Predicting the behavior of a drilled shaft wall retaining highly expansive soil
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A full scale drilled shaft retaining wall was constructed in the highly expansive soil of Manor, Texas, to advance our understanding of the behavior of walls in highly expansive soils. The wall was monitored for a total period of four years; during the monitored period the state of Texas experienced severe drought conditions and the retained soil was inundated via a manmade pond. The monitored wall did not experience a point of fixity, instead, the wall experienced global movement towards the excavated side. Analytical predictions of the wall during short-term and long-term conditions miss-predicted the deflection and bending moment profiles, and could not estimate the wall behavior during transition state towards the long-term conditions. The Reese wall was simulated in a numerical model using the Finite Element method. A framework is developed in this study that can describe the swelling behavior of soil. The framework relies on two soil properties, first, a relationship between effective degree of saturation and effective stress, second, a relationship between stiffness, effective stress and voids ratio. Comparison between measured and predicted deflection and bending moment profiles showed that the proposed framework could result in reasonable deflection and bending moment predictions during dry and inundated saturation conditions. The predicted short-term deflection and bending moment profiles best matched the measured profiles when a constitutive model that accounts for small strain stiffness nonlinearity was adopted. The numerical model was used to segregate the superimposed wall deflection profile obtained during long-term conditions. The study concluded that the short-term conditions accounts for 20%, dissipation of the excess pore-pressures accounts for 30%, the additional hydrostatic pressures accounts for 10%, saturation change related factors accounts for 15%, and change in soil properties on the excavation side accounts for 25% of the total deflection. Parametric analyses concluded that the short -term and long-term behaviors of the Reese wall are not very sensitive to building stiffer and deeper walls . The long-term behavior of the Reese wall is sensitive to construction season, the hardening properties of soil, and the relationship between effective stresses and effective degree of saturation .