccentric loads. The influence of eccentricity, web thickness, eaves thickness, base splint thickness, bolt strength, and bolt diameter on the load-bearing and bending performance of BFW joints was investigated through further parametric evaluations. A four-parameter exponential moment-rotation model was developed based on the numerical results, demonstrating its accurate representation of failure modes, load-displacement curves, and moment-rotation curves observed in full-scale tests. The load-bearing and bending performance of the BFW joint exhibited a predominantly positive correlation with parameters such as web thickness, eave thickness, bolt strength, and bolt diameter; however, the effects of these parameters were inconsistent. The influence of bolt strength and diameter was found to be the most significant, while the effect of splint thickness was minimal, indicating a considerable level of redundancy. As eccentricity increased, there was a decline in both load-bearing and bending performance of the BFW joint. Finally, a comparison between the results obtained from fitted formulas and numerical as well as experimental data revealed that the moment-rotation model accurately described the bending performance of the BFW joint under eccentric loads. • Developed and validated a finite element model of the BFW joint. • Parametric studies revealed the influence of geometrical and material parameters on BFW joint performance. • Proposed a four-parameter exponential model to represent the moment-rotation characteristics of BFW joints. • The formulas for calculating the ultimate moment resistance and initial bending stiffness of BFW joints are presented. [ABSTRACT FROM AUTHOR]

• Bearing capacity of disconnectable coupling joints is presented. • Load-displacement curves, load-strain curves and failure modes of three joints are obtained. • Parametric investigations are conducted to study their effects on the yield load and initial compression stiffness. • Calculation formulas are proposed. Disconnectable coupling (DC) joint is an important connecting device in support system, and its bearing capacity, which is usually inaccessible, has a crucial impact on the support system's bearing capacity. In order to quantitatively study the bearing capacity of a DC joint and propose relatively accurate formulas for calculating its yield load and compression stiffness, indoor axial loading tests were carried out on three DC joints in this paper, and a series of numerical simulations was performed by using the finite element method (FEM) of ABAQUS. Firstly, load-displacement curves, load-strain curves and failure modes of three joints were obtained. Secondly, the numerical results were verified by experimental results in failure modes and load-displacement curves. Subsequently, parametric studies were conducted to analyze the influence of the steel wedge dimensions, steel tube wall thickness, middle-rib plate height and middle-rib plate shape on the yield load and initial compression stiffness of the DC joints. Finally, calculation formulas for estimating accurately the yield load and initial compression stiffness of the DC joints were obtained. [ABSTRACT FROM AUTHOR]

This paper describes the key influences of yaw excavation loadings on ground displacement and segmental stress for a curved shield tunnel. The influences are investigated through finite element models, the reliabilities of which are validated through comparisons to field data and analytical solutions. Multiple case studies of different curvature tunnels and their comparison to straight-line tunnels are presented. Under the dual action of overcutting and construction loadings, the surface settlement of the curved tunnel is larger than that of the straight-line tunnel. The horizontal displacements at the inner and outer sides of the curved tunnel are asymmetric with respect to the tunnel axis. This asymmetry can increase significantly during yaw excavation of over one ring width. Yaw excavation loadings have a significant influence on the horizontal and vertical displacements of the ground within a span of shield length starting from the position of the hydraulic jacks until the back. The circumferential compressive stress, axial tensile stress, and axial compressive stress of newly installed segment of the curved tunnel are greater than those of the straight-line tunnel. Interestingly, the stress increments increase linearly with yaw severity. The results are of benefit to suggest improvements for practical construction procedures. [ABSTRACT FROM AUTHOR]

Maintaining the stability of the tunnel face during the construction of the submarine shield tunnel is the prerequisite for safe construction. A series of face instability model tests under saturated strata were carried out. The earth pressure, the evolution of the soil arch area and the amount of soil entering the soil groove caused by the instability of the tunnel face under different face water pressure conditions were studied. A series of numerical simulations were carried out to analyze the effects of tunnel face water pressure. The results show that the vertical earth pressure and horizontal earth pressure at different positions show a gradual decrease with the increase of the baffle backward distance, and the smaller the water pressure ratio, the more obvious this law is. According to the test results, the decrease of the water pressure ratio of the tunnel face can significantly increase the soil intake of the soil tank, which indicates that the collapse range above the tunnel face is large. The trend of instability region obtained by numerical simulation is consistent with the test monitoring results. This provides a reference for the construction of submarine shield tunnels. • Geomechanical model tests are carried out. • The pore water pressure and earth pressure are studied. • The evolution process of the soil arch area and the soil inflow volume of soil tank are investigated. • The failure areas is analyzed. [ABSTRACT FROM AUTHOR]

• Geomechanical model tests are carried out to investigate tunnel face passive failure with different burial depths in sandy cobble strata. • The earth pressure and lateral stress ratios of the stage of excavation face passive instability are studied. • The evolution process of the failure area of the tunnel face during the instability stage is investigated. • The comparison of the failure areas obtained from the geomechanical model test with numerical simulation is analyzed. Urban rail transit construction will inevitably encounter tunnel working conditions with extremely complex surrounding environment and buried deep shield tunnel, and the stability of the tunnel surface cannot be ignored. A series of passive instability geotechnical model tests were carried out on the tunnel faces at different burial depths. The earth pressure, lateral earth pressure coefficient and soil arch area evolution law caused by passive instability of the tunnel face in sandy cobble stratum were studied. Once the preset position is reached, the rotation is stopped using the cutterhead and the screw excavator and the shield machine continues the jack, simulating passive instability of the tunnel face. The results show that the soil pressure in the horizontal earth pressure is significantly more affected by the passive instability of the tunnel face than the vertical direction. The soil in front of the excavation caused by the ejection of the shield machine is squeezed and moved forward, resulting in a decrease in horizontal earth pressure perpendicular to the direction of shield tunnel excavation. The results of the passive instability region obtained by numerical simulation are larger than those obtained by model experiments, because the numerical simulation method fails to consider the compacting effect caused by the extrusion of sandy cobble formations. It can be found that the uplift value of C/D = 1.0 is significantly greater than that of C/D = 1.5, which also confirms the conclusion that the instability area with a relatively small burial depth is larger and develops farther to the front of excavation. [ABSTRACT FROM AUTHOR]

• A series of geomechanical model tests were performed to investigate face instability. • The earth pressure and lateral pressure coefficient was investigated. • The evolution process of the failure area of the tunnel face was studied. • The comparison of the failure areas with existing methods was analyzed. This paper aims to study the influence of relative density on the working face stability of shield tunnel in sandy cobble stratum. A series of geomechanical model tests were conducted for shield tunnels excavating through loose sample (LS), medium dense sample (MS) and dense sample (DS), respectively. Relative densities of LS, MS and DS are 0.35, 0.55, and 0.75. The method of continuous rotation of spiral excavators while shield excavators stop tunneling is adopted to simulate the instability of tunnel face. Experimental results effectively reveal the variation characteristic of vertical and horizontal earth pressure and lateral pressure coefficient of shield tunneling. The evolution of the failure zone and soil arch height of strata with different densities was explored. The failure area and collapse range obtained from the model test were compared with the existing method. The effect of relative density on the horizontal earth pressure in the instability stage of the tunnel face in the sandy cobble strata is greater than that of the vertical earth pressure. In addition, increasing the relative density can effectively increase the lateral pressure coefficient as well as the stability of the tunnel face. The existing methods have deviations in analyzing the instability area of the tunnel face in the sandy cobble strata with different relative densities. The research in this paper provides a reference for the construction and theoretical analysis of sandy cobble strata shield tunnel engineering. [ABSTRACT FROM AUTHOR]

Based on the three-dimensional hydraulic head distribution model and the upper bound theorem of the limit analysis, a new model was established to calculate the limit support pressure in shield tunnel faces. A series of numerical simulations were conducted to evaluate the accuracy of the proposed model and the obtained results were compared with those of other classical analytical methods. It is found that the obtained analytical solutions are in good agreement with the numerical simulations and the proposed method outperforms other methods in terms of accuracy. In the present study, the influence of the water level, internal friction angle, burial depth, and water pressure on the stability of the tunnel face is analyzed. The performed analyses reveal that the limit support pressure is negatively correlated with the internal friction angle, while the burial depth does not affect the limit support pressure of the shield tunnel face in subsea tunnels (C/D ≥ 1). Meanwhile, it is found that as the water level and the water pressure on the tunnel face increase, the limit support pressure increases linearly, and the failure area extends to the front of the tunnel face and decreases in height. • A calculation formula is derived to analyze the stability of tunnel face in saturated soil. • The analytical solutions proposed in this paper excels the solutions of other existing methods. • The influence of water level, C/D and internal friction angle on the stability of the tunnel face is investigated. • The effect of the water pressure of the tunnel face on the stability of the tunnel face is explored. [ABSTRACT FROM AUTHOR]

• A series of geological tests and numerical simulations have been conducted for tunneling through sandy cobble strata. • Influence of face instability on the surface and stratum subsidence is investigated for tunnels with different burial depths. • Progressive settlement characteristics of sandy cobble strata are presented. The tunnel face stability is a key issue to ensure the engineering safety. Combined with model tests and numerical simulations, this paper focuses on progressive settlement characteristics of sandy cobble strata for shield tunnels during the instability process. Burial depths are the main parameter in this study, and ratios of burial depth and tunnel diameter were set as 0.5, 1.0 and 2.0, respectively. The results show that the surface settlement value decreases with the increase of the burial depth ratio. In addition, the time of local instability is negatively correlated with the burial depth ratio. The soil disturbance range of tunnel face instability with relatively large burial depth is significantly smaller than that with small burial depth. This provides a reference for the research on the strata deformation caused by the instability of the tunnel face in the sandy cobble strata. [ABSTRACT FROM AUTHOR]

• A series of geomechanical model tests were performed to investigate tunnel face failure with different relative densities in sandy cobble strata. • Influence of relative densities on the failure process was investigated. • Evolution law of the stratum deformation during the instability process of the tunnel face is analyzed. This paper aims at influence of relative density on deformation and failure characteristics for a shield tunnel in sandy cobble strata. A series of model tests were performed for tunnels with different relative densities of 0.35, 0.55, and 0.75. The evolution law of the stratum deformation during the instability process of the tunnel face was analyzed. The soil disturbance range of tunnel face instability with different relative densities was explored. The results show that relative density has a significant impact on the extent of surface subsidence. The stratum deformation caused by the instability of tunnel face in the medium dense and dense sandy cobble strata only occurs significantly behind the tunnel face, while the stratum with loose sandy cobble has significant stratum deformation behind and in front of the tunnel face. The method of improving the relative density can be used to reduce the deformation of the sandy cobble strata. [ABSTRACT FROM AUTHOR]

The lattice parameters, energy band structures, density of states, and optical absorption spectra of Gd-doped, N-doped, and Gd/N co-doped anatase TiO 2 were calculated by the first-principles based on the density functional theory. The calculated results indicate that the three kinds of doping all induce lattice distortion for TiO 2 , but the structures still keep unchanged. Gd doping introduces an empty energy band in the forbidden band of TiO 2 , and N doping introduces an impurity energy level above the maximum valence band. Gd/N co-doping forms an impurity energy level and a full-filled energy band in the forbidden band of TiO 2 , where the impurity energy level lies above the full-filled energy band. The experimental results for the photocatalytic activity enhancement of TiO 2 by the Gd/N co-doping can be explained perfectly from the calculation results. [ABSTRACT FROM AUTHOR]

• Influence of dilation angle on tunnel face passive instability was investigated. • A new analytical model considering partial failure and dilation angle was proposed. • The accuracy of the proposed model was validated by comparing with other models. This paper aims at analyzing the influence of non-associated flow rule on passive face instability for shallow shield tunnels. The influence exerted by dilation angle on the limit support pressures, the failure zones and partial failure ratios is investigated by numerical simulations. Based on the failure zone obtained from numerical simulation, a log-spiral mechanism is proposed. The upper-bound theorem is employed to acquire the limit support pressures, failure zones and partial failure ratios. The analytical results indicate that dilation angle has a significant influence on the limit support pressure and failure mechanisms. Finally, by comparison with the numerical models and existing analytical models, the results indicate that the proposed log-spiral model has a certain accuracy in analyzing the face instability of blow-out. [ABSTRACT FROM AUTHOR]

• Analytical solutions of additional stresses for a curved shield tunnel is presented. • Additional stresses caused by construction loadings and soil loss are obtained. • A case study is performed. This paper focuses on analytical solutions of additional stresses for a curved shield tunnel. General equations of additional stress caused by construction loadings were deduced by rewritten Mindlin solutions, and additional thrust and friction force were considered. In addition, theoretical formulae of additional stress caused by soil loss were deduced based on the three-dimensional image theory, and the actual processes of synchronous grouting and over-excavation were considered. Then, by using a curved tunnel in Zhuhai City, China as a case study, the distribution laws of additional stress along the directions of advancement and circumference were investigated. Under the coaction of construction loadings and soil loss, it was found that the distributions of σ x and σ y along the advancement direction for curved tunnels are similar to those for straight-line tunnels. However, the soil around a curved tunnel is more likely to yield because the difference between the normal stresses in two directions is greater than that for soil around a straight-line tunnel. Additional stresses caused by soil loss along the circumferential direction for a curved tunnel were found to no longer have the characteristics of strictly axial symmetry. The values of compressive stress σ x and σ y at the outer side of the curved tunnel were found to be greater and smaller than those at the inner side, respectively. As the curvature radius decreases, the maximum tensile stresses σ x and σ y for curved tunnels were found to decrease and increase, respectively. Furthermore, an insufficient quantity of injection grouting will trigger detrimental effects to nearby structures during the approaching excavation. [ABSTRACT FROM AUTHOR]

• Investigates the progressive failure phenomenon of the shallow tunnel roof by virtue of the functional catastrophe theory. • The failure mechanism proposed can not only predict the 'underground' collapse but also the 'spalling' collapse. • The comparisons of the results between analytical predictions are validated. Collapse mechanism for the tunnel or underground cavern is important for the support system design. This paper investigates the progressive failure phenomenon of the shallow tunnel roof under the condition of plane strain by virtue of the functional catastrophe theory. Firstly, considering the plastic strain energy as an index for the state of the studied system, the analytical solutions for the profile curves of the collapsing blocks from the shallow tunnel roof including the 'underground' collapse and 'spalling' collapse are deduced on the basis of the nonlinear power-law failure criterion. Moreover, the criterions are derived to estimate whether the progressive failure phenomena including the 'underground' collapses and 'spalling' collapses for shallow tunnel roof would occurr or not. Then, the analytical prediction obtained from this paper for the shallow tunnels is compared with the existing analytical prediction for the deep tunnels. Finally, the comparisons of the results between analytical prediction obtained from this paper and two existing model tests are conducted to demonstrate the validity of the proposed analytical methodology. [ABSTRACT FROM AUTHOR]

Rainfall infiltration is one of the main triggers of slope failure. Based on the upper bound theorem of limit analysis, this work presents an analytical stability analysis of a 3D vertical cut slope subjected to rainfall infiltration. An analytical model that can directly provide pore water pressure change at any depth and time is adopted to calculate the time-dependent matric suction and shear strength of unsaturated soil during the rainfall infiltration process. Thereafter, based on a 3D rotational failure mechanism of a slope, the energy balance equation is built, and the factor of safety (FoS) of the slope is consequently determined in conjunction with the strength reduction technique. The influences of the 3D characteristics of the slope and rainfall patterns on both FoS and failure pattern of the slope are investigated. It is found that the 3D characteristic of slope is a key factor which determines the FoS of slope. Different rainfall infiltration patterns lead to diverse variation rules of both the FoS solutions and the critical failure patterns of slope. However, these rainfall patterns with a same accumulated rainfall result in the same FoS solution of slope at the end of rainfall infiltration. The present work may provide guidance on the stability analysis and preliminary design of slopes subjected to rainfall infiltration. [ABSTRACT FROM AUTHOR]

For deep-buried shield tunnels in sand, it is difficult to determine the loosening earth pressure in front of tunnel face due to the significant soil arching effect during excavation. Considering the soil arching effect and the correlation between the relative displacement of soil and the arching deformation patterns, this paper proposed a new analytical model of loosening earth pressure in front of tunnel face. This soil arching effect refers to the load transfer of parabolic soil arch, the height of shear bands and the lateral stress ratio on both sides of rectangular arch. Formulas for calculating the three-dimensional loosening earth pressure were deduced. Then the reliability of this model was verified through comparing the results from the proposed model and the three-dimensional trapdoor experiments. Subsequently, this model of loosening earth pressure was introduced into a five-truncated cones model to compute the limit support pressure on tunnel face. Finally, comparisons of the proposed model and classical models as well as typical centrifuge model tests were conducted. Comparative analysis shows the proposed model of loosening earth pressure excels the classical models, and the failure zone predicted by the proposed model is in good agreement with that obtained from centrifuge model test. [ABSTRACT FROM AUTHOR]