Tunnel Axis Research Articles

Theoretical investigation of the resistance effect of embedded isolation piles on tunneling-induced lateral ground movements

This paper presents an isolation pile–soil lateral interaction model that considers not only the relative linear sliding at the pile-soil interface but also the pile group–soil interaction. The model allows for the calculation of the pile–soil interaction force using the elastic continuum method combined with the displacement compatibility relationship at the pile–soil interface, thus enabling the total lateral ground displacement to be obtained. The proposed method is validated by comparisons with the elastic foundation method (EFM) and the boundary element method (BEM). The advantages of the proposed method in calculating the lateral ground deformation resisted by isolation piles are demonstrated. The mechanical mechanism of the isolation pile’s lateral resistance effect on ground deformation can be summarized as follows: the combination of positive and negative resistance effects drives the lateral ground displacements along the depth direction from the original inhomogeneity caused by the tunnel excavation to a relatively homogeneous state. The soil parameters including Poisson’s ratio, internal friction angle and ground volume loss; the isolation pile parameters including the distance of the tunnel axis from the pile axis, the pile length, the buried depth of the pile top and the relative pile bending stiffness; and isolation pile–soil interface parameters including relative pile shaft–soil stiffness and relative pile tip–soil stiffness all exert a significant influence on the lateral resistance effect of the isolation pile. In light of that the resistance effects at different depths below the surface are not uniform, it is of the utmost importance to assess the resistance performance of the isolation pile in accordance with the location and lateral deformation requirements of the protected structure in actual engineering.

Noise Radiation from a partially opened and elevated tunnel-tube

Road or railway tunnels are considered in noise prediction programs generally by neglecting any emission from the tunnel structure between the openings and replacing each tunnel mouth by additional sources simulating the sound radiated from inside to outside through these openings. The sound pressure level inside the tunnel can be derived from the analog model of a room formed by a slice cut out of the extended tunnel with two perfect reflecting planes perpendicular to the tunnel axis. The paper presents a methodology for the case of an elevated tunnel tube with an upper ventilation gap running over the entire length of the tunnel to calculate the sound pressure levels in the surrounding area more approximately using engineering models like ISO 9613-2 or others and more detailed using a particle method developed to account for complete 3-dimensional propagation problems.

Mechanical response analysis of primary support for shallow buried loess tunnel under surface surcharge

At present, the research on the influence of surrounding soil deformation induced by tunnel construction under the action of surcharge is generally based on the situation after the tunnel has been built, and less consideration is given to the existence of surface surcharge near the planned route of the tunnel when the tunnel is not built. Therefore, based on the Luochuan tunnel under construction, this study monitors the deformation of shallowly buried loess tunnels under different surcharge conditions and analyzes the influence of varying surcharge conditions on the deformation and stress of the tunnel through numerical simulation to determine the effective range of surface surcharge. The results show that the influence of surcharge load on tunnel stability is the most significant when located at the tunnel axis, and the influence degree increases with the increase of load. The adverse effects of surcharge load mainly occur in the range of 2 times the tunnel diameter. Once the range is exceeded, the internal force of the tunnel support structure is not sensitive to the surcharge load. In engineering, the surface surcharge can be controlled within the safety displacement limit by referring to the displacement calculation results.

Mathematical modelling for strata deformation caused by rectangular pipe jacking construction in composite layered ground

In this study, analytical solutions of vertical deformation of ground surface and horizontal displacement of strata are derived combining the Mindlin solution and the mirror method due to rectangular pipe jacking tunneling in composite strata, which considers the combined effect of five factors of additional excavation pressure, friction of rectangular pipe jacking and soils, segment-soil friction, grouting filling and strata loss, respectively. The theoretical calculation results were verified against the measured data in two project cases. Moreover, effect factors of rectangular jacking pipe cross-sectional dimensions, embedment of tunnel axial depth, elasticity modulus on the interlayer and the Poisson's ratio of the interlayer on strata deformation is investigated. The results imply that the theoretical calculation values obtained using this method are more closely correlated with the observed values compared to those computed using the single stratum model. The primary cause of terrene upheaval in front of the working surface is the increased excavation pressure on the working face and the horizontal displacement of the deep soils and the surface subsidence behind the excavation face is resulting from the soil loss as the main influencing factor. The varying cross-section size of pipe jacking is able to impact on the vertical deformation of the soil, but it has a limited impact on the lateral displacement of the strata. The affection of the buried depth of the tunnel axis on strata deformation is more notable in the rectangular pipe jacking construction. As the axial tunnel depth growth, the ground surface maximum subsidence value gradually decreases, while the crest value of horizontal distortion mildly increases. When the rise of the interlayered modulus of elasticity, the maximum earth surface subsidence enlarged gradually while the subsidence trough slight diminution. Moreover, the greatest horizontal displacement exhibits a relatively minor fluctuation, but there is a trend of upward movement in the position. The influence of Poisson's ratio of the interlayer on the strata deformation is comparatively weak.

Study on InSAR deformation information extraction and stress state assessment in a railway tunnel in a plateau area

Introduction: The study proposes a method for evaluating stress distribution in high-altitude Tibetan Plateau railway tunnels using high-precision radar satellite time-series interferometric synthetic aperture radar technology.Methods: To effectively monitor and prevent geological hazards during the construction process, this method i employed, as it serves as a component of advanced geological prediction and surrounding rock deformation monitoring technology for high-altitude tunnels, particularly in the Dongelu Tunnel of the China–Tibet Railway. The study utilizes time-series interferometric synthetic aperture radar to obtain deformation information for Dongelu Tunnel area between 2022 and 2023 from Sentinel- 1A orbit images. This quantitatively investigates the upper mountain body and line-of-sight direction along the tunnel. The deformation characteristics are correlated with high-frequency and high-precision automated vertical displacement monitoring results, determining the spatiotemporal distribution of tunnel deformation. In this study, a model that determines the vertical stress state of the Dongelu Tunnel under loading near the entrance and evaluates its health status was established.Results: The results show that the surface deformation of the mountain above the tunnel axis develops slowly and is relatively small, with a maximum vertical deformation rate of 1–3 mm/year. The average stress on the tunnel arch is 5.54 MPa, with a fluctuation range of 0.01 MPa. Temporal Q9 changes in various parts of the tunnel are periodic, with maximum fluctuations observed in December 2022. The study reveals inconsistent surface settlement of the tunnel arch and mountain above it, causing minor vertical stress changes. As the tunnel construction progresses, vertical stress variation shows periodicity because of an initial imbalance in internal stress within the mountain. Stress fluctuations near the tunnel entrance occur during the initial excavation phase, gradually diminishing as the project progresses and internal stress stabilizes.Discussion: The proposed tunnel monitoring and stability assessment method can reduce its impact on engineering construction and provide guidance for advanced geological prediction.

Influence of stress and geology on the most prone time of rockburst in drilling and blasting tunnel: 25 tunnel cases

Rockburst exhibits different occurrence time characteristics during drilling and blasting in tunnel excavation, posing challenges to the safe and efficient construction of tunnels. In this study, 25 tunnels with rockburst hazards were examined. By employing the clustering method, we analyzed the characteristics of the most prone time (MPT) for rockburst. Furthermore, we investigated the contribution degree and influence mechanism of stress and geological factors related to the MPT of rockburst. The outcomes revealed that distinct tunnels exhibit diverse rockburst-prone times, leading to varying hazards and losses. The higher the maximum principal stress and the angle between it and the tunnel axis, the earlier the rockburst occurs. Moreover, the MPT of rockburst is influenced by both lithological types, macro and micro rock structures. When the joint intersects with the maximum principal stress at a small angle, rockburst occurs earlier. The stress direction, UCS, attitude of the dominant joint, and stress magnitude stand out as the principal controlling factors. The findings of this research can serve as a basis for assessing the MPT of tunnel rockburst, timing rockburst risk control measures, and selecting appropriate mitigation strategies.

Noise radiation from a partially opened and elevated tunnel-tube

Road or railway tunnels are considered in noise prediction programs generally by neglecting any emission from the tunnel structure between the openings and replacing each tunnel mouth by additional sources simulating the sound radiated from inside to outside through these openings. The sound pressure level inside the tunnel can be derived from the analog model of a room formed by a slice cut out of the extended tunnel with two perfect reflecting planes perpendicular to the tunnel axis. The paper presents a methodology for the case of an elevated tunnel tube with an upper ventilation gap running over the entire length of the tunnel to calculate the sound pressure levels in the surrounding area more approximately using engineering models like ISO 9613-2 or others and more detailed using a particle method developed to account for complete 3-dimensional propagation problems.

Prediction of adjacent single pile deformation induced by tunnel excavation based on the Pasternak model

The construction of metro tunnels in soft ground would cause significant settlement of the ground surface and deformation of buildings and their foundations in the vicinity of the tunnels. The deformation laws of the pile of the neighbouring structures induced by the tunnel construction have not yet been fully identified. This paper analyzed the impact mechanism of tunnel construction on piles based on the Pasternak model, deduced the calculation methods of additional horizontal displacement and additional internal force of piles, and introduced three solution methods. The computational method results have been validated through numerical simulations using coupling of discrete element method and finite difference method and compared to select laboratory data. The results show that the model accuracy is better when the tunnel axis burial depth is less than the pile bottom burial depth. The analysis shows that the tunnel burial depth significantly influences the displacement distribution of the adjacent single pile, while the impact on the peak displacement is insignificant. The thickness of the elastic layer (C) is inversely related to the maximum horizontal displacement and internal force, but it does not impact the distribution patterns of the displacement and internal force. For thickness of the elastic layer (C), the bending moment’s point is constant at 2 m above and below the tunnel axis, whereas the shear force’s point remains constant at the buried tunnel axis’s depth and 4 m above the tunnel axis.

Research on stress field inversion and large deformation level determination of super deep buried soft rock tunnel

Understanding the characteristics and distribution patterns of the initial geo-stress field in tunnels is of great significance for studying the problem of large deformation of tunnels under high geo-stress conditions. This article proposes a ground stress field inversion method and large deformation level determination based on the GS-XGBoost algorithm and the Haba Snow Mountain Tunnel of the Lixiang Railway. Firstly, the hydraulic fracturing method is used to conduct on-site testing of tunnel ground stress and obtain tunnel ground stress data. Then, a three-dimensional model of the Haba Snow Mountain Tunnel will be established, and it will be combined with the GS-XGBoost regression algorithm model to obtain the optimal boundary conditions of the model. Finally, the optimal boundary condition parameters are substituted into the three-dimensional finite-difference calculation model for stress calculation, and the distribution of the in-situ stress field of the entire calculation model is obtained. Finally, the level of large deformation of the Haba Snow Mountain Tunnel will be determined. The results show that the ground stress of the tunnel increases with the increase of burial depth, with the maximum horizontal principal stress of 38.03 MPa and the minimum horizontal principal stress of 26.07 MPa. The Haba Snow Mountain Tunnel has large deformation problems of levels I, II, III, and IV. Level III and IV large deformations are generally accompanied by higher ground stress (above 28 MPa) and smaller surrounding rock strength. The distribution of surrounding rock strength along the tunnel axis shows a clear "W" shape, opposite to the surface elevation "M" shape. It is inferred that the mountain may be affected by geological structures on both sides of the north and south, causing more severe compression of the tunnel surrounding rock at the peak.

A three-dimensional numerical study on the stability of layered rock spillway tunnels in alpine canyon areas

Rock masses in alpine canyon areas exhibit strong heterogeneity, discontinuity, and are subject to strong tectonic effects and stress unloading, leading to extremely complex distribution of in-situ stress. In addition, the occurrence of layered rock masses makes it more complex, with obvious anisotropic mechanical properties. This study proposes a comprehensive method for evaluating the stability of layered rock spillway tunnels in a hydropower station in an alpine canyon. First, the failure criterion and mechanical model of layered rock masses considering the anisotropy induced by the bedding plane and the true triaxial stress regime were established; an inversion theory and calculation procedure for in-situ stress in alpine canyon areas were then introduced. Finally, by using a self-developed numerical tool, i.e. CASRock, the stability of the layered rock spillway tunnel in a hydropower station was numerically analyzed. The results show that, affected by geological structure and stratigraphic lithology, there is significant differentiation in the in-situ stress in alpine canyons, with horizontal tectonic stress as the main factor. The occurrence of layered rock masses in the region has a significant impact on the stability of surrounding rock, and the angle between the bedding strike and the tunnel axis as well as the bedding dip both exert a significant influence on the failure characteristics of the surrounding rock.

Analytical poro‐elastic solution of deep lined tunnels in anisotropic rock with consideration of tunnel face advance

AbstractThis paper aims at deriving a closed‐form solution for deep lined tunnels within a saturated anisotropic poro‐elastic medium. The derivation of the solution is carried out with the assumption of plane strain conditions along the tunnel axis, an isotropic elastic liner, a steady‐state flow, and perfect contact between the liner and rock. For this purpose, the complex potential function approach pioneered by Lekhnitskii for the anisotropic elastic body was used to develop the mechanical response of the rock mass. A complex hydraulic potential function is also introduced to solve the steady state fluid flow. Then the well‐known Biot theory is chosen to describe the hydro‐mechanical coupling of the anisotropic saturated rock. The stress and displacement solutions of both the liner and the surrounding rock, considering the tunnel face advance with respect to the considered section, are derived based on the principle of the convergence‐confining method. Comparisons with previous closed‐form solutions for isotropic case and finite element solution for anisotropic case were made to show the accuracy of the current closed form solution. Sensitivity analysis is performed based on this analytical solution to highlight the effect of some rock parameters on the stress and displacement of the liner.

Deformation behavior and damage characteristics of surface buildings induced by undercrossing of shallow large-section loess tunnels

The ground movement during the construction of shallow loess tunnels can easily cause deformation damage to surface buildings. Most the current studies focus on the damage soft soil and rock tunnels to independent buildings, and there are few studies on the case of building groups in loess areas. Using the new Xi’Yan Railway Luochuan Tunnel as a case study, we conducted on-site testing to study building settlement and crack development characteristics. Three-dimensional numerical simulations were carried out to analyze settlement, flexure deformation, and main tensile strain distribution characteristics of the buildings at different buried depths. The study determines the extent of damage resulting from differential settlement and tension cracks. The results show that construction during the upper, middle, and lower bench stages results in significant ground volume loss, leading to a ’wide and steep’ settlement pattern with a maximum settlement value of 567 mm. Building cracks exhibit positive and inverted splayed shapes, with lengths ranging from 0.5 to 6.0 m and widths between 0 to 170 mm. As buried depth increases, maximum settlement, flexure deformation, and main tensile strain of buildings also increase. The severe damage range of buildings initially increases and then stabilizes, with the maximum range caused by differential settlement and tensile cracks being 34 m and 29 m from the tunnel axis, respectively. Based on the analysis of building damage characteristics, it was determined that a combination of surface measures and measures within the tunnel should be used to control building damage caused by tunnel construction. These research findings can serve as valuable references for similar projects.

Limitations in Tunnel Portal Design: An Evaluation Using Numerical Models and Line Surveys

In this study, engineering geology and geotechnical design studies of a highway tunnel project, located on the route of Zonguldak-Amasra-Kurucasile, was expressed. Owing to the low overburden thickness the subjected slope tunnel, especially the right tube in accordance with the project kilometer incremental direction, will be exposed to asymmetrical load after commence of the excavation. Besides, thicknesses between right tube right wall and the slope face in this section has decreased up to 6 m level. Moreover, as the tunnel is passing under the 1st grade archeological protection area, some of the site investigation studies, such as geotechnical drilling and site laboratory works could not have been performed. Thus, this study is explaining the determination of excavation support system of slope tunnel by using engineering geology studies and numerical models. As the tunnel site is located under the 1st grade archeological protection area, any of the required geotechnical site investigation drilling studies and corresponding site testing was not performed on the tunnel axis. Instead of this, line surveys, local sampling, and internationally accepted rock mass classification studies (RMR, Q, GSI) were performed on the rock mass outcrops, which are positioned against to the Black Sea. At the conclusion of these studies, rock mass engineering properties were determined through the utilization of empirical equations that incorporate data derived from site investigation studies and laboratory test results as input.

Automatic tunnel point cloud creation using photogrammetry and deviation analysis of excavation and shotcrete surfaces

AbstractDuring new Austrian tunnelling method excavation, it is necessary to carry out an analysis of the compliance of the actual surfaces with the theoretical lines prescribed in the support types for each tunnel excavation step. With our own software solutions, we created point clouds of the excavation and shotcrete of the primary tunnel support through the automated process of photogrammetric data. Together with the tunnel axis and theoretical profiles, the georeferenced and filtered point clouds were then used in the analysis of the deviation from the theoretical lines of excavation and primary support shotcrete and shotcrete thickness. The final products of the independent analysis are deviation profiles and unwrapped extrados views with numerical results and a color legend.

Automated extraction of tunnel leakage location and area from 3D laser scanning point clouds

Water leakage is one of the common tunnel disease problems. Fast and accurate detection is crucial for timely management of leakage disease. This paper introduces a method for automatically extracting the location and area of tunnel leakage from 3D laser scanning point clouds. The method involves three key steps: segmenting the point cloud data along the tunnel axis based on the width of the tube sheet, correcting the intensity of the point cloud using a linear intensity correction model, and binarizing the point cloud data to extract the leakage area and calculate its area. To evaluate the performance of the proposed methodology, water leakage detection software is prepared based on the method, and tests are carried out in the urban subway tunnels in the leakage disease-producing sections. The results show a detection accuracy of 92 % and an improvement in detection efficiency of 7–8 times. The method proposed can be used to quickly and accurately extract the location and area of water leakage from point cloud data.

Deformation characteristics and instability mechanism of transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel

To investigate the deformation characteristics and instability mechanism of the transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel, take the example of Beijing East Sixth Ring Road into the ground reconstruction project. Using the field experimental monitoring method and numerical simulation method, after verifying the accuracy of the model, this manuscript begins to unfold the analysis. The results show that, without any deformation prevention and control measures, The basement raft of the underground structure of the transportation hub will produce a deformation difference of 18 ​mm, and the tensile stress is more than 1.43 ​MPa, the inhomogeneous deformation and structural cracking will lead to structural instability and groundwater surges, which seriously affects the safe operation of the transportation hub station. When control measures are taken, the deformation and stress of the base raft slab of the underground structure of the transportation hub are within the prescribed limits, which can ensure the safe operation of the station. The displacement of the base slab of the underground structure in the horizontal direction of the cross-section is all pointing to the east, and the overall trend is to shift from the first tunnel to the backward tunnel. The horizontal displacement of the base slab in the direction of the tunnel axis all points to the beginning of the crossing, and the displacement of the slab in the vertical direction is distributed as "rising in the middle and sinking in the surroundings". For a two-lane super-large diameter shield tunnel penetrating an underground structure, there are two mechanical effects: unloading rebound and perimeter rock pressure. The above deformation characteristics are the superposition effect produced by the two, and this fine assessment of the deformation of the raft foundation provides a scientific basis for formulating the deformation control countermeasures of the crossing project. At the same time, it makes up for the blank of the double-track super-large diameter shield tunnel down through the transportation hub project.

Full-scale experimental, numerical, and theoretical research on the spatio-temporal evolution of the flow structure in longitudinal and semi-transversal ventilated tunnels

This paper presents full-scale experimental, numerical, and theoretical research on the spatial and temporal structure of airflow for different modes of ventilation system operation in a road tunnel. The tunnel under investigation is equipped with a semi-transverse ventilation system. There are 19 pairs of axial jet fans in each tunnel tube and 164 air supply vents on both sides of a tube located just above the road surface. A set of seven stand poles with mounted vane anemometers were arranged along the tunnel tube axis. Different configurations of axial jet fans and air supply vents were employed, and changes in airflow velocity were recorded. Since the main objective of the study is to achieve a deeper understanding of the examined phenomena, a numerical model of the flows in the tunnel was built, and the acquired data was used to validate it. Some theoretical considerations are provided and also validated. All of this together reveals a very uneven distribution of longitudinal air velocity along the tunnel axis. Then, time constants when switching the fans on and off are determined. It is shown that the time needed to achieve a stable flow after the fans are turned on is in the order of five minutes, and the decay time after the fans are turned off is much longer; it takes about 15 min to calm down the flow. Next, it is determined that the transverse air supply significantly changes the airflow structure: the average longitudinal air velocity at the inlet portal was up to 25% lower than without it, while values at the outlet portal were similar. Finally, it is indicated that axial fans that operate in the suction mode are similarly efficient to those in the pumping mode.

Diagnosis and Monitoring of Tunnel Lining Defects by Using Comprehensive Geophysical Prospecting and Fiber Bragg Grating Strain Sensor.

Tunnel excavation induces the stress redistribution of surrounding rock. In this excavation process, the elastic strain in the rock is quickly released. When the maximum stress on the tunnel lining exceeds the concrete's load-bearing capacity, it causes cracking of the lining. Comprehensive geophysical exploration methods, including seismic computerized tomography, the high-density electrical method, and the ultrasonic single-plane test, indicated the presence of incomplete distribution of broken rock along the tunnel axis. Based on the geophysical exploration results, a carbon-fiber-strengthened tunnel simulation model was established to analyze the mechanical characteristics of the structure and provide a theoretical basis for sensor deployment. Fiber Bragg grating (FBG) strain sensors were used to measure the stress and strain changes in the second lining concrete after carbon reinforcement. Meanwhile, one temperature sensor was installed in each section to enable temperature compensation. The monitoring results demonstrated that the stress-strain of the second lining fluctuated within a small range, and the lining did not show any crack expansion behavior, which indicated that carbon-fiber-reinforced polymer (CFRP) played an effective role in controlling the structural deformation. Therefore, the combined detection of physical exploration and FBG sensors for the structure provided an effective monitoring method for evaluating tunnel stability.

Study on creep characteristics of granite of deep tunnel affected by joint orientation

Joints are an important part of rock masses and the spatial relationship between joint orientation and in situ stress (or tunnel axis) has a significant impact on the deformation, strength, and failure behavior of the surrounding rock. To study the influence of joint orientation on creep characteristics of deep hard rock, the true triaxial creep tests were performed in the laboratory on natural jointed granite under different loading angles ω (defined as the angle between the strike of the joint plane and σ2-direction) conditions. The test results show that ω has a significant effect on the time-dependent deformation and failure characteristics of the jointed rock. As ω increases, there is a decrease in creep deformation, steady creep rate in the σ3-direction, and value of the DI index (used to evaluate the difference in the time-dependent deformation in the σ2- and σ3-directions). Stress-structure-controlled failure (sliding along the joint plane) occurs when ω ≤ 30°. However, when ω > 30°, the failure of the jointed granite is not affected by joint and stress-controlled failure occurs. The stress-structure-controlled time-dependent failure evolution enters a stage that is dominated by shear cracks earlier than stress-controlled failure according to AE results. In addition, the time-dependent failure went through stages of microcracks initiation and interaction, stable crack growth and unstable crack propagation. And when the time-dependent failure evolution enters the unstable crack propagation stage, the nature of the cracks changed from tensile-dominated to shear-dominated.

Influence of tunnel axis stress on mechanical response and fracture characteristics of rock surrounding tunnel subjected to gradient stress

Influence of tunnel axis stress on mechanical response and fracture characteristics of rock surrounding tunnel subjected to gradient stress