Secondary Lining Research Articles

Large deformation characteristics and treatment effect for deep bias tunnel in broken phyllite: A case study

The support structure of deep buried tunnel often encountered bias load of during construction in weak layered strata. This paper studied the support structure failure behavior and surrounding rock deformation mechanism with Wuduxi Tunnel as an engineering case. The tunnel presents the damge phenomenons such as primary support cracking, steel arch distortion, secondary lining sidewall extrusion under asymmetrical load and high geostress. Firstly, the laboratory test was producted to research the engineering characteristics of the broken phyllite. The field test results show that the surrounding rock pressure is unevenly distributed around the tunnel, the primary support is all under pressure and the secondary lining is partial in tension. The surrounding rock pressure distribution shows an ellipsoidal distribution consistent with the trend of the rock stratum. The maximum vault settlement and horizontal convergence are 165.58 mm and 282.56 mm, respectively, and the convergence rate is far more than the stable deformation rate in the specification, which proves that the existing specification is not applicable to the large deformation deep buried bias highway tunnel with soft rock. Furthermore, the construction methods of “double primary support-secondary lining” are proposed to control the large deformation of surrounding rock. The field test is carried out to verify the feasibility of the double layer primary support. The field test show that the large deformation can be effectively controlled, and the support structure was stable without crack and damage, which ensured the construction safety of the deep buried bias tunnel in broken phyllite.

Analysis of the Stability and Mechanical Characteristics of the Jointed Surrounding Rock and Lining Structure of a Deeply Buried Hydraulic Tunnel

On-site monitoring and numerical simulation have been combined to analyze the stability of the jointed surrounding rock and the stress inside the lining structure of a sample deeply buried hydraulic tunnel. We show that the deformation around the tunnel was mainly concentrated in the range 51.37 mm∼66.73 mm, the tunnel circumference was dominated by shear failure, and the maximum plastic zone was about 3.90 m. When the shotcrete treatment was performed immediately after the excavation, the deformation of the surrounding rock was reduced by 58.94%∼76.31%, and the extension of the plastic zone was relatively limited, thereby leading to improvements in terms of the stability of surrounding rock. When the support was provided at different time points, the stress of the surrounding rock in the shallow part of the tunnel was improved everywhere. In the tunnel section with high ground stress and joint development, when 10 cm steel fiber concrete spray layer and 40 cm C25 concrete secondary lining were used, the maximum tensile stress on the lining structure was 0.89 MPa, i.e., it was less than the tensile strength of concrete, which indicates that the internal force of the lining can meet the overall requirements.

Analysis of Construction Monitoring and Control of Tunnels Crossing Broken Faults and Water-rich Geology

In view of the poor geology such as tunnel engineering crossing faults or passing faults, the construction of surrounding rock and support is complicated. During construction, it is necessary to ensure the stability of the surrounding rock and supporting system, and ensure the timing of the secondary lining construction. For this reason, through the analysis and processing of monitoring data, the law of stratum change is mastered, and the supporting parameters and construction methods are adjusted and revised at the same time, so as to provide the best information for the tunnel surrounding rock and supporting lining construction.

RESISTANCE TO CRACK PROPAGATION OF HIGH-PERFORMANCE CONCRETE

<jats:p>This paper discusses the results of investigations on the resistance to crack propagation carried out as part of a large-scale project to develop high-performance concretes (HPCs) for the secondary lining of a low and intermediate level waste disposal shaft. Four HPCs were investigated, in which the quantity of the binder component and the proportions of the two cements and the silica fume in it were varied. We have also added steel fibers to one HPC. The wedge splitting test method was used to determine the resistance to crack propagation. The results obtained show that all the HPC investigated achieve good resistance to crack propagation. The addition of steel fibers further improves this resistance.</jats:p>

Experimental and numerical research on the influence of steel arch frame corrosion on security of supporting system in subsea tunnel

Subjected to high chloride ion content in subsea, underwater structure will be corroded in different degree in the service environment, which will shorten the durability of the structure. Subsea tunnels are often constructed by drilling and blasting method, and microcracks are inevitable in primary support due to blasting impact. The cracks provide channels for chloride ion, sulfate ion in seawater and oxygen in air, which leads to steel arch frame corrosion in primary support. Corrosion will reduce the bond strength and bearing capacity of the supporting system, thus reducing the service time of the subsea tunnel. Based on Xiang'an subsea tunnel, the effect of steel arch frame corrosion on the supporting system was studied. First, the accelerated corrosion test and push-out test were carried out, the bond-slip degradation constitutive model between corroded I-shaped steel and concrete was proposed based on damage variables. Then, the degradation constitutive model was introduced into ANSYS to simulate the influence of corroded I-shaped steel on the overall mechanical behavior and safety of the subsea tunnel. Results of model indicated that with the increase of corrosion ratio, the internal stress of the I-shaped steel, sprayed concrete and secondary lining increased, and the corresponding safety factors all decreased.

An analysis of the support loads on composite lining of deep-buried tunnels based on the Hoek-Brown strength criterion

The composite lining load of a deep-buried tunnel is one of the key problems in tunnel support design. This study establishes four support cases to discuss the loads on primary support and secondary lining. A support load solution method is proposed based on the Hoek-Brown strength criterion by considering the stress release coefficient and the distal positions of bolts. According to engineering measurement, the displacements and loads of support structure calculated by elastoplastic theory are consistent with field measurement and numerical simulation which verifies the reliability of the theoretical method and studies the influence of support parameters on support load and bearing ratio. Results show that GSI, support time and support thickness have a great impact on support load, among which the combination of several factors may lead to the change of the main bearing structure. The higher the surrounding rock grade is, the higher the secondary lining bearing ratio will be. The support bearing ratio based on the Hoek-Brown strength criterion is consistent with field monitoring. The theoretical work done in this research can provide suggestions for engineering practice.

Evaluation of the effect of using fiber reinforcement in tunnel linings for metro projects

Metro (subway) is an advanced public transport infrastructure system in urban areas with high capacity. The traffic operation of a metro is not affected by other vehicle traffic thanks to underground tunnels. With these benefits metro lines are preferred to solve the traffic problem in urbanized cities such as Istanbul, which is the focus of this study. Metro projects require huge amounts of budgets to be built. Putting these projects into service in targeted time is of great importance. The objective of this study is to minimize total metro construction project time by utilizing fiber reinforcement in tunnel linings. In this research, using fiber reinforcement to construct primary (initial) tunnel linings and secondary (final) tunnel linings of the metro projects are analyzed in terms of project duration. After comparison of two railway tunnel projects, evaluations and observations of a completed metro project revealed that using fiber reinforcement for either the primary lining or the final lining of tunnels reduces construction time of metro station tunnels by 25%. In addition, using fiber reinforcement to construct both the final lining and the primary lining of tunnels reduces construction time of the metro station tunnels and the whole metro project by 47% and 22%, respectively. The results of this study can be useful for completing challenging metro projects and putting it into service within the targeted time.

Experimental Study on Instant Grouting with Formwork for Tunnels

Voids between primary support and secondary lining of existing tunnels pose a serious threat to safety and have become a key challenge for tunnel engineering. Due to the poor bonding performance between concrete slurry backfill and lining concrete, the integrity of supporting structures cannot be guaranteed. In recent years, vault grouting with formwork has proved to be effective in solving this problem. However, few studies have focused on the selection of grouting materials and associated grouting process parameters. In this paper, a slight-expanding concrete slurry is selected as the grouting material. The early strength growth trend of the slight-expanding slurry is explored via laboratory tests. The compatibility of the slight-expanding slurry and the lining concrete is analyzed by comparing the slump, expanding diameter, water retention and compressive strength. Bonding-body specimens were fabricated using a mold developed for this work. Furthermore, we compare the compressive strength and failure mode in order to investigate the bonding properties between the sight-expanding slurry and lining concrete at different grouting intervals and pressures. A reasonable set of operational parameters is subsequently proposed. Finally, field tests undertaken in an expressway tunnel in south China are performed in order to determine the impact of grouting with formwork on tunnel lining, while the grouting effect at the vault is evaluated using a ground penetrating radar. The slight-expanding slurry exhibited a high early strength and rapid hardening. Adding slight-expanding slurry to lining concrete at a volume ratio of 1:0.2 increased the slump, diameter and compressive strength by 13.4%, 15.6%, and 25.0%, respectively. When a grouting interval is less than 6 h, the pressure of grouting with formwork should be no less than 0.2 MPa, while for a grouting interval of 8 h, the grouting pressure should be no less than 0.4 MPa. The grouting pressure of 0.4 MPa exerts a limited effect on the existing secondary lining concrete, and the stress increment produced by grouting accounts for 6–17% of the total increment. The results presented can provide a reference for future tunnel construction.

Study of Temperature Field Distribution in Topographic Bias Tunnel Based on Monitoring Data

In recent decades, numerous tunnels have been built in the cold region of China. However, the temperature field of topographically biased tunnels in the monsoon freeze zone has not been sufficiently studied. In this study, we monitored the temperature of the surrounding rock in two topographic bias sections of the Huitougou Tunnel and analyzed the results by fitting them to the monitoring results. The results showed that the temperature of the surrounding rock on both sides after tunnel excavation varied periodically in an approximate triangular function. As the distance from the cave wall increased, the annual average temperature of the surrounding rock did not change significantly, the amplitude decreased, and the delay time increased, while the annual maximum temperature decreased, and the annual minimum temperature increased. The heat generated by blasting, the heat of hydration of the primary and secondary lining, and the decorated concrete all caused a significant increase in the temperature of the surrounding rock within 4 m for a short period of time. Both construction and topographic factors led to asymmetry in the distribution of the surrounding rock temperature in different ways. The results of this paper are intended as a reference for other studies on temperature in deviated tunnels.

Characteristics and treatment measures of lining damage: A case study on a mountain tunnel

Lining damage is a crucial issue affecting the operation mountain tunnels, as it diminishes the bearing capacity and shortens the service life of tunnels. Investigation and treatment of lining damage are essential for enhancing the safety and prolonging the service life of tunnels. This paper presents a case study on the characteristics and treatment measures of the lining damage of a mountain tunnel by field investigation, numerical simulation and in-situ monitoring. To better understand the operational status of the tunnel structures subject to lining damage, water leakages, cracks and voids behind the lining are detected to obtain the distribution and morphological characteristics of lining damage. Detection results show that voids behind the lining are the main cause of lining cracking, and thus, the mechanical performance and failure mechanism of lining structures with voids are evaluated by numerical simulation. Based on the results, treatment measures of lining damage are adopted, including crack grouting, shotcrete support, and reconstruction of the secondary lining. Finally, the effectiveness of treatment measures is investigated by analyzing field monitoring data. Lessons learned from this case study are discussed, thus providing a reference for the treatment of lining damage in other tunnels.

Mechanical responses in the construction process of super-large cross-section tunnel: A case study of Gongbei tunnel

This paper presents a case study of super-large cross-section tunnel in Zhuhai, China. The excavation section of Gongbei tunnel is 336.8 m2. The construction method of freezing pipe roof and five-bench fourteen-step excavation is expected to be adopted, which is the first case in the world. The tunnel construction risk is great because the stratum which the tunnel passes through is mainly silt and the construction procedure is complex. In addition, the load-transfer mechanisms in tunnelling construction are not clear. In this paper, the field test method and numerical simulation were utilized to study the development and distribution of ground deformation and support deformation during the construction of Gongbei tunnel, and the mechanical responses of tunnel support structure in the tunnelling construction were investigated. The results showed that the ground deformation was uplifted with the excavation of the tunnel due to the freezing and grouting of the surrounding rock. The vault deformation during the excavation process was fluctuating due to Gongbei tunnel was excavated in several steps, which was generally in the state of settlement first and then heave. The peripheral convergence around the tunnel increased first and then tended to be stable with the excavation progress. The removal of temporary support had a slight impact on the convergence around the step C. Due to the existence of the pipe roof and freezing soil, the tunnel supporting stress was small, which ensure the safety of the tunnel structure. Stress results of steel frame of initial support showed that the vault and invert bent to the inside of the tunnel, and the side wall bent to the outside of the tunnel. The bending moment of the secondary lining was larger than that of the initial support due to the ring forming of the secondary lining separately, and the secondary lining might be damaged locally. After the temporary support was removed, the overall stress of the initial support and secondary lining increased slightly. The stress concentration of the secondary lining was relieved after thawing. The interface stress between secondary lining and tertiary lining was large. This case study might severe as a practical reference for similar tunnelling constructions.

Effect of voids on the seismic vulnerability of mountain tunnels

Void defects directly affect the dynamic response of tunnels. These defects have been recognised as an important factor that exacerbates seismic damage and the destruction of tunnel linings. Existing studies that consider the tunnel-void dynamic interaction use deterministic analysis methods, but they lack a quantitative analysis based on a probability method, which can reflect the random nature of earthquakes and structures. In the present work, a series of 2D nonlinear dynamic analyses of tunnel seismic response that consider the tunnel-void interaction is carried out by using the incremental dynamic analysis method. The automatic extraction of the resulting data and the calculation of the maximum damage index (DImax) during the seismic response process are performed by a Python program. The fragility curves of the tunnels are obtained with consideration of void defects. The effects of void type, void location, void size, surrounding rock classification and seismic direction on the vulnerability of the tunnels are investigated. Results show that void size and type and surrounding rock condition exert considerable effects on the seismic vulnerability of tunnels. The presence of voids behind linings leads to increased tunnel vulnerability, which presents a nonlinear increase with the increment of void size. The degree of influence of void size on vulnerability varies with void location. Tunnels with voids between surrounding rocks and the primary support are more vulnerable than those with voids between the primary support and the secondary lining. Hence, void type cannot be ignored. The effects of voids on vulnerability become evident when tunnels are embedded in weak surrounding rocks. The vulnerability under the horizontal seismic direction is apparently greater than that under the vertical direction at the same seismic intensity. However, the sensitivities of vulnerability to seismic directions vary with different void locations.

Applying the new corrugated steel plate (NCSP) liner in the seasonally frozen tunnel to enhance the insulation capacity of linings

Frost damages of the tunnel in cold and seasonally frozen areas seriously affect its operation safety and service life. To better prevent frost damages in seasonally frozen areas, a new corrugated steel plate (NCSP) liner is proposed to improve the insulation capacity of tunnel linings. Firstly, design parameters and construction technologies of the NCSP liner are introduced. Then, taking the Yushuchuan tunnel in Jinlin Province of China as a background, numerical models were built to explore temperature fields of the tunnel with the NCSP liner, and the theoretical insulation effect of NCSP liner was obtained. Afterwards, a field test with a duration of four years in the Yushuchuan area was conducted to verify temperature field results and the effectivity of the NCSP liner. The results show that the freezing-line moves from surrounding rock to secondary lining after the NCSP liner is adopted, and no frost damage has been found again in the four-year field test. The thermal insulation performance of seasonally frozen tunnels has been dramatically improved with the application of the NCSP liner. The conclusion of this paper can provide a scientific reference for the prevention and control of the frost damage of tunnels in seasonally frozen areas.

Structural monitoring and analyses on the stability and health of a damaged railway tunnel

In this paper, a study of stability and health of a newly-built railway tunnel is presented. The field test was implemented to monitor the secondary lining due to the significant cracking behaviors influenced the stability and health of the tunnel structure. Surface strain gauges were installed for monitoring the status of crack openings, and the monitoring outputs demonstrated that the cracks were still in the developing stage. Additionally, adjacent tunnel and poor condition of surrounding rock were identified as the causes of the lining cracking by systematically characterizing the crack spatial distribution, tunnel site and surrounding rock conditions. Reconstruction of partial lining and reconstruction of the whole secondary lining were designed as the maintenance projects for different cracking regions based on the construction feasibility. For assessing the health conditions of the reinforced lining, embedded strain gauges were set up to continuously measure the strain and the internal force of the reconstructed structures. For the partially reconstructed lining, the outputs show the maximum tensile elongation is 0.018 mm during 227 days, which means the structure has no obvious deformation after maintenance. The one-year monitoring of fullsection was implemented in the other two completely reconstructed cross-sections by embedded strain gauge. The outputs show the reconstructed secondary lining has undertaken the pressure of surrounding rock with the time passing. According to the calculated compressive and tensile safety factors, the completely reconstructed lining has been in reliable and safe condition during the past year after reinforcement. It can conclude that the aforementioned maintenance projects can effectively ensure the stability and health of this tunnel.

Mechanical responses of surrounding rock mass and tunnel linings in large-span triple-arch tunnel

In this study, based on the construction of a large-span triple-arch tunnel, the authors focus on the surrounding rock mass deformation characteristic, evolution process of rock mass load, and mechanical behaviors of tunnel linings. Numerical modelling is used for rock mass deformation analysis. The leading tunnel excavation would disturb the rock mass of the lagging tunnel and cause its pre-deformation. As the middle tunnel lagged behind the two side tunnels, it showed much larger pre-settlement than the side tunnels. The field monitoring method is used to obtain the rock mass pressure, contact pressure between the tunnel linings, and steel stresses inside the tunnel linings. At the initial phase, the rock mass pressure and contact pressure of the linings rapidly increased; then, the monitored pressures tended to be stable until the rock mass was disturbed by the following excavation steps. Most of the steel stresses within the tunnel linings were compressive stresses and considerably lower than the yield strength, which meant that the tunnel linings were in a safe working state. The middle tunnel excavation is the most significant part of the triple-arch tunneling. It caused a significant increase in the rock mass load of the side tunnels, particularly the lateral load on sidewalls. The secondary lining of side tunnels shared most of the new increased load caused by middle tunnel excavation. Therefore, the lateral load-bearing capacity of the triple-arch tunnel was suggested to be improved. The rock mass load was symmetrically distributed along the central axis, but there was considerable bias load on the top and bottom of the division walls between the middle and side tunnels, which meant that the bending resistance and anti-overturning capacity of the division walls should be strengthened. According to the mechanical responses of the tunnel, some engineering suggestions are proposed for large-span triple-arch tunnelling. The results of this study can provide references for the design and construction of large-span triple-arch tunnels.

Causal Analysis on the Lining Exfoliation and Treatment Design of an Operational Tunnel

According to the actual situation of the secondary lining of a expressway tunnel in Chongqing, this paper analyzed the specific reasons for lining exfoliation with corresponding test reports. According to this, a quick treatment scheme for lining exfoliation is proposed, which can make the treatment timely and effective, and suggestions for treating similar diseases in tunnels are put forward, which can provide reference for similar projects.

Damage Mechanisms of Soft Rock Tunnels in the Western China: A Case Study on the Dujiashan Tunnel

In the Western China, soft rocks, in particular, phyllites are very widespread. With the increase of soft rock tunnels in recent years, the secondary lining cracking of newly-built tunnels have frequently occurred. In this work, a case study on the Dujiashan Tunnel in the Western China was conducted in order to get insight into the damage mechanisms of such soft rock tunnels in the strong earthquake zone. Furthermore, for the engineering background, the cracking characteristics, on-site monitoring data, influencing factors and damage causes for the the second lining of Dujiashan Tunnel were also investigated. It was demonstrated that with the concentration of the bending moment and shear stress, the reduction in axial pressure appeared on the lining structure at the cavities due to local collapses. Moreover, the aftershocks of the Wenchuan earthquakes could further weaken the strength characteristics. It was revealed that the secondary lining measures were useful for the reinforcement of the Dujiashan Tunnel, and the treatment measures could achieve mainly the backfilling collapse cavities, leading to reinforcing the surrounding rocks, preventing the cracking behavior, strengthening lining, and smoothing drainage. It is therefore suggested that for the newly-built soft-rock tunnels, especially those located in strong earthquake zones, the use of the secondary lining should be at the appropriate time and backfilling the cavities due to local collapses timely, and all the factors are important for the protection and reinforcements of the surrounding rocks to ensure the safety of the tunnel structure.

Analytical Method for Segmental Tunnel Linings Reinforced by Secondary Lining Considering Interfacial Slippage and Detachment

The reinforcement of shield tunnels with secondary linings is a widely used method to enhance the overall rigidity of tunnels; therefore, ensuring tunnel safety during construction and operational periods. According to a new composite curved Euler beam theory, an analytical method will be proposed to analyze a shield tunnel that is reinforced by a secondary lining, in which the radial joints and the interaction between the segmental lining and the surrounding soil will be simulated by a series of concentrated and distributed springs, respectively. In contrast to the radial rigid connection that was assumed in previous studies, radial detachment and tangential slippage between the segmental and secondary linings will be allowed. The solutions for the internal forces and deformations will be derived using the state-space method with arbitrary loads and joint distributions. In addition, the proposed method will be extended to cases with partial reinforcement that have a segment of secondary lining and a reinforcement connected by bolts. The proposed method will be validated using finite element numerical simulations. In addition, the variations in the internal forces and deformation for the soil reaction stiffness under different joint and interfacial stiffnesses will be examined. The results indicate that the internal forces and deformations of the linings decreased with the increase of soil reaction spring stiffness, and the interfacial radial spring stiffness had a more significant influence on the axial force transfer between the linings.

Frame Structure and Engineering Applications of the Multisource System Cloud Service Platform of Monitoring of the Soft Rock Tunnel

Throughout engineering construction, large deformation disasters in soft rock tunnels are encountered increasingly frequently. Therefore, structural health monitoring not only ensures accurate construction management but also provides a basis for dynamic adjustment of the support structure. The existing monitoring technology has certain shortcomings, such as poor anti-interference ability, non-real-time operation, and great security risks. Consequently, high-precision real-time monitoring has become a key scientific issue in tunnel engineering. For this work, multisource information fusion technology was adopted, while data security reserve systems, such as cloud server (ECS) based on the fiber Bragg grating multisource sensing system, cloud database (RDS), and cloud website, were embedded into the No. 2 inclined shaft of the Muzhailing tunnel. Based on the negative Poisson’s ratio (NPR) anchor cable control technology for large deformation of the soft rock in the No. 2 inclined shaft of the Muzhailing tunnel, reasonable and effective intelligent monitoring was carried out for tunnel construction. Monitoring and early warning cloud service platforms, based on the Internet of Things and cloud technology, could quickly produce query and statistic tunnel monitoring information. The monitoring system provided the collection, transmission, storage, processing, and early warning information sending of data, such as NPR anchor cable axial force, steel arch stress, deep surrounding rock displacement, surrounding rock deformation, and contact pressure between primary support with secondary lining. This monitoring system ensured construction safety and provided monitoring application case support for the related problems of similar projects.

Fatigue damage and residual life of secondary lining of high-speed railway tunnel under aerodynamic pressure wave

To investigate the fatigue behaviours of tunnel secondary lining under the aerodynamic effects produced by the running high-speed railway (HSR) trains, we proposed a dual fatigue damage accumulation model (DFDAM). In our model, a nonlinear variable load model was nested inside an equal-damage nonlinear model. The nonlinear variable load model was used to calculate the fatigue damage of a tunnel secondary lining after a single HSR train travelled through the tunnel, and the equal-damage nonlinear model was adopted to calculate the fatigue damage after multiple HSR trains travelled through the tunnel. Our proposed model was verified by comparison with laboratory fatigue testing results obtained by other researchers. The proposed model was also used to study the aerodynamic fatigue behaviours of a practical HSR tunnel project. The results show that the damage accumulation produced during the train running inside the tunnel is approximately the same as that of after an HSR train tail leaves the tunnel exit. Thus, after an HSR train leaves the tunnel exit, the influences of the aerodynamic pressure on the tunnel secondary lining cannot be ignored. The damage accumulation of a tunnel secondary lining associated with multiple HSR trains passing increases monotonically with the increase of the consumed life fraction. In contrast, the residual life of the fatigue damage decreases monotonically. This study can serve as a reference for studying the operational safety of HSR tunnels.