Concrete Lining Research Articles

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.

COMPARATIVE STUDY ON TUNNEL LINING CONCRETE STRENGTHENED WITH CARBON-FIBER COMPOSITE CABLES AND SHEETS

Most lining concretes of road tunnels in Japan have been gradually deteriorated by aging and various environmental effects. The study focuses on a strengthening system for tunnel lining concrete (TLC) subjected to external forces. Carbon fiber (CF) sheets are often used in TLC for preventing concrete exfoliation. The strengthening effect of CF sheet for TLC was not sufficiently known. The experimental study conducted a mock-up loading test to examine failure mode and load-capacity of the TLC model bonding CF sheet. In addition, the study prepared TLC models strengthened with near-surface mounted (NSM) technique using carbon-fiber composite cables (CFCC). The strengthening effects of CF sheet and NSM-CFCC were quantified and compared via the mock-up loading test. The experimental study revealed that the TLC model bonding CF sheet failed by intermediate-crack-induced debonding at around 100 kN, and the load carrying capacity was almost equivalent to the capacity of non-strengthened TLC model. On the other hand, the NSM-CFCC strengthened TLC model indicated higher ductility after concrete cracking and superior load capacity. The experimental study confirmed the NSM-CFCC as an effective strengthening system for TLC members.

Investigation of cracking mechanism of the first tunnel lining during double-arch tunnel construction

To solve the engineering problem of the first tunnel lining cracking caused by the second tunnel construction of double-arch highway tunnels, a research method combining distributed optical-fibre monitoring, inversion analysis and numerical simulation that can reflect lining cracking was presented. Optical fibres were laid on opposite sides of the steel arches inside the first tunnel lining. Embedded optical-fibre monitoring was conducted continuously during the second tunnel driving. Based on the fibre-optic strain profile, the lining cracking was deduced and warned in time. The mechanical behaviour of the steel arch was investigated by the inversion analysis, which took into consideration the integrated impact of axial force and flexural moment. A two-dimensional (2D) load-structure method–based numerical model was established, considering the influence of different load distributions in each construction condition. The total strain rotating crack constitutive model was applied to reflect the cracking behaviour of concrete lining in the simulation, and the model was calibrated and verified in the laboratory. Comparative analysis between the simulated strain distribution and the distributed optical-fibre monitoring results was carried out. The deformation mode and crack distribution of the lining were analysed. The cracking mechanism was explained. Specifically, the second tunnel construction led to the loading at the top of the middle partition wall and the release of rock pressure in the first tunnel. Under these load changes, the secondary lining of the first tunnel cracked on the inner side of the top of the middle partition wall owing to tension, and compression-bending failure occurred near the right arch foot. Finally, the influence of the parameters on the lining force was analysed, and a construction optimisation scheme was proposed.

Analytical Study on Retrofitting Concrete Retaining Wall with Concrete Lining

Today, retaining walls are gaining importance with the developing transportation networks. Different solutions are made in the design of retaining walls according to the land structure and ground condition. Various retrofitting methods are used in damaged retaining walls. Especially in recent years, natural disasters in Turkey have also affected the retaining walls. There may be damage and collapse in the retaining walls during and after the disaster. It is predicted that in the event of a possible collapse in the event of a disaster, loss of life and property may also occur. After the disaster, even if the retaining walls have not collapsed, they are damaged. In this case, collapse may occur in the next disaster due to collapse or environmental vibrations. It is also known that in post-disaster situations, it is vital that the transportation network remains active in order to deliver the necessary aid to the region. For all these reasons, in this study, the concrete lining method, which is one of the retrofitting methods of retaining walls, is mentioned. Thus, the effect of the concrete lining method applied on an exemplary retaining wallon modal parameters has been demonstrated. In this comparative study, it was observed that the stiffnessof the retaining wall increased with the concrete lining method. As a result of this study, it is suggested to retrofitting the retaining walls with the concrete lining method, taking into account the state of the walland environmental factors.

Impact Analysis and Optimization of Key Material Parameters of Embedded Water-Stop in Tunnels

Leakage diseases frequently occur in mountain tunnels, and the lining joints are weak waterproof links. In order to solve the problems such as insufficient waterproof technology for existing tunnel joints, this paper relies on the scientific and technological project of the Hubei Provincial Department of Transportation to optimize the key parameters of the tunnel water-stop material and uses numerical simulation methods to analyze the impact of the hardness of the water-stop and the bond strength between the water-stop and concrete on its deformation and waterproof ability. Through the adhesion test, the optimization method of the bond strength between the water-stop and concrete is explored. The results show that: (1) the deformation stress of the water-stop will increase with the increase in hardness and reducing the hardness of the water-stop can improve its stress deformation state. Considering that low hardness increases the risk of damage and reduces the quality, it is recommended that the hardness be 55–60 (HA). (2) The adhesion between the water-stop and the concrete lining is the key to waterproofing the water-stop. Increasing the adhesion between the water-stop and the concrete is an effective optimization method. However, to prevent excessive deformation stress, it is necessary to optimize the geometric structure of the water-stop simultaneously. (3) Placing an epoxy–quartz sand coating on the surface of the water-stop can increase the adhesive force between the water-stop and the concrete. When the thickness of the epoxy layer is 2 mm, and the particle size of quartz sand is 26–40 mesh, the effect is best.

Automated pixel-level crack monitoring system for large-scale underground infrastructure – A case study at CERN

In concrete tunnel linings, cracks usually appear and develop as an early sign of structural degradation prior to severe intolerable serviceability damage. The monitoring and assessment of crack spatial distribution can highlight long-term tunnel structural behavior and facilitate tunnel maintenance. This study describes a remote and automated system for conducting crack monitoring at a pixel-level scale using robot-mounted imaging technology. This system collects crack images remotely and stitches them together to create a panorama image of the tunnel surface. Employing transfer learning, this study fine-tunes and improves the state-of-the-art semantic segmentation model with a lightweight backbone, DeepLab V3plus, to detect cracks automatically. A novel smooth blending prediction method is implemented on the panorama to present long-distance tunnel crack distribution, alleviating misclassification problems encountered in high-resolution image inference. In addition, transfer learning, tailored loss functions, and regularization techniques have been developed based on the CERN tunnel crack database characteristics to maintain high performance and generalization of the proposed method.Field trials conducted in tunnels at CERN demonstrate the feasibility of the proposed crack monitoring system. Results show that the proposed system allows the identification of severe crack-damaged tunnel sections and specific crack patterns, which can be related to the structural behavior of the tunnel lining.

Cracking Pattern and Bearing Capacity of Steel Fiber-Reinforced Concrete Single-Layer Tunnel Lining

In recent years, steel fiber-reinforced concrete (SFRC) single-layer linings have been used in tunnel engineering. Compared to plain concrete single-layer linings, SFRC single-layer linings demonstrate enhanced bearing capacity, durability, and sustainability. Existing studies primarily focused on the mechanical properties of SFRC; however, limited investigations have been conducted on the cracking pattern of SFRC linings. This study uses laboratory tests to examine the influence of steel fiber content and aspect ratio on the mechanical properties of concrete, such as compressive strength and elastic modulus. After the recommended content and aspect ratio of steel fiber are proposed through tests, the cracking pattern and safety performance of plain concrete and SFRC linings under surrounding rock pressure are studied using a similar model test. The test results indicate that the recommended steel fiber volume fraction and aspect ratio for CF35 SFRC are 0.58% and 70, respectively. Due to the effect of loose load, cracks initially develop on the inside of arch crowns in both plain concrete and SFRC single-layer linings. Subsequently, new cracks appear on the inside of the lining floor and the outside of the two wall feet. Numerous narrow cracks with rugged and winding expansion paths can be found on SFRC single-layer linings. Conversely, plain concrete single-layer linings exhibit fewer cracks with larger widths along a straighter path. The initial cracking load of a single-layer lining made of plain concrete is 0.027 MPa, whereas for a single-layer lining made of SFRC, it is 0.04 MPa. This indicates that SFRC can effectively enhance the initial cracking load of lining structures. In the event of damage to the lining, the most critical area for the plain concrete single-layer lining is at the two wall feet, where the minimum safety factor is 1.66. However, for the SFRC lining in the same location, the safety factor is 2.7, resulting in a 62.7% increase in safety.

Experimental study on similar materials for tunnel lining concrete in geomechanical model tests

In geomechanical model tests, a reasonable proportioning of similar materials is one of the keys to ensuring that the physical and mechanical properties of the model match those of the prototype. Using gypsum, white cement, barite powder, quartz sand, and water as raw materials, a similar material of tunnel lining concrete was developed by orthogonal design. The density, compressive strength, elastic modulus, and tensile strength of the similar material were measured, which were evaluated using range analysis. Meanwhile, the mechanical parameter relationship was studied between the similar material specimens with different sizes. The results show that the similar material has a large range of physical and mechanical parameters, and can be used in the model test with a large unit weight; its ratio of compressive strength to tensile strength is 8.31–16.12, which conforms to the mechanical properties of concrete. The aggregates/cementing materials ratio has the largest impact on the material density, while the water/cementing materials ratio has the greatest influence on the strength and elastic modulus of the material. There is a good fitting relationship between the mechanical parameters of cylinder specimens and the mechanical parameters of cube and prism specimens, so cylinder specimens can be prepared for mix proportioning tests during trial preparation of the similar material. The physical and mechanical performance of grade-C25 concrete and grade-C40 concrete can be well simulated by the developed similar material. The research can provide a reference for the selection of similar materials for lining concrete in similar model tests.

A Case Study on Capstone Design Education in the Construction Field Using 3D Printer : Focusing on the Concrete Form Liner

A Case Study on Capstone Design Education in the Construction Field Using 3D Printer : Focusing on the Concrete Form Liner

Numerical modeling in ground penetrating radar-based assessment of concrete lining and space behind it

Numerical modeling in ground penetrating radar-based assessment of concrete lining and space behind it

Integrated approach for quality control of fibre-reinforced sprayed concrete for tunnel lining

The quality control of fibre-reinforced sprayed concrete (FRSC) for tunnel linings has evolved significantly in recent years. One of the main innovations concerns the control of FRSC in the lining using small-scale tests of cores extracted from the tunnel instead of the traditional approach, based on the characterization of panels sprayed on moulds. This study combines experimental and numerical investigations to evaluate if constitutive models derived from small-scale tests, such as the double punch test (DPT) and double-edge wedge splitting (DEWS) test can be used to predict the behaviour of larger panels in the round panel test (RPT) ASTM C1550. Results confirm the link between the new and the traditional approaches. Findings demonstrate that small-scale tests can be considered as a viable method to evaluate the mechanical behaviour of FRSC both in regular quality control programs and for verifying an existing tunnel lining condition.

Effects and interactions of scouring abrasion and external sulfate attack on deterioration of lining concrete: Experiments and preliminary modeling

The conventional tests of dynamic water scouring abrasion (DWSA) on lining concrete for hydraulic discharge tunnel do not consider concomitant sulfate ions that may exist in aggressive aqueous environment and alter the mechanisms and deterioration kinetics of DWSA. In this study, an abrasion-erosion testing system based on natural conditions of the environment has been used to evaluate the influence of volumetric concentration of sediment and the velocity of the scouring flow on abrasion-erosion synergism of lining concrete. To this end, lining concretes were subjected ambient conditions similar to that in drainage tunnel, spillway and stilling basin geographic locations, while implementing abrasion and accelerated external sulfate attack (ESA) test alternately prior to various physical and microstructural analyses. A dynamically decrease of properties on a macroscopic scale was observed, as well as an increase of precipitated ettringite, leached calcium, harmful pore (>200 nm) and sheeted radial micro-cracks, in lining concretes exposed to sediment-laden flow simulated for discharge, which were involved in the co-occurrence of complex degradation mechanisms in specimens exposed to DWSA-ESA. Results indicate that a water body with a high-velocity flow and a high sediment concentration significantly accelerates the sulfate attack on concrete. In contrast, a water body with a low-velocity flow and a low concentration of sediment alleviates the traverse of sulfate ions in concrete due to the inside-out pressure potential. The implications of these synoptic findings may informatively improve the design of abrasion and erosion resistance for concrete when dual exposure to ESA and abrasion is occurred in hydraulic tunnel engineering.

A review of test Methods, issues and challenges of Large-Scale fire testing of concrete tunnel linings

This article provides a summary of substantial aspects pertaining to the design of concrete tunnel linings subjected to serious fire exposure. Compared to building fires, the air temperature rise of tunnel fires is more significant within a few minutes due to the confined space. This is of concern to tunnel designers as rapid temperature rise has shown to be a dominant factor in relation to concrete spalling. The dramatic European tunnel fires that occurred in 1999 and 2001 led to the development of new regulations and recommendations, including new guidelines recommended by the European Federation of National Associations Representing producers and applicators of specialist building products for Concrete (EFNARC 132F r3:2006) and Efectis R0695:2020. These regulations were intended to offer tunnel designers some scope on how to test for concrete spalling with particular focus on explosive spalling of concrete given that, in general, tunnels are at greater risk than other structures. This is principally due to the high heating rate and the high initial moisture content present. To date, full scale experimental works have been limited and not as extensive as those of small to medium scale unloaded specimens exposed to elevated temperatures. This paper summarizes recent research on large scale concrete tunnel lining tests exposed to fire conditions. The methodologies, questions, and challenges regarding large-scale fire tests on tunnel lining concrete and the current design guidelines are highlighted. First, this review examines published large-scale testing including unloaded and loaded applications. Secondly, a discussion surrounding the issues faced in testing, including the effects of loading, size reduction, boundary conditions, inclusion of polypyrene fibers and steel reinforcement is presented. Finally, current design guidelines for tunnel fire safety are reviewed and recommendations for future structural fire testing of full-scale tunnel elements was presented.

Comparative response of tiled finishes and bonded fire resistive coatings for normal weight concrete tunnel liners under high-intensity one-sided heating

Experimental tests were performed to examine the relative fire resistance provided by several bonded coatings for normal weight concrete (NWC) panels that emulate a tunnel liner: ceramic tiling on mortar, spray-applied fire resistive material (SFRM), and intumescent paint (IP). Sixteen panel specimens (150-mm [6-in.] thick, 457-mm [18-in.] wide, and 610-mm [24-in.] tall) were subjected to one-sided heating using a gas-fired radiant panel, which can apply heat flux at intensities similar to hydrocarbon fuel fire. All specimens were cast from a single batch of NWC (approx. 40 MPa compressive strength) with a single curtain of steel reinforcing bars at 38-mm (1.5-in.) cover to the heated face. All specimens were vertically loaded to a service level of compressive uniaxial stress (approx. 14% of ambient specified compressive strength), which remained relatively constant during each test. Four bare concrete panel specimens were tested as a control group, and a ceramic tile finish was installed on six specimens in accordance with a current state department of transportation specification. The other six specimens were coated with fire resistive material (three each with SFRM and IP) at thicknesses corresponding to a 1-hr fire resistance rating per manufacturer specifications. Thermally-induced explosive concrete spalling was observed in 3 of 4 control specimens, 4 of 6 tiled specimens, and none of the 6 SFRM/IP coated specimens. The tiled finishes delaminated and eventually became fully detached from the concrete surface, thus providing negligible fire resistance compared to that provided by the SFRM or IP. Temperature time histories recorded within the outer 25-mm (1.0-in.) thickness of the heated concrete were used to evaluate the relative thermal resistance of each surface finish, as well as to validate a simplified thermal numerical model used for a brief parametric study. Post-fire removal of the surface finishes is also demonstrated.

Analytical Approach to Evaluating the Influence of the Compressible Layer on the Time-Dependent Response of Deep Soft-Rock Tunnels

The application of the compressible layer in linings provides a feasible and safe solution to addressing the problems of the excessive deformations of surrounding rocks and support failure in the deep soft-rock tunnels. However, there still has not been a well-constructed method to report the mechanical responses of the tunnels supported by such a support system. The objective of this study is to provide an analytical approach to estimating the influence of the compressible layer on the tunnel performance. The mechanical model of the tunnel supported by the compressible layer and concrete lining within the viscoelastic–plastic geomaterial was established. The corresponding analytical solutions for the tunnel displacement and lining pressure are provided, where the influences of the stress path, tunnel face advancement, and installation delay of supports are considered. The effectiveness and reliability of the proposed model are validated by using the numerical calculation, and a good agreement between the analytical and numerical results are obtained. Finally, a comprehensive parametric investigation is carried out, including the influences of the yielding stress, yielding length and elastic modulus of the compressible layer and the lining installation time. The important findings are provided and several useful recommendations are proposed for the design of this supporting system.

Numerical study of seismic resistance of prefabricated circular tunnel linings

Prefabricated circular tunnel linings are used in the construction of tunnels using the shield method, which significantly increases the speed and reduces the cost of building highways. Many methods have been developed for designing seismic resistant tunnel linings. Due to simplicity, analytical methods are usually used for preliminary design. In this case, the presence of joints between the blocks of the ring and between the rings is not taken into account. Compared to analytical methods, numerical methods, especially three-dimensional (3D), allow the most explicit consideration of the problem being solved. However, due to their complexity and time-consuming nature, 3D numerical models are only rarely used. In most reinforced concrete prefabricated linings, the deformation at the joints has a significant effect on the deformation of the rings. Thus, the magnitude and distribution of internal forces largely depend on the distribution and characteristics of the joints. Therefore, one of the most important factors in the design of a circular tunnel lining is the effect of segment connections on its overall behavior. This paper compares the internal forces that occur in the tunnel lining, determined using analytical analysis and numerical simulation in a three-dimensional formulation. When using numerical analysis methods, seismic loads are considered as quasi-static. However, almost all quasi-static analyzes presented in the literature include the same assumptions as closed form solutions and therefore have the same limited applicability. The main disadvantage of quasi-static models is that they do not take into account changes in the behavior of the structure over time.

Experimental and analytical investigation of precast fiber-reinforced concrete (FRC) tunnel lining segments reinforced with glass-FRP bars

A hybrid use of glass fiber-reinforced polymer (GFRP) reinforcement and fiber-reinforced concrete (FRC) could be a viable option for producing durable precast concrete tunnel lining (PCTL) segments. There is, however, a gap in the literature regarding the behavior of GFRP-reinforced FRC PCTL segments with typical amounts of reinforcement. This paper presents results obtained from both experimental and analytical studies on the behavior of GFRP-reinforced FRC PCTL segments under bending load (flexure). Four full-scale tunnel segment specimens were constructed and tested monotonically under three-point bending load. The influence of concrete type, reinforcement ratio, and tie configurations on the cracking behavior, deflection behavior, failure mechanism, load-carrying capacity, strain behavior, and deformability was evaluated. There is a limited analytical procedure available to predict the shear and flexural capacities of GFRP-reinforced FRC PCTL segments. Therefore, an analytical investigation was carried out in order to propose and evaluate different methods for predicting the flexural and shear capacities of such elements. The results indicate that the use of FRC significantly improved the cracking behavior and failure mechanism while also increasing the load-carrying capacity and deformability by 12% and 71%, respectively. Increasing the reinforcement ratio by 86% enhanced the post-cracking stiffness and peak load by 92% and 31%, respectively, while reducing the service-load crack width by 57%. According to the analytical investigation, the introduced direct method based on the stress–strain behavior of the FRC and the proposed simplified method based on ACI 440.1R-15 could predict the flexural capacity of GFRP-reinforced FRC PCTL segments with high accuracy. Furthermore, the method proposed to modify CAN/CSA S806-12, R2017 to consider the contribution of fibers in shear transferring mechanism yielded rational conservative values for the shear capacity of GFRP-reinforced FRC PCTL segments.

Real-time tunneling risk forecasting using vibrations from the working TBM

Tunnel Boring Machines (TBMs) are effective tools for excavating tunnels through various soil and rock strata, especially in complex urban areas. During excavating, hazards overlooked during site investigation, such as abrupt geological changes, buried obstacles like boulders and building foundations, fault zones, and water-bearing regions, significantly increase the risks of cutter damage and tunneling accidents. Geophysical methods have been proposed during tunnel excavation to predict these potential hazards ahead of the cutter face. With the existence of a metallic TBM and subsequently installed concrete tunnel lining, the performance of electromagnetic geophysical methods such as ground-penetrating radar and DC resistivity tomography are greatly hampered, despite their success in the traditional open tunnels. In this study, we present a passive seismic method to forecast the tunneling risks ahead of the TBM cutterhead. This method uses the working TBM as the source and predicts the velocity/density changes in front of the TBM by delineating the reflected seismic energy from the noisy recordings. The key to this technology is seismic interferometry, which transforms the chaotic ambient noise into interpretable seismic profiles. We utilize beamforming and semblance analysis to extract the traveltime information from the passive records. After velocity inversion and calibration, we map the arrival-time of a reflection event to a seismic impedance interface ahead of the cutterface. To test the proposed method, we demonstrate the process on a simulated passive seismic record after laying out its theoretical foundations. We present a field application of our method where geological interfaces are predicted in real time as the excavation progresses. The field data results match well with the muck density and TBM parameters measured after excavation and hence demonstrate the applicability of our method in complex urban environments for tunneling risk reduction.

Objective-level resilience assessment of circular roadway tunnels with reinforced concrete liners for vehicle fire hazards

A framework is presented to quantify the objective-level resilience of reinforced concrete liners of circular tunnels when exposed to enclosed vehicle fire hazards. By assessing the loss of functionality due to fire-induced damage, the framework enables a decision-basis evaluation of the efficiency of various fire mitigation methods for specific tunnel conditions. In this study, the fire-induced damage of concrete tunnel liners due to strength loss and spalling is stochastically simulated and classified based on typical post-fire repair procedures and damage evaluation. The resilience assessment is conducted using Monte Carlo Simulation in combination with a fast-running tool for calculating the thermal impact from vehicle fires on the inside surface of the tunnel liner (developed by the authors in previous work). The proposed approach accounts for uncertainties associated with both the vehicle fire (particularly the combustion energy) and the tunnel conditions (i.e., geometry, dimensions, and the presence of longitudinal ventilation and/or fixed fire-fighting systems (FFFS)). A parametric case study is used to quantitatively demonstrate the effectiveness of FFFS for reducing post-fire losses of tunnel functionality. Other parameters such as tunnel dimensions, traffic restrictions for vehicles with heavy fire hazard risk, and installation or upgrade of the tunnel ventilation system show somewhat less effectiveness for reducing fire-induced damage.

Failure process and tensile stiffness of shield tunnel with reinforced concrete inner lining under internal water pressure

Shield method have been commonly used in water conveyance tunnels. To improve the bearing capacity of a shield tunnel under internal water pressure, a reinforced concrete lining is constructed inside the segmental linings to form a composite lining structure. However, cracks typically occur in reinforced concrete inner linings. In this study, a prototype test was performed to investigate the failure process of a composite lining. Based on the test observations, the progressive failure process of the composite lining experienced four stages. In the elastic stage, the stress and deformation of the composite lining increased linearly with the internal pressure, and no cracks appeared. In the cracking stage, cracks first occurred in the inner lining near the joints and were subsequently uniformly distributed along the circumferential direction. In the joint damage stage, the cracking of the inner lining caused more internal pressure to transmit to the segmental lining. As the internal pressure increased, compressive damage occurred in the handholes of the segmental joints. Finally, in the failure stage, the damage to the joints deteriorated and more internal pressure was borne by the rebar of the inner lining. Shear failure typically occurred at the welding point of the inner-lining rebar, followed by joint fracture near the welding point. Finally, the composite lining lost its ability. The test results showed that cracking of reinforced concrete inner lining remarkably decreased the tensile stiffness of composite lining. Consequently, the joint opening and convergence of the tunnel developed at a higher rate, posing a threat to the operational safety of the tunnel. The tensile stiffness is a key factor related to the deformation and bearing capacity of a shield tunnel. Therefore, an analytical solution was established to calculate the tensile stiffness of the composite lining after cracking. The analytical solution matched the test results well. In addition, the effects of the thickness and reinforcement ratio of the inner lining were analysed. The results suggested that increasing the reinforcement was more beneficial in improving the tensile stiffness of the composite lining.