This project will use the geotechnical centrifuge as (a) a research tool to investigate the behavior and remediation of organic contaminants in aquifer systems, and (b) an educational tool to integrate physical modeling studies into civil and environmental engineering curricula. Geotechnical centrifuge modeling is an experimental method that allows the small-scale physical modeling of complicated problems affected by gravitational forces under realistic, but well controlled, boundary conditions. By using this method, both soil stress distributions and gravity (or buoyancy)-driven fluid displacements can be replicated at a reduced scale in a laboratory environment. Correct (scaleable) replication of these effects is not possible outside a centrifugal field unless a full-scale field experiment is carried out. For this reason, the geotechnical centrifuge offers an ideal tool for the physical modeling of many geo-environmental and geotechnical engineering problems.
The research component of this project proposes to use the geotechnical centrifuge to investigate (i) the effects of unstable nonaqueous phase liquid (NAPL) flow and soil heterogeneity on NAPL movement through the vadose zone; (ii) the mechanisms determining NAPL entrapment in saturated soils under a range of flow conditions, and (iii) factors affecting the performance of two recent NAPL remediation technologies, air sparging and surfactant-enhanced hydraulic flushing. The results of this program will produce experimental results representative of field behavior that can be used to (i) quantify the timing and rate of aquifer contaminant loading due, for example, to a surface NAPL spill; (ii) provide estimates of NAPL volume in aquifers under given hydraulic conditions; and (iii) develop quantitative guidelines for the deployment of two emerging remediation technologies. Data from the study will also be invaluable for the parameterization, testing and validation of conceptual transport models and numerical codes.
The educational plan will use the geotechnical centrifuge as a vehicle for introducing hands-on-experience and problem based learning into the civil and environmental engineering (CEE) undergraduate curricula. The objectives of the educational plan are to (i) develop a means of allowing CEE students to see the effects of their engineering design, and (ii) to explore whether the fundamentals of engineering mechanics can be better taught by exposing students to principles of physical modeling and scaling.
The project will make use of the geotechnical centrifuge facility in the Department of Civil and Environmental Engineering at MIT. This facility consists of a 1.0 m radius balanced arm centrifuge, which is capable of spinning a 90 kg package of soil around a central axis at 400 rpm, and a new 1.0 m diameter mini-drum centrifuge, which is capable of spinning a 1000 kg annulus of soil around a central axis at 1000 rpm. Both centrifuges will be used in the execution of this work.
