1、河北大学 2012 届本科生毕业论文 （设计） 1 1 Basic mechanics of soils Loads from foundations and walls apply stresses in the ground. Settlements are caused by strains in the ground. To analyze the conditions within a material under loading, we must consider the stress-strain behavior. The relationship between a stra
2、in and stress is termed stiffness. The maximum value of stress that may be sustained is termed strength. 1.1 Analysis of stress and strain 1） Special stress and strain states 2） Mohr circle construction 3） Parameters for stress and strain Stresses and strains occur in all directions and to do settle
3、ment and stability analyses it is often necessary to relate the stresses in a particular direction to those in other directions. normal stress = Fn / A shear stress = Fs / A normal strain = z / zo shear strain = h / zo Note that compressive stresses and strains are positive, counter-clockwise shear
4、stress and strain are positive, and that these are total stresses (see effective stress). 1.1.1 Special stress and strain states In general, the stresses and strains in the three dimensions will all be different. There are three special cases which are important in ground engineering: 河北大学 2012 届本科生
5、毕业论文 （设计） 2 General case princpal stresses Axially symmetric or triaxial states Stresses and strains in two dorections are equal. x = y and x = y Relevant to conditions near relatively small foundations, piles, anchors and other concentrated loads. Plane strain: Strain in one direction = 0 y = 0 Rel
6、evant to conditions near long foundations, embankments, retaining walls and other long structures. One-dimensional compression: Strain in two directions = 0 x = y = 0 Relevant to conditions below wide foundations or relatively thin compressible soil layers. Uniaxial compression x = y = 0 This is an
7、artifical case which is only possible for soil is there are negative pore water pressures. 1.1.2 Mohr circle construction Values of normal stress and shear stress must relate to a particular plane within an element of soil. In general, the stresses on another plane will be different. To visualise the stresses on all the possible planes, a graph called the Mohr circle is drawn by plotting a (normal stress, shear stress) point for a plane at every possible angle. There are special planes on which the shear stress is zero (i.e. the circle crosses the normal stress
