Deep Mixing Technology For Mitigation Of Swell-shrink Behavior Of Expansive Soils Of Moderate To Deep Active Depths

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Civil & Environmental Engineering

Expansive soils are well known for their cyclic shrink-swell behavior due to seasonal related moisture changes. These cyclic movements of expansive soils are due to physico-chemical changes at particle level that are dependent on mineralogical composition of these soils. The subsoil depths susceptible to moisture changes are known as active zones and based on previous studies vary from shallow to deep depths. Movements from these active depths reflect to the surface and cause considerable damages to overlying infrastructures. These damages are slow and time dependent as the in situ moisture fluctuations are slow and continue with time. Since the current chemical modification methods are ineffective for stabilization of expansive soils with moderate to deep active depths, researchers proposed deep soil mixing (DSM) technique using chemical binders. The effectiveness of this technique in minimizing swell-shrink behavior of expansive subsoils up to considerable depths was verified in present research by conducting comprehensive laboratory and field studies. Results from laboratory studies revealed that all combinations of lime and cement type binders produced shrink and swell potentials less than 0.5 and 0.1%, respectively. The strength properties of soils treated with binder compositions containing > 75% lime and 75% cement are about 1.8 to 5.2 times and 5 to 12 times the untreated soil strength. Simplified linear ranking analysis yielded combined lime-cement treatment (25% lime+75% cement) at 200 kg/m3 and 1.0 water-binder ratio as one of the best performing stabilizer and the same was adopted in the construction of two pilot DSM treated test sections. Quality assessment studies conducted during construction of test sections indicated that both field stiffness and strength values are 40 % and 20 to 30 % lower, respectively, compared to laboratory treatments. QA/QC studies based on laboratory, non-destructive and mineralogical data indicated consistent degree of mixing of soil-binder columns was achieved in field. Subsequent, field monitoring and non-destructive studies of DSM treated sections revealed that the overall performance as compared to untreated sections was successful in minimizing swell-shrink movements related to seasonal moisture changes.