|M.Sc Student||Rammah Khader|
|Subject||Effect of Ageing on the Behavior of Overconsolidated Clay|
|Department||Department of Civil and Environmental Engineering||Supervisor||Mr. Dimitry Val|
Previous experimental and theoretical studies have revealed that important soil properties such as strength and stiffness are in fact higher than the values commonly used in design. It is believed that the higher stiffness and strength develop due to aging effect. Aging has been widely studied and investigated both in the field and laboratory during the past three decades. A number of researchers have shown that maintaining soil samples under permanent stress in drained conditions increases soil strength and stiffness. At the same time a number of cases have been reported when no aging effect has been detected.
The main disadvantage of previous studies investigating the aging effect is that they were largely based on experiments, which were conducted using conventional laboratory equipment and without verification of test results by other techniques. The thesis presents experimental research of the effect of aging on overconsolidated clay samples using a highly sensitive computerized triaxial workstation with accurate stress path control triaxial cell. This equipment allows to use both static and dynamic methods to determine properties of aged clay samples.
The static method is based on the use of local strain measurement devices incorporated in the triaxial cell. The dynamic method is based on the Bender Element technique. In this technique a shear wave is created by the Bender Element transmitter and after it propagates through a soil sample is received by the Bender Element receiver. Elastic soil stiffness is then estimated using the velocity of the shear wave propagation.
Soil material used in this research as well as the preparation of soil samples are described. Trial testing programs, which were carried out at the beginning of this research, along with the difficulties associated with each of the programs are then presented and discussed. Subsequently, a successful testing program, which was eventually selected for the research, is presented. The program includes a series of consolidated undrained triaxial tests on overconsolidated remolded Kaolin samples aged for different periods in a triaxial cell; both static and dynamic methods are used in the tests.
All results of the test program are presented and discussed. In particular, it is shown that in overconsolidated Kaolin samples, which were tested in this research, the effect of aging was observed only in the range of very small and small strains and then it disappeared at larger strains. The thesis ends with conclusions and recommendations for further research.