川藏公路地质环境与整治改建方案的思考

川藏公路由于地质环境复杂、建设标准低、后遗病害多,抗灾能力差,泥石流、滑坡、山崩、雪害、水毁等自然灾害频繁发生,公路阻车断道严重。国家投入巨资进行整治改建,并取得了明显的效果,但由于自然环境特殊、影响因素复杂,许多特大型、大型工程地质病害问题还没有可行、可靠的解决方案。本文通过分析川藏公路沿线的地质环境和灾害特点,总结历年整治改建和经验的教训,提出川藏公路建设的途径、可能达到的目标和应采用的原则。

CHARACTERISTIC OF RAYLEIGH WAVES IN TRANSVERSELY ISOTROPIC FLUID-SATURATED POROUS MEDIA

Fluid phase in the porous media has great influence on the propagation characteristic of Rayleigh waves. Though many researches have been carried out on the propagation of Rayleigh waves in the fluid saturated porous media, the emphasis is mainly focused on the isotropic solid skeleton and the non-viscous fluid. The effects of fluid viscosity on the propagation characteristic of Rayleigh waves are seldom calculated or discussed. However, clarification of the characteristic of Rayleigh waves in the anisotropic viscous-fluid saturated porous media have significant meaning in many practical fields such as oil extraction engineering, protection and control of pollution in geophysics and hydrology.In this paper, the propagation characteristic of Rayleigh waves in transversely isotropic viscous-fluid saturated porous media is studied based on Biot's theory under the assumption that the symmetry axes of the transversely isotropic skeleton and dynamic permeability are parallel to the vertical axis of the borehole. With consideration of the dissipation due to the fluid viscosity and the compressibility of the solid grains, the three-dimensional complex characteristic equation of Rayleigh waves in the transversely isotropic fluid saturated porous media for the real frequency domain is derived by introducing the dynamic permeability, and the existing conditions are also given. The Rayleigh wave speeds and particle traces in different sagittal planes are calculated. The effects of the porosity and the fluid viscosity on the propagation of Rayleigh waves are numerically simulated. The analytical results show that when the fluid viscosity is taken into account, the Rayleigh wave speed is frequency dependence, which is different from the situation when the solid skeleton is isotropic or the fluid viscosity is omitted. The Rayleigh wave speed is not only decided by the velocity of fast and transverse waves in the solid skeleton, but also affected by the velocity of the slow waves.