TEST METHOD

In this test, as in many consolidation tests (Taylor, 1948), a constant axial load applied using an external loading frame was instantaneously applied to a sample of unconsolidated material that was laterally constrained. The axial load produced an excess pore fluid pressure along the length of the sample, except at the bottom of the sample. The bottom of the sample was drained so that there was no excess pore fluid pressure; the pressure at the bottom of the sample was atmospheric. Fluid flowed from the sample bottom because of this pressure gradient, and the total amount of fluid discharged was measured as a function of time. Figure F2A is a diagram of the apparatus and the assumed boundary conditions. Figure F2B is an idealized pressure profile along the length of the sample with increasing time. This test differed from the usual consolidation test in that the process was not repeated for larger axial stresses after the pore pressure dissipated. We were most interested in the hydraulic conductivity and specific storage, not the past stress history of the samples.

Immediately after the core was recovered, a 6-in length of whole-round core was cut and stored under refrigeration until testing. Samples for testing from these cores were removed from the whole-round core using a piston core sampler with the same diameter as the Manheim squeezer (diameter = 4.25 cm). The initial lengths of the samples were ~3 cm. In most cases, two samples were tested from each whole round, one sample oriented with its axis parallel to vertical and one with its axis perpendicular to vertical. The samples were loaded individually into the Manheim squeezer, which was then placed in the load frame and loaded to a predetermined axial stress.

Figure F3 is a diagram of the Manheim squeezer. After the core was loaded into the Manheim squeezer, the axial load was applied using a hydraulic ram in a loading frame. The axial loads were held relatively constant (±10%) by watching and adjusting the load as needed over the course of a test. The axial loads were measured using a mechanical gauge on the hydraulic ram. These loads were greater than those commonly used in consolidation tests because of the limited dial resolution and accuracy of the gauge on the hydraulic ram. The lowest possible accurate reading of the gauge (2000 lb) corresponded to an axial stress of 6.3 MPa on the sample. This corresponds to a burial depth of ~230 m, if the contribution to effective stress from pore pressure is neglected.

The fluid discharge as a function of time was measured using a 10-mL syringe and a stopwatch. The assumption of incompressible mineral grains and water, common to soil mechanics (Wang, 2000), allowed the volume of water displaced from the sample to be converted to axial displacement using the cross-sectional area of the cylinder,

w = volume of water discharged/cross-sectional area of cylinder, (1)

where w = axial displacement.

Although this method is experimentally simple, it may introduce errors in measurement due to frictional effects between the syringe plunger and cylinder. If >10 mL of fluid was discharged, the full syringe was quickly replaced with an empty 10-mL syringe. The time needed for 10 mL of discharge was generally greater than an hour, so the discharge rate was low and no fluid was lost. A test was generally run for several hours, with the operator holding the axial load constant and recording data until there was no more discharge from the sample.