Para explosiones subterráneas, una capa de poco o mediano espesor cerca de la cavidad de una explosión se puede considerar como una estructura de cáscara teórica. Los productos de detonación transmiten la energía efectiva de los explosivos a esta cáscara, que se expandirá produciendo la deformación irreversible del medio circundante. Basados en la conservación de masa, las zonas incompresibles y las condiciones de contorno, se pueden establecer los campos de velocidad cinemática factibles en la zona plástica. A partir de la teoría del equilibrio límite, este trabajo determina las ecuaciones de resistencia de los materiales correspondientes a los diferente campos de velocidad cinemática posibles. Combinado con las condiciones iniciales y condiciones de límite, se resuelven las ecuaciones de movimiento y de resistencia de materiales, respectivamente. Se encuentra que la profundidad crítica de entierro está relacionada positivamente con un factor sin dimensiones de impacto, que refleja las características de los explosivos y el medio ambiente. Por último, se da un ejemplo, lo que sugiere que este método es capaz de calcular la profundidad crítica de enterramiento y los resultados calculados son consistentes con los resultados empíricos.
1. Introduction
Underground explosions have been studied for different purposes [1]. They can be classified into contained explosions (or camouflet explosions), bulging explosions, and cratering explosions. Contained explosions occur when the depth of burial of the explosive is sufficiently deep [2] and the model best suited to such conditions is an explosion in an infinite medium [3]. Bulging explosions occur when the depth of burial of the explosive is within a certain range [4] and are best modelled as explosions in a semi-infinite medium. Cratering explosions may occur in various ways when the depth of burial of the explosive is relatively shallow and they are best modelled as explosions in a semi-infinite medium [5]. A widely accepted zonal model divides the medium near the cavity into a grinding zone, a radial cracking zone, and an elastic zone [6], which can be the basis for the study of bulging and cratering explosions. Owing to their significant military and engineering application, bulging and cratering explosions have arisen widespread concern for a long time. Actually, bulging and cratering explosions are more complex subjects which should take the influence of the free facet into consideration in dynamic models.
At present, the cratering mechanism of blasting can be divided into three kinds of effects: compressional stress wave effects, tensile reflected wave effects, and gas pressure effects. Since crushing and plastic deformation are omnipresent in the medium surrounding the explosive source, compressional stress wave effects predominate. After Hino [7] proposed the concept of blastability coefficient, reflected tensile wave effects have been widely accepted and increasingly investigated by other researchers. To clarify the role of gas pressure in the fragmentation of an underground blast, Kutter and Fairhurst [8] designed a system of model tests in which the combustion products were simulated by pressurised oil. They concluded that the gas pressure played an important role in blasting. Hagan agreed with this view and coined the term “pneumatic wedging” to describe previous observations [9, 10]. Meanwhile, many other researchers, such as Dally et al. [11], Dally et al. [12], and Harries [13], verified the reasonability of the aforementioned view in different ways. However, these research findings exhibit fundamental mechanisms of explosive cratering and cannot be used to solve most practical problems. Therefore, researchers have to formulate different hypotheses or conduct many tests to obtain any more practical computational formulae.
Nowadays, the widely used theories for calculating the explosive charge or the depth of burial of cratering explosions include Livingston’s crater theory [14, 15], Boreskov’s formula [16], Langefors’ formula [17, 18], Vlasov’s formula [19, 20], and Pokrovskii’s formula [21, 22]. However, these theories cannot… Leer más >>
Fuente: http://www.hindawi.com
