Development of Design Guideline for Deep Soil Mixing (DSM) to Stabilize Expansive Soils using Fly Ash as the Stabilizer

Deep soil mixing (DSM) is a ground improvement technique used to improve the ground by in-situ stabilization of soft soil using stabilizers such as cement, lime and fly ash for depths greater than 1.5 m. To date, there are no studies focusing on developing a design guideline for DSM method to treat expansive soil using fly ash. Therefore, aim of this study was to develop a design guideline for DSM to stabilize expansive soil using fly ash as the stabilizer. Four different expansive soil samples obtained from Digana, Sri Lanka were treated with 10 25% fly ash by weight. A series of swell pressure tests were conducted on the untreated and treated samples to calculate the surface heave of the expansive soil – fly ash composite ground for different area ratio values (10 60%). Altogether sixteen heave versus area ratio design charts were developed for various fly ash contents and DSM column lengths (2 8 m). Further, spacing versus area ratio charts were developed for different diameters of the DSM columns for square and triangular arrangements. Based on the findings, it was noticed that incorporation of fly ash into expansive soil reduces the swell pressure significantly (53 – 86% reduction compared to the untreated expansive soil). The developed heave versus area ratio design charts can be used for the design and construction of DSM columns in expansive soils using fly ash as the stabilizer to maintain the total heave within the project specified limit. On the whole, DSM technique can be successfully used to treat expansive soils using fly ash as the stabilizer.