饱和土介质中爆炸波传播的时间特征试验研究

介质中的波速变化规律在很大程度上反映了介质的物理力学特征。本文对在Φ90 0平面波加载器中进行的饱和土试验所反映的波速变化规律进行了深入的分析。试验表明 ,在比较小的爆炸波荷载作用下饱和土中的压力波速可以从约 5 0m/s上升到 4 75m/s,同时饱和土的体积应力应变关系在比较小的爆炸波荷载作用下便会呈现递增硬化特征 ,并与非饱和土介质存在很大的区别。认识这些现象对饱和土本构关系的研究非常有益 ,对了解饱和土中波的传播规律和确定地下结构上的荷载也有很大的帮助

Experimental Investigation on Time Characteristics of Explosive Wave Propagation

The wave speeds reflecting mechanical properties of media are measured in Φ900 plane blast load generator. This paper investigates the time characteristics of explosive wave propagation in saturated soils. The experiment results indicate that the velocity of stress propagation can increase from 50 m/sec to 475 m/sec under relatively small loading in saturated soils, and consequently the volumetric stress strain relation presents the character of increasing hardening; these phenomena are greatly different from that of unsaturated soils. All these results are helpful to studying the constitutive relation and the wave propagation regularity, and conduce to obtaining the design loading on the underground structures in the saturated soils. For the first loading, the rise time decreases with the increasing of the depth firstly, and then the rise time increases with the increasing of the depth. For the other three loading, the rise time decreases monotonously with the increasing of the depth, and the trend of the turning to shock wave exists. This phenomenon differs greatly from that of elastic-plastic geo-materials such as unsaturated soils and sands. For the latter materials, the rise time always increases in the direction of the wave propagation because of its plasticity. In addition, the greater of the overpressure on the ground, the shorter of the rise time.During the loading, the mechanical properties could be drawn by using the wave velocity in most cases. In this paper, three types of wave velocity are discussed: the initial stress propagation velocity C_0, the incident wave peak stress propagation velocity C_1 and the peak reflected stress propagation velocity C_2.The variation regularity of C_1 is the same as that of C_0. Further more, the comparison of C_0 and C_1 in the same time of loading show that C_0 is less than C_1 above a certain depth, and the value of C_0 is larger than C_1 under the depth.The value of C_2 is monotone increasing with the increasing of the depth, the maximum of C_2 appears in the bottom, and equal to 475 m/sec, greater than those of C_0 and C_1.Through comparing of C_0, C_1 and C_2, an especial phenomenon can be deduced: the wave velocity isn't proportional to stress in soils directly, on condition that the density can be considered as the constant approximately. The compression modulus E can be calculated, and has the character: the compression modulus during the early stages of small loading is greater than that under moderate loading, and with the further increasing of loading the compression modulus increases remarkably. This is the main reason why it is easy to generate the shock wave or discontinuous wave in partially saturated soils.