Như đã nêu trong chương trước, sự biến dạng của đất được xác định bởi stresse hiệu quả, đó là một biện pháp cho các lực lượng liên lạc giữa các hạt truyền. Các biến dạng đất là một hệ quả của các chuyển vị địa phương ở cấp độ của các hạt cá nhân. Trong chương này, một số trong những khía cạnh chính của những biến dạng sẽ được thảo luận, và điều này sẽ dẫn đến tính chất chất lượng của các mối quan hệ giữa căng thẳng và căng thẳng. Trong chương sau những mối quan. | Chapter 12 STRESS STRAIN RELATIONS As stated in previous chapters the deformations of soils are determined by the effective stresse which are a measure for the contact forces transmitted between the particles. The soil deformations are a consequence of the local displacements at the level of individual particles. In this chapter some of the main aspects of these deformations will be discussed and this will lead to qualitative properties of the relations between stress and strain. In later chapters these relations will be formulated in a quantitative sense. Compression and distorsion In the contact point of two particles a normal force and a shear force can be transmitted see Figure . The normal force can only be a compressive force. Tension can not be transmitted unless the soil particles are glued together. Such soils do exist . calcareous soils near the coast of Brazil or Australia but they are not considered here. The magnitude of the shear force that can be . transmitted depends upon the magnitude of the normal force. It can be expected that if the ratio of I shear force and normal force exceeds a certain value the friction coefficient of the material of the par. ticles the particles will start to slide over each other which will lead to relatively large deformations. . . The deformations of the particles caused by their compression can be disregarded compared to these . . sliding deformations. The particles might as well be considered as incompressible. This can be further clarified by comparing the usual deformations of soils with the possible elastic deformations of the individual particles. Consider a layer of soil of a normal thickness say 20 m that Figure Particle contact. is being loaded by a surcharge of 5 m dry sand. The additional stresses caused by the weight of the sand is about 100 kN m2 of MPa. Deformations of the order of magnitude of or even 1 are not uncommon for soils. For a layer of 20 m thickness a deformation of
