Masters Theses

Abstract

"This investigation is concerned with a thermal rock fragmentation system employing heat to create subsurface thermal inclusions. The effectiveness of this system as applied to three different rock types is studied. The rock types are Dresser basalt, Charcoal gray granite, and Sioux quartzite. Also, the influence of temperature dependent material properties is investigated.

The actual three-dimensional problem of in situ rock fragmentation involves parallel rows of equally spaced holes drilled to a constant depth. A heat source at the bottom of each hole creates a thermal inclusion resulting in a stress field causing fracture.

Axisymmetric models of the fragmentation system were obtained by considering the typical planes of symmetry and nature of the actual three-dimensional problem. These models were used to study the fracture characteristics of the three hard rock types and to investigate the influence of temperature dependent material properties. The hard rocks were characterized as homogeneous, linearly elastic, isotropic brittle materials. The problem was formulated within the framework of the linear, uncoupled theory of elasticity. Analyses were performed using both ambient and temperature dependent thermal and thermoelastic material properties. The temperature and stress solutions were obtained using finite element approximations. Fracture predictions were based on the Griffith and the McClintock-Walsh modified Griffith fracture criteria.

Using temperature dependent thermal and thermoelastic material properties it was found that for any given fracture length there was a definite order in fracture completion time among the three rock types, using various combinations of temperature dependent and ambient material properties indicated that the heat transfer problem is governed by the quartz content of the particular rock type. The complete fracture problem was not governed by any one particular rock characteristic. Rather, the thermal rock fragmentation problem is a problem with complex interaction among the highly temperature dependent thermal and thermoelastic material properties.

For the temperature dependent material properties study, the dimensionless fracture time ratio, t*f; was found to be related to the dimensionless fracture length ratio, L*, according to the equation, t*f = (L*)3. This result suggests that small hole spacings should be used for an optimum fragmentation configuration.

Although fracture completion times, at a given hole spacing, were different for each rock type the fracture patterns were found to be functions of the problem geometry only. For a given hole spacing the fracture pattern characteristics were identical for each of the three rock types"-- Abstract, pp. ii-iii

Advisor(s)

Lehnhoff, T. F., 1939-

Committee Member(s)

Davis, Robert L.
Flanigan, V. J.

Department(s)

Mechanical and Aerospace Engineering

Degree Name

M.S. in Mechanical Engineering

Publisher

University of Missouri--Rolla

Publication Date

1974

Pagination

x, 79 pages

Note about bibliography

Includes bibliographical references (pages 75-78)

Rights

© 1974 James Dale Scheller, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 3065

Print OCLC #

6013590

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