Journal of Geo-Engineering Sciences

Design guidelines of foundation anchors and piles embedded in fluidized sand comprises understanding of installation processes, defining constitutive parameters and establishing analysis techniques. These fundamental aspects have been investigated by a series of laboratory model tests designed to evaluate the mechanism taking place during pile installation through the influence of downwardly-directed vertical water jets in the geometry of fluidized cavities in saturated sands. Measurements indicate fluidization geometry to be controlled by combined effects of jet velocity and the ratio of particle and jet diameters which can be conveniently expressed by the Froude number of particles. Characteristics of the fluidized zone geometry prior and after fluidization indicate considerable reduction of relative density of fluidized samples. Limit equilibrium analysis using geotechnical parameters approaching critical state provided indicative horizontal stress levels to estimate the uplift skin friction of model steel piles.

A numerical model is developed for studying the transport of colloids in a coupled fracture-matrix system with double layer fracture-skin. The governing equations describing colloid transport along the fracture and diffusion into fracture-skin layers as well as rock-matrix, normal to the fracture axis are coupled with each other. The coupled non linear equations are solved numerically with fully implicit finite difference method. Sensitivity analysis is performed to investigate the effect of various colloid properties on the colloid concentration in the multiple porosity fractured system. Colloid remobilisation and filtration has been accounted in the model. Results suggest that the inclusion of a second fracture-skin layer has a marginal effect on the transport mechanism of colloids. As colloid velocity increases, the diffusion of colloids into the fracture-skin decreases due to the low residence time available for the colloids. High first layer fracture-skin thickness and porosity enhances the diffusion of colloids from the aqueous phase of the fracture into the skin considerably resulting in low colloidal concentration within the fracture. Variation in the porosity as well as thickness of the second layer of the fracture-skin has negligible effect on the colloidal concentration in the fracture. The colloid transport mechanism in fractured porous media is marginally affected by the multiple porosity system, or in other words additional layers of fracture skin. High filtration coefficient and low remobilisation coefficient result in low colloidal concentration within the fracture.

The focus of this paper is to present a new evaluation method for strength gain in very soft soils when using cementation as a means of improvement. This test procedure was created due to great difficulty encountered in molding specimens for compression and tensile tests in very soft clays and silts. The test consists in the measurement of the maximum force applied to embed a flat base rod into a soil mass using high sensibility dynamometric rings. The maximum pressure (maximum force divided by the flat base rod area) recorded up to 30 mm embedding of the rod into the soil mass is adopted as reference and has been shown to have direct linear correlation to Brazilian tensile tests. A correlation was set to a range of different materials encouraging its use in engineering practice. The main advantages of the proposed test are the easiness to mold specimens, the option of carrying out multiple tests in a single specimen and the possibility of carrying out tests outside the laboratory environment.