Effect of Suction on Volumetric Yielding Behavior under Different Initial Conditions for Fine-Grained Soils


The unsaturated soils are difficult to consider within the framework of classical (saturated) soil mechanics. In general, the unsaturated soil is stiffer than the saturated one (hardening), so the location and slope of normal consolidated line (NCL) or the volumetric yielding behavior of unsaturated soil is different from the saturated behavior. This work investigates the volumetric yielding behavior of unsaturated soil; by determine the One-dimensional normal consolidated lines (NCL’s) under different suctions. Two materials namely pure Calcigel bentonite (100B) and a mixture of 30% Calcigel bentonite and 70 % Haider sand (30B) were prepared at two initial conditions (i.e. slurry and loose states). In this type of test, after reaching to the designed suction, the net stress is increased through the test while the suction is kept constant. Thirteen 30B specimens and two 100B specimens were tested under constant suction condition. The constant applied suction in this study was varied from 0 kPa till 39000 kPa because of the possibility to increase the preconsolidation pressure (yield stress) more than 24000 kPa (the maximum limit of the used one-dimensional high stress consolidation equipments). Two techniques (i.e. axis translation technique and vapor equilibrium technique) were used to apply and control suction on tests. The controlled-suction one-dimensional high stress consolidation tests results show that the position and the slope of NCL’s depend on both net stress and suction. The NCL’s either, for low suction value, has void ratio lower than the saturated NCL (associated with slope lower than the saturated NCL), or the NCL has void ratio higher than the saturated NCL (associated with slope higher than the saturated NCL) for higher suction value.