dc.contributor.author	Britton, Jeremy Paul	en
dc.contributor.committeecochair	Little, John C.	en
dc.contributor.committeecochair	Filz, George M.	en
dc.contributor.committeemember	Mitchell, James K.	en
dc.contributor.committeemember	Westman, Erik C.	en
dc.contributor.committeemember	Widdowson, Mark A.	en
dc.contributor.department	Civil Engineering	en
dc.date.accessioned	2014-03-14T20:15:09Z	en
dc.date.adate	2001-08-15	en
dc.date.available	2014-03-14T20:15:09Z	en
dc.date.issued	2001-08-08	en
dc.date.rdate	2002-08-15	en
dc.date.sdate	2001-08-13	en
dc.description.abstract	Soil-bentonite cutoff walls are commonly used to contain contaminants in the subsurface. A key property in determining the effectiveness of a cutoff wall is its hydraulic conductivity. There are important difficulties and uncertainties regarding the accuracy of commonly used methods of measuring the hydraulic conductivity of cutoff walls. When predicting contaminant transport through cutoff walls, common practice is to use the average hydraulic conductivity of the wall. There are some cases, however, such as circumferential cutoff walls with inward hydraulic gradients, where it is also important to consider the variability in hydraulic conductivity from point to point in the wall in contaminant transport studies. A pilot-scale facility was envisioned where subsurface barrier issues such as those mentioned above could be studied. In 1998, the Subsurface Barrier Test Facility (SBTF) was constructed. In this facility, pilot-scale subsurface barriers can be installed using real construction equipment and tested in a controlled environment. The effectiveness of various methods of measuring the hydraulic conductivity of cutoff walls was studied by building and testing three pilot-scale soil-bentonite cutoff walls at the SBTF. The following currently used test methods were evaluated: API tests on grab samples, lab tests on undisturbed samples, piezometer tests (slug tests), and piezocone soundings. The use of slug tests in cutoff walls was improved in this research in the areas of avoiding hydraulic fracture and accounting for the close proximity of the trench walls. The SBTF allows for measurement of the global, average hydraulic conductivity of an installed pilot-scale cutoff wall, which is a useful value to compare to the results of the above-mentioned tests. The two main factors differentiating the results of the different test methods used for the pilot-scale walls were remolding and sample size. Remolding of the API samples significantly reduced the hydraulic conductivity of these samples compared to the hydraulic conductivity measured in lab tests on undisturbed samples, which were of similar size. For the other tests, the degree and extent of remolding were less significant compared to in the API tests. For these tests, the scale of the measurement is believed to be the main factor differentiating the results. Hydraulic conductivity was found to increase as the sample volume increased, with the global measurement of the average hydraulic conductivity producing the highest value. The influence of variability in hydraulic conductivity on contaminant transport through cutoff walls was studied from a theoretical standpoint using the one-dimensional advection-diffusion equation. Charts were developed that can be used to estimate the flux through a cutoff wall based on knowledge of the average hydraulic conductivity of the wall and an estimate of the variability in hydraulic conductivity. Data sets of hydraulic conductivity from lab tests on soil-bentonite samples from four cutoff wall case histories were used to estimate typical values of variability. The contaminant transport analyses showed that the effect of variability may be significant when the hydraulic gradient opposes the concentration gradient, which is the case for a circumferential cutoff wall with an inward hydraulic gradient. The goal of a circumferential cutoff wall with an inward hydraulic gradient is to reduce the outward diffusive flux of contaminant by inducing an inward advective flux. The effect of variability in hydraulic conductivity is to reduce the effectiveness of this scheme.	en
dc.description.degree	Ph. D.	en
dc.identifier.other	etd-08132001-175622	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-08132001-175622/	en
dc.identifier.uri	http://hdl.handle.net/10919/28642	en
dc.publisher	Virginia Tech	en
dc.relation.haspart	01_Title_page.pdf	en
dc.relation.haspart	02_Abstract.pdf	en
dc.relation.haspart	03_Acknowledgements.pdf	en
dc.relation.haspart	04_Table_of_Contents.pdf	en
dc.relation.haspart	05_List_of_Figures.pdf	en
dc.relation.haspart	06_List_of_Tables.pdf	en
dc.relation.haspart	07_Chapter_1.pdf	en
dc.relation.haspart	08_Chapter_2.pdf	en
dc.relation.haspart	09_Chapter_3.pdf	en
dc.relation.haspart	10_Chapter_4.pdf	en
dc.relation.haspart	11_Chapter_5.pdf	en
dc.relation.haspart	12_Chapter_6.pdf	en
dc.relation.haspart	13_Chapter_7.pdf	en
dc.relation.haspart	14_Chapter_8.pdf	en
dc.relation.haspart	15_Bibliography.pdf	en
dc.relation.haspart	16_Appendix_A.pdf	en
dc.relation.haspart	17_Appendix_B.pdf	en
dc.relation.haspart	18_Appendix_C.pdf	en
dc.relation.haspart	19_Appendix_D.pdf	en
dc.relation.haspart	20_Appendix_E.pdf	en
dc.relation.haspart	21_Vita.pdf	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	hydraulic conductivity	en
dc.subject	contaminant transport	en
dc.subject	soil-bentonite cutoff walls	en
dc.subject	Subsurface Barrier Test Facility	en
dc.title	Soil-Bentonite Cutoff Walls: Hydraulic Conductivity and Contaminant Transport	en
dc.type	Dissertation	en
thesis.degree.discipline	Civil Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en

Soil-Bentonite Cutoff Walls: Hydraulic Conductivity and Contaminant Transport

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