A hydrogeologic study of an unstable open-pit slope, Miami, Gila County, Arizona.

Persistent Link:
http://hdl.handle.net/10150/190998
Title:
A hydrogeologic study of an unstable open-pit slope, Miami, Gila County, Arizona.
Author:
Earl, Thomas Alexander,1941-
Issue Date:
1973
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
An unstable slope in an open-pit copper mine in Arizona was analyzed after a 250,000-ton slope failure had occurred. Data on all available time-dependent hydrogeologic factors were analyzed utilizing multiple regression techniques in order to build a mathematical model of the slide displacement. This allowed determination of those factors which were most influential in promoting instability. It was determined that a ground-water rise of approximately one foot, and rainfall in the week prior to the failure, were the most important factors contributing to this particular slide. This is believed to be due primarily to an increase in cleft-water, or hydrostatic, pressure, with seepage forces contributing a significant but relatively constant shear component. Because instability was observed to extend beyond the original slope failure, a dewatering analysis was undertaken. A steady-state finite element flow system model series was developed by progressively incorporating subsurface information, as well as water table location. The ground-water flow system within the granitic host rock was then simulated as a continuum, and a flow net derived. Analysis of this flow net, combined with known ground-water discharge into the open pit, comprised the basis to estimate the coefficient of permeability to be approximately 4 gallons/day/foot². This value was then utilized in a preliminary dewatering analysis incorporating standard aquifer equations to predict possible drawdowns. The computed drawdowns suggest that pumping rates on the order of 10 gallons/minute/well from a line of 12 wells spaced 50 feet apart would produce approximately 100 feet of drawdown after 1 year of pumping. Results of stability analyses for various ground-water levels indicated that when the water table is lowered by dewatering, a steeper slope could be maintained in the open pit. Such steepening could be as much as 1° when the water table is lowered one-half to one-quarter the height of the slope (135 feet), and approximately 4½° when the slope area is completely drained.
Type:
Dissertation-Reproduction (electronic); text
Keywords:
Hydrology.; Slopes (Soil mechanics); Landslides.; Strip mining -- Arizona -- Gila County.
Degree Name:
Ph. D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Harshbarger, John W.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleA hydrogeologic study of an unstable open-pit slope, Miami, Gila County, Arizona.en_US
dc.creatorEarl, Thomas Alexander,1941-en_US
dc.contributor.authorEarl, Thomas Alexander,1941-en_US
dc.date.issued1973en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractAn unstable slope in an open-pit copper mine in Arizona was analyzed after a 250,000-ton slope failure had occurred. Data on all available time-dependent hydrogeologic factors were analyzed utilizing multiple regression techniques in order to build a mathematical model of the slide displacement. This allowed determination of those factors which were most influential in promoting instability. It was determined that a ground-water rise of approximately one foot, and rainfall in the week prior to the failure, were the most important factors contributing to this particular slide. This is believed to be due primarily to an increase in cleft-water, or hydrostatic, pressure, with seepage forces contributing a significant but relatively constant shear component. Because instability was observed to extend beyond the original slope failure, a dewatering analysis was undertaken. A steady-state finite element flow system model series was developed by progressively incorporating subsurface information, as well as water table location. The ground-water flow system within the granitic host rock was then simulated as a continuum, and a flow net derived. Analysis of this flow net, combined with known ground-water discharge into the open pit, comprised the basis to estimate the coefficient of permeability to be approximately 4 gallons/day/foot². This value was then utilized in a preliminary dewatering analysis incorporating standard aquifer equations to predict possible drawdowns. The computed drawdowns suggest that pumping rates on the order of 10 gallons/minute/well from a line of 12 wells spaced 50 feet apart would produce approximately 100 feet of drawdown after 1 year of pumping. Results of stability analyses for various ground-water levels indicated that when the water table is lowered by dewatering, a steeper slope could be maintained in the open pit. Such steepening could be as much as 1° when the water table is lowered one-half to one-quarter the height of the slope (135 feet), and approximately 4½° when the slope area is completely drained.en_US
dc.description.notehydrology collectionen_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.typetexten_US
dc.subjectHydrology.en_US
dc.subjectSlopes (Soil mechanics)en_US
dc.subjectLandslides.en_US
dc.subjectStrip mining -- Arizona -- Gila County.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairHarshbarger, John W.en_US
dc.contributor.committeememberMayo, Evans B.en_US
dc.contributor.committeememberBull, William B.en_US
dc.contributor.committeememberCall, Richard D.en_US
dc.contributor.committeememberLacy, William C.en_US
dc.contributor.committeememberAbel, John F.en_US
dc.identifier.oclc213096693en_US
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