Deep Soil Mixing for Mitigation of Problematic Soils

Deep soil mixing (DSM) is a method that is commonly employed in the field of civil engineering construction in order to improve the physical and engineering properties of weak problematic soils. The process involves penetrating the rotary augers into the problematic soil and mixing it with different types of binder materials such as cement, lime-cement or some waste materials, resulting in an increase in the strength and reduction of compressibility of the soil. This study investigates the strength and stability of loose sand that has been modified with Portland cement alone and in combination with different waste replacement materials such as waste brick dust (WBD) and waste marble dust (WMD) through a series of laboratory tests. The study aims to develop a design procedure for assessing the highest strength and volume change in deep soil mixing (DSM) application, considering the factors such as the type of binder, binder-soil ratio (B/S), water-binder ratio (W/B) and curing time. The study consists of two parts. The first part includes the determination of the most effective soil-binder mixtures that will be used in the construction of the DSM columns. The experimental investigations include sitting time, bulk density, unconfined compression test, and microscopic image analysis using a stereoscopic microscope. In addition, stress-strain behavior and modulus of elasticity of the soil-binder mixtures are analyzed at different curing periods of 7 and 28 days. Second part of the study evaluates the performance of the DSM columns constructed in the model test tank with the loose sand placed in it. The behavior and performance of the DSM columns constructed with using different replacement binder materials (WBD and WMD) and with different binder-soil ratios (10, 15 and 20) are analyzed in the model test tank by using one dimensional loading frame. In the study, ex-situ deep soil mixing method is iv used for the construction of the DSM columns. From the loading test, the loaddeformation curves are obtained for each binder-soil ratio and the failure modes of the DSM columns, bearing capacity and subgrade modulus values are obtained. The findings of the research indicate that utilization of 20% waste brick dust as a replacement material in a binder-soil ratio of 20% leads to better improvement due to strong interlocking between the sand particles and the binder materials and results in higher strength of the DSM columns. Similarly, the optimal replacement percentage of waste marble dust (WMD) is determined to be 10% at a binder-soil ratio of 20%. In DSM model reinforced sand, it is observed that the bearing capacity of sand soil is enhanced in all cases of DSM applications: single and group of ex-situ DSM column. The columns with WMD exhibit the greatest bearing capacity and subgrade modulus in both single and group of DSM columns and also in both end-bearing and floating column application. Overall, the incorporation of WBD and WMD as replacement materials in loose sand mitigation seems to be a promising technique for improving the geotechnical properties of such soils and has the potential to generate significant cost savings and environmental benefits.