Browsing by Author "Nelson, John D., advisor"

Now showing 1 - 3 of 3

Open Access
Comparison of direct shear and triaxial tests for measurement of shear strength of sand
(Colorado State University. Libraries, 1991) Rahman, Jamshed, author; Nelson, John D., advisor; Siller, Thomas J., committee member; Mielke, Paul W., committee member
To ascertain the shear strength parameters of soils for engineering purposes is fundamental to soil mechanics and basic for designing earth-bearing and earth-retaining structures. Direct shear and triaxial tests are the most popular laboratory methods to determine these parameters. The direct shear test is used widely because it is simple and quick. The test has several disadvantages, however. The non-uniform stress-strain behavior, the rotation of principal planes during the test, and the imposition of the failure plane are chief among them. The triaxial test was designed as a possible alternative that eliminates some of these disadvantages. Direct shear test results are always comparable to those of the triaxial test; the difference usually is negligible from a practical point of view. Researchers have tried to unfold the intricacies involved in the direct shear test especially the complicated stress-strain behavior that a soil experiences during this test. Data, however, are lacking that determine the difference and establish a correlation between the results of the two tests. This study compares the two tests for measurement of shear strength parameters of sand. Triaxial and direct shear tests were performed on silica sand under the same density and normal stress conditions. Five sets of triaxial tests and 20 direct shear tests each were performed using four different makes of direct shear machines. The results of the direct shear tests were compared with those of the triaxial tests considering the latter as benchmarks. The possible effect of the structural features of the direct shear equipment on results was briefly studied. The results showed that the shear strengths from direct shear tests are higher than those from the triaxial tests. All four direct shear machines gave cohesion values different from each other and higher than the benchmark value. The Soiltest and Wykeham Farrance machines gave almost the same friction angle that was higher than the benchmark value by 4 degrees. The friction angle value from the ELE machine was higher by 2.7 degrees while those from Clockhouse machine were lower by 4.5 degrees as compared to the benchmark value.
Open Access
Design principles for foundations on expansive soils
(Colorado State University. Libraries, 2007) Chao, Kuo-Chieh, author; Nelson, John D., advisor; Overton, Daniel, advisor
The design of foundations for sites having expansive soils is one of the greatest challenges facing geotechnical engineers today. Intolerable heave of foundations on expansive soils often affects critical safety aspects of structures. Therefore, it is imperative that design of foundations for expansive soils includes analyses of expected heave and consequences of foundation movement over the design life of the structure.
Open Access
Solute transport by a volatile solvent
(Colorado State University. Libraries, 1987) Brown, Glenn O. (Glenn Owen), author; McWhorter, David B., advisor; Nelson, John D., advisor; Warner, James W., committee member; Durnford, Deanna S., committee member
Reclamation and impact analysis of retorted oil shale piles will require prediction of water and solute transport rates over the entire solution content range, down to and including the relatively dry region. In such dry materials, vapor transport of water affects the transport of solutes. Experimental measurements of transport coefficients in relatively dry oil shale have brought forward longstanding questions concerning the mechanics of combined liquid-vapor flow. Principal among these is the apparent inability of porous media to transport solutes at low solution contents. In an attempt to ensure proper interpretation of experimental data, a new theory of solute transport by combined liquid-vapor flow has been developed, and new analytical solutions for transient flow have been obtained. The solutions show that the relative magnitudes of the separate transport coefficients produce many of the flow features seen in experimental data, and significant liquid transport can occur in regions without apparent solute transport. This development is new and represents an addition to the understanding of solute transport. These methods and results can be applied to other problems in multiple phase transport, such as hazardous waste disposal, mine reclamation, and soil leaching.