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The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding of particle contacts. Due to interlocking, particulate material may expand or contract in volume as it is subject to shear strains. If soil expands its volume, the density of particles will decrease and the strength will ...
Expressions in terms of cohesion and friction angle [ edit ] Since the Drucker–Prager yield surface is a smooth version of the Mohr–Coulomb yield surface , it is often expressed in terms of the cohesion ( c {\displaystyle c} ) and the angle of internal friction ( ϕ {\displaystyle \phi } ) that are used to describe the Mohr–Coulomb yield ...
This theory, which considers the soil to be in a state of plastic equilibrium, makes the assumptions that the soil is homogeneous, isotropic and has internal friction.The pressure exerted by soil against the wall is referred to as active pressure.
Angle of internal friction for some materials Material Friction angle in degrees Rock: 30 ° Sand: 30 ° to 45 ° Gravel: 35 ° Silt: 26 ° to 35 ° Clay: 20 ° Loose sand 30 ° to 35 ° Medium sand 40 ° Dense sand 35 ° to 45 ° Sandy gravel > 34 ° to 48 °
The angle of internal friction is thus closely related to the maximum stable slope angle, often called the angle of repose. But in addition to friction, soil derives significant shear resistance from interlocking of grains. If the grains are densely packed, the grains tend to spread apart from each other as they are subject to shear strain.
The results of the tests on each specimen are plotted on a graph with the peak (or residual) stress on the y-axis and the confining stress on the x-axis. The y-intercept of the curve which fits the test results is the cohesion, and the slope of the line or curve is the friction angle. Direct shear tests can be performed under several conditions.
φ′ is the effective internal angle of friction. K pγ is obtained graphically. Simplifications have been made to eliminate the need for K pγ. One such was done by Coduto, given below, and it is accurate to within 10%. [2] = (+) ′ + ′
As shown in Figure 6, to determine the stress components (,) acting on a plane at an angle counterclockwise to the plane on which acts, we travel an angle in the same counterclockwise direction around the circle from the known stress point (,) to point (,), i.e., an angle between lines ¯ and ¯ in the Mohr circle.