INFLUENCE OF MICA CONTENT ON DYNAMIC SHEAR MODULUS OF SANDY SOILS Seda DURUKAN 1 , Ender BAŞARI 2 1 Manisa Celal Bayar University, Manisa Vocational School of Higher Education, Manisa-Turkey 2 Manisa Celal Bayar University, Department of Civil Engineering, Manisa-Turkey 1 seda.durukan@cbu.edu.tr, 2 ender.basari@cbu.edu.tr Abstract: The Gediz River Delta soils contain abundant flatty (platy) mica grains. Mica grains can alter static and dynamic engineering characteristics of sandy soils due to their flatty shapes. In this study, influence of mica grains on dynamic shear modulus of sandy soils in Gediz River Delta was investigated. Maximum shear modulus (Gmax), which is a major parameter in dynamic soil response analyses, can be obtained at small deformation amplitudes. Therefore, it is determined through measurement of shear wave velocity. Shear wave velocity provide valuable information about dynamic characteristics of soils. So it is very important to determine the shear wave velocity with high accuracy for dynamic soil response analysis. In this respect, firstly engineering boreholes were drilled and sandy soil samples were recovered along the borehole depth. The mica content of the samples was determined by means of X-RD analysis method. Then test sample contain 1.5%, 10% 20% mica grains were prepared to represent the Gediz River soils. Shear wave velocity of the sand samples were determined with bender element tests under 100 kPa cell pressures in triaxial test device. Followed by the bender element tests maximum shear modules were determined. End of the test program, shear wave velocity of the dense (Dr:55%) samples were determined as 249 m/sn, 214 m/sn and 187 m/sn for 1.5%, 10% and 20% mica content respectively. Mica was reduced the shear wave velocity in considerable percentage about 25% rate. Smiler effect was observed on the maximum shear modules and it is determined as 111.6 MPa, 82.4 MPa, and 62.9 MPa for 1.5%, 10%, 20% mica contents respectively for dense samples (Dr:55%). 20% mica content was reduced the shear wave velocity about 44% rate. Keywords: Sand, mica content, shear wave velocity, maximum shear modulus Introduction Soil properties especially dynamic properties are determined by the empirical relations, although there are special tests for this purpose in the geotechnical engineering. The tests have high cost and perform of the tests requires long time. For this reasons, dynamic properties of the soil are determined by means of Standard Penetration Tests (SPT), Coni Penetration Tests (CPT), and Dynamic Penetration Tests (DPT) etc. Use of the empirical relations based on SPT, CPT, and DPT may lead to error in dynamic soil response analyses for the soils which contain abundant platy grains. In this respect, an experimental study was conducted on sandy soils which are deposited by Gediz River and contain abundant platy mica grains. The shape of the soil grains are mainly depended on their geological origin and environmental conditions. Alluvial deposits formed by the Gediz River in the west Anatolia are good examples for the soils which contains abundant platy grains. The foundation of Gediz Basin contains rocks which consist of mica minerals (Tabban, 1980) so alluvial deposits in the Gediz Basin may contain about %20 platy mica grains (Başarı, 2012). In the literature, there are many studies about influence of grain shape on soil behaviors (Santamarina & Cho, 2004). The studies mainly focused on angularity or roundness of grains (Thevanayagam, 2007). Grain shape effects on shear wave velocity were explored by some researchers. Cho et al. (2006) conducted a series bender element tests on rounded and crushed sands. The test results of the Cho et al. (2006) are given in Figure 1. According to Cho et al (2006), shear wave velocity increase with roundness as seen in Figure 1. Shear wave velocity of rounded sand samples is higher than shear wave velocity of angular sand samples. Angularity of the sand grains cause an increase voids between the grains this effect leads to decrease in density of media which shear waves propagate in its. Also, angularity of the grains causes a decrease contact surface area between sand grains. Decreases both of contact surface area and density of media leads to decrease shear wave velocity in soil. Stresses on contact surfaces between grains have a significant role on energy transmission between grains. High stress on the contact surface creates more stable structure in soil, so energy can transferred more easily between grains. In Figure 1 mean effective stress indicates stress on contact surfaces. High mean effective stress means high stress on contact The Online Journal of Science and Technology - October 2017 Volume 7, Issue 4 www.tojsat.net Copyright © The Online Journal of Science and Technology 87