Secondary Lining Research Articles

Geo-stress Characteristics of Schist of Erdaoya Tunnel and Physical Properties of Rock Masses

Erdaoya tunnel in the highway connecting Shiyan (Hubei province) and Manchuan, (Shanxi province) was studied in the study. Various problems occurred in the construction of the tunnel, including large deformation of surrounding rocks, cracks of preliminary supports and secondary linings as well as creeping down and collapse of surrounding rock masses along schistosity planes. In which, the most serious problem was large deformation of surrounding rocks, which not only dramatically delayed the normal construction progress of the tunnel, but also brought a huge challenge for the safety of builders. In order to solve this problem, detailed investigations were made on site in the study to reveal the regional geological, engineering geological and hydrogeological conditions of the tunnel. By conducting geo-stress measurement on site, the characteristics of geo-stress field of Erdaoya tunnel were analyzed from four aspects, including magnitudes of stress, coefficient of lateral pressure, orientation of stress and the relationship between magnitudes of geo-stresses and depths. By applying the DIPS software for interactively analyzing geological locator data, structure characteristics of rock masses were analyzed for preferred structural planes and schistosity planes in the tunnel site. Furthermore, the authors tested the physical and hydrological properties of the rock specimens collected on-site. So various physical properties (density, void fraction, and wave velocity) and water absorption hydrological property of schist were obtained, which provide underlying parameters support for the deformation and support of surrounding rocks of the tunnel.

Hydraulic Performance of Organo Clay Enhanced Sand Bentonite as Secondary Liner

The leakage of petroleum from the storage tanks poses a serious threat to soil and groundwater. Hence an additional layer of impermeable material is usually provided as secondary containment systems in underground and above ground storage systems meant to store petroleum products. However the use of conventional mineral liner material is found to be ineffective for their use in secondary containment system to contain organic fluids. The conventional liner materials such as compacted sand–bentonite (SB) mixtures needs to be amended with materials of high organic sorption capacity. Therefore studies were carried out to assess the hydraulic performance of sand bentonite mixture amended with different percentages of organo clay (SOB) and to evaluate their possible use in secondary containment of petroleum product. The hydraulic conductivity of different SOB mixtures compacted at optimum conditions was evaluated with water and diesel as permeants. The coefficient of permeability was measured for various mixtures under different loads varying from 0 to 300 kPa. The permeability coefficient was evaluated both for loading and unloading cases. A decrease in the coefficient of permeability with diesel by an order of two, was observed on increasing the organo clay content from 0 to 10% in SB mix, where as a reverse trend was noted with water as permeant. The hydraulic performance of SOB mixture was found to be largely influenced by the proportion of organo clay, the nature of pore fluid and the applied pressure suggesting a need for careful proportion of mixture to be used as secondary liner.

Fuzzy Synthetic Evaluation of the Long-Term Health of Tunnel Structures

A tunnel is a coupled system of the surrounding rock and the supporting structure. The health status of a tunnel structure is complex and is influenced by various factors. In addition, these factors are coupled and interacted with each other, which calls for the linguistic description of the tunnel safety level. In this paper, we describe the health status of a highway tunnel structure in terms of four levels: safe; basically safe; potentially unsafe and unsafe. Based on the analysis of the safety characteristics of the tunnel structure and its proposed safety level, this research develops a multi-level fuzzy synthetic evaluation model for the long-term safety evaluation system of a tunnel structure. The Cang Ling Tunnel, which has embedded sensors to measure the stress values of the secondary lining and the contact pressure, is used as an example to study the proposed method. The results show that the structure of the entire Cang Ling Tunnel is in almost a safe condition under the current conditions, which is consistent with the actual operational situation.

Implementation of a long-term monitoring approach for the operational safety of highway tunnel structures in a severely seismic area of China

Summary With the rapid development of highway and railway transportation in China, many tunnels are constructed at the same time within the same region. It has become a challenge how to control dynamically such a large number of tunnel structures in long-term operation and ensure their safety. In this work, we focus on the construction of common characteristics of these tunnels built during the same period in the same region. In particular, we propose a concept and a systematic component of long-term health monitoring and develop a representative system of tunnel structure for such regional tunnels. Aiming at the engineering background, we consider the soft-rock tunnels in the Guang-Gan Expressway (GGE), which are located at the core of the Wenchuan earthquake zone, taking the Dujiashan Tunnel as a representative project. Based on the loading data of the secondary lining from long-term monitoring, the fuzzy model is employed to evaluate the structure conditions for its safety. On the basis of such theoretical analysis, we therefore establish the relationships between the representative project and other soft-rock tunnels, and then the structural safety status of the nonrepresentative project is deduced and achieved. The present study shows that the vast majority of segments of the soft-rock tunnels on the GGE are safe. At the same time, the network transmission hardware platform and security evaluation with the alerting software system are installed successfully for those tunnels. Using the long-term health monitoring and representative system of tunnel structure for soft-rock tunnels at the core of the Wenchuan earthquake zone, real-time monitoring and management of the safe status of all the soft-rock tunnels on the GGE across the entire life cycle can be realized.

Field Monitoring of Deformations and Internal Forces of Surrounding Rocks and Lining Structures in the Construction of the Gangkou Double-Arched Tunnel—A Case Study

Double-arched tunnel is a special and complex underground structure which needs to be monitored carefully during construction. Taking the Gangkou tunnel as the engineering background, this paper presents a case study of field monitoring of a representative double-arched tunnel. Typical cross sections were chosen in each class of surrounding rock masses in the tunnel area and different types of sensors were embedded in designed locations, and the deformations and forces of both surrounding rocks and lining structures were monitored systematically. The dynamic evolution as well as the spatial distribution characteristics of the monitoring data including the internal displacements of surrounding rocks and the contact pressures between surrounding rocks and primary linings, the axial forces in rock bolts and the internal forces in both steel arches and secondary linings were analyzed. The monitoring and analysis results show that the deformations and forces of both surrounding rocks and lining structures are directly related to the construction procedures, geological conditions and locations in the double-arched tunnel. According to the results, some reasonable suggestions were provided for the improvement of the tunnel construction. This study will provide useful reference and guidance for the design, construction and monitoring of similar engineering projects in future.

A new type support structure introduction and its contrast study with traditional support structure used in tunnel construction

Referencing the design method of frame-core wall structure used in super high-rise building, a new type supporting system of grid steel frame-core tube was designed, and the structure composition and assembly method for each element were illustrated. A field test was conducted in Jinpingyan tunnel located in the area influenced by 2008 Wenchuan earthquake and the settlement of surrounding rock, internal displacement of surrounding rock, pressure between surrounding rock and primary support, internal force of support arch, axial force of rock bolts, pressure between primary support and secondary lining, and strain of secondary lining were measured to compare under two different support arches of common I-shape steel arch and new type support structure. Moreover, a 3D numerical analyses using FLAC3D software were conducted and the numerical results were compared with results of field test. It was suggested that the new type support structure played a significant role to control the large deformation of surrounding rock.

Performance of the Prestressed Composite Lining of a Tunnel: Case Study of the Yellow River Crossing Tunnel

This paper presents the performance of a new prestressed composite lining applied in shield tunnels for water conveyance. The Yellow River Crossing Tunnel of the Middle Route Project of the South-to-North Water Division Project is adopted in this study as a case, and a three-dimensional finite element model is established to analyse the stress distribution and deformation feature of the prestressed composite lining when the tunnel is under the assembly condition, the tension condition and the water-filled condition. The finite element model is verified by comparing with the results of the full-scaled simulation experiment. The calculation and analysis results reveal that further open of the segmental joint gaps can be limited and full circumferential compression of the secondary lining can be realized when the tunnel is under the water-filled condition, which are conducive to long-term operation of the prestressed composite lining. The membrane has a significant effect on preventing stresses from being transmitted between the segmental lining and the secondary lining. The numerical calculations are verified by the results of the full-scaled simulation experiment, and the three-dimensional numerical model combined with the analysis method used can simulate the structural characteristics and the bearing mechanism of the prestressed composite lining.

Study on Mechanical Characteristics of Tunnel Support System in Sandy Cobble Stratum

Because the sand gravel stratum with loose structure, good gradation, easy disturbance, poor stability, deformation and other characteristics of long duration, large deformation and collapse failure phenomenon is extremely easy to cause in the tunnel construction, leading to a primary support structure for strong deformation or even destruction, serious impact on the tunnel construction and safety, is one of the main problems encountered in tunnel construction. The paper based on the engineering background of Gongboxia sand gravel stratum tunnel, studied the Sandy pebble tunnel primary support stiffness and the influence of strength characteristics, also mechanical impact characteristics of secondary lining and timing. By studying the mechanical behavior of tunnel support system, the paper puts forward the parameters of the initial support of the sand gravel tunnel, and makes clear the relationship between the stress of the supporting arch and the stress of the lining and the timing of the two lining. The research results can provide supporting design reference for sand pebble stratum tunnel and similar projects.

Propagation of Cracks in the Secondary Lining of Tunnels Subjected to Asymmetrical Pressure and a Safety Evaluation

This paper aims to study the way cracks propagate in the secondary lining of tunnels subjected to asymmetrical pressure and to determine the corresponding safety evaluation standards. To achieve this, a cracked part of the secondary lining of the Gucheng-Zhuxi expressway tunnel in Hubei, China was studied under asymmetrical pressure. Using fracture mechanics, the propagation laws and characteristics of the cracks on different scales are analyzed under different asymmetrical pressures and at different positions. The study is based on stress-intensity factor theory and uses ANSYS finite-element software. The results show that crack width (b) has a small effect on crack propagation in the lining structure. On the other hand, crack depth (h) has an obvious effect. The stress-intensity factors at asymmetrically-loaded positions are found to be clearly larger than those at symmetrically-loaded positions. That is, an asymmetrical pressure distribution promotes the propagation of cracks at asymmetrically-loaded positions (and inhibits that at symmetrically-loaded positions, to some extent). When the value of h falls in the range from 3 to 12 cm, the cracks propagate in a stable manner in asymmetrically-loaded positions; at a depth of 15 cm, the propagation becomes unstable. Thus, a crack depth of h = 12 cm can be regarded as the critical value signaling the onset of instability and failure of the secondary lining when considering the safety margin required of the lining structure. Combining the existing safety evaluation standards for cracks with a new evaluation index—the crack depth h—we propose a new safety evaluation standard that is suitable for cracks in the secondary lining of the Gucheng-Zhuxi expressway tunnel under asymmetrical pressure. In addition, suggestions are made for properly treating different types of crack.

Numerical analysis on the mechanical performance of supporting structures and ground settlement characteristics in construction process of subway station built by Pile-Beam-Arch method

Pile-Beam-Arch (PBA) method is an effective approach to control the surface settlement induced by excavation to construct the subway station, especially when the station is located in the urban area with dense buildings. Based on the numerical analysis model of practical engineering, the whole construction stages of the subway station built by PBA method are simulated in this paper. The mechanical performance of supporting structures (such as piles, beams, arches, secondary lining and backfill concrete) and surface settlement characteristics during construction are investigated. The results show that the pre-supporting system of piles, beams and arches is formed in the stage of soil excavation under main tunnel arch; Station hall plate and backfill concrete are two key structures to ensure the support stiffness of PBA supporting system. In addition, compared to the bottom-up method, the top-down method for the secondary lining construction can obviously reduce the internal force of supporting structures and the surface settlement. Combined with in-situ monitoring data, three increase stages of surface settlement and the corresponding settlement ratio are gained and the characteristic of surface settlement trough is also analysed. This study is helpful for further understanding the support mechanism of PBA method and the increase law of the ground settlement during the construction of the station built by PBA method.

Determining the Cause of Damages in a Multiarch Tunnel Structure through Field Investigation and Numerical Analysis

AbstractA case of damages in the secondary lining of a multiarch tunnel is studied by field investigation and numerical analysis, which is subject to asymmetry pressure and buried at shallow depth....

Structural properties and durability of a sprayed waterproofing membrane for tunnels

A sprayed waterproofing interlayer between primary and secondary tunnel linings has the potential to create composite structural interaction between them, mainly in circumferential flexure. This depends on the bond between sprayed surfaces and on the structural and chemical properties of the material. Data on bond is reviewed. Recent tests in tension, compression and shear to determine the structural properties of a particular elastomeric waterproofing material are presented, analysed and discussed. Values for Young’s modulus and the shear modulus G are proposed, for serviceability verifications that include limitation of crack width caused by excessive local flexure.It is concluded that where sufficient bond is present, composite action arising from transfer of circumferential shear between the linings can be relied upon to improve performance in service for short-term and accidental situations. This allows for reduction of stiffness during the first few years. There is no evidence from tests lasting up to 2.2years that significant further reduction would occur, but prediction of 100-year performance remains difficult.

The Effect of Redistribution of the Mixing Water of the Concrete Lining on its Quality

In the heart of the processes of formation of physical and mechanical properties of secondary lining of underground structures is the residual water-cement ratio, which indicates the extraction of the mixing water of the concrete mixture under the action of external pressure forces. This article examines the nature of the redistribution of the mixing water in the concrete lining of the tunnels. Under the influence of radial and axial forces from laid concrete mix there is an increase in water-cement ratio in the direction from the sole to the vault head of the tunnel. This leads to deterioration of physical and mechanical properties of the lining in the roof part of the tunnel. When calculating the strength and water resistance of the secondary concrete tunnel lining the characteristics of the concrete type by strength and waterproof, adjusted by the weakest part of the lining – its roof part – should be taken into account. The analysis of influence on the technology of erection of the lining is given.

Effect of soft layer on seismic response of subway station in layered stratum

The seismic behavior of subway and highway tunnel has been an important topic followed the seismic damages of several structures in recent large earthquakes. Soft layer is often encountered in engineering site, and it is often located with normal strata. There have been limited literatures concerned on seismic performance of subway station with the presence of soft layer. Flac3D is employed to investigate the effect of soft layer on seismic response of subway station structure in earthquake. The effect of soft layer locating below subway station is firstly studied. Then the seismic response of subway station against location of soft layer is further investigated. The relative displacement, acceleration and safety factor of secondary lining, and internal force of central column are highlighted. It is found from numerical results that effects of the two cases are similar when soft layer locates below or above subway station and both beneficial for improving the safety of subway station compared with the case without soft layer. The case when soft layer locates below subway station is more preferable than the case above. It is also found that in the case when soft layer is within the range of subway station, it will greatly amplify the acceleration and internal force of secondary lining, especially for the part that is close to soft layer, and the influence degree gradually decreases with the increase of relative distance to soft layer. As a result, soft layer is generally beneficial for improving stability of subway station, but it should be avoided to be located within the range of subway station to ensure the stability of subway station.

Identification of magnesia–chromite refractory degradation mechanisms of secondary copper smelter linings

Used direct-bonded magnesia–chromite refractory bricks from a secondary Cu smelter were collected to characterize the degradation occurring during application. Based on this post-mortem analysis, lab scale experiments were designed using the direct-bonded refractory type and a fused grain magnesia–chromite refractory. Firstly, the infiltration behavior of a Cu–CuxO and a Cu–CuxO–PbO mixture was investigated. Secondly, the influence of temperature and the prior infiltration of a Cu–CuxO mixture on the infiltration of the ZnO containing fayalite slag was determined. The combination of the post-mortem study and the lab scale tests allowed a more comprehensive understanding of the evolution of the refractory microstructure during degradation. Likewise, it allowed to evaluate how certain parameters, such as temperature and refractory type, affect the infiltration and degradation behavior. As a consequence, conclusions can be drawn about measures to minimize refractory wear in copper smelter linings.

Dynamic response of a double-lined shield tunnel to train impact loads

A three-dimensional numerical finite element model was established by Abaqus to study the time-history curves of train-to-tunnel impact forces for impacts at different velocities, train configurations and oblique-impact angles. A concrete plastic-damage model was used to study the dynamic responses of a double-lined shield tunnel to train impacts by the HHT time-integration scheme. Model simulations showed that the impact force was related to the velocity and angle of the train at impact, as well as the train configuration. Two categories of characteristic force vs. time curve were found for the train-to-tunnel impact, and multi-peak Gaussian fitting was used to interpret the first category. The dynamic response increases with greater impact velocity and impact angle, while it greatly reduces when the thickness of the secondary lining is increased. Most of the tensile damage was seen ahead of the impact point (in the direction of travel), and compressive damage was concentrated behind, above and below the impact point. The average maximum tensile damage was found to exceed the compressive damage.

Effect of ventilation on the thermal performance of tunnel lining GHEs

A tunnel lining ground heat exchanger (GHE) uses surrounding rock as heat source and transfers heat through absorber pipes buried in the tunnel lining. In order to evaluate the effect of ventilation on the thermal performance of tunnel lining GHEs, thermal response field tests considering ventilation were performed in Linchang tunnel, and a 3D numerical model of tunnel lining GHEs was built and verified with the field monitoring data. The study results show that (i) the ventilation has a significant influence on the temperature field of surrounding rock; (ii) the heat exchange rate rises exponentially as convective heat transfer coefficient (CHTC) increases, and it increases significantly with the decreasing thickness of secondary lining; (iii) the heat exchange rate presents a linear variation as the inlet temperature increases, the growth gradient of the heat exchange rate rises exponentially as the CHTC increases and decreases gradually with the running time increase.

Numerical analysis and field monitoring tests on shallow tunnels under weak surrounding rock

The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring tests and numerical analysis were done. The mechanical characteristics of shallow tunnels under weak surrounding rock and the stress—strain rule of surrounding rock and support were analyzed. The numerical analysis results show that the settlement caused by upper bench excavating accounts for 44% of the total settlement, and the settlement caused by tunnel upper bench supporting accounts for 56% of the total settlement. The maximum axial force of shotcrete lining is 177.2 kN, which locates in hance under the secondary lining. The maximum moment of shotcrete lining is 5.08 kN·m, which locates in the arch foot. The stress curve of steel arch has three obvious stages during the tunnel construction. The maximum axial force of steel arch is 297.4 kN, which locates in tunnel vault. The axial forces of steel arch are respectively 23.5 kN and −21.8 kN, which is influenced by eccentric compression of shallow tunnel and locates in hance. The results show that there is larger earth pressure in tunnel vault which is most unfavorable position of steel arch. Therefore, the advance support should be strengthened in tunnel vault during construction process.

Comparative Analysis of Excavation Schemes for a Tunnel Constructed through Loose Deposits

AbstractBecause of weak surrounding rock, tunnels constructed in loose deposits are prone to collapse, and secondary linings commonly suffer excessive deformation. Therefore, it is important to select an appropriate excavation scheme, which will affect both tunnel construction safety and subsequent tunnel operations. This paper takes the Tingziba tunnel, a highway tunnel shallowly buried in loose deposits of diluvial and proluvial origin, as an example. During construction, this tunnel experienced many instances of vault collapse and advanced support destruction. Isotropically consolidated drained (CD) compression tests were carried out on reconstituted specimens to obtain the mechanical parameters of the loose deposits. Three-dimensional modeling was performed to simulate stress and deformation distributions in the tunnel after excavation by three different schemes, i.e., up and down bench tunneling, three-bench tunneling, and single-side heading tunneling. The comparative analysis results showed that si...

Mechanical behaviour of a sprayed concrete lining isolated by a sprayed waterproofing membrane

A waterproofing membrane has an important role in a sprayed concrete lined (SCL) tunnel. In this study, the mechanical behaviour of an SCL with a sprayed waterproofing membrane was investigated by laboratory testing. Two different types of tests were performed to examine the behaviour at different parts of an SCL tunnel linings around a tunnel junction. A four-point bending test was conducted to investigate the behaviour of tunnel linings under a large bending moment, which would represent a section near the opening of a tunnel junction. An eccentric compression test was conducted to investigate the behaviour of tunnel linings under a large compressive axial force (hoop stress) and a relatively small bending moment, which would represent a section at the opposite side of the opening of a tunnel junction. Both test results indicate that an SCL with a sprayed waterproofing membrane behaved as a composite section with very limited slip at the interfaces. Designing the primary lining, the waterproofing membrane and the secondary lining of an SCL tunnel as a composite section could have significant practical implications including time and cost savings.