Nearby Tunnel Research Articles

Three-dimensional numerical analysis of twin tunnelling in two-layered soil strata

Tunnelling induces stress change and displacement in the ground. The excavation of a new tunnel in stratified soil can trigger different patterns of stress redistribution, which may adversely influence nearby tunnels. Research on multi-tunnel interaction has mainly been performed on the assumption of a uniform ground. The effects of different soil stratifications on tunnelling interaction remain poorly understood. In this paper, three-dimensional numerical parametric studies verified by previous centrifuge tests were carried out to analyse the twin tunnelling effects in two-layered soil. An advanced hypoplastic constitutive model that can capture stress-, path-, and strain-dependency of soil behaviour is adopted. Numerical cases investigated include perpendicular twin tunnelling in two sand layers with different relative densities and the location of the interface between the two sand layers. It is revealed that larger settlements and a wider surface settlement trough occur when tunnelling in two-layered soil strata than in a uniform ground. This is because of the wider and larger soil arch induced in two-layered soil strata. The structural response including tunnel deformation, induced bending moment, and induced hoop stress of the existing tunnel can be greater when tunnelling in layered soil strata than in a uniform ground owing to larger stress relief. Moreover, the combination of bending moment and hoop stress can exceed the M−N failure envelope of the structure in layered soil. A conventional simplified assumption of a uniform ground can underestimate of the influence of new tunnel excavation on existing tunnels, resulting in unsafe designs.

Numerical Simulation Study on the Impact of Deep Foundation Pit Excavation on Adjacent Rail Transit Structures—A Case Study

Excavation in foundation pits can result in serious issues for nearby tunnel structures like deformation, differential settlement, and seepage damage, which profoundly impact project timelines and potentially endanger life and property safety. Therefore, it is imperative to investigate these impacts before and after construction and to facilitate timely adjustments of construction measures and reinforcement where possible. In this study, a foundation pit construction project near a rail transit line is employed as a case to comprehensive study the impact of on-site deep foundation pit excavation on adjacent rail transit structures by numerical simulation. A three-dimensional finite-element model of the foundation pit based on site geological characteristics and construction procedures is established to study the excavation and maintenance processes. Through analysis of key parameters including soil deformation, displacement, shear force, and bending moment of the tunnel structures, the designed protective structure is found to have effectively mitigated soil deformation, ensuring the stability of the foundation pit. As excavation progresses, lateral soil deformation and vertical uplift gradually increase but remain within specified control values. During various excavation stages, the maximum displacement of the tunnel structure gradually increases, with the increase rates of maximum settlement being 29.09%, 20.51%, and 6.45%, respectively. This indicates a gradual enhancement of the stability of the tunnel structure. Additionally, excavation of the foundation pit has a significant impact on the bending moment distribution of the tunnel structure but does not affect the axial force and shear force of the tunnel structure. The findings of this study offer crucial scientific insights for evaluating the safety and stability of construction near tunnel structures.

WOA: Wombat Optimization Algorithm for Solving Supply Chain Optimization Problems

Supply Chain (SC) Optimization is a key activity in today’s industry with the goal of increasing operational efficiency, reducing costs, and improving customer satisfaction. Traditional optimization methods often struggle to effectively use resources while handling complex and dynamic Supply chain networks. This paper introduces a novel biomimetic metaheuristic algorithm called the Wombat Optimization Algorithm (WOA) for supply chain optimization. This algorithm replicates the natural behaviors observed in wombats living in the wild, particularly focusing on their foraging tactics and evasive maneuvers towards predators. The theory of WOA is described and then mathematically modeled in two phases: (i) exploration based on the simulation of wombat movements during foraging and trying to find food and (ii) exploitation based on simulating wombat movements when diving towards nearby tunnels to defend against its predators. The effectiveness of WOA in addressing optimization challenges is assessed by handling the CEC 2017 test suite across various problem dimensions, including 10, 30, 50, and 100. The findings of the optimization indicate that WOA demonstrates a strong ability to effectively manage exploration and exploitation, and maintains a balance between them throughout the search phase to deliver optimal solutions for optimization problems. A total of twelve well-known metaheuristic algorithms are called upon to test their performance against WOA in the optimization process. The outcomes of the simulations reveal that WOA outperforms the other algorithms, achieving superior results across most benchmark functions and securing the top ranking as the most efficient optimizer. Using a Wilcoxon rank sum test statistical analysis, it has been proven that WOA outperforms other algorithms significantly. WOA is put to the test with twenty-two constrained optimization problems from the CEC 2011 test suite and four engineering design problems to showcase its ability to solve real-world optimization problems. The results of the simulations demonstrate that WOA excels in real-world applications by delivering superior solutions and outperforming its competitors.

Comprehensive data set of in situ hydraulic stimulation experiments for geothermal purposes at the Äspö Hard Rock Laboratory (Sweden)

Abstract. In this article, a high-resolution acoustic emission sensor, accelerometer, and broadband seismometer array data set is made available and described in detail from in situ experiments performed at Äspö Hard Rock Laboratory in May and June 2015. The main goal of the hydraulic stimulation tests in a horizontal borehole at 410 m depth in naturally fractured granitic rock mass is to demonstrate the technical feasibility of generating multi-stage heat exchangers in a controlled way superiorly to former massive stimulations applied in enhanced geothermal projects. A set of six, sub-parallel hydraulic fractures is propagated from an injection borehole drilled parallel to minimum horizontal in situ stress and is monitored by an extensive complementary sensor array implemented in three inclined monitoring boreholes and the nearby tunnel system. Three different fluid injection protocols are tested: constant water injection, progressive cyclic injection, and cyclic injection with a hydraulic hammer operating at 5 Hz frequency to stimulate a crystalline rock volume of size 30 m × 30 m × 30 m at depth. We collected geological data from core and borehole logs, fracture inspection data from an impression packer, and acoustic emission hypocenter tracking and tilt data, as well as quantified the permeability enhancement process. The data and interpretation provided through this publication are important steps in both upscaling laboratory tests and downscaling field tests in granitic rock in the framework of enhanced geothermal system research. Data described in this paper can be accessed at GFZ Data Services under https://doi.org/10.5880/GFZ.2.6.2023.004 (Zang et al., 2023).

Evaluation of the Dynamic Stability of Underground Structures Assuming a Hydrogen Gas Explosion Disaster in a Shallow Underground Hydrogen Storage Facility

Amid the ongoing global warming crisis, there has been growing interest in hydrogen energy as an environmentally friendly energy source to achieve carbon neutrality. A stable and large-scale hydrogen storage infrastructure is essential to satisfy the increasing demand for hydrogen energy. Particularly for hydrogen refueling stations located in urban areas, technological solutions are required to ensure the stability of adjacent civil structures in the event of hydrogen storage tank explosions. In this study, a numerical analysis using equivalent trinitrotoluene (TNT) and Concrete Damage Plasticity (CDP) models was employed to analyze the dynamic behavior of the ground in response to hydrogen gas explosions in shallow underground hydrogen storage facilities and to assess the stability of nearby structures against explosion effects. According to the simulation results, it was possible to ensure the structural stability of nearby buildings and tunnel structures by maintaining a minimum separation distance. In the case of nearby building structures, a distance of at least 6 to 7 m is needed to be maintained from the underground hydrogen storage facility to prevent explosion damage from a hydrogen gas explosion. For nearby tunnel structures, a distance of at least 10 m is required to ensure structural stability.

Numerical analysis of the effect of ventilation door on the propagation characteristics of gas explosion shock waves

Ventilation door are commonly found in tunnels and other underground engineering ventilation structures, disaster periods using its explosion isolation, explosion relief, wind regulation characteristics for disaster prevention and mitigation is of great significance. This paper numerically simulates the propagation characteristics of the gas explosion shock wave in the nearby tunnel when the ventilation door are opened at different degrees, and analyzes the influence mechanism of the opening degree on the change law of the shock wave overpressure distribution in the nearby tunnel. The results show that the shock wave forms a strong turbulence area (high pressure area) on both sides in front of the ventilation door, and the area range and the overpressure value decrease with the increase of the opening degree; the ventilation door reduce the intensity of the shock wave, so that the overpressure behind the ventilation door decreases, and the smaller the opening degree, the lower the overpressure behind the ventilation door. The secondary explosion formed shock wave and the ventilation door reflected shock wave meet to form a stronger shock wave, which leads to different opening degrees of ventilation door, its before, after the roadway and after the bifurcation of the main roadway in the measured points of the overpressure change curve is different, the main difference is that the peak overpressure for the first wave or the second wave peak. The peak overpressure in the tunnel before and after the ventilation door decreases and increases respectively with the increase of the opening length, and the overall decay of the peak overpressure at 5 m and 10 m before the ventilation door is 49.56% and 4.04% respectively and only has an effect on the peak overpressure in main tunnel within 20 m from the bifurcation.

Induced Deformation and Protection of a Hybrid Timber–Masonry Historical Structure from Adjacent Metro Tunneling

The construction of the tunnels of Metro Line 4 and Gulou Station in central Nanjing poses a potential threat to the nearby historic building, Gulou Tower, due to the relatively small spacing and the deteriorated structure behaviors. Two aspects are important for the protection of Gulou Tower: (i) reducing the soil movement caused by the tunnel–station construction and (ii) increasing the total stiffness of this sensitive building. This research first presents the main features of two tunnels and the triple-arch tunnel as the connection between the two tunnels and Gulou Station. The details of the excavation means and construction procedures of the tunnels, together with the engineering measures that tend to reduce soil disturbance during tunnel excavation, are presented. Meanwhile, to improve the overall stiffness of Gulou Tower, additional support for the masonry terrace and the upper timber structure is also discussed. Moreover, the construction procedures of the tunnels and the station that could influence the settlement development of Gulou Tower are also suggested. The measured ground settlement and structure displacement are found to be limited to the allowable values, indicating that the aforementioned protective measures are adequate to protect hybrid timber–masonry historical structures nearby tunneling.

Testing and Analysis of the Vibration Response Characteristics of Heavy-Haul Railway Tunnels and Surrounding Soil with Base Voids

This paper discusses research on the dynamic response characteristics of a heavy-haul railway tunnel and the surrounding soil under the conditions of substrate health and a base void. The detection results of the base condition of 20 double-track tunnels for a heavy-haul railway show the main distribution law of base voids. Based on this, a 1:20 scale test model of a heavy-haul railway tunnel is established. The vibration load of the train is established by a vibration exciter arranged at the tunnel invert. The dynamic response and attenuation law of a heavy-haul railway tunnel lining structure and the surrounding soil are tested using acceleration sensors, strain gauges, and soil pressure boxes. The research results show that most of the diseases are concentrated below the heavy-haul line. The base void causes the peak acceleration of the nearby tunnel invert to increase by 55.6%. Tunnel annular construction joints reduce the conductivity of the vibration waves in the axial direction of the tunnel. The acceleration attenuation rate of the soil above the tunnel invert is significantly less than that under the invert. The base void reduces the acceleration of the nearby soil layer by 19.4% and increases the stress on the surface of the nearby tunnel invert by 21.3%, and the stress change amplitude increases by 0.55%. The tunnel structure in the area of the base void experiences fatigue damage. The base void causes the compaction and bearing capacity of the nearby soil to decrease and the softening speed of the tunnel basement soil layer to increase. Therefore, for the basement damage to heavy-haul railway tunnels, “early detection, early treatment” should be performed.

Numerical study on the lateral soil arching effect and associated tunnel responses behind braced excavation in clayey ground

This study uses numerical simulation to investigate the soil arching effect behind a braced excavation in clayey ground and derive an insight into the mechanisms behind the nearby tunnel responses. The numerical results are validated by field measurements of a well-documented case history. It is found that the lateral excavation-induced loosened zone is located behind the position with maximum wall deformation. The arching zone develops above the loosened zone and the stable zone is formed at the peripheral. Ground stress is transferred from the loosened zone to the adjoining stable zone and arching zone. The stress transfer along the arching zone drags the soil against the bracing and increases the lateral earth pressure around the upper part of the wall, where the soil is in passive stress state. The stress transfer along the shear plane increases the lateral earth pressure within the stable zone, where the soil is also in a passive state. The stress transfer induced by the minor principal stress arching in the loosened zone increases the radial load on the tunnel crown for the tunnel located entirely in the loosened zone. In addition, the tunnel deformation and bending moment associated with the arching effect are discussed.

Numerical investigation on the thermo-mechanical behaviour of twin energy tunnels

Energy tunnel provides an innovative and efficient approach to harvesting geothermal energy. Some investigations on a single energy tunnel have been reported in the literature. This study investigated the behaviour of twin energy tunnels in two configurations (i.e., parallel and perpendicularly crossing) by using a thermo-hydro-mechanical coupled numerical model developed and validated in previous work. The responses of ground and a tunnel (denoted by ET1) to three thermo-activation modes were determined: cooling ET1 itself alone (ET1active), cooling a nearby tunnel alone (ET2active), cooling both tunnels simultaneously ((ET1 + ET2)active). The computed results reveal that the interaction between two tunnels becomes negligible when the clear distance reaches four times the tunnel diameter. When the clear distance is smaller, the interaction could impact the tunnel and soil displacements. In ET1active and (ET1 + ET2)active, the vertical responses (i.e., ground settlement, ET1 settlement and vertical convergence) in both tunnel configurations can be close to or even exceed the allowable values in tunnel management guidelines, depending on ground and tunnel conditions. The horizontal responses of ET1 (i.e., horizontal displacement and convergence) are always insignificant. The thermo-activation of ET2 alone has minor effects on ET1, except a strong impact on ET1 settlement in the case of crossing tunnels.

Soil Heterogeneity Effects on Bridge Piles Deformation under Shield Tunnelling Disturbance

This research examines the impact of soil heterogeneity on the bridge piles beneath a nearby tunnel excavation using Monte-Carlo stochastic analysis. Sensitivity analysis is specifically used to the variation of stratum range, variation coefficient (COV), and fluctuation distance of the soil Young’s modulus. Meanwhile, the reliability evaluation approach is also applied to systematically examine the impact of COV on the likelihood of a pile failing. The findings suggest that more consideration should be given to the degree and range of geological parameter variations in the strata surrounding the tunnel. The horizontal and vertical fluctuation distances in this project are predicted to be around 18 m and 4.5 m, respectively. The fluctuation range influences the frequency of low stiffness zones in the soil. Additionally, the variation coefficient has a significant effect on the pile deformation, presenting a positive association. The pile deformation exhibits an increasing tendency in the wake of the growing variation coefficient. More significantly, the increase of the COV will directly lead to a rising failure probability of the pile settlement. According to extensive Monte-Carlo simulation calculations, the simulation results considering the variability of soil parameters have a certain deviation from the deterministic in the perspective of probability statistics. It is quite necessary to attach importance to the soil heterogeneity effects in the pile foundation stability under construction disturbance.

Numerical modelling of the response of two heritage masonry buildings to nearby tunnelling

Controlling building displacements induced by tunnelling is a major issue in densely urbanised areas, particularly for listed heritage structures. Major tunnelling projects provide opportunities to assess the ability of advanced numerical models to address this issue, in conjunction with the large amount of monitoring data that are gathered during the works. This paper considers the case of two Grade-I listed buildings (St. Mary Abchurch and Mansion House) affected by the Bank Station Capacity Upgrade in London (UK) where complex excavation works were conducted to improve the existing underground infrastructure. Both conventional and innovative monitoring was carried out to control the effect of tunnel construction on these buildings. Following the works, three-dimensional finite element analyses were conducted by adopting a semi-coupled modelling approach. In these analyses, the pre-existing damage in the buildings prior to tunnelling has been considered by adjusting the properties of embedded solids that are used to idealise the structure. The analyses also considered salient aspects that are often neglected in routine risk-assessment procedures, such as the excavation modelling sequence covering both pilot tunnelling and enlargement, the skew building-tunnel alignment, and the effect of closely spaced tunnel excavations on surface ground deformations. The results highlight the challenges associated with idealising historic structures with semi-coupled models; nevertheless, they encourage the integrated use of innovative monitoring systems and advanced numerical modelling as a tool to control the process of tunnel excavation in complex urban environments.

Цифровое моделирование аэроупругого взаимодействия подвижного состава с портальными сооружениями перевальных тоннелей

Purpose: Development of mathematical models allowing to investigate the processes of aeroelastic interaction of a rolling stock with portal buildings of passover tunnels in dynamic and quasi-stationary setting with the use of deformable mobile nets and FrozenRotor methods. Methods: we present mathematical models and ways of their realization in two- and three-dimensional setting in program complexes Comsol Multiphysics and Solid Works Flow Simulation on the basis of numerical solution of Reynolds averaged NavierStoks Method (RANS) method equations. Results: The results of numerical research of velocity and pressure fields nearby tunnel portal zone, obtained with the help of developed mathematical models for the case of rolling stock entrance into a tunnel, ‘re given. Practical importance: It’s revealed that at train entrance into a tunnel, air mass runaway by a rolling stock is made with significant delay owing to effect of viscous friction force between an air and tunnel walls as well as inside air volume which fills a tunnel.

Influence of tunnel failure on the existing large-diameter tunnel in improved soil surround

In this paper, the effect of failure of a temporary opening on the stability of nearby existing large diameter tunnel in cement-treated soils is discussed. Firstly, the centrifuge model set-up and procedure for studying the interaction of large diameter parallel tunnels in improved soil surround were developed. The stability of existing first tunnel, stress-redistribution around the first tunnel and influence zone due to the failure of second tunnel were studied. The results of the centrifuge tests were then used to develop a numerical model in a geotechnical finite element software package GeoFEA version 9 for parametric studies. The dominant failure mode of improved soil surround, stress redistribution in surrounding soil as well as the surface deformations obtained from the finite element analysis were found to be similar to the observations from centrifuge tests. The influence of failure of second tunnel was evident when the spacing between the two tunnels was kept as 2.3 times the tunnel diameter even for the stronger and thicker first tunnel. On the other hand, the influence of failure of second tunnel was found to be negligible when the spacing between the tunnels was increased to 3 times the tunnel diameter, for both the stronger and weaker first tunnel. The distortion in the first tunnel was observed as asymmetric ovalization for centre-to-centre spacing of 2.3 diameters or less, but was absent for spacing of 3.0 diameters with cover-to-diameter ratio of 1.25. Larger spacing is necessary for deeper tunnels to eliminate the interaction effects due to failure of nearby tunnel.

An analytical model for face stability of tunnels traversing the fault fracture zone with high hydraulic pressure

The issue of tunnel face stability traversing the fault fracture zone with high hydraulic pressure has been addressed based on a new three-dimensional limit equilibrium model. First, the finite element numerical simulation is conducted to reveal the effects of the differences in permeability coefficient of strata on both sides of the geological interface on the distribution of seepage flow field nearby tunnel face. With this discovery, an existing universal approximate formula for hydraulic head nearby tunnel face is modified to accurately calculate the hydraulic head distributions under this scenario. Second, introducing the effect of geological interface, a new limit equilibrium model that consists of a trapezoid and a prism is proposed. The distributed loading exerted by the prism upon the trapezoid is deduced by considering the effects of seepage force and geological interface. Then, limit support pressure is derived according to the limit equilibrium state of the trapezoid. Finally, the comparison of the predicting results of the proposed limit equilibrium model with the results of the numerical simulations and the existing failure mechanism is performed, which indicates that the proposed trapezoid-prism model can well predict the tunnel face stability traversing the fault fracture zone with high hydraulic pressure.

Foundation enhancement for reducing tunnel-building seismic interaction on soft clay

Seismic tunnel-soil-building interaction in high plasticity soft clays can led to important ground motion variability that affect medium to low rise buildings located adjacent to the underground structure. This paper presents a numerical study aiming at establishing the performance of an enhanced foundation system to be used as a mean to reduce detrimental interaction and enhanced the seismic performance of mid to low buildings located nearby tunnels. Initially, interaction effects are revised considering the effect that frequency content, intensity, and strong ground motion duration have on the interplay between incoming seismic waves reflected in the tunnel, and the energy feeding back from the building swinging back and forth during a large earthquake. Series of three-dimensional finite difference models were developed. Seismic analyses considered both normal and subduction events with a return period of 250 years were carried out. Finally, the seismic performance of the enhanced foundation system was established. From the results gathered in here, it was clearly established the effectiveness of the proposed system to reduce both foundation ground motions and building seismic demand.

Deep learning based method of longitudinal dislocation detection for metro shield tunnel segment

This paper presents a longitudinal dislocation detection method using an accurate tunnel segment joint labeling algorithm featured by deep CNNs (Convolutional Neural Networks). This method is proposed to be four steps. First, a mobile scanning system is used to acquire 3D point clouds of metro shield tunnels. Then, we use cylinder projection to generate tunnel surface depth images from 3D point clouds for segment joint labeling. Subsequently, two deep CNNs are designed to accurately label the segment joints on the depth images. The first CNN can roughly locate the segment joint positions, and the second precisely label the segment joints. Based on the labeled segment joints, two point data sets are obtained on both sides of each segment joint. By using the RANSAC algorithm, the two point sets can fit into two planes, the equation of which is then calculated to generate the dislocation value of the tunnel segment. Experiment results show that this method can label segment joints integrally and accurately without being affected by nearby tunnel equipment. Compared with traditional image edge detection algorithms (Canny and Sobel with Hough Transform), the CNNs are more powerful in labeling segment joints. When the distance measuring accuracy of scanner is 1.2 mm + 10 ppm, the internal and external accuracy of our detection method are evaluated to be 0.4 mm and 0.9 mm respectively. Compared with the scanning line method, the external accuracy of our method is higher and more reliable when there is tunnel equipment around segment joints.

Innovative monitoring of the response of a heritage masonry building to nearby tunnelling in London Clay

Heritage masonry structures require detailed monitoring during nearby underground construction, to address the concerns of building owners and mitigate uncertainties relating to the soil–structure system. This paper discusses innovative displacement and strain monitoring of a listed masonry church undergoing ground movements due to nearby tunnelling in London Clay. In addition to conventional surveying and tilt monitoring, laser scan displacement monitoring and fibre optic strain sensing was conducted. Prior to construction, point clouds of the structure were used to map pre-existing geometric distortions in the structure. During construction, detailed monitoring of displacements and strains was conducted across the building facades and the tower. The same techniques were also used to monitor the painted dome of the church where conventional displacement monitoring was not feasible. With a focus on the new engineering insight provided by the innovative monitoring techniques, the impact of the underground construction activities on the church is discussed in this paper. The proposed sensing techniques provide new data on the influence of pre-existing damage and tunnel advance on soil–structure interaction.

Cracked Equivalent Beam Models for Assessing Tunneling-Induced Damage in Masonry Buildings

This paper proposes simple numerical models that simulate the influence of tunneling-induced ground movements on masonry buildings founded on shallow strip footings. The focus is on developing an improved understanding of the impact of structural discontinuities due to pre-existing cracks and joints between adjacent buildings. The soil–structure system is idealized with equivalent Timoshenko beams connected to a homogenous elastic half-space with rigid links. The flexibility of the equivalent beam at the location of the crack or building interface is determined using linear-elastic fracture mechanics. The proposed models are first applied to a generic numerical example. Then, they are used to interpret the detailed displacement and strain measurements gathered from a masonry church during nearby tunneling. The results show that pre-existing cracks can have variable influence on the soil–structure interaction depending on their extent and position relative to the building and settlement trough. For the investigated case study, the proposed models illustrate how pre-existing large cracks in the hogging zone localized deformations and how the interaction between adjacent buildings drastically altered response mechanisms.

Simulating the effects of braced excavation on the adjacent tunnel using numerical method

It is inevitable that the construction of braced excavation is in the vicinity of existing tunnels. Therefore, it is necessary to assess the influence of braced excavation on the nearby tunnel. Using two-dimensional (2D) numerical method, this study is conducted to investigate the response of existing tunnel induced by overlying excavation. A series of scenarios are carried out, with consideration of relative locations of tunnel with respect to overlying excavation. The results demonstrate that different distortion of the tunnel will occur with the variety of relative locations between the tunnel and the braced excavation. Additionally, the excavation-induced tunnel responses show a decrease trend with an increase distance between the tunnel and excavation. In this regard, the study can provide a useful reference for evaluating the influence of braced excavations on nearby structures.