mod4 Flashcards
Youngs Modulus
E = direct stress / direct strain
Shear Modulus
G = shear stress / shear strain
Bulk (volumetric) modulus
K = lateral strain / volumetric strain
Poisson’s ratio
v = lateral strain / direct strain
Stiffness degradation curve
- soil stiffness may be altered by changing the loading direction
- stiffness will also be different in the case of a pre-loaded or over-consolidated soil, compared with a soil undergoing first time compression
Gibson soil
soil becomes stiffer with depth
Layered soil
layers of different stiffness due to different geological formations
Boussineq’s solution
- isotropic
- homogenous
- half-space
isotropic
same properties in all directions
homogenous
same properties everywhere
half-space
assuming a body of infinite depth and lateral extent, so that it occupies half of “all space”
a few cautionary cases which lead to significant deviation from ideal Boussineq results
- where there are discontinuous lenses or “inclusions” of higher or lower stiffness
- where extensive plastic yielding of the soil occurs due to relatively high surcharges or very soft soil
Newmark’s method
- draw a plan sketch of the foundation outline, such that the length for the scale line equals the depth of the plane of interest z and so that the point of interest x is centred on the chart
- count the number of blocks Nq covered by the foundation loading (group together partial blocks)
- delta stress(z) = sum(Nq) * q / Nt
Nt = 200 for general chart
Fadum’s chart
- for rectangular footings
- determines the stress at a corner of rectangle L x B at a depth of z
- m = L/z
- n = B/z
Potential shortcomings of using vertical stress and strain behaviour to determine settlements
- assumes that most deformation is vertical compression, so short-term settlements due to shear at constant volume cannot be calculated
- division into only two layers of soil is crude - more layers would be better
