Tunnel Floor Research Articles

Research on damage characteristics and contact interface evolution behavior of double-block ballastless track considering tunnel floor heave

Excessive railway tunnel floor heave (TFH) will reduce the durability of the track structure and jeopardize train operation safety. The TFH characteristics were fitted into cosine and bilinear curves according to the monitoring data. A nonlinear failure analysis model of double-block ballastless track under TFH was established. The deformation transfer law, structural damage mechanism and the interlayer bonding interface failure evolution of the track structure under different TFH characteristics were explored. The results show that the deformation of TFH can be well mapped to the track. The amplitude transfer ratio is less than 100 %. The maximum wavelength transfer ratio under the cosine and bilinear TFH is 129.3 % and 127.5 %, respectively. To avoid the damage of track structure, when the wavelength is 10 m, the amplitude of cosine and bilinear TFH should be controlled at 2.5 mm and 0.5 mm respectively. When the wavelength is greater than 10 m, the amplitude can be appropriately increased. To avoid interlayer bonding cracking, the cosine and bilinear amplitudes with a wavelength of 10 m should be controlled at 5 mm and 1.5 mm, respectively. The track-tunnel interlayer debonding failure under the cosine curve occurs at the edge of the TFH, while the bilinear curve occurs at the center and edge of the TFH. The gaps under the cosine and bilinear TFH exhibit double-peak and multi-peak shapes, respectively. This study can provide theoretical guidance for controlling the performance degradation of track structure caused by TFH.

Effect of Tunnel Floor Heave on the Deformation and Damage Behavior of Ballastless Track Structures in High-Speed Railways

The extensive development of high-speed railways in mountainous areas has underscored the significant challenge posed by tunnel floor heave, affecting the operational reliability of ballastless tracks. Such heave induces track deformation and structural impairments, critically undermining the operational safety and track serviceability. This investigation enhances the understanding of ballastless tracks’ mechanical responses to tunnel floor heave by introducing a sophisticated nonlinear analytical model that encapsulates the interplay between the track system, tunnel infrastructure, and the encasing geological environment. Utilizing the concrete damaged plasticity approach to model the track’s concrete structure, this research integrates these parameters with the track’s numerical representation, taking into account the role of internal reinforcement. Through an in-depth examination of track deformation, the interstitial gap, and damage progression within the track, it is demonstrated that comprehensive consideration of both the material’s constitutive model and reinforcement structuring is imperative. The analysis results indicate that the heave’s amplitude and wavelength exert limited influence on the deformation amplitude ratio, whereas variations in heave characteristics significantly alter the wavelength transmission ratio, engendering a distinct “M” shaped gap profile. It is observed that the propensity for material damage escalates in areas experiencing pronounced tensile stress, particularly under conditions of reduced wavelength and increased amplitude heave, necessitating prioritized attention in track maintenance protocols.

Study on Influencing Factors and Prediction of Tunnel Floor Heave in Gently Inclined Thin-Layered Rock Mass

In recent years, the construction of new railway tunnels worldwide has become increasingly challenging due to larger cross-sections, deeper burial depths, higher in situ stress, and more complex geological conditions. During both construction and operation, some tunnels have encountered significant issues with floor heave. This paper begins by identifying the primary causes of deformation and instability in tunnel floor structures through an investigation and statistical analysis. It then examines floor heave across more than 20 railway lines, summarizing the types, generation mechanisms, and mechanical models associated with this issue. Additionally, extensive survey data indicate that tunnel floor heave is most likely to occur in gently inclined thin-layered rock masses. Therefore, using a tunnel passing through the plate suture zone in such a rock mass as a case study, numerical simulations, theoretical analyses, and on-site monitoring were conducted. This study systematically analyzed the influence of single and multiple factors, as well as the mechanical behavior of the support system, on tunnel floor heave in gently inclined thin-layered surrounding rock. Furthermore, several key models were proposed: a tunnel floor heave estimation and load formula based on a mechanical model, a dynamic relationship between surrounding rock support force and tunnel floor heave using the Nishihara model, a tunnel floor settlement estimation formula based on deformation statistics, and a tunnel floor heave energy prediction model utilizing the B-P neural network algorithm. These conclusions have been validated and widely applied in practical engineering, providing a robust theoretical foundation and technical support for future tunnel construction.

Visualization Of Freestream Vortices In The NASA Langley 4-Foot Supersonic Unitary Plan Wind Tunnel

Streamwise vortices present in the freestream of the NASA Langley 4-Foot Supersonic Unitary Plan Wind Tunnel have been observed experimentally for the first time. A high-energy, burst-mode laser system was used to conduct time-resolved planar laser Mie scattering in the freestream of this facility. The freestream of the facility was observed over Mach numbers ranging from 2.4 to 4.6 and (unit) Reynolds number between 3.3 × 106 to 14.8 × 106 1/m. Apparent vortical structures were observed in the tunnel freestream at Mach numbers ≤ 3, with little difference observed for varying the Reynolds number. With further increasing Mach number, protrusive and oscillatory vertical ‘sprite’ structures were observed emanating from the tunnel floor boundary layer. Neither of these structural phenomena has been observed before experimentally in the facility and acts to confirm and inform predictions made in computational fluid dynamic simulations of the facility.

Restraint effect of partition wall on the tunnel floor heave in layered rock mass

Restraint effect of partition wall on the tunnel floor heave in layered rock mass

Experimental study of the temperature profile induced by the tunnel wall fire plume at various source-ceiling heights

The smoke temperature profile beneath the ceiling of tunnel is one of the most important parameters to evaluate the tunnel fire risk and guide the early fire detection. This paper investigates experimentally the temperature profile induced by the tunnel wall fire plume at various source-ceiling heights. A series of experiments were carried out in a reduced-scale tunnel and a burner combustion inside. The burner elevation above the tunnel floor was changed at the center of the tunnel, and it attaches the side-wall of the tunnel to simulate the wall fire plume evolution with fire growth inside the tunnel. The temperatures beneath the ceiling were measured by the thermocouple array at the corner between the ceiling and side-wall of the tunnel. The maximum temperature beneath the ceiling could be correlated by the heat release rate and the source-ceiling height. A new characteristic parameter model considering the virtual point source at the side of the tunnel was proposed firstly considering the tunnel fire scenario to describe the tunnel plume temperature profile. The obtained experimental data and proposed temperature profile model in this work provide a basic understanding of the heat/thermal impact on the tunnel wall fire plume.

Study of dust pollution control effect based on orthogonal test and CFD numerical simulations.

To control the diffusion of high concentrations of coal dust during tunnel boring and minimize the threat to the life and health of coal miners, theoretical analysis, numerical simulations, and field measurements were combined in this study. First, computational fluid dynamic simulation software was used to simulate the generation of dust particles and their transport pattern in the tunnel. Subsequently, an innovative orthogonal test was performed to study the effect of four ventilation parameters [the pressure airflow rate (Q), distance between the air duct center and heading face (LA), distance between the air duct center and tunnel floor (LB), and distance between the air duct center and nearest coal wall (LC)] on dust diffusion. According to the orthogonal test results, the optimal ventilation parameters for effective dust control are as follows: Q = 1400 m3/min, LA = 7 m, LB = 2.8 m, and LC = 1 m. The optimized set of ventilation parameters was applied to the Wangpo 3206 working face. The results show that dust diffusion in the tunnel was effectively controlled and that the air quality was sufficiently improved.

Design of a robotic platform for hybrid wind tunnel experiments of floating wind farms

Wind tunnel experiments incorporating factors like realistic ambient wind conditions, merging of multiple wakes, and active wake controls are needed to understand and improve modeling of floating wind farms. A key technology for this kind of experiments is the robotic system emulating the wind turbine motion. This article addresses the design of a robotic platform with three degrees-of-freedom (surge, pitch, and yaw) specifically tailored for wind tunnel experiments on floating wind farms. This robotic system aims to accurately reproduce the motion spectrum of floating wind turbines of 10-22MW and to simulate rotor-atmospheric wind interactions. The robotic platform has a compact design to be positioned in multiple units inside the wind tunnel and avoid disturbing the wake of the wind turbine on top of it. To achieve these goals, the wind turbine is partially integrated in the robotic platform that employs a parallel kinematic scheme and has all actuators close to the wind tunnel floor.

Experimental investigation on biaxial mechanical properties of laminated rock and floor heave mechanism of tunnel based on DIC

Floor heave at the bottom of a tunnel is a common defect during tunnel service. To study the deformation behavior and failure characteristics of the floor, laminated sandstone specimens with precracked U-shaped grooves were prepared, and a series of biaxial compression tests were carried out in the laboratory. Two typical floor structures of a tunnel (with and without inverts) and four lateral stress levels (σ2 = 0, 5, 10 and 15 MPa) were considered. The effects of lateral stress and inverted structure on the deformation and failure characteristics of the floor were investigated. The displacement, strain evolution and failure extent of the floor were analyzed based on the digital image correlation (DIC) technique. The testing results show that the stress concentration at the U-shaped grooves of the specimens can be effectively reduced by the inverted structure. The specimen with an invert can bear more axial deformation and axial stress than that without an invert. The V-shaped notch failure behavior occurred near the tunnel sidewalls for the specimen without an invert, and it occurred in the middle of the tunnel floor for the specimen with an invert. The failure intensity of the V-shaped notch was positively related to the lateral stresses. With the increasing of axial stress, the heave displacement at the tunnel floor gradually increased, while the settlement displacement of the sidewall showed a trend of first increasing and then decreasing. The tensile strain concentration area of the floor undergoes a process of increasing and then decreasing and finally transforms to compressive strain. The failure characteristics of the sandstone specimen observed in the laboratory tests are consistent with the phenomena in real tunnel engineering. In addition, the deformation and failure mechanism of the tunnel floor was analyzed. The key points for the treatment of tunnel floor heave are put forward based on the testing results.

Characteristics of carbon dioxide fracturing in comparison to conventional water hydraulic fracturing: Evidence from acoustic emission monitoring of small-scale field experiments

We conducted small-scale field hydraulic fracturing (HF) experiments using carbon dioxide (CO2) and water as fracturing fluids. A hole was drilled 10–14 m below the tunnel floor into hot granitic rock whose temperature can form CO2 supercritical state at HF pressure. Under the same injection rate of 10 mL/min, the volume of the acoustic emission (AE) hypocenter distribution induced by CO2 HF was approximately 27 times larger than that induced by water HF. In addition, when evaluating injectivity improvement through Injecting/Fall-Off Tests (IFOTs) using gaseous CO2 and water before and after CO2 HF and water HF, respectively, the injectivity of rock around the HF hole was improved by around 400 times larger by CO2 HF in comparison to a few times larger by water HF. The results suggest that CO2 HF can stimulate a much larger region and improve injectivity much more than water HF. In contrast, it has more possibility of leaking injected fluid through the stimulated region. On the other hand, when comparing the focal mechanisms of AE events in both CO2 HF and water HF with their occurrence times and locations, we found a tendency for tensile-dominant events to occur in intact rock, in contrast, shear-dominant events occur with a linkage between cracks, that is, the interaction of cracks. This finding suggests a solution for the paradox of the mechanism of HF in which shear events dominate in AE monitoring in actual production fields where there are various discontinuities and cracks, although the elastic theory expects tensile fractures.

Time-Dependent Change in Carpal Tunnel Cross-Sectional Area and Transverse Carpal Ligament Thickness Using Serial Magnetic Resonance Imaging Studies—An Anatomical Study

Idiopathic carpal tunnel syndrome (CTS) is a common compressive neuropathy. Aging and female sex are risk factors, but the reasons are unclear. The purpose of this study was to evaluate whether identifiable radiographic changes resulting in a decrease in carpal tunnel area (CTA) over time exist. A database search of a multicenter, academic, tertiary institution from 1998 to 2021 identified 433 patients with serial wrist magnetic resonance images (MRI) at least 5 years apart. Fifty-six met the inclusion criteria with adequate films to measure CTA and transverse carpal ligament (TCL) thickness at the same slice location-the carpal tunnel inlet, hook of the hamate, and carpal tunnel outlet-independently by two observers who were blinded to each other's measurements. Rates for the change in CTA and TCL thickness were calculated at all three locations. Thickness of the TCL increased, whereas that of the CTA decreased over time. Inlet CTA decreased by 0.9 mm2 per year (95% CI: 0.34-1.5), outlet CTA decreased by 1.8 mm2 per year (95% CI: 1.2-2.5), and CTA at the hook of the hamate decreased by 1.6 mm2 per year (95% CI: 1.0-2.0 per year). The TCL thickened by 0.02 mm per year at all three sections. Taller patients had a decreased rate of CTA loss. In this select cohort, TCL thickened and CTA decreased with time. TCL thickening accounted for about half of the variation in CTA, suggesting that this is a possible contributor to this change. Hypertrophy of the carpal tunnel floor may account for the remaining variation in CTA. The question of whether these results are reliable and generalizable to the general population, or a major influence in the pathophysiology of CTS, is unknown. Small decreases in CTA and thickening of the TCL occur with aging. Whether this is a contributing factor in the development of CTS requires further study.

Integration of in‐mine seismic and GPR surveys to gain advanced knowledge of Bushveld Complex orebodies

AbstractImproving the exploration of deep‐seated mineral deposits and assessing the stability of the mine pillars require that geophysical techniques are deployed in a fast and cost‐effective manner with minimal environmental impact. This research presents results from in‐mine reflection seismic experiments and a ground penetrating radar (GPR) survey conducted at the Maseve platinum mine, South Africa. The research aims to develop and implement methods to image platinum group metal (PGM) deposits and geological structures near mine tunnels and assess the stability of pillars. The seismic experiments were conducted using a sledgehammer source (10 lb), conventional cabled geophones (14 Hz), and a landstreamer with 4.5 Hz vertical component geophones. The GPR survey was conducted using a Noggin 500 GPR system with 500 MHz centre frequency. An image of the underlying orebody and geological structures down to 100 m from the mine tunnel floor (∼500 m below ground surface) was produced. We correlated the coherent reflections beneath the tunnel floor with a known Upper Group (UG2) PGM orebody. The final seismic section shows that the UG2 mineralisation is dissected by near‐vertical dykes, faults and fractures. These structures, faults in particular, are interpreted to have been active post‐mineralisation, implying that they may have contributed to the current complex geometry of the deposit. Four GPR profiles were collected around a stability pillar adjacent to the seismic lines. The radargram sections were processed to improve the signal‐to‐noise ratio (S/N). The results show different patterns of fracturing and stress‐induced structures. These fractures were shown to be sub‐vertical and, possibly, constitute complex micro‐structures within the pillar, which could compromise the pillar stability and integrity. The study demonstrates that in‐mine seismic and GPR surveys can be cost‐effective and valuable for mineral exploration.

Effect of dynamic loading orientation on fracture properties of surrounding rocks in twin tunnels

For expedited transportation, vehicular tunnels are often designed as two adjacent tunnels, which frequently experience dynamic stress waves from various orientations during blasting excavation. To analyze the impact of dynamic loading orientation on the stability of the twin-tunnel, a split Hopkinson pressure bar (SHPB) apparatus was used to conduct a dynamic test on the twin-tunnel specimens. The two tunnels were rotated around the specimen’s center to consider the effect of dynamic loading orientation. LS-DYNA software was used for numerical simulation to reveal the failure properties and stress wave propagation law of the twin-tunnel specimens. The findings indicate that, for a twin-tunnel exposed to a dynamic load from different orientations, the crack initiation position appears most often at the tunnel corner, tunnel spandrel, and tunnel floor. As the impact direction is created by a certain angle (30°, 45°, 60°, 120°, 135°, and 150°), the fractures are produced in the middle of the line between the left tunnel corner and the right tunnel spandrel. As the impact loading angle (α) is 90°, the tunnel sustains minimal damage, and only tensile fractures form in the surrounding rocks. The orientation of the impact load could change the stress distribution in the twin-tunnel, and major fractures are more likely to form in areas where the tensile stress is concentrated.

Analysis of thermo-mechanical damage around tunnel and deposition boreholes of an underground nuclear waste disposal facility at the Forsmark site (Sweden) by 3D coupled FDEM simulations

This study focuses on rock damage potentially developing in the near-field of a planned underground nuclear waste repository at the Forsmark site (Sweden). In hard, crystalline rocks, mechanical damage in the form of spalling may be induced during construction by overstressing of the excavation periphery. During operation, thermal damage may develop due to additional thermo-elastic stresses forming in response to the increasing rock temperatures induced by the heat-emitting spent nuclear fuel. Prediction of damage occurrence, location, and extent is critical for an effective repository design and long-term safety assessment as it may negatively affect the long-term isolation properties of the host rock. In this paper, the response of underground structures was studied using a novel 3D coupled thermo-mechanical simulator based on the finite-discrete element method (FDEM). It is the first numerical study to date that explicitly captures both mechanical and thermal fracturing processes while using the latest repository design and site-specific geomechanical input data. A sensitivity study is performed to investigate different combinations of rock mechanical properties, in-situ stresses, and deposition tunnel geometry on the host rock behaviour. Rock mass deconfinement is shown to promote the development of tensile damage in the tunnel sidewalls and floor with fracture surfaces growing parallel to the excavation boundaries. The negative effects deriving from the adoption of a relatively narrower tunnel cross-section and from an increase of horizontal in-situ stresses are highlighted. Thermo-mechanical analyses capture the rock mass behaviour following an increase of borehole surface temperature to 100 °C. Numerical results indicate that the temperature evolution is affected by the shape of the underground cavities and their distance from the heated boreholes. The coupled thermal expansion of the rock induces additional stresses which, in turn, promotes further damage. Despite this increase, however, the total amount of induced rock damage at final conditions remains relatively low.

Service performance of CRTS II ballastless track in high temperature tunnel

Considering the dynamic balance of heat conduction between tunnel floor and track structure, heat convection and heat radiation between track surface and air, a finite element model for the temperature field of CRTS Ⅱ ballastless track in the high temperature tunnel is proposed and the dynamic responses of the vehicle-track coupling system are studied. Firstly, the influences of the temperature of the tunnel floor on the temperature distribution and warpage of the track are investigated. Secondly, the dynamic responses of the VTCS excited by the additional irregularity of the track induced by the temperature of the tunnel floor are investigated, and the effects of track deformation on dynamic characteristics at different speeds are compared. The findings demonstrate a linear relationship between the maximum and minimum temperatures of the upper and lower surfaces of the track slab and the temperature of the tunnel floor. In comparison to rail, the maximum displacement of the slab is larger, and the warpage deformation with symmetrical distribution of the track slab is characterized by concave in the middle and arching on both sides. The fastener stiffness has no effect on the deformation of the slab, but the vertical displacement of rail increasess as the fastener stiffness enlarge. Temperature load enlarges the excitation of the wheel-rail system so that intensifies the dynamic response. The faster of the speed of vehicle is, the effect of additional track irregularity on the dynamic response is the more pronounced. The research reveals the mechanism of high temperature tunnel on the service state of track, which supplies a theoretical basis for the design and maintenance of track.

Modeling Railway Track Mechanical Behavior with Under Tie Pads and Under Ballast Mats

Under tie pads (UTPs) and under ballast mats (UBMs) are used in rail track construction to reduce track stiffness and increase the size of the ballast contact area where it meets track support elements either above the ballast (ties) or below the ballast (e.g., subgrade, bridge deck, or tunnel invert). Limited information on the in-track performance of UTPs or UBMs is available. The University of Florida recently completed a research program to monitor track performance and track support changes using a UBM and UTPs in the Virginia Avenue Tunnel in Washington, DC. Researchers measured parameters to estimate the effect of a UBM and UTPs on tunnel invert pressure, tie bottom pressure, and track deflection. A control condition without a UBM or UTPs was not available for testing; however, Volpe developed a finite element track model for estimating track behavior without a UBM or UTPs. The modeling results highlighted the individual contributions of both a UBM and UTPs to stress reduction on the ties and tunnel floor. The model included features that simulate the load chains that can develop in clean granular materials leading to high peak stresses and ballast and structure degradation. The modeling results revealed that a UBM and UTPs might reduce the average stress on the ties and tunnel floor by 5% to 20% when the ballast was well compacted. The peak stresses from ballast load chains, or edges, may be reduced by 50% or more.

Study on failure mechanism and treatment measures of floor heave of high-speed railway tunnel in the interbedded surrounding rock with high geostress

The tunnel floor heave is easy to occur in the interbedded surrounding rock with high geostress, which has a serious impact on the safety of the tunnel structure and the normal operation of the tunnel. Through field investigation, numerical simulation, and in-situ monitoring, this paper studies the failure mechanism and corresponding treatment measures of the floor heave of a high-speed railway tunnel from various aspects such as geostress, surrounding rock structure, and bottom structure. The results show that the high horizontal geostress, the structure of interbedded surrounding rock, and the weak inverted arch are the reasons for the tunnel floor heave failure. Under the condition that high horizontal geostress acts on the structure of interbedded surrounding rock mass, the underlying rock layer under the tunnel will undergo cyclic deformation or failure, and the tunnel will show floor heave failure. Based on the research results, treatment measures such as removal and replacement of the inverted arch, anchor cable and anchor bolt anchoring were taken to treat the foundation and overall track bed of the tunnel. After the treatment, an automated monitoring system was established to monitor the displacement of the inverted arch, surrounding rock pressure, and steel stress for three years. Based on the analysis of monitoring results, this treatment plan can effectively control the tunnel floor heave. The research results can provide reference for the prevention and control of other tunnel floor heave failures.

Dynamic damage and response characteristics of the tunnel by FEM modeling and field trials

The dynamic response characteristics of the tunnel and the stability of the surrounding rock are crucial to its safety of the tunnel. Combining the numerical simulation software and field measurement results, the change of peak particle vibration (PPV) and stress were analyzed, based on the longitudinal wave data from the acoustic tests, the blasting damage effects under the action of different blasting counts, including different locations in the deep part of the surrounding rock, were investigated. The results show that: (1) in the vertical direction of the tunnel, the PPV of the tunnel floor and tunnel sidewall is larger, the PPV of the tunnel top is the second, and the tunnel arch shoulder and arch foot is the smallest; (2) under the action of blasting, the stress concentration at the tunnel bottom and arch foot is easier, and the stress monitoring should be strengthened; (3) The depth of damage at different distances was 1.5 m and 3.0 m, respectively, and the depth of damage to the surrounding rock increased from 2.5 m to 4.0 m when the number of blasts was 10 and the number of blasts was 10.

Physical modelling of the interaction between a tunnel and a building in a liquefying ground and its mitigation

The fast growth of the built environment in liquefaction-prone areas requires new design challenges to be overcome. A significant soil shear strength and stiffness loss associated to soil liquefaction, possibly occurring during severe earthquakes, may induce effects on buildings and on shallow and light structures such as urban tunnels. In densely urbanised areas, interaction between underground and aboveground structures may results in a detrimental combination of such effects.The paper discusses the results of a series of centrifuge tests carried out at the Schofield Centre (Cambridge, UK) modelling the dynamic interaction between an urban tunnel and a building in sand undergoing cyclic liquefaction. Four reduced-scale models were tested at increased gravity to model a prototype 60 times larger. A rectangular aluminium frame embedded in a layer of homogeneous Hostun sand represented a section of a metro tunnel. An aluminium sway frame represented a simple building founded in the same layer, at a side of the tunnel. The experimental results show that in typical urban spacing, sand liquefaction in the foundation ground affects the reciprocal interaction between the kinematic of the tunnel and the building.Centrifuge modelling investigated whether it is possible to mitigate or prevent such interference by improving ground through the addition of hydrated laponite beneath the tunnel floor or as lateral vertical barrier between the building foundation and the tunnel. The results also show the importance of temporary structures – often used to support soil excavation during cut-and-cover tunnel construction – in reducing the effects of interaction between the tunnel and the building in the liquefying soil.

Temperature effects of ballastless track and dynamic responses of vehicle-track coupling system on tunnel floor with high temperature

Temperature has a great implication for the structural behavior of the ballastless track, however, there are few studies on the temperature effect of ballastless track and the dynamic responses of vehicle-track coupling system (VTCS) on tunnel floor with high temperature. In this paper, the finite element model is established to investigate this problem. The correctness of the model is verified by the test platform for the temperature field of track slab. The temperature stresses and warp deformations of the ballastless track on tunnel floor with high temperature are investigated, and then the additional irregularities of rail induced by the high temperature are used to study the dynamic responses of the VTCS. The results show that the longitudinal temperature stress of the track bed slab is the largest, and the stress increases nonlinearly with the increase of temperature. The maximum vertical deformation of the rail is less than that of the track bed slab. With the increase of the temperature, the dynamic responses of VTCS enlarge nonlinearly and the running safety index of the vehicle deteriorates. The limit value with 50 ℃ of the temperature difference between the tunnel floor and the environment is recommended. This paper provides the theoretical support for the design, maintenance and repair of the ballastless track in the tunnel with high temperature.