Tunnel Lining Research Articles

Evaluation of the Damping Layer between the Tunnel Lining and Surrounding Rock via a Shaking Table Test

This paper primarily investigates the protective effect of the damping layer in tunnel lining structures under dynamic loads. A series of shaking table tests was conducted to investigate the seismic response mechanism of tunnel linings and the influence of surrounding rocks using the Wenchuan earthquake (magnitude 8.0) as a reference. The results show that the effect of the damping layer protection measures is accurate using the efficiency evaluation method for the damping layer under seismic excitation. The lower the excitation acceleration is, the better the effect will be. In addition, the damping coefficient is introduced to optimize the efficiency evaluation method for the damping layer. Among the factors influencing the seismic response of lining structures, the type of surrounding rock has a significant impact while the thickness of the damping layer has a relatively lesser influence. In seismic intensity areas of equal magnitude, an increase in the damping layer thickness leads to a more noticeable effect. In the different seismic intensity areas, the difference in the protection effect with the change in thickness is no longer obvious with the increase in seismic intensity. Moreover, the presence of a damping layer alters the intrinsic vibration characteristics of the tunnel lining structure, creating a space for deformation between the lining and the surrounding rock.

Evaluation of Hydraulic Tunnel Lining Durability Based on Entropy–G2 and Gray Correlation–TOPSIS Methods

Under long-term water flow, the physical and chemical properties of hydraulic tunnel linings are more likely to deteriorate than those of road tunnels, thus affecting the normal operation of tunnels. Evaluating the durability of hydraulic tunnel linings can help to grasp the durability of tunnels in a timely and accurate manner and provide a basis for the routine maintenance of tunnels. This paper proposes new methods for evaluating the durability of hydraulic tunnel linings. Firstly, the types of tunnel defects are divided, the durability indices corresponding to the defects are selected scientifically, and a hydraulic tunnel durability evaluation index system is established. Then, the G2 method is modified by the entropy value method to make it a subjective and objective weighting method, which can make the weights fit the reality while the calculation is easy, and the TOPSIS method is modified by the gray correlation degree to optimize the judgment criteria between the evaluation scheme and the ideal solution. Finally, the practicality and accuracy of this method are verified by the calculation of the five sections of a tunnel with lining durability grades of A, B, C, B, and C, respectively, which matched the calculation results of the RAGA-PP method in the related literature.

Stresses in sprayed concrete tunnel linings at Heathrow Terminal 4

A wide variety of instrumentation was deployed during construction of the sprayed concrete lined tunnels at Heathrow Express Terminal 4 station in the mid-1990s, some of which is still functioning and is accessible for the taking of readings today. This paper presents a nearly 20-year history of stress in the primary lining of the concourse tunnel measured using radial and tangential pressure cells on and in the sprayed concrete. Data from tangential pressure cells require careful interpretation and the new and complete methodology for achieving reliable results described in previous work by the authors was used to provide the stress history from construction into the long term. This is a unique case study in terms of both the detail and interpretation of the measurements and the time period over which measurements have been taken. The results show that pressure cells are very sensitive and respond to changes in stress due to nearby construction activities and also that, after construction has ceased, stresses stabilise at a value well below the full overburden pressure (the vertical total stress at tunnel axis level).

Numerical Simulation of PFRC Fracture Subjected to High Temperature by Means of a Trilinear Softening Diagram.

Fibre-reinforced concrete (FRC) has been used for decades in certain applications in the construction industry, such as tunnel linings and precast elements, but has experienced important progress in recent times, boosted by the inclusion of guidelines for its use in some national and international standards. Traditional steel fibres have been studied in depth and their performance is well-known, although in recent years new materials have been proposed as possible alternatives. Polyolefin macro-fibres, for instance, have been proven to enhance the mechanical properties of concrete and the parameters that define their behaviour (fibre length, fibre proportion or casting method, for instance) have been identified. These fibres overcome certain traditional problems related to steel fibres, such as corrosion or their interaction with magnetic fields, which can limit the use of steel in some applications. The behaviour of polyolefin fibre-reinforced concrete (PFRC) has been numerically reproduced with success through an embedded cohesive crack formulation that uses a trilinear softening diagram to describe the fracture behaviour of the material. Furthermore, concrete behaves well under high temperatures or fire events, especially when it is compared with other construction materials, but the behaviour of PFRC must be analysed if the use of these fibres is to be extended. To this end, the degradation of PFRC fracture properties has been recently experimentally analysed under a temperature range between 20 °C and 200 °C. As temperature increases, polyolefin fibres modify their mechanical properties and their shape, which reduce their performance as reinforcements of concrete. In this work, those experimental results, which include results of low (3 kg/m3) and high (10 kg/m3) proportion PFRC specimens, are used as reference to study the fracture behaviour of PFRC exposed to high temperatures from a numerical point of view. The experimental load-deflection diagrams are reproduced by modifying the trilinear diagram used in the cohesive model, which helps to understand how the trilinear diagram parameters are affected by high temperature exposure. Finally, some expressions are proposed to adapt the initial trilinear diagram (obtained with specimens not exposed to high temperature) in order to numerically reproduce the fracture behaviour of PFRC affected by high temperature exposure.

Aerodynamic behavior of flaky spalled blocks in high-speed rail tunnel lining under slipstream

As high-speed railway tunnels continue to serve for long periods of time, the tunnel lining is subjected to long-term cyclic tension and compression from train aerodynamic loads, thereby causing cracks to propagate and spalled blocks to fall off, which severely impact the safety of train operation. This paper is based on the improved delayed detached eddy simulation (IDDES) method and establishes a 3D fluid–solid coupling calculation model of spalled block-high-speed train-tunnel-air. Explores the differences in the motion trajectory and force of spalled blocks falling off at different peeling times under the impact of a high-speed train traveling at 300 km/h, and investigates the relationship between the spalled blocks and the changes in train aerodynamic flow field structure and aerodynamic pressure during the motion process in order to understand the aerodynamic behavior and flow field structure mechanism of spalled blocks. Under the action of slipstream, the spalled blocks exhibit a combined form of translation and rotation while falling, with the translation mainly occurring in the longitudinal (X-axis) direction and the rotation being most obvious around the Z-axis. Some significant differences are observed in the translational trajectory and rotational angle of the spalled blocks in the vertical and horizontal directions at different peeling times, and the longitudinal displacement distance is 3 to 38 times the horizontal displacement distance. The maximum rotational angle of the spalled block that peels off when the train head arrives is along the Z-axis.

The Safe Load-Bearing Capacity of Railway Tunnel Linings under High-Pressure and Water-Rich Conditions

High water pressure has been identified as the direct cause of water seepage problems in tunnels. Consequently, it is imperative to ascertain the safety load-bearing limits of tunnel linings in high-pressure, water-rich strata. In this study, FLAC3D (V5.0) numerical simulation software was employed to establish seepage models of tunnels under high-pressure, water-rich conditions, taking an actual engineering project as a reference. The hydrostatic pressure on tunnel linings under various conditions, including different permeability coefficients of the surrounding rock, grouting rings, levels of the water table, and coordinates of lining positions, was computed. By extracting the results of these simulations, correlations between lining water pressure and various parameters were analyzed, and preliminary hydrostatic pressure calculation formulas were deduced. Through regression analysis using SPSS (19.0) software, a general calculation formula for lining water pressure was derived. Given similar surrounding rock conditions, it was revealed that railway tunnel lining types adhere to a universal standard. The calculation formula for lining water pressure, when integrated with lithostatic pressure in the seepage model, facilitates the computation of the maximum pressure head that the tunnel lining can withstand under different conditions. A tabulation summarizing safe water head heights under various conditions is also presented, which enables rapid consultation of the safe load-bearing range of tunnel lining under corresponding conditions. This study provides a new calculation method for the lining water pressure of a water-rich railway tunnel, filling the literature gap. The safe tunnel head query table provides a new research approach for the design of water-rich tunnels. The research method in this article is rare in the literature, and the research approach has obvious innovations. The findings of this study have the potential to provide a theoretical foundation and data reference for the structural design of tunnel linings and the remediation of related issues.

Tunnel lining crack expansion and maintenance strategy optimization considering train loads: A case study.

Cracks in concrete tunnel linings are inevitable during service life. It is necessary to keep abreast of the cracking condition of the lining and formulate reasonable inspection and maintenance measures to ensure operational safety. Considering the influence of train loads on the safety and service performance of cracked linings, the expansion process of lining cracks and the maintenance strategy of tunnels during the service period was investigated. The impact of detection probability and maintenance measures on the service life of tunnel lining and the cost of detection and maintenance of cracked lining in the whole life cycle was analyzed; the optimization calculation model of tunnel lining crack detection and maintenance strategy based on genetic algorithm was established with the multi-objective optimization function of maximizing the service life of detection and maintenance and minimizing the total cost of detection and maintenance of fatigue cracks. The optimization analysis of lining crack expansion, detection, and maintenance was carried out for an operational railroad tunnel. Finally, an optimization analysis of lining crack expansion and maintenance was carried out in a railway tunnel. The results show that the stress intensity factor at the tip of the lining cracks is the same as the train load waveform; the magnitude of the stress intensity factor approximately satisfies the exponential function relationship with the depth of cracks; the fatigue service life of cracked lining is positively correlated with the cost of inspection and maintenance; the adoption of the necessary maintenance and the increase in the number of inspections and maintenance have a better economy while meeting the expectation of the service life. According to the Pareto solution set, the management can formulate the inspection and maintenance strategy based on the tunnel's expected life and maintenance budget.

Development of normalized acoustic response analysis for soil-structure contact state evaluation

Abstract: Introduction. Impulse response testing is currently one of the most common methods of acoustic express diagnostics of the foundation slabs and other plate-like structures state, but is relatively uncommon in the Russian Federation. A modification of this technique, based on the analysis of normalized response parameters, is being actively developed by Russian specialists to assess the quality of soil-structure contact. The issue of developing of the new informative parameters and criteria for identifying of anomalies associated with contact violations is topical.
 Aim. The purpose of the work is to inform specialists about the capabilities of the normalized acoustic response analysis method for localizing zones of soil-structure contact violation. It is proposed to apply the attribute "void index" and an auxiliary criterion for data analysis based on the nature of the distribution of attribute values.
 Materials and methods. The features of the normalized acoustic response testing metodologia for soil-structure contact violations searching are described. The method for calculating the attribute "void index" for the data of the technique is shown. A criterion for the selection of anomalous areas is proposed, based on the data analysis of the nature of the distribution of attribute values.
 Results. Verification of the "void index" attribute application for searching for zones of soil-structural contact violation is shown on the results of a survey of a tunnel liner physical model with a known position of the void. An example of the results of a survey of a slab at the base of an underground car park shows the use of a "void index" in conjunction with the normalized signal energy attribute. A method for statistical processing of the results is proposed, which supplements the traditionally used "three sigma" criterion. 
 Conclusions. A method of the "void index" attribute application to localize zones of soil-structure contact violation for the normalized acoustic response analysis method is shown. A method for statistical data processing is proposed, considering the nature of the distribution of response attributes.

Propagation characteristics and control technology of blasting vibration in neighborhood tunnel

During the tunnel construction process using the drilling and blasting method, the induced blasting vibration always poses a great threat to the stability and safety of the adjacent tunnel supporting structure. To improve the efficiency and safety of tunnel blasting construction, the vibration propagation and peak particle velocity (PPV) distribution of the lining of an excavated tunnel were investigated during the blasting of an adjacent tunnel located in Guangxi province. The evolution process and distribution characteristics of the PPV of the lining of adjacent tunnels were monitored and analyzed. The results show that the maximum blasting vibration velocity of the lining of the adjacent tunnel can be shown as: PPVx > PPVz > PPVy; hence, the PPVx plays a significant role in the vibration of the adjacent tunnel. According to the tensile stress failure criterion, the PPV threshold was determined to be 12.7 cm/s in this study. To control the damage of surrounding rock induced by the blasting vibration, compound wedge-shaped cutting technology, stress wave dislocation superposition technology, and pre-splitting blasting technology were employed to reduce the impact of blasting vibration on the excavated tunnel.

Recent Progress in the Cracking Mechanism and Control Measures of Tunnel Lining Cracking under the Freeze–Thaw Cycle

With the rapid increase in the scale and number of tunnels in cold regions, the frost damage problems, such as cracking of the lining structure under the action of freeze–thaw cycles are becoming increasingly prominent. This review article collects and sorts out the frost damage phenomena that occur in the lining structure of tunnels in cold regions under the action of freezing and thawing cycles, classifies the frost damage phenomena into structural frost damage and non-structural frost damage, and proposes that the research on the mechanism of lining frost damage and its prevention measures should focus on lining cracking. According to the damage degree of the freeze–thaw cycle to the lining structure and its influence on tunnel operation, the cracking mode and cracking stage of lining are introduced. The analysis focuses on the mechanism of cracking in lining structures subjected to freeze–thaw cycles, considering the external force caused by frost heaving, the alteration of mechanical properties in lining concrete, and the internal changes in the microstructure of the concrete. Additionally, the factors that contribute to the occurrence of lining cracking are summarized. Based on this, corresponding control measures have been organized to provide reference for the development of cracking of the lining structure under the action of freeze–thaw cycle.

Experimental investigation on fire damage to staggered segmental lining of shield tunnel

Fire is a significant hazard to the safe operation of tunnels, causing extensive damage and deterioration to the lining. This research proposed a prototype test of a shield tunnel staggered segmental lining under stratum loads subjected to fire. The fire followed the ISO834 standard curve; the maximum temperature reached 1144.9 °C and lasted 195 min. The temperature evolution law of the lining is positively correlated with the distance from the fire source and negatively correlated with the depth of the lining. The fire surface of the lining undergoes severe cracking and peeling, accompanied by water seepage and water vapour escaping during the fire. The concrete spalled severely on the fire surface of the lining, the maximum depth and area reached 65 mm and 3.05 m2, respectively, and the reinforcement near the fire source was exposed after the fire. The mechanical behaviour of the entire lining was damaged by fire, and that in the fire area was more significant than that in the non-fire area, and the damage degree of the joint was more significant than the segment. Every mechanical parameter of the lining changes significantly during the firing process and only partially recovers during the cooling, with significant residual values. The ultimate bearing capacity of the lining after being damaged by fire was about two times the preset stratum load. And the failure characteristic of the lining damaged by fire was the plastic failure of the joints in the fire area. Specifically, in the fire area, there were numerous wide cracks, some joints were crushed, and some inner reinforcement yielded, while in the non-fire area, there were only a few micro-cracks on the segment and a few cracks on the joints. The research conclusions can also provide a reference for the post-disaster assessment of tunnel fire.

Methods for calculating aerodynamics inside high-speed railway tunnel lining cracks and predicating stress intensity factors

PurposeThis study aims to propose a series of numerical and surrogate models to investigate the aerodynamic pressure inside cracks in high-speed railway tunnel linings and to predict the stress intensity factors (SIFs) at the crack tip.Design/methodology/approachA computational fluid dynamics (CFD) model is used to calculate the aerodynamic pressure exerted on two cracked surfaces. The simulation uses the viscous unsteady κ-ε turbulence model. Using this CFD model, the spatial and temporal distribution of aerodynamic pressure inside longitudinal, oblique and circumferential cracks are analyzed. The mechanism behind the pressure variation in tunnel lining cracks is revealed by the air density field. Furthermore, a response surface model (RSM) is proposed to predict the maximum SIF at the crack tip of circumferential cracks and analyze its influential parameters.FindingsThe initial compression wave amplifies and oscillates in cracks in tunnel linings, resulting from an increase in air density at the crack front. The maximum pressure in the circumferential crack is 2.27 and 1.76 times higher than that in the longitudinal and oblique cracks, respectively. The RSM accurately predicts the SIF at the crack tip of circumferential cracks. The SIF at the crack tip is most affected by variations in train velocities, followed by the depth and length of the cracks.Originality/valueThe mechanism behind the variation of aerodynamic pressure in tunnel lining cracks is revealed. In addition, a reliable surrogate model is proposed to predict the mechanical response of the crack tip under aerodynamic pressures.

Biorthogonal wavelet energy entropy method with different time windows for strong interference processing of GPR signals

In the light of the shielding effect of the strong reflection signal generated by the steel bars and the inhomogeneous of concrete materials on the weak signal in the tunnel lining detection, a high-resolution GPR image processing method of biorthogonal wavelet energy entropy in different time windows is proposed. Wavelet analysis has the characteristics of multiresolution, and wavelet entropy can represent the energy distribution characteristics of signals in different time windows with different scales. Firstly, the discrete biorthogonal wavelet transform is applied to decompose the original GPR image into subimages with different frequencies and different spatial local changes. Secondly, appropriate time windows are selected for wavelet entropy adaptive threshold processing of each subimage in the light of the different amplitude ratio of effective signal to strong interference in each subimage, and finally the reconstructed image after removing the strong reflection is spectrally whitened. Both the forward simulations and actual measurement results show that the method can effectively remove strong reflection interference, clear weak signals, and maintain the continuity of the reflection events, and compared to the conventional pulse deconvolution, predictive deconvolution and wavelet entropy methods with the same time window, this method has a more thorough interference removal effect, and the effective signal performance is more obvious, which proves the effectiveness and accuracy of the proposed method in improving the resolution of GPR image and highlighting weak signal.

Dynamic response of shallow-buried circular composite lining tunnel with imperfect interface under SV waves

In this paper, the dynamic response of lined shallow-buried composite lining tunnel with imperfect interface in semi-infinite elastic medium under plane SV waves is studied, and the spring model is introduced to describe the imperfect interface relationship among the surrounding rock, the isolation layer, the primary support layer and main support layer. By using the wave function expansion method, the analytical solutions of displacements and stresses are presented. The interacting effects of the interface properties and the buried depth under different dimensionless frequencies are discussed. The results show that the peak values of the dynamic stress in the linings gradually shift to the upper part of the tunnel with the increase of dimensionless frequency, and the maximum dynamic stress in the linings also tends to decrease. The dynamic stress around the main and primary support layers increases when the interfaces are weakly bonded, and the effect of transverse springs is greater than that of normal springs. The tunnel with diminutive buried depth has a larger dynamic stress under the low-frequency SV waves. Reducing the stiffness in the isolation layer will lead to the increase of dynamic stress in the surrounding rock, while the dynamic stress in the main and primary support will be weakened.

Coupling effect between tunnel lining heat exchanger and subway thermal environment

If the waste heat generated during the long-term operation of a subway cannot be effectively eliminated, it will lead to the deterioration of the tunnel thermal environment and thermal pollution of the underground space. A subway source heat pump system (SSHPS) with a tunnel lining heat exchanger is an effective technique for addressing this problem. The present studies mainly focus on the design and performance optimisation of front-end heat exchangers and lack the analysis of the influence of heat exchanger operation on the thermal environment within the tunnels. Based on a demonstration project of an SSHPS in a cold region of China, this study established a coupled heat transfer model involving tunnel air, a lining heat exchanger, and surrounding rock and built a system simulation module in the TRNSYS platform. Based on the validated system simulation module, the coupling effect between the lining heat exchanger operation and the tunnel thermal environment was analysed under different tunnel environment conditions. The results show that when the heat produced in the tunnel increases at the rate of 100 W/m, the heat transfer between the heat exchanger and the tunnel air decreases by 4.35 W/m2 in the cooling season, and increases by 4.36 W/m2 in the heating season. In the cooling season, when the surrounding rock temperature rises by 2 °C, the heat released by the heat exchanger to the surrounding rock decreases by 3.6 W/m2, while that to the tunnel air increases by 0.68 W/m2. The results indicate that the heat generated by subway operations directly affects the heat transfer efficiency between the tunnel lining heat exchanger and tunnel air. The increase in the temperature of the surrounding rock causes the heat exchanger to release more heat to the tunnel air and vice versa. It is suggested that when the subway tunnel heat generation or heat exchanger operation has adverse effects on the tunnel environment, the operating condition of the tunnel heat exchanger should be adjusted accordingly to prevent the tunnel air temperature from exceeding the design limits. This study can provide a reference for the engineering design of subway tunnel lining heat exchangers.

Research and Development of Self-Waterproofing Concrete for Tunnel Lining Structure and Its Impermeability and Crack Resistance Characteristics.

This research paper systematically investigates the combined influence of fly ash, cementitious capillary crystalline waterproofing (CCCW) materials, and polypropylene fibers on the mechanical properties and impermeability of concrete through comprehensive orthogonal tests. Microscopic morphological changes in the concrete induced by different composite materials are examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) testing. The objective is to facilitate a beneficial synergetic interaction among these materials to develop highly permeable, crack-resistant concrete. Key findings of this study are: (1) The study unveils the impact of the concentration of three additive materials on the concrete's compressive strength, tensile strength, and penetration height, thereby outlining their significant influence on the mechanical properties and impermeability of the concrete; (2) An integrated scoring method determined the optimal composite dosage of three materials: 15% fly ash, 2% CCCW, and polypropylene fibers at 1.5 kg/m3. This combination increased the concrete's compressive strength by 12.5%, tensile strength by 48.4%, and decreased the average permeability height by 63.6%; (3) The collective introduction of these three materials notably augments the hydration reaction of the cement, resulting in denser concrete microstructure, enhanced bonding between fibers and matrix, and improved concrete strength and durability.

Study on the Seismic Response Characteristics of Shield Tunnels with Different General Segment Assembly Methods and Widths

Shield tunnels assembled with general ring segments are widely used in urban areas. Segment assembly methods and widths cause changes in the mechanical properties of the structure and influence the seismic response of shield tunnels. To investigate the influence of the assembly method and width of the general ring segment on the seismic performance of a shield tunnel, a three-dimensional refined soil–structure dynamic interaction finite element model of the shield tunnel was established based on ABAQUS, and the mechanical response and joint deformation of the general ring lining under seismic loads were studied. The simulation results show the following: (i) The overall deformation of the tunnel lining is not significantly affected by the assembly method, and the difference is only 5.24% under a 0.4 g earthquake. (ii) The seismic responses of general ring tunnels with different assembly methods are quite different, and the mechanical properties of the shield tunnel assembled with the straight assembly method are better than those of the shield tunnel assembled with staggered joints, but the deformation of the structure is larger. Under the action of a 0.1 g earthquake, the radial force, circumferential force, and bending moment of the staggered 90° assembly tunnel are respectively reduced by 13.6%, 11.1%, and 17.8% compared with the staggered 45° assembly structure, but the maximum intra-opening deformation increases by 0.19, 0.58, and 2.4 mm, respectively. (iii) The internal force distribution of the bolts is controlled by the deformation of the joint; compared with the CF90 and TF assembled tunnels, the mechanical properties and deformation characteristics of the CF45 and CF90 assembled tunnels are more reasonable. (iv) The extrados and intrados joint opening deformation and shear dislocation of the 1.2 m wide general ring segment under the staggered assembly increase by 1.2 mm and 1.03 mm, respectively, compared with the 1.5 m wide segment, while the radial force, circumferential force, and bending moment are reduced by 24.4%, 36.5%, and 41.7%, respectively, indicating that the seismic performance of the shield tunnel with a segment width of 1.5 m is better than that of the shield tunnel with a width of 1.2 m.

Seismic vulnerability of shield tunnels in interbedded soil deposits: Case study of submarine tunnel in Shantou Bay

This paper presents a numerical approach for deriving seismic fragility curves for a submarine shield tunnel subjected to transverse ground shaking in interbedded soil deposits. To simulate the nonlinear behavior of soils, PM4Sand and HS-small constitutive models were adopted. In contrast, the closed-form elastic design method or elastic–plastic design method was used for modeling the shield tunnel lining considering the effect of joints on the seismic performance of structures. Fully coupled numerical analyses provided a satisfactory interpretation of the seismic responses of soil–structure systems considering the effects of groundwater level and soil–tunnel interaction. Subsequently, free-field peak ground acceleration was selected as the intensity measure. The ratio of maximum bending moment to capacity bending moment or permanent joint rotation of the tunnel lining was selected as the damage measure, combined with incremental dynamic analysis, a series of fragility curves were generated. In this study, one-dimensional equivalent-linear earthquake site response analysis was implemented to validate the nonlinear dynamic analysis under weak earthquakes. However, the analysis overestimates the amplitude periodic vibrations in interbedded soil deposits under strong earthquakes. Additionally, numerical results show that the examined tunnel is prone to slight or moderate damage under ground shaking, and its joints are more vulnerable to damage than its segments. The fragility curves constructed were compared with existing fragility curves, highlighting the significant effects of local soil profiles, groundwater conditions, soil–tunnel interaction, and segmental joints on the seismic vulnerability of shield tunnels in a submarine environment. The developed fragility functions contribute to the prediction of seismic damage to submarine shield tunnels of similar characteristics, enabling the rapid and efficient response of structures to disasters in ocean engineering.

Experimental and numerical evaluation for tunnel structural stability of fiber concrete lining with different crack features under train load

Cracks are prone to occur in the secondary tunnel lining with the action of train loads, which will cause tunnel failure and adversely affect the long-term safety of tunnels. This paper conducts a series of material tests and numerical simulations to investigate the stability of fiber concrete tunnel linings with different crack features under train load. Through material tests for three different fiber and conventional concrete, the crack extension rule is discovered by combing digital image correlation (DIC) technology. The plastic damage constitutive relation of concrete is used to obtain the damage parameters. Then, the three-dimension numerical model is established to evaluate the stress intensity factor and stable coefficient of safety of tunnel lining. Moreover, four cases are determined to indicate the effect of cracks on the failure mechanisms of the tunnel lining structure. The influence of stability of lining structure with crack at different location, depth, width, inclination angle, train speed and grade of surrounding rock is analyzed.

Water transport in cracks controlled by digital image correlation in wet sprayed concrete with and without an EVA based co-polymer admixture

Experiments were undertaken on wet sprayed concrete discs to investigate the effect of cracking on capillary suction and permeation through sprayed concrete for tunnel linings. The 98 mm diameter, 50 mm thick discs were cracked by tensile splitting, with the crack widths controlled and measured by digital image correlation and also checked by microscope measurements. Both a standard sprayed concrete mix and a mix containing an EVA (ethylene–vinyl-acetate) based co-polymer powder were tested. Cracks increased the rate of capillary suction compared to uncracked samples, due to rapid rise of water in the crack and absorption occurring over the surface area of the crack in addition to the area of the base of the disc. Discs with wider crack widths exhibited a higher rate of water permeation per area of crack. Inclusion of the EVA based co-polymer reduced the rate of capillary suction and the permeation flow rate coefficient (measured flow / theoretical viscous laminar flow) for a given crack width compared to the standard mix. Self-healing occurred both during water permeation and water storage of cracked discs. The use of CT scanning to measure the crack through the full thickness of a disc was explored and compared to crack width measurements made at one surface of the disc only.