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
Advantage of calculating settlements from standard solutions
- possible to obtain estimates of undrained settlements due to shearing as well as those eventual settlements due to consolidation
Concern with calculating settlements from standard solutions
settlements from standard solutions should be used with care as they are sensitive to the elastic parameters assigned to the soil\
