A laboratory testing program was conducted on cement-treated soil mixtures fabricated to represent materials produced by the wet method of deep mixing. The testing program focused on investigating the influences that variations in laboratory testing conditions and in the mix design have on measured property values. A base soil was fabricated from commercially available soil components to produce a very soft lean clay that is relatively easy to mix and can be replicated for future research. The mix designs included a range of water-to-cement ratios of the slurries and a range of cement factors to produce a range of mixture consistencies and a range of unconfined compressive strengths after curing. Unconfined compressive strength (UCS) tests and unconsolidated-undrained (UU) triaxial compression tests were conducted. Secant modulus of elasticity were determined from bottom platen displacements, deformations between bottom platen and cross bar, and from LVDT's placed directly on the cement-treated soil specimens. Five end-face treatment methods were used for the specimens: sawing-and-hand-trimming, machine grinding, sulfur capping, neoprene pads, and gypsum capping. Key findings of this research include the following: (1) The end-face treatment method does not have a significant effect on the unconfined compressive strength and secant modulus; (2) a relationship of UCS with curing time, total-water-to-cement ratio, and dry density of the mixture; (3) the secant modulus determined by bottom platen displacements is significantly affected by slack and deformations in the load frame; (4) the secant modulus determined by local strain measurements was about 630 time the UCS; (5) typical values of Poisson's ratio range from about 0.05 to 0.25 for stress levels equal to half the UCS and about 0.15 to 0.35 at the UCS; (6) Confinement increased the strength at high strains from less than 20% the UCS to about 60% the UCS. In addition to testing the cured mixtures, the consistency of the mixtures were measured right after mixing using a laboratory miniature vane. A combination of the UCS relationship along with the mixture consistency may provide useful information for deep mixing contractors. / MS / Deep mixing is a ground improvement technique that mixes cement with in-situ soil to improve the quality of the soil for supporting embankments, buildings, and other facilities. Deep mixing is also used for earth retention and to form subsurface seepage barriers. When the cement is added in dry powder form, the process is called the dry method of deep mixing, and when the cement is added in the form of cement-water slurry, the process is called the wet method of deep mixing. When using the wet method, both the water-to-cement ratio of the slurry and the amount of slurry added to the soil have important effects on the strength of the cured mixture. Laboratory mixtures are often tested in advance of field mixing to estimate the proportions of cement, water, and soil necessary to produce the desired outcomes. The laboratory test conditions influence the test results, and a wide variety of test conditions are used in practice. This research investigated different testing conditions and different mix designs to demonstrate their impacts on laboratory test results.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/88437 |
| Date | 19 September 2017 |
| Creators | Nevarez Garibaldi, Roberto |
| Contributors | Civil and Environmental Engineering, Filz, George M., Castellanos, Bernardo Antonio, Mitchell, James K. |
| 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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