NonAqueous Pore Fluids

Mustafa Erten

Mary Goff

Project Team Members

In collaboration with:

Dr. R. Gilbert and

Dr. D. Reible

Chadi El Mohtar, Ph.D.

Assistant Professor

Geotechnical Engineering

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In situ capping is a remediation alternative for contaminated sediments which has been implemented to contain contaminants in sediments in rivers, lakes and ponds. One concern with in situ capping is that the additional load due to the in situ cap may cause consolidation-induced mobilization of Non-Aqueous Phase Liquids (NAPL). Therefore, it is important to understand the behavior of NAPL contaminated soils under consolidation. The difficulties of testing river-bed sediments are that these sediments usually are very soft, have very high porosities and very compressible. In addition, the contaminants in these sediments should be contained during testing. The primary objective of this research is to investigate the behavior of NAPL contaminated sediments under anisotropic consolidation.

For this research, a testing system was developed to simulate the consolidation of very soft sediment specimens. A specimen preparation method was introduced to prepare reconstituted NAPL contaminated sediments in the laboratory. Consolidation tests were performed on sediment specimens at various NAPL contents and porosities. Kaolinite and Anacostia sediments were used for the sediments solids phase. A low viscosity mineral oil, Soltrol 130 was used to represent the NAPL phase. Consolidation tests were performed to evaluate the performance of organophilic clay against NAPL. Organophilic clays were either placed as a layer on the top or mixed with the sediment. Consolidation tests were performed on clean sediment specimens collected from the field and mixed with NAPL in the laboratory. The results showed that NAPL mobilization was negligible below a threshold NAPL content. Hydraulic conductivities increased with increasing NAPL content up to four orders of magnitude. In addition, the results indicated organophilic clay can be effective containing and/or adsorbing NAPLs in sediments.

Consolidated Undrained and Consolidated Drained triaxial tests were performed on the specimens. The constructed specimens were subjected to consolidation stages ranging from 0.6psi to 29psi in confining pressure. The main focus of the study was on low confining pressures. After consolidation the specimens were sheared either undrained or drained. Both tests were utilized in order to see the difference in the pore pressures generated. Failure envelopes were developed for the different oil contents that contained three dimensions included the shear strength, the effective stress, and the pore pressure difference between the pore oil pressures and the pore water pressures. Also, the behavior of oil-dominated versus water-dominated was determined. Results from the 100% water specimens were comparable to previous data. The shear strength for the 100% oil specimens was higher than the 100% water specimens, but lower than the 90% oil and 70% oil specimens. The 50% oil specimens resulted in a great deal of variability on whether the specimen was water-dominated or oil-dominated. The main conclusion was that the Kaolinite had an increase in strength with the introduction of mineral oil.

Relevant Referred Publications

1. Erten, M., Gilbert, B., El Mohtar, C, and Reible, D. "Development of a laboratory procedure to evaluate the consolidation potential of soft contaminated sediments," ASTM Geotechnical Testing Journal: Innovations in Characterizing the Mechanical and Hydrological Properties of Unsaturated Soils, Vol 34 Issue 5, September 2011. [PDF]

2. Mustafa B. Erten, Chadi S. El Mohtar, Danny D. Reible, Robert B. Gilbert. "Consolidation Properties of NAPL Contaminated Sediments" GeoCongress 2012: State of the Art and Practice in Geotechnical Engineering, Oakland, CA, March 25-29, 2012. [PDF]

3. Mustafa B. Erten, Danny D. Reible, Robert B. Gilbert, Chadi S. El Mohtar "The Performance of Organophilic Clay on NAPL Contaminated Sediments under Anisotropic Consolidation," Journal of ASTM International STP 1554, Vol. 5, Restoration of Aquatic Environment, Nov. 2012, DOI: 10.1520/STP104214. [PDF]