Hydro-Mechanical Analysis of Unsaturated Collapsible Soils andtheir Stabilization

Collapsible soils are defined as soil that has a low dry density, lowmoisture content and high capacity for applying a large vertical stress with a small compression at dry state, but then experience much larger collapses after wetting. To solve this problem, fly ash (a by-product from the burning of coal in the electric power plants) is currently in use for soil stabilization in some countries like USA, Japan, Scandinavian countries, India, and some other countries and has several recommendations and regulations. In Germany, however, fly ash is a variable material with large amount and low cost and still is not used for soil-stabilization very common. The present study is an attempt how the use of fly ash to improve the geotechnical properties of unsaturated collapsible soil. The experimental programs are consisting (i) physical and chemical properties tests (ii) hydro-mechanical properties tests (including oedometer test, unconfined compressive strength (qu), soil-water characteristic curve (SWCC) and suction control-collapse test), (iii) electromagnetic properties tests (including permittivity and conductivity test for non/fly ash stabilized soil at different cases and (iv) seismic wave tests level (including Vs and Vp wave velocity test for non-stabilized soil and ultrasonic Vs and Vp wave velocity testing as non-destructive method for the fly ash-stabilized soils. The summary of the present study illustrated the following findings: The addition of fly ash to the natural collapsible soil led to a reduction of the plasticity index, an increase in the optimum moisture content and a decrease in the maximum dry density. This is due to the ionic exchanging between the free Ca+2 in fly ash and Na+1 in clay minerals of soil which caused a reduction in size of diffused water layer, flocculation and agglomeration of the clay particles...


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