Tunnel Portal Research Articles

Attribute recognition model and its application of risk assessment for slope stability at tunnel portal

Due to large span and complex construction technology, the portal section of tunnel is vulnerable to the threats of latent slope failures such as landslide, spalling and collapse. In the present paper, to ensure the construction safety of tunnel, the attribute recognition model of risk assessment for the slope stability at tunnel portal was established by using attribute mathematics theory. The integrated degree of rock mass, lithological feature, geological structural feature, weathering degree, seismic intensity, gradient, rainfall and construction factors were selected as the indices of the risk assessment for the stability slope at tunnel portal with grading criteria of each index. Moreover, the weights of the assessment indices were determined by the judgment matrix constructed from analytic hierarchy process. The attribute measurement functions were used to compute attribute measurement of single index and synthetic attribute measurement. The identification and classification of risk assessment for the slope stability at tunnel portal were assessed using the confidence criterion. For practical purposes, the stability of slope located in portal of an actual Tunnel, i.e., Jiefangcun Tunnel in Cheng-Lan Railway, was evaluated based on the previously established attribute recognition model. The corresponding risk treatment measures were then proposed based on the assessment results and monitor results to ensure the construction safety of tunnel portal.

Oblique tunnel portal effects on train and tunnel aerodynamics based on moving model tests

The objective of this study was to investigate the effects of oblique tunnel portals on train and tunnel aerodynamics using a 1:20 scale moving model device. Transient pressure and micro-pressure waves were measured using pressure sensors as the train model travelled through various tunnel models at a speed of 350km/h. The mitigation physical mechanism of oblique tunnel portal on the initial compression wave was explained. Experimental results showed that oblique tunnel portals had obvious mitigation effect on- the pressure gradient and micro-pressure wave induced by the train model passing through the tunnel model. A hat oblique tunnel portal combined with a buffer structure with top holes was particularly effective.

Numerical investigation on an array of Helmholtz resonators for the reduction of micro-pressure waves in modern and future high-speed rail tunnel systems

Previous research has proposed that an array of Helmholtz resonators may be an effective method for suppressing the propagation of pressure and sound waves, generated by a high-speed train entering and moving in a tunnel. The array can be used to counteract environmental noise from tunnel portals and also the emergence of a shock wave in the tunnel. The implementation of an array of Helmholtz resonators in current and future high-speed train-tunnel systems is studied. Wave propagation in the tunnel is modelled using a quasi-one-dimensional formulation, accounting for non-linear effects, wall friction and the diffusivity of sound. A multi-objective genetic algorithm is then used to optimise the design of the array, subject to the geometric constraints of a demonstrative tunnel system and the incident wavefront in order to attenuate the propagation of pressure waves. It is shown that an array of Helmholtz resonators can be an effective countermeasure for various tunnel lengths. In addition, the array can be designed to function effectively over a wide operating envelope, ensuring it will still function effectively as train speeds increase into the future.

Analytical solution for the stress and deformation of rock surrounding a cold-regional tunnel under unequal compression

Frost damage is one of the main factors to affect the stability of cold-regional tunnels. It often occurs in the tunnel portal where the horizontal stress and vertical stress are generally not equal. To ensure the construction safety of cold-regional tunnels and to propose new theoretical insights for their analysis and design, an analytical calculation model for a cold-regional tunnel under unequal compression is established in this paper. During the analysis process, this model is decomposed into an excavation model and a frost heaving model. The excavation model is solved using a complex variable function method. Combining the supplemental equation built by the numerical results, the frost heaving model is also addressed using an iteration method. The total stress and deformation are obtained by the superposition of the results of the two models. An example is introduced to obtain the stress field of the lining and surrounding rock of cold-regional tunnels. The reason for the size relation between the radial stress and the circumferential stress at different angles is explained. Then, the range for the negative circumferential stress at different angles is determined. Moreover, the conclusion is also drawn that the radius of zero frost heave displacement is independent of the linear strain induced by frost. Finally, it is found that frost heave induced an incremental stress difference in the lining, which results in damage to lining. The calculation method and results can provide a guide for the construction of cold-regional tunnels.

Analysis of the aerodynamic effects of different nose lengths on two trains intersecting in a tunnel at 350 km/h

The three-dimensional compressible Navier-Stokes equation and k-ε turbulence model are used to simulate the flow and pressure waves caused by two trains passing each other in a tunnel. The simulation results were verified by comparison with the results of a full-scale experiment. This simulation results indicate that the positive peak of the initial compression wave on the tunnel wall has a logarithmically decreasing trend with increasing nose length. This tendency is more obvious near the tunnel portal than in the tunnel, and the positive peak caused by a train with a nose length of 12m at a distance of 20m from the tunnel entrance is 10.26% less than that caused by a train with a nose length of 4m. Throughout the intersection process, the peak-to-peak amplitude of body surface pressure decreases with increasing longitudinal distance from the front nose tip. The influence of different nose lengths on the surface pressure on the train body is mainly concentrated at the front and rear of the train. The fluctuation amplitude of the surface pressure on the head car with a 4m nose is 1.63 times that of a head car with a 12m nose. The amplitudes of the lateral force and overturning moment are also influenced by the nose length, with the strongest effect on the head car and a stronger effect on the middle car than on the tail car. A shorter train nose results in a more significant influence on the train total drag. As the nose length changes from 4m to 7m, the maximum total drag decreases by 6.71%; however, as the nose length changes from 9m to 12m, the maximum total drag decreases by only 0.16%.

Rock Mass Classification and Assessment of Stability of Critical Slopes on National Highway-22 in Himachal Pradesh

ABSTRACT Rock slopes require geo-engineering evaluation to assess the instability of critical slopes leading to landslides particularly in Himalayan terrain where rocks are highly jointed, fractured and weathering prone. Interplay of discontinuities in the rocks coupled with other parameters is one of the prime causes of failure of slopes. Engineering rock mass classification, such as, rock mass rating (RMR) and slope mass rating (SMR) along with geological strength index (GSI) have widely been used for stability assessment of rock slopes above tunnel portals, and these classifications are employed here for assessment of stability of slopes of critical nature along Rampur-Powari highway in Himachal Pradesh. In the present study, out of 154 numbers of slopes, a total of 29 have been selected for assessment of their criticality by employing RMR, SMR and GSI.

Anatomıc femoral tunnel drilling in acl reconstruction without using of an accessory medial portal and evaluation of femoral tunnel positioning using 3-d computed tomography

Background and Purpose:Characterization of the insertion site anatomy in anterior cruciate ligament reconstruction has recently received increased attention in the literature, coinciding with a growing interest in anatomic reconstruction. The purpose of this study is to report a modified novel transportal technique to approach the center of anatomical femoral footprint in anterior cruciate ligament (ACL) reconstruction and to investigate the accurate femoral tunnel position with 3-dimensional computed tomography (3D-CT). Materials-Methods: We evaluated 11 patients who underwent primary ACL reconstruction using a modified transportal technique to approach the center of anatomical femoral footprint in single bundle ACL reconstruction with hamstring autograft. Their femoral tunnel positions were investigated with 3D-CT postoperatively according to the quadrant method by three orthopedic surgeons.Results:According to the quadrant method with 3D-CT, the femoral tunnel was measured at a mean of 33,49% ± 5,59% from the proximal condylar surface (parallel to the Blumensaat line) and 32,93% ± 3,82% from the notch roof (perpendicular to the Blumensaat line) with good interobserver (intraclass correlation coefficients [ICC], 0,991and 0,858, respectively with 0,975 – 0,997%95 CI) and intraobserver reliability (ICC, 0.875 and 0.893, respectively with 0,663 – 0,956%95 CI).Conclusions:Our modified transportal technique is anticipated to provide anatomical placement of the femoral tunnel during ACL reconstruction than the former traditional transtibial techniques. This technique is reproducible and also easier to perform than classic transportal technique does not need extra arthroscopic portal.3D

Monitoring of Transport Tunnel Deformation at the Construction Stage

The analysis of normative documents related to geodetic support of transport tunnel construction showed that for now there are no integral monitoring methods providing surface tunnel structure observation. Therefore, the authors substantiate a new technological scheme of geodetic monitoring of portal parts of a tunnel under construction. To collect data about displacements of tunnel portal structures it is suggested that control points should be fixed by reflective tape or rotating prisms, and their coordinates should be located in an object's coordinate system. It is suggested that an original geodetic base should be fixed as geodetic points of forced centering out of zone of virtual deformations. Deformation control benchmarks heights should be measured by trigonometric leveling. It is shown that RMS error in measuring the heights of points of geodetic monitoring network should not exceed 4mm. It is found that required accuracy in network building can be provided by III class leveling. To collect data about the depth of weak soils, located close to tunnel portals, as well as the borderlines of their sliding, it is for the first time suggested that surveys should be conducted using borehole inclinometer. The research proves that on pre-portal sites boreholes should be placed close to the group of deformation control benchmarks.

Numerical investigation of Pollutant Dispersion around two Adjacent Super-long Urban Road Tunnels

Super-long urban road tunnels have become prevalent in China recently. This study established a three-dimension CFD model containing two adjacent super-long urban road tunnels to estimate characteristics of pollution dispersion outside the tunnels. The results indicated that crossflow between two adjacent tunnels was quite severe, which contributed to carbon monoxide concentration was almost 50 ppm exceeding the 10 ppm limit of National Standard in China for 1h exposure level when exhaust shafts were absent. When the shafts exhausted 80% pollutants from the tunnel portal, crossflow between two adjacent tunnels could at least decrease to 20% of the conditions without shafts. The simulation results could not only demonstrate the importance of shafts for super-long urban road tunnels, but also provide a fundamental and guideline for evaluation of urban environment and design of the tunnel exhaust shafts, including locations and types.

Two-dimensional Finite Element Based Parametric Analysis of South Portal Slope, Rohtang Tunnel, India

Slope failures associated with large-scale displacements and high strains in geomaterials have often resulted in large loss of life and properties in the Himalayan terrain. These slope failures bear a substantial relation to high-intensity rainfall events [1].One such slope is located at south portal of Rohtang tunnel, numerous slope failures due to the effect of fluctuating water table and rainfall events had already occurred. This paper describes variation in strength reduction factor (SRF) by a two-dimensional finite element based numerical modelling under four dominate strength reduction parameters. A total of one thirty-five analysis has been performed to obtain SRF values considering two sets of parameters. Three type of rocks constituting the slopes are Phyllitic quartzite, Quartzitic phyllite and Migmatite gneiss. Physico-mechanical behaviour of these rocks are investigated as per ISRM and BIS standards. The role of pore water pressure, joint inclination, slope angle and water table within the slope and its effect on failure is discussed in this paper.

入口緩衝工があるトンネル坑口から発生する新幹線騒音の評価

入口緩衝工があるトンネル坑口から発生する新幹線騒音の評価

Impact of operation on the geometric parameters of the track in ballastless track transition area

The paper deals with the methodology and results of diagnostics in test sections near the tunnel portals of newly built tunnel Turecký vrch on modernized line Nove Mesto nad Vahom – Puchov. Based on the diagnostics results, transition areas are problematic sections of the construction. Transition areas were subjected to detailed analysis and based on trends of the development of geometric quantities are determined trends which predict time of needed maintenance. In order to optimize existing transition areas the design of transition in ANSYS software was modelled and problematic spots of construction were defined.

Acoustic model of micro-pressure wave emission from a high-speed train tunnel

The micro-pressure wave (MPW) radiated from a tunnel portal can, if audible, cause serious problems around tunnel portals in high-speed railways. This has created a need to develop an acoustic model that considers the topography around a radiation portal in order to predict MPWs more accurately and allow for higher speed railways in the future. An acoustic model of MPWs based on linear acoustic theory is developed in this study. First, the directivity of sound sources and the acoustical effect of topography are investigated using a train launcher facility around a portal on infinitely flat ground and with an infinite vertical baffle plate. The validity of linear acoustic theory is then discussed through a comparison of numerical results obtained using the finite difference method (FDM) and experimental results. Finally, an acoustic model is derived that considers sound sources up to the second order and Green's function to represent the directivity and effect of topography, respectively. The results predicted by this acoustic model are shown to be in good agreement with both numerical and experimental results.

Simulating the Impacts and Assessing the Vulnerability of the Central Artery/Tunnel System to Sea Level Rise and Increased Coastal Flooding

Highway tunnels along the coast are critical infrastructure and represent one of the more sensitive components of a transportation network to coastal flooding. By their very nature, large portions of these tunnels are beneath present sea level and the tunnel entrances and the equipment necessary to operate the tunnels such as vent buildings may or may not be above present flood thresholds. The Central Artery/Tunnel (CA/T) system in coastal Boston, Massachusetts USA is a vital link in the regional transportation network and is comprised of more than 160 lane-miles (more than half of them in tunnels), 6 interchanges and 200 bridges. While not examined here, the CA/T system relies upon other infrastructure systems to fully function, such as the electrical grid. The ADvanced CIRCulation model (ADCIRC) coupled with the Simulating WAves Nearshore (SWAN) Model was used for storm surge modeling. SLR scenarios were selected for four distinct time periods (2013, 2030, 2070, and 2100) to bracket the potential future sea level rise outcomes for the Boston Harbor area and a Monte Carlo statistical approach was utilized to estimate the probability of flooding throughout the Boston Harbor region. The vulnerability analysis was based solely upon exposure, defined as flooding experienced at CA/T systems when at the thresholds of the design flood standards that governed the original design of the CA/T. The extent of flood vulnerability under current climatic conditions is fairly limited with low exceedance probabilities. By late 21st century, however, there is considerable flooding at Tunnel Portals and other buildings and structures. Both local adaptation options such as flood walls protecting individual assets or gates protecting tunnel portals and regional plans blocking major flood pathways were evaluated. In complex systems such as the CA/T, the number and spatial extent of vulnerable areas increase over time as sea level rises and the intensity of storms increase, suggesting that local adaptations may be most applicable in the near-term and regional based adaptations (safeguarding multiple areas for multiple stakeholders) will become more cost effective and necessary solutions in the long-term. Focusing first on local actions also means that the CA/T owner is less reliant on other organizations and agencies to manage the CA/T adaptation as it will own the land necessary for any changes and will only have to manage its own efforts. The regional plan has the co-benefits that it will protect more assets in the region than just the CA/T and there is the possibility that the cost can be shared among more agencies and organizations than just the owner.

Instability Mechanism of Du Yun Pass Tunnel Entrance Weathered Stacking Area Analysis

The stability of the tunnel portal section under poor terrain and geological condition has always been the focus of construction safety. The stability problem has become more complex for the erosion accumulation area under the valley. In this paper, firstly the stability of the tunnel portal is classified. Combined with engineering cases, the FEM numerical method is used to simulate the supporting structure and construction process of the tunnel. Based on the distribution of the plastic zone and displacement of surrounding rock, the mechanism of the instability of the tunnel portal is analyzed. Through the optimized construction scheme that arranges pile foundation in tunnel arch foundation, the bearing capacity of foundation has been greatly improved, which has effectively prevented the instability of surrounding rock caused by the slope deformation and foundation settlement. The conclusions that have been drawn in this paper can be used for reference for related projects.

Shaking table tests on seismic measures of a model mountain tunnel

A series of three dimensional (3D) shaking table tests were carried out to investigate the mechanism and effect of seismic measures of mountain tunnel using a scaled model based on a real tunnel. Key technical details of the experiment, including similarity relations, seismic measures simulation, boundary conditions, sensor layout, modeling methods, and ground motion input were presented. Main seismic measures, including reinforcing surrounding rock with anchors, increasing lining flexibility with steel wire mesh, and installing seismic isolation layer between reinforced surrounding rock and tunnel lining, were investigated in this study. Experiment results show that: (1) adding a layer of steel wire mesh in the tunnel lining can improve the flexibility and seismic performance and also may effectively prevent radial cracks from crossing the lining; (2) installing a geofoam isolation layer between the reinforced surrounding rock and the tunnel lining reduces dynamic earth pressure by 70–90% for the lining without a seismic isolation layer; (3) the flexible joints can effectively avoid global failures of tunnel lining for they reduce dynamic strain and bending force in the tunnel lining and decrease the seismic energy transmission along the lining in axial direction; (4) reinforcing surrounding rock with anchors significantly reduces dynamic earth pressure and strain of the lining by about 50%. In addition, the length of seismic reinforcement for general mountain tunnel portal is recommended to be 50m from the tunnel portal along the axial direction.

Application of Hyperstatic Reaction Method for Designing of Tunnel Permanent Lining, Part II: 3D Numerical Modelling

Underground structures often have abrupt changes in structural stiffness or ground conditions such as junctions of tunnels, tunnel portal in slopes, and niches in road tunnels. At these locations, stiffness differences may subject the structure to differential movements and generate stress concentrations. Because of adversity in these issues, they need a three dimensional analysis. This paper proposes a numerical approach to the hyperstatic reaction method (HRM) for three dimensional analysis of permanent tunnel linings. In this paper, three dimensional numerical modelling is performed by considering hyperstatic reaction concepts. Designing is done for Manjil-Rudabar freeway project, Tunnel No. 2. The numerical analyses performed for Operational Design Earthquake (ODE) and Maximum Design Earthquake (MDE) loading conditions. Then interaction diagram between axial force and bending moment used for investigating the capacity of tunnel lining. The numerical results show that although more axial forces are created in tunnel lining for ODE condition, but the points in the P-M diagrams are located in the furthest distance to the diagram border (tunnel supporting system); because of less bending moment in this condition. Therefore, the safety factor in ODE condition is more than MDE condition. This numerical processing presented that the HRM is a proper, fast, and practical method for tunnel designers.

Importance of Results Obtained from Geotechnical Monitoring for Evaluation of Reinforced Soil Structure – Case Study

Abstract In the case of realized geotechnical monitoring (GTM) of reinforced retaining wall in difficult geological conditions is demonstrated the important role at realisation of transport infrastructures, which are often realized in insufficient quality due to inappropriate geotechnical parameters from survey works or not fitted well design of structure at certain conditions. This can result in large deformations of structure, or losing stability or structure life-time is very limited and remediation work is complicated and expensive. There was built on the modernized railway line Bratislava – Trenčín, closed to Zlatovce, overpass and connected road embankments on the route of first class I/61. Structure was designed as a bridge over the railway track before the northern portal of the railway tunnel Turecký vrch was open. A part of the embankment and overpass was a retaining wall reinforced by geosynthetics. The results of the geotechnical monitoring of this wall were afterwards simulated using finite element method (FEM) and results of this comparison are the scope of this article.

Occupational Safety and Health in Tunnelling in Rocks Formations Potentially Containing Asbestos: Good Practices for Risk Assessment and Management

In tunnelling operations, Occupational Safety and Health (OS&H) and Environmental Protection of the areas close to the tunnel portal become even more critical in case of rock formations potentially containing asbestos, quartz, radioactive elements, etc. In order to limit the workers’ exposure and the environmental impact becomes in these cases of paramount importance to preliminarily analyze and quantify the possible presence of the pollutants in the rock and, if necessary, to implement suitable measures to avoid/minimize their emission from the winning and mucking operations. However, in case of asbestos minerals, to obtain reliable results from the preliminary analysis is a challenging task, due to the complex patterns of occurrence of asbestos within the host rock. Consequently, the definition of special monitoring, alarm and control systems is essential during the tunnel excavation. The paper summarizes the results of a thorough study aimed at defining the most suitable monitoring techniques in uncertain situations and the residual criticalities, essentially due to the delay between the beginning of the pollutant release at the tunnel face and its detection. The final part of the work deals with the possible innovative prevention solutions suitable to minimize the previously mentioned delay and ensure the safety of the workers along the time necessary to stop the activities and evacuate the tunnel, on hold of the activation of a special “asbestos” organization.

NATM터널의 공종별 환경부하 특성 분석

국내 외 기후변화 대응 체제의 강화에 따라 전 세계적으로 온실가스 감축을 위한 노력을 기울이고 있다. 건설 분야에서는 건축물을 중심으로 온실가스 저감을 위한 연구가 활발히 이루어지고 있으나, 온실가스 이외에 지구환경에 영향을 미치는 각종 오염물질을 고려한 종합적인 환경부하 저감을 위한 연구는 다소 부족하다. 이에 본 연구에서는 NATM터널을 대상으로 LCA (Life Cycle Assessment, 전과정 평가) 방법론을 이용하여 공종별 환경부하 특성을 분석하였다. 분석 결과, 라이닝콘크리트공, 숏크리트공, 갱문 및 개착터널 등 7대 공종이 NATM터널의 주요 환경부하 공종으로 나타났으며 전체 환경부하량의 89.22%를 차지하는 것으로 나타났다. 또한 대표공종들의 연장(m)당 환경부하량을 산정하여 비교 분석한 결과 개착구간에 해당하는 갱문 및 개착터널 공종의 환경부하량이 가장 큰 것으로 나타났으며, 전체 터널 구간을 대상으로 할 경우 라이닝콘크리트공과 숏크리트공에서 환경부하량이 많이 발생하는 것으로 분석되었다. 본 연구의 결과는 설계초기단계에서 환경부하 대표공종의 물량을 개략적으로 산출하여 전체 환경부하량을 추정하는 모델 개발 시 활용할 수 있을 것으로 판단되며, 향후 친환경 SOC건설을 위한 환경부하 관리방안을 수립하는데 큰 역할을 할 것으로 기대된다. Many countries are trying to reduce a greenhouse gas to step up their fight against climate change. There are many studies related to building only for reducing a greenhouse gas in construction area but studies related to reducing a comprehensive environmental load including various pollutants that affects the global environment are lacking. This study aims to analyse the characteristics of environmental load by work type for tunnel projects. Analysis showed that seven work types, including lining concrete, shotcrete, tunnel portal and open-cut tunnel work, etc., are representative works generated environmental load. These seven works represent 89.22 percent of total environmental load. In addition, comparison results of environmental load per tunnel's length by work type showed that a major factor of environmental load is caused by a tunnel portal and open-cut tunnel work with relatively short length (excavation length). And lining concrete and shotcrete work are larger than any other environmental load with tunnel's total length. It is expected that the result of this study will be used to make a estimation model for environmental load using approximate quantity survey of representative work types in the early stage of tunnel design. And it will be play a considerable role in establishing of environment management plan for sustainable infrastructure construction.