现今斜坡工程安全设计理论的根本缺陷与灾难后果

滑坡及其灾难在世界各地、经现代岩土工程设计施工的斜坡中不断地发生。论文提出、分析和论证了造成工程斜坡滑坡的一个本质原因。它就是现代斜坡工程安全设计理论存在根本缺陷。这个缺陷表现在3个方面。第一,土体抗剪强度参数（有效黏聚力和有效内摩擦角）在斜坡安全设计中假定为常数,不随土体孔隙和含水率的增大而减低到零,孔隙水对土体剪切强度的影响仅体现在孔隙水压强对有效应力的影响。第二,经典岩土力学理论（特别是有效应力原理和排水固结理论）仅能预测外部加载产生土体压剪、孔隙率减小、土体强度增大的岩土稳定工况过程。它们不适用于外部卸载造成土体拉张、孔隙率增大、土体强度减少的岩土破垮工况过程。第三,斜坡安全系数是土体抗剪强度与施加剪切应力的比值。由于土体强度本值（品质）很低,加固工程增加这个比值安全系数达到设计最小值时所能够提供的强度本质（品质）增加量也就不高。斜坡工程岩土体的强度和品质没有得到能够防治岩土体拉张变形和滑垮的根本改善和增强。从而,工程人员必须精心全力地确保低品质斜坡工程岩土不破垮和滑塌。可是,又由于工程斜坡众多和它们的降雨、场地和环境变化较大,上述3个方面现代斜坡工程安全设计理论的根本缺陷可以导致：达到安全设计标准的工程斜坡,在施工和营运过程中,能够发生滑垮、产生灾难后果。本论文特别认为,经典岩土力学理论是仅适用于完全压剪的,应称为压剪岩土力学理论。提出了应该建立既适用压剪又适用拉剪的、新的土力学理论和防抗岩土灾害设计方法。

Fundamental drawbacks and disastrous consequences of current geotechnical safety design theories for slopes

The fundamental drawbacks and their disastrous consequences of the current geotechnical safety design theories for slopes are pointed out, analyzed and evaluated. The drawbacks are as follows: (1) The shear strength parameters of soils (effective cohesion and angle of internal friction) are assumed to have constant values in the design theories. However, they are changeable and can be reduced to zero due to the progressive tensile deformation and increase in void ratios and pore-water contents in the slope soils. (2) The classical theories of soils (such as the effective stress principle and soil consolidation theory) are valid only under the condition of compressive-shearing loading with reduction of soil voids and pore-water contents. They are not suitable to the condition of tensile-shearing loading with increase of soil voids and pore-water contents. This condition is actually what happened during the process of slope failure and landslide. (3) The factor of safety is a ratio of the soil shear strength to the downward sliding shear stress. As the shear strength of soils is small, its increase according to the ratio is very small, which cannot make substantial improvements to the soil quality and resistance to failure. Accordingly, failures and landslides in engineered slopes can commonly occur around the world although geotechnical engineers put tremendous efforts in preventing and controlling their occurrences. The classical soil mechanics is only applicable to the soils subjected to complete compression and shear loading condition, and is a completely compression-shear soil mechanics theory. A new soil mechanics and new geotechnical design methods applicable to soils subjected to either the compression-shear or tension-shear loading conditions shall be developed.