In-Situ Undrained Shear Strengths and Permeabilities Derived from Piezometer Measurements

Abstract

Existing theories and models describing stress changes and consolidation-time effects around a pile were used to derive in-situ permeabilities and undrained shear strengths from piezometer probe measurements in smectite- and illite-rich soils. Permeabilities derived from piezometer measurements are in reasonable agreement with laboratory measurements, and calculated undrained shear strengths agree well with strength measurements using standard field and laboratory techniques. Undrained shear strengths Su were estimated using insertion pressures Ui, determined from both the 10.2- and 0.8-cm-diameter probes, and the relationship, Ui = 6 × Su. A strength measurement determined with the small diameter probe inserted in the disturbed zone of a previously emplaced 2.5-cm-diameter cylinder showed a significant strength reduction equal to half the value determined for the soil (strength) in the zone unaffected by the implanted cylinder. Differences in decay rates were significant, indicating severe soil disturbance in close proximity to the cylinder. Multisensor piezometer probes (2), 10.2 cm in diameter, were deployed in shallow-water fine-grained smectite-rich soils of the Mississippi delta. Pore-water pressures were measured at subbottom depths of 6.5, 12.6, and 15.6 m. Insertion pressures, time-dependent pore pressure decay, and ambient excess pore pressures were determined. Single sensor piezometers (2), 0.8 cm in diameter, were developed for deep-ocean investigations. Before high pressure testing (55 MPa), probes were inserted in reconstituted illitic marine soil to depths of 16.9 and 26.4 cm below the soil-water interface. Insertion pressures and their decay characteristics were monitored. Significant differences were observed in the pore-pressure decay rates produced by the small and large diameter probes. Decay times for the induced pressures to reach t100 values were on the order of tens of hours for the large diameter probes, whereas the t100 values of the small diameter probes were on the order of minutes. These differences in decay times were a function of the differences in probe diameters (radii) and soil permeabilities.

Measurement of hydraulic properties in deep lake sediments using a tethered pore pressure probe: Applications in the Hamilton Harbour, western Lake Ontario

“…At higher penetration rates this spherical distribution around the tip becomes more oblate or radial in nature, similar to that generated along the shaft [Elsworth, 1991]. If the assumption is made that the excess pore pressures near the lower port dissipate essentially in a radial fashion, a convenient analogy can be made between the insertion of the sediment probe in lakebottom sediments and the driving of a friction pile in saturated soils [Bennett et al, 1985].…”

“…Schultheiss [1990] provides a comprehensive chronology of piezometer probe development for oceanic applications. Bennett et al [1985] To our knowledge, the only documented study to use a piezometer probe in freshwater was that of Cartwright et al [1979], who used a probe to estimate bottom-sediment hydraulic gradients in southern Lake Michigan. Using a tethered probe, Cartwright et al [1979] measured hydraulic gradients in bottom sediments at depths of 48-140 m as part of a study investigating trace metal loadings to the lake from regional groundwater discharge.…”

“…This must be accounted for when expressions involving both types of parameters are involved. However, in sediments with more of a random soil fabric (as might be expected in the upper "mucky" portion of deep-lake bottom sediments) nearly isotropic conditions generally exist [Bennett et al, 1985]. The probe is connected electronically to a data acquisition system via Belden © 8447 six-pair, unshielded audio sound and control cable.…”

“…Schultheiss [1990] provides a comprehensive chronology of piezometer probe development for oceanic applications. Bennett et al [1985] describe the use of shallow-water and deep-ocean probes developed as part of the U.S. Sandia National Laboratories Seabed Disposal Program to provide in situ data on pore-water pressures and related geotechnical properties of submarine soils on the Mississippi delta. Schultheiss and McPhail [1986] used a freefalling, partially disposable probe to measure pore-water advection (groundwater flow) in deep-water environments.…”

Analysis and application of in situ pore pressure measurements in marine sediments

“…In recent years, in situ pore pressure measurements in seafloor sediments have been made in different geological settings to determine pore pressure gradients and to estimate in situ physical properties of the sediments [Bennett and Faris, 1979;Abbott et al, 1984;Bennett et al, 1985;Hurley, 1989;Hurley and Schultheiss, 1990]. These studies were mainly carried out by scientists who are interested in hydrothermal circulation in the oceanic crust and by engineers interested in in situ geotechnical properties of marine sediments as they apply to problems of subseabed waste disposal and offshore construction.…”