Parallel Tunnels Research Articles

Ground Behavior of Parallel Tunnels in Response to Variations in Groundwater Flow

With the steady expansion of urban development, the importance of tunnel design and construction has increased, particularly with respect to changes in the groundwater level. Excavation without considering groundwater variations can destabilize tunnels; and this problem has been exacerbated by recent climate change-induced groundwater level fluctuations. This study evaluates the impact of various factors, such as filler width, lateral earth pressure coefficient, and groundwater flow, on tunnels by analyzing the ground behavior around parallel tunnels in Korea. The findings reveal that an increase in filler width reduces settlement and displacement, while the coefficient of lateral earth pressure affects convergence displacement to a higher degree than other settlements. Moreover, steady flow conditions are observed to wield a more pronounced impact on ground behavior than unsteady ones. These findings emphasize the importance of thoroughly evaluating groundwater flow characteristics during tunnel excavation and provide essential data for the future design and construction of parallel tunnels.

Construction simulation and scheme optimisation of complex underground cavities

Underground cavities have complex spatial structures and geological settings, their arrangement is dense and crisscrossed. The construction system involves multiple work surfaces, levels, and processes. The close integration of construction simulation with actual production conditions is crucial for enhancing the guidance that simulation results provide for practical engineering. Therefore, from the perspective of optimizing construction organization and management, this article comprehensively considers various factors in the construction process, innovatively introduces the principle of production line balance and the concept of rule cycle, and combines technology and management, an underground cavities construction simulation system (UCCSS) is developed. In UCCSS, a hierarchical model is built and calculation are performed on models with different construction methods by modifying the parameters as per the actual engineering characteristics. The simulation results are comprehensively analysed to determine the optimal construction programme. An application case is proposed based on the construction organisation design of the long and parallel diversion tunnels at the CB Hydropower Station. The results show that the system has good practicality and credibility and can provide guidance for the construction organisation design of underground cavities with various features.

Formation mechanism of micro-seismicity difference between rockbursts in deep-seated parallel tunnels

Deep-seated parallel tunnels are highly susceptible to rockbursts owing to the geological environment and engineering disturbances caused by adjacent tunnel excavations. However, accurately predicting these is challenging. The temporal and spatial characteristics of microseismic (MS) events and rockbursts in parallel tunnels can be jointly analyzed owing to their similar occurrence environments. However, although the left and right tunnels exhibited similar rockburst features during the construction of the Gaoloushan highway tunnel, noticeable differences in the MS events were observed. To clarify the cause of this phenomenon, the mechanisms of the influences of the buried depth, rock mass structure, hydrogeological conditions, construction parameters, blasting disturbance, and other factors on the MS activities of the left and right tunnels were investigated. Our findings suggested that the original geological occurrence environments, including the buried depth, rock mass structure, and hydrogeological conditions, were the primary reasons for the MS differences between the left and right tunnels. There was no obvious correspondence between the tunneling speed and evolution of the MS events. The influences of the section change and blasting on the MS anomaly were restricted by the geological environment and surrounding rocks. The results provide valuable insights into the effects of geological conditions and construction parameters on the formation mechanisms of rockbursts and MS events and may assist in developing an effective early warning strategy, as well as in preventing and controlling rockbursts in parallel tunnels or tunnel groups.

Optimizing stability design of support system for the parallel tunnels excavation crossing a fill slope

Optimizing stability design of support system for the parallel tunnels excavation crossing a fill slope

3D numerical investigation of the interaction between interchange tunnels at different angles

The development of subway and highway tunnels has led to the spatial intersection of tunnels, significantly impacting tunnel deformation, lining stress, and ground settlement during construction. To study the influence of critical parameters such as the cross angle and centre-to-centre distance on the tunnel performance, a series of numerical simulations were carried out. The influence range and magnitude of stress in the spatial cross tunnel under different cross angles were determined. The results indicated that as the crossing angle increased, the stress on the lining decreased, and the vault displacement increased. Meanwhile, the parallel tunnels showed opposite tendencies. Based on these results, the crossing angle of the cross tunnels was suggested to be greater than 45°. Parallel tunnels should be considered individually because the loading is symmetrically distributed. Considering the vault displacement and von Mises stress of the lining, it is recommended that the tunnel spacing be greater than 2D. The numerical model was validated against field data, and the findings of this study can be useful in designing cross tunnels.

Stability analysis and failure mechanism of multiple parallel soft-rock tunnels considering the random distribution of rockmass joints

In order to investigate the failure mechanism of multiple parallel tunnels considering the random distribution of rockmass joints, this paper conducts in-depth study on the instability characteristics, deformation mechanism and active deformation control methods of deep jointed soft-rock tunnels. A rockmass joint generation technique considering the random distribution characteristics of geometric parameters has been established and validated. Compared to the ordinary single-hole tunnel, the failure mode of the double-hole tunnels with parallel adit is much more complex, with the deformation mainly reflected on the outer side of the left and right holes. The surrounding rock pressure is concentrated at both ends of the normal direction of the bedding plane. Narrowing the distribution range of joint dip angle will exacerbate the asymmetry of surrounding rock deformation, and a larger range of joint dip angle can make the stress characteristics of the supporting structures more uniform. Increasing the joint trace length will gradually increase the overall displacement of the surrounding rock and reduce the number of yielding blocks. As the density of joints increases, the stress in the surrounding rock becomes more uniform, but it can lead to more fractured rockmass, reduced the deformation stability, and is not beneficial for the formation of key structural layers. The active deformation control method suitable for deep jointed soft-rock tunnels is proposed and applied. Under conventional passive support schemes, the surrounding rock faces a high risk of instability collapse, with a failure probability exceeding 20%. The active deformation control concept represented by prestressed support and grouting reinforcement can effectively improve the safety factor of surrounding rock and reduce the instability probability of rockmass. For the deep stratum with developed joints, it is difficult to effectively apply high prestressing force to the internal stable structural layer. Therefore, a long-bolt with full-face grouting scheme shall be considered to actively reinforce the deep jointed rockmass.

Investigation on Response of Site of Typical Soil–Rock Composite Strata in Changchun Induced by Shield Construction of Parallel Twin Tunnels

Underground engineering construction will inevitably change the stress state of surrounding strata, which will force a negative impact on the surrounding environment, even leading to the large deformation and damage of some adjacent structures. With a focus on the deformation of a typical soil–rock composite stratum site in the construction of Changchun Metro, relying on the shield construction of a parallel twin tunnel project between Northeast Normal University Station and Gong-Nong Square Station, which belongs to the Changchun Metro Line 1, the site deformation characteristics during the shield driving process of parallel twin tunnels were studied. Based on the data obtained from field monitoring and numerical simulation, ground settlement in shield driving was analyzed, the settlement trough was studied with the Peck formula, and the action of shield driving on the adjacent tunnel was discussed. Moreover, the influence range of shield driving was suggested, and the interaction between the twin tunnels with different axis spacings in shield driving was discussed. Some regular results obtained can provide support through data for similar projects in Changchun, China.

Stability of Asymmetric Parallel Tunnels in Cohesive-Frictional Soils

Stability of Asymmetric Parallel Tunnels in Cohesive-Frictional Soils

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Water inflow analysis is critical for subsea tunnel construction. However, existing studies largely concentrate on the inflow issues pertaining to single-hole tunnels. To address current practical engineering problems, a three-hole parallel configuration is common for subsea tunnels, which may alter water inflow patterns due to the influence of their seepage fields. Herein, numerical simulations are conducted to investigate the water inflow characteristics of a three-hole parallel subsea tunnel. Specifically, the impact of various factors on the water inflow phenomenon, including the permeability coefficient of the surrounding rock, the depth of the seawater, the depth of the tunnel, the spacing between tunnels, and the relative size of the tunnels, are comprehensively studied. Furthermore, based on the principles of the analytic hierarchy process and fuzzy mathematics, an exhaustive assessment framework is developed to evaluate the water inflow of three-hole parallel subsea tunnels. The results indicate that there is a mutual influence between the three parallel tunnels, differing from the predicted water inflow, which is overestimated in a single-hole tunnel model. Therefore, the water inflow assessment for a three-hole parallel subsea tunnel system should account for the inter-tunnel influences. The findings of this study offer valuable insights for the design of waterproofing and drainage systems in three-hole subsea tunnels.

Large highway tunnels under operating metro lines in the soils of Santiago – Design and Control approach

AbstractThe Américo Vespucio Oriente II Concession (AVOII), part of the Urban Transport System of the Metropolitan Region of Santiago, Chile, includes the closure of the 65 km Américo Vespucio Ring in highway standard. The project involves the construction of two mostly parallel urban soil tunnels 5.2 km in length and three lanes in each direction and it will run below the existing Américo Vespucio Avenue. At the same time, it goes below the underground Metro Line 4 currently in operation. Skava Consulting SpA was hired by Metro as an expert reviewer of underground and surface works. The objective is to ensure that the existing Metro structures will not be affected by the construction or the operation of AVOII. The work involved highly complex 3D models. In search of a more efficient way to review the design, it was agreed to do finite difference models in the critical areas of the project. A total of 32 proper models were created. All of them proved to be useful in validating and correcting findings or deviations in the original design. Considering the above, and that the project runs at depths of 40 m in average – which for Santiago soil is uncommonly deep – it faces the challenge of an extremely low tolerance for disturbances in the surrounding ground. For this reason, specific subway rail deformation criteria must be fulfilled, and the surface and subsurface deformations must be monitored very frequently during the construction of the tunnel, due to commence in 3Q 2023.

Bending performance of Y-shaped joints of subway station built by enlarging two parallel shield tunnels

Based on the characteristics of the Y-shaped joint of a subway station built by enlarging two parallel shield tunnels, a bending mechanical model of the segmental joint was proposed. The model was used to characterize the cracking and crushing of concrete, the yielding of the bolt, and the damage of the segmental joint. Theoretical equations were derived for the bending stiffness of the joint under various forms of joint opening. Bending experiments were conducted on full-scale models of the joints under different structural configurations. The results demonstrated that the nonlinear properties of the joint structure were evident under loading and that the bending stiffness of the joint initially increased and then decreased. The computed values were in good agreement with the experimental results for the pre-embedded connector joint when lc was 0.5 times the height of the compression zone, where lc was the effect depth of the compressive deformation of the outer edge of the concrete. The axial force had a great influence on the bending stiffness. The mechanical performance of the joint was influenced not only by the change in the stress–strain curve of the concrete from the rising stage to the descending stage but also by the structural morphology of the rotational angle of the joint.

Influence of the door opening on the pressure transient caused by the high-speed subway train passing through the double-track tunnel with the mid-partition wall

Double track tunnel with mid-partition wall is a widely used subway tunnel. In such tunnels, in order to avoid the fire door on the middle partition wall from invading the gauge, the fire door is often removed to form door openings. The existence of door opening connects two parallel tunnels, which affects the aerodynamic effect caused by high-speed subway train passing through the tunnel. In this study, a double track tunnel with mid-partition wall was taken as an example to analyze the aerodynamic effect of high-speed subway train under the door opening conditions, moreover, the surface pressure of two adjacent tunnels and train surface pressure was also analyzed. In addition, the propagation mechanism of pressure wave in open door tunnel was analyzed in detail, and the superposition law of branch pressure wave caused by open door was pointed out. The results indicated that the presence of door openings is beneficial for controlling the peak pressure on the tunnel surface and train surface. For a door opening with a cross-sectional area of 5 m2 (cross-sectional area ratio of 0.116), when the door opening is located 300 m and 700 m away from the tunnel entrance, the peak positive pressure can be reduced by up to 21.9 % and the peak negative pressure can be reduced by 21.1 %. The cross-sectional area and number of door openings have a limited effect on reducing the peak pressure of the tunnel. Compared to the number of door openings, the position of the door opening has a more significant impact on the peak pressure inside the tunnel and on the surface of the train.

Impact of Micro-NPR bolt on the mining of deep-buried phosphate via the room-and-pillar method

Large and complex goaf groups have formed as a consequence of mining activities in the Yichang Phosphate Mine. These goaf formations have given rise to recurring engineering challenges and disasters, including roof collapse and pillar damage, primarily attributed to excessive ground pressure. Owing to the working principle and mechanical properties of traditional PR bolts, the preload cannot be applied to the surrounding rock immediately after excavation, resulting in considerable roadway damage. To address the problem of large deformation control in deep mines, a damage mechanics model of a roof-and-pillars mine was established to analyse its deformation and damage characteristics. A physical model experiment was performed to analyse the damage state of the roof and pillars in a deep-buried phosphate mine with twin roadways using the room-and-pillar method. The objective was to examine the effectiveness of the PR and micro-NPR(negative Poisson's ratio) bolt support systems under real conditions. Experimental results indicated that the micro-NPR bolt effectively strengthened the roof and pillar, enhanced the strength and stiffness of the pillar, and prevented pillar extrusion and roof collapse. These findings bridge the gaps in the existing theoretical frameworks, technical research, and engineering applications of the micro-NPR support, promoting technological innovation in the phosphate mining industry. This study provides a reference for the state change and support research on the surrounding rock after the excavation of twin parallel tunnels under specific conditions.

Study on the Influence of an Under-Crossing Parallel Double-Line Shield Tunnel on the Existing Tunnel Structure

Extra care should be taken when new tunnels pass through an existing tunnel. If it is not handled properly, this will affect the operation safety of the existing line, and bring security risks to the train’s operation. In order to study the impact of an under-crossing parallel double-line shield tunnel on the existing shield tunnel structure, the influence of tunnel construction on the deformation of overlying strata was analyzed, and the formula for estimating the formation settlement at depth Z below the surface, caused by the excavation of a double-tunnel parallel tunnel, was deduced. Then, a series of three-dimensional finite element numerical simulations were carried out. We analyzed and systematically studied the adverse effects of the tunnel structure of Guangzhou subway Line 5, caused by the tunneling of subway Line 18, evaluated its structure and operational safety, and provided suggestions for site construction. This research demonstrates the following conclusions. (1) The tunnel structures of subway Line 5 and Line 18 are mainly in the strongly weathered argillaceous siltstone stratum, and lightly weathered argillaceous siltstone stratum, respectively, and the stratum where the Line 18 tunnel is located is relatively safe. (2) According to three-dimensional finite element numerical simulation analysis, during the shield-tunneling process of subway Line 18, the maximum X horizontal displacement, the maximum Y horizontal displacement, and the maximum Z vertical displacement of the tunnel structure in subway Line 5 are 1.09, 3.50, and 4.55 mm, respectively. It is considered that the impact of the shield-tunnel penetration of subway Line 18 on the tunnel structure of subway Line 5 is relatively controllable, and does not affect the structure and operational safety. (3) It is suggested that settlement monitoring should be strengthened within the range of 12 m (about 1.5 tunnel diameter D). before and after the excavation axis of the underpass tunnel, and it is necessary to carry out local reinforcement treatment, to prevent adverse effects on the operation of the existing tunnel.

Experimental and numerical studies on the seismic response of adjacent horizontal parallel tunnels

Several studies have investigated the seismic performance of single-tunnel structures. However, few studies have focused on the interactions between adjacent tunnels during earthquakes. The interaction mechanisms and influence ranges between tunnels during earthquakes are not clear. Shaking-table tests and numerical parameter analyses were employed to explore the interaction mechanism between two horizontal parallel tunnels during an earthquake. The main influencing factors were tunnel factors (tunnel net spacing, diameter, and buried depth), ground motion factors (type and amplitude), and site soil types. The calculation and analysis results indicate that the net spacing of the horizontal parallel tunnels is a key factor in determining the interaction of close-distance tunnels. The interaction was most apparent when the net spacing of the tunnels was between one and two times the tunnel diameter, which is the most common net spacing used in practical engineering. In addition, the tunnel diameter, buried depth, ground-motion type, amplitude, and soil type can significantly influence the tunnel response. The results of this study can serve as a reference for the seismic design of adjacent horizontal parallel tunnel structures.

Quantitative evaluation of service health condition for cutting tools on cutterhead in long-distance mechanized shield tunneling

Inspection, repair and replacement of mechanized shield cutting tools is a necessary but time-consuming, dangerous, risky and costly process. Yet, the current practice of cutting tool inspection and management does not always result in anticipated benefits. In this paper, a quantitative method for evaluating the overall service health condition (OSHC) of a cutterhead was proposed for the first time and applied to two parallel twin tunnels in Beijing Daxing International Airport Express Line. The findings indicate that one shield performed well without wear inspection and cutting parts replacement. However, the cutterhead of the other shield with mismatched new and old cutting parts after inspection and partial replacement had an unexpected worse OSHC in the subsequent tunneling. A quantitative relationship between the OSHC of a cutterhead and tunneling distance was proposed to guide the determination of an inspection shaft location for performing on-demand cutting tool inspection and replacement. The proposed method has the potential to enable data-driven, on-demand cutting tool inspection and management that is critical for achieving faster, less disruptive and cost-saving tunneling, especially beneath a highly populated urban area.

Effect of Oblique SV Wave on the Seismic Response of Mountain Tunnel

In order to study the dynamic response of parallel mountain tunnels under the oblique incidence of seismic waves, based on the display finite element method and using viscoelastic artificial boundary, the oblique incidence of three-way seismic waves was realized by angular incident mode. The displacement and stress distribution characteristics of the tunnel lining under different propagation angles and vibration angles of SV waves were studied. The results show that the oblique incidence of SV wave has a certain effect on the displacement of the double tunnel, the forces in the tunnel are symmetrical and the axis displacement increases with the increase of incident angle, and the vertical displacement changes greatly. The stress of the tunnel lining under the oblique incidence of the SV wave is elliptical. The peak value of the maximum principal stress appears at the maximum span on both sides, and the maximum principal stress decreases with the increase of the vibration angle. The maximum principal stress of the right tunnel is flat. The minimum principal stress of the left and right holes decreases with the increase of vibration angle, and the minimum principal stress of the left hole is 90°∼270°. The distribution of the minimum principal stress in the range is large. Mises stress increases with the increase of the incidence angle of seismic waves.

Seismic response analysis of close-distance cross tunnels: Shaking table test and numerical parameter analysis

There are many research results on the seismic performance of single tunnel structure presently, but there are relatively few studies on the interaction of cross tunnels with different angles at close range during earthquakes, and the degree and scope of interaction between tunnels during earthquakes are not clear. A series of shaking table tests and numerical parameter analysis are conducted to study the interaction mechanism, influence degree and range of closely spaced intersecting tunnels under earthquake in this paper. The shaking table tests of soil-single tunnel, soil-upper and lower parallel tunnel and soil-upper and lower vertical tunnel are designed and performed firstly. The rationality of the numerical method is verified based on the test data accordingly. Finally, a comprehensive parameter analysis is carried out for the full-scale tunnel, in which the tunnel factors (crossing angle, diameter, buried depth), ground motion factors (type, amplitude) and the influence of site soil type were considered. The results show that the crossing angle between tunnels is the key factor affecting the seismic response of soil-tunnel system. The ground acceleration, internal force, and deformation of tunnel structure increase with the increase of crossing angle between tunnels, which should be paid more attention. In addition, the tunnel diameter, buried depth, seismic characteristics and soil type can significantly affect the response of tunnel structure. The research results can provide a reference for the seismic design of close-distance cross tunnel structures.

Derivation and validation of a similarity law for free-flight wind tunnel tests of parallel stage separation

Aiming at the safety problem of the stage separation of parallel reusable high-speed air vehicles, this paper studies the unsteady test method and focuses on deriving a similarity law of parallel stage separation free-flight wind tunnel tests. The new similarity law considers the influences of aerodynamic force and gravity on the motions of the two stages, as well as the influence of aerodynamic interference between the two stages on each other’s motion. From the perspective of multi-angle physical equations, the conditions to ensure that the two-stage separation trajectory of a wind tunnel test is similar to that of a real air vehicle are derived innovatively, so as to ensure the authenticity and credibility of wind tunnel test results. The similarity law is verified by an HIFiRE-5 air vehicle, and the separation trajectories of wind tunnel tests and the real air vehicle are obtained by numerical simulation. The research shows that the similarity law derived in this paper can ensure that wind tunnel free-flight tests have the ability to predict the two-stage separation characteristics of real parallel vehicles. By analyzing the separation trajectory curve of the typical state, it is found that the new method can ensure that the trajectory error of a wind tunnel test does not exceed 1%, which indicates that this method is credible. The establishment of the new method lays the foundation for subsequent wind tunnel tests and provides support for research on the safety of the stage separation of parallel reusable air vehicles.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ УКРЕПИТЕЛЬНОЙ ЦЕМЕНТАЦИИ ПОРОД НА НАПРЯЖЁННОЕ СОСТОЯНИЕ ОБДЕЛОК ПАРАЛЛЕЛЬНЫХ ТОННЕЛЕЙ

The results of determining the stress state of the rock mass and the lining of two parallel tunnels constructed under the slope are presented, obtained using the developed analytical calculation method, which is based on the solution of the plane problem of elasticity theory, obtained using the mathematical apparatus of the theory of functions of a complex variable. The obtained results illustrate the influence on the stress state of the elements of the geomechanical system under consideration of the order of tunneling, the lag in the construction of the lining from the face, as well as the appearance of zones of reinforced soil around the tunnel walls. During the study, a computer program was used that implements the developed method, which makes it possible to effectively perform multivariate calculations in the design of underground structures and for research purposes.