Experimental investigations on mechanical behavior of unsaturated subgrade soil with lime stabilization and fiber reinforcement : final report.

SP107B4JIn the present report, experimental investigations on mechanical behavior of unsaturated subgrade soilwith fiber reinforcement and lime stabilization were conducted.The soil samples were collected from the soil/aggregate laboratory at the Maryland State HighwayAdministration (MD-SHA), Maryland Department of Transportation. The experiments were carried out toinvestigate physical and mechanical properties of subgrade soil that was mixed with geofiber and lime.The reinforced and stabilized soil with fiber and lime is considered as a composite material.Investigations in this study included two phases. In the first phase, the investigation was for staticbehavior of composite subgrade soil under the compressive shear loading. In the second phase, theinvestigation emphasized dynamic behavior of reinforced and stabilized soil under cyclic shear loading. Inthis research, three aspects of investigations are presented.First, new constitutive models for static and dynamic loading were established for composite material.In the present report, elastic constitutive relationship was assumed to describe both the linear andnonlinear shear stress-strain relations of composite material. Static behavior was described with anonlinear elastic model, and dynamic behavior was expressed with a linear elastic model. For thenonlinear model, elastic shear modulus was assumed to be a function of multiple variables such as shearstrain, contents of fiber and lime, confining pressure, and the curing period of samples. In contrast, for thelinear model, elastic modulus was not only defined as a function of confining pressure, contents of fiberand lime, and the aging period of samples but also repetitions of cyclic loading. For convenience ofexperimental investigation, the shear stress-strain relation in a three-dimensional stress space reduced tothat in a quasi-triaxial stress space in which the conventional triaxial shear tests were conducted.Second, experimental investigations and calibration of constitutive models were conducted. Experimental data from laboratory tests were utilized to verify and justify the linear or nonlinear elasticmodel suggested in this report. Constitutive parameters of linear and nonlinear models were investigatedand calibrated using experimental results from both static and dynamic triaxial shear tests. The linearregression method was adopted to find constitutive parameters. The constitutive relationship of thecomposite material made of soil, fiber and lime was established once constitutive parameters for the linearand nonlinear models were determined. The elastic shear moduli were investigated, for example, theinitial shear and tangential moduli in the nonlinear elastic model under static loading, and the shear orresilient modulus in the linear model under cyclic loading. Moreover, for static loading, the Coulomb \u2013Mohr\u2019s failure criterion was applied. The strength indices c and \u3c6 were studied for the composite soil withfiber and lime. A linear relation was introduced to describe parameters c and \u3c6 as a function of fiber andlime content, and the sample-curing period. The coefficients of the linear relation for parameters c and \u3c6versus fiber and lime content, and sample aging time were found using the experimental data.Finally, impacts of fiber and lime as well as other factors that affect mechanical behavior of thecomposite material were discussed. Impact factors on shear moduli were introduced for both the linearand nonlinear models. The impact factors for the nonlinear model under static loading were defined toexhibit effect of variables such as cell pressure, fiber and lime contents, and the sample-curing period onthe initial modulus and soil strength, namely parameters 1/A and 1/B related to the shear modulus G. Incontrast, the impact factors for the linear model under cyclic loading were introduced to show effect of thesame variables (\u3c30, mF, mL and t) plus the repetition of cyclic loading on resilient modulus and dynamicbehavior of composite soils