مهندسی عمران شریف (May 2018)
A MODIFIED HYDROMECHANICAL MODEL FOR UNSATURATED BEHAVIOR OF COLLAPSIBLE SOILS UNDER CONSTANT MATRIC SUCTION AND VARIABLE MEAN NET STRESS
Abstract
Many parts of the world mainly in arid and semiarid zones, including Iran, are covered with Aeolian deposits of collapsible loessial soils. This kind of soil exists in many parts of Iran especially in Eastern part of the country from North to South. Loessial deposits are characterized with high void ratio, visible root type open pores, low density, and low water content. The natural slopes in Loessial deposits are nearly vertical and this geomorphological feature is an indication of the presence of Loess in that area. Loessial deposits normally have high strength and low deformability under natural water content or dry conditions. However, when they are subjected to excessive wetting while under a present or increasing load, the metastable structural bonds of the soil will break, and sudden large excessive deformations and collapse of the soil occur, which may lead to severe damages to or total destruction of the structures built on such soils.Many researchers have studied this behavior mainly using double oedometer tests to assess the amount of anticipated collapse under certain loads. However, few of them studied the behavior of such collapsible soils in an unsaturated soil mechanics context. Most of such researches were conducted on reconstituted specimens and very few among them studied undisturbed or intact samples. However, in order to assess the hydro-mechanical behavior of this type of soils, numerous unsaturated triaxial tests have been conducted using a modified unsaturated triaxial device at Sharif University of Technology on undisturbed loessial samples taken from the city of Gorgan. In this paper, the results of some of the performed tests under applying constant matric suction and variable mean net stresses were re-analyzed by considering classical unsaturated soil mechanics concepts, and a new modified hydromechanical constitutive model was presented to predict the hydromechanical behavior of collapsible soils. The outcome of this research was proved promising, and the comparison between the results of the tests and the predicted values using the proposed method showed results of the tests and the predicted values using the proposed method showed very good agreement.
Keywords
