A laboratory study on the use of lime columns to improve expansive soils

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2021-9-09
Özkan, İlyas
Expansive soils are well-known for their cyclic shrink-swell behavior due to seasonal moisture changes. These cyclic movements of expansive soils are due to physicochemical changes at the particle level that are dependent on mineralogical composition of these soils. The soil depths susceptible to moisture changes are known as active depths and based on previous studies vary from shallow to deep depths. Movements from these depths reflect to the surface leading to considerable deformation to overlying infrastructures. Therefore, it is necessary to improve the expansive soils prior to any construction activity on these soils. Since several available methods are unsuitable for deep soil stabilization, soil improvement with lime column technique is studied in this research. Lime column technique has been applied for stabilizations of expansive soil. However, lime column which contains lignosulfonate has not been studied in the literature. The main objective of this study is that investigation of influence of lignosulfonate on lime column technique. Laboratory testing program is conducted with a high plasticity clay specimen consisting of kaolinite and bentonite mixed in laboratory. The change of unconfined compressive strength, swelling potential, coefficient of permeability, CEC and SSA of the treated specimen during the stabilization process is studied. The effect of scale of specimens on the test results were studied using different size boxes. Lime diffusion into the soil is a considerable factor in this technique. Lignosulfonate as an additive material is added to the lime column to accelerate lime diffusion into the soil. The effectiveness of the lime column technique in both minimizing swell behaviour and changing the strength of expansive soils up to considerable depths are investigated in the present research by conducting comprehensive laboratory studies. The effectiveness of lignosulfonate lime column (LLC) treatment method is evaluated in terms of reducing heave movements of underlying expansive soils. A new method is proposed in this study: the combined improvement method (CIM) which includes three techniques that are prewetting, lignosulfonate lime columns, and geotextile+anchor. While the treated specimens with LLC included 37 pieces column, the number of the columns installed in treated specimen with CIM is only 19. The change of soil parameters are analyzed by testing both treated samples and untreated samples. The results of the free swell test, CBR test showed that both improvement methods strengthen the soil properties with the curing period. Besides, the change of properties of specimens taken from a region placed between the columns was observed by using the free swell test, unconfined compressive strength test, SEM-EDX analysis. The outputs of these tests and analyses indicated that the soil properties improved with these methods as follows: The height of the lime column should be the depth of the active zone during the lime column stabilization. The swelling potential of the treated specimen with the lime column method decreases as the water content of the lime columns increase. The addition of the lignosulfonate to lime columns increases the diffusion rate of the lime particles into the expansive soil specimen prepared in this study. The calcium lignosulfonate type is more effective than the sodium lignosulfonate for stabilization. The unconfined compressive strengths of the treated specimens with lignosulfonate lime columns are greater than the untreated specimens. The treated specimen with CIM is more stable and resistant to volumetric change than both the other treated specimens and untreated specimens prepared in this study. Also, the improvement process of the CIM method is faster than the other methods applied in this study. In this study, a design method (CIM) was developed and it has been shown that the high swelling potential of subgrade clay layers, in the active depth, can be reduced to low swelling potential values by this method.

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Citation Formats
İ. Özkan, “A laboratory study on the use of lime columns to improve expansive soils,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.