Development Of A New Device To Evaluate Stabilization Durability Of Expansive Soils By Addressing Wetting/drying And Leachate Issues
Lad, Priya Pravin
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Expansive soils have been known to cause deterioration among all aspects of civil infrastructure for many years primarily due to the presence of clay minerals like Montmorillonite. Replacing these problematic soils is not a viable solution in that it is costly and time consuming.Although many stabilization techniques are available, chemical stabilization has proven to be an important tool in arresting the swell/shrink behavior of expansive soil, which is a major source of distress problems for most infrastructures built on this type of soils. Of the chemical stabilizers available in the market, lime and cement stabilizers are the two most widely used chemical additives for improving expansive clays and increasing the overlying structures integrity; they improve the soil's workability, strength, swelling potential, and bearing capacity. Generally, lime stabilization develops due to base-exchange and cementation between the clay particles and lime (Croft, 1967). On the other hand, cement stabilization improves soil properties as a result of cementitious bonds between the calcium silicate and aluminate hydration products present in cement and soil particles (Nelson and Miller, 1992).Furthermore, durability of the stabilization is an important aspect for any chemical stabilization design. To assess the durability of the stabilization design, chemically treated soil samples are subjected to wetting/drying studies to understand the longevity of the stabilization under climatic changes from summer to winter and vice versa. The samples are also subjected to leachate studies to determine the permanency of the stabilization due to rainfall infiltration. Both of these studies are often conducted as separate studies on separate soil samples. However, in reality the wetting process and the rainfall infiltration occur simultaneously. Hence, a new research study was undertaken in which an attempt was made to combine both phases of durability studies and perform a combined study that addresses both the wetting/drying and leachate aspects of durability. For this purpose a new device was developed which can replicate rainfall infiltration and wetting processes simultaneously. This process reduces the time required for durability studies by half and the data obtained show that this approach is repeatable and provides new insights in understanding the durability of the chemical stabilization.A total of four soils were chosen along the pipe alignment in the IPL pipeline project for this study. These soils vary from low to high compressibility having plasticity index values ranging from 26 to 62, indicating medium to high expansiveness. Additionally, if these soils are used in the pipe bedding or haunch regions, they can cause excessive swelling pressures in the presence of water and damage the pipe, hence these soils were stabilized with either lime or cement-fly ash and were tested for durability in the newly developed combined device. Volumetric strains, weight changes, unconfined compressive strength changes and calcium ion concentrations were monitored over the course of the study. Many mix designs underwent durability, yet all four soils were stabilized effectively with 3% cement-10% fly ash as the treated soils completed 14 cycles of durability and maintained their strength. Although previous studies have shown similar results when tested with the conventional methods, further testing is recommended with both the conventional and combined methods for soils with similar PI. These additional tests will help further understand the similarities in the modified (combined) approach and the conventional methods.