Tunnel Intersection Research Articles

Stability Analysis of a Station-TBM Tunnel Intersection Applying Innovative Techniques

Tunnel construction using a tunnel boring machine TBM may encounter a coordination difficulty where the machine may reach the station site before the station completion. A construction solution for such a station-TBM intersection is vital. In the Cairo Metro Tunnel-Line 3, Heliopolis station, infrequent construction sequence was adapted, where the station transverse diaphragm walls were firstly installed to let the tunnel boring machine entering the station vicinity and erecting the tunnel lining within and after the station. Afterward, the longitudinal diaphragm walls of the station were installed parallel to the tunnel line. In view of that, the tunnel parts enclosed by the station were required to be safely demolished, followed by completing the remaining station elements. The process of removing the lining segments within the station involves a risk of instability of the existing tunnel because of excessive deformations. Therefore, innovative four construction techniques were suggested and numerically inspected to find an optimal sequence of executing such a hard construction condition. Numerical models, established by the 2-D finite element software, PLAXIS, were adopted in a staged analysis to simulate the construction phases till the critical phase of removing the tunnel segments, where the tunnel stability was considerably reduced. At that point, stability analysis was performed to examine the liability of the four demolishing scenarios. These scenarios include partial filling the tunnel with sand at the demolishing location, and/or using internal or external link members. Lastly, the optimal technique to remove the lining segments inside the station considering stability, economy and time-saving, was decided.

Centrifugal modeling of continuous shallow tunnels at active normal faults intersection

Both traffic and water conveyance tunnels’ networks are being extended in many earthquake-prone areas as to its faulting sense. Active fault and tunnel intersections lead to an intense coercive displacement of tunnel lining. Here, a series of 1/60 scale centrifuge tests are run on such intersections normal dip-slip fault mechanism. Experimental surface faulting model of 60 degrees is applied on a set of soil and tunnel models through a fault simulator box. The Location and the mechanism of failure together and damage states of the modeled tunnels are assessed, and the fragility curves related to each damage state are plotted. Tunnels are very vulnerable to normal faulting; therefore, a displacement of about 20 to 30 cm could generate the initial cracks in the lining. Any increase in displacement would lead to cracks expansion and enlarging the displacement to 50 cm, causing soil and rockfall into the tunnel, thus blockage. Fault rupture propagation is assessed in soil deposits with and without tunnel. The effects of fault displacement and tunnel collapse on the ground surface, including fault scarp, graben and sinkhole, are observed and assessed. The existence of each one of these surface features can be a potential risk for both surface and buried structures.

Application of Improved Single‐Hole Superposition Theory in Nonequal Cross‐Section Tunnel Intersection

With the excavation towards the intersecting tunnels’ direction, the impact on the surrounding rock stress between the two tunnels will gradually decrease, but how it decreased is not clear. At present, engineers often directly superimpose the stress in the triangular area of the crossing tunnel when calculating the stress in this area (single‐hole superposition theory). The theory is also used as the main theory to consider the surrounding rock stress for support which is difficult to explain the situation of nonuniform cross‐section centers not in the same plane. The safety level of support is mainly determined by construction experience which is unable to determine how to adjust the support level with the increase in the horizontal distance of intersecting tunnel, causing the insufficient utilization of materials. This paper derives theoretically the stress calculation of the triangular area of circular cross tunnels with different cross sections and analyzes the surrounding rock stress law of the intersecting tunnels triangular area from different cross‐section dimensions (the difference in diameter between the two tunnels is twice, 3 times, and 4 times) and different intersection angles. And the results show that, compared with the case of equal tunnel diameters, the stress influence area of the surrounding rock in the triangle area mainly expands to the side of the small section with the increase of the cross‐section difference of the intersecting tunnels; the dangerous area of the surrounding rock in the triangle area moves vertically to the small section; the safest condition is the two tunnels with 90° intersecting angle. The theoretical calculation model of this paper is verified by the previous research results.

Effects of High‐Pretension Support System on Soft Rock Large Deformation of Perpendicularly Crossing Tunnels

The control mechanism of prestressed support system is studied by means of three‐dimensional discrete element numerical simulation, theoretical analysis, and field measurement. The actual project is selected to analyze, and the control effect is demonstrated. The theoretical analysis results show that the prestressed support can improve the self‐bearing capacity of surrounding rock, which is conducive to the stability of the surrounding rock. The numerical calculation shows that, under the control of the long and short cables, the prestress can spread effectively and form two bearing arches. The deformation is difficult to control, which is in the arch crown and the arch shoulder of the tunnel intersection. However, the deformation of the surrounding rock decreases with the increase of prestress. Through the analysis of the measured results, it shows that the pretension support design scheme can effectively control the large deformation of the surrounding rock.

Progressive deformation and mechanical behaviour of intersecting tunnels in soft ground

Stress concentrations and large ground deformations are sources of major concern during the construction of tunnel intersections. Such problems are even more critical in urban areas with buildings affected by the induced progressive ground movements. Therefore, particular considerations have to be taken into account for such projects. This paper deals with the effects of the underground openings on primary tunnels (tunnel intersection) using detailed three-dimensional finite-element models on a case study – Hakim tunnel project, Tehran, Iran. The effects of different stages of construction of intersections on stress distribution and ground deformation are evaluated. Moreover, the effective trailing distance of different faces of the tunnel from the centre of the intersection and the effect of tunnel drilling on internal forces of the shotcrete lining are discussed. The results showed that the values of the surface settlement remain almost unchanged at a distance approximately twice the equivalent diameter of the child tunnel from the intersection centreline. Also, the increase in the circumferential bending moments near the intersection is non-significant compared with the changes in the longitudinal bending moment. It was found that the circumferential and longitudinal bending moments next to the intersection can increase by up to 250 and 350%, respectively.

Research on Intersection Signal Timing Optimization Based on Eliminating Secondary Queuing Time

This paper takes Guanzhou Tunnel Intersection in Guangzhou Higher Education Mega Center as an example, first uses PARAMICS to simulate the traffic condition, then uses Webster method to optimize the intersection, besides, a simplified signal optimization method based on reducing the number of secondary stops is proposed. Finally, intersection evaluation indicators are compared and analyzed.

Shaking table tests on the intersection of cross passage and twin tunnels

The abrupt structural change at the intersection of cross passage and twin tunnels is a potential risk when earthquakes strike. This paper addresses the seismic responses of the cross-passage intersection by shaking table tests. Test data from six cases are presented, where white noise and synthetic earthquake motions are adopted. Discrepant responses between the cross passage and the twin tunnels are described by acceleration data. The extent of discrepancy is quantified statistically. Influence of this discrepancy is evaluated in two directions: dynamic strains of the linings in the transverse direction and circumferential-joint extensions in the longitudinal direction. Since the earthquake-induced dynamic strains are relatively small, they are considered as an insignificant factor. However, there are considerable circumferential-joint extensions near the cross passage. Two simplified models are proposed to estimate the joint extensions in a pseudo-static way. Each model is corresponding to a unique pattern of longitudinal deformation caused by the discrepant responses of the intersection. Test results are compared with analytical results.

Innovative solutions for intersection of TBM tunnel and station in Riyadh Line 5 metro

One of the main problems when constructing a metro line using a tunnel boring machine (TBM) is the coordination of the construction of the tunnel with the excavation of the stations that it will intersect, being possible to reach the stations before their complete excavation. This paper presents a solution to this problem, one which has been implemented in the Riyadh Metro L5. This solution allows the construction of the tunnel and the later excavation of the station, while maintaining the operation of the TBM and the tunnel lining.

Combined Anterior Cruciate Ligament and Posterolateral Corner Reconstruction by Hamstring Tendon Autografts Through a Single Femoral Tunnel by Graft-to-Graft Suspension and Fixation

An untreated posterolateral corner (PLC) injury in patients with a torn anterior cruciate ligament (ACL) may be a leading cause of ACL reconstruction failure. Combined ACL and PLC reconstruction is discussed in few studies in the literature. Femoral tunnel intersection in combined reconstruction has been reported to be high. Short grafts may render combined reconstruction undoable. This Technical Note describes a technique that allows a combined ACL and PLC reconstruction. The ACL graft is a 4-stranded hamstring tendon graft from 1 limb. The PLC graft is a doubled semitendinosus tendon graft from the contralateral side. One femoral tunnel is used connecting the femoral attachment of the PLC on the lateral wall of the lateral femoral condyle to the anatomic femoral ACL footprint on the medial wall of the lateral femoral condyle. The PLC graft is suspended on the ACL graft to be anchored on the cortex of the lateral femoral condyle with added fixation by an interference screw (Arthrex, Naples, FL). The PLC graft limbs are used for open reconstruction of the fibular collateral ligament, popliteus tendon, and popliteofibular ligament. This Technical Note describes a technique of combined ACL and PLC reconstruction with hamstring tendon autografts through a single femoral tunnel using graft-to-graft suspension and fixation.

The impact of EPB pressure on surface settlement and face displacement in intersection of triple tunnels at Mashhad metro

The impact of EPB pressure on surface settlement and face displacement in intersection of triple tunnels at Mashhad metro

Study on deformation behavior at intersection of adit and major tunnel in railway

Behavior of rock mass in the intersection between adit and major tunnel is a complicated three-dimensional problem, the increasing support load and additional tunnel deformation may endanger tunnel stability during construction. To understand the deformation behavior of rock mass in the intersection, a 3D numerical analysis was conducted. Comparing the monitoring data, the distribution of the plastic zone, the extrusion displacement of working face and the deformation of the sidewall in the adit and major tunnel were studied. Following analysis results, the distribution and potential influenced area of the intersection in the adit and major tunnel were analyzed. The principle of detection and reinforcement in the intersection were also discussed.

Appraisal of Highway Tunnels Construction on the Active Railroad Tunnel Operational Reliability in the City of Sochi

The article highlights a set of researches performed to ensure the operational reliability of the railway tunnel with the highway tunnels constructed above it in the city of Sochi. The tunnel intersection on the highway includes 2 parallel tunnels with the length of 544,1 and 557,8 meters. Engineering-geological conditions are classified as complex: three tunnels on the problem area are located in the low and reduced strength mudstone with the inclusion of lenses and interlayers of Sandstone. According to the results of the theoretical research, limit value of the strength and deformation parameters of railway tunnel lining were determined. Stress-strain state of lining in nearly real-life conditions is determined. The work program for permanent automated geodetic monitoring of the highway tunneling allowed us to obtain information about possible changes in the technical state of railway tunnel lining. The complex of performed measures allowed ensuring the safety of construction work of the highway tunnel and continuous movement of Tuapse-Adler trains passing through central areas of Sochi.

A study of Tibial Osseous Tunnel intersection when reconstruct PCL and POL simultaneously

A study of Tibial Osseous Tunnel intersection when reconstruct PCL and POL simultaneously

Deformation and mechanical characteristics of tunnel lining in tunnel intersection between subway station tunnel and construction tunnel

Deformations and stress distributions in tunnel intersection areas are more complicated than those in common tunnels. The literature on deformations and stress distributions in tunnel intersections, in which the intersecting tunnel is in a different section, is limited. The Shangxinjie subway station in Chongqing, China, was selected to investigate the deformation, stress and plastic zone responses of a tunnel intersection using numerical simulations. Based on the numerical results, the scopes of influence with respect to the deformation, stresses and possible failure modes of the tunnel lining were further studied. The numerical results show that the deformation in a section close to the tunnel intersection was larger than the deformations in distant sections. Compared with the common section, the crown settlement reached the maximum value at the tunnel intersection, and the maximum rate of increase was approximately 28%. The range of the plastic zone at the tunnel intersection was much larger than that in the other areas, and it was mainly located in the side wall and tunnel crown. In the longitudinal direction, the lengths of the scopes of influence were 2.4 B and 1.6 B with respect to the deformation and stress, respectively. The magnitudes of the internal forces in the longitudinal and circumferential directions were almost equal. The bending moments of the tunnel lining within 135° and 225° significantly changed, but the axial force decreased dramatically. Tensile and compressive failures may occur at the tunnel intersection and in a section 5m away. Locally thickening the supporting structures is suggested to improve the stability of the tunnel.

Mapped infinite patches for the NURBS based boundary element analysis in geomechanics

A formulation of infinite NURBS patches is presented which allows the modeling of infinite surfaces with the NURBS based boundary element method. Applications are the modeling of long tunnels and of the ground surface in geotechnical work. To achieve an infinite surface, special mapping functions are used for describing the geometry. For the description of the displacements either a constant variation is assumed simulating plane strain conditions or it is assumed that the displacements decay to zero at infinity. The theory and implementation details are presented. Test examples show that the proposed formulation works well for the simulation of long tunnels and of the ground surface. Finally a practical example of a tunnel intersection is presented.

Numerical Analysis on Interaction Induced by Crosswise Tunneling

A position conflict exists between Harbin Urban Rail Transit Line No.1 and the branch tunnel of "7381" civil air defense tunnel. Intense tunnel interaction occurs when Line No.1 is perpendicularly tunneled across the branch tunnel. The investigation of the interaction is necessary. A 3D numerical simulation is established using FLAC3D and the vault deformation around the tunnel intersection is analyzed. The vault settlement of Line No.1 increases by 1.4 times during crosswise tunneling, while the vault settlement of branch tunnel increases 21.0mm in addition. The affected region of the tunnel intersection is further revealed. The affected length of the vault of Line No.1 and branch tunnel is 7.5 times the diameter and 6 times the width respectively. In combination with monitoring data, the reinforcement effect is studied at last. Both the vault settlement and surface settlement are well controlled in the tunnel intersection.

Effect of Cross Passage Construction on the Structural Safety of Collapse Reinforcement Segment of Existing Tunnel

On the basis of the engineering background of cross passage construction in the Chen Yu Tunnel project, the collapse section above the intersection of the existing tunnel is selected to establish finite element model. Considering the effect of cross passage construction and the local weakening area of surrounding rock on the safety of existing tunnel structure, the strength of the shotcrete supporting structure of existing tunnel intersection is checked, and the security of the existing tunnel is evaluated. This research is of great practical significance and a certain reference value for the plan and design upon the construction of tunnel engineering.

Tunnel Intersection in Combined Anatomic Reconstruction of the ACL and Posterolateral Corner

Femoral tunnel intersection in combined anterior cruciate ligament and posterolateral corner reconstruction has been reported to be high. The purpose of this study was to examine the risk of intersection between an anatomic femoral anterior cruciate ligament tunnel created with a retrograde reaming device and femoral lateral collateral ligament reconstruction tunnels of varying trajectory in a synthetic femur model.

Nonlinear dynamic failure process of tunnel-fault system in response to strong seismic event

Strong earthquakes and faults have significant effect on the stability capability of underground tunnel structures. This study used a 3-Dimensional Discrete Element model and the real records of ground motion in the Wenchuan earthquake to investigate the dynamic response of tunnel-fault system. The typical tunnel-fault system was composed of one planned railway tunnel and one seismically active fault. The discrete numerical model was prudentially calibrated by means of the comparison between the field survey and numerical results of ground motion. It was then used to examine the detailed quantitative information on the dynamic response characteristics of tunnel-fault system, including stress distribution, strain, vibration velocity and tunnel failure process. The intensive tunnel-fault interaction during seismic loading induces the dramatic stress redistribution and stress concentration in the intersection of tunnel and fault. The tunnel-fault system behavior is characterized by the complicated nonlinear dynamic failure process in response to a real strong seismic event. It can be qualitatively divided into 5 main stages in terms of its stress, strain and rupturing behaviors: (1) strain localization, (2) rupture initiation, (3) rupture acceleration, (4) spontaneous rupture growth and (5) stabilization. This study provides the insight into the further stability estimation of underground tunnel structures under the combined effect of strong earthquakes and faults.

Numerical Analysis of Deformation Influence of Horizontal Adit Construction on Main Tunnel Intersection Structure

The 3D finite element simulation are adopted to study the surrounding rock deformation regularity of main tunnel during the horizontal adit construction stage．The Zhongtiaoshan highway tunnel is taken as an example. The research results are shown as follows：Horizontal adit excavation destroys the original arching effect of the main tunnel, which leads to stress concentration at the intersection of primary supporting structure. The first excavation step plays an important play in the surrounding rock deformation of the intersection. The influence range of the main tunnel which due to the horizontal adit excavation is 1.2D.