Current trends in the development of soil mechanics

Abstract

In the 1920s, K. Terzaghi, who was a combination of geologist and engineer, set forth the principles of soil mechanics. In the 1930s, N. M. Gersevanov, being an outstanding en- gineer and mathematician, basing himself on the works of K. Terzaghi and the theory of elasti- city, gave a mathematical direction to soil mechanics based on the relation between stresses and strains. This direction in the Soviet Union and abroad attracted the attention of prom- inent theoreticians and now occupies a dominant position in soil mechanics. Whereas Ter- zaghi regarded soil as a real physical body, scientists of this direction conceive soil as abstract force equations with constant parameters -- moduli of various purposes. Thus two directions have become established in soil mechanics: physical and mathematical. The latter gave no few interesting solutions, for the practical realization of which moduli are neces- sary. The formulas recommended by the Construction Norms and Regulations (SNIP) 11-15-74 for calculating bases with respect to deformations are founded on moduli, including the re- commended soil tests with a 5000-cm 2 plate. This is natural since the moduli of deformation are only abstract mathematical parameters and not real physical indices. However, soils are natural, and it is impossible to separate soil mechanics from natural sciences, among which a leading place belongs to physics, and therefore no matter how rig- orous and sophisticated the mathematical concepts existing in soil mechanics only those of them which to not contradict the basic laws of physics as, for example, the conditions of the conservation of mass and energy, can be considered correct. The theory of elasticity co~responds completely to these conditions. The theory of consolidation due to seepage and the principle of incompressibility of the soil mass do not contradict the condition of con- servation of mass. I could not fit into these conditions the hypotheses of linear and n~n- linear deformations of soils as applied to compressible soils with consideration of a change in their porosity. It is possible that one of the readers can do this. And only after im- posing on these conditions physical conditions, which must include not only the conditions of the conservation of mass and energy but also other physical laws, will it be possible to raise them to the rank of theories. Soil mechanics is an applied science called on to study the behavior of soils in rela- tion to their state of stress. In this connection soils can be only in two states -- solid or liquid. In a solid state under stress (effective of course) all soils experience only elastic deformations and retain their structure. In a liquid state soils, depending on prop- erties and stresses, behave either as very viscous fluids with a density unvarying under stress, which is described by the majority of rheological relations, or consolidate in the case of impossible or hampered expansion as, for example, in consolidometers, or swell in the case of free expansion. The same occurs also in shear, since thin layers of liquid soils form in the shear planes. The boundary between the liquid and solid state, depending on the character of flow, is determined by the strength characteristics, which represent the ulti-