Free-fall penetrometers (FFPs) are an attractive tool for the rapid characterization of sediments in the nearshore and coastal areas. To improve their measurement capabilities, modern FFPs can be equipped with pore pressure sensors. Pore pressure measurements are extensively used in traditional cone penetration testing, but their usage and interpretation is still limited for FFP testing. This thesis represents an effort to advance the interpretation of pore pressure measurements from FFP testing.
Data was collected using the torpedo-shaped FFP BlueDrop during surveys at Herschel Island, YT, Yakutat, AK, Clay Bank, VA, and Yorktown, VA. Additionally, test deployments in the laboratory were performed in kaolin clay. Data analysis was focused on pore pressure measurements during these deployments. Two major advancements regarding current data analysis of FFP pore pressure measurements were explored: 1) a method based on fluid dynamic principles was proposed to correct the pressure recordings for the dynamic flow effects due to the high-velocity fall and impact. The results show that using Bernoulli’s theorem coupled with the concept of pressure coefficients results in good agreement between measured and hydrostatic pressures during the free-fall and initial penetration stage. 2) Pore pressure dissipation curves measured by the penetrometer at rest at maximum penetration depth were also studied. The mechanisms behind the non-standard dissipation curves were explored. The results suggest that non-standard dissipation curves can be interpreted by correcting according to Sully et al.’s (1999) extrapolation technique. The technique can also be used with data from an unsaturated or clogged filter. / Master of Science / An increasing use of nearshore and offshore areas for the development of infrastructure such as pipelines, cables, renewable energy harvesting devices, and measures against coastal erosion warrants the development of specialized methods for investigating the stability of the seabed. Portable free-fall penetrometers represent a cost-efficient approach to characterize shallow seabed sediments, but there are challenges associated with deriving geotechnical design parameters from these novel instruments.
This study aims at developing a better understanding of the pore pressure (the pressure developed in the water in the soil’s voids) data obtained during free-fall penetration testing. The pore pressures developed during the penetration of the penetrometer is dependent on the soil type, and is often used to correlate to it. This study used data obtained from field surveys at Herschel Island, YT, Clay Bank, VA, Yakutat, AK, and Yorktown, VA. Additionally, controlled tests were performed in the laboratory in an instrumented seabed. This study resulted in a novel method to correct the pressure data from the penetrometer for dynamic fluid flow effects and validation of an interpretation technique for dissipation curves to obtain the time required for consolidation, based on initial results.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83800 |
| Date | 28 June 2018 |
| Creators | Mumtaz, Muhammad Bilal |
| Contributors | Civil and Environmental Engineering, Stark, Nina, Castellanos, Bernardo Antonio, Green, Russell A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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