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Geotechnics

Ground stress, pore pressure, permeability and shear strength

Stresses in the ground are expressed as..... Total stress, effective stress or pore water pressure
The stress developed between two solid particles in contact acts in..... One direction only (normal to the plane of contact between them)
The stress developed in the pore water.... Is a hydraulic pressure and acts equally in all directs
Define total stress On a plane within a soil mass, being the force per unit area transmitted in a normal direction across the plane
Define effective stress On a plane, representing the stress transmitted through the soil skeleton only
Define pore pressure Being the pressure of the water filling the void space between solid particles
What is the relationship between them? Total stress = effective stress + pore pressure
Describe effective stress and explain its importance On a plane, representing the stress transmitted through the soil skeleton only. It is important because a change in effective stress can cause changes in strength and volume/shape, of the soil
Settlement occurs..... as the volume of the soil layers change
What is the coefficient of lateral earth pressure? The ratio of the horizontal effective stress to the vertical principal effective stress
Vertical effective stress will vary..... Linearly with depth
Horizontal effective stress will vary.... depending on the degree of consolidation of the ground
The "at rest" condition implies what? That no deformation occurs
How do you calculate the lateral total stress? add the pore water pressure
At any depth, the pore pressures.... in all directions are equal
In Darcy's experiment, what three things did he find? That flow was proportional to: the head difference the cross-sectional area inverse of the soil sample length
The pores in soils are so small that.... The flow through most soils is steady and laminar
Define laminar flow Occurs when fluid flows in parallel layers, with no disruption to the layers
When would ground water flow occur? When there is a difference in the total head between two points in a soil mass
What did Darcy conclude from his experiment? Q = K x A x [change in head/ change in length}
i = change in head/change in length What is i? The hydraulic gradient
V = Q/A What is V? The Darcy/superficial velocity
Q = K x A x [change in head/ change in length} What is K? Coefficient of permeability
Define the shear strength of a soil The maximum internal resistance to applied shearing forces
Define the internal friction angle It is a measure of the shear strength of a soil
Define cohesion A measure of the forces that cement particles of soil
Define un-drained shear strength The shear strength of a soil when sheared at a constant volume
Define the critical or ultimate state Stresses reached when continuous shearing occurs at constant shear stress and constant volume
Define dilation Is a measure of the change of volume of a soil when it is distorted by shear
What are the three main uses of shear strength of soil Slope stability Retaining Wall Bearing capacity/Foundations
The internal friction angle and cohesion are known as what? The shear strength parameters
Created by: Civilman