Soil mechanics Flashcards
Mechanical properties of soil largely depend on….
grain size
mineralogy
water content
Shear strength
Ability to resist shear
Consistency
Strength which hold soils together
Consolidation
decrease in volume under stress
Fluids cannot resist…..
shear at rest
High shear stresses occur in minerals….
with high shear strength
Soil has mixed properties because….
mix of water (can’t resist) + solid (can resist)
2 components of stress in soil
soil skeleton
pore water
Effective stress =
total stress - pore fluid pressure
Cohesion
point where failure crosses y axis
Consistency dependent on….
Water content
Clays can be described as…
- solid
- semi-plastic
- plastic
- liquid
Plasticity index =
Liquid limit - plastic limit
Activity =
plasticity index / % clay minerals
greater A - more plastic
Primary consolidation involves…
expulsion of water
considerable and fast
progress until PWP = 0
Secondary consolidation involves…
restructuring
small and slow
If particles loosely packed…
compression will occur
If particles already tightly packed…
shear -> dilation
Dilation/compression leads to
soil reaching critical state
In critical state…
continued deformation without change in V or stress
Loose packed soils show gradual….
increase in shear stress until they reach critical state
At critical state the rock is….
stable
Densely packed soils reach a..
peak strength
up to this dilation increases at a rapid rate
Beyond peak strength
any increase in dilation = lowered strength
Between Peak strength and critical state is dangerous because…
strength falls towards critical state as strain increases
