The effects of secondary compression in soft clay can be a significant design issue in structures sensitive to ground movements and differential settlements. This thesis investigates the effects of surcharging on secondary compression. The aim of the thesis was to determine if the creep phenomenon is reduced by the use of surcharge loading. The research expands on previously findings and attempts to empirically define the deformation known as creep in regard to post-surcharge behaviour. The marine clay samples used were undisturbed clay, from the Brisbane River Delta in Southeast Queensland.
Experiments revealed that the preconsolidaton pressure of the undisturbed samples was approximately 1.3 times the overburden pressure of the sample due to the aging process. The test specimens were given a load of 100 (kPa) in excess of the preconsolidation pressure to simulate a construction surcharge. Portions of this load were then removed until the anticipated construction design load was achieved. This rendered the specimens to be overconsolidated with an over consolidation ratio (OCR) ranging from about 1.1 to about 1.3. The specimen was then left to creep for approximately 10 days with an additional test extending for 30 days. Subsequent loading stages were preformed to obtain required parameters for computational analysis.
Creep effects were observed to be slightly delayed in specimens experiencing an unloading cycle. The magnitude of the coefficient of secondary compression, Cα, for the surcharged samples was similar to that of specimens on the virgin compression curve of a normally consolidated clay, 1.3%. Surcharging soil to reduce the effects of secondary compression appears to only slightly delay the effects of creep settlements but does not reduce their severity.