Investigation of seismic excitation as a method for flow enhancement in porous media

The concept of using dynamic excitation to enhance fluid flow in a porous medium began to arise in the mid-twentieth century. The initial spark of interest in the subject spurred numerous laboratory investigations throughout the latter half of the twentieth century to identify the mechanisms at work, and to develop field techniques for practical application of the technology. Several prominent laboratory and field studies have been published; however, there are some deficiencies that facilitate the need for further investigation. Groundwater flow and soil dynamics are two distinct areas of research. There is little in common between the two subjects and there is no consideration of soil dynamic properties in any of the reviewed papers. This study will attempt to bridge the gap between these two areas of research.;The flow test results are inconclusive, likely because the input signal amplitudes utilized are simply not large enough to cause a measurable increase in fluid flow rates. Also, increased flow rates observed in previous studies may be the result of local increases in fluid pressure that increase the fluid flow rate, rather than an added inertial component or porosity dilation.;From the additional data obtained during this study, it appears there are some general conclusions that can be drawn regarding the dynamic properties of sands with varying degrees of saturation. The damping ratio of the unsaturated sand increases 270% in torsional mode and 74% in axial mode with a 133% increase in grain diameter. In general, damping is minimal at the partially saturated and saturated conditions and much higher in the dry condition. The damping ratio at dry condition is 243% more than in the partially saturated condition in torsional mode and 37% in axial mode for the Barco sand, and 1170% more in torsional mode and 59% in axial mode for the Indusmin sand.;Calculation of the Poisson ratio using the shear and longitudinal wave velocities yields some interesting results. For the dry and saturated conditions, the computed values are within the range of a loose to medium-dense sand specimen; however, the values computed for the partially saturated condition in both sands are an order of magnitude lower and are quite close to the reported value for the mineral quartz. In general, the Poisson ratio increases for high strains; 7.4% for the Barco sand and 6.3% for the Indusmin sand.;The objective of this research is to attempt to determine how dynamic excitation of a soil matrix affects saturated single-phase fluid flow. This question is investigated through an extensive literature review of previous studies conducted on this topic, as well as through experimentation designed to replicate the mechanisms responsible for this phenomenon. Experimentation on coarse soil samples is conducted using a modified Stokoe-type resonant column device that allows a quantification of the effects of torsional and axial excitation, frequency of vibration, and strain level. This type of testing in the both the torsional and axial mode has never been conducted before using a resonant column; the Poisson ratios computed using the complimentary data has never been published in the literature.;Future study must be able to characterize the dynamic properties of the soil specimen and NAPL droplets, in addition to quantifying the observed increase in flow. Therefore, the main recommendation of this study is the design of equipment which is capable of not only measuring the response of a soil specimen to dynamic stimuli, but is also capable of accurately measuring flow through the specimen. The optimal design will probably be based on the design of the resonant column. However, effort must be made to ensure the device does not impede flow through the matrix, and it is recommended that all flow connections be located on the exterior of the confinement chamber to minimize the potential for gas leaks into the specimen. Thought should be put into the type of NAPL to be utilized and the degree of sorption to organics. Membranes and plastic tubing should be selected to minimize NAPL loss due to sorption.