Tunnel Lining Research Articles

Distress detection in tunnel lining from MLS data

As tunnels age, deterioration of their inner lining worsens, necessitating continuous inspections and evaluations to monitor their condition and implement preventive measures against potential structural damage, thereby avoiding service disruptions. Traditional methods involve visual and manual inspections, leading to temporary closures and resource consumption. The Mobile Laser Scanner (MLS) technique, which is based on LiDAR (Light Detection And Ranging) technology, allows the modeling of the tunnel intrados using a point cloud, without disrupting traffic. Our study introduces a methodology for tunnel intrados analysis utilizing an automated point cloud unrolling algorithm rooted in the RANSAC (RANdom SAmple Consensus) method. Intensity values are examined to identify potential water infiltration, while roughness values evaluate surface integrity and reveal cracks or protruding steel bars. Despite being limited to two types of distress, our research facilitate the identification of tunnel sections necessitating immediate intervention, allowing for the prioritization of high-risk areas, or issuing alerts.

Accuracy of Ground Penetrating Radar (GPR) in locating post-tensioned cables

The inspection and assessment of post-tensioned (PT) bridges is a complex issue, first involving the evaluation of the conservation status of the cables. One of the most crucial pieces of information to be confident with is the cables’ location since it allows the success of all subsequent tests in the tendons (both non-destructive and destructive) and is critical in the bearing capacity of the beam in bending and shear as well. Many non-destructive techniques (NTDs) are studied and employed by the scientific community and practitioners for the cables’ trace determination in PT beams; one of the most promising is the Ground Penetrating Radar (GPR). This technique is commonly employed in the location of metallic elements, both under the ground (pipes, utilities, etc.) and inside the concrete (reinforcements, ducts, etc.). The GPR technology exploits electromagnetic waves typically in the range of 1000-5000 MHz in the inspection of structures and tunnel lines. The variation of electromagnetic properties of the materials results in changes in the speed of travel, attenuation, and redirection of signals. The present research deals with the determination of the GPR accuracy in locating cables in PT structures. A laboratory testing campaign on specially designed samples was conducted for this aim. The tested walls contain both metallic and plastic ducts.

The 365 km tunnels assessment along ASPI Motorways Network – Key findings addressing risk analysis procedures and structural conditions evaluation and strategy of interventions

An extraordinary assessment plan, performed on 365 km of motorway tunnels, has been carried out in Italy since 2020 starting with detailed inspections and testing. Hundreds of laser scanning kilometres and ground-penetrating radargrams, thousands of concrete compressive strength tests, endoscope inspections and flat-jack tests have been performed so far. Tens of thousands structural defects were detected and several square meters of temporary safety measures installed as well. This allowed to acquire a significant amount of knowledges about the current condition of the asset. According to the process defined by the new Italian Regulations, the dataset analysis provides an insight into the condition of the asset, guiding the entire maintenance process. The visual and detailed inspections frequency is driven by the simplified risk analysis outcome and further safety evaluation are designed based on multidisciplinary criticality. A comprehensive approach, based on in-depth knowledge of the characteristics of the existing tunnel, has been engineered for structural risk, with a focus on tunnel “history” (excavation stages and techniques, construction materials, etc.), design and dimensioning approaches (e.g. Kommerel’s graphical method), identified as standard methods for the tunnel construction period from literature review. Additional analyses are carried out for likely local structural failure modes of tunnel lining (punching and flexural strength of residual concrete layers, spalling hazard of concrete thickness anomalies due to temperature variations). When re-lining is needed, the design of a new shell aimed to ensure at least the same structural performance of the original one is addressed, including seismic loads that were neglected in the original design. The tunnel assessment, from inspections to re-lining works passing through risk analysis, is an on-going process open to be improved in the upcoming years within a wider asset management strategy.

Adhesion performance of alkali-activated material for 3-dimensional printing of tunnel linings at different temperatures

Adhesion performance of alkali-activated material for 3-dimensional printing of tunnel linings at different temperatures

Determination of local stiffness for the joint of tunnel lining in the simulation

In the numerical simulation of shield tunnel, the treatment of joints will greatly affect the accuracy of numerical analysis. Because the stiffness of the joint is lower than the stiffness of segments, the local weakening method is adopted in this paper , which can simulate the stiffness heterogeneity in the transverse and longitudinal directions of the tunnel lining. In the method, lower local stiffness is used for the joint which is the connection between segments and rings of lining, while the stiffness of segments keeps to be unchanged. The local stiffness of the joint, which is represented by the elastic modulus of the joint in the simulation, is the key point. To verify the validity of the method, multiple full-scale experiment [11-14] objects are analyzed and the simulation results are compared to the experiment data. Then the empirical formula of elastic modulus of the weakening joint is proposed by analyzing the three-ring lining in a full-scale experiment under different assemblages. Further, the empirical formula of elastic modulus for the joint is expanded to the large-diameter tunnel and super-large-diameter tunnel. It provides a good reference for the determination of elastic modulus of the joint in the simulation of shield tunnel.

Performance Analysis and Related Data Utilization of Rapid Crack Inspection Technology for Railway Tunnel Lining Surface

Performance Analysis and Related Data Utilization of Rapid Crack Inspection Technology for Railway Tunnel Lining Surface

Structural safety of existing masonry-tunnel-linings: a methodology derived from existing buildings approaches

Masonry linings were the primary solution for tunnels before the introduction of reinforced concrete. As a result, many tunnels with masonry linings have been in operation for over a century and may exhibit damage due to ageing and prolonged water infiltration. Currently, there are no specific regulations for the static verification of masonry tunnels. These tunnels share characteristics and problems with historic masonry structures such as bridges and building facades. Therefore, the scientific literature and normative references developed for masonry heritage structures were here considered. This work focuses on estimating the masonry strength of tunnel linings. To demonstrate the proposed methodology and the addressed problems, the ‘Giovi’ tunnel on the historic Genoa-Valle del Po motorway in Genoa, Italy was selected as an exemplary case. The masonry’s resistance is measured in situ using flat-jacks and estimated using methodologies proposed for both new and existing buildings. The comparison of these methodologies highlights the unique characteristics of tunnel linings, including thick mortar bed-joints and massive curved masonry walls, with only one free face.

Harmonic Response Analysis of Seismic Excitations on Tunnel Linings

Tunnel linings, depending on their geographical locations, are exposed to various magnitudes of seismic loads. Ensuring that these linings resist seismic perturbations without exhibiting failures, such as crack initiation or propagation, is paramount. In the presented study, the structural stability of tunnel linings under pronounced seismic excitations was rigorously evaluated. Seismic excitations, in compliance with the IS 1893: 2002 code for both zone II and zone III conditions, were administered. Computer-Aided Design (CAD) modelling, static structural, and harmonic excitation analyses were meticulously conducted via the ANSYS finite element analysis (FEA) simulation package. From these comprehensive analyses, critical zones within the tunnel linings were identified under varying excitation frequencies. It was observed that, predominantly, these critical regions are situated at the corners of the tunnel linings, specifically in the bottom areas. Distinct maximum and minimum induced normal stresses within the tunnel structure were ascertained. Under a seismic excitation of .1g, a maximum reaction force of 1232.1 kN was derived. Conversely, for a seismic excitation of .16g, the reaction force peaked at a 1Hz frequency with a magnitude of 1971.3 kN. These findings furnish pivotal insights into the structural performance of tunnel linings when subjected to seismic disturbances, providing tunnel engineers and designers with invaluable knowledge to augment the resilience and safety of tunnel infrastructures.

Evaluation of environmental and economic compatibility of different types of segment linings based on the structural performance with some aggravating factors

The performance of supporting systems can be significantly affected by aggravating factors that contribute to segmental tunnel lining damage. Based on previous studies and statistical data, the excessive thrust force and defect in support conditions are the crucial factors that can aggravate the damage of segmental linings during the installation stage. This study aims to evaluate the effect of influential factors, including the excessive thrust force, the incomplete contact of loading shoes, configuration of loading shoes, defect gap thickness, and segment type. In addition, a series of numerical simulation are performed to investigate the impact of the influential factors on the performance of three different segmental lining types, including conventional reinforced concrete segment, recycled steel fiber reinforced concrete segment, and new hybrid design recycled steel fiber reinforced concrete segment. The results indicated that numerical modeling can accurately simulate stress concentration and damage patterns of segmental lining in different conditions. This method can provide useful information about the performance of segmental tunnel linings, considering essential phenomena that are neglected in traditional design methods, such as the effect of incomplete contact of the support area, and the thickness of circumferential gap. Numerical analysis of segmental tunnel lining behavior by considering different conditions can help reduce undesirable consequences and construction costs. The results indicated that the increase in the thickness of the gap significantly increase in crack opening and destructive damages. While, the configuration of the loading shoes affects the amount of crack openings, the number and position of these cracks; the effect of this parameter is very lower compared to the presence of defects in the supporting area. Finally, it was concluded that the hybrid design showed high efficiency for all investigated conditions, in terms of structural performance, environmental impact and economic compatibility.

Investigation on Existing Tunnel Response to Piles Construction: A Numerical Study

Deep foundations are frequently built close to existing tunnels in the urban environment. Tunnels can only withstand very small movements. The construction of bored piles and/or the subsequent loading of the piles may result in unbearable movements or stresses that could result in cracking of the tunnel linings, which worries obstacles to the tunnel structure. This research presents an understanding of the interaction issue and investigates and evaluates various geometric factors that determine the effect of the construction of the pile on the existing tunnel. However, numerical modeling was established utilizing a modified Mohr-Coulomb constitutive model for the soil strata. Numerous factors have been examined, including different locations of the pile tip to the tunnel centerline as well as variable pile diameters and lengths. The numerical analysis results revealed that the bending moment decreases as the distance from the tunnel increases from 8 to 12 m and then remains constant, while the shear stress is not affected considerably. In addition, the shear stress and bending moment increase with pile diameter and length due to the increased confinement caused by the pile. The spacing has a considerable effect on the horizontal displacement with very little effect on the vertical displacement. Moreover, there is an increase in the shear force developed in the tunnel lining with pile diameter for different spacings between the tunnel and pile. This increase becomes smaller as the pile length increases. At small spacing between the pile and tunnel (8.3 m and 12.5 m), the bending moment in the tunnel lining decreases as the pile length increases. Doi: 10.28991/CEJ-SP2023-09-016 Full Text: PDF

A Point Cloud Segmentation Method for Dim and Cluttered Underground Tunnel Scenes Based on the Segment Anything Model

In recent years, point cloud segmentation technology has increasingly played a pivotal role in tunnel construction and maintenance. Currently, traditional methods for segmenting point clouds in tunnel scenes often rely on a multitude of attribute information, including spatial distribution, color, normal vectors, intensity, and density. However, the underground tunnel scenes show greater complexity than road tunnel scenes, such as dim light, indistinct boundaries of tunnel walls, and disordered pipelines. Furthermore, issues pertaining to data quality, such as the lack of color information and insufficient annotated data, contribute to the subpar performance of conventional point cloud segmentation algorithms. To address this issue, a 3D point cloud segmentation framework specifically for underground tunnels is proposed based on the Segment Anything Model (SAM). This framework effectively leverages the generalization capability of the visual foundation model to automatically adapt to various scenes and perform efficient segmentation of tunnel point clouds. Specifically, the tunnel is first sliced along its direction on the tunnel line. Then, each sliced point cloud is projected onto a two-dimensional plane. Various projection methods and point cloud coloring techniques are employed to enhance SAM’s segmentation performance in images. Finally, the semantic segmentation of the entire underground tunnel is achieved by a small set of manually annotated semantic labels used as prompts in a progressive and recursive manner. The key feature of this method lies in its independence from model training, as it directly and efficiently addresses tunnel point cloud segmentation challenges by capitalizing on the generalization capability of foundation model. Comparative experiments against classical region growing algorithms and PointNet++ deep learning algorithms demonstrate the superior performance of our proposed algorithm.

The rock mechanical relevance of anisotropy in tunnel design

AbstractThe assumption of an isotropic material behaviour is still common practice for tunnel design. Strictly speaking, this assumption is only valid if the influence of directional dependencies on the resulting deformations and stresses is marginal. In lithologies that have a high degree of anisotropy, such as shales and phyllites, the orientation characteristics of material properties such as strength and stiffness should be taken into account in order to avoid serious misinterpretations of the bearing capacity and deformation characteristic of the surrounding rock and the tunnel lining. The main focus is to accurately distinguish between the different types and terminology of anisotropy.

Study on the Fracture Resistance of Mixed Fiber Concrete Lining in a Reverse Fault Tunnel

With the increasing complexity of engineering environments in tunnel construction, some projects are located in areas with adverse geological conditions, including areas prone to fault movements and other geological hazards. Fiber-reinforced concrete can significantly enhance structural performance in such challenging conditions. Currently, the application of high-performance steel-polypropylene fiber in tunnel linings and its anti-fault performance are quite limited. Therefore, this paper focuses on studying the application of steel-polypropylene mixed fiber-reinforced concrete in tunnel lining under reverse fault movements. In this paper, the constitutive relationship of mixed fiber-reinforced concrete is modified based on literature data. Utilizing the Najar formula, fiber-related variables were designed, and a three-dimensional numerical simulation model of a reverse fault tunnel was established. By designing various parameter combination cases, the structural response of tunnel linings was calculated and studied. then the influence patterns of mixed fiber parameters on the anti-fault performance of tunnel linings are summarized, the relationships between main variables are explored, and a reasonable value range for the two fibers is determined, which can provide guidance for practical engineering.

Numerical study of mechanical response of shield tunnel under vehicle collision

Shield tunnels account for an essential part of the urban highway system, which are more likely to encounter terrible traffic accidents during daily operation. There is a risk of collision between the errant vehicle and the shield tunnel when a traffic accident occurs. This paper establishes a refined numerical model of the shield tunnel based on the Wuhan Yangtze River Tunnel and the vehicle numerical model. Considering the four factors (vehicle weight, speed, collision angle, ground reaction coefficient), an orthogonal test scheme designing 9 simulation cases is proposed. During the collision, the dynamic responses (opening and dislocation of segment joints, stress, and plastic damage of shield tunnel lining) are studied. Results show that the anti-collision wall and segment lining are damaged to varying degrees, and bolts and reinforcement bars in the collision area reach their yield strength; meanwhile, segment joints appear to have irreversible opening and dislocation. According to the extremum difference analysis of orthogonal simulation results, vehicle weight and speed are the two leading factors in structural responses, the contribution degree of which is significantly larger than collision angle and ground reaction coefficient in structural responses.

Numerical simulation method and deterioration analysis of load-bearing performance of tunnel linings containing cold joints in plain concrete

Cracking in tunnel linings is a common issue in tunnel engineering, with the main cause being construction-induced defects. As a construction-induced defect in a lining, a cold joint affects the bearing capacity of the lining, and the effect of cold joints on the bearing performance deterioration of linings remains unclear. In this study, 180 high-speed railroad tunnels built in Grade III surrounding rock areas were investigated to determine their degradation states, and the distribution of lining cracks in these tunnels was explored on the basis of different factors. Subsequently, three-point bending experiments were conducted on concrete components with different pouring interval cold joint. Based on the experimental results, a computational unit applicable to cold joint simulation was proposed, and the unit parameters were inverted. Finally, the unit was applied to establish a tunnel model with cold joints and to analyze the deterioration effect of cold joints on the bearing performance of the lining. The cracks caused by cold joints in the lining of a structure were found to extend perpendicular to the lining surface, and this can greatly affect the overall strength of the structure. It's important to consider the impact of cold joints on the lining. In order to simulate these cold joints, cohesive elements were used to calculate the maximum stress and stiffness degradation of the lining with and without cold joint elements. The results showed that there were only small differences, indicating that cohesive elements are effective for simulating cold joints. Two cracking patterns were identified, the dorsal tension misalignment model and the medial tension misalignment model, which are related to the stress state of the cold joints. It's necessary to pay attention to cold joints in the inner tensioned area of the lining and those that exceed the final setting time of concrete during pouring.

Effect of laying length on dynamic heat transfer characteristics of capillary heat exchangers in urban subway tunnel lining

The subway tunnel is a typical semi-enclosed underground space, which poses challenges in dissipating the waste heat generated by subway operations and may result in thermal environment deterioration of urban underground spaces. However, by incorporating heat exchangers into the tunnel lining, the subway can be transformed into an “energy tunnel” that effectively addresses this issue. Capillary heat exchanger (CHE) is a common type of tunnel lining heat exchanger. Recent studies have investigated its heat transfer properties and influencing factors under the assumption of homogeneity, neglecting the variability of heat transfer properties along the CHE tube. The present study developed a numerical model of tunnel-lined CHE utilizing water as the circulating medium, based on a demonstration project in Qingdao. Subsequently, an analysis was conducted to investigate the evolution of heat transfer properties for different laying lengths. The simulation results indicate that as the laying length increases from 2 to 10 m, the fluctuation range of outlet temperature decreases significantly from 10.6 °C to a mere 0.4 °C. Moreover, there is a noticeable decrease in average heat transfer per unit length from 1.9 W/m to only 0.4 W/m; however, this is accompanied by an impressive increase in average heat transfer efficiency from 28 % up to an impressive level of around 61 %. Based on the aforementioned results, it is recommended that the optimal length range for a tunnel-lined CHE should fall within 4 to 6 m. The findings of this study can serve as a valuable theoretical reference for the practical engineering applications of CHEs in urban tunnel lining.

An overview of the research trends on fiber-reinforced shotcrete for construction applications

Abstract In this study, data mining, followed by the scientometric analysis of fiber-reinforced shotcrete (FRS), was carried out for knowledge mapping, co-citations, and co-occurrence. The information needed for the analysis was retrieved from the Scopus search engine. Important publishing sources, keyword analysis, writers with the most contribution in citations and publications, the most-cited articles, and the regions most actively engaged in FRS research were identified throughout the data review process. Moreover, the need for FRS, the major constraints associated with their usage, and their possible solutions were discussed. The analysis of the bibliographic data showed that research publications on FRS progressed inconsistently till 2015, and over the past 6 years (2016–2021), publication numbers increased steadily, which exhibited the interest of academics in fiber-reinforced materials. The analysis of keywords in the field showed that the most common FRS research keywords are shotcreting, shotcrete, steel fibers, FRS, and fiber-reinforced materials. Keyword analysis showed that FRS is typically used for tunnel rock support and lining. Based on the review of relevant literature, research gaps have been identified, and future research has been suggested.

Novel corrugated tube–rubber–concrete flexible joint for lining water conveyance tunnels crossing reverse Faults: Numerical analysis of dislocation resistance performance

When water conveyance tunnels cross seismic fault fracture zones, significant deformation may occur, threatening the structural integrity of the tunnel. To resolve this problem, a novel corrugated tube–rubber–concrete flexible joint (CTRCFJ) for improving fault resistance is proposed for the first time. The effectiveness of the CTRCFJ was evaluated using advanced three-dimensional non-linear finite element analysis. The design parameters of the CTRCFJ, including rubber width, corrugated tube interval, and corrugated tube width, were selected based on the distribution of the axial bending moment of the lining structure. An orthogonal test was performed to determine the optimal combination of parameters. The effects of the number of crests, different steel grades, and wall thickness of the corrugated tube on the fracture resistance of the CTRCFJ are investigated. Results show that the CTRCFJ can effectively improve the dislocation resistance performance of composite lining water conveyance tunnels crossing reverse faults by reducing axial compression and bending strain. This study provides a reference for the structural design of composite lining structures that can cross reverse faults.

Nonlinear seismic response and damage evolution of a mountain tunnel: Multi-scale simulation by IBEM-FEM coupled method

Studying dynamic response and damage assessment of mountain tunnels is paramount in earthquake engineering. This paper proposed a novel method, the indirect boundary element method-finite element method (IBEM-FEM) coupled method, aimed to concurrently simulate the amplification effect of kilometer-scale mountain topography and the damage evolution in a centimeter-scale lining tunnel section. The proposed method involves two fundamental steps. Initially, the input motion on the truncation boundary within the mountain is accurately determined using the indirect boundary element method (IBEM). Subsequently, the nonlinear dynamic behavior of the tunnel structure and its adjacent area is analyzed by the finite element method (FEM) based on the results from the previous step. This study numerically simulates the seismic damage and failure mechanisms of a mountain tunnel considering three influence factors: incident wave types, incident wave intensities, and surrounding rock mass grades. The results indicate that mountain topography amplifies the seismic response, thereby affecting the dynamic behavior of the tunnel. Under the incidence of SV-waves and P-waves, the dynamic damage distribution patterns of the tunnel lining are significantly different. Moreover, as seismic wave intensity increases, the peak values of tunnel stress exhibit a non-monotonic increasing trend. The surrounding rock mass grade also significantly affects the dynamic response and damage distribution of the mountain tunnel. Overall, the proposed IBEM-FEM coupled method can effectively consider complex mountain topography and is applicable for evaluating the nonlinear seismic response of mountain tunnels.

Traditional cultivation and management practices of agarwood (Aquilaria malaccensis) in Golaghat district of Assam

A few plant species of the Thymelaeceae family are highly valuable and demanding because it contains resinous oil in their stem, branches, and roots. Agarwood (Aquilaria malaccensis) is one of them, which is found primarily in Assam and adjoining region of North Eastern parts of India as well as in other countries of South and South East India. In Assam, the plant is profusely cultivated in Golaghat, Jorhat and Sivasagar districts. Naturally, stem of the older plant is infected by fungal consortia via the holes made by stem borer. The blackish infection appears inside the stem along the line of the borer tunnel and valuable resinous oil can be extracted through water distillation from the black, infected wood. The agar oil has great demand in international market and is used in manufacturing perfume, incense stick, fragrant smoke, and pharmaceuticals industry. Since ancient time, people of this region have been cultivating Aquilaria with the methods adopted from traditional knowledge and found better success of infection and oil yield. Documentation of this traditional knowledge of Aquilaria malaccensis is of significant importance for promoting its cultivation among the people of this region before the knowledge is lost forever. The knowledge will also be useful for developing scientific method of commercial cultivation of this perennial tree. In this paper, we are discussing the traditional method of cultivation of Aquilaria malaccensis including seedling preparation, cultivation, intercropping and management practices. Agar is propagated through seeds for growing healthy seedlings; and cultivation practices of the plant are of utmost concern for harvesting valuable oil. Extensive field survey has been conducted at Golaghat district of Assam, India to document the method of cultivation and management practices of the plant. The results obtained from the field study were analyzed and interpreted for understanding the importance of this traditional cultivation practice.