爆炸波在饱和土介质中传播时压力变化规律的试验研究

Experimental Investigation on Pressure Variation during Explosion Wave Propagation in Saturated Soils

介绍了在Φ900平面波加载器中进行的饱和土爆炸波传播试验,通过试验比较系统地研究了爆炸波在饱和土自由场中的传播规律及其在刚性边界上的反射问题。试验表明饱和土中的气体含量是控制波传播规律的主要因素,在深度方向上自由场应力峰值可能随深度增加,而在刚性边界上荷载反射系数可能>2。对饱和土与非饱和土中波传播规律的区别,在确定饱和土中结构的设计荷载时必须给予极大的关注。

The experiment of explosion wave propagation in saturated soil is accomplished in Φ900 plane blast load generator. In this paper, the explosion wave propagation in free field and its reflection on the rigid boundary are investigated. The experimental results indicate that the air content in saturated soils plays the most important role in the wave propagation; the peak incident pressure might increase alone with the depth of soil specimen; the reflection coefficient might be larger than 2. The laws of explosion wave propagation in saturated soils are very different from that of unsaturated soils according to experimental results, special attention must be devoted to the determination of the loading on the structure buried in the saturated soils. Two main experimental phenomena are expatiated further: 1. The reflection coefficient on the rigid obstacle The incident wave loading of free field cannot be measured directly on the bottom, consequently, the reflection coefficient cannot be calculated directly. As a makeshift, the free field stress P3 is determined by using extrapolation method, a sample point is removed by its illogicality in the first loading. The value of P_4P_3 in the bottom is the reflection coefficient on the rigid obstacle. A tendency to an increase in the reflection coefficient is observed, the maximum is 2.259, and greater than 2.0. It is noticed that the real value of P_4 must be greater than the current value due to the peeling of some soft rings, and the value of P_4P_3 in the bottom should be increased. In a word, the reflection coefficient in the rigid obstacle might be greater than 2.0. This is coincident with the results of saturated soils experiment by Huang^()and saturated porous medium experiment by V. E. Dontsov^(). 2. The 'Inverse-attenuation' Phenomenon The inverse-attenuation phenomenon is defined as the increasing of the incident wave stress in the direction of the wave propagation in the free field, it is easier to appear in partially saturated soils than in the unsaturated soil and dry sands. The necessary condition is an increase of the acoustic impedance in the direction of the wave propagation, if the effects of the plasticity and viscosity etc. are relatively weak, the combined actions will result in the rising of the case. For unsaturated soils and dry sands, the action of the later factor is very great, the case is seldom seen. By contraries, for the partially saturated soils, the increase of saturation in the depth direction might be remarkable, and the compressibility decreases proportionally, compared with the unsaturated soils, the effects of the plasticity and viscosity etc. is relatively weak.