Tunnel Floor Research Articles

Full waveform inversion method for horizontally inhomogeneous stratified media

Full waveform inversion method is an approach to grasp the physical property parameters of underground media in geotechnical nondestructive detection and testing field. Using finite-difference time domain (FDTD) method for elastic wave equations, the full-wave field in horizontally inhomogeneous stratified media for elastic wave logging was calculated. A numerical 2D model with three layers was computed for elastic wave propagation in horizontally inhomogeneous media. The full waveform inversion method was verified to be feasible for evaluating elastic parameters in lateral inhomogeneous stratified media and showed well accuracy and convergence. It was shown that the time cost of inversion had certain dependence on the choice of starting initial model. Furthermore, this method was used in the detection of nonuniform grouting in the construction of immersed tube tunnel. The distribution of nonuniform grouting was clearly evaluated by the S-wave velocity profile of grouted mortar base below the tunnel floor.

The flow rate of people during train evacuation in rail tunnels: Effects of different train exit configurations

An exploratory study of a train evacuation inside a tunnel was performed in order to study the effects of different train exit configurations on the flow rate of people through the exit. A total of 84 participants in the ages 18–40years took part in the experiment, which was carried out on two separate days and involved 18 evacuation scenarios. The statistical analysis of the experiment demonstrated that the average flow rate capacity of the train exit was .3 persons per second and meter (p/s m) door width, including all scenarios. Four variables related to the train exit configuration were identified to significantly affect the flow rate of people: (1) a reduction of the train exit height increased the flow rate of people with on average .026p/sm; (2) a change of tunnel floor material from concrete to macadam increased the flow rate of people with on average .015p/sm; (3) an emergency ladder present in the train exit reduced the flow rate of people with on average .064p/sm; and (4) a complete failure of the lighting inside the train reduced the flow rate of people with on average .029p/sm. In addition, qualitative observations revealed a deferential behaviour among the participants in the train, caused by the people outside the train. It is therefore believed that the population density outside the train will significantly determine the flow rate capacity of the train exit during an evacuation.

Study of Radiant Interference Based on Model of Electric Locomotive in Underground Tunnel

This paper put forward a finite element method to study the radio transmission in tunnel electromagnetic environment. The author makes use of software simulation to study the rectangular tunnel model.When varying the electric parameters of tunnel wall, ceiling and floor, this may somewhat influence the propagation characteristics of electromagnetic wave.In order to study the interference properties of underground electric locomotive ,this paper put forward a moment of method (MoM) model to analysis electromagnetic compatibility in roadway.The author makes use of FEKO software to simulate its time-varying and non-linear characteristics ,the simulation results are in good agreement with experimental data .In the end it can be concludeed that this model has practical significance to estimate electromagnetic interference in coal mine. DOI: http://dx.doi.org/10.11591/telkomnika.v11i9.3253

Movement speed and exit choice in smoke-filled rail tunnels

An evacuation experiment including 100 individuals was performed inside a tunnel in order to study the effectiveness of different way-finding installations and to collect data on movement speeds and human behaviour. The participants took part in the experiment individually, and no group interactions were studied. The experiment tunnel was 200m long and an emergency exit was located 180m into the tunnel. In addition, emergency signs including distances to nearest exits were located every eight meters on both sides of the tunnel. The tunnel was filled with artificial smoke and acetic acid, which produced a mean light extinction coefficient of 2.2m−1. Participants had been told that they would participate in an evacuation experiment, but they had not been informed about the layout of the tunnel or the technical installations. The average movement speed was found to be approximately 0.9m/s, independent of tunnel floor material examined. The experiment also demonstrated the importance of the emergency exit design. A loudspeaker, which provided people with an alarm signal and a pre-recorded voice message, was found to perform particular well in terms of attracting people to the exit, independent of which side of the tunnel the participants were following.

Rock mass damage induced by rockbursts occurring on tunnel floors: a case study of two tunnels at the Jinping II Hydropower Station

Rockbursts occurring on tunnel floors are a special form of failure encountered in tunnel projects, where the failure is characterized by uplift, fracturing, and severe shocks of the tunnel floor. Extremely intense rockbursts were encountered during the excavation of the headrace tunnels 2 and 4 at the Jinping II Hydropower Station. In this study, results of comprehensive analysis conducted using the combination of numerical methods, experiments, and onsite survey to analyze the occurrence and development process of the rockburst are presented. In addition, the degree and extension range of the surrounding rock mass damage were estimated using the failure approaching index and the local energy release rate. The results of the analysis presented in this study are expected to advance the existing knowledge of special rockburst forms and may also serve as a reference for the design of resistant measures for other similar rockbursts.

SSRL Performance Enhancements

SSRL plans an ambitious program of beam line upgrades including replacing some existing wigglers with in vacuum undulators as well as developing up to five new in vacuum undulator beam lines resulting in as many as 10 undulator beam lines in a fully built out SPEAR3. SSRL also plans accelerator upgrades in the near future to further reduce the effective beam emittance to ≈ 6 nm and minimize vertical motion of the tunnel floor. By upgrading the injector rf system to a frequency commensurate with SPEAR3 and operating the electron gun in photo-cathode mode, top-off injection can be implemented in a multi-bunch pulse train mode. Short pulse operation for ultrafast pump/probe science is accomplished with a few-ps low-alpha configuration in either a few discrete buckets or in a hybrid mode with discrete buckets and hundreds of other buckets filled to higher charge and longer pulse length. All of these improvements are part of a coordinated plan to provide the User community with reliable operations and increased experimental capability.

Modelling fracture propagation and failure in a rock pillar under mechanical and thermal loadings

The Äspö Pillar Stability Experiment (APSE) was conducted to study the rock mass response in a heated rock pillar between two large boreholes. This paper summarizes the back calculations of the APSE using a two-dimensional (2D) fracture propagation code FRACOD. To be able to model all the loading phases of the APSE, including the thermal loading, the code was improved in several ways. A sequential excavation function was developed to model promptly the stepwise changing loading geometry. Prior to the modelling, short-term compressive strength test models were set up aiming to reproduce the stress–strain behaviour observed for the Äspö diorite in laboratory. These models simulate both the axial and lateral strains of radial-controlled laboratory tests. The volumetric strain was calculated from the simulations and compared with the laboratory results. The pillar models include vertical and horizontal 2D models from where the stress in the pillar wall was investigated. The vertical model assesses the stability of the experimental rock volume and suggests the resultant stress below the tunnel floor in the pillar area. The horizontal model considers cross-sections of the pillar between the two large boreholes. The horizontal model is used to simulate the evolution of the stress in the rock mass during the excavation of the boreholes and during and the heating phase to give an estimation of the spalling strength. The modelling results suggest that the excavation-induced stresses will cause slight fracturing in the pillar walls, if the strength of the APSE pillar is set to about 123MPa. Fracture propagation driven by thermal loading leads to minor spalling. The thermal evolution, elastic behaviour and brittle failure observed in the experiment are well reflected by the models.

Reduced-scale Experimental Research on Fires in Tunnels with Natural Ventilation

The 1/15 reduced-scale experiments were conducted using the Froude number conservation to investigate smoke diffusion characteristics in tunnel fires with natural ventilation. The effects of some factors such as: heat release rate, shaft distance, shaft size, train blockage and smoke curtain were studied. A porous bed propane burner, placed on the tunnel floor, was used to simulate the fire source. A series of K- type thermocouples were used to measure tunnel ceiling smoke temperatures. A hotwire anemometer was used to measure smoke volume rate and smoke temperature in the ventilation shaft. The experimental results indicated that all factors, except for the smoke curtain, have no major effect on the dimensionless ceiling temperatures in the fire section of the tunnel. Moreover, the fire size and train blockage do not have a significant effect on the dimensionless ceiling temperatures in the non-fire section of the tunnel. Nevertheless, the dimensionless ceiling temperatures in the non-fire section of the tunnel decreased with the decrease of the shaft distance and the increase of the shaft size. When the smoke curtain is used in the tunnel, the dimensionless ceiling temperatures in the fire channel are higher than in the case when the smoke curtain is not used. Moreover, there is no smoke in the evacuation channel. The fire size and train blockage do not have a considerable effect on the dimensionless temperatures and smoke volume rates in the shaft. Nonetheless, the dimensionless smoke temperatures in the shaft decrease with the increase in the shaft distance or the shaft size. Moreover, dimensionless smoke flow rates through the shaft increase with the decrease in the shaft distance or the increase in the shaft size.

Ground‐penetrating radar investigation inside a karstified limestone reservoir

In this paper, we present ground‐penetrating radar (GPR) investigations performed along a 3.7 km long tunnel located inside a lower Cretaceous limestone massif of south‐eastern France. This fractured massif is mainly characterized by water circulation and karstic structures. This kind of geological formation contains a large part of the fresh underground water resources of the world and is also considered as an analogue of Middle East oil reservoirs. Since tunnel walls are covered by thick reinforced concrete, direct geological observations are impossible.After some preliminary tests, the entire tunnel was investigated using 250 MHz shielded antennas. Data are generally of very good quality, with reflection time up to 400 ns (down to 18 m under the tunnel floor with a velocity of 9 cm/ns). We correlate the GPR signal along the tunnel with surface geological observations: the upper part of the investigated formation (Bedoulian) displays prominent stratigraphic reflectors while the lower part (Barremian) does not. Numerous diffractions are observed in both formations and can be related to karstic features.These investigations allow to better constrain the geological context along the tunnel, necessary for future hydrogeological studies. We conclude that this tunnel offers a unique opportunity of performing GPR measurements within a karstified limestone massif.

Finite Element Analysis of Damage in Tunnel Floor Through Strength Reduction

Finite Element Analysis of Damage in Tunnel Floor Through Strength Reduction

Numerical studies on tunnel floor heave in swelling ground under humid conditions

A humidity diffusion based numerical model is proposed to simulate the floor heave processes of swelling rock tunnel when it exposed to high humidity. The phenomenon of swelling in tunneling is treated as a humidity–mechanical coupled process, i.e. the stress redistribution as well the water vapor diffusion around the tunnel is taken into account. This allows one to model the observed floor heaves realistically without considering the complex chemical processes induced by water–rock interaction. Furthermore, the development of heave and pressure over the course of time can be studied. The swelling rock is considered as an elasto-plastic material with damage threshold, which allows one to predict the large heaves of a tunnel floor that are often observed in-situ. The relationship between the mechanical damage and humidity diffusion are discussed at the mesoscopic level. By studying the influence of parameters in the numerical model on the floor heave behavior, the time-dependent deformation and failure processes of tunnel under high humid condition are discussed in detail. The deformations at the floor level are larger than that of sidewalls interpreted here as a consequence of different humid boundary conditions. The numerical results provide a better understanding of time-dependent behavior of floor heave of tunnel under the high humid condition.

Corner separation effects for normal shock wave/turbulent boundary layer interactions in rectangular channels

AbstractExperiments are conducted to examine the mechanisms behind the coupling between corner separation and separation away from the corner when holding a high-Mach-number ${M}_{\infty } = 1. 5$ normal shock in a rectangular channel. The ensuing shock wave interaction with the boundary layer on the wind tunnel floor and in the corners was studied using laser Doppler anemometry, Pitot probe traverses, pressure sensitive paint and flow visualization. The primary mechanism explaining the link between the corner separation size and the other areas of separation appears to be the generation of compression waves at the corner, which act to smear the adverse pressure gradient imposed upon other parts of the flow. Experimental results indicate that the alteration of the $\lambda $-region, which occurs in the supersonic portion of the shock wave/boundary layer interaction (SBLI), is more important than the generation of any blockage in the subsonic region downstream of the shock wave.

Numerical Simulation of Air Pollutant Distribution in Urban Tunnels

Numerical simulation of air pollution dispersion inside tunnels is a suitable method for studying air pollutants’ spatial distribution and for evaluating the tunnel’s ventilation efficiency. In the present work, Fluent 6.2, a computational fluid dynamic software, has been used for full-scale numerical simulation of air flows and carbon monoxide (CO) concentrations inside the Resalat Tunnel of Tehran. Fans and vehicles are simulated with source of momentum and porous jump boundary conditions, respectively. Also, source of air pollutants, i.e., vehicle emissions, is simulated as uniform area source in the tunnel floor. Modeling results for concentrations of CO are validated by measurement data in 24 points adjacent to the fans inside the tunnel. Calibration of model indicated that the moving wall porous jump method for simulation of vehicle geometry and their effects, momentum source for fans modeling, standard k − ϵ scheme for turbulence modeling, and hexahedral mesh type are proper choices for the developed model. The results show a good correlation (R = 0.9) between modeling and measurement data. Five different scenarios (namely 1–vehicles to be stopped, 2–fans off, 3–two vertical ventilation ducts considered in the tunnel, 4–vehicles with Euro-IV emissions standard instead of Euro-II, and 5–blowing power of fans increased to twice the present) are examined for CO concentrations inside the tunnel. The numerical simulations for these scenarios are modified using a relation between measurement data and modeling results. Following the modification, results show that at the last measurement point (near the end of the tunnel), concentrations of CO is 59, 77, 9, 23, and 14 ppm for the five mentioned scenarios, respectively, and it is 32 ppm for normal condition. Hence, appropriate measures may be undertaken by the city authorities for air quality improvements in urban tunnels.

Superior techniques for disposal of highly radioactive waste (HLW)

The Swedish Nuclear Fuel and Waste Management Company (SKB) has recently worked out a concept, KBS-3V, for disposal of highly radioactive waste in the form of spent reactor fuel and asked for the Government’s approval and licensing. It implies blasting of tunnels at about 400 m depth and boring of large-diameter canister deposition holes extending vertically from the tunnel floor. The rock stresses will be critically high in the construction phase and lead to failure by spalling when the heat pulse from the canisters evolves. The canisters will be surrounded by dense expansive “buffer” clay for minimizing groundwater flow around and along them but the long-term performance of either of them is not adequately proven and the placement impractical and risky. Four major changes of the concept would make it satisfactory. One involves reorientation of the deposition holes from vertical to 45° inclination in two directions for reducing the risk of rock failure. A second is to prepare ready-made stiff units of “supercontainers” with highly compacted blocks of clay tightly surrounding the canisters for simpler and safer installation of clay blocks and canisters. A third is to surround the supercontainers by clay mud that provides the dense buffer with water from start and supports the surrounding rock when the thermal pulse begins to raise the rock stresses. A fourth is to replace the proposed smectite-rich buffer by clay with higher chemical stability and lower but sufficient expandability. A possible fifth change can be to manufacture homogeneous copper canisters of HIPOW type, which would radically reduce the risk of contamination of groundwater by released radionuclides.

Analysis of tectonic structures and excavation induced fractures in the Opalinus Clay, Mont Terri underground rock laboratory (Switzerland)

Excavated in the Opalinus Clay formation, the Mont Terri underground rock laboratory in the Jura Mountains of NW Switzerland is an important international test site for researching argillaceous formations, particularly in the context of deep geological disposal of radioactive waste. The rock laboratory is intersected by naturally formed tectonic structures, as well as artificial fractures primarily formed as a consequence of tunnel excavation and the associated stress redistribution. The description and characterisation of tectonic and artificial structures is, in many cases, of key importance for interpreting the results of the various in situ experiments conducted in the rock laboratory. Systematic small-scale mapping of the tunnel walls and floor, and adjacent niches, provides basic information about the geometry and the kinematics of the geological fractures intersecting the underground laboratory. A compilation of all tectonic structures identified is presented in this paper. The underground laboratory is located in the backlimb of the Mont Terri anticline, a NNW-vergent imbricate fault-bend fold, which is characterised by a pronounced along-strike asymmetry resulting from variously oriented inherited faults. The total shortening accommodated by this structure was estimated by mass (area) balancing to be approximately 2.1 km. The Mont Terri area is significantly affected by N- to NNE-striking normal faults of the Eo-Oligocene Rhine–Bresse transfer zone and by ENE-striking faults of Late Variscan age. Depending on their orientation with respect to the transport direction towards the NNW, these faults served as oblique and frontal ramps during the subsequent Jura thrusting in the Late Miocene. The various fault systems identified in the underground rock laboratory clearly correlate with the regional-scale structures. In addition to classical structural analysis, the anisotropy of magnetic susceptibility was measured to determine the magnetic fabric and strain imprint of the Opalinus Clay. Results indicate a well developed magnetic fabric with a magnetic foliation close to the bedding, and with two distinct magnetic lineations which are probably related to the Mont Terri anticline folding and layer-parallel shortening prior to the folding. Strain imprint is more pronounced in the overturned forelimb, which is consistent with the structural data.

Numerical Simulation Research on Earthquake Induced Dynamic Responses of Underground Tunnel

A number of nodes at different strata positions of tunnel roof were selected as research objects, the law between the roof deformation and the speed or acceleration time-history of horizontal and vertical direction were simulated on conditions of inputting earthquake wave at particular lacation of deep tunnel floor. With the gradually increasing distance from tunnel top surface, the “high -low-high” law of peak values were performed in speed time-history and acceleration speed time-history curves. One peak value was overally performed on vertical speed time-history curves, but multiple peak fluctuation was indicated in vertical acceleration time-history, horizontal speed and horizontal accelaration time-history curves.

Deformation Analysis of Jiagar Twin-Bore Tunnel in Tibet

Twin-bore tunnel is the better and useful structure form of wide span under complex conditions, and the Jiagar Tunnel is the Twin-bore tunnel of the expressway from Lhasa City to Gonggar International Airport. In the paper, we studied the deformation characteristic of the tunnel during two construction scheme, the sequential and whole excavation, by the numerical simulation of FLAC3D code. We obtained that the key points deformation characteristic was similar, the obvious part of the x-displacement is the joint of the tunnel roof and the side wall and the y-displacement is the midpoint of the tunnel floor. And the sequential excavation is better than whole excavation.

Ski Jumping Takeoff in a Wind Tunnel With Skis

The effect of skis on the force-time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

Measurement of the state of tunnel lining and floor by Full-Rotating Laser Scanning Method

Measurement of the state of tunnel lining and floor by Full-Rotating Laser Scanning Method

A New Technology of Rapid Sealing Roadway in Luotuoshan Coal Mine

After the large water accident with the serious collapse occurred in Luotuoshan coal mine, to achieve rescuing emergency rapidly, the scheme with blocking up water was adopted. The concerned technical measures include forming blocking up water wall‘s skeleton through injecting two-fluid slurry into tunnel, filling these gaps in skeleton with high flow under static pressure condition, reinforcing alluvium on the tunnel floor with high pressure, and filling tiny cracks in block up water wall with draining. The tunnel was blocked up successfully in only 54 days and the effect reaches 99.97%. The successful application of these technical measures provided valuable experiences that can draw lessons for engineering works under similar conditions in the future.