Physical modeling of seismic soil-structure interaction of embedded structures

This thesis investigates seismic soil-structure interaction of buildings with embedded basement stories founded in clayey sons. The thesis is divided into three sections comprising: (i) the development and characterization of two model clays; (ii) design, fabrication, and commissioning of a laminar soil container for use on a small shake table and (iii) experimental and analytical investigations of seismic SSI. The results presented in this thesis provide new insight into seismic SSI of partially embedded buildings and should assist researchers who wish to perform seismic scaled model tests using small capacity shaking tables.;First, the thesis describes a laboratory study that was performed to characterize a synthetic clay called glyben. Glyben consists of bentonite mixed with glycerin. The laboratory results show that both the dynamic shear modulus and damping ratio of glyben vary with shear strain similar to that seen in natural clays. However, the damping ratio of glyben is significantly higher than natural clays. In addition, it is shown that the dynamic properties of glyben are strongly influenced by thixotrophy and temperature, and that glyben exhibits time-dependent volumetric compression alter the application of isotropic consolidation pressure, which can be interpreted using consolidation theory. To conclude, a modular neural network (MNN) is developed, trained and tested using experimental data in order to predict the influence of various factors on the dynamic properties of glyben. It is shown that the MNN is able to adequately predict the dynamic properties of glyben.;Next, a new synthetic clay called modified glyben is developed and its dynamic properties are characterized using a combination of bender element, cyclic triaxial and resonant column tests. This study shows that the dynamic properties of modified glyben are strongly affected by the pore fluid viscosity, which can be varied by altering the ratio of glycerin-to-water in the pore fluid. By decreasing the ratio of glycerin-to-water in the pore fluid, researchers can decrease the vane shear strength, dynamic stiffness, damping ratio and coefficient of consolidation of modified glyben. Modified glyben is shown to have a normalized shear modulus versus shear strain amplitude response that is independent of the confining stress, and glycerin-to-water ratio. The dynamic shear modulus is fully characterized by measuring the small strain shear modulus (Gmax) versus the confining stress and glycerin-to-water ratio; the damping ratio is characterized versus shear strain amplitude and glycerin-to-water content. It is shown that modified glyben that has a glycerin-to-water ratio of 25% gives a synthetic clay, which: (i) does not consolidate significantly with time during the first 10 days after application of confining stresses, (ii) has a damping ratio that is very close to that of natural soils, (iii) does not desiccate with prolonged exposure to air, (iv) can be used multiple times without degradation of dynamic properties, and (v) has dynamic stiffness and undrained strength that can be adjusted by varying the fluids content and glycerin-to-water ratio.;After developing modified glyben, the design, fabrication and commissioning of a single axis laminar soil container is described. The laminar soil container was designed to overcome the base shear limitations of a small shaking table situated in the Boundary Layer Wind Tunnel at the University of Western Ontario. This thesis describes the design and presents the results of shaking table tests performed using modified glyben as the model soil. The laminar container is shown to maintain 1-D soil column behaviour. In addition, the dynamic behaviour of the modified glyben during scaled model tests was found to be consistent with the behaviour measured during cyclic laboratory tests.;To conclude, embedment effects on seismic SSI of buildings with embedded basement stories are studied using the laminar shear box and shaking table. The laminar shear box was filled with modified glyben to create a model soil deposit. Then, a model building with various embedment depths was designed, and embedded in the model soil deposit. The laminar container, model soil, and model building were then tested seismically using the shaking table to study the effects of embedment depth, foundation mass and superstructure on the dynamic system parameters. The results showed that the system period decreases for tall-slender structures, whereas it increases for short-squat structures with the increasing embedment depth. The damping ratio remained almost unchanged for studied SSI systems. Overall, the scaled model tests results are the first of their kind that confirm two analytical approaches for assessing seismic SSI.;Key words: Soil structure interaction, Synthetic clays, Non-linear soil behaviour, Laminar soil container, Embedded basement stories, Dynamic system parameters.