Effect of unconfined compressive strength of rock on dynamic response of shallow unlined tunnel (original) (raw)
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The response of rock tunnel when subjected to blast loading: Finite element analysis
Engineering Reports, 2020
In the past few decade tunnels were targeted to explosives and that resulted in sizeable structural damage. The increase in the strategic importance of tunnel construction has increased the demand for the blast-resistant design approach. The present paper considered an internal blast loading on a rock tunnel constructed in Quartzite rock. A three-dimensional finite element model of the tunnel has been developed in Abaqus. The diameter of the tunnel has been kept constant to a two-lane transportation tunnel. However, the thickness of the concrete liner, depth of overburden, and mass of explosive charge has been varied to understand the response in different possible conditions. The Jones-Wilkins-Lee, Concrete Damage Plasticity, and Mohr-Coulomb material models have been used for the modeling of trinitrotoluene, concrete, and rock respectively. Blast has been formulated through Coupled-Eulerian-Lagrangian technique. The tunnel at 12.5 of the depth of overburden has been found 2.7-times more blast resistant than 5 m. Moreover, the extent of damage in shallow depth tunnels found to be more than the tunnels at higher depth of overburden. K E Y W O R D S Abaqus, blast, coupled-Eulerian-Lagrangian, rock, tunnel 1 INTRODUCTION Underground structures have become an essential part of the metro cities. Construction of the underground structures, especially tunnels for the efficient movement of humans and goods has resulted in the investment of a massive amount of money in the underground space. Therefore, underground structures, especially rock tunnel, have been an active area of research since the mid-19th century. 1-4 Tunnels are considered as high-risk zones due to the presence of numerous patronage in confined space at a single location. 5 Some of the manmade hazards in the tunnels that have caused severe loss of life and property are Bayrampasa metro tunnel attack, London underground metro attack, Moscow metro tunnel attack, Minsk metro bombing, and Saint Petersburg metro attack. 6 Therefore, the blast resistant design of tunnels and other underground utility structures is required. Scientists and researchers have carried out blast-related studies using different approaches. 7-12 Wu et al, 13 carried out the study for the blast wave-induced shock wave propagation in jointed rockmass. They concluded that the characteristics This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Numerical analysis of underground tunnels subjected to surface blast loads
Frattura ed Integrità Strutturale
The increased terrorist attacks on important public structures and utilities have raised the vital necessity for the investigation of performance of structures under blast loads to improve the design and enhance the behavior of structures subjected to such threats. In this study, 3-D finite element analysis is used to study the effect of surface explosions on the response of RC bored tunnels. The soil behavior is modelled using Drucker-Prager Cap model. Two types of soil are investigated, and the blast load is considered through various weights of TNT explosive charges at heights of 0.50 m and 1.0 m from ground surface. To study the effect of horizontal standoff distance, six different horizontal distances are considered. The results show that the soil type has a significance effect on tunnel response due to surface blasts. Also the weight and the location of charge have a great effect on the safety of the tunnel. Finally, a parametric study is established to define the borders of th...
International Journal of Rock Mechanics and Mining Sciences, 1997
Sub-surface structures provide attractive alternatives for storage of explosives and other military hardware. These facilities are commonly constructed at shallow depths where rocks have undergone extensive weathering and the geologic system contains joints and discontinuities. For underground munitions storage structures, risk and performance assessment studies have to be conducted to qualify the site and establish the "clear zone" in case of accidental detonation. At high loading densities, accidental detonation of a munitions storage facility can lead to rupturing of the overburden cover and creation of a hazardous fragment environment. The degree and extent of the "clear zone" is controlled by the overall characteristics of the geologic and engineered systems. Rock joint spacing is considered to be important in prediction of the hazardous range of blast-induced fragments and associated impact energy. A full scale tunnel explosion test was conducted in 1988 in the desert of California. The tunnel was constructed in a weathered, jointed, igneous rock mass with several well defined discontinuities. The information from the overall characteristics of this tunnel was used to construct five scaled model tunnels, with simulated joints and discontinuities, under physical modeling at 1-g. The loading densities used in two of the model tests were equivalent to that of the full scale event. For the other three tests, loading densities were changed in order to determine the effects of the explosive weight on the jointed rockmass response. The tests reported in this paper are unique in terms of size and simulation method. Five large test beds were constructed in trenches filled with model material simulating the full scale jointed rockmass with through-going discontinuities at 20:1 scale. Geometric and strength related properties were scaled, whereas the density scale factors were maintained at unity. The model materials were formulated in such a way that similitude conditions between the properties of the full scale rock mass were maintained. Test beds were constructed by step-by-step casting of the model materials into the excavated trenches. Impedance characteristics of the model materials were matched with those of the host-ground for realistic simulation of the ground shock propagation. This paper provides a brief discussion on the tests performed and elaborates on the applicability and the economics of the physical modeling for studies related to explosives-underground-structures interaction.
Blast Loading Resistance of Metro Tunnel in Shale Rock: A Coupled-Eulerian-Lagrangian (CEL) Approach
American Journal of Civil Engineering and Architecture, 2022
The internal blast loading condition in a tunnel constructed in three-layered shale rock has been incorporated using a coupled-eulerian-lagrangian (CEL) approach in this paper. In this research, the three weathered stages of shale were studied, namely minimally, medium, and highly weathered shale in three layers. As we got closer to the earth's surface from the deep beneath, the weathering of the shale rock accelerates. The overburden depth has been changed to integrate several parametric scenarios in an elastoplastic finite element model with dimensions of 60m x 60m x 60m. The presence of 100kg of trinitrotoluene (TNT) as an explosive is expected A 100kg of trinitrotoluene (TNT) explosive is assumed to be suspended in the air at the middle of the tunnel entrance at an equal distance from all sides. To recreate genuine in-situ conditions, the TNT sphere and air inside the rock tunnel were modeled using the CEL approach. Mohr-Coulomb, Concrete Damage Plasticity, and Johnson-Cook constitutive material models were used to mimic the elastoplastic behavior of various materials, including rock, concrete, and steel bars. To make a reinforced concrete liner, a cage of steel bars has been inserted in the concrete liner by interaction constraints. The tunnel was first buried in the upper layer of shale, with a 5m overburden depth. The tunnel's position has also been altered for overburden depths of 15m, 25m, and 35m. Overburden depth and crown displacement are inversely proportional, according to the results obtained in the form of acceleration, velocity, and displacement for rock. Furthermore, the reinforced concrete liner used in this simulation study exhibits no damage in terms of compression, although a small tensile failure is visible in all scenarios.
Dynamic Analysis of Underground Tunnels Subjected to Internal Blast Loading
2013
In the recent decades, explosion incidents caused by terrorist activities have become a growing threat to the human civilization and civil infrastructure. Underground tunnels used for roadway and railway, utility lines and water pipe lines are an indivisible part of the modern civil infrastructure. Blast loading inside tunnel may cause numerous lives and severe damage of properties. Internal explosion in tunnel may lead to multiple reflections of the blast induced shock wave and the result in channeling of the shock wave. The underground tunnels are seldom designed adequately for sustaining the blast loading. Hence, in order to safeguard the tunnels from blast loading, it is necessary to understand the response of these structures when subjected to blast. Experimental determination of the response of underground tunnels under blast loading often becomes difficult due to socio-political issues. Hence, advanced numerical analysis of tunnels subjected to blast loading is of utmost impo...
Rational Analysis of Tunnels Subjected to Different Explosieve Loads
Due to the progressive development of military destructive weapons such as conventional weapons, a consequence development of the fortified structures is essential. One of the most important types of the fortified structures is tunnel in rock media. A numerical simulation of ground shock from detonations in rock is extremely demanding, requiring hydrodynamic computer codes, combined with non-linear dynamic codes based on discrete elements, discrete fracture and finite elements, which is a very complex approach. The basic premise of this work is studying the response of tunnels in rock-media exposed to high explosion loads, which help the designers and military engineers in estimating displacements, stresses and over all damage in the tunnels due to wave propagation generated by that explosion loads. The numerical analysis is carried out using finite element technique, the commercial software package, AUTODYN; version 4.3 was used to perform three-dimensional nonlinear dynamic analysis used in this study. This program is probably the most extensive code dealing with explosive loads in the world. This paper, gives an overview of simpler approach, based on the use statistically treated of the finite element results with physical principles and analytical solutions to idealized cases. This approach mostly ends up in easy to use closed form prediction equations, which thus constitute a rational tool for practical solution of commonly encountered ground shock problem. In this study, simple equations are developed for different responses of rock tunnel in different parameters based on a regression analysis of the results of a 72 3D-F.E. models.
Blast Response and Failure Analysis of a Segmented Buried Tunnel
Structural Engineering International, 2015
Underground tunnels are vulnerable to terrorist attacks which can cause collapse of the tunnel structures or at least extensive damage, requiring lengthy repairs. This paper treats the blast impact on a reinforced concrete segmental tunnel buried in soil under a number of parametric conditions; soil properties, soil cover, distance of explosive from the tunnel centreline and explosive weight and analyses the possible failure patterns. A fully coupled Fluid Structure Interaction (FSI) technique incorporating the Arbitrary Lagrangian-Eulerian (ALE) method is used in this study. Results indicate that the tunnel in saturated soil is more vulnerable to severe damage than that buried in either partially saturated soil or dry soil. The tunnel is also more vulnerable to surface explosions which occur directly above the centre of the tunnel than those that occur at any equivalent distances in the ground away from the tunnel centre. The research findings provide useful information on modeling, analysis, overall tunnel response and failure patterns of segmented tunnels subjected to blast loads. This information will guide future development and application of research in this field..
Vulnerability analysis of tunnel linings under blast loading
International Journal of Protective Structures
In the present study, a comparative assessment on the performance of conventional and advanced tunnel lining materials subjected to blast loading is done using a three-dimensional non-linear finite element analysis procedure. The conventional tunnel lining materials analyzed herein are plain concrete, steel, reinforced cement concrete, and steel fiber–reinforced concrete. The advanced tunnel lining materials analyzed herein are dytherm, polyurethane, and aluminum syntactic foam sandwich panels with steel–foam–steel composites. The pressure generated by 10 kg Trinitrotoluene (TNT) is applied to each element on the inner wall of the tunnel which has an effect equal to the scaled distance Z = 1.16 m/kg1/3. Analyses are conducted by varying the thickness of lining materials for a tunnel built in rock domain. The response of the tunnel lining materials, for example, deformation, stresses, and strains generated at different interfaces, is compared with each other to assess the best suitab...
A review on the performance of the underground tunnels against blast loading
Journal of Structural Engineering & Applied Mechanics, 2021
The tunneling system has become an important part of the present infrastructure system in all over the world. Therefore, it has become important to ensure the safety of the tunnels against any type of man-made blasting activities or other accidental blasting occurrence. In order to evaluate the performance of the tunnels against blast loading, a detailed review is carried out. Based on the review in the last couple of decades, the various parameters such as tunnel lining materials, tunnel shapes, tunnel lining thickness, tunnel burial depth, charge weight and standoff distance are high influences on the performance of underground tunnels against blast loading. It was observed that the tunnel roof and the tunnel wall center are most vulnerable to the blast loads. Also, it was found that more of the tunnel lining thickness results in lesser deformation at the tunnel roof and the tunnel wall center. The increase in the burial depth of the tunnel would reduce the extent of damage to the...
Behavior of Sedimentary Rock Tunnel against Rigid Projectile Impact
Applied Sciences
The tunnels in present-day cities are experiencing varying degrees of loading conditions ranging from static to extreme loading. Therefore, the stability of underground tunnels needs to be analyzed and understood for safer and strengthened design. The present study was conducted to simulate the impact loading conditions due to a missile traveling at a velocity of 5 Mach for different rock tunnels. The nonlinear continuum finite element analysis has been carried out through Abaqus and Explicit. The four different types of sandstones considered in the present study include Kota, Jamrani, Singrauli, and Jhingurda sandstones. An elastoplastic Mohr–Coulomb constitutive material model has been considered to model the behavior of rock surrounding the tunnel opening. The tunnel has an opening of 7 m in diameter (d), and 50 m in height and breadth, with 50 m of longitudinal length. The deformation and stress in the rock and the damage to the concrete lining have been compared in different ca...