Effect of repeated loading on the strength of clay

The behaviour of soils under dynamic loading conditions has been studied. There exists a large amount of data indicating that a reduction of strength in a soil takes place but that the amount of this reduction is limited. On the other hand some authors claim that such a reduction is not possible because the ultimate undrained shear strength of a given saturated soil depends only on its void ratio and structure. In this paper it is attempted to bring some clarification to this conflict and in doing so the Critical State Model is employed. Fifty-eight dynamic and nine static triaxial tests have been conducted on samples consolidated from a water content twice the liquid limit to different consolidation pressures. The soil used in experiments is ‘Arnavutköy Kaolini’ with a liquid limit of w_L = 65% and plastic limit w_P = 30%. The results of the present series of tests indicate that the main effect of dynamic loading is on the increase of the pore water pressure which in turn causes the soil to behave like an overconsolidated soil. Previous research has shown that the void ratio of an overconsolidated soil sample decreases at the shear zone during shearing. All the results expressed above, as well as the results of tests conducted during this research, indicate that a reduction in the shear strength occurs in a normally consolidated clayey soil due to the repeated loading application.