TESTS FOR FLOW ALONG VERTICALLY STRATIFIED POROUS-MEDIA INTERFACES

Two test methods were developed to detect preferential flow along the grout/clay interface in a cylindrical clay sample with a cementious gr out core. One test detects preferential flow along the interface by ta king ratios of the specific discharge in different regions of the spec imen as measured with a triple-ring permeameter. The other test detect s preferential flow along the interface by taking ratios of the veloci ty in different regions of the sample as measured by timing voltages c hanges as a sodium chloride solution passes through the sample. The re sults of both tests indicate that preferential flow does occur in the short term along the grout/clay interface. Comparing the velocity rati os to the specific discharge ratios, it is shown that small volumes of liquid travel rapidly along the interface. While the tests lend insig ht to the mechanisms of the preferential flow, caution must be used in applying the results of such laboratory scale specimens to the field situations. Changes to the equipment and procedures for future testing are suggested to improve reproducibility.