The AASHTO LRFD Bridge manual states (C10.6.2.4.3) "In practice footings on cohesive soils are most likely founded on overconsolidated clays, and settlements can be estimated using elastic theory (Baguelin et al., 1978) or the tangent mdodulus method (Janbu, 1963, 1967). Settlements of footings on overconsolidated clay usually occur at approximately one order of magnitude faster than soils without preconsolidation, and it is reasonable to assume that they take place as rapidly as the loads are applied".
We have mostly overconsolidated clays here in West Michgan, and my colleagues typically consider such clay to be incompressible. I have never felt comfortable discounting the clay consolidation entirely, especially in areas of deep fills where the stress will act very deeply. I have always thought of these clays in the context of a recompression index and consolidation theory, but perhaps Janbu's work explains this better.
Do any of you use the tangent modulus method to estimate settlement in overconsolidated clay? Has it been your experience that such settlements occur very rapidly? It doesn't seem intuitive to me. Is the tangent modulus method more applicable for higher overconsolidation ratios?
We have mostly overconsolidated clays here in West Michgan, and my colleagues typically consider such clay to be incompressible. I have never felt comfortable discounting the clay consolidation entirely, especially in areas of deep fills where the stress will act very deeply. I have always thought of these clays in the context of a recompression index and consolidation theory, but perhaps Janbu's work explains this better.
Do any of you use the tangent modulus method to estimate settlement in overconsolidated clay? Has it been your experience that such settlements occur very rapidly? It doesn't seem intuitive to me. Is the tangent modulus method more applicable for higher overconsolidation ratios?