The Influence of Selected Parameters on Cycling Process on Cohesive Soils Shear Characteristics at Small Strain
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Publication date: 2010-03-31
Archives of Civil Engineering 2010;56(1):89-107
The subject of the paper comprises a cohesive soil response to a cyclic loading applied in the rangeof small strains (10⁻⁵ ÷ 10⁻³). To this end tests of undrained cyclic shear in a triaxial compressionapparatus were carried out on homogeneous material – kaoline from Tułowice. The tests werecarried out on a modernised test bed, enabling full saturation of samples using the back pressuremethod, as well as a precise, intra-chamber measurement of small strains. Maintaining a constantdeviatoric stress amplitude for NC and OC soils, the effect of its size (A = 0.75∆q or A = 0.375∆q) as well as the influence of strain rate on material characteristics “deviatoric stress (excess pore waterpressure) – axial strain” and effective stress paths were tested. While analysing the results obtained,a phenomenon of closing and stabilising initially open and moving loops were found, in contrast toproposal by Jardine [8]. The observed increments in the axial strain during cyclic loading operation,at the same levels of lateral effective stress, were greater for normally consolidated than for over-consolidated soils. At the same time, at each next cycle, these increments were smaller and smaller,assuming even the value equal to zero for the tenth cycle. Similar relationships occurred during theincrease in the pore water pressure during the cyclic load action. For the set number of cycles n = 10 they were that small – max. 46% (and decreasing with each consecutive cycle) that they did notresult in weakening of the material. Taking the trend of decreasing ∆u increments into account itwas possible to accept that the conclusion considered was right irrespective of the cycles’ number.
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