Cover Tunnel Research Articles

FE analysis of the influence of sliding on the seismic strain transfer ratio between the ground and cut and cover tunnels in contact with bearing stratum

FE analysis of the influence of sliding on the seismic strain transfer ratio between the ground and cut and cover tunnels in contact with bearing stratum

Rotational springs for localized crack modeling in structural concrete

AbstractThis paper presents a mechanical and numerical approach to model localized deformations occurring in concrete structures with less than minimum reinforcement. The presented models are based on, and validated against large‐scale experiments conducted in a previous study to investigate the behavior of a less than minimally reinforced slab in the framework of the structural safety assessment of an existing cut and cover tunnel. The model deploys rotational springs embedded in a nonlinear finite element analysis to capture deformations concentrating in an inclined crack. An iterative solution procedure ensures equilibrium and compatibility in the inclined crack section by adjusting the spring stiffnesses, which depend on the acting loads. A case study shows that the localized crack has a minor effect on the global structural behavior. In contrast, localization strongly influences deformations and stress resultants in the crack, and compressive membrane action significantly impacts the load–deformation behavior of the localized crack, which is relevant particularly for the shear strength.

Developments in Seismic Vulnerability Assessment of Tunnels and Underground Structures

Underground structures are being constructed at an increasing rate in seismic prone areas, to facilitate the expanding needs of societies. Considering the vital role of this infrastructure in densely populated urban areas and interurban transportation networks, as well as the significant losses associated with potential seismically induced damage, its assessment against seismic hazard is of great importance for stakeholders, operators, and governmental bodies. This paper presents a state-of-the-art review of current developments in the assessment of seismic vulnerability of tunnels and underground structures. Methods for the development of fragility functions for the assessment of bored tunnels in rock or alluvial, and cut and cover tunnels and subways in alluvial, against ground seismic shaking and earthquake-induced ground failures are presented. Emphasis is placed on the estimation of the capacity of the examined structures, the selection of appropriate intensity measures to express seismic intensity, the development of rational probabilistic seismic demand models and the estimation of epistemic and aleatoric uncertainties, related to the seismic fragility of underground structures. Through the discussion, acknowledged gaps in the relevant literature are highlighted.

Effect of geofoam as cover material in cut and cover tunnels on the seismic response of ground surface

Effect of geofoam as cover material in cut and cover tunnels on the seismic response of ground surface

Roertunnel: Tunnel elements constructed in building pit for in situ part of tunnel

The construction of the A73 highway from Venlo to Maastricht (the Netherlands) involved the construction of the 2.4 km long, dual two lane Roertunnel near the city of Roermond. The Roertunnel consists of a somewhat deeper part crossing the quite small River Roer and its 1 km wide flood Valley, continued by a 1.4 km long shallow tunnel alongside the southern part of Roermond. The water levels in the River Roer vary from low water (summer conditions) to high water levels and possibly flooding of the Valley (spring conditions). Environmental conditions were severe, prohibiting amongst other for dewatering.The project was tendered the Ministry of Public Works and Water Management (Rijkswaterstaat RWS as a design and build contract. The tender documents included a reference design developed by the client for the crossing of the Roer Valley. This design consisted of a cast in situ piled cut and cover tunnel constructed in a building pit formed by temporary sheet piles and closed off at its bottom by a unreinforced concrete slab supported by tie down piles. This concept was designed to avoid dewatering of the building pit.In view of the ground conditions, an immersed tunnel was a more cost effective solution compared to the proposed reference design. However, an immersed tunnel appeared at a first glance not to be feasible as the small depth and width of the River Roer does not allow transportation of tunnel elements over the River from any remote dry dock, and as a dry dock in the vicinity of the tunnel location could not be created as dewatering was not allowed. The careful analysis of the geotechnical data indicated the local presence of a 5 m thick silt layer of low permeability over a length of 350 m along the tunnel alignment at the eastern side of the Roer Valley. This offered the opportunity to create a dry dock of length of about 350 m along the alignment of the tunnel by means of sheet piles reaching into the silt layer, avoiding any dewatering. The dry dock has been used for the construction of the four immersed elements of a total length of about 600 m in two batches. Finally the dock was used to construct the remaining part of the crossing of the Valley as a cast in situ tunnel.A gravel bed foundation consisting of nine berms per tunnel segment has been preferred above sand flow to mitigate the risk of weakening of loose sand in case of earthquake.The paper describes the concept and the various aspects of the design of the immersed tunnel constructed in a dry dock along the tunnel alignment. A section of the paper is devoted to the interaction of structural design and gravel bed design.

Attenuation Potential of Geofoam as Cover Material in Cut and Cover Tunnels during Earthquakes

ABSTRACT In this paper, attenuation potential of expanded polystyrene (EPS) geofoam as the embankment material of cut and cover tunnels during static and dynamic loads was assessed by a series of numerical analyses, verified against experimental study. The geofoam is found to have excellent capabilities to attenuate the static and dynamic loads of the tunnel lining. The layout of the geofoam directly influences its attenuation potential. The efficiency of the geofoam is increased as the level of the acceleration of the input motion increases. The study demonstrates that the geofoam performs well as a protective material for underground tunnels during earthquakes.

Waterproofing for buried decks

Buried decks are an increasingly common feature in the modern built environment. This increase may be partly attributed to growing awareness of the need for sustainability. Green roofs, sustainable urban drainage, water attenuation and even parks and farms are being located on top of ground floor roof structures and cut and cover tunnels. Waterproofing of these decks is vital in order to use the space created beneath and, also, to prolong the life expectancy of the structure.This research explores some of the available best practice guidance and then compares the key waterproofing design features with opinions from industry. Opinions are gathered through seventy-eight questionnaire respondents made up of UK based professionals dealing with waterproofing of buried decks.This research suggests that buried deck waterproofing design can reduce risk by employing the following features: (a) reinforced concrete structural deck, (b) fully-bonded waterproofing membrane, (c) waterproofing laid to a gradient to falls, and (d) provision of a drainage void over the waterproofing layer.As a result of these findings this paper calls for more authoritative best practice guidance on buried deck waterproofing design in a bid to reduce pressures in procurement that lead to weaker waterproofing design choices.This research may be of interest to those involved in the design and construction of underground structures including cut and cover tunnels, station boxes, malls, basements and more. The research identifies some fundamental features of podium deck waterproofing design and clarifies which design choices are perceived to deliver more robust waterproofing than others.

Dynamic response of cut and cover tunnel section under blast loading

In the present study, three-dimensional nonlinear finite element analysis is used to investigate the dynamic response of cut and cover tunnel subjected to blast loading. The analyses are performed using a dynamic explicit analysis tool in ABAQUS. The blast load is modeled using the CONWEP blast function available in ABAQUS. The reinforced concrete section is modeled using three-dimensional solid elements and stress–strain response of concrete is simulated using a concrete damaged plasticity model. The reinforcements are modeled using three-dimensional truss elements, and material properties are simulated using a metal plasticity model with isotropic-linear-elasticity. The parametric studies have been performed to evaluate the performance of key structural elements of cut and cover facilities, i.e., top slab and walls considering (1) different cover thickness (buried depth-d) of tunnel to height of tunnel ratio (d/H) (2) explosive charge weight. The mitigation measure using steel polypropylene hybrid fiber-reinforced concrete (HFRC) was also explored to improve the performance of the sections studied. It is observed from results that the displacement of tunnel increases with an increase in charge weight and decreases with an increase in d/H ratio. It can be observed from damage assessment that tension accumulation is the governing factor for the damage of reinforced concrete sections of the cut and cover tunnels and the extent of damage is observed to be reduced by increasing d/H ratio, i.e., increasing burial depth. The intermediate wall of the cut and cover section is the most critical element to avoid the progressive collapse of the structure. It is observed that the use of HFRC in the tunnel as an alternative to conventional concrete improves the blast-resistant capacity of the tunnel.

An analytical and applied blasting approach to facilitate rock-socketed bored pile excavation

Conventional bored piling excavation technique in a rock formation is a time-consuming and costly operation due to excavation speed. Blasting can be a useful method for the reduction of rock strength before bored pile excavation by breaking the rock in an area as large as the bored pile diameter. In this way, the drawbacks of pile driving operation can be minimized in terms of project time and cost. In this study, the usability of blasting was investigated in order to increase the speed of conventional bored piling excavation. For this aim, an analytical method based on the airy stress function was established to determine the fragmentation zone that provides sufficient fragmentation to facilitate the bored pile excavation operation in a motorway cut and cover tunnel project. In the model, the detonation pressure, the tensile strength of rock, explosive properties, and drill hole diameter were taken into consideration. The developed model was tested by three different blasting designs and a non-blasting excavation to verify its applicability for the bored pile excavation in the site. As a result, the suggested blasting method can be used in rock-socketed bored pile driving studies to obtain a fragmentation zone as much as pile diameter in order to increase excavation speed and reduce cost and to provide expected excavation performance. This study introduced a first in the literature that the blasting technique was used as the first stage of bored pile excavation. In addition, the developed method can be applied by revising according to different rock conditions and it can be used as a basic pre-design approach.

<b>Recent Trends in Design Technology of Cut and Cover Tunnels for Railways</b>

Cut and cover tunnels for railways in Japan are designed according to the Design Standards for Railway Structures and Commentary (Cut and Cover Tunnels). The standard was published about 15 years ago. Subsequently, the design of railway structures, except tunnels, shifted to a performance-based design system. Therefore, a committee was established to revise the Design Standards for Railway Structures and Commentary (Cut and Cover Tunnels) in 2014. The committee completed a draft new set of standards in 2017. This paper discusses recent trends in the design technology of cut and cover tunnels for railways, with a focus on the contents of the committee's revised draft.

제로터 오일펌프 커버의 터널 유무에 따른 펌프성능 및 진동특성에 대한 해석적 연구

The CFD analysis on the performance of the rotor oil pump in the automatic transmission with and without the tunnel in the cover was carried out theoretically. Model 1 has a tunnel on the cover and Model 2 does not have one. As the rotating speed increases from 1,000 to 6,000 rpm, the discharged flow rate of Model 1 increases from 10.65 rpm to 64.67 rpm and volumetric efficiency increases from 81.3% to 87.8%. The Model 2 shows the similar discharged flow rate and volume efficiency with those of the Model 1. The torque load of Model 1 increases from 3.21 N·m to 3.38 N·m with increasing from 1000 to 2,000 rpm, and the Model 2 shows almost similar one. However, at the high speed like 6,000 rpm, the torque load of Model 2 is 4.37 Nm, which is 2.4% higher than that of the Model 1. The reason is that the presence of cover tunnel can decrease pulsating pressure and vibration. Therefore, the application of cover tunnel in the gerotor pump can increase performance and decrease sound and vibration.

A Numerical Study on Parameters Affecting Seismic Behavior of Cut and Cover Tunnel

Underground structures and facilities constitute the underlying and infrastructural part of modern urbanization and are used for a wide range of applications, including urban underground railroad and urban road tunnels, silos etc. Underground structure’s construction method depends on such factors as the ground conditions, the ground water conditions, the tunnel span and the buried depth. The cut and cover method is an engineering technique for underground construction with low buried depth in urban areas. Furthermore, some urban underground facilities have been constructed in areas with risk of seismic activity which be resistant to both static and seismic loads. Therefore, seismic response of such shallow tunnels which are usually constructed by cut and cover method is of great importance and is investigated in this paper. Numerical analyses were performed on a shallow tunnel subjected to S-wave by using FLAC software, and the effects of different parameters are investigated. The maximum forces and bending moments in the tunnel lining during the earthquake motion for two earthquakes i.e., Tabas and Gilroy were compared and it was found that at all levels of maximum acceleration of input motion, seismic forces on tunnel structures during the Tabas earthquake were more critical which is related to the Arias intensity of the input motion. Increasing the buried depth of shallow tunnel and the enlargement of the tunnel span lead to more seismic forces on tunnel structures. Furthermore, with the increasing rigidity of the tunnel to the surrounding soil, additional dynamic forces in the tunnel lining will be more, however the stresses in the tunnel lining are reduced.

A review of CPT based axial pile design in the Netherlands

Because of the deltaic nature of the Netherlands, deep soft soil deposits are widespread. Due to the population density exploitation of underground space is vital for commercial developments and transport networks. Piles are used as primary support elements in deep excavations, cut and cover tunnels, quay walls, flood defences and to provide uplift resistance to the base of tunnels and basements. This paper examines empirical correlations linking the Cone Penetration Test (CPT) end resistance qc and the resistance of deep foundations in sand. It is found that correlations between qc and pile end resistance are independent of pile diameter. However, the impact of installation method, residual load, plugging and sand creep should be considered. In the case of shaft resistance, constant correlation factors between qc and average shaft resistance are possible for non-displacement piles. For the case of displacement piles, correlations that include the effects of friction fatigue and pile plugging during installation are recommended.

Numerical modelling of effects of different multipropped excavation depths on adjacent single piles: comparison between floating and end-bearing pile responses

Owing to a shortage of land, high-rise buildings are increasingly preferred to meet the development and economic growth of major cities in the world. The construction of high-rise buildings often requires deep foundations such as single piles or pile groups when the underlying soil and rock strata do not have sufficient bearing capacity. On the other hand, underground basements are constructed to facilitate inhabitants in the buildings for parking. Development of underground transportation systems consist of tunnels, excavations for basement construction and cut and cover tunnels. These excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. This research presents three-dimensional coupled consolidation analyses (using clay hypoplastic constitutive model that takes account of small-strain stiffness) to investigate the responses of a floating and an end-bearing pile due to adjacent excavation at different depths in clay. It was revealed that the maximum induced bending moment in both types of piles after completion of excavation in all the cases is much less than the pile bending moment capacity (i.e. 800 kNm). Moreover, the end-bearing piles were subjected to significant dragload due to negative skin friction. In contrast, no significant changes in load distribution along floating piles were computed.

3D Numerical Modeling of Pile Group Responses to Excavation-Induced Stress Release in Silty Clay

Development of underground transportation systems consists of tunnels, basement construction excavations and cut and cover tunnels which may encounter existing pile groups during their construction. Since many previous studies mainly focus on the effects of excavations on single piles, settlement and load transfer mechanism of a pile group subjected to excavation-induced stress release are not well investigated and understood. To address these two issues, three-dimensional coupled-consolidation numerical analysis is conducted by using a hypoplastic model which takes small-strain stiffness into account. A non-linear pile group settlement was induced. This may be attributed to reduction of shaft resistance due to excavation induced stress release, the pile had to settle substantially to further mobilise end-bearing. Compared to the Sp of the pile group, induced settlement of the single pile is larger with similar settlement characteristics. Due to the additional settlement of the pile group, factor of safety for the pile group can be regarded as decreasing from 3.0 to 1.4, based on a displacement-based failure load criterion. Owing to non-uniform stress release, pile group tilted towards the excavation with value of 0.14%. Due to excavation-induced stress release and dragload, head load of rear piles was reduced and transferred to rear piles. This load transfer can increase the axial force in front piles by 94%.

Resistivity Tunnel Monitoring System

The development of an urban area must be supported by the construction of infrastructure such as public facilities. The crowded of urban area in Indonesia increasingly requires the existence of a mass transportation mode that is capable of carrying passengers in large amounts and relatively quickly. Recently Jakarta has proposed the construction of the MRT (Mass Rapid Transit) with underground lines utilize tunnel technology. Tunnel system was chosen as an alternative solution socioeconomic problems in the land problem and conditions of the existing urban planning. The geographical position of Indonesia is located in the equatorial zone which is the weather conditions have high levels of weathering and moisture or high humidity, this condition may result in changes in the level of strength of rock of the tunnel system in a relatively fast. In the construction of public facilities with the tunnel system need monitoring system the condition of the tunnel to avoid the dangers that may occur due to the failure of a tunnel system. To determine the level of moisture and water content in the rock or overburden a tunnel can be determined by utilizing the resistivity method. Resistivity method is a geophysical method that measures the magnitude of the resistivity of a material. Changes in moisture content and humidity levels of rock or soil in an area can be indicated by a change in the value of resistivity of rock or soil. In the measuring of the resistivity method needed good design to provide accurate information, especially if it will be used as a monitoring system for a tunnel. Development of measuring the resistivity method, and in particular data processing is done with the aim of optimizing the measurement process and the measurement results can be interpreted easily and be able to demonstrate a phenomenon that occurs in rocks or soil cover tunnel.

Effect of drained static shear on cyclic deformation behavior of K0-consolidated sand

The K0-consolidated soil elements beneath structures like quay walls, bridge abutments, cut and cover tunnels and similar structures may be subjected to static shear involving the rotation of the principal stress prior to cyclic loading, which results in the presence of initial shear stress. A hollow cylindrical apparatus was employed and a series of drained cyclic tests was conducted to examine the effects of the initial shear stress induced by drained static shear prior to the application of cyclic loading. Both the initial vertical stress and the initial torsional shear stress were considered in the drained cyclic deformation behavior. The experimental observations indicate that the initial vertical stress accelerates the accumulation of vertical permanent strain during the first 100 cycles only when the initial vertical stress exceeds the value corresponding to the K0-consolidated stress state. The average growth rate of strain increases due to the presence of the initial torsional shear stress. A Critical Static Shear Line (CSSL), initiating from the K0-consolidated stress state in the (σz−σθ)−2σzθ plane, divides the volume change responses into contraction and dilation in subsequent cyclic loading. To account for the combined effects of the initial vertical stress and the initial torsional shear stress on the deformation behavior, a modified model is proposed to predict the vertical permanent strain.

PARAMETERS AFFECTING THE STRUCTURAL ANALYSIS OF A TUNNEL STRUCTURE EXPOSED TO FIRE

Behaviour of cut-and-cover tunnels exposed to fire should be analysed by using a realistic structural model that takes account of mechanical and thermal effects on the structure. This has been performed with the aid of Finite Element (FE) software package called SOFiSTiK in parallel, for two types of elements as a scope of research project financed by the German Bundesanstalt für Straßenwesen BAST. Since the stiffness of the structure at elevated temperatures is highly affected, a realistic model of structural behaviour of the tunnel could be only achieved by considering the nonlinear analysis of the structure. This has been performed for a 2–cell cut and cover tunnel by taking account of simultaneous reduction of stiffness and strength and the time-dependent increasing indirect effects due to axial constraints and temperature gradients induced by elevated temperatures. The thermal analyses have been performed and the effects were implemented into the structural model by the multi-layered strain model. The stress–strain model proposed by EN 1992-1-2 is implemented for the elevated temperature. Since there was sufficient amount of Polypropylene fibres in the concrete mixtures, modelling of spalling was excluded from the analysis. The critical corresponding stresses and material behaviour are compared and interpreted at different time stages. The main parameters affecting the accuracy and convergence of the results of structural analysis for the used model are identified: defining a realistic fire action, using concrete material model fulfilling the requirements of fire situation in tunnels, defining appropriate time intervals for load implementations. These parameters along with other parameters, which influence the results to a lesser degree, are identified and investigated in this paper.

개착터널에 대한 지진 시 동적수치해석에 관한 연구

지진 시에 지하구조물은 지상구조물보다 더욱 안전한 것으로 간주되어 왔으나, 1995년 고베지진 시 발생한 지하철터널의 피해 이후 지하구조물의 피해 사례가 점점 증가하고 있다. 본 논문에서는 풍화토로 되메움한 개착식 터널과 주변 지반의 지진 시 거동을 Mohr-Coulomb모델을 이용하여 수치해석을 수행하였다. 지반의 측면 경계조건, 인장강도, 최대지진가속도에 따른 개착식 터널과 주변 지반의 변위 및 터널 라이닝에 작용하는 응력을 예측하였다. 지반의 측면 경계조건(자유장 경계조건과 일반 경계조건)과 주변 지반의 인장강도의 변화에 따라 계산된 변위와 응력은 상당한 차이를 나타냈다. 좌우경계조건이 자유장 조건인 경우에는 지반의 잔류변형이 거의 발생하지 않았으나, 구속된 일반 조건인 경우에는 지진으로 인한 주변 및 기초 지반의 융기로 인한 잔류변형이 크게 발생하였다. 하지만 주변 및 기초 지반의 인장강도를 점착력의 100%로 가정하였을 경우 개착식 터널은 측면 경계조건이나 입력된 최대가속도에 관계없이 잔류변위는 1 cm 이내로 무시할 수준이다. 뿐만 아니라, 최대변위 발생 시 및 최종 단계에서 터널 라이닝에서 발생하는 응력은 모두 허용응력 이내이므로 안전한 것으로 판단된다. 동적 수치해석에서는 주변 지리적 조건을 고려하여 적절한 경계조건을 설정하고 인장강도와 같은 지반의 물성치를 정확하게 구하는 것이 매우 중요한 것으로 판단된다. Underground structures such as a tunnel have been considered as safer than structures on the ground during earthquake. However, severe damages of underground structures occurred at subway tunnel during 1995 Kobe Earthquake and such damages are gradually increased. In this study, a dynamic behavior of a cut and cover tunnel surrounded by weathered soils is investigated using Mohr-Coulomb Model. Parametric study was carried out for boundary conditions, tensile strength, and earthquake magnitudes. The results of numerical analyses in terms of ground deformations and stresses acting on the lining were quite dependent on the side boundary condition (free or fix conditions) and tensile strength of surrounding soils. The ground was deformed upward at the end of earthquake when the side boundary condition was fixed, whereas residual deformations were not predicted when it was free. When the tensile strength of a soil was set to the same as its cohesion, residual deformation was less than 1cm, regardless of side boundary conditions or input accelerations. In addition to that, stress conditions at the maximum deformation and end of earthquake were within an allowable range and considered as safe. Proper boundary conditions and material properties such as tensile strength are quite important because they may significantly impact on the results of dynamic analyses.

3F22 STUDY ON THE AREA OF CAUTION FOR CHLORIDE ATTACK IN SUBWAY BOX TYPE TUNNELS(Condition Monitoring-Infrastructure)

Tokyo Metro has been studying chloride-induced deterioration of subway tunnels by investigating tunnel bodies and taking countermeasure methods. From the resent results of the study, it had become clear that chloride-induced deterioration of subway tunnels almost always occurs at boundaries of areas leaking with chloride. For this reason, we studied potential areas that have chloride-induced deterioration in cut&cover tunnels by investigating the positional relation between tidal rivers and chloride leakage areas. As the result, it was found that the areas are 50m or more below the edges of tidal rivers. Then, seen from the viewpoint of advection-diffusion of chloride in the underground water, we verified the validity of the result by underground density flow analyses.