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This research investigates the influence of matric suction on the variation of shear modulus and damping ratio of a silty soil in very small to medium shear strain levels. A set of laboratory experiments including three bender elements tests in addition to three resonant column-torsional shear tests have been carried out on unsaturated Firuzkuh silt specimens. In this regard, an unsaturated triaxial cell equipped with a set of bender elements and a resonant column-torsional shear device that can apply and control matric suction have been used. All specimens had an initial void ratio of 0.7 and were tested in various matric suctions under a net mean stress of 50 kPa. For this purpose, the axis translation technique has been implemented for applying matric suction, and High Air Entry Value (HAEV) ceramic discs have been used for air-water control of unsaturated silt specimens. According to the results, a significant variation of shear modulus and damping ratio has been observed with changes in matric suction and shear strain level. The output data indicate that shear modulus increases with increasing matric suction while the damping ratio decreases with an increase in matric suction. In addition, shear modulus and damping ratio decrease and increase with increasing shear strain, respectively.

Collapsible soils such as loess are particular types of problematic soils, whose collapse potential have caused severe damages to the buildings and structures. Loess is susceptible to large and sudden volume reduction upon wetting in constant normal stress or upon increasing normal stress in constant water content or a combination of these two stress paths. In this research both of these collapse induced paths: wetting and stress paths are investigated on undisturbed specimens of a Loess to observe the effect of various parameters on the collapse behavior of the tested soil., Seven controlled matric suction unsaturated oedometer tests have been conducted on undisturbed specimens taken from loessial soil of Gorgan, a city in Golestan province in Iran to study the collapse mechanisms of this type of soils. Two identical sets of unsaturated oedometer apparatuses designed and developed at Sharif University of Technology, with the capability of controlling matric suction have been utilized. In these tests, the matric suction, vertical net stress, volumetric water content, and vertical deformation of the samples have been controlled and recorded. Tests have been performed under two separate stress paths: constant matric suction with varying vertical net stress (loading and unloading) and constant vertical net stress with varying matric suction (wetting and drying). Obtained results show the high collapse potential of the tested soil and significant effects of stress path, matric suction, and vertical net stress on the collapse behavior of the tested soil.

The flow dynamics of dry granular flows is significantly affected by a prominent feature of a granular mass known as dilatancy. Although their rheological behaviour has been characterised by way of friction and dynamic dilatancy laws, the role of dilatancy in a granular flow has not been much appreciated. In this study, using a vane rheometer, an experimental investigation was conducted on uniform glass beads of d = 3 mm at different initial relative densities (15 ≤ Dr ≤ 66%) and shear rates that spanned over four orders of magnitude. The flow characteristics in terms of effective friction, volume change and velocity field were obtained and evaluated. The effective friction shows a descending–ascending pattern corresponding to a transitional behaviour from a velocity-weakening solid-like behaviour to a velocity-strengthening liquid-like behaviour. The volume-change measurements show that all specimens dilate and reach almost the same density at each shear rate. The velocity field follows a Gaussian pattern characterised by the slipping velocity at the boundary, the interlayer slippage between particles and the interlayer disorder of the particles. A new non-monotonic friction law and a dynamic dilatancy law are presented as governing rheological laws based on the inertial number and by introducing an effective dilation coefficient. This effective dilation coefficient successfully captures the role of dilation-induced secondary vortex flows in the dry granular flows. [ABSTRACT FROM AUTHOR]

Preloading is a popular technique in ground improvement works on soft compressible soils. Observational methods such as the Asaoka or hyperbolic methods are widely used in practical applications to assess final settlement and the degree of consolidation during preloading. In this paper it is argued that the major cause of inaccuracy in the final settlement predicted by the Asaoka method, especially in the early stages of preloading (short assessment periods), is neglect of the effects of creep in Asaoka's solution. This may also be the cause of the lack of agreement between observational methods and the piezometer method at higher degrees of consolidation. In this paper a method is proposed that can improve ultimate settlement predicted by the Asaoka method, by considering the effects of creep. By applying this method to two sets of settlement-time data available in the literature, it was found that the final settlements can be estimated with greater accuracy compared with the Asaoka method, even in the early stages of consolidation. Additionally, the proposed method can predict future settlements accurately. The degrees of consolidation predicted by this method showed good agreement with pore pressures recorded in piezometers. [ABSTRACT FROM AUTHOR]