Experimental Investigation Of The Interaction Between A Shock Wave And A Sand Layer

The dynamical behavior of granular materials subjected to the loading of the explosive impact is closely related to a variety of phenomena, such as earthquake, soil explosion and explosion shock protection, which involved the interaction between shock waves and material skeletons, and the mutual coupling between gas filtration and granular layer compression. In order to study the evolution of shock waves in different samples of quartz sand layers and stress-strain response of the sand layers, this thesis established an experimental platform, based on the technology of shock tube system, to carry on system research on the interaction between shock wave and sand layer. We analyzed the influence of gas filtration, sand particle diameter and moisture content to propagation process of the transmitted wave and compaction wave, as well as sand stress-strain relations.By recording the high-speed photograph of the sand layer during the shock wave impact a uni-axial compression take place we can get the sample compressions, from sample different depth, along the direction of propagation of the impacting shock wave. And then we can calculate the rate of the compression changes with the layer depth. Based on installing couples of transducer at different cross-section along the side-wall and at the end-wall of the shock tube test section which was filled with the sand material, one transducer without isolation plug measures the total stress acting on it while the other with isolation plug measures only the pore pressure exerted on it by the gaseous phase of the sand layer. By means of the presented experimental technique the time histories of the pore pressure and the total stress are obtained. By subtracting the pore pressure curve from the total stress curve we can get the compaction stress curve. The pore pressure curve and the compaction stress curve represent the changes of the local pressure resulting from the propagation of the transmitted wave and compaction wave respectively. After it propagates into the sand layer, the transmitted wave evolves to compression wave with its pressure rising rate decreasing with the depth of the sand layer. In the superficial sand layer the amplitude of the pore pressure will eventually rise to P5. The compaction wave has a sharp initial peak stress whoes width less than 1ms, and then the compaction stress at the superficial sand layer decay rapidly under the influence of the rarefaction wave, but the compaction stress at the deep sand layer will decay to one steady pressure which is much smaller than P5.The gas filtration effect can increase the amplitude of the pore pressure and the pressure rise rate. Even gas filtration effect can increase the amplitude of the stess slightly at the superficial layer, its effect has little contribution on the deep layer. With the increase of the sand particle diameter, the porosity and permeability of the sand layer increase, resulting in gas filtration effect becoming more obvious and the amplitude of the pore pressure is much higher. With the increase of the moisture content, the pore pressure and the compressive stress at the superficial layer increase due to the frictional dissipation weakened by the lubricating effect of the interstitial fluid. Moreover, due to the drainage and the liquid exudation at the bottom of the test section, the relevance between the compressive stress and the moisture content is not so significant.The peak stress values registered at the side and at the end-wall can be used as approximations for the lateral stresses and the axial stresses. By comparing the stress-strain relations of different samples, we found that the gas filtration strengthen the dynamic response of the sand layers, and the dynamic Young’s modulus is significantly higher than the case of without gas filtration. A small amount of interstitial water makes the compression of the sand layer more difficult, and increases the dynamic Young’s modulus. The drainage effect is much more obvious as the water content increases, inducing a large number of pores to soften the sand layers and making the sand layer more easily compressed. The quantitative breakage extent of the samples after dynamic loading are obtained with CAMSIZER. Without gas filtration effect the breakage extent of the samples increase. And a small amount of interstitial water can increase the breakage extent of the samples due to the higher stress.