Assessment and stabilization of micaceous soils

Abstract

Mica is a mineral widely distributed around the world. This mineral generally occurs in igneous, sedimentary and certain metamorphic rocks and, if breaks down from the parent rocks, shows a unique platy structure and high elasticity. These features may affect performance of soils adversely which mica lies in, causing instability concerns to construction work or infrastructure systems involving the micaceous soils. One of the solutions is to assess the adversities arising from occurrence of mica and, using chemical and mechanical techniques, to stabilize the micaceous soils. The research presented in this thesis was conducted to develop the solution and to provide suitable guidance to implement it. The research was divided into three important aspects: i) assessing the effect of mica content on the mechanical properties of clays, ii) stabilizing the micaceous soils mechanically or chemically with jute fiber, lime, granulated blast furnace slag (GBFS), and slag-lime, and iii) formulating the stabilization outcomes using the surface response methodology and optimizing the stabilization. Different contents of mica were added to the soils to form the micaceous soils for testing. The experimental program consisted of consistency limits, standard Proctor compaction, unconfined compression (UC), direct shear and scanning electron microscopy tests. The test results suggested that the liquid and plastic limits exhibited a linearly increasing trend with an increase in the mica content. The rate of increase in the plastic limit, however, was observed to be greater than that of the liquid limit, thereby leading to a gradual transition towards a non-plastic behavior. The spongy nature and high-water demand of the mica minerals led to higher optimum water contents and lower maximum dry unit weights with an increase in the mica content. Under low confinement conditions, the strength properties were adversely affected by mica. However, the closer packing of the clay and mica components in the matrix under high confinement conditions offsets the adverse effects of mica by inducing the frictional resistance at the shearing interface. A series of soil stabilization attempts were made to reinforce the micaceous soils. The combined capacity of mechanical stabilizer, jute fiber and different cementitious binders such as lime, GBFS and slag-lime, were examined towards ameliorating the inferior properties of micaceous clays. The test results indicated that the inclusion of fiber consistently improved the ductility and toughness of the composite, and the addition of cementitious binders into soil-fiber composite further improved the connection interface, and thus led to the improvements in the composites’ strength, stiffness and toughness. Moreover, a non-linear, multivariable regression model was developed to quantify the peak UC strength as a function of the fiber content, slag content and the curing time, and the predictive capacity of the proposed models was examined and further validated by statistical techniques. A sensitivity analysis was also carried out to assess the relative impacts of the independent regression variables on the UC strength. The proposed regression model contained a limited number of fitting parameters, all of which can be calibrated by a standard experimental effort, as well as simple explicit calculations, and hence implemented for preliminary design assessments and predictive purposes. Response surface methodology (RSM) was employed to design the experiments, to evaluate the results and finally to optimize the binders’ content. The results showed that slag exhibited a noticeable synergistic effect and greatly contributed to the stabilization of micaceous soils with the presence of fiber or polyacrylamide. The RSM-based optimization was able to determine the additives dosage in terms of targeted UC strength values, and based on the developed models, to identify the most efficient dosage of improving micaceous soils for backfilling or other construction works. This research has delivered important outcomes for publications. The publications are listed below: J-H Zhang, A Soltani, A Deng and M Jaksa, 2019. Mechanical performance of jute fiber-reinforced micaceous clay composites treated with ground-granulated blast-furnace slag. Materials. DOI: 10.3390/ma12040576 J-H Zhang, A Soltani, A Deng and M Jaksa, 2019. Mechanical behavior of micaceous clays. J Rock Mech Geotech Eng. DOI: 10.1016/j.jrmge.2019.04.001 J-H Zhang, A Deng and M Jaksa, 2019. Mechanical behaviour of micaceous soils stabilized by lime, slag-lime with fibers. Written in manuscript style for submission in one month J-H Zhang, A Deng and M Jaksa, 2019. Optimization of slag and fiber/polymeric agent to reinforce micaceous soils using response surface methodology. Written in manuscript style for submission in one month