Huon Li

In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 1: Measurements

Abstract In situ porosity and permeability were measured on Great Bahama Bank sediments using electrical conductivity and permeability probes. Core samples were recovered at the probe measurement sites for laboratory determinations of porosity and permeability. Penetration depths of cores and probes were approximately 2.5 m subbottom. In situ porosities of the oolitic sands for depths of 0–2.5 m subbottom ranged between 36% and 50%, and at sites in the somewhat muddier oolitic sediments the porosities ranged from 42% to 61%. The in situ permeabilities ranged from 0.0032 cm/s (3.3 darcys) to 0.068 cm/s (71 darcys) at the sites where porosities were determined. Laboratory values of porosity are comparable to values obtained by in situ measurements; however, laboratory permeability values are approximately an order of magnitude lower than in situ values. The reduced permeability measured in the laboratory is attributed to disturbance of the microfabric during coring, transport, and laboratory sampling. A det...

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.

In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 2: Microfabric

Abstract Selected oolitic sediments from the Great Bahama Bank were studied to assess (1) the role of microfabric in determining porosity and permeability, and (2) particle packing relationships, i. e., grain support versus matrix support. Scanning electron microscopy and light microscopy revealed that the sediment consists of ooids, which are the major constituents of the sand‐size fraction, supported by a matrix composed predominantly of aragonite needles. The supporting matrix of aragonite needle clusters, which constitutes only about 10–20% of the total sediment dry weight, is the microstructural characteristic that increases the porosity and lowers the wet bulk density compared to a grain‐supported microfabric characteristic of clean sands. The presence of a fine‐grained matrix reduces the permeability of these sediments relative to clean sands. The influence of the microfabric is clearly reflected in the mass physical and depositional (particle packing) properties of the sediment. Laboratory values ...

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.

The Significance of Sediment-Flow Dynamics on Clay Microstructure Development: Riverine and Continental Shelf Environments

The highly variable dynamics of coastal and continental shelf waters have a significant effect on the transport and deposition of sedimentary materials. The complex sediment transport mechanisms in continental shelf waters involve the interactions of multiphase flows of solids, liquid, and organics (dissolved and particulate) with multicomponent chemical and minerals species. Also biological processes are pervasive. Fine particles are transported as individual particles and floccules of various sizes and they interact with the fluid flow. The solid particle coagulation, breakup, deposition, erosion, and transport processes and mechanisms depend on the tidal cycles as well as the waves and currents. Particle associations at the sediment water interface are directly related to the particle associations in the suspension, and thus the microstructure at the sea floor is considered to be related to the floe sizes in the water column. The particles (individual particles and floes) in suspension that are deposited eventually at the depositional interface are the fundamental “building blocks” of the bottom sediment.

Calculation of permeability coefficients of soils and marine sediments

Abstract A BASIC program is described which calculates permeability coefficients from data obtained by laboratory measurement using a variable-head permeability apparatus. The program also calculates two quantities from the experimental data which are functions of hydrostatic pressure change and time interval, respectively. Output is printed and stored in a data file for statistical processing or graphical presentation using a commercial software package. A data collection method is explained which permits the recognition of sample disturbance, such as the formation of large flow channels, arising during the course of testing. Use of the program is demonstrated using data for three natural sediment samples tested on a variable-head permeability apparatus with back pressure.

Effect of source depth on shallow water tomography

While the theory of paraxial approximation is applied to the research of momentum and orbital angular momentum (OAM), the analytical expressions of momentum and OAM of vortex beam are derived. Based on the analytical expression, the distribution and propagation of the momentum and OAM of the Gaussian vortex beam is investigated in free space. Theoretical analysis and numerical simulation show that the values of the radial and angular components of momentum are close to each other, and they are far smaller that the value of the longitudinal component of momentum. The three components of momentum of the beam will expand along the radial direction during propagation in the cross section. The maximum positions of the three components are different, which problem is dependent on the topological charge and the beam width of the source beam. The whole integration results of the three components on the cross section shows the conservation of the momentum of the beam. Besides, the OAM of the Gaussian vortex beam will also expand along the radial direction during propagation. The maximum position of the OAM is the same as that of longitudinal component of the momentum. The whole integration result on the cross section confirms the conservation of the OAM of the Gaussian vortex beam while propagating.