Secondary Lining Structure Research Articles

Study on the stressing state features of basalt fibre concrete lining structure under sulphate erosion

Basalt fibre (BF) is an environmentally friendly material with excellent corrosion resistance. When tunnels cross gypsum rock strata, the gypsum rock will dissolve sulphate and erode the supporting structure, thus affecting the safe operation of the tunnels in the long term. Adding BF to the supporting structure of gypsum rock tunnels can improve its resistance to sulphate erosion. This paper took Wuzhishan Tunnel as a case, and first determined the sulphate concentration of the gypsum rock stratigraphic environment at the site; then, analysed the change of mechanical properties of basalt fibre concrete (BFC) before and after sulphate erosion by mechanical tests; finally, examined the deformation and force characteristics of the BFC secondary lining structure by numerical simulation. The results showed that the bridging effect of BF fibres and the stable spatial network structure formed inside the concrete enhanced the mechanical properties of BFC and its ability to resist sulphate erosion. However, due to the agglomeration effect of BF fibres, too much BF would reduce the mechanical properties and erosion resistance of BFC. At a BF content of 6 kg/m³, BFC had the strongest ability to resist sulphate erosion, and the cube compressive strength, axial compressive strength, and modulus of elasticity of BFC were the highest, with 47.8 MPa, 33.6 MPa, and 38.7 GPa, respectively. The dense calcium silicate hydrate (C-S-H) gel, generated near the BF, enhanced the connection between the cementitious and the aggregate, inhibited the development of microcracks within the concrete, and reduced the erosion channels for sulphate ions. The maximum displacement of the BFC secondary lining structure was reduced by 20.15 % compared to plain concrete (PC) after sulphate erosion. The secondary lining structures consisting of both BFC and PC were stressed the most at footing. The secondary lining structure composed of BFC had better deformation resistance and higher strength than PC.

Research on Energy Absorption Characteristics of Polypropylene Foam Concrete Buffer Layer in High Ground Stress Soft Rock Tunnel

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.

Safety Analysis of Secondary Lining of Yulinzi Tunnel Based on Field Monitoring

In order to assess the safety of the secondary lining in water-rich Loess Tunnel, this study relies on the Yulinzi Tunnel project to continuously monitor the stress of the steel reinforcement in the secondary lining and analyze the temporal variation of the steel strain. Based on this data, the temporal variation and distribution characteristics of the internal forces of the structure were obtained through section force calculation. The safety factor of the secondary lining structure was evaluated by calculating the safety factor of the structure. It was found that the variation of the safety factor with time conforms to the exponential function, and the fitting results of different measurement points were good. This could be used to predict the future safety factor of the tunnel and evaluate its long-term safety, which has practical guidance significance for actual engineering projects. In addition, the long-term stress and structural deformation characteristics of the tunnel were obtained through numerical simulation.

Model experiment and support optimization analysis of primary support arch cover excavation of large-section metro station in sandy mudstone stratum

The span and height of the Xietaizi metro station of Chongqing Rail Transit Line 18 are all larger than 20 m. The concept of “primary support arch cover” is adopted in the construction method, which aims to give full play to the bearing capacity of sandy mudstone, greatly improve the construction efficiency, and reduce the economic cost. In this paper, the model experiment of primary support arch cover excavation of large-section metro station in sandy mudstone stratum was carried out and the progressive failure process of the initial arch cover was revealed. It is found that the ground surface settlement is not strictly symmetrical about the station center, which is more significant in the case of the measuring points are far away from the central axis of the cavern. Since the support structure installed, the steel arch stresses and anchor axial forces at the inner and outer sides are in a rapid growth stage, and then shows a slow growth trend until stable. For the stresses at the inner and outer sides, the steel arch at the left arch shoulder is characterized by overall compression. The vertical displacements and convergence of the station are more prominent than the horizontal displacements and convergence, which indicates that the significance of control the settlement of the arch crown. The vertical convergence of the station is mainly caused by the settlement of the crown. When the level of loading is large, the number of longitudinal cracks will be increased as penetrating crack and the bulging phenomena will occur at the left arch shoulder of the secondary lining structure. Based on the numerical simulation, the whole dynamic procedure of construction is optimized from the demolition timing of temporary support. The vertical displacements and horizontal convergences for overall demolition schemes are smaller than those for stepping demolition with the excavation of middle guide holes.

Study on structural mechanical characteristics and safety warning of NATM tunnel in aquifer

With sustainable developments in transportation facilities, the construction of the undersea tunnel has become inevitable. Controlling the construction and operation of the undersea tunnel structures dynamically and ensuring their safety is of primary concern. Therefore, using the rich water mountain section of the Lujiazhi subsea tunnel constructed by NATM (New Austrian Tunnelling Method) as a case study, an intelligent real-time tunnel health monitoring system integrating tunnel monitoring, wireless transmission and safety assessment was developed. The monitoring results show that the surrounding rock water pressure, earth pressure and stress of the secondary lining structure experienced stages of rapid change, continuous change and stability. The tunnel substructure is relatively weak as a whole, and the left invert is the weakest part of the whole structure. It was suggested to optimize and reinforce the tunnel substructure accordingly. The rationality of the tunnel drainage system and reliability of field test data are verified by numerical simulation. Finally, the real-time fuzzy comprehensive evaluation model of tunnel operation safety conditions based on online monitoring data is established to realise the real-time evaluation and early warning of Lujiazhi tunnel structures’ health conditions. HIGHLIGHTS An intelligent real-time tunnel health monitoring system is developed. The deformation characteristics of submarine tunnel are revealed. The submarine tunnel drainage system rationality of lining structure are proved. The safety evaluation model of submarine tunnel structure is proposed.

Evaluation method of highway quality and safety based on finite element analysis

With the continuous advancement of China's transportation infrastructure, the number and proportion of highway tunnels in expressway construction are increasing year by year. In order to accurately evaluate the quality and safety of highway tunnel engineering, the finite element analysis is used to evaluate the quality of highway tunnel secondary lining structure, the slotting method is used to analyze the working stress of tunnel secondary lining structure, and the load on the secondary lining structure is inversely analyzed combined with the finite element three-dimensional model to evaluate the quality and safety of tunnel secondary lining structure. The test results show that the error rate of working stress of secondary lining structure deduced by combining slotting method and finite element analysis is 2.22%, the average error rate of vertical uniformly distributed load analysis of two lane and three lane highway tunnels is 7.09%, and the average error rate of horizontal lateral pressure coefficient analysis is 16.37%. The numerical errors are within the acceptable accuracy range of actual highway tunnel engineering. Using finite element analysis to analyze the quality and safety of highway tunnel can accurately evaluate the quality and safety of secondary lining structure of tunnel engineering, and provide effective data reference for actual quality evaluation and defect reinforcement of tunnel engineering.

Mechanical and Numerical Simulation on Weathered Argillaceous Siltstone under Cyclic Loading

Secondary lining cracking always occurs in existing tunnels when the tunnel passes through the weathered argillaceous siltstone layer, which seriously affects the safety of the tunnel. In order to study the mechanical properties of weathered argillaceous siltstone and the cracking law of the secondary lining, this study analyzes the relationship of accumulative plastic strain between the dynamic stress amplitude and static deviator stress, as well as the cracking law of the secondary lining of the sample. The results show that under cyclic loading, there are obvious accumulative plastic strain in weathered argillaceous siltstone; the bearing capacity of the secondary lining structure at the biased part shows an evident increase than that of others with cracking generating faster. The research results provide a reference for the safety and operation of the tunnel that runs through the weathered argillaceous siltstone layer.

Grouting Design of Rich Water Tunnels and the Calculation of Distance between Annular Blind Pipes

The rich water tunnel often uses “water blocking and drainage limiting” waterproofing and drainage systems. On the one hand, the drainage system is set behind the lining to reduce the water pressure. On the other hand, the stratum grouting is used to control the discharge flow of groundwater. In the drainage system, it is important to determine the distance between the annular blind pipes, but there is no clear calculation formula, which leads to the designer often relying on experience. First, the groundwater drainage system is constructed. Based on Darcy’s law and the law of conservation of mass, the formula for calculating the seepage discharge and the seepage pressure with the parameters of annular blind pipe spacing is derived. At the same time, the design parameters of the grouting circle are optimised, and then the formula of annular blind pipe spacing is derived according to the design value of the antiwater pressure of the secondary lining structure and the allowable seepage discharge of the tunnel. Finally, based on the case study of the Hongtu extra‐long tunnel under construction, it is verified by field monitoring data. The results show that (1) grouting reinforcement is an important means to reduce water seepage, and tunnel water seepage can be adjusted by changing the thickness and permeability coefficient of the grouting reinforcement circle, in which the thickness of the reinforcement circle should not be too large, and the permeability coefficient should not be less than 1/80 of the surrounding rock permeability coefficient; (2) according to the derived formula, the water pressure of the secondary lining structure decreases in a parabolic manner from the middle of the two rows of annular blind pipes to the place where the annular blind pipes are set; (3) the allowable water seepage of the tunnel and the design value of the water pressure resistance of the lining structure should be considered when determining the distance between annular blind pipes; and (4) based on the derived formula, the distance between the annular blind pipes in the test section of the Hongtu extra‐long tunnel is determined to be 8 m.

Research and Analysis on the Supporting Structure of the Second Lining of the Tunnel in the Phyllite Stratum

The reasonable construction of the secondary lining structure of the tunnel is an important link to ensure the stability of the surrounding rock of the tunnel. Taking a phyllite stratum tunnel project in Jiangxi as the background, the Flac3D finite difference software was used to numerically simulate and analyze the supporting structure of the secondary lining. The impact of support timing on surrounding rock stress. The calculation results show that with the progress of the construction step, the main period of the displacement of the vault is after the excavation of the upper section of the tunnel before the upper section support; The plastic zone of the surrounding rock changes obviously, especially above the tunnel, and finally the plastic zone develops to the ground; the stress of the surrounding rock shows a decreasing trend with the increase of the time of the secondary lining. The research results can provide certain guiding significance for the construction of the second lining of the tunnel under similar geological conditions.

Safety Analysis of the Secondary Lining Structure of Existing Tunnel with Cracks

Because cracking of the secondary lining is one of the most common diseases in road tunnel, it is of great practical significance and theoretical value to analysis and research on the safety of lining structure of existing tunnel with cracks. Based on crack models of fracture mechanics, the calculation method of safety evaluation for the secondary lining structure of existing tunnel with cracks was discussed through numerical analysis. The bearing capacity of non - destructive lining and cracked lining was analyzed and compared by model tests. Results showed: (1) the finite element method of fracture mechanics could be used to evaluate the safety of the secondary lining structure of existing tunnel with cracks. (2) The size order of the required load when the cracks occurred in the different parts; The arch foot is smaller than the vault; the vault is smaller than the haunch; the haunch is smaller than the invert. (3) When the crack was located at the crown and arch foot, it had the most significant influence on the safety of lining structure. (4) The bearing capacity of the lining structure declined because of cracks, and it decreased by 37.5% when there was longitudinal crack at the bottom of the inverted arch of tunnel.

Study on load distribution characteristics of secondary lining of shield under different construction time

With the massive construction of underwater shield tunnels, the single segmental lining is unable to meet long-term safety requirements in many cases; thus, the double-lining shield tunnel has attracted increasing attention in recent years. The construction time of the secondary lining is a key factor for the mechanical properties of a double lining. In this paper, taking the Shiziyang shield tunnel as the example, we investigate the interaction between shield segment and secondary lining under different construction times by similar model tests. According to the load variation characteristics of the segment and secondary lining structures under different construction times, the load distribution law of a secondary lining structure under the condition of different external loads is analyzed in detail. The results show that (a) the ability of the double-lining structure to bear the external load as a whole will not be changed by a different construction time of the secondary lining, although the bearing capacity at different locations is influenced. (b) Due to the nonuniformly distribution of the stiffness of each part of the segment, the segment and secondary lining have a noncoordinated deformation under the external load. The distribution pattern of the earth pressure outside the segment gradually changes from a uniform distribution to a nonuniform distribution with the delay of the construction time of the secondary lining. In the meantime, the distribution of contact pressure of the joint surface tends to gradually transform from an irregular distribution to a symmetrical distribution along the circumferential direction. (c) The bearing performance of the secondary lining is more stable with the delay of the construction time of the secondary lining during construction, which is more beneficial to the bearing performance of the double-lining structure. In the actual project, it is recommended that the secondary lining be applied when the external loads of the segments are up to 83–100% of the design load, which is beneficial to the bearing performance of the secondary lining.

Shock Reduction Techniques for a Submarine Tunnel

Considering the effects of seepage and dynamic pressure, defining a rock mass as a saturated porous media, and using the finite element method, a dynamic fluid–structure interaction model of a subsea tunnel with a viscous spring artificial boundary is established. Adopting rubber and foam concrete as shock absorption layers and inputting both horizontal and vertical earthquake waves, the time history curves of the first principal stress at key points in the secondary lining structure are comparatively analyzed based on the presence and absence of shock absorption layers. The principal stress peaks are also analyzed. The damping effect of the shock absorption layer is studied. The results show that the peak and principal stresses at the main parts of the tunnel lining structure decrease after the shock absorption layer is established. Obvious decreases occur in the vault and inverted arch. A certain degree of peak stress reduction is also observed after the shock absorption layer is established. Establishing the shock absorption layer does not change the spectrum characteristics of the tunnel structure. Foam concrete shock absorption is recommended because the damping effect of foam concrete is more observable than that of rubber.

Construction Simulation and Stress Characteristics of Large Span Tunnel Crossing Fault Fracture Zone

Combined with the engineering of a large span tunnel passing through the fault fracture zone, the settlement of the crown in the fault zone is studied. The stress situation of the secondary lining in the fault is analyzed. The influence zone of fault fracture zone is put forward based on the first principal stress of structure. The results show that: (1) The fault fracture zone has great influence on the settlement of the crown when the step method is used, and the settlement value is 2.14 times that of the fault free zone. (2) The fracture convergence zone will obviously postpone the convergence time of crown settlement. In this case, 2nd construction steps are delayed. (3) The fracture pressure zone will obviously increase the lateral pressure of the secondary lining structure, which is 1.3 times of that in the fault free zone. The tensile stress concentration of the secondary lining walls at the fault is 1.17 times of that without faults. (4) Based on the first principal stress of the secondary lining wall, the width of the fault is 16m, and its influence area is about 3.5 times of its own width.

Optimization of Supporting Structures and Parameters of Tunnels in Soft Phyllite

The study investigated the extra-long Shuangxiling tunnel in soft phyllite within Nanchang–Ningdu highway in Jiangxi province, China. The supporting scheme of reducing the size and density of anchor rods while strengthening the stiffness and strength of preliminary support was put forward aiming at the repeated occurrence of great deformation of surrounding rocks during tunneling. Moreover, two groups of comparative supporting schemes were introduced for comparison. Based on the numerical simulation, the study calculated the amount of displacement deformation, stress on anchor rods, development of plastic zones, stress on shotcrete, and stress on secondary lining structure under different supporting schemes. By conducting field monitoring test, the surrounding rock deformations and pressures under different supporting schemes were monitored and measured in real time. The research results showed that after strengthening the stiffness and strength of preliminary support, the surrounding rock pressure on the supporting structure increased. It limited the preliminary stress release rate of surrounding rocks, protected the integrity of surrounding rocks and controlled the sustained deformation of surrounding rocks. However, weakening the size and density of anchor rods had an insignificant effect on the whole supporting effect. The result of field test was basically consistent with that obtained through numerical simulation, which theoretically and practically verified the scientificity and feasibility of the supporting scheme of weakening the size and density of anchor rod while strengthening the stiffness and strength of preliminary support. The research result provides references for the support optimization of similar tunnels along the highway.

Structure Optimization for the Support System in Soft Rock Tunnel Based on Numerical Analysis and Field Monitoring

Optimization of the support used when constructing tunnels in soft surrounding rock has long been a hotspot in engineering. To control the deformation of soft rock and ensure construction safety, this paper proposes a support scheme involving weakening the anchor bolts while enhancing the rigidity and strength of the primary supports. This was realized by combining the large deformations that often occurred during the construction of the Youfangping tunnel of the Gucheng-Zhuxi expressway. Moreover, the scheme was analyzed and compared with the original scheme and one involving weakening the anchor bolts. In addition, the displacement deformations, force conditions on the anchor bolts, development of plastic zones, stress on the shotcrete, and force conditions on the secondary lining structure were analyzed via numerical simulation for the different support schemes. Concomitantly, three groups of experimental sections were selected on-site to monitor and measure the deformations and force conditions of the surrounding rock for these three support schemes. The numerical simulations and field-monitoring results show that weakening the anchor bolts has a small effect on the overall support provided by the support system. However, it can simply the process and reduce engineering costs. Moreover, increasing the rigidity and strength of the initial supports can effectively control the large deformations in the surrounding rock. Therefore, a support scheme in which anchor bolts are weakened while the rigidity and strength of the initial supports are enhanced, as presented in this paper, proves to be feasible method of support optimization. It also provides a useful reference for optimizing other similar tunnels along the expressway.

Research on Mechanical Characteristic of Weak Surrounding Rock Large Span Double and Multi-arch Tunnel Construction

According to construction scheme of some weak surrounding rock large span double and multi-arch tunnel works, finite element value simulation method is adopted to research weak surrounding rock deformation characteristic, anchor bolt mechanics characteristic, preliminary support and secondary lining structure mechanical characteristics, etc, and the research result shows that: repeatedly disturbance of excavation of middle pilot tunnel and subsequent supporting excavation shall easily reduce surrounding rock strength in the range of middle wall top and middle line of arch top of left and right pilot tunnels, therefore, prior to excavation of middle pilot tunnel, surrounding rock of tunnel top shall be pregrouting reinforced to improve integrated strength of surrounding rock of arch top, max. accumulated settlement displacement of tunnel is 19.45mm, max. horizontal convergence displacement of side wall of left and right tunnel is 9.71mm, max. vertical upheaval displacement of middle wall bottom is 8.82mm, above displacement can all be within controlled range satisfying design requirement; max. plastic zone vertical depth of upper side of left and right tunnel arch top is respectively 1.23m and 2.06m, inverted arch bottom plastic zone vertical depth is 2.74m and 3.37m, radial depth of middle plastic zone of side wall of left and right tunnel is respectively 0.87m and 1.73m, mutual impact range of spatial effect of tunnel face of left and right tunnel is 3 folds tunnel span. This research shall be referred to by similar tunnel design and construction.

Research on Mechanical Characteristic of Weak Surrounding Rock Large Span Double and Multi-Arch Tunnel Construction

According to construction scheme of some weak surrounding rock large span double and multi-arch tunnel works, finite element value simulation method is adopted to research weak surrounding rock deformation characteristic, anchor bolt mechanics characteristic, preliminary support and secondary lining structure mechanical characteristics, etc, and the research result shows that: repeatedly disturbance of excavation of middle pilot tunnel and subsequent supporting excavation shall easily reduce surrounding rock strength in the range of middle wall top and middle line of arch top of left and right pilot tunnels, therefore, prior to excavation of middle pilot tunnel, surrounding rock of tunnel top shall be pregrouting reinforced to improve integrated strength of surrounding rock of arch top, max. Accumulated settlement displacement of tunnel is 19.45 mm, max. Horizontal convergence displacement of side wall of left and right tunnel is 9.71 mm, max. Vertical upheaval displacement of middle wall bottom is 8.82 mm, above displacement can all be within controlled range satisfying design requirement; max. plastic zone vertical depth of upper side of left and right tunnel arch top is respectively 1.23 m and 2.06 m, inverted arch bottom plastic zone vertical depth is 2.74 m and 3.37 m, radial depth of middle plastic zone of side wall of left and right tunnel is respectively 0.87 m and 1.73 m, mutual impact range of spatial effect of tunnel face of left and right tunnel is 3 folds tunnel span. This research shall be referred to by similar Tunnel design and construction.

Analysis of the Sensitivity of Influencing Factors on Tunnel Secondary Lining Structure Stress

AbstractOn the basis of the load-structure model and FEM and taking the secondary lining of the Qingdao-Rongcheng intercity railway tunnel as a research object, sensitivity analysis of the influencing factors on the secondary linings internal forces is conducted via the sensitivity coefficient method. The influencing factors are the elastic resistance coefficient of surrounding rock, the secondary lining thickness, the elastic modulus of secondary lining, and the lateral pressure coefficient, whose values are taken from engineering practice. The analysis result shows that (1) to crown bending moment, the descending order of the sensitivities of the influencing factors are secondary lining thickness, elastic resistance coefficient of surrounding rock, lateral pressure coefficient, and elastic modulus of secondary lining; (2) to crown axial force, the descending order is lateral pressure coefficient, elastic resistance coefficient of surrounding rock, secondary lining thickness, and elastic modulus of secon...

隧道二次衬砌监测的非线性回归分析研究

The performance degradation of secondary lining is the main disease that affects the tunnel operation. Therefore,safety analysis on the secondary lining structure by optical fiber communication technology means importance to the tunnel operates health.According to the actual monitoring data,which is monitored by the optical fiber Bragg grating strain sensor embedded on the secondary lining of Tianxin tunnel,the best typical function model are selected for the non-linear regression analysis and then the regression curves which reflect the strain development variation trend are obtained.Results indicate that test methods achieved the judgment of tunnel structure stability by forecasting support nursing structure(monitoring points)strain trend,judging support nursing effect and analyzing on current and eventually tunnel stability of supporting structure.

Numerical Analysis of Advanced Displacement in Construction Progress of Tunnel Excavation with Weak Surrounding Rock

Analysis of advanced displacement in construction progress of tunnel excavation with weak surrounding rock is carried out by numerical method and comparison of model test result. In allusion to the problems of regional landslides and extruded large-deformation seriously impacting the stability of rock mass in construction process of large-section tunnel with weak surrounding rock, the elastic-plastic numerical simulation relying on Liangshui tunnel of Lan-Yu railroad is conducted on mechanical behaviors and deformation steric effect of tunnel construction and the calculation results are compared with the modeling data. The research results show that: the steric effect of excavation face is the dominant factor in the incidence of working face and the stress of surrounding rocks gradually releases from excavation face; the range of 0.5~1 times the cave diameter around rock mass in front of working face is the disturbance range and the key area of stabilization and reinforcement for wake surrounding rock. According to the analysis and construction practice, the supporting structure of large-section tunnel with weak surrounding rock should be established as soon as possible to control the displacement change of surrounding rock in the range of load-bearing ring, reduce disturbance and improve the self-bearing capability of surrounding rock. Because of the distinct excavation steric effect of weak surrounding rock, the secondary lining structure must be established in time to bear the later pressure and restrict the large displacement of surrounding rock. The research results can provide reliable basis for engineering stability control of analogous tunnels.