A novel debonding failure test method for polyurea-composite anti-seepage coatings in water conveyance tunnels

In the lining of water conveyance tunnels, the expansion joint is susceptible to leakage issues, significantly impacting the long-term safety of tunnel operations. Polyurea is a type of protective coating commonly used on concrete surfaces, offering multiple advantages such as resistance to seepage, erosion, and wear. Polyurea coatings are applied by spraying them onto the surfaces of concrete linings in water conveyance tunnels to seal the expansion joint. These coatings endure prolonged exposure to environmental elements such as water flow erosion, internal and external water pressure, and temperature variations. However, the mechanism of polyurea coating's long-term leakage prevention failure in tunnel operations remains unclear. This study is a field investigation to assess the anti-seepage performance of polyurea coating in a water conveyance tunnel project located in Henan Province, China. The testing apparatus can replicate the anti-seepage conditions experienced in water conveyance tunnels. An indoor accelerated aging test plan was formulated to investigate the degradation regular pattern of the cohesive strength between polyurea coating and concrete substrates. This study specifically examines the combined impacts of temperature, water flow, and water pressure on the performance of cohesive strength. The cohesive strength serves as the metric for predicting the service lifetime based on laboratory aging test data. This analysis aims to evaluate the polyurea coating's cohesive strength on the tunnel lining surface after five years of operation.

Water conveyance tunnels perform an important role in water-diversion projects. With a water conveyance tunnel transferring water, the conflict between urban crowded ecology and agricultural water can be relieved. Research shows that there is a significant need for a more objective and accurate inspection of water conveyance tunnels during operation. Hence, we investigate the use of a single-beam scanning sonar to detect a water conveyance tunnel and generate a three-dimensional point cloud model, which can be used to make objective predictions for surface defects. First, a cobweb-like grid matrix was proposed to grid discrete points to establish the topological relationship of the point cloud. Second, a denoising method fusing acoustic properties and intensity was used to filter the noise in the acoustic point cloud. Third, an optimal echo extraction technology based on a second-order differential model was proposed to obtain a high-precision point cloud of the tunnel. Experiments show that the proposed denoising method and optimal echo extraction method are superior to traditional algorithms commonly used in ground point clouds, with good results achieved at real test sites.

A water conveyance tunnel is narrow and enclosed with a complex distribution of flow field. The performance of sensors such as Doppler log, magnetic compass, sonar, and depth gauge used by conventional underwater vehicles in the tunnel is greatly affected and can even fail. Aiming at the special operating environment and operational requirements of water conveyance tunnels, this paper designed an architecture suitable for pressurized water conveyance tunnel-detection autonomous underwater vehicles (AUVs). The tunnel-detection AUV (called AUV-T in this paper) with the architecture proposed in this paper could easily and smoothly complete inspection tasks in water conveyance tunnels, and field tests have verified the effectiveness of the architecture. Since an AUV in a water conveyance tunnel cannot go to the surface to rescue itself, in order to ensure its safety we designed the heterogeneous dual-CPU (Central Processing Unit) hot redundancy system based on dual communication lines. The reliability analysis showed that the system can significantly reduce the probability of AUV failure and ensure that the AUV can still be recovered even if it fails in the tunnel.

Shield double-layer lining structure is used to bear large internal water pressure in water conveyance tunnel engineering, but the mechanism of joint stress of structure and force transmission between linings is still unclear. In this paper, a stress calculation model of the double-layer lining structure of shield water conveyance tunnel considering the influence of transition layer between the inner lining and the outer lining is presented. By analyzing the inner lining and outer lining separately, the calculation formulas of radial displacement and circumferential stress are obtained. Then, according to the deformation coordination condition, the relationship between the inner and outer lining radial displacements is established. Thus, the magnitude of the unknown interaction force among the structures is calculated. Finally, through the stress analysis of the lining structure, the axial force, shear force, and bending moment acted on the structure are obtained. By comparing finite element calculation results with analytical calculation results, the rationality of analytical solutions is verified. Based on the proposed analytical method, the influence of inner lining thickness and material parameters of transition layer on the internal force and deformation of lining structure is analyzed. The results show that with the increase of the thickness of the inner lining, the axial force and bending moment increase, while the internal pressure shared by the outer lining decreases. The larger the elastic modulus of the transition material, the smaller the difference between the internal force and deformation of the inner and outer linings.

Prestressed concrete linings enhance the crack resistance and durability of lining structures by embedding prestressed tendons in concrete linings, applying pretension, and locking them with anchorages to make the linings pre-compressed, thus counteracting tensile stresses induced by external loads. This makes them the preferred lining form for large-section and high-head water conveyance tunnels. However, in seismic-prone areas, such linings are vulnerable to seismic-induced structural damage. This paper systematically reviews the research achievements in seismic resistance and shock absorption, covering aspects of seismic performance analysis, application of shock absorption technologies, numerical simulation, and experimental studies, and deeply discusses the existing problems in current research. The study shows that the application of shock absorption materials, design of shock absorption structures, and passive control shock absorption technologies can effectively reduce the damage to the linings of water conveyance tunnels during earthquakes.

The water conveyance tunnel has been widely applied in tunnel engineering, which may be subjected to compressive stress and shear stress from rock and faults, respectively. The internal pressure caused by water in the tunnel will make the appearance of cracks and propagation, resulting in disasters. In order to study the effects of the cracks and compressive stress on the cracked tunnel model, a plane model containing a circular hole with two unequal cracks under the compression loads, shear stress and internal pressure was established in this study. Complex variable function and conformal mapping function were implemented to theoretically derive the stress intensity factors (SIFs) at the crack tip in the rock mass, the numerical simulation was conducted to validate the theoretical solutions. The results indicate that the numerical results using the ABAQUS code were in good agreement with the theoretical solutions. The effects of compressive stress, shear stress, internal pressure, crack length and crack inclination angle on model II SIFs were discussed, the initiation angle and initiation pressure of different rock materials were also studied. When the crack inclination angle changes from [Formula: see text] to [Formula: see text], the tunnel is easily destroyed. With the increase of the right crack length, the increasing rate of the SIFs increases quickly first and then linearly, however, the left crack length has a slight effect on SIFs. When the crack inclination angle is [Formula: see text], the crack initiation angle reaches the maximum value.

Centrifugal modeling of continuous shallow tunnels at active normal faults intersection

Because of the ultra-large scale calculation and strong nonlinear calculation of fluid structure interactions (FSIs), the numerical simulation and analysis of water hammer impacts in an ultra-large water conveyance tunnel are difficult. The hybrid modeling method is used to simulate water hammer impacts in an ultra-large water conveyance tunnel. The method can not only yield water hammer simulations along the full tunnel length, but also the detailed structural responses of the segment linings. In the finite element model, the pressure and velocity of fluid field is solved with FLUENT and then applied to the structure as the initial conditions or boundary information. The structural field is solved with the finite-element program LS-DYNA. The interaction between two physical fields is realized using ALE (Arbitrary Lagrangian-Eulerian) description. The structural response of a large-diameter double-line water conveyance tunnel in Shanghai under the impact of water hammer is analyzed. The results presented the propagation of water hammer pressure in the long-distance water conveyance tunnel and the effects on tunnel linings.

Retrieval of siltation 3D properties in artificially created water conveyance tunnels using image-based 3D reconstruction

Based on the concrete damage plasticity constitutive model (CDP model) of ABAQUS software, the dynamic response of high pressure internal water conveyance tunnel during earthquake is simulated, and the dynamic response and dynamic damage law of high internal water pressure water conveyance tunnel structure under surrounding rock grade, buried depth and seismic wave intensity are analyzed. The research shows that the surrounding rock grade is closely related to the dynamic response and damage characteristics of the lining structure of the water conveyance tunnel. The dynamic damage of the tunnel under grade Ⅲ surrounding rock is only 0.08, which is far less than 0.83 under grade Ⅳ surrounding rock. It can be considered that it will not cause great damage to grade Ⅲ surrounding rock under earthquake. The surrounding rock grade is better, which can provide more stable support and reduce the stress and vibration of the structure. If the tunnel is in the seismic zone, the buried depth can be used as one of the design control indexes in the tunnel design. The lining damage is mainly distributed at the top and upper arch waist of the tunnel. With the increase of the buried depth of the tunnel, the dynamic damage amount increases from 0.021 to 0.081, then to 0.085. the damage of the lining structure also increases. This may be because the deep buried tunnel is more constrained by the underground rock and soil layer, thereby reducing the transmission of seismic load. The change of seismic wave intensity can directly affect the damage characteristics of tunnel lining structure. The dynamic damage mainly occurs at the vault and arch waist, and the damage area expands from the vault and arch waist to the side wall and corner. The increase of seismic wave intensity will lead to dramatic changes in the stress of the structure, which will lead to more complex and serious damage.

A parametric study on friction-loss in water conveyance tunnels considering misalignment of precast concrete segments

In this paper, the structural responses and failure characteristics of a new type of water conveyance tunnel lining structure subjected to reverse fault conditions were numerically investigated by considering multiple loads and interaction separation modes between different structural layers. This study proposes a new evaluation standard for the safety level of the damage state of the composite lining water conveyance tunnel. It also discusses the influences of fault dislocation displacement (Δf), dip angle (β), and the mechanical properties of the surrounding rock in the fault fracture zone on the water conveyance tunnel response and damage. The results indicate that the buckling failure of the steel tube under axial compression is the dominant failure mode of the composite lining structure. With increasing fault dislocation displacement, the axial compressive strain and circumferential shear strain of the composite lining are most severely damaged on the sliding plane. With decreasing fault dip angle, the axial compressive strain of the composite lining weakens, while the bending and shear strains increase. The increase in rock stiffness in the fault fracture zone reduces the damage scope but increases the composite lining structural damage severity. Overall, the numerical results of this study provide a better understanding of the failure mode and damage process of composite lining water conveyance tunnels under reverse fault conditions; therefore, this study can serve as a reference for composite lining structure disaster assessments.

A new type of composite lining structure consisting of segments, steel pipes, and concrete lining can be adopted in the water conveyance tunnel to bear large internal water pressure. However, there is still no effective analysis model and calculation method for the parameter influence effect of this new composite lining. In this paper, the load structure method and the elasticity theory are adopted, the stress analysis model and theoretical calculation method of a new type of composite lining of water conveyance tunnel are given, and the influence law of lining structure parameters is studied. Each part of the shield assembled lining is regarded as a stressed spring, and a formula for calculating the equivalent elastic modulus of the overall structure at the joint of the lining under partial tension and partial compression is given. The stress and deformation of each layer of lining are deduced based on the theory of thick-walled cylinders. According to the actual project, the rationality of the calculation method is verified by comparing the results of finite element analysis, and the influence of the thickness of intermediate concrete lining and inner lining parameters on the distribution of force transmission among lining layers is further analyzed. The results show that the radial displacement and circumferential stress of each layer of lining structure decrease with increasing the thickness of the concrete lining. The larger the elastic modulus of the inner lining material is, the smaller the radial displacement of each lining structure will be, but the circumferential stress of the inner lining will increase. In addition, when the thickness of the steel pipe lining is reduced or the internal water pressure is increased, the circumferential stress and radial displacement generated by the inner lining will increase. This analysis model and method considering the deformation coordination relationship solves the problem of setting the parameters of the lining structure and has obvious advantages in the calculation of the stress and deformation of the new composite lining water conveyance tunnel structure, which can provide a theoretical basis for related engineering design.

Deep‐buried soft soil water conveyance tunnels traversing multiple geological layers are susceptible to structural damage under dynamic internal water pressure. The cross‐layer stratum is particularly sensitive to adverse conditions, such as dynamic internal water pressure and high external water loads. Using the pressurized water conveyance tunnel from the Central Yunnan Water Diversion Project as a case study, numerical analysis of tunnel lining segments under dynamic internal water pressure was conducted using the finite element method (FEM). The mechanical behavior and stress distribution of the lining segments under different water conveyance schemes—including empty, semi‐filled, and filled cases—were systematically analyzed in terms of lining stress, deformation, longitudinal and circumferential displacements, and bolt stress. The results indicate that the lining segments experience the maximum external water pressure under an empty case, with the transverse and longitudinal stresses of the lining bolt identified as a critical weak position. As water transitions from an empty to a semifilled status, horizontal expansion deformation of the lining decreases, stress distribution becomes more uniform, and stress concentrations are observed in the vault region. Further transitioning to a filled status leads to a gradual balance between internal and external pressures, resulting in convergent structural deformation. Moreover, the largest lining deformations occur in cross‐layer stratum where the tunnel passes through soft‐hard soil layers. Additionally, the assembly angle of the lining segments significantly influences the structural stress. As a result, both geological conditions and segment assembly angles should be considered during tunnel design to optimize performance.

When constructing water conveyance shield tunnels under high internal pressure, composite linings are preferred over single-layer segmental linings due to the superior water tightness and load-bearing capacity. A triple-layer composite lining, consisting of an outer segmental lining, internal steel tube, and self-compacting concrete (SCC) filling, has recently been applied in a large-scale water conveyance tunnel project in China. However, its structural behavior under external overburden and internal water pressures remains poorly understood. This study investigates the mechanical behavior of the triple-layer composite lining through full-scale loading tests using a novel platform that simulates external and internal pressures. Results show that the composite lining remains highly elastic under combined loads with an internal pressure of 0.4 MPa. When the internal pressure increases to 0.6 MPa, cracks first appear in the SCC layer near segment joints, propagating uniformly and leading to stress redistribution. Studs on the steel tube-SCC interface strengthen bonding, reducing debonding at this interface while slightly increasing debonding at the SCC-segment interface. Despite localized SCC damage, the lining maintains excellent serviceability under cyclic pressure fluctuations. This study offers valuable insights for the design and construction of water conveyance shield tunnels with triple-layer composite linings, particularly in high-pressure environments.