Degree Type

Dissertation

Date of Award

1981

Degree Name

Doctor of Philosophy

Department

Civil, Construction, and Environmental Engineering

Abstract

The 600 km Transgabon Railroad is being built through mountainous West Equatorial African rain forest in the Republic of Gabon. Here, plate tectonic investigations have identified the Precambrian metamorphic system as identical to a gradational metamorphic series in eastern Brazil. Rocks were variously reported as sericitic schists, graphitic quartz, and phyllites;Samples of excavated schists were taken during construction from the railroad right-of-way of the nearly vertical multicolored beds, being used in embankments as high as 35 m. From one site, composite samples weighing 667 N each were taken of individual colored layers, red, yellow, white, and black, at a depth of 30 m. The red layer was also sampled at a depth of 8 m, and a representative mixed sample was taken from the adjacent fill area. At a second site, 50 km eastward, a grey-green micaceous schist, more highly metamorphosed, was at the 35 m depth;Following arrival at Iowa State University, samples were examined by X-ray diffraction and electron microscopy, containing quartz, mica, and possibly kaolinite, halloysite, and cholorite minerals. Elemental analyses detected the presence of aluminum, silica, iron, and potassium in all samples, with manganese present only in the micaceous sample. Standard engineering tests placed all samples in the ASSHTO A-4 classification, close to the boundary of A-5, being non-plastic or with low plasticity indexes, and with liquid limits from 30-38;Specimens prepared near in situ compacted unit weight of 16kN/M('3) and moisture content of 18%, were subjected to the Iowa K-Test. This test quickly and accurately assesses strength parameters of soil materials. Continuous monitoring during a test enabled the discrete determination of ratios of minor to major principal stresses, strains in minor and major principal stress directions, strain ratios, and volumetric relationships. Angle of internal friction varied with unit weight and moisture content from about 26(DEGREES)-40(DEGREES); cohesion ranged from 11.5-73.4 kPa. The lower friction angles were generally exhibited by the white and black schists;Following a critique and historical review of achievements in soil mechanics, a model was postulated and investigated based on novel precepts from reported work in mathematics, plasticity theory, laboratory studies, and field observations. An orthogonal system of curves defined by cycloids and catenaries representing major and minor principal stress directions for a semi-infinite earth mass was presented, and its adaptation shown for analysis of high compacted embankments. Based on results of the Iowa K-Test and the mathematical model, earth pressure and settlement predictions were made, and stability calculations along a cycloidal rupture surface were shown. Procedures were seen to be compatible with simplified hand calculations or computerized finite element techniques, and produced realistic values.

DOI

https://doi.org/10.31274/rtd-180813-6042

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Darwin Eugene Fox

Language

en

Proquest ID

AAI8122513

File Format

application/pdf

File Size

231 pages

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