جستجوی مقالات مرتبط با کلیدواژه "تونل" در نشریات گروه "پدافند غیرعامل"

Today, the use of tunnels is one of the favorite strategies of armies as well as guerilla forces, and in many cases it is considered one of the important factors of victory. Due to the high contrast of the specific electrical resistance of tunnels with the host environment, the specific electrical resistance method can be called as the most powerful near-surface method for detecting such structures. In this study, conventional electrical tomography arrays have been simulated in order to detect tunnels using the forward modeling method. Based on the obtained results, the dipole-dipole, polar-dipole and Wenner-Schlumberger arrays have the best response in their sections to the presence of the tunnel, and the Wenner array has a weaker sensitivity than all of them. Also, in this study, based on the principle of changing the geometrical  parameters (depth and size) of the tunnel as well as the conductive overburden, solutions have been proposed to hide the tunnels from the field of view of the arrays.

Examining the thermal behavior of concrete lining of tunnels against thermal loads is of special practical importance. The purpose of this research is to investigate the behavior of fiber concrete lining tunnels with rectangular, semicircular and horseshoe sections under the effect of thermal load in a specific time history. In this regard, numerical simulations have been carried out using Abaqus finite element software. Stress-time and deformation-time graphs in fiber concrete coating under the effect of thermal loads have been investigated. Fiber concrete in this research, which is considered as cover in tunnel sections, is of steel fiber concrete type with a volume percentage of 0.5 to 1.5. Also, in addition to the common design loads, the sections are subjected to thermal loading conditions. According to the obtained results, the strength of the investigated sections depends on the amount of steel fibers in the concrete in addition to the appearance. Investigations show that the cross-section with horseshoe shape has the best performance against thermal load and the increase of fibers up to 1.5 volume percent of concrete compared to tunnel linings with a lower volume percentage of fibers leads to stability in a longer period of time.

The purpose of this study is to investigate the effect of blast wave trap on reducing the detonation effect in tunnels and its effect on reducing the load on the explosion-proof door end of the tunnels and to analyze the types of doors in order to determine which type has the best performance against detonation. To this end, the propagation of the waves induced by the explosion of TNT-type beams with different weights is simulated in the tunnel span with a blast wave trap. The AUTODYN hydrocode is used for numerical simulations. The simulation and numerical modeling are compared and validated with analytical and empirical relationships of previous studies. Considering the maximum pressure applied to the tunnel intersection, the proper location of the blast wave trap, the optimal blast wave trap length and its effect on the maximum value of the tunnel end pressure are investigated. The output of the load applied to the end of the tunnel (location of the explosion-proof door) resulting from this time-dependent explosive load modeling is transferred to ABAQUS software to analyze and compare the types of explosion-proof doors. From the point of the load exerted on explosion-proof doors, hinged doors with different flat and arched geometries are analyzed using ABAQUS software and the maximum displacement and von-Mises stress of the doors are compared. The results show that the arch door performs better than the flat door.

Explosions at the entrance of tunnels and underground spaces can lead to losses. To decrease side effects of such explosions, some approaches like dead_end, bends, geometric barriers and anti-explosion doors are available. Using geometric barriers, especially the waveguides, is the most commonly used and economical way. The purpose of this paper is to investigate the effect of the angle of rotation of the longitudinal axis (bend) and the local variation of the tunnel area on reducing the impact of explosions. Appropriate angle of rotation of the longitudinal axis and suitable location for local variation of the tunnel cross section in line with the tunnel are calculated, by numerical analysis, using Abaqus software.  Finally, proper characteristics are used to propose a method, requiring the least drilling in construction (the most economical method), and generating the highest reduction in the effects of the explosion (the highest vulnerability reduction) in explosions near and away from the span. The results show that the localized change in the tunnel cross-section at the end of the direct path and the change in the angle of rotation of the long axis from 135 ° to 90 ° (90 °) will lead to the greatest reduction in pressure.

Underground structures, especially tunnels, are among the most strategic structures for all countries, and they are a potential target of enemy weapons. Therefore, the safety of these structures and the related studies are of the great importance. In the present study, the explosion phenomenon at the surface of the ground and the effect of its wave on the tunnels which are the most important buried structures is investigated by using nonlinear dynamic analysis by ANSYS-AUTODYN software. The effect of the blast wave propagation in soil was simulated with a full geometry in a 3D environment and after ensuring the accuracy of the results, the effect of the tunnel burial depth and the geometry of the cross section in reducing the destructive effects of the explosion on the tunnel were evaluated in a 2D environment. The results indicate that increasing the depth of the buried tunnel and also using sections such as circle, horseshoe, vertical ellipse and egg shape are effective in reducing the destructive effects of the explosion on buried tunnels.

Underground tunnels, play an important role in protecting important installations from various forces including explosions. Surface and penetrating blasts could deteriorate tunnel surcharge, enveloping space and exerting a lot of load on the tunnel lining. Therefore, to withstand the blast, blast load should be taken into account in tunnel design, in such a way that the tunnel could bear the loading caused by devastation of surrounding soil and rock. One of the widely used criteria for assessing failure of tunnel and underground structures due to blast loads is “Peak Particle Velocity”. In the present paper, this criterion is employed in order to investigate the behavior of underground tunnels under blast load using of explicit dynamic nonlinear finite element software LSDYNA. Then, the effect of cross-section on tunnel under blast load is investigated by comparing the peak participle velocity parameter, displacement of center of roof and Von-Mises stress on the rectangular and horseshoe cross-section. It has been shown that, with equal dimension, the environment enveloping the rectangular cross-section possesses higher resistance than horseshoe cross section.

The entrance of defensive underground structures is vulnerable to blast loading. Deliberate use of prominence in the final lining of the tunnel, one of the ways of dealing with the effects of the blast wave and reduce the vulnerability to degradation. In this study, the software (AUTODYN) the explosions in the line with the distance from the mouth of the tunnel simulated and then the effects of deliberate prominence at the end of the tunnel cover Performed directly.The amount of airflow (overpressure) discussed and finally considering the size prominence of the tunnel and reducing the amount of pressure are expressed. The results show that using prominence can Reduce overpressure inside the tunnel For acceptable.

Blast wave trap is one of the ways to deal with and reduce the effects of blast wave inside the secure underground structures. In this paper, the effect of blast wave trap on reducing the overpressure in the main route of the tunnel has been studied. Accordingly, the blast wave propagation of different explosives in various distances from the tunnel entrance including blast wave trap is simulated. Autodyn software is employed for numerical simulation. Based on the ratio of the overpressure applied to blast wave trap to obtained overpressure of the main route after blast wave trap, the appropriate distance and optimum length of the blast wave trap is calculated. The results presents that using blast wave trap can significantly reduce the overpressure applied to the blast wave trap zone. Besides, higher values of overpressure before blast wave trap zone leads to an increase of optimum length of blast wave trap along with more pressure reduction.

One of the ways for reduction the effects of blast wave in tunnel lead to an underground structure is using from blast wave trap. In this paper discussed about the effect of angle's blast wave trap on reducing overpressure entered in main row of tunnel. In this regard, propagation's blast wave of bombs with different weights simulated in distance 1 meter from entrance tunnels with blast wave trap with angle 45,90,135 degrees. simulation of this regard have been done by numerical autodyn software. According to rate of overpressure intered in the place of the bend and overpressure have been obtained for main way ofter bend, percent of increase of preesure obtained. the result of study present that, with increasing angle's blast wave trap, percent of decrease preesure will be biger and its rate depend on overpressure intered in tunnel before bend.

Among the most important factors that influence the decision making and planning in passive defense such as structural hardening and especially underground structures such as tunnels and subways are situation estimate and their response to dynamic loading (caused by an explosion). In this regard, one of the effective factors influencing the amount and distribution of load blasting on an underground structure, is burial depth of the structure and condition of soil reinforcement. Therefore, considering the depths of the tunnel of interest (9 and 12m from the tunnel) and four layers of reinforcement (the distance of one meter from each other), computer simulations using ABAQUS software and comparing the obtained results was implemented. In fact, in many cases structural design (e.g a section of tunnel structures) the geometry and depth of the tunnel as a certain value to the project designer were considered necessary in order to achieve the specific goals of the project, while there are no restrictions in terms of soil reinforcement. In this mode, the best conditions for soil reinforcement can be selected. Simulation results show that by increasing the depth of the tunnel from the depth of 12 meters downward, the impact of blast wave on the behavior of underground structures will be depreciated and for explosive charge, depth of 12m can be introduced as the safe depth for tunnel construction with the soil characteristics and an explosion equivalent to 1000 kg TNT. Moreover, by increasing the reinforcing layers of geogrid to three layers, the reduction of possible damage to the underground structure is observable.

Tunnels are one of the access elements to underground structures playing a vital role in passive defense. In regard to the high cost of constructing tunnels, many methods have been presented to improve and make such projects more cost effective. One of the common methods in our country to construct tunnels is the ditching and firing. In tunnel construction using ditching and firing, the explosive features are determined, taking the stone material of the tunnel site into consideration. The number and diameter of blast holes, type and the amount of explosive material to be used and the explosion pattern, as well, are among the items to be determined. One way to reduce the costs is to use the appropriate type and amount of the explosive material which is in turn, dependent on knowing the specifications of the explosive material and tunnel site stone. The explosive material is especially important due to properties such as density, blast velocity, impedance, energy in mass unit and pressure. Therefore, the type and explosive material for every stone should be exactly identified. Predicting the destruction intensity is dependent on long experience, repeating several explosions and observing the results. In general, after several explosions and observing the results,the optimum amount of explosive material will be determined with trial and error. The explosion simulation before performing the main operation can be one of the appropriate methods to reduce time, costs and predicting better explosion-induced results. In this essay, the equations governing blast wave propagation are solved using limited numerical elements and the behavioral model of RHT has been used as the criteria of separation and submission of stone material. The results of this research indicate that in order to choose reliable explosive material to destroy stones, the most effective variable is the amount of energy on the mass unit of that explosive material. The analytical results of the project sensitivity can be used to reduce the costs of underground passive defense projects.