Joel Lipkin

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. 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.

Application of piezometer probes to determine engineering properties and geological processes in marine sediments

Abstract Single-sensor piezometer probes, 8 mm in diameter were developed and tested for deep-ocean geotechnical investigations in support of the Subseabed Disposal Program. Two probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi) during a scaled (0.28:1) simulation experiment conducted at the David Taylor Naval Ship Research and Development Center (DTNSRDC) in Annapolis, Md. Testing was performed for 30 days with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. The piezometers sensed very small (approximately 1.7 kPa [0.25 psi]) pore-water pressure events during the process of carrying out other experimental objectives. The pressure sensors exhibited excellent sensitivity and stability during other deep-ocean simulated laboratory pressure tests for periods of up to 750 h. In addition to the measurements of ambient and dynamic pore-pressure response to environmental forces, the piezometer test data can be used to derive the in-situ undrained shear strengths and permeabilities of seabed sediments. The piezometer probe technology is providing a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits.

Deep-ocean piezometer probe technology for geotechnical investigations

Two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations. These probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi). Testing was performed for a period of five weeks under high hydrostatic pressure with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. During deep-ocean simulated pressure tests, the sensors exhibited excellent sensitivity and stability. These developments in piezometer-probe technology provide a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits.

Dynamic yield-strength determination at elevated temperatures after nanosecond pulse heating

An experimental method is described that has been used to determine the yield strength of 6061-T6 aluminum after extremely short times at elevated temperature. The method combines electron-beam pulse heating and onedimensional stress-wave loading. A 3.5-MeV pulsed electron-beam source (pulse width of 70 nanoseconds) is used to deposit energy uniformly through the thickness and along a limited region of a slender aluminum rod. An axial compressive stress wave, produced by projectile impact on one end of the rod, propagates into the heated region a few microseconds after energy deposition.The nanosecond electron-beam pulse increases the internal energy of the material before it can expand to equilibrium dimensions at the elevated temperature. Additional time is therefore required for the specimen to equilibrate mechanically through the propagation of radial release waves which originate at the stress-free boundary of the sample. The deformation produced by these radial relief waves is coupled with microstructural changes that also contribute to a reduction in the yield strength of the material at elevated temperature, as well as at room temperature following electron-beam heating.

Using An Imaging Infrared Radiometer To Measure Time-Dependent Temperature Distributions

Time-dependent temperature distribution data were obtained from cylindrical nylon test specimens deformed in torsion. The temperatures were measured with an infrared radiometer and calculated with image analysis software. These data provide a clear picture of the evolution of the specimens surface temperature profile prior to and during strain localization and failure. Measurements like these will be used to evaluate parameters in a material model now under development. The data will also help establish the validity of existing numerical methods.

Localized flow of nylon-6,6 rods under torsional loading

Torsional loading of solid rods is used to determine how the flow stress of nylon-6,6 depends on loading rate and temperature. Relatively modest rate sensitivity and very strong temperature dependence contribute to a high probability of strain localization during shearing of this material. The severity of this localization is assessed by using an imaging infrared radiometer to measure the evolution of a samples surface temperature profiles are used to determine the limit of uniform deformation in a sample. Fundamental material properties are then derived unambigously from torque versus angle of twist data.