Numerical Approximation of Blast Loads on Confined Dry-Stacked Masonry Wall

This research intends to numerically study the out-of-plane behaviour of confined dry-stacked masonry (CDSM) walls against blast loading. CDSM is a mortarless interlocking masonry system consisting of Hydraform blocks laid in stretcher bond with reinforced concrete (RC) confining elements. A nonlinear numerical model is developed using advanced finite element hydrocode ANSYS-Autodyn to study the response of CDSM walls subjected to explosive loads. Four different test cases using a charge weight of 4 kg, 8 kg, 12 kg, and 16 kg of Wabox explosive are investigated numerically. The results obtained from numerical simulation are validated with the experimental tests results. The numerical results are found in good agreement with the experimental results. The ability of the numerical model is studied to correctly predict the pressure-time history in pressure gauges installed on walls and compared with experimental data. Peak incident overpressures obtained in these numerical tests ranged from 240 to 1000 kPa. Likewise, the damage patterns obtained from the numerical simulations are compared with available experimental results which show a satisfactory agreement. This study helps to check the response of CDSM structures against blast load which can be used for the construction of blast resisting design of buildings.

PPV and Frequency Characteristics of Tunnel Blast-Induced Vibrations on Tunnel Surfaces and Tunnel Entrance Slope Faces

Tunnel blast-induced vibration probably causes damage to the rock mass surrounding the tunnel surface and also to the rock mass of the slope at the tunnel entrance. It is important to simultaneously monitor the vibration on the tunnel surface and on the tunnel entrance slope face, especially when the blasting work face is close to tunnel entrance. During blasting excavation of the traffic tunnel at Baihetan hydropower station, vibration monitors were installed both on the tunnel surface and on the tunnel entrance slope face. Based on the monitoring data, a comparative study is conducted on the peak particle velocity (PPV) and frequency characteristics of the vibrations at these two locations. A three-dimensional FEM simulation of the tunnel blast is then performed to verify the field test results. The field monitoring and the numerical simulation show that there is significant difference between the vibration on the tunnel surface and that on the tunnel entrance slope face. The vibration on the tunnel surface has greater PPV and faster attenuation, while the tunnel entrance slope face has higher frequency and faster reduction rate in the center frequency. These differences are attributed to the different wave types and wave propagation paths. The tunnel surface is mainly surface waves transmitted through the damaged rock mass around the tunnel profile, while the tunnel entrance slope face originates mainly from the body waves transmitted via the undamaged rock mass inside the mountain. The comparisons of the monitored vibrations with the velocity limits specified in the Chinese standard show that the most dangerous vibration that may exceed the limit occurs on the tunnel surface. Therefore, the maximum charge weight used in the tunnel blast is determined by the vibration on the tunnel surface. Under different control standards, the allowable maximum charge weight per delay is further discussed.

Blast Loading and Its Effects on Building

Terrorist assaults have become more common in recent years. Their main purpose is to destroy important structures such as areas of defense, hospitals, schools, buildings. Due to the explosion, high pressure is generated and the blast time is also very short, but it can damage the structure from outside and inside. Which can cause a lot of damage to human life. There has an influence on the nation's economy. Like the earthquake and wind load, the blast load should also be designed, keeping in mind the important structures that have to be avoided from the explosion. In this research paper, six story R.C.C. Structures exposed to explosion loads are analyzed. We study the effect on the building by changing the weight of the explosive and the distance between the explosion source and the building. The IS 4991-1968 code has been used to calculate the parameters of the explosion pressure waves. The program ETabs 2019 has been used to analyze the effect of blast load. The structure has been modified by providing shear walls to reduce excessive displacement due to blast loading on the building. The results of the analysis are compared after adding the shear wall with the general building model. The result was that after the addition of the shear wall, the effect of blast loading is greatly reduced. Keywords: Blast phenomena, Standoff distance, detonation charge weight (TNT), Front face pressure, Side face pressure, ETABS, RCC, Blast waves, explosive effects, Story Displacement, Storey Drift, Overturning Moment, Shear wall.

Evaluation of internal blast resistance of bi-directionally prestressed concrete tubular structure according to ANFO explosive charge weight

When extreme loading from an internal is applied to prestressed concrete (PSC) structures, serious property damage and human casualties may occur. However, existing designs for PSC structures such as prestressed concrete containment vessels (PCCV) do not include features to protect the structure from the blasts. Therefore, the internal blast resistance capacity of PSC structures is evaluated by internal blast tests on bi-directional PSC tubular members. The goal of the study was to obtain the structural behavior data from an internal detonation. The ANFO charges were detonated at the center of the mid-span of the tube specimen with a standoff distance of 1,000 mm. The data acquired included blast pressure, deflection, strain, crack pattern, and prestressing loss. The data are used derive the equations to calculate the required internal blast charge weight to fail a real-scale PCCV and to calibrate a commercial simulation program to be used for internal blast simulations.

Experimental Study on the Damage Characteristics of Polymer Slabs Subjected to Air Contact and Close-In Explosions

As a new antiseepage reinforcement material, polyurethane grouting material has been widely studied in terms of its static mechanical properties. However, research on its dynamic mechanical properties is relatively rare. In this research, considering the influence of the explosive charge weight, the air contact and close-in explosion experiments of polymer slabs were carried out. The failure mode and damage spatial distribution characteristics of polymer slabs were explored. Pressure time history curve of air shock wave was obtained using an air shock wave tester. The influence of polymer slabs on the propagation of air explosion shock wave was compared and analyzed. The results show that, under the air contact explosion, the polymer slab mainly suffers local damage, while under close-in explosion, overall damage is the main damage mode. With the increase of the explosive charge weight, the failure mode of the polymer slab transits from surface crack and slight spalling to local and whole crushing.

Prediction of flyrock throw distance in quarries by variable selection procedures and ANFIS modelling technique

This study suggests application of variable reduction procedures for flyrock prediction. It was aimed to create robust and non-complex predictive models. Eleven operational blast parameters and rock mass properties were measured in an aggregate quarry. Dominant parameters for flyrock occurrence were determined by multivariate statistical methods. Two parallel ANFIS models were developed for flyrock prediction. The first ANFIS model was constructed based on the results of stepwise regression. Burden-hole diameter ratio, in-situ block size and specific charge are the input parameters of ANFIS 1. The second ANFIS model was created based on the results obtained by factor analysis. Burden-hole diameter ratio, bench height- burden ratio, number of holes and charge weight are used as input parameters for ANFIS 2. The calculated mean absolute percentage errors are lower than eight percent for the ANFIS predictions. The median absolute errors are lower than 5 meters. The study also investigates alternative accuracy measures to evaluate forecasting performance. Standardized errors, normalized errors and Nash–Sutcliffe Efficiency (NSE) were found to be useful for model validation. It is concluded that more than a single model can be created for a specific site. Pre-statistical analysis for variable reduction increases performance of the predictive models. Burden appeared to be a significant parameter for flyrock throw.

Investigating the Effect of the Geometry of RC Barrier Walls on the Blast Wave Propagation

Evaluating the performance of several types of reinforced concrete barrier walls subjected to blast loads is the target of this research paper. A parametric study is carried out for nine RC barrier wall systems with different geometries modelled in the three dimensions with different configurations and variable parameters. ANSYS Autodyn software version 18.2 is used to model and analyse these systems using three-dimensional explicit dynamics analysis. The nine systems are studied under the effect of several parameters, such as explosive charge weight (W) and the stand-off distance from the explosion source to the wall (R). Their effect on the wall damage and its deformations and the pressure-induced at different locations are analysed. Eighteen reinforced concrete barrier wall models are studied to achieve this research goal. Comparisons between the results showed the deformation performance of the 60° concave face with planar back walls and the walls with the constant base of 1.0-meter-thick up to 0.5-meter-high with a face hunch up to 2.0-meter-high are better than all other studied walls. However, the concave face-convex back wall that has 70° curvature mitigate the pressure behind the wall by 10% regardless of its deformation.

Investigation and Control of the Blasting-Induced Ground Vibration under Cold Condition

This paper focuses on the investigation and control of the blasting-induced ground vibration under cold condition. The mechanical performance and wave propagation characteristics of the frozen rock mass are quite different from that of the conventional condition. Laboratory tests were implemented to investigate the wave impedance of rock mass in the frozen, saturated, normal, and drying states. Results reveal the longitudinal wave velocity could be enlarged by 40 percent in the frozen state. Then long-term monitoring of blasting vibration was implemented based on the blasting excavation of the Fengman hydropower station reconstruction project in the north of China. Results demonstrate the PPV and frequency both attenuate much slower when the rock mass is frozen, and the obvious turning points of PPV could be found between different temperatures, where the change of the PPV relationship happens. At last, numerical simulation of the blasting seismic wave attenuation and the response in the protected structure was implemented. The equivalent freezing simulation method was proposed and verified with the site experiment data. Results demonstrate that the attenuation coefficient decreases obviously as the frozen depth of the rock mass increases. The dynamic degree response in structure is much stronger and the maximum charge weight per delay was limited more strictly under the frozen condition. A most adverse frozen depth was determined when the charge weight per delay gets the minimum value. With the above control approaches, a total of 676 blasting was completed in Fengman hydropower station reconstruction and no case of excessive measurement could be found.

A review on the performance of the underground tunnels against blast loading

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 tunnel caused by effects of surface blast loading. The stiffness and strength of the ground media may be enhanced against the effects of blast loading by grouting measures. The studies revealed that the lining materials possessing blast waves absorbing properties can be best suited to be used in tunnel linings. Further, it was observed that more damage was caused to the tunnels due to the magnitude of the charge weight. An increase in the blast load causes a significant increase in the fracture area, residual stress and lateral displacement caused to the tunnel by the action of blast load. The standoff distance of the blast load from the tunnel also plays a significant role in the damage of the tunnel. More is the distance between the charge and the tunnel, lesser damage caused to the tunnels. In addition to that, the lining thickness was predicted and the trend was calibrated and fitted logarithmically with the available results. Based on the observation from the literature, it is concluded that the use of a single lining material in the tunnel against blast loading was studied predominantly in the couple of decades. Further, the performance of the tunnels in combination of different tunnel lining materials against blast loading was found limited. The influence of barriers to save the underground tunnels against blast loading was found limited.

A Re-Look Into Modified Scaled Distance Regression for Prediction of Blast-Induced Ground Vibration

Underground blasts are conducted for deep excavations, tunneling, or mining activities. Scaled distance regression analysis is performed in industry to estimate peak particle velocity from charge weight and distance. For addressing the uncertainties in estimating safe charge weight for controlled blasting, 95% confidence expression is generally used. For addressing inaccuracies arising from superimposition of blast waves in multi-hole blasting when using attenuation equation developed from single-hole blast data, a modified approach was proposed in literature. This article presents comparisons to establish that industrial practice of scaled distance regression would be as satisfactory as the proposed modified approach, when various performance measures (including parsimony) are considered together. Furthermore, industrial practice of using 95% confidence expression generated from sufficient data (say, 40 numbers) would result in safe charge weight estimation, whereas modified scaled distance approach (mean expression) could still result in few non-conservative values.