爆炸应力波作用下层理介质断裂的动焦散实验分析

利用爆炸加载动焦散试验系统,进行了有机玻璃的透射式动焦散试验.记录了含层理介质裂纹扩展的全过程,发现裂纹穿过层理偏移一定距离后继续扩展的现象.给出了爆炸荷载作用下裂纹尖端应力强度因子随时间的瞬态变化曲线.对爆炸应力波在层理介质中引起断裂的机理进行了进一步的研究,讨论了层理对应力波传播的影响.利用应力波传播理论分析,得出层理中裂纹与层理后裂纹产生的机理不同,为层理岩体定向断裂控制爆破研究提供了新方法.

含垂直层理介质在切缝药包爆破下裂纹扩展行为的试验研究

岩体中层理对切缝药包爆生裂纹的扩展有重要影响。本文采用焦散线方法研究垂直层理介质在切缝药包单孔/双孔爆破下爆生裂纹的扩展规律。结果表明:与无层理介质相比,在垂直层理介质中,切缝药包单孔爆破下爆生裂纹的扩展速度下降,炮孔一侧裂纹扩展的最终长度降低约15.5%;爆炸应力波在层理处产生的反射波使相向扩展爆生裂纹尖端的应力强度因子K^d_Ⅱ增大、K^d_Ⅰ降低,抑制了爆生裂纹的扩展,且炮孔距离层理越近,层理对该侧炮孔处裂纹的阻碍效应越强;切缝药包双孔同时起爆时,相邻炮孔产生的爆炸应力波对相向扩展的爆生裂纹有促进作用,使裂纹尖端的应力强度因子和裂纹扩展速度均显著提高,裂纹直接穿过垂直层理继续扩展,提高了层理岩体中爆生裂纹定向扩展的能力,裂纹扩展的最终长度较单孔爆破时增大50%以上。研究结果为层理岩体中开展切缝药包定向断裂爆破提供参考。

含预制双层理的半圆盘模型冲击试验

通过含预制双层理的半圆盘缺陷介质来模拟真实岩体受到冲击荷载下的断裂特性,采用焦散线实验方法测量了试件破坏过程中裂纹尖端的动态应力强度因子的数值及裂纹扩展轨迹、速度等数值。实验表明:当取层理面与预制裂纹之间的角度为变量时,角度减小对裂纹扩展有着阻碍作用,60°试件穿过了两道层理,45°试件和30°试件未能穿过第二道层理面,且三者裂纹扩展时经过第一道层理面的偏移量分别为20.6 mm、32.3 mm、26.6 mm。三种试件在裂纹未扩展至层理面前的开裂只受到Ⅰ型应力强度因子的影响,开裂主要受拉应力作用,后期的开裂机制变得复杂,受到两种应力强度因子作用,且在层状岩体中,层理面的结构相对薄弱,容易在受到冲击荷载下发生开裂。研究结果对于工程实例中层状岩体的结构强度的研究有着重要的参考价值。

BISQ model based on a Kelvin-Voigt viscoelastic frame in a partially saturated porous medium

Taking into account three important porous media mechanisms during wave propagation （the Biot-flow, squirt-flow, and solid-skeleton viscoelastic mechanisms）, we introduce water saturation into the dynamic governing equations of wave propagation by analyzing the effective medium theory and then providing a viscoelastic Biot/squirt （BISQ） model which can analyze the wave propagation problems in a partially viscous pore fluid saturated porous media. In this model, the effects of pore fluid distribution patterns on the effective bulk modulus at different frequencies are considered. Then we derive the wave dynamic equations in the time-space domain. The phase velocity and the attenuation coefficient equations of the viscoelatic BISQ model in the frequency-wavenumber domain are deduced through a set of plane harmonic solution assumptions. Finally, by means of numerical simulations, we investigate the effects of water saturation, permeability, and frequency on compressional wave velocity and attenuation. Based on tight sandstone and carbonate experimental observed data, the compressional wave velocities of partially saturated reservoir rocks are calculated. The compressional wave velocity in carbonate reservoirs is more sensitive to gas saturation than in sandstone reservoirs.

Mathematical treatment of wave propagation in acoustic waveguides with n curved interfaces

There are some curved interfaces in ocean acoustic waveguides. To compute wave propagation along the range with some marching methods, a flattening of the internal interfaces and a transforming equation are needed. In this paper a local orthogonal coordinate transform and an equation transformation are constructed to flatten interfaces and change the Helmholtz equation as a solvable form. For a waveguide with a flat top, a fiat bottom and n curved interfaces, the coefficients of the transformed Helmholtz equation are given in a closed formulation which can be thought of as an extension of the formal work related to the equation transformation with two curved internal interfaces. In the transformed horizontally stratified waveguide, the one-way reformulation based on the Dirichlet-to-Neumann （DtN） map is then used to reduce the boundary value problem to an initial value problem. Numerical implementation of the resulting operator Riccati equation uses a large range step method to discretize the range variable and a truncated local eigenfunction expansion to approximate the operators. This method is particularly useful for solving long range wave propagation problems in slowly varying waveguides. Furthermore, the method can also be applied to wave propagation problems in acoustic waveguides associated with varied density.

A New Numerical Solution of Fluid Flow in Stratigraphic Porous Media

A new numerical technique based on a lattice-Boltzmann method is presented for analyzing the fluid flow in stratigraphic porous media near the earth's surface. The results obtained for the relations between porosity, pressure,and velocity satisfy well the requirements of stratigraphic statistics and hence are helpful for a further study of the evolution of fluid flow in stratigraphic media.

Seismic Waves in Layered Media

This paper is organized as follows. After a discussion of the differential equations for wave propagation in the horizontally stratified medium and of the initial and boundary conditions, the displacements are derived on the free surface of the layered medium for plane waves when a point source is located on the s-th imaginary boundary at the depth -s （physical parameters of the layers s and （s ＋ 1） are put to be identical）. Then, the source will be represented as a single force of arbitrary orientation and a general moment tensor point source. Further, ＂a primary field＂ for a point source will be introduced. Matrix method for the solution of the direct seismic problem is considered based on the matrix method of Thomson-Haskell and its modifications.

Energy flux characteristics of seismic waves at the interface between soil layers with different saturations

Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium,the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained.Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids(i.e.,water and gas)flow in the interstices.Three compressional waves(i.e.,P1,P2,and P3 waves)and one shear(i.e.,S wave)wave exist in the unsaturated soils.The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly.At last,numerical computations are performed and the results obtained are respectively depicted graphically.The variation of the energy ratios with the incident angle,wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail.The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves,but also by the saturations of the upper and lower soil layers.It is also verified that,at the interface,the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected.This study is of importance to several fields such as geotechnical engineering,seismology,and geophysics.