The physical properties of coal measures rocks and their bearing on the technique of roof bolting

Johnston, Archibald G (1957) The physical properties of coal measures rocks and their bearing on the technique of roof bolting. PhD thesis, University of Glasgow.

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The investigations here described can be sub-divided into four main sections, viz. (A) The Physical Properties of Coal Measures Rock, (B) Photo-elastic Investigations, (C) Underground Observations and (D) The Testing of Plaster Models. The contents of each section are outlined below. SECTION A: The various methods employed for the determination of the physical properties of rock are discussed. The use of electrical resistance strain gauges for the measurement of Young's Modulus and Poisson's Ratio of several rock types from the Scottish Coalfields is described. The factors which affect the ultimate strength of stratified rocks are discussed and an attempt is made to predict the total strain which will develop in rock under a given stress after a known time. The results obtained indicate the influence of "time-strain" in computing the stress distribution around an underground excavation. Micro-graphs of the specimens tested are included in an appendix. SECTION B: Details of the apparatus used and the models con-structed for the two-dimensional photo-elastic investigations of any roof bolting systems are given. The functions of roof bolts as a "suspension support" and in the formation of a "compound beam" are analysed. The use of bolting to form a "keystone" in arched shaped roadways is also investigated. The results show the value of bolts in minimising shear stresses at the interfaces of the beds. The Importance of pre-tensioning the bolts by equal amounts is also emphasised by the isochromatic diagrams. SECTION C: The behaviour of roof bolts installed in an advancing longwall roadway is described. The performance of three types of steel bolts - slot and wedge, expansion shell, wedge and sleeve - and several "wooden bolts" is discussed. Details of the apparatus used for the measurement of bolt tension and strata movements are given. An attempt to measure 'in situ' rock strain by electrical resistance strain gauges is described. The results show a relaxation of bolt tension a few days after installation. The several factors which Influence the behaviour of bolts installed in moving strata are discussed. Several illustrations shewing the improvements in roadway maintenance where roof bolting is used in conjunction with arched girders are given. SECTION D: To study the behaviour of bolts after the strata around the excavation have been loaded beyond the "elastic limit", plaster models of the underground roadways were made and tested to destruction in the laboratory. The models were loaded in a vertical compression testing machine. A photographic record of the tests and a detailed analysis of the results are given.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: G Hibbard
Keywords: Mining engineering
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-73574
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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