The Role of Horizontal Stress in the Formation of Valley Stress Relief Features in Flat-Lying Sedimentary Rocks
Cole, Todd M.
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Permalink
https://hdl.handle.net/2142/83383
Description
Title
The Role of Horizontal Stress in the Formation of Valley Stress Relief Features in Flat-Lying Sedimentary Rocks
Author(s)
Cole, Todd M.
Issue Date
2008
Doctoral Committee Chair(s)
Alberto S. Nieto
Department of Study
Civil Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Language
eng
Abstract
The objective of this thesis is to demonstrate, largely by numerical modeling, the general mechanisms by which the features mentioned above are formed. First, evidence supporting the existence of a regional horizontal stress, well in excess of gravitational considerations, will is presented. This evidence will include a database of in situ measurements so that an estimate of the magnitude of this stress can be obtained for the analysis to follow. Second, a detailed description of valley features obtained from the literature is put forth. Also, field observations of these features by the writer, conducted in the Pittsburgh, Pennsylvania area are described. Third, a review of previous analytical studies of stresses and stress relief features around valleys is discussed. Fourth, a detailed numerical analysis performed by the writer is presented. The initial step in this analysis is a geometric study of elastic models. The purpose of this analysis stage was to examine stress distributions around stream valleys of various shapes and sizes using isotropic, linear elastic models without the inclusion of material plasticity. Stress conditions include gravitational loading as well as a regional horizontal stress. The results of this analysis were compared to previous studies. Next, a layered geologic sequence including plastic slip along bedding is modeled using the results of this analysis. Parameters examined as part of this stage of the study include bedding thickness as well as bedding plane strength. Rock material between bedding surfaces remains elastic. Based upon the results of this stage, a plastic material model was implemented for the rock material between bedding surfaces. Material plasticity included both tensile yielding and shear (compressive) yielding. The purpose of this portion of research was to model the formation and geometry of valley stress relief features observed in the field. Based upon this analysis, general mechanisms for the formation of valley stress relief features are proposed. These mechanisms include the formation and geometry of extensional features observed in valley walls as well as compressional features observed in valley floors.
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