Laboratory evaluation of shear modulus and damping ratio of Sands stabilized using polyvinyl acetate resin and rubber powder under cyclic loading Marjan Safari marjan.safari@cv.iut.ac.ir 2020/09/19 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Farsi Supervisors: Dr. M. A. Rowshanzamir, mohamali@cc.iut.ac.ir Soil improvement by adding different materials has always been of interest to researchers. One of the most commonly used methods to improve the mechanical properties of sandy soils is the addition of polymers and scrap tire waste, that resulting in improved soil properties under static and dynamic loads. When an earthquake occurs, the energy generated by different waves reaches the earth's surface. An accurate understanding of earthquake behaviour is needed to reduce earthquake damage and to prevent other harmful effects such as liquefaction, landslides, etc. Earthquake analysis is not possible without knowing the dynamic parameters of the soil. These parameters are the damping ratio and shear modulus of soil. The steps of this study included a series of static tests on sand and sand samples improved with polyvinyl acetate resin at 1, 2 and 3 percent as well as 0, 4, 8 and 12 percent rubber powder and also a series of cyclic triaxial tests with an optimum amount of polyvinyl acetate resin obtained from unconfined Compression tests and 4, 8 and 12% rubber powder under 100 kPa of cell pressure and different cyclic stress ratios of 0.15, 0.3 and 0.45, respectively.The increase or decrease process in the dynamic properties of the soil is influenced by the regnant matrix in the soil due to the amount of resin and rubber powder in it. The presence of resin due to increasing the hardness and then decreasing the energy absorption in the soil element caused that increased the shear modulus and damping ratio so that the shear modulus in the cyclic stress ratio of 0.15 to 0.4 MPa in pure soil to 30.61 MPa and damping ratio from 50.12 in pure soil to 15.2 in stabilized soil with 2% resin. Also, in studying the effect of increasing cyclic stress ratio of the most important results, were observed a decrease in shear modulus and increased damping ratio in All samples. By adding rubber powder of up to 4% to the resin-stabilized specimens to adhere as much as possible the resin grains to the soil and powder particles, the soil matrix will still be hard to sample, so that the shear modulus at a cyclic stress ratio of 0.15 increases by 1.37 times Equilibrium and damping ratio decreased by 0.5 times compared to the stabilized sample with 2% resin. By increasing the rubber up to 8% due to overcome the relative softening effect of the rubber on the resin, the shear modulus at the same stress ratio decreased by 0.76 times and the damping ratio increased by about 1.4 times than of the 2% resin along with 4% powder samples. Finally, a slight increase in shear modulus and a decrease in the damping ratio were observed, with a 12% increase in rubber powder . Keywords Soil stabilization, Sandy soil, Cyclic triaxial test, Shear modulus, Damping ratio, PVAc resin, Rubber powder.