Twin Tunnels Research Articles

A case study of newly tunnels over-crossing the existing subway tunnels

Due to the continuous expansion of congested urban areas, many new tunnels are inevitable to over-cross the existing subway lines and may even affect the operation of existing lines. It is vital to investigate the response of existing tunnel caused by over-crossing tunneling. In this study, a case history of closely spaced twin tunnels excavated above the existing tunnels in soft soil stratum was presented. The deformation of the existing tunnels induced by the excavation of the new tunnels was automatically monitored. In-situ monitoring results showed that the vertical displacement of the existing tunnels was mainly uplift and its development showed obvious phase characteristics. The increase rate of the vertical displacement in Phase I and II induced by the second over-crossing was smaller than that of the first over-crossing. A superposition method was employed to describe the uplift section characteristics of the existing tunnels. The influence ranges of tunnel excavation on the left and right lines of the existing tunnels were approximately 5.5D and 4.5D, respectively. The torsional deformation of the rail bed and the convergence of the existing tunnels are explored, and the reasons for the changes of the over-crossing sections are analyzed at the same time.

Experimental study on the mechanical behavior and deformation characteristics of lining structure of super-large section tunnels with a small clearance

The knowledge of the mechanical behavior and deformation characteristics of lining structure of super-large section tunnels with a small clearance can help to optimize the tunnel lining design and reduce the construction costs. Based on Xinwu twin tunnels with eight lanes in China, a reduced-scale model experiment was carried out to investigate the deformation characteristics, the crack behaviors, the ultimate bearing load and internal force of the super-large section tunnels under different clearances. The results show that the positions in order (from largest to smallest deformation) are as follows: crown, right spandrel, left spandrel, invert, springs. 12 m (about half the width of tunnel) can be considered as the smallest reasonable spacing for large section tunnels in grade IV surrounding rock. With the increase of loading level, the cracks mainly appeared at the invert and the springs of the two tunnels. After the secondary lining was damaged, the deformation of each measuring point did not decrease but gradually increased with the clearance. These findings can provide significant reference data for the design optimization and safety assessment of super-large section tunnels with a small clearance.

Experimental and numerical analysis of deformation behaviour of tunnels under static loading conditions

The constant growth of cities has led to a shortage of land in metro areas as a result; numerous transportation issues must be addressed. The design of underground structures has proved to be very successful in overcoming these issues, as they have solved numerous traffic problems in major cities. However, due to their heterogeneous behaviour, these underground structures are extremely vulnerable to damage or failure. As a result, it is very important to keep underground structures secure under various loading conditions. This research aims to determine the deformation behaviour of single and twin tunnels under static loading conditions. The present study is divided into two steps. Firstly, laboratory experiments are carried out on small-scale physical simulated tunnels models. Secondly, numerical simulation of physical simulated tunnel models was carried out to determine the deformation that occurs at various points in the tunnel model. Then the results obtained from the experimental and numerical study are compared and validated. From the results, it is observed that experimental testing results are in good agreement with numerical modelling results. It is also observed that if the parameters are well selected for numerical analysis, it can be an easy and less time-consuming method for finding out strength and deformation behaviour for analysis and design of the tunnel. Therefore it can be concluded that the testing methodology which is proposed in this study can be used for the safe and economical design of both single and twin tunnels that are subjected to static loading conditions.

Effect of Geometric Parameters and Construction Sequence on Ground Settlement of Offset Arrangement Twin Tunnels

A parametric study that examines the ground surface settlement due to the excavation of shallow offset arrangement twin tunnels is presented. Offset arrangement tunnels are those that run parallel to each other, but at different elevations. The study focuses on the influence of both the construction sequence and various geometric parameters on the induced soil settlement. A series of three-dimensional finite element analyses was carried out to investigate the settlement behavior and interactions between offset arrangement twin tunnels excavated in clay using a simplified mechanized excavation method. Analyses were carried out for three cover-to-diameter (C/D) ratios, three possible construction sequences, five angular relative positions, and five angular spacings. In addition, settlement data were also investigated by varying horizontal and vertical spacings while keeping the angular spacing constant. The total settlement of the excavated twin tunnels and the settlement induced solely by the new second tunnel are both presented, and special attention was paid to identifying the dominant geometric parameters. The observed data trends from this study are generally consistent with the limited data available in the literature. This study confirmed a few perceived behaviors. First, angular relative position better describes the settlement behavior in comparison to angular spacing. Second, the effect of the vertical distance is noticeably more significant than that of the horizontal distance between the two tunnels. Third, excavation of the lower tunnel at first induces higher total ground settlement than when the upper tunnel is excavated first or when both tunnels are excavated concurrently. Fourth, settlement due to the construction of the newer tunnel decreases with the increase in the cover depth. In addition, two design charts have been proposed to calculate the settlement induced from a new second tunnel excavation and the eccentricity of the maximum total settlement relative to the center of the new tunnel.

A Simplified Method for Predicting Tunneling-Induced Ground Movement considering Nonuniform Deformation Boundary

Stochastic medium (SM) theory is a practical method in ground settlement prediction, while its nonintegrable double integral form makes the solution process complicated. A simplified analytical solution based on the SM theory is developed to predict the ground movement in tunneling excavation. With the simplified solution, the ground movement for single tunnel and twin tunnels could be predicted based on the gap parameter G and influence angle β. A feasible approach is developed to estimate these two parameters using the maximum ground settlement Smax and tunnel design parameters, including tunnel depth H and diameter R. The proposed approach can be used to predict the ground movement curve for both circular and noncircular cross section tunnels. To validate its accuracy, the results predicted by the simplified procedure are compared with those obtained by the SM theory and measured in situ. The comparisons show that the current results agree well with those obtained by the SM theory and measured in situ. The comparison of five tunnels in literature illustrates that the simplified method can provide a more reasonable prediction for the ground movement induced by tunneling.

Stability Analysis of Tunnel by External Force Increment Method

A new tunnel stability analysis method is proposed which is the external force increment method (EFIM) to transform the traditional tunnel stability ratio (<I>N</I>). The EFIM can be defined as the field stability raito (<I>N</I>_f), which consists of two newly defined parameters, namely the natural stability ratio (<I>N</I>_n) and the critical stability ratio (<I>N</I>_c). The relationship between the field stability ratio (<I>N</I>_f) and the change of external force is given. The tunnel stability plane and tunnel stability analysis plot are constructed. Based on this, the relationship between the field stability ratio (<I>N</I>_f) and the critical stability ratio (<I>N</I>_c) when the initial tunnel is stable or unstable is determined. According to the field stability rate (<I>N</I>_f), the critical stable state can be achieved with the tunnel by increasing two ways: one is to increase the external load to act on the external force on the tunnel, and the other is to reduce the internal support force of the tunnel. The relations for reaching the critical stability ratio (<I>N</I>_c) of the two EFIM are given respectively. The upper bound solutions of single tunnel, twin tunnels with the same diameter and twin tunnels with different diameters are analyzed by this method. The results show that the EFIM is reasonable and feasible for stability analysis of tunnel.

Effects of Large-Scale Twin Tunnel Excavation on an Existing Pile Group: Three-Dimensional Centrifuge Modeling

Effects of Large-Scale Twin Tunnel Excavation on an Existing Pile Group: Three-Dimensional Centrifuge Modeling

Seismic Response of Undrained Twin Tunnels

Seismic Response of Undrained Twin Tunnels

Comparison of different damping materials during train vibration at twin tunnels by similarity experiment and DEM

To reduce the disturbance of train vibration to adjacent tunnels during the operation of near-distance twin tunnels, three reduction methods are proposed. In this paper, the vibration mitigation effects of steel plate (SP), concrete zone (CZ), and double liner (DL) on their tunnels and adjacent tunnels during train vibration are compared by scale model and discrete element method (DEM). The distance between twin tunnels is 0.25 D, where D (6.2 m) is the diameter of the tunnel. The results show that CZ can produce a good vibration isolation effect on the first tunnel (T1) and second tunnel (T2). At the same time, SP has a good vibration isolation effect on the liner and surroundings of T2 but has the potential to increase the dynamic characteristics of T1 surroundings. The vibration mitigation effect of the DL on T1 and T2 is the same, and the ratio of weakening effect is about 30%–50%. In summary, the most recommended vibration isolation method in practical engineering is CZ. This study provides a reference for studying the vibration mitigation effect on adjacent tunnels during operation.

Investigation of Twin Tunnel Deformation with Umbrella Grouting Protection &amp; NATM Tunneling using 3D Finite Element: Case Study Cisumdawu Tunnel

Cisumdawu Tunnel is a twin tunnel 472 m long located in Sumedang. Twin tunnel construction can cause additional ground settlement and tunnel deformation. The tunnel construction method used is the New Austrian Tunneling Method (NATM) and umbrella grouting protection system. The principle of NATM is to maximize surrounding soil capacity to support its weight and balance the stresses around the tunnel. Investigation of tunnel deformation is important to know tunnel structure behavior and avoid possible failure. This research aims to know tunnel deformation and the effect of twin tunnel construction on the deformation and ground settlement. The data used such as tunnel geometry, monitoring data, pressuremeter test, and the drilling test. The 3D analysis will be performed for a single tunnel and twin tunnel using Midas GTS-NX, and monitoring data will be used for verification analysis. The 3D FEM help to model the soil condition and construction stage according to the actual condition. The analysis results show the maximum tunnel deformation that occurs from the beginning of the tunnel construction is 12.64cm. If the deformation starts to be calculated following the monitoring reading time, after the excavation at the monitoring point, the maximum deformation of the analysis results is 3.3&amp;4.4cm, where the monitoring shows maximum deformation of 3.3&amp;4.3cm. Through the results, it can be said that the analysis using 3D FEM with pressuremeter test parameter represents actual conditions. Twin tunnel construction side-by-side increases ground settlement and lateral tunnel deformation significantly. Hence, it shows that tunnel analysis using 3D FEM recommends for future investigation of tunnel deformation.

Probabilistic analysis for twin tunneling-induced longitudinal responses of existing shield tunnel

This paper performs a probabilistic-based analysis for evaluating the longitudinal responses of the existing shield tunnel to the twin tunneling underneath. A deterministic model based on the two-stage analysis method is proposed for calculating the twin tunneling-induced deformations of existing tunnels. An efficient metamodel is built using sparse polynomial chaos expansions to surrogate the deterministic model and carry out the sensitivity analysis. Afterward, the metamodel and Monte Carlo simulation method are combined to assess the failure probabilities of the tunnel deformations exceeding allowable thresholds under given volume losses. The analysis results show that uncertainties of the random parameters lead to a significant effect on the tunnel responses and failure probabilities, indicating the necessity of probabilistic analysis on this problem. The uncertainties in the greenfield soil settlement dominate the assessment of the tunnel settlement, and the parameters associated with the soil-tunnel interaction influence the curvature radius and joint deformations more remarkably. An approximately linear increase in the allowable volume loss can be seen with increasing horizontal distance between twin tunnels. The reduction in the skew angle strengthens the influence of the failure mode of the tunnel settlement on the probabilistic evaluation of the system.

Physical Investigation of Deformation Behaviour of Single and Twin Tunnel under Static Loading Condition

This paper presents a new testing method for the problems encountered in field testing. To this end, single-tunnel and twin-tunnel small-scale rock models are prepared in the laboratory. A new methodology is proposed to encounter problems that are faced during field testing. The test results show that rock strength characteristics, overburden pressure, and tunnel spacing have important effects on the stability of underground structures. For rocks with poor strength properties, the damage degree is greater. When the strength property of rock changes, the deformation value of unlined tunnels changes from 21.05% to 27.58%, while that of lined tunnels changes from 11% to 21.42%. Also, in the twin tunnel, the deformation value reduces from 20% to 15.78% when the spacing between the tunnels is increased. For the measurement of stress and deformation in tunnels, the results obtained from experiments are analyzed. The method adopted in this study helps determine the tunnel’s design parameters to make it safe under overlying static loads. Finally, the key factors affecting the stability of underground structures are determined by simulating the field conditions through experimental research.

Role of Shear Deformability on the Response of Tunnels and Pipelines to Single and Twin Tunneling

Tunneling can compromise the safety and serviceability of existing buried infrastructure because of settlements, crack openings, dislocations, and material strains. A continuum-based soil-structure interaction model, implementing an equivalent Timoshenko beam, is used to evaluate the excavation-induced settlements and longitudinal deformations of existing tunnels and pipelines. Both single and twin tunneling scenarios are examined. The shear flexibility of shield and sprayed concrete lining tunnels may be significant. This increases tunneling-induced settlements while it decreases tilt, curvature, and the associated bending moment, with implications for optimal monitoring installations. In this work, a new dimensionless shear factor is introduced, governing the relative importance of shear and bending deformations and accounting for the settlement trough width. This can be used to evaluate if a pure-bending, shear-dominated, or mixed deformation mode should be expected. Design charts to assess existing infrastructure affected by either single or twin tunnels are proposed.

Interaction and control measures of shallow-buried shield twin tunnels with small clear-distance

Interaction and control measures of shallow-buried shield twin tunnels with small clear-distance

Twin tunneling–induced deep-seated landslide in layered sedimentary rocks

Twin tunneling–induced deep-seated landslide in layered sedimentary rocks

An Analytical Solution for 2D Dynamic Structure-Soil-Structure Interaction for Twin Flexible Tunnels Embedded in a Homogeneous Half-Space

The interaction between subway tunnels is investigated by using a 2D analytic model of a twin tunnels system embedded in a homogenous half-space. The closed-form analytical solution for tunnel displacement response is derived through the wave function expansion method and the mirror method, and the correctness of the solution is verified through residuals convergence and comparison with the published results. The analysis focuses on the effects of tunnel relative stiffness on tunnel–soil–tunnel interaction. Tunnel relative stiffness has a great influence on tunnel displacement response. For small tunnel relative stiffness, tunnel displacement amplitude can be enlarged by 3.3 times that of single rigid tunnel model. The response of the tunnel–soil–tunnel interaction system depends not only on the distances between tunnels but also on the frequency of the incident wave and the incident angle. The strength of the interaction between the tunnels is highly related to the tunnel spacing distance. The smaller the distance between tunnels, the stronger the interaction between them. When the distance between tunnels reaches s/a = 20, the interaction between tunnels can be ignored. It is worth pointing out that the seismic design of underground tunnels should consider the interaction between tunnels when the tunnel distance is small.

Support Pressure for Undrained Stability of Horseshoe-Shaped Twin Tunnels with Semi-Elliptical Roof in Clay

Support Pressure for Undrained Stability of Horseshoe-Shaped Twin Tunnels with Semi-Elliptical Roof in Clay

Detection and numerical simulation of blasting-induced damage in shallow-buried twin tunnels with small spacing

In order to study the damage effect of blasting load on the surrounding rock of shallow-buried small spacing twin tunnels, the shallow-buried tunneling section of the south extension project of Shunhe Expressway is taken as the engineering background. Firstly, based on the dynamic damage evolution and Hoffman failure criterion, an anisotropic dynamic damage constitutive model for rock materials is established. Then, by using the secondary development function of the LSDYNA software, the constitutive model is applied to the numerical simulation of the tunnel blasting damage. Finally, based on the acoustic wave measurement theory, the wave velocities in the surrounding rock of the shallow-buried small spacing twin tunnels before and after blasting were measured by using non-metallic ultrasonic detectors, and the damage of the surrounding rock is evaluated from changes in wave velocity. The applicability of the anisotropic dynamic damage constitutive model and the accuracy of the numerical results are verified by comparing the numerical simulation results with the field test results. The numerical simulation results show that the maximum damage radius of single-hole blasting is 0.58 m, and the maximum damage depth is 1.88 m. According to the damage threshold of the rock mass, the horizontal failure range of the rock mass can reach 0.14 m, and the failure depth is 1.70m. According to the field test, the damage degree of the middle intercalated rock is higher than that of the other parts of the surrounding rock in the alternate blasting excavation of the double track tunnel. The damage depth of the surrounding rock caused by blasting excavation is about 0.5 m, which is close to the simulation results, and verifying the accuracy of the anisotropic dynamic damage constitutive model. The research results have a certain guiding role on the blasting excavation and damage control of shallow-buried twin tunnels with small spacing..

Study on the control of construction impacts of shield tunnels in close proximity to sensitive buildings

The construction of interchange passages, which are important appurtenances to metro traffic, often has problem of close proximity to existing buildings. This paper takes the shield excavation project of interchange passage at Jinjiadu Station of Hangzhou Metro Line 2 and Line 4 as an example, and aims to study the impact of shield on existing buildings when crossing them in close proximity. The shield excavation area has a minimum clearance of 1.09 m from the bottom of the station, and the twin tunnel cross a total of six lattice piles with a closest distance of 0.176 m. In order to reduce the impact of the shield excavation on the existing buildings, the excavation area was pre-reinforced with permafrost reinforcement protection measures. A 3D finite element model was built to study the deformation of the existing building under the reinforcement measures. By studying the key construction parameters, the results show that in this project a smaller Propulsion pressure and grouting pressure and a larger grouting volume can effectively reduce the impact of construction on the existing building.

Construction of twin tunnel in weak and blocky rock mass by using arch supporting method

Design of tunnel excavation and support system in weathered and blocky rock mass is usually a principal challenge in tunneling. In this study, the excavation method of twin tunnel was newly taken into consideration in the condition of weak rock mass, the section size of tunnel was reasonably determined, and new supporting method was established. Firstly, the mechanical characteristics of the project rock mass were determined in each section of tunnel using in-situ point load test (PLT) and RocLab software. Then, design of twin tunnel excavation from mono-tunnel excavation in the weak parts of rock mass was proposed and section of twin tunnel joint was reasonably determined based on the safety and stability of the twin tunnel joint by FLAC3D. Finally, the sequential excavation method of combining top heading and benching with arch supporting method (ASM) was newly proposed and the validity of this method was determined by the numerical simulation modeling. Introducing ASM for the support system ensured the support strength in the excavation tunnel. Advanced excavation scheme and the support system have been successfully applied to ensure the safety and conveniency of the target tunnel construction, with about twice reduction of construction time and 1.5 times raising of stability factor. As a result, proposed method in this paper can be used to all manual tunnelling and underground structures in weak and blocky rock mass.