Low-Gradient Permeability Testing of Fine-Grained Marine Sediments

Abstract

A back-pressured consolidation system has been modified to allow direct permeability measurements of fine-grained, low-permeability soils and marine sediments. The system allows for high back pressures (3100 kPa), axial flow in either direction with fresh or saltwater permeants, constant head tests at low gradients, and falling head tests. Low-gradient tests are conducted with a static head or with falling head methods, and high gradients are maintained with a sensitive air-pressure control system. The unit can also be used to study temperature effects in the range of 2 to 200°C. The apparatus and procedures are described, and a summary of test results is presented. Results of low-gradient constant head tests have agreed very well with falling head tests. Coefficient of permeability values in the range of 10−6 to 10−9 cm/s have been measured. No evidence of a threshold gradient has been indicated at higher void ratios approximating in situ conditions, but small threshold gradients were observed at relatively low void ratios.