Field and laboratory measurements of small strain dynamic shear modulus G_max

An in situ geotechnical laboratory was established on one location of the pre-existing analogue 3D seismic network in Ohrid, N. Macedonia originally installed in the 80’s with the support of USGS. The in-situ laboratory is located in the central urban part of the city of Ohrid and consists of a nine-story building site with two accelerometers installed on the building, 4 instruments installed at the foundation level as well as one surface and three downhole accelerometers installed 125 meters down the bedrock. With the recent activities, real time recording, and health monitoring processes were enabled at the location. A comprehensive geotechnical investigation program consisting of geotechnical investigations and multiple geophysical measurements on one hand, and direct simple shear and triaxial tests of the obtained soil specimens in the lab on the other hand. The objective of the investigations presented in this paper was focused on estimation of the small strain dynamic shear modulus along with comparison of three different approaches, namely, two types of lab tests, direct simple shear test and cyclic triaxial test as well as in situ geophysical investigation of shear wave velocity. A valuable contribution can be made by comparison of different methods of measuring the soil stiffness parameter and defining the level of axial/shear strain to which this value is associated. The exact value of soil stiffness is crucial for further numerical modelling, simulation and verification of the results in the in-situ geo laboratory.