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The friction coefficient is an empirical (experimentally measured) structural property that depends only on various aspects of the contacting materials, such as surface roughness. The coefficient of friction is not a function of mass or volume. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block.
But in addition to friction, soil derives significant shear resistance from interlocking of grains. ... A lateral earth stress coefficient, K, is defined as the ratio ...
If the coefficient of static friction μ s is known of a material, then a good approximation of the angle of repose can be made with the following function. This function is somewhat accurate for piles where individual objects in the pile are minuscule and piled in random order.
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 °
K a = Coefficient of active pressure w = weight density of soil h = depth of the section (below top soil) where the pressure is being evaluated. β = angle that the top surface of soil makes with the horizontal. φ = angle of internal friction of soil. The expression for passive pressure is: = where:
The adhesion railway relies on a combination of friction and weight to start a train. The heaviest trains require the highest friction and the heaviest locomotive. The friction can vary a great deal, but it was known on early railways that sand helped, and it is still used today, even on locomotives with modern traction controls.
The coefficient of lateral earth pressure, K, is defined as the ratio of the horizontal effective stress, σ’ h, to the vertical effective stress, σ’ v.The effective stress is the intergranular stress calculated by subtracting the pore water pressure from the total stress as described in soil mechanics.
Typical stress strain curve for a drained dilatant soil. Shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that a soil can sustain. . The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding of particle contac