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Underground structures play an important role in achieving the requirements of rapid urban development such as tunnels, parking garages, facilities, etc. To achieve what is needed, new transportation methods have been proposed to solve traffic congestion problems by using of high-speed railway and subway tunnels. One of the issues in urban spaces due to tunnel excavation is considerable surface settlements that also induce problems for surface structures. There are a variety of published relationships concerned with field measurements and theoretical approaches to evaluating the amount of the maximum surface settlement value due to tunneling. This paper studies the ground surface settlement caused by the Greater Cairo Metro – Line 3 - Phase-1. This project was constructed by a slurry shield Tunnel Boring Machine (TBM). Therefore, this work consists of two parts. The first part presents the details of the project and monitoring results field and laboratory geotechnical investigations in order to determine the soil properties. The second part is to the comparison between the field measurements and theoretical approaches for surface settlement due to tunneling construction. At the end of the works, the results show that the more convenient methods which approach the field measurements, and the major transverse settlement occurs within the area about 2.6 times the diameter of the tunnel excavation. Doi: 10.28991/cej-2020-03091617 Full Text: PDF

Based on full-scale field trials, this study investigated the mechanical properties of geocell-reinforced asphalt pavements. The field site is a four-lane highway in Hubei province in China. The dynamic load tests were performed for the geocell-reinforced and unreinforced pavement under three different conditions of axle loads and running speeds. The static load tests were carried out under three different axle loads which were the same as the dynamic load tests. The dynamic and static responses were studied in relation to the peak of the longitudinal strain, creep strain, and the improvement factors. Field trial results revealed that the longitudinal strain peak value of the pavement structure reinforced by Polypropylene geocell was significantly reduced in comparison with the pavement response without geocell. In addition, the reinforcement system had a certain inhibiting effect on the creep strain and the improvement factor increased with increasing axle load and decreased with increasing speed. Under 100 kN axle load, the improvement factors were 0.78, 0.68, 0.54, and 0.39 at speeds of 0, 20, 40, and 60 km/h. Under 150 kN axle load, the improvement factors were 0.96, 0.89, 0.75, and 0.61 at speeds of 0, 20, 40, and 60 km/h. Under 200 kN axle load, the improvement factors are 1.21, 1.1, 0.97, and 0.79 at speeds of 0, 20, 40, and 60 km/h. This research helps to provide a new and effective method of asphalt pavement reinforcement.

Ballast tamping is considered as an important maintenance process for railway infrastructures and has a large influence on the capacity of any railway networks. But optimizing the plan of that process is a complex problem with a high cost. This paper discusses optimizing tamping operations on ballasted tracks to improve the track geometry and reduce the total maintenance cost. A mathematical model for this problem in the literature is improved here by including the restriction on the resources (tools, workers and budget) in the model and including constant/variable values for track possession cost and available resources. The optimal solutions obtained for all instances are found by using the global optimization. Besides, a numerical study is presented to test and evaluate the model performance. The results show that the proposed model can be adopted by the infrastructure manager (IM) to make suitable tamping scheduling decisions under normal or private conditions; however, the private conditions lead to an increase of the final cost compared to that of the normal ones. Doi: 10.28991/cej-2020-03091601 Full Text: PDF

Closely-spaced side-by-side mechanized twin tunnels are commonly used in urban metro transit systems. The aim of this paper was to investigate the influence of tunnel construction on an adjacent existing tunnel using the 3D discrete element method (DEM) and propose a new method to protect the existing tunnel. The first tunnel at the left side was initially included in the DEM model. The construction of the second adjacent tunnel at the right side was then modelled in phases. Displacement, stress variation, porosity variation, and coordination of surroundings of the first tunnel were investigated. The results showed that the excavation of the second tunnel had a great negative impact on the existing tunnel surroundings when the distance of twin tunnels was less than the diameter of the tunnel. The maximum horizontal displacement occurred at the angle of 45° and was equal to 103 mm. The influenced area of the existing tunnel is the surroundings between the tunnel crown and the spring line on the second tunnel side near the tunnel lining. The composite reinforcement method consists of pasted fiber reinforced plastic (FRP) sheet method and grouting in a specific area; thus, the structure safety and the normal operation of the existing tunnel nearby can be guaranteed. The protective method can give reference for similar project.

Train vibration from closely aligned adjacent tunnels could cause safety concerns, especially given the soaring size of the tunnel diameter. This paper established a two-dimensional discrete element model (DEM) of small (d = 6.2 m) and super-large (D = 15.2 m) diameter cross-river twin tunnels and discussed the dynamic characteristics of adjacent tunnels during the vibration of a train that runs through the tunnel at a speed of 120 km/h. Results in the D tunnel showed that the horizontal walls have the same horizontal displacement (DH) and the vertical walls have the same vertical displacement (DV). The stress state of the surroundings of the D tunnel is the decisive factor for DH, and the distance from the vibration point to the measurement point is the decisive factor for DV. Results in the comparison of the d and D tunnels showed that the D tunnel is more stable than the d tunnel with respect to two aspects: the time the tunnel reaches the equilibrium state and the vibration amplitude of the structure’s dynamic and static responses. The dynamic characteristic of the d and D tunnel is significantly different. This research is expected to guide the design and construction of large diameter twin tunnels.

Tunnels excavated through weak rock masses using the Shallow Tunneling Method (STM) call for rigid lining support to withstand and constrain the mobility of the unstable rock where its performance needs to be assessed with field measured data in case of potential failure. For fear of any further hazards after the occurrence of a rock fall at chainage km 86,685 m in the Longsheng Tunnels, the monitoring plan was specially modified to accurately obtain the relative vertical and horizontal displacements of the steel rib component in the arch-shaped composite rigid primary lining that was simply placed on the heading. In this paper, the weak rock masses’ interaction with the rigid lining is treated as unknown distributed loads divided into radial and tangential directions, where the influence line theory is applied to better understand the response of the lining so as to facilitate a displacement-based back analysis for unknown rock mass loads and the resultant stress outcome. By comparing the back analyzed stress outcome with the measured one, the proposed performance assessing method for the unclosed arch-shaped lining was proven to be time efficient with acceptable accuracy, which is of considerable application potential and can provide a reference for similar engineering.

Floods result in many problems, which may include damage to cross-river tunnels. The cross-river tunnel, as a new style of transportation, deserves a large amount of attention. In this paper, a large-scale cross-river tunnel model is proposed based on discrete element method (DEM). Micro parameters used in the model are calibrated by proposing a triaxial numerical model. Different in situ strata, high water pressures of normal flood-water levels and random vibration levels induced by running trains are taken into account to evaluate the dynamic characteristics of a high-stress tunnel in deformation and stress analysis. The results show that the upper half of the tunnel, including the concrete lining and the surroundings, is at higher risk than the lower half. Vibration waves transferring into the surroundings undergo an amplification process. The particles of the surroundings at the vault of the tunnel separate and move downward and then reassemble during the dynamic vibrations. The vibration levels, represented by particle accelerations, are lower under flood conditions than those under normal conditions. As train speed increases, the acceleration of the track and particles in the foundation increases, accompanied by a decrease in deformation.

This paper presents an optimization model for the problem of optimal scheduling of tamping actions on ballasted tracks. The model extends an existing one in the literature by including the unused life costs for track sections in the objective function and introducing available workforce constraints in the model. The aim is to obtain an optimal schedule for tamping actions minimizing the total cost in a finite time horizon using global optimization. The results of numerical study show that consideration of track layout in the problem leads to a significant increase in the total number of tamping actions and the amount of unused life for track sections. It is also found that it is important to use a big value for available workforce in the problem in order to reduce the total cost. The proposed model presents a more realistic solution for the studied problem than the existing work in the literature.

In China, a large number of passengers during peak period are a key problem issue that results in a peak load on the subway tunnel. The irregular vibration due to the overloading of train will cause critical damage to rail track and foundations. Due to the lack of field monitoring data, the effects of trainload-induced irregular vibration to the stability of concrete foundation and surrounding area remain a crucial scientific challenge. In current study, a cross-river tunnel in Wuhan subway 2nd line was selected as a case study. The numerical model was developed by using the discrete element method with the consideration of rail track, sleeper, concrete lining, and surrounding strata. Irregular vibration levels induced by train operation with different loads, which included the normal load and peak load, were applied to the rail. Stress, vertical and radial displacement, and particle acceleration in the rail, sleeper, concrete lining, and surroundings were calculated during the numerical simulation. The results revealed that with the increasing of trainload, the settlement of the rail track increases linearly. The symmetrical position on both sides of the concrete lining was compared and showed that the radial displacement and hoop stress of the particles are evenly distributed. The vibrational frequency of the concrete lining was closely associated with the load frequency. The symmetrical trend of radial displacement of particles in the surroundings showed that the value decreased with increasing distance from the outer edge of the lining. The effective distance of train irregular vibration load in the horizontal path is more than 4.0 m, which should be considered when an adjacent tunnel is constructed simultaneously.

Day by day the call to solve traffic congestion problems is increasing. Subway tunnels and high-speed railway are commonly used for transportation. Therefore, tunnel construction induces soil movement, which in turn affects the stability and integrity of adjacent existing buildings. A series of numerical simulations have been established to investigate the effects of tunnel construction of the Greater Cairo Metro–Line 3-Phase-1 on adjacent pile cap foundations of Garage El-Attaba building. Many parameters have been investigated such as tunnel diameter and the distance between pile and tunnel at different tunnel axis and deep and shallow tunnel. After thorough analysis of the results’ simulation, it was found that the tunneling induces additional axial forces and bending moment as well as increasing axial settlement and lateral deflection. Moreover, the results obtained from the parametric study for the shallow and deep tunnel show that the tunnel depth has a much significant effect on piles responses. Finally, the tunnel diameter has an impact on pile responses as well as the pile cap foundation influenced by the tunnel when the tunnel is in very close vicinity of the pile, and its effect is modest to negligible if located far away from the buildings.

In this paper, a new type of geocell is used to reinforce asphalt mixture to improve its performance. For the reason, an experimental evaluation of the effect of high-temperature resistant geocell reinforcement on compressive strength, tensile strength, Shearing property, water stability and fatigue performance in asphalt mixture has been developed. So, uniaxial compressive test, splitting test, uniaxial penetration test, freeze-thaw splitting test and splitting fatigue test were carried out under different temperature conditions. The results show that after geocell reinforcing, the compressive strength and tensile strength of the asphalt mixture are enhanced, the shear performance is improved due to the high temperature flow deformation is restrained, and the strength reduction rate after freeze-thaw cycle is less than that of unreinforced asphalt mixture, the fatigue life is also increased. This indicates that the geocell obviously improves various aspects performance of the asphalt mixture.

A two-dimensional ballasted railway tracks model utilizing the discrete element method (DEM) with PFC is proposed to analyze the dynamic characteristics of the concrete sleeper, clustered ballast stones and the silty clay subgrade under irregular vibration levels caused by train passes the track. Another model for reducing the track vibrations by using concrete slab is conducted. This is novel to analyze the influence of irregular vibration levels on railway track by using DEM and to consider a simple solution for high settlement and vibrations of track. The concrete sleeper is idealized as a collection of expansive bonded particles assembled together. Ballast stones are modeled as clusters of rock’s properties with different particle numbers. The subgrade has the micromechanical properties of silty clay. The micro parameters of concrete slab are the same as those of sleeper. Analyses have done to reveal the microscale interaction in each layer with different train speed. It demonstrates that the velocity of particles decreases with the depth location increases. As irregular vibration levels progressed, the discrete ballast stones disperse horizontally in certain area. With the increase of train speed, the acceleration of the track increases, however, putting up the same velocity curves. The effect of impact load on railway foundation decreases with the depth increases, especially when the ballast dissipates the kinetic energy. Concrete slab has advantages in reducing the settlement and vibrations of the track.

The increasing number of twin-tunnels constructed in river-crossing subway traffic compels the designers to explore its dynamics performance in the excavation progress. The characteristics of particle accelerations of the granular medium in the surroundings are the important factors to reflect the excavation disturbance. In the construction process of the twin-tunnels, the excavation of the second tunnel (named tunnel_2) will be conducted when the first tunnel (named tunnel_1) is stable. In this paper, a three-dimensional scale model of the cross-river twin-tunnels is established utilizing the discrete element method (DEM) with PFC3D, the model aims to investigate the influence of the twin-tunnels construction on the surroundings. The numerical results show that the accelerations of the particles in the surroundings around tunnel_2 are larger than those around tunnel_1 both in horizontal and vertical directions. Kinetic energy transfers as a transverse wave and is dissipated by the friction resistance and the damping effect as the transmission distance increasing in the surroundings.

Twin-tunnels are widely constructed in large cities because of their many advantages. The first tunnel (named tunnel_1) constructed before a period time than the second tunnel (named tunnel_2) which is to reduce the disturbance between twin-tunnels. In this paper, a three-dimensional scale model of twin-tunnels is established utilizing the discrete element method (DEM) with PFC3D, this model aims to investigate the difference of the vertical displacements and the horizontal displacements of the surroundings in construction process. The numerical results indicate that the peak vertical and horizontal displacements of the surroundings around tunnel_2 are larger than those around tunnel_1. The vertical and horizontal displacements of particles decrease with the distance from the out edge of the twin-tunnels shield lining increases. The existence and evolution of soil arching during tunneling process exert great influence on the stress state and deformation of twin-tunnels surroundings. The peak horizontal displacements are larger in the lateral points of twin-tunnels, while the peak vertical displacements are larger in the vault and bottom points, the tunnel excavation leads the particles around the twin-tunnels move to new location to achieve new equilibrium state. The peak vertical and horizontal displacements occur in own tunnel excavation process, whereas the adjacent tunnel construction affects the displacements as well. The excavation and existence of tunnel_1 have magnified effect on the vertical and horizontal displacements of tunnel_2.

Cross-river tunnel as one of the underground constructions is complicated during its construction. For stability of tunnel excavation, it is emergency to analyze the dynamic characteristics of tunnel deformation under high water pressure. Therefore, a cross-river tunnel model is proposed based on DEM in this paper. Stiffness of particles decreases during excavation process which is as one of excavation methods. Porosity ratio of original porosity over its value at different excavation time has been considered. Radial displacements of particles at different angle around the tunnel are detected during excavation process. It shows that large deformation occurs at the vault of the excavation zone which accompanies with large radial displacement. The upper half of the tunnel performs larger deformation than the lower half part which results in many cracks in the concrete lining, the high water pressure may play an crucial role in it.

The non-recurrent traffic congestion triggered by crashes is one of the most important factors that undermine the traffic efficiency of urban road networks. In this article, an improved cellular automaton model was proposed to simulate the non-recurrent congestion triggered by crashes in grid networks with signalized intersections. Four rules were adopted to represent vehicle movements on road sections and intersections. The network speed is adopted to capture the propagation and dissipation of the non-recurrent congestion. The effect of main influencing factors of crashes on the road network was evaluated through the simulation. Simulation results showed the incident duration and areas affected by the distance between the crash point and the upstream intersection, the number of closed lanes, and the crash duration. In addition, the stop-start wave was observed in the simulation. The realistic findings from the simulations validated the model to have the potential for practical applications in the analysis of the non-recurrent congestion triggered by crashes.

A three-dimensional twin tunnels scale model was established utilizing the discrete element method (DEM) with PFC3D. This model aims to investigate the displacement (in horizontal and vertical directions) and deformation of the first tunnel lining in four different cases which the clear distance of twin tunnels are 5, 10, 15 and 20 m during the second tunnel construction process. The numerical results indicate that the clear distance between twin tunnels and the distance between the measurement points of the first tunnel and the excavation area of the second tunnel are two most critical factors that influence the displacement and deformation of the first tunnel lining. Meanwhile, the soil arching effect, gravity, water pressure and lateral pressure also have an impact on the behavior of the first tunnel. The maximum disturbance of horizontal and vertical displacements occurred in the time points of finishing of the second tunnel. However, the horizontal displacement of the first tunnel is much more sensitive to the vertical displacement. The first tunnel turns to the right and down in direction while having an anticlockwise rotation (φ) during the process of construction of the second tunnel. In addition, the displacement and deformation of the lining of the first tunnel are critical to monitor, and the necessary precautions should be taken to decrease the risk of craze. In conclusion, the influence of the second tunnel excavation on the first tunnel lining could be neglected when their distance is more than 15 m.

The setting of the pre-camber is influenced by lots of factors. Normally, the pre-camber of steel truss girder is set by changing the length of the top chords, which leads to high local stress located between the upper chords and endangers structural stability. In order to obtain ideal pre-camber setting, this paper puts forward a new method to set it by only changing the length of inclined chords, an optimizing model, integrally considering theoretical pre-camber, additional counterforce and stress, is established by applying nonlinear-programming-based temperature rising-and- lowering method, whose optimal solution is solved by MATLAB software. Exampled by one three- span continuous steel truss arch bridge, the results show that, the new method is precise and functional, which can provide reference to similar bridges.

A fuzzy synthetic assessment model of construction safety in a mountainous freeway is established as well as a relevant safety assessment factor system. The weights of factors are calculated by analytic hierarchy process, and the influence sequence of assessment is determined. Choosing Cauchy distribution, subjection function of factor sets and judging matrix were obtained. Safe evaluation vector was calculated and the safety status grade of the freeway was estimated through fuzzy synthetic assessment. The construction safety status of five work sites in Hubei Hurongxi Freeway is evaluated by using fuzzy synthetic evaluation model. Construction safety evaluation ranks and degrees of all work sites were calculated. Results show that the situations of safety control management and the security of the third work site should be strengthened. Results also reveal that the whole safety on the spot can be determined by adopting fuzzy assessment. Also, corresponding preventive and improvement measures are provided.

Carbon fiber – glassgrid anti-ice asphalt pavement is always accompanied by heat conduction, convection and radiation in the process of heat generation. The temperature in the upper layer will be lower in freezing weather so that less heat loss is caused by radiation, and the heat conduction and convection may mainly affect the temperature distribution in road structure layers. The paper built a pavement finite element model for carbon fiber – glass fiber grille anti-ice asphalt pavement by ANSYS, determined the temperature field boundary and initial conditions, calculated and determined the input power under different ambient temperatures, wind speeds, ice thicknesses and analyzed the ice-melting time.

With the rapid development of the national economy, frequent construction safety accidents on mountainous freeways have become the focus of social attention. It is a priority to establish a construction safety early-warning system of freeways in the mountainous region in order to change the passive situation of safety management. From the viewpoint of system engineering, the model of a construction enterprise safety capability was established with the basic principle of analytic hierarchy process. Taking characteristic vectors of paired comparison matrices as weights of every factor, the influence sequence of the assessment factors was determined. Results reveal that production safety liability systems and hazard installation control are key factors that influence construction enterprise safety capability. In order to improve the safety status in construction enterprise, following measures are important in establishing healthy production safety liability systems and reinforce hazard installation control. Analysis shows that the assessment index system of enterprise safety construction based on analytic hierarchy process reflects the key factors that influence construction enterprise safety capability and provides corresponding improvement measures.

A finite element model of tire contacting with pavement has been established using software ANSYS. Pavement mechanical response has been analyzed under the condition of smooth and friction contact between tire and pavement, and compared with that of the uniform load. The distribution of tire pressure has been analyzed; the influence of pavement mechanical response by the friction between tire and road also has been discussed. Results show that: the tire pressure on the road surface is not evenly distributed, but parabolic shape distribution along the driving direction is distributed. There are stress concentrations on both sides of the tire when considering the friction between tire and pavement. The road surface vertical displacement is basically the same under three conditions; the pavement surface maximum vertical stress and maximum shear stress under smooth contact condition were greater than that under friction contact condition. For the vertical stress under uniformly distributed load condition, stress concentration phenomenon is appeared in the loading area; but the horizontal shear stress is very small, only about 20% of the both contact model.

The electrical and mechanical performance of carbon fiber (CF)/carbon black (CB) lightweight concrete (LWC) depends on CF content, preparation method and sand ratio. As CB content is 0.83 vol.%, CF content is more than 0.49 vol.%, and resistivity of CF/CB LWC is less than 102 Ω·cm, Compressive strength and flexural strength reach more than 30 MPa and 5 MPa, respectively. Results show that using a new type of CF mat to prepare CF/CB LWC is an effective method. An experimental pavement model set up in the field using CF/CB LWC can melt snow in real time in spite the snowfall is about 10mm/h.

Using conductive asphalt concrete (CAC) as a type of electro thermal element to melt snow and ice on highways is one of the most efficient, convenient, safe and environmental conservative methods. This paper focused on the influence of components on electrical and mechanical properties on CAC. Results show that the electrical performance of CAC depends on conductive filler content, types of conductive filler, and asphalt aggregate ratio. In order to realize the function of melting snow and ice, the best method to prepare CAC is to use both graphite powder (298# scale graphite) and short carbon fibers (CF) as mixer-filler. As the asphalt aggregate ratio is 8.0, the content of graphite is 50 wt.%, and CF content is between 2.5%~4.0 wt.%, resistivity of CAC is close to or less than 10 2 Ω.cm. Marshall stability and flow value of CAC are also up to the national standard.

The shortest path algorithm is critical for dynamic traffic assignment and for the realization of route guidance in intelligent transportation systems (ITS). In this paper, a hybrid Particle Swarm Optimization (PSO) algorithm combined fluid neural network (FNN) to search for the shortest path in stochastic traffic networks is introduced. The algorithm overcomes the weight coefficient symmetry restrictions of the traditional FNN and disadvantage of easily getting into a local optimum for PSO algorithm. Simulation experiments have been carried out on different traffic network topologies consisting of 15–70 nodes and the results showed that the proposed approach can find the optimal path with good success rates and also can find closer sub-optimal paths with high success ratio for all the tested traffic networks. At the same time, the hybrid algorithms improve greatly the efficiency of the convergence of the fluid neuron network, and decrease the computation time of optimization path.

The push-over analytic method has been widely employed to study aseismatic performance of bridge structure. Given proper conditions, this efficient and straightforward method can conduct as reliable as more complicated methods. However, most push-over analyses are based on single-degree-of-freedom (SDOF) system and basic vibration mode of the structure, which may be not suitable for long-span and high-pier bridge. Through finite element analysis, this paper compares the seismic response of continuous girder bridge between the method considering basic vibration mode only and the method considering higher-order vibration modes. A dynamic time-history analysis of the bridge is also conducted to determine the reliability of the push-over analytic method considering higher-order vibration modes.

The climate and natural conditions are comparatively arid and in the western area of China. Many highways, passing through the desert fringe or hinterland are endangered by the wind and tignum is scarce along the roads. The non-burnt brick, being made of aeolian sand, utilizing cementations material has many advantages such as high strength, corrosion-resistance, water-fast, frost resistance, and so on. This paper summarizes the results of the experimental investigation on the non-burnt brick, which demonstrates that the brick used in road kerb and slope protection can not only minimize the engineering cost, but also decrease the sand erosion. The practice shows that the brick being made of aeolian sand used in road has a good effect on engineering economy and road protection. This provides a new kind of protective material for road construction in desert areas.

Simply supported bridges are common bridges in China which have exhibited considerable vulnerabilities in past earthquake events. This paper takes a bridge in BaoTou as a case, by means of the finite element method (FEM) software MIDAS/CIVIL. Elastic response spectrum analyses are conducted for this bridge with different span lengths, number of spans, and pier height. The results show that bridges with the same length but divided into a smaller number of spans are found to be more vulnerable to earthquake excitations than those with larger number of spans. Increasing span length is also found to have a negative impact on the seismic capacity of the bridge. Also, the height of the piers may add to the risk of damage to the bridge during an earthquake. This study will serve as a reference to another bridge downstream, which has the same length and same spans but different deck width.

Road surface ice refers to an ice layer formed after the ice rain agglomerates on the cold road surface. In cold damp mountainous area during the winter, the coagulant ice easily forms on the road surface and substantially reduces the skid resistance ability of the road, thus resulting in decreased road traffic navigability. Traditionally, some conventional ways, such as dusting the salt and sand, paving grass mats, or mechanically removing the ice, have been used to improve the skid resistance ability of roads. But these traditional ways of removing the snow and melting the ice not only have worse efficiency in removing the ice, but reduce the function of the road’s surface. They also lead to breaching the breach of beauty of scenic spots pollution of environment. By analyzing the functional effect of salt deicers, a new type of active anticoagulation-ice road (storage-salt road) is put forward in the paper. The concept of storage-salt road is explained, the functional mechanism of melting ice on the storage-salt road is analyzed, the combined schemes for structural layers of the storage-salt road are designed, and the environmental application to road structural layers is also studied; The practice has proven that, by using the storage-salt road, surface ice can be effectively removed from those cold damp mountainous roads. The exploration and application of storage-salt roads shall promote the progress of research on the coagulant ice prevention technology in the area where the ice rain frequently occurs in our country. It is of great importance to improving the technical level of the road construction field in our country.