Laboratory Study of the Plastic Behavior of Silty–Sand under Repeated Loading   Gh. Behzadi Sari Technical Collage, Sari, Mazandaran, Iran E-Mail: gh–behzadi@ saritc.ac.ir Asskar JanAlizadeh Choobbasti Noshiravani University of Technology, Babol, Mazandaran, Iran E-Mail: Asskar@nit. ac.ir
			ABSTRACT

The materials of pavement layers are subjected to repeated traffic loading. Under each cycle of loading both resilient and permanent deformations will happen. Permanent deformation is an important factor in flexible pavement design. The main objective of this paper was to find the plastic behavior of silty-sand sub-grade soils under repeater loading. In order to achieve this objective, the results of laboratory repeated load tri-axial tests with a Universal Testing Machine (UTM) apparatus were obtained to characterize the residual deformation of a silty sand sub-grade material of the Beerburrum trial was located in Queensland Australia. Various levels of confining stress, stress ratio, moisture content and relative density were applied to samples. The analysis of permanent deformation results indicated that the well known model e_p = IN^S can be used to estimate the accumulated strain at any number of loading cycles. The parameter S (the slope of line in loge_p / logN plot) was found to increase linearly with deviator stress. The parameter ‘I’ (the intercept in loge_p / logN plot or plastic strain at the first loading cycle) was found to be most sensitive to deviator stress. The test results also indicated that ‘I’ increased with increasing moisture content and decreased as dry density increased. The analysis of results revealed that an exponential relationship existed between the ‘I’ value and deviator stress. This relationship was used to develop a constitutive model for silty-sand material based on the above well-known model. The obtained constitutive model would be able to predict the plastic strain under any number of loads at any specified stress level.

Keywords: Pavement; Traffic; Plastic Behavior; Sub-grade; Deviator Stress; Repeated Loading.

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