Deformation around a mine shaft in salt AND Rock mechanics at international minerals &amp; chemical corporation (Canada) limited
Authors: Barron K , Toews N A , Zahary G 
Published: July 2017

The recovery of potash from the vast deposits in Saskatchewan has presented conditions unique in Canadian mining history. Recognizing this, The International Minerals and Chemical Corporation (Canada) Ltd. proposed that research be initiated, in both the potash
and the overlying salt, to obtain information pertinent to mine design, stability, safety and economy. This resulted in a cooperative research program involving the company, Dr. S. Serata, consultant, and the Mines Branch, Dept. of Mines and Technical Surveys, Ottawa. Initial studies were made in
the unlined portion of the shaft in the salt above the potash beds. Measurements were made of displacements, relative to the shaft axis, of points on the surface of the shaft and within the solid surrounding the shaft. A diametral extensometer and an extensometer to measure the longitudinal
deformation of boreholes around the shaft were used. The objective of these measurements was to obtain data on the creep (or deformation as a function of time) of salt around a simple opening and to correlate this data with theoretical ideas on the behaviour of the material. A successful correlation
would contribute considerably to a better understanding of material behaviour and of loading conditions and thus aid the solution of the problems in the design of openings in salt. A further objective was to investigate whether such data might be used as an indication of shaft stability; this is
particularly important in relation to both safety and maintenance. This paper presents the measurements obtained and the approach taken to their interpretation by the Mines Branch. It is shown that the radial displacement, U r , for a point in the solid at a radius r from the shaft axis may be
expressed in the form: Ur = .-PB(a2 /r) logio(1 + bt) where B and b are constants, a is the shaft radius,, t is the time and p is the pressure. In particular, the results obtained for points at depths of 4, 7 and 10 .feet in the walls of the 18-foot diameter shaft are represented by: U r = 7x10 -31a
2/A log io +(t/2.. 70)( where Ur , a and r are in inches and t is the time in days. Surface points do not conform to the 1/r proportionality, but the times function is the same. The form of the above results suggests that this type of measurement may be used to determine the shear creep function of
the material in situ. This is important in correlating laboratory and field studies. The divergence OE the surface data from the general relationship at depth in the shaft wall indicates the possibility that a -change in material properties has occurred between the surface and 4-.foot depth. There
is insufficient data available to pronounce on shaft stability in this case other than to say that there is no evidence of a loss of stability owing to excessive deformation .during the time of measurement. It appears however, that a method might be developed., based on measurements of this type,
for monitoring shalt stability with respect to the effects of excessive deformation. On the basis of certain assumptions, a possible method of estimating stress from deformation measurements is proposed. The assumptions are in part, substantiated by the data available. Additional measurements are
suggested that are needed to confirm the above results. With further work it should be possible to provide analytical data to assist in the judgement of shaft stability and in the design of excavations in salt. AND Considerable emphasis has been placed on rock mechanics at this highly
mechanized potash mine to insure that safe mining conditions prevail. Underground conditions are ideal for the study of ground movement. To insure maximum safety, tests to destruction in the mine are not permitted. Evaluations of ground stability are based on laboratory work and underground
measurements. Ground movement is measured on bolts anchored in the roof, floor, and walls of the openings with specially designed instruments. The pattern of vertical and horizontal closure of an opening with time is shown, and strain patterns in the roof and walls are
calculated.