Ba Baudet

Effect of the Porosity/Cement Ratio on the Compression of Cemented Soil

AbstractThe compression behavior of an artificially cemented soil was analyzed by the adjusted porosity/cement index using a correlation established in the recent literature. It was found that for each value of this index, defined as the ratio of porosity to the volumetric cement content, there was a unique normal compression line (NCL). The NCLs of the cemented specimens for each adjusted porosity/cement index did not converge with the NCL of the uncemented silty sand at large stresses, but reached a line parallel to it. The NCL of the cemented sand plotted further from the NCL of the uncemented sand as the porosity/cement index decreased.

Characterization of the surface roughness of sand particles using an advanced fractal approach.

The surface roughness of soil grains affects the mechanical behaviour of soils, but the characterization of real soil grain roughness is still limited in both quantity and quality. A new method is proposed, which applies the power spectral density (PSD), typically used in tribology, to optical interferometry measurements of soil grain surfaces. The method was adapted to characterize the roughness of soil grains separately from their shape, allowing the scale of the roughness to be determined in the form of a wavevector range. The surface roughness can be characterized by a roughness value and a fractal dimension, determined based on the stochastic formation process of the surface. When combined with other parameters, the fractal dimension provides additional information about the surface structure and roughness to the value of roughness alone. Three grain sizes of a quarzitic sand were tested. The parameters determined from the PSD analysis were input directly into a Weierstrass–Mandelbrot function to reconstruct successfully a fractal surface.

Coupling of Ageing and Viscous Effects in an Artificially Structured Clay

A series of short term isotropically consolidated drained triaxial compression tests was conducted to investigate the influence of cementation, total curing time and strain rate on the stress-strain behaviour of cement-mixed kaolin. The research suggests that the behaviour of cement-mixed kaolin can be described by a unique stress-plastic strain-time relationship independently of strain (curing) history. Both the peak strength and the small strain stiffness were observed to be dependent on the total curing time. The small strain stiffness normalised for stress level showed a continuous linear increase with logarithm of total curing time, while the tested samples of cement-mixed kaolin reached an apparent plateau for peak strength after about one day of curing. The post-peak critical state strength was in contrast seen to be constant with curing time. In relation to findings in the literature and in this study, the coupling of ageing and viscous effects is discussed. It is suggested that there must be a point (characteristic strain rate) at which the behaviour of both artificially and naturally structured clays changes from being dominated by ageing effect to being predominantly viscous.

Performance of Fiber Reinforcement in Completely Decomposed Granite

Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses. Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses.

Physical properties controlling water repellency in synthesized granular solids

Y . S a u l i c k a, S . D . N . L o u r e nç o a, B . A . B a u d e t b, S . K . W o c h e c & J . B a c h m a n n c aDepartment of Civil Engineering, Haking Wong Building, The University of Hong Kong, Pokfulam Road, Hong Kong, China, bDepartment of Civil, Environmental and Geomatic Engineering, University College, London, Gower Street, London WC1E 6BT, UK, and cInstitute of Soil Science, Faculty of Natural Sciences, Leibniz University Hannover, Herrenhaeuser Street 2, 30419 Hannover, Germany

Modelling Isotropic and Kinematic Hardening of Granular Materials with a Thermodynamical Approach

The thermodynamic framework for continuum mechanics can be applied to model granular and porous materials. Broadly speaking, there exists two approaches: the French school approach and Ziegler’s approach. Despite the fact that they both have the same foundations, differences between them emerge regarding the way in which stored energy is accounted for. This is illustrated here by applying the two approaches to the classical Von Mises kinematic and isotropic hardening models. In Ziegler’s approach, the stored energy is solely used for the kinematic hardening, as opposed to the French school approach in which the stored energy is allowed in both cases of hardening. In spite of which modelling approach is taken, we will show how certain modifications to these theories have to be made in order to develop the classical modified Cam Clay model, which emphasises the difference between the classical and the thermodynamic formulations.