Physical scale modeling of geotechnical structures at one-G

Abstract

The use of physical scale modeling techniques for geotechnical applications is investigated. The scaling laws to relate a prototype structure to a model are developed for the centrifuge modeling technique and for the laboratory (or one-g) environment. A theory based on critical or steady state concepts for the constitutive scaling of the behavior of the soil in a one-g model is investigated. A series of one-g models of varying configurations was constructed in a laminar box and subjected to earthquake like motions on a shake table. A total of 73 tests was performed. Most tests were constructed of saturated Nevada sand placed in a loose and dense state in adjacent halves of a laminar box, and the results of these tests were compared with a similar centrifuge test (Model 3) which was performed as part of the VELACS study. Some of the one-g models were constructed with an alternate model sand and an alternate pore fluid to investigate these modeling variations. One-g models were also constructed with the sand at a uniform density throughout the laminar box. The research indicates that there is a significant conflict between the time scaling for dynamic processes and dissipation processes in both the centrifuge and one-g techniques, which means that excess pore pressures generated in the model saturated sand by a simulated earthquake will be less than what would occur in the same sand in the real prototype. This effect is generally more severe in the centrifuge. This implies that model tests performed to investigate liquefaction, flow failure problems, and/or deformation problems in saturated sands may significantly underestimate the potential behavior of the prototype. In addition to the above, the research provides insight into the behavior of adjacent loose and dense sands and indicates the potential for high excess pore pressures to develop in the dense sand. Current practice ignores the potential for liquefaction in dense sands or the development of cyclic mobility in the assessment of the seismic performance of geotechnical structures.