The purpose of this thesis is to show, using computer simulation of flow systems in a variety of hypothetical slopes, how different geological environments affect the groundwater flow regime, which in turn is fundamental to the stability of a slope. Galerkin's method is used to derive a finite element program to model two dimensional, saturated, steady state flow through anisotropic and heterogeneous rigid porous media. An understanding of the regional geology is required in order to understand the regional flow system. The following points are illustrated. a. In anisotropic media, the most adverse groundwater condition for slope stability occurs when the major axis of conductivity lies down the dip of the slope. b. Depending on their characteristics, faults, contacts and dykes can be either detrimental or favourable in their effect on the flow system. Careful field investigation is required to establish that effect. c. Deep weathering commonly causes a confining zone of low conductivity, a situation very detrimental to stability. d. Stress relief fractures on valley walls can adversely influence the effect of groundwater on stability. e. A regional aquifer can cause high pore pressure development beneath a valley. f. Fluctuations in the regional groundwater system can cause instability in Pleistocene terraces. g. The presence of an underlying less conductive zone or unit can have an adverse effect on the flow system. Conductivity contrasts of less than two orders of magnitude can cause pore pressure development critical to stability. Three other points are demonstrated which have direct application to slope stability analysis and control. 1. The pressure head distribution on rock wedges can be nonlinear rather than the commonly assumed linear distribution. 2. The introduction of a reservoir at the toe of a slope can influence the groundwater regime well above the reservoir surface; even a low reservoir can cause, the change required to cause instability. 3. Piezometric measurements and drainage systems must penetrate through any less conductive unit that might be acting as a slide plane. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Thesis (M.S.)--University of Nevada, Reno, 2008. / "December, 2008." Includes bibliographical references (leaves 85-89). Online version available on the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

A comprehensive methodology of hydraulic testing in fractured rocks is presented. The methodology utilizes geological and geophysical information as background. It consists of conventional single-hole packer tests in conjection with a newly developed cross-hole packer test. The cross-hole method involves injecting fluid into a packed-off interval in one borehole and monitoring hydraulic head variations in packed-off intervals in neighboring boreholes. Borehole orientation is unrelated to the principal hydraulic conductivity directions which, therefore, need not be known a priori. The method yields complete information about the directional nature of hydraulic conductivity in three dimensions on a scale comparable to the distance between the test boreholes. In addition to providing all six components of the hydraulic conductivity tensor, the cross-hole method also yields the specific storage of the fractured rock mass. While the theory behind this method treats the rock as a homogeneous, anisotropic, porous medium, the test provides detailed information about the degree to which such assumptions may actually be vaild in the field. The method may also be useful as a tool for detecting, in the vicinity of the test area, major fractures or faults that have not been intercepted by boreholes. Preliminary results from a granitic site near Oracle in southern Arizona are presented together with details of the instrumentation designed and constructed specifically for that site.

A groundwater flow model was constructed for the Rincon Valley area and Mesilla Basin. The system is dominated by the complex interaction of the Rio Grande, canals, laterals, and drains with groundwater pumping. The primary purpose of the model was to aid the New Mexico -Texas Water Commission in assessing options for water resources development in the Lower Rio Grand Basin from Caballo Reservoir in New Mexico to El Paso, Texas. One such assessment was to evaluate the effect of secondary irrigation releases from Caballo Reservoir on the water budget. In addition, the model will eventually be linked to a surface water model (BESTSM) being utilized by the New Mexico -Texas Water Commission to evaluate water supply alternatives for El Paso, Texas. Stress periods were specified on a seasonal basis, a primary irrigation season from March through October and a secondary irrigation season from November through February. Analysis of model output indicates that groundwater pumping decreases Rio Grande flows, secondary irrigation season releases do not alter the water budget significantly, and that recharge and discharge from aquifer storage are strongly related to the season.

Intact and fractured rock samples were studied in the laboratory in order to understand more fully the mechanism of closure of fractures subjected to high confining stresses and the resultant effect on specimen permeability. Confining stresses applied to the specimens ranged from 3.0 to 20.0 MPa, and the closure of fractures was observed by monitoring the change in the hydraulic conductivity of the specimens. Test results suggest that some resealing may occur due to crushing and realignment of mineral grains along a fracture surface. The closure of fractures is dependent upon the strength of the rock mass, the physical nature of the fracture, and the fluid pressure present in the fracture. Fracture closure is highly time dependent, and a number of nonlinear pressure flow relationships have been identified. These deviations are thought to represent two fundamentally different processes, the most important of which are turbulence in the flow and fracture expansion.

Project Completion Report OWRT Project A- 076 -ARIZ The work upon which this publication is based was supported in part by the United States Department of the Interior as authorized under the Water Research Act of 1964, as amended. / Constant head borehole infiltration tests are widely used for the in situ evaluation of saturated hydraulic conductivities of unsaturated soils above the water table. The formulae employed in analyzing the results of such tests disregard the fact that some of the infiltrating water may flow under unsaturated conditions. Instead, these formulae are based on various approximations of the classical free surface theory which treats the flow region as if it were fully saturated and enclosed within a distinct envelope, the so- called "free surface." A finite element model capable of solving free surface problems is used to examine the mathematical accuracy of the borehole infiltration formulae. The results show that in the hypothetical case where unsaturated flow does not exist, the approximate formulae are reasonably accurate within a practical range of borehole conditions. To see what happens under conditions closer to those actually encountered in the field, the effect of unsaturated flow on borehole infiltration is investigated by means of two different numerical models: A mixed explicit - implicit finite element model, and a mixed explicit -implicit integrated finite difference model. Both of these models give nearly identical results; however, the integrated finite difference model is considerably faster than the finite element model. The relatively low computational efficiency of the finite element scheme is attributed to the large humber of operations required in order to reevaluate the conductivity (stiffness) matrix at each iteration in this highly nonlinear saturated -unsaturated flow problem. The saturated -unsaturated analysis demonstrates that the classical free surface approach provides a distorted picture of the flow pattern in the soil. Contrary to what one would expect on the basis of this theory, only a finite region of the soil in the immediate vicinity of the borehole is saturated, whereas a significant percentage of the flow takes place under unsaturated conditions. As a consequence of disregarding unsaturated flow, the available formulae may underestimate the saturated hydraulic conductivity of fine grained soils by a factor of two, three, or more. Our saturated -unsaturated analysis leads to an improved design of borehole infiltration tests and a more accurate method for interpreting the results of such tests. The analysis also shows how one can predict the steady state rate of infiltration as well as the saturated hydraulic conductivity from data collected during the early transient period of the test.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy