Sharif Digital Repository

The soil-water retention curves (SWRC) is an unsaturated soil mechanics hydro chemical state surface, which expresses the relationship between the soil suction and water content. The soil-water retention curve could describe the water adsorption and desorption process that happened in soils. The difference between the desorption or drying retention curve and the adsorption or wetting retention curves in a specific soil specimen indicates the hydraulic hysteresis phenomenon. Generally, the amount of water remaining in the drying process is greater than the amount of water adsorbed in the wetting process at a certain amount of suction. Suction due to the combined effects of capillary and... 

Early efforts in soil dynamics have shown that the analysis of soil behavior under cyclic or random loading conditions is highly dependent on some representative material properties, the dynamic shear modulus, the Poisson’s ratio, and the damping ratio. Of particular interest is the value of dynamic shear modulus for strains less than 10-6 defined as the maximum or small strain shear modulus Gmax. Improvements in experimental unsaturated soil mechanics have led to the definition of trends between Gmax with different parameters most notably unsaturated stress state, degree of saturation and void ratio. However, the tests in these studies were mostly conducted on specimens experiencing... 

The shear modulus of soils is a key material quantity which is frequently used in the evaluation of wave propagation through soil layers in dynamic response analyses for many geotechnical systems. The shear modulus, G, is defined as the slope of the shear stress-strain hysteresis loop and is significantly influenced by the shear strain amplitude induced in a soil specimen. Of particular interest in geotechnical engineering, the value of shear modulus for strains less than 10-6 defined as the small strain shear modulus, Gmax. The early experimental studies on the shear modulus of water-saturated or dry soil showed that shear modulus is highly dependent on mean effective sress, p´, and void... 

Shear modulus and confined modulus are important parameters for static and dynamic analysis in geotechnical applications. Elastoplastic and nonlinear constitutive models has been formulized by these parameters. Cyclic simple shear apparatus had been developed by mounting bender element and ultrasonic sensor to measure continuous shear wave and pressure wave velocities for determination of G_max and M.For this purpose two new pedestals have been fabricated on which HAE ceramic disc and sensors were mounted. A pressure control panel and a hanging column system have been designed to apply high and low matric suction with high accuracy.At first two small strain tests were conducted for... 

One of the most important parameters in dynamic analysis is small-strain shear modulus of soils (Gmax). Additionally, due to the seasonal variations and traffic loading, determination of constraint modulus (M) of subragde soils is of great importance. Seasonal Variations such as evaporation, evapotranspiration and precipitation causes subgrade soils to be on unsaturated state. Therefore, there is an extending need to study the influence of matric suction and degree of saturation on maximum shear modulus and constraint modulus in the design and analysis of earthen structures.In this study, we employed a dynamic simple shear apparatus in order to fully understand variations of Gmax and M with... 

Results of previous studies on silt and clay indicated that variations in the small strain shear modulus, Gmax, during drying had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material properties and inter-particle forces, different behaviour in Gmax is expected for sand. Although considerable research has been devoted in recent years to characterize the behaviour of Gmax of sand during drying, rather less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during wetting. In the study presented herein, an effort was made to characterize the variation of Gmax for specimens of sand during... 

Results of an advanced suction controlled triaxial test device in an attempt to define the constitutive relationship between suction stress and matric suction (Suction Stress Characteristic Curve, SSCC) for unsaturated sand was presented. The suction stress is a macroscopic stress that incorporates the effects of capillary van der Waals forces cementation, and electrical double-layer repulsion into the definition of effective stress for unsaturated soils. Results of previous studies on silt and clay indicated that variations in the suction stress, during drying path had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material... 

Laboratory studies to investigate the effects of different saline concentrations (such as sodium chloride or calcium chloride) on the soil water retention behavior of clayey soils and their volumetric changes have received much attention recently. However, many previous studies have investigated these effects in only one path of the SWRC (wetting or drying path) and the effects of saline concentration on hydraulic hysteresis have not been considered. In addition, researchers have frequently studied these effects on SWRC on clay samples, and little research has been done on collapsible soils. Therefore, the most important purpose of this study is to investigate the effects of increasing... 

Evaluation of the seismic-induced settlement of an unsaturated soil layer depends on several variables, among which the small strain shear modulus, Gmax, and soil’s state of stress have been demonstrated to be of particular significance. Recent interpretation of trends in Gmax revealed considerable effects of the degree of saturation and hydraulic hysteresis on the shear stiffness of soils in unsaturated states. Accordingly, the soil layer is expected to experience different settlement behaviors depending on the soil saturation and seasonal weathering conditions. In this study, a semi-empirical formulation was adapted to extend an existing Gmax model to infer hysteretic effects along...