Vertical Effective Stresses from Multi-Piezometer Array System (MPAS) Pore Pressure Measurement at the Coastal Oil-Spill Simulation Facility
Abstract
This report describes and examines the excess pore water pressures generated in a sand bed subjected to gravity water waves as measured by piezometer probes of the Multi-Piezometer Array System (MPAS). Experiments were conducted a medium-sized wave tank (2.1 m wide, 2.4 m deep, and 30 m long), floored by 1 m of uniform, saturated, medium dens to dense fine sand covered by 1.2 m of sea water. Two MPAS probes were embedded 0.30 m in the sand bed (with integral sensor and amplifier housing extending 0.68 m above the bed) and positioned 6.1 m apart. The first probe had a mass of 32 kg and was supported on the sand surface by a thin ring footing, whereas to the second probe steel angles were added beneath the ring footing to serve as shear keys and increasing the mass to 57 kg. Multiple trains of 60 + uniform waves were created with wave heights (trough to crest) up to 0.4 m and a wave period of 5 sec. Excess pore water pressures measured by the MPAS probes were found to differ from theory in that changes in vertical effective stress in the sediments apparently are not tied with vertical total stress at the sediment/water interface, i.e., effective stresses are decreasing in the sediments when predicted total stresses are increasing, and vice versa. Also, large differences in measured excess pore water pressures were observed between the probe with thin ring footing and that with added steel angle weighting/shear keys, in similar total stress environments, indicating that factors other than changes in total stress, i.e., the probes, base configuration, and /or integral electronics housing, are influencing the measured pore water pressures.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 22, 1999
- Accession Number
- ADA372439
Entities
People
- Glen R. Andersen
- S. P. Gonzales
Organizations
- Texas Engineering Experiment Station