Parametrical static analysis on group studs with typical push-out tests

Group studs are known as shear connectors in steel and concrete composite structures. By now, many composite bridges have been characterized by long lateral cantilevers. The shear studs are actually under biaxial action consisting of shear force and action in light of lateral bending moment on concrete slab induced by long cantilever and passing by moving loads. Moreover, lateral bending moment may even lead to the initiation of bending-induced concrete cracks. These two situations can both affect mechanical performance of group studs. Thus, a parametrical FEM analysis was carried out, in which damage plasticity was introduced to simulate material nonlinear behavior. In the analysis, lateral bending moments respectively inducing maximum concrete crack widths of 0.1 mm and 0.2 mm, shank diameters of 13 mm, 16 mm, 19 mm and 22 mm and stud heights including 80 mm and 100 mm were parameters. It was found that mechanical behavior of group studs with large shank diameter would be less affected by biaxial action and initial bending-induced concrete cracks seemed unfavorable to stud shear stiffness. On the other hand, typical push-out tests were executed to investigate reductions of shear stiffness and shear capacity of group studs. The reliability of FEM analysis was also verified based on the tests. In addition, stud shear capacity evaluations according to several design specifications were presented. It indicated shear capacity evaluation of Eurocode 4 got a relatively large safety factor. Moreover, the applicability of these specifications for group studs on shear capacity evaluation was also discussed.     

Numerical study of the depth and cross-sectional shape of tunnel under surface explosion

Recently, blasting loads have come into consideration because of the large number of intentional or unintentional events that affected important structures around the world, obviously indicating that the topic is relevant for purposes of structural design and reliability analysis. This paper has evaluated the dynamic responses of buried tunnel in depths of 3.5, 7, 10.5 and 14 m for surface detonation of 1000 kg TNT charge in a surrounding sandy soil. The Kobe box shape subway tunnel was used as an example to evaluate and compare with semi ellipse, circular and horseshoe shape tunnel. The finite element software LS-DYNA has been used to model and to analyze the outcome of this project, specifically to be modeled in the area of the second interaction due to explosion. The results indicate that the circular and horseshoe tunnels are less resistant to demolition than the box shape tunnel however the semi ellipse tunnel is more resistant than the box shape tunnel.     

Artificial Ground Freezing to excavate a tunnel in sandy soil. Measurements and back analysis

The paper is dedicated to the case history of a 13 m wide, 17 m high and 40 m long service tunnel at Toledo Station, previously constructed in a deep open shaft and belonging to the Line 1 of the Napoli underground network. The existing Line 1 has been recently extended with a new stretch consisting of five new stations connected by twin rail tunnels for a total length of about 5 km. Toledo Station main shaft is located by a side of the line and it is connected to the pedestrian platforms by the above mentioned large size service tunnel. The station is situated in the historical center of the city of Napoli, under a deeply urbanized area. In Fig. 1 a longitudinal section of the main shaft of the station and of the large service tunnel with the above and surrounding buildings is sketched. The focus of this paper is on the settlement caused by the tunnel excavation and on the use of the Artificial Ground Freezing (AGF) technique to allow the safe excavation of the large crown of the service tunnel, located about one half in a silty sand layer and one half in yellow tuff, well below the groundwater table.     

Design and optimisation of laser scanning for tunnels geometry inspection

The use of terrestrial laser scanning technology in engineering surveys is gaining an increasing interest due to the very high spatial density of the acquired data. Recent improvements regarding the speed, accuracy, software algorithms and the fall in price have introduced a high potential for large scale applications of this technology in highly demanding engineering environments such as tunnels. Railway tunnels, in particular those of a long length, create challenges for surveyors due to their elongation to obtain satisfactory geometry of the scanned data. The purpose of this paper is to give an optimal solution for surveying tunnel geometry using laser scanning technology to reliably inspect railway tunnels and create “as-built” documentation.The proposed methodology provides optimisation of scanning parameters, scans registration, the georeferencing approach and the survey control network design. The maximal size of the scanner shifting along the tunnel alignment is primarily conditioned by factors including the incidence angle of the laser beam and the point density distribution. The authors introduce the so-called arbitrary georeferencing approach in long tunnel scanning that controls the point cloud geometric distortions to the required limits and contributes to time and material resources savings. Optimal design of the survey control network ensures the required positional accuracy and the reliability of the measurements, together with a cost effective approach to tunnels surveying.The proposed methodology is followed by the empirical results of the modelling and profiling of 12 tunnels in a single track railway. The lengths of these tunnels are from 60 m to 1260 m, with a total length of 3.5 km. Due to the specific geometry of the case study tunnels, the maximal favourable laser incidence angle is 78° with a distance of 13 m and consequently the optimal size of the scanner shifting along the tunnel alignment is 26 m. The survey control network is designed with the condition that the optimal reliability factors are within the required limits for engineering networks. A priori estimation of the control network positional uncertainty and a posteriori adjustment results shows that the achieved positional accuracy of the control points is approximately five times better than the requested absolute accuracy of the tunnel model: σ_m = 2 cm. On the largest tunnel example it is shown that the arbitrary georeferencing approach assures that the optimal registration error size is within the requested limits.     

Key protection techniques adopted and analysis of influence on adjacent buildings due to the Bund Tunnel construction

The Bund Tunnel is 14.27 m in diameter. It is the first application of super diameter earth pressure balanced shield (EPBS) in China. There are many historical buildings along the construction line, and the minimum horizontal distance from the building to the tunnel side varies from 1.7 m to 30 m. Considering the importance of these historical buildings and the complicated construction processes, it is essential to adopt effective protection techniques to ensure safety during the tunnel construction. Three kinds of protection techniques are presented in this paper. Firstly, underground cut-off wall built by bored piles is used to separate the buildings and tunnel when the minimum horizontal distance from the building to the tunnel side is less than 5 m. Secondly, the grouting reinforcement technique is adopted when the minimum clear distance is between 5 m and 10 m. Finally, if the minimum clear distance is larger than 10 m, the optimized construction parameters are selected to reduce the influence induced by the EPBS excavation. The deformations of some typical buildings are monitored. The results of this project will be a useful reference for similar future projects.     

Maximum surface settlement based classification of shallow tunnels in soft ground

Prediction of the maximum surface settlement due to shallow tunnelling in soft grounds is a valuable metrics in ensuring safe operations, particularly in urban areas. Although numerous researches have been devoted to this issue, due to the complexity and a large number of the effective parameters, no comprehensive solution to the problem is available. In this study, a shallow tunnel classification system (STCS), based on maximum settlement, is proposed. The STCS holds on the results of several tunnelling projects around the world. The classifier categorises a tunnel based on geometry, ground, and performance characteristics. A decision tree classification method, after training with 20 cases, was successful to predict the maximum settlement for 14 tunnelling projects. The maximum surface settlement predictions were in the form of assigning a class label to each tunnel. Four tunnel classes were defined as follow: (i) class A (maximum settlement < 9.9 mm), (ii) class “B” (10 ⩽ maximum settlement < 19.9 mm), (iii) class “C” (20 ⩽ maximum settlement < 29.9 mm), and (iv) class “D” (maximum settlement ⩾ 30 mm). The most explanatory independent variables were selected, by the STCS, as follow: tunnel depth, diameter, volume loss, and normalised volume loss. The proposed classification scheme can be employed as a decision making aid in settlement prediction/prevention in shallow tunnelling in soft grounds. The STCS is proposed as a supplemental tool to the observational methods, and it is not expected to be a stand-alone measure for settlement.     

Upgrading the Arlberg tunnel to current safety standards

Austrian road tunnels within the Trans-European Road Network (TERN) must fulfil the requirements of the Directive 2004/54/EC (European Commission, 2004) not later than April 2019. This regulation has to be applied to all tunnels in the TERN with a length of more than 500 m, whether they are in operation, under construction or at design stage, and aims at ensuring a minimum level of safety for road users. One of the main features of this directive is the requirement for providing an egress possibility to a safe environment every 500 m throughout the whole tunnel.The Arlberg road tunnel has a length of some 15.5 km and is in operation for more than 35 years. It is a single tube tunnel operated with bi-directional traffic, but carries a quite low traffic volume. Hence, the construction of a second tube is not really cost effective. Currently the tunnel is equipped with a transversal ventilation system with remotely controlled smoke extraction dampers providing smoke extraction every 100 m. The maximum distance between egress possibilities to a save environment is some 1500 m. Due to the high costs of a construction of a second tube or a parallel running escape gallery, a novel solution was found. The existing fresh air duct will be used as safe escape way between the existing egress possibilities. This solution has big impacts on the ventilation system and on the requirements for thermal structure protection of the new egress ways, i.e. the fresh air duct. In order to overcome this problem, massive changes in the ventilation design have to be performed, accompanied by the installation of a high-pressure water-mist system for structure protection.     

Tests and numerical study of ultra-high strength steel columns with end restraints

High strength steels with the nominal yield strength more than 460 MPa have begun to be applied in the construction of many steel structures, but there are short of sound researches on the major axis buckling behavior of such steel welded I-section columns, especially for the ultra-high strength steels having the nominal yield strength more than 690 MPa. In this paper, the experimental research is described on the overall buckling behavior about the major axis of ultra-high strength steel compression I-section columns with end restraints. In this research 8 columns made from 2 kinds of ultra-high strength structural steels S690 and S960, with nominal yield strengths of 690 MPa and 960 MPa, respectively, were tested. Based on the test results, the finite element analysis (FEA) model was validated to analyze this behavior of ultra-high strength steel columns, and the buckling strength of pin-ended columns fabricated from such steels were calculated by the verified FEA model, which were compared with the design buckling strengths according to the Eurocode 3, the American specification for structural steel buildings ANSI/AISC 360–05, and the Chinese codes for steel structures design GB50017-2003 respectively. It shows that the major axis nondimensional buckling strengths of the ultra-high strength steel compression columns, whose buckling curve is type b according to Eurocode 3 and GB50017-2003, are much higher than that calculated according to the column curve b, even higher than the curve a₀ in Eurocode 3 and the curve a in GB50017-2003 on average, and they are also higher than the design values according to ANSI/AISC 360–05. It is therefore indicated that the buckling strength about the major axis of the ultra-high strength steel I-section columns is improved a lot compared with the ordinary strength steel columns on a non-dimensional basis, and the column curve a₀ and curve a can be adopted to design this behavior in Eurocode 3 and GB50017-2003, respectively. Besides, there is no obvious difference between the major axis nondimensional buckling strengths of the pin-ended I-section columns fabricated from these two kinds of ultra-high strength steels: S690 and S960. These research works will provide the test basis to complete the buckling design method and theory of the ultra-high strength steel columns, and also be helpful for the application of ultra-high strength steel structures.     

Drip sealing of tunnels in hard rock: A new concept for the design and evaluation of permeation grouting

This paper presents a new pre-excavation grouting concept to prevent dripping and reduce the inflow into a railway tunnel. For this purpose, the tunnel’s roof was drip-sealed using colloidal silica and the walls and invert of the tunnel were grouted with cement. The grouting design process followed a structured approach with pre-investigations of core-drilled boreholes providing parameters for the layout. Water pressure tests and pressure volume time recordings were used for the evaluation. Results showed that the design was successful: the total transmissivity was reduced from 4.9 × 10^?08 m²/s to the measurement limit (1.6 × 10^?08 m²/s), and the dripping was reduced to eight spots from the roof. Improved rock characterisation showed that the grout hole separation was within the transmissivity correlation length and that grouting efficiency depends to a large extent on the dimensionality of the flow system of the rock mass.     

Safe velocity of on-fire train running in the tunnel

The safety of a running train on fire in a tunnel is a key issue for rescue operations, and the train velocity is mainly related to its safety. In this study, the relationship between the wind velocity and heat release rate (HRR), temperature field around the train, and flame/smoke pervasion rule were investigated under the conditions of variable train velocity, fire location, and fire source location. Beijing Metro was considered as a typical example, in which the safe velocity was estimated to be ∼41.83 km h⁻¹. Assuming the occurrence of fire at the center of the train, the numerical simulations of the flow field using the sliding grid of CFD were performed for a full-scale tunnel under different HRRs. When the fire source reached to the target section, the velocities of all the monitoring points rapidly increased. The velocities increased as the train tail arrived at the target section. The velocities at the measuring points increased with the increase in height, excluding the value of the position with a distance of 0.025 m from the tunnel ceiling. The average temperature and concentration of smoke in the annular space between the train and tunnel ceiling had the minimum values when the running train on fire moved with a speed of 45 km h⁻¹. Thus, the safe velocity of a subway train on fire should be managed between 41.83 km h⁻¹ and 45 km h⁻¹.     

Experiments of evacuation speed in smoke-filled tunnel

Among tunnel fire safety strategies, evacuation speed in smoke, which is the basic evacuation performance characteristic, is one of the most important factors when assessing safety. An evacuation experiment in a full-scale tunnel filled with smoke has been done in order to clarify the relation between extinction coefficient up to Cs = 1.0 m⁻¹, which includes Cs = 0.4 m⁻¹ as a Japanese road tunnel fire prevention standard, and evacuation speed. The maximum, minimum and mean values of normal walking speeds are almost constant regardless of the extinction coefficient. As for the emergency evacuation speeds, the maximum speed is largely influenced by extinction coefficient, decreasing rapidly from 3.55 m/s at Cs = 0.30 m⁻¹ to 2.53 m/s at Cs = 0.75 m⁻¹ while the minimum and mean speeds are almost constant with a slight decrease as Cs increases. The maximum evacuation speed trends in the present experiments and those in Frantzich and Nillson (2003, 2004) and Fridolf et al. (2013), lie on the same decreasing logarithmic curve as a function of extinction coefficient.     

Service life prediction of a concrete bridge structure subjected to carbonation

Carbonation-induced corrosion in concrete may often occur in a high carbon dioxide environment. In this study, the risk of carbonation of a concrete bridge in an urban area was evaluated by measuring the carbonation rate and concrete cover depth in three different parts: the sound, cracked and construction joint parts of cover concrete. The average carbonation rate was ordered by the sound > joint > cracked parts, and the concrete cover depth measured by an ultrasonic detector indicated the slightly greater value than the designed one (50.0 mm). Then, the carbonation-free service life at the depth of the steel was calculated, based on in situ information, by the safety factor method and the Monte Carlo simulation. The service life calculated by the two methods was mostly identical. The sensitivity of the carbonation rate and concrete cover depth to the time to carbonation at the depth of the steel was mathematically determined.     

Characteristics and mechanisms of large deformation in the Zhegu mountain tunnel on the Sichuan–Tibet highway

The Zhegu mountain tunnel is a typical long, deep-buried highway tunnel at a high altitude, subjected to low temperatures and high geostress. The tunnel is excavated in carbon phyllite and slate at depths of up to 1000 m below ground, which has resulted in extreme deformation, especially in a depth of 3 m from the tunnel perimeter. The maximum deformation was monitored to be 60 cm, with a maximum deformation speed of 39.3 mm/day. In addition, it took 60–120 days to complete 90% of the deformation. The deformation of the Zhegu mountain tunnel is characterized by serious subsidence of the arch, squeezing outwards of sidewalls, buckling failure of sidewalls and local collapse. The swelling of soft rock is found not to be a main factor of large deformation in the subject tunnel. Three mechanisms of large deformation are derived based on the characteristics and geological conditions, which are plastic flow of soft rock, shear sliding of wedges, and bending of thin-layered soft rock.     

Possibility of using roof openings for natural ventilation in a shallow urban road tunnel

Naturally ventilated urban vehicular tunnels with multiple roof openings have increased in China. Unnecessary gas (polluted air or fire smoke) are expected to be exhausted out through openings. Whether its safety standards can be satisfied or not still needs to be verified. In this paper, a safe CO concentration was firstly discussed, and a heat risk level of very high to extreme up to 46 °C was given. Secondly, a real 1410 m tunnel was proposed, and a 1/10 scale model tunnel was reproduced. Ambient winds of 0.95 m/s in prototype and 0.3 m/s in model were considered. Under normal traffic test, a track circuit was constructed with model vehicles moving on it to form traffic wind, and once the air velocity was larger than 0.31 m/s, the airflows were found to be not relevant to the Reynolds number. The traffic winds were weakened by openings. For three of all tested traffic, the actual air velocities were larger than the required ones, so its air qualities were satisfied. In firing test, two sets of burning experiments were conducted with which the heat release rates (HRR) were 8.35 kW and 13.7 kW. Large amounts of smoke were exhausted out of openings, and the high-temperature was not significant. Full-scale numerical simulations were carried out to verify the experimental results respectively using Fluent 6.0 for normal traffic and FDS 4.07 for firing. The simulations were compared well with the experiments. Further FDS simulations show that the openings’ mass flow rates are influenced little by ambient temperature; with the increasing length of the buried section, much smoke accumulate inside leading to a high temperature; having 4–5 openings in one shaft group is oversize in the actual engineering design.     

Influence of traffic force on pollutant dispersion of CO,NO and particle matter (PM2.5) measured in an urban tunnel in Changsha,China

Environmental safety issues and ventilation problems caused by the construction of urban tunnel have increasingly been attracting people’s attention. Previous studies in China have mainly focused on vehicle emissions and ventilation control technologies in road tunnels, resulting in a research gap on urban tunnel ventilation engineering design. Therefore, a detailed monitoring investigation was conducted from May 22 to June 2, 2013 in Changsha Yingpan Road Tunnel, China. The study aim was to measure the traffic characteristics, air velocity and the carbon monoxide (CO), nitrogen oxides (NO_x) and fine particulate matter (PM_2.5) concentrations in this tunnel, which has two lanes per bore and multiple ramps. Measurement results show that during the workday morning peak, the maximum traffic flow was 1560 passenger-car-unit/h per lane with vehicle speed around 33.6 km/h in the eastbound tunnel, the average air velocity was 3.07 m/s, and the proportion of the light-duty vehicles (LDV) was 97.3%. Under the traffic force (not open fan), the CO and NO average concentrations at the main tunnel outlet were 20.3 ppm and 1.65 ppm, respectively. The gas pollutant concentrations are effectively controlled within the multiple-ramps tunnel and the design air volume flow is noticeably reduced. The traffic air flow was found to provide 32.5% of the required air volume to dilute NO_x in blocked traffic condition (vehicle speed of 10 km/h). In addition, the PM_2.5 concentration is mainly affected by the value of background outside the tunnel. The result can provide a quantitative assessment method to support pollutant concentration control and contribution of requested air volume by traffic flow in urban complex structure tunnel.     

Dowel Bar Retrofit (DBR) performance in Texas

In the last 10 years, TxDOT has utilized Dowel Bar Retrofit (DBR) in five projects. International Roughness Index (IRI), Falling Weight Deflectometer (FWD), Rolling Dynamic Deflectometer (RDD), and coring were employed to evaluate DBR effectiveness in those five projects. Different versions of special specifications were utilized for each DBR project. The main variables in different versions of the specifications are grout material and slot width requirements. Out of the five projects, four projects (SH73, SH73/SH87, US69, and US287) have performed to the designers’ satisfaction. Those four projects demonstrated that DBR was able to improve Load Transfer Efficiency (LTE) and minimize reflective cracking on an AC overlay. The US69 project reveals that after DBR, Diamond Grinding (DG) should be applied to restore the ride quality. Faulting of greater than 25 mm has been successfully corrected by DBR and DG on the US287 project, which still provides good ride quality after 6 years of service. The experiences from these four projects suggest that DBR with either DG or an AC overlay can be used effectively to extend pavement life and restore the ride if it is done properly.However, on the US59 project, the DBR performance is unsatisfactory. Visible faulting of 6.4 mm–9.4 mm developed in less than 2 years. It was found that the primary cause for the unsatisfactory performance was excessive voids under the dowel bar, which prevented proper load transfer at the joint. X-ray tomography results indicate that approximately 50% of the area under the dowel was void. The following four main variables were investigated in the laboratory for potential causes for voids around dowels: (1) time of placement after grout mixing, (2) vibration time of grout, (3) slot width, and (4) maximum aggregate size. It was found that maximum aggregate size, in the range of 9.5 mm–12.7 mm was not a critical factor for the consolidation of the grout. Although slot width above 63.5 mm may be beneficial, it was not a critical factor for grout consolidation either. The factors that had significant effects on consolidation of the grout were time of placement after mixing and vibration time. Delayed placement of the grout without vibration led to substantial voids. These two factors might be the causes for the voids under dowels that led to poor performance of DBR on US59.The most significant factor for the consolidation of grout materials is vibration. Although vibration has been included in the current Texas Department of Transportation (TxDOT) special specifications for DBR, it should be properly enforced to ensure optimum consolidation. Based on the test results, 20 s of vibration is recommended for each slot. In addition, it is preferable to place grout into the slots before the initial set takes place, or within the manufacturers’ recommended working time.     

Challenges and strategies involved in designing and constructing a 6 km immersed tunnel: A case study of the Hong Kong–Zhuhai–Macao Bridge

A 6 km immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge (HZMB) has been designed and funded. Once completed in 2016, the HZMB Tunnel will break the record of the 5.8 km BART Tunnel in the United States, although it will soon be overtaken by the ∼20 km Fehmarn Tunnel between Denmark and Germany that is to be completed in 2020. Construction of the HZMB Tunnel was started in 2011 and more than ten elements thus far have been installed on the site. This paper presents details about the challenges and solutions for the design and construction of the HZMB Tunnel on a strategic level. Special features of the HZMB Tunnel include a long length of 6 km, a deep water depth of almost 45 m, and a thick backfill of 23 m. Challenges include severe marine environment, strict requirements for waterproofing, construction of sections connecting the tunnel with artificial islands, and tunnel stability after future excavation of fairway trenches. Moreover, the HZMB Tunnel is challenged by possible sand liquefaction in seismic events, conservation of white Chinese dolphin, and waterway dispersion during construction. Details about the strategies are given in order to improve the immersed tunnel design and construction methods.     

Pulsations during large-scale fire tests in the Runehamar tunnel

Four large-scale fire tests have been carried out with heavy goods vehicle (HGV) cargos in the Runehamar tunnel in Norway. During two of the fire tests, large pulsations of the gas flow inside the tunnel were observed. These pulsations were registered only when the measured HRR was higher than 125–135 MW. Two different periods of pulsations were registered, short periods of approximately 4 s and longer periods of approximately 18 s. In the article, the pulsations are presented and explanations are given, using a frequency response analysis based on an impedance approach. Using this approach, the authors were able to find the intrinsic resonances of the system, which were close to the periods of 4 and 18 s found in the experiments. Several factors can affect the pulsations, but the calculations show that the oscillation periods are properties of the system. The analyses show further that at certain frequencies (close to those found during the tests), a small disturbance in the flow can create large amplitudes in the pressure. It is proposed that this phenomenon should be studied in conjunction with future full scale tunnel tests.     

Probabilistic assessment to predict the time to corrosion of steel in reinforced concrete tunnel box exposed to sea water

This study concerned the service life prediction, in terms of chloride-induced steel corrosion, of a concrete tunnel-box structure placed on seabed. To calculate the time to steel corrosion, the rate of chloride transport in the identical concrete mix to the structure was tested, and the chloride threshold level for corrosion was assumed by a literature review from 65 published data. Then, the Monte Carlo Simulation was used to calculate the probability of steel corrosion and its corresponding service life, assuming that the corrosion initiates at 10% of the probability of corrosion. As a result, the service life depended on the time dependency of chloride transport. The service life was equated to 31, 51, 85, and 147 years, at 0.1, 0.2, 0.3 and 0.4 of the age factors, respectively, while the time independent model indicated only 27 years of the service life. Finally, methods to raise the service life were discussed.