Initial stresses in soils
This chapter deals with the initial state of stress in soils, which occurs before any external loading has been applied. The effect of water in soils will be studied and the very important concept of effective stress is introduced. Water enters soils through infiltration and forms aquifers or groundwater. When a soil profile presents several pervious and impervious layers it may lead to the formation of phreatic, confined or artesian, and perched aquifers. The state of stress can only be determined if one knows the stresses occurring on three perpendicular planes. Therefore, in addition to vertical stresses, one must know horizontal stresses in order to determine the initial state of stress. The chapter also discusses Terzaghi’s experiment to demonstrate the effective stress principle, effective stresses in hydrodynamic conditions, vertical and horizontal effective stresses in a soil element, and Mohr’s circles.