ABSTRACT

Title of Document: IMPROVEMENT OF DYNAMIC PROPERTIES AND SEISMIC RESPONSE OF CLAY USING FIBER REINFORCEMENT

Behzad Amir Faryar, Doctor of Philosophy, 2012

Directed By: Professor M. Sherif Aggour, Department of Civil and Environmental Engineering

In recent years, earthquakes have caused heavy damage to buildings and infrastructure. One of the causes of heavy damage due to earthquake motions is the role of soft clay in amplifying bedrock ground motions. Improving the soil conditions at a site in order to mitigate earthquake damage can be one of the methods of modifying site conditions and thus reduce its effects on the seismic site response. The inclusion of randomly distributed short virgin polypropylene fibers (C3H6) in clay has proven to significantly improve the static geotechnical properties of clay such as shear, compression, tensile strengths, and so on. These improvements have triggered great interest in the possibility of mixing fibers with clay to improve the clay's dynamic properties. Because the percentage of fibers is currently arbitrarily chosen by users, a procedure was set up in this study to determine the optimum fiber content for a fiber-clay composite.

Experimental testing was performed using the Resonant Column Method to obtain both the shear modulus and the material damping for a clay and the fiber-clay composite to determine the effect of fiber inclusion on the dynamic properties of clayey soil. The research showed that the inclusion of fiber at optimum fiber content as a ground improvement technique can improve the dynamic properties of soft clayey soils at low shear strain. Test results indicated that both the shear modulus and damping increased. Hence, the inclusion of fiber in clay can provide a double benefit for the dynamic response of a site by increasing the stiffness of the site and reducing its amplitude of vibration. General formulas for shear modulus and damping were developed as functions of the shear strain amplitude for the clay and for fiber reinforced clay.

The effect of fiber inclusion on the seismic site response using two different earthquake motions was also studied. One-dimensional wave propagation analysis was performed to investigate the effect of the modification of the clay dynamic properties using fibrillated fiber reinforcements on the site response. The results indicated that by modifying the clayey soil using fiber, the seismic site response can be improved.