Double-arch Tunnel Research Articles

Modeling test study on influence mechanism of large-span double-arch tunnels in proximity to existing tracks

This paper aims to study the influence mechanism of the large-span double-arch tunnels in proximity to existing tracks using 1 g model test. A novel non-contact device able to measure settlements automatically is developed to improve the test accuracy. During the test, the strata settlement, surrounding rock stress and track deformation induced by tunnel excavation are measured simultaneously. The results show that: (1) The excavation of the double-arch tunnel induces an asymmetric “W”-shaped horizontal surface settlement. The horizontal surface settlement near the centerline of the first excavation side is the largest. (2) The U-shaped groove structure exhibits an “M”-shaped deformation, while its structure produces bulges near the maximum horizontal surface settlement. (3) After excavation, the longitudinal surface settlement gradually decreases along the excavation direction, which causes the tilting or bottom voids of the U-shaped groove structure. The U-shaped groove structure may experience torsional shear damage under the load imposed by the train.

Influence of Thickness of the Partition Wall on the Bearing Capacity of Double-Arch Tunnel Under Different Buried Depth

Influence of Thickness of the Partition Wall on the Bearing Capacity of Double-Arch Tunnel Under Different Buried Depth

Performance of double-arch tunnels under internal BLEVE

Double-arch tunnels, as one of the popular forms of tunnels, might be exposed to boiling liquid expanding vapour explosions (BLEVEs) associated with transported liquified petroleum gas (LPG), which could cause damage to the tunnel and even catastrophic collapse of the tunnel in extreme cases. However, very limited study has investigated the performance of double-arch tunnels when exposed to internal BLEVEs and in most analyses of tunnel responses to accidental explosions. The TNT-equivalence method was used to approximate the explosion load, which may lead to inaccurate tunnel response predictions. This study numerically investigates the response of typical double-arch tunnels to an internal BLEVE resulting from the instantaneous rupture of a 20 m3 LPG tank. Effects of various factors, including in-situ stresses, BLEVE locations, and lining configurations on tunnel responses are examined. The results show that the double-arch tunnels at their early-operation ages are more vulnerable to severe damage when exposed to the BLEVE due to the low action of in-situ stress of rock mass on the response of early-age tunnels. It is also found that directing the LPG tank to different driving lanes inside tunnels can affect the BLEVE-induced tunnel response more significantly than varying the configurations of tunnel lining. Moreover, installing section-steel arches in the mid-wall can effectively improve the blast resistance of the double-arch tunnels against the internal BLEVE. In addition, the prediction models based on multi-variate nonlinear regressions and machine learning methods are developed to predict the BLEVE-induced damage levels of the double-arch tunnels without and with section-steel arches.

Optimization of blasting construction and vibration control technology of multi arch tunnels without central partition walls

The construction technology for multi arch tunnels without central partition walls is a new design method for multi arch tunnels. The construction technology of multi arch tunnels without central guide tunnels eliminates side and central guide tunnels, which not only accelerates construction progress but also ensures construction quality and safety. The excavation and support of the rear tunnel of a double-arch tunnel without a central partition are crucial to ensuring the overall stability of the tunnel structure. A combination of manual mechanical excavation and blasting excavation in some areas was used in the excavation and construction of the rear tunnel of the Chenjiachong Tunnel on the Chuyao Expressway in Yunnan in addition to damping materials and measures in the lining of the front tunnel, ensuring the safe excavation of the rear tunnel and the prevention of the lining of the front tunnel from cracking because of earthquakes, The on-site vibration monitoring results of the tunnel indicate that this technology has achieved good results. Overall, the optimized construction technology without a central partition greatly shortens the construction period and improves economic benefits. The construction method is simple and feasible and can be flexibly selected according to the surrounding rock conditions. This study can provide a reference for the construction of other highway tunnels in mountainous areas.

Damage and reliability analysis of double-arch tunnel without a middle pilot tunnel under blast load

In this study, a new type of multi-arch tunnel construction method is proposed. This effort is undertaken due to the many disadvantages of the traditional multi-arch tunnel construction method. Furthermore, this method omits the construction of a middle pilot tunnel, and it has the advantages of safety, high efficiency, and being economical. When using the method of continuous arch tunneling without a middle pilot tunnel, the blasting of the first tunnel and the following tunnel has a greater impact on the surrounding rock damage, as well as on the supporting structure of the same cross-section. Therefore, this study uses LS-DYNA finite element software to construct a three-dimensional numerical model. In addition, the perimeter rock damage law and mechanical response characteristics of the supporting structure in the same cross-section of the first tunnel, as well as the following tunnel after blasting without a middle pilot tunnel, are analyzed. At the same time, the results of the study are based on optimizing the blasting program, and these are then applied to the field. Through the results, it is found that, after blasting a continuous arch tunnel without a medial pilot tunnel, the surrounding rock damage in the arch cross-region of the double-arch tunnel (where the arch top and the arch shoulder are more significant) and the effective stress of the supporting structure exceed the strength design value. In addition, the maximum adequate pressure is distributed in the medial diaphragm wall. With the optimized blasting scheme, the range of the peripheral rock damage is reduced by a maximum of 67%, and the effective stress in the supporting structure is reduced by 25.9–64.8%. The research results are of great significance in terms of improving construction safety, economic efficiency, and project quality, as well as in promoting the research and development of new work methods for double-arch tunnels.

Exploration of Advanced Geological Prediction for the Double-arch Highway Tunnel in Karst Area

Combined with the construction method of a highway double-arch tunnel in the karst area, a comprehensive advanced geological prediction method combining geological radar and advanced horizontal drilling is proposed, and the comprehensive advanced geological pre- diction method is successfully applied to the construction of a highway double-arch tunnel in a karst area of Guangxi. The result of site con- struction proves that the method has a satisfactory forecasting effect.

Prediction of bearing capacity of cracked asymmetrical double-arch tunnels using the artificial neural networks

Cracking in lining structures has the potential to seriously weaken the lining's carrying capacity. In this paper, the failure performance of cracked lining was firstly obtained by model tests and numerical simulations. An artificial neural network model was subsequently developed using extensive simulation data derived from the verified numerical model, to forecast the capacity loss in cracked double-arch tunnels. The results showed that: (1) The cracks caused the linings to undergo localized crushing failure, which greatly reduced the double-arch tunnels' load-bearing capacity. The cracked linings entered a stable working stage with cracks initially and then progressed directly to the destabilization stage, displaying hidden and sudden characteristics; (2) The neural network model, developed using a large number of numerical simulations, demonstrated outstanding predictive performance and accurately forecasted the load-bearing capacity of double-arch tunnels; (3) The depth of the cracks was the principal factor influencing the load carrying capacity decrease in double-arch tunnels, particularly in the vicinity of the void; (4) The structural capacity diminished swiftly when crack depth surpasses 30% of the lining's thickness, and larger voids and cracks closer to the voids amplified the lining-bearing capacity loss for equivalent crack depths.

Research on the dismantling of double-arch tunnel after long-term service—the case study of Huangmeishan Tunnel demolition project

Mountain tunnel structures are subject to a variety of diseases with increasing service life. Earlier tunnels may need to be demolished and expanded because of the poor serving capacity. But few studies of tunnel demolition projects are available. Based on the demolition project of Huangmeishan Tunnel, this paper discusses the demolition scheme of the double-arch tunnel, calculates the stability of the slope, and investigates the defects and material performance in the tunnel. The water leakage in the tunnel mainly occurred at the mid-partition wall and the drainage pipe was clogged severely. The largest width of the crack detected is 15 mm. Material performance tests indicated that the concrete material strength exceeded the design values. In the loading test, the largest displacements of the tunnel arch and haunch were 1.73 and 1.32 mm, which verified the safety of heavy vehicles in construction. Finally, suggestions are given to avoid similar phenomena in other tunnels during the design, construction, and operation phase. The novelty of this study lies in its comprehensive analysis of a tunnel demolition project. The findings of this study contribute to enhancing the knowledge and understanding of tunnel demolition and support the safe and efficient execution of future demolition projects.

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

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

Research on Construction Sequences and Construction Methods of the Small Clear-Distance, Double-Arch Tunnel under an Asymmetrical Load

A small clear-distance, double-arch tunnel under an asymmetrical load combines the characteristics of small clear-distance, tunnels and double-arch tunnels, and the influence of an asymmetrical terrain must be considered. Its construction stability is a problem worth studying. This paper used the Wengcun tunnel as the engineering background. Midas/GTS finite element analysis software was used to study the effects of eight excavation sequences and two excavation methods on tunnel stability. The results showed that the deformation and force of the tunnel were asymmetric under the asymmetrical terrain. Both middle partition walls were deformed towards the shallowly buried side, and the shallowly buried side was deformed to a greater extent. Excavating shallow side tunnels first can effectively mitigate the impact of asymmetric terrain. The arch settlement of the Center Diaphragm Excavation Method is 1.33 cm, which is smaller than the three-step excavation method of 1.48 cm; however, this difference is not significant. The Three-bench Excavation Method was more efficient. Based on the conclusion of a numerical simulation, the construction site adopted the construction sequence of excavating the shallowly buried side tunnel first and adjusted the excavation method to the Three-bench Excavation Method.

Shaking table test on the seismic response and reinforcement measures of double-arch tunnels in mountainous areas

Double-arch tunnels are commonly used in mountainous areas but are more vulnerable to earthquake damage than single-hole tunnels due to their large span and weak joints between the main tunnel and the centre wall. This study aims to understand the seismic response and damage characteristics of double-arch tunnels and provide design advice. A large-scale shaking table test was conducted in a high-intensity seismic zone, using strip reinforcement as seismic measures. Results show that peak accelerations of the inverted arch of tunnels increase as peak accelerations of seismic waves increase. Peak accelerations of the centre wall increase until peak loading accelerations achieve at 0.4 g. Large peak internal forces are mainly concentrated at the bottom of tunnels and near the centre wall. For the centre wall, bending moments are significantly influenced by structural abruptness at the junctions between the centre wall and the main tunnel, whereas axial forces are more evenly distributed in the centre wall. Seismic waves with high energy at low frequencies excite peak responses of strains and bending moments for the centre wall, especially at the wall top. Parts of the main tunnel connecting to the centre wall are in an adverse stress state, with the bottom and vault of tunnels being susceptible to cracking. Penetration cracks are likely to occur in the inverted arch and vault of tunnels as peak accelerations of seismic waves gradually increase. However, after penetration cracks appear in each of these two parts, further cracking is more likely to occur in the inverted arch, especially during strong seismic shaking. The overall forces in double-arch tunnels with strip reinforcement are significantly reduced, but there is little reduction in force for the bottom and outside of the lining.

Mechanical Characteristics of an Open-Buried Double-Arch Tunnel during Construction

The open excavation and concealed construction method is widely adopted for the construction of bias double-arch tunnels. However, the mechanical behavior of the tunnel during the whole construction period by using the open excavation and concealed construction method is not well understood, and the basis for construction organization and optimization is lacking. Based on an open-buried double-arch tunnel on Xiajuan Road, Changsha City, China, on-site monitoring was carried out in terms of the deformation of the steel arch in the primary lining, the stress of reinforcement in the secondary lining, and the deformation of the surrounding rock during the construction process. The correlation between the vault settlement rate and the steel arch strain was analyzed. The results show that the maximum vault settlement and settling rate of the left and right caverns occur at different locations due to different supporting conditions. The peripheral displacement experiences a process of convergence inward and extension outward. The compressive steel stress in the secondary lining of the right cavern is greater than that in the left cavern, except for the points at the arch waist. The backfill above the left cavern reduces the loading on the lining of the right cavern, but it increases the loading on the left cavern. The bias effect of the open-buried double-arch tunnel is well controlled and balanced when the open excavation and concealed construction method is adopted.

Time-Varying Response Analysis of Surrounding Rock Construction Mechanics of a Double-Arch Tunnel without a Middle Pilot Tunnel and Suggestions for Tunnel Construction

Abstract This research carries out the model test and numerical simulation, studying the time-varying response regularity of surrounding rock construction mechanics. The purpose was to ensure the construction safety of a double-arch tunnel without a middle pilot tunnel and to prevent rockburst or large deformations of surrounding rock in a stress concentration areas. To resist shear deformation of the steel arch of the first tunnel, during construction of the secondary lining of the lower step of the following tunnel near the side of the first tunnel, shear reinforcement is added to form a shear wall. To resist the stress of upward uplift in the inverted arch area, the spacing of steel reinforcements in the inverted arch is encrypted to reduce disturbance to the supporting structure. To reduce disturbance to the first tunnel caused by the blasting construction of the following tunnel, this article carried out the SHPB test on field rock samples and suggests that the reserve 2 m width of the surrounding rock (the lower heading of the following tunnel near the side of the first tunnel) is mechanically broken.

Calculation of Pressure on the Shallow-buried Double-arch Tunnel Without Middle Drift

Compared with the traditional double-arch tunnel, the double-arch tunnel without middle drift has the obvious advantage of improving the construction progress. However, the surrounding rock pressure calculation method and evolution law for it is unclear. Based on a limit equilibrium analysis, a method to calculate the surrounding rock pressure is proposed with considering the sequential excavation of the two tunnels. A numerical analysis is conducted to verify the rationality of this method. The dynamic evolution and spatial distribution characteristics of surrounding rock pressure are pointed out, i.e., the vertical pressure acting on the first tunnel increases with the second tunnel being excavated, and the vertical pressure acting on the first tunnel is greater than that of the second tunnel. The excavation impact coefficient ζ and the bias coefficient η are defined to quantitatively analyze the pressure characteristics. Two key factors influencing the coefficients including the depth of the tunnel and the surrounding rock characteristic have been analyzed. The results demonstrate that both the ζ and η increase with increasing the depth of tunnel. Besides, the two coefficients increase when the friction angle increases between 30° and 40°, but decreases after exceeding 40°. The analytical results are consistent with the numerical calculation results, which can provide a reference for similar engineering projects.

Study on Dynamic Response Characteristics of Shallow-Buried and Unsymmetrical-Loaded Double-Arch Tunnel

Study on Dynamic Response Characteristics of Shallow-Buried and Unsymmetrical-Loaded Double-Arch Tunnel

Analysis of Mechanical Performance of Double-Arch Biological Channel in the Operation Period considering the Effect of Fluid-Solid Coupling

In order to solve the problem that highway development needs to cross environmentally protected areas, which results in the cutting off of wildlife habitats and fragmentation of the biosphere, on-road biological passages are established in many places. This paper carries out a numerical analysis of the biased load, caused by the backfill of the biological channel, the environment, and the seepage problem of the backfill under rainfall conditions. By comparing the pore water pressure’s test data in backfill with the modeling result data, the influence law of biased pressure load on open hole lining during running period, and the law of water pressure change are derived. The analysis shows that: (1) the backfill soil has a restraining effect on the double-arch tunnel, and the side arch ring’s deformation of the backfill decreases with the increase of the height of the backfill; when backfilling on both sides is flush with the top of the cave and continuing to backfill at the cave’s top, the arch ring near the higher mountain deforms greater because of the mountain’s pressure. (2) The internal force of the channel and the temperature are closely relevant, and the value is gradually stable without the influence of construction or other causes. (3) Pore water pressure variation correlates with seasons: the water pressure is lower in winter and higher in summer. After the pore water is saturated, the monitoring data does not change with the increase of rainfall.

Numerical Simulation on the Response of Adjacent Underground Pipelines to Super Shallow Buried Large Span Double-Arch Tunnel Excavation

The excavation of a shallow buried tunnel may cause stress redistribution in surrounding rock, and cause deformation, damage, and even destruction of adjacent underground pipelines. The land part of the Haicang undersea tunnel in Xiamen of China was a super shallow buried large span double-arch tunnel. Its construction was restricted by both underground excavation safe and adjacent pipeline protection. Multiple groups of working conditions were designed considering the relative position of pipe and tunnel, pipeline and tunnel construction parameters. Numerical simulation was used to study the influence of pipeline horizontal distance, buried depth, pipeline diameter, pipeline wall thickness, pipeline shape, pipeline material and excavation method on the response of adjacent underground pipelines. The results show that the relative position of pipe and tunnel, and the construction method of the double-arch tunnel have a great influence on pipeline deformation. Pipeline material, pipeline diameter and excavation method have a great influence on pipeline stress. The construction method was the key factor affecting the stress and deformation of the pipeline. The three-step reserved core soil method can effectively control the stress and deformation of underground pipelines. The research results can provide a reference for similar projects.

Numerical Simulation of Ultra-Shallow Buried Large-Span Double-Arch Tunnel Excavated under an Expressway

The temporal and spatial effects of a complicated excavation process are vital for an ultra-shallow buried large-span double-arch tunnel excavated under an expressway in service. Numerical simulations are urgent and necessary to understand the effect of the total construction process. Taking Xiamen Haicang tunnel as a research object, the total excavation process of three pilot tunnels and the three-bench reserved core soil method of an ultra-shallow buried large-span double-arch tunnel with a fault fracture zone under an expressway was simulated using software FLAC3D. The deformation of the surface, surrounding rock, underground pipelines, tunnel support structure and partition wall of the three pilot tunnels and the main tunnel was analyzed, and the dangerous areas and time nodes were obtained. When the tunnel was excavated to the fault fracture zone, the deformation of the surface and surrounding rock increased significantly. The rock and soil within 20 m behind the excavation surface of the pilot tunnel were greatly disturbed by the excavation. During the excavation of the main tunnel, the horizontal displacement of the middle partition wall moved slightly towards the main tunnel excavated first. The research results can provide a reference for the construction design of double-arch tunnels.

Dynamic Risk Assessment of Ultra-Shallow-Buried and Large-Span Double-Arch Tunnel Construction

Ultra-shallow-buried and large-span double-arch tunnels face complex risks during construction. The risk sources are hidden, complicated, and diverse. The dynamic risk assessment problem cannot be solved satisfactorily by using the static method as an insufficient amount of research has been conducted. The land part of the Xiamen Haicang double-arch tunnel was selected as the background for the dynamic risk assessment of ultra-shallow-buried and large-span double-arch tunnel construction. The construction process was divided into five stages: pre-construction preparation; ground and surrounding rock reinforcement; pilot tunnel excavation; and the single-and the double-tunnel excavations of the main tunnel. Through consultation with tunnel experts, six first-level and thirty second-level risk evaluation indexes were proposed. The benchmark weight of the dynamic risk assessment index was determined by using the analytic hierarchy process. The weight of the risk evaluation index was revised according to the monitoring data and the construction stage. The fuzzy evaluation matrix of the construction risk membership degree was obtained by using the fuzzy comprehensive assessment method, and the calculation results were analyzed using the subsection assignment method. Control measures were suggested according to the risk assessment results. The risk assessment result of the double tunnel excavation stage of the main tunnel was level II, and the risk level was the highest among the five construction stages. The risk assessment result of the ground and surrounding rock reinforcement stage was level IV, and the risk level was the lowest. The dynamic construction safety risk assessment based on the fuzzy comprehensive assessment method is more timely, accurate, and reasonable than the traditional assessment method. The method can be adopted in similar engineering projects.

Experiment and Numerical Simulation on Grouting Reinforcement Parameters of Ultra-Shallow Buried Double-Arch Tunnel

For an ultra-shallow buried double-arch tunnel with a large cross-section, the arching effect is difficult to form in surrounding rock, and grouting method is often adopted to reinforce the surrounding rock. Hence, examining the grouting reinforcement parameters is of great significance for potential failure and collapse prevention. The land part of Haicang undersea tunnel was selected as a case study; laboratory experiments, theoretical analysis, and numerical simulation were performed to determine the grouting solid strength and grouting reinforcement parameters. The effects of different water–cement ratios on slurry fluidity, setting time, bleeding rate, and sample strength were studied by laboratory experiments. A method was proposed to determine the shear strength parameters of grouted surrounding rock through the grout water–cement ratio and the unconfined compressive strength of the rock mass. Numerical simulations were performed for grouting reinforcement layer thickness and the water–cement ratios. The deformation and stability law of tunnel surrounding rock and its influence on surrounding underground pipelines were obtained considering the spatial effect of tunnel excavation and grouting reinforcement. The reasonable selection range of grouting reinforcement parameters was proposed. The initial setting time and bleeding rate of cement slurry increased with the increasing water–cement ratio, while the viscosity of cement slurry and sample strength decreased with the increasing water–cement ratio. The shear strength parameters of grouted surrounding rock were determined by the water–cement ratio of grout and unconfined compressive strength of rock mass before grouting. When the thickness of grouting reinforcement layer h = 1.5 m and the water–cement ratio of grout was suggested η = 0.85, the surface settlement, the deformation of the vault, and the deformation of the nearby pipeline all met the design. Moreover, the construction requirements were more economical. Research results can provide a reference for the selection of grouting reinforcement parameters for similar projects.