The performance of a 235 m deep circular shaft wit~ a finished diameter of 4.3 m, excavated by conventional shaft construction techniques in clay shale, was monitored by measuring the rock mass displacement field, the rock stress changes which occurred during the shaft advance, and the stress build up in the cast-in-place concrete liner. The project, the local geology and the instrumentation program is described. The field observations are discussed with particular emphasis on their interpretation to determine the in situ stress field.


Ein 235 m tiefer, kreisförmiger Schacht mit einem Durchmesser von 4,3 m wurde mit konventioneller Bauweise in weichem Tonschiefer erstellt. Das Verhalten des Gesteines und des schachtausbaues wurde durch Messungen der Felsverschiebungen mit Mehrfach-Messankern, der Felsspannungsanderungen wahrend des Schachtvortriebes und der Dehnungen im Betonring beobachtet. Das Projekt, die lokale Geologie sowie die Messeinrichtungen sind beschrieben und die Auswertung der Messresultate ist erlautert. Spezielles Gewicht wurde dabei vor allem auf die Bestimmung des urspruenglichen Spannungsfeldes gelegt.


La performance d''un puits circulaire d''une profondeur de 235 m et d''un diamètre de 4,3 m, creuse suivant les techniques conventionnelles de construction de puits enschiste argileux, a ete etudiee par le mesurage du camps de deplacement de la masse rocheuse, les changements de contrainte du roc pendant la construction du puits, et la progression des contraintes sur le revêtement en beton. Le project, la geologie locale et le programme d''instrumentation sont decrits. Les observations sur le terrain sont interpretees pour determiner le champs de contraintes en place.


The design of underground openings in the soft and weak bedrock underlying large areas of the prairie provinces of western Canada has been primarily empirical and the dimensioning of the opening supports is often based on rules developed for comparable rock types in other parts of the world. Their applicability to the local conditions has never been proven and little quantitative data has been collected to describe accurately the rock properties and to evaluate the performance of existing openings. This inhibits more rational design and construction procedures.

The sinking of a vertical shaft at Kipp near Lethbridge in southern Alberta provided an excellent opportunity to collect shaft performance data for the rational design of future adits to this coal mine. For this purpose, it was necessary to determine the in situ stress field, to observe the deformations near the opening, to determine the rock mass deformation properties, to determine the strength properties by laboratory tests, and to monitor the load development on the support to verify lining design.

In this paper, we present a brief overview of the project with a qualitative description of the performance of the shaft. This is followed by a detailed interpretation of observations made to evaluate the existing field stresses at the site.


The prospective mine is located approximately ten kilometers north-west of Lethbridge, on the southern edge of the Alberta Plains (Figure 1). The mine is being developed by Petro Canada Exploration Inc. to exploit part of the bituminous coal of the extensive Lethbridge Coal Field. Several coal mines have operated in this area since the early 1880''s but most mines have been inactive over the last two decades. Recent increases in world coal prices make underground mining in this area viable and one additional major project is presently under development nearby.

The shaft with a finished diameter of 4.32 m was sunk by Thyssen Mining Construction of Canada Ltd. between February and November, 1980 using conventional shaft sinking methods. The bedrock was excavated by drilling and blasting 1.8 to 2.4 meter deep, half floor benches. The shaft was lined with a cast-in-place concrete lining with variable thickness depending on the overbreak. The specified thickness was

(Figure in full paper)

300 mm for the first 70 m, 400 mm to a depth of 130 m and 500 mm, 600 mm, 700 mm to depths of 175 m, 220 m and 235 m, respectively. The lining construction generally followed one to two shaft diameters behind the shaft bottom. Ready-mix concrete with a specified strength of 35 MPa was poured behind segmental slipforms. Shaft sinking through the bedrock progressed at a rate of about 3 to 4 meters per day. Except during 4-day work stoppages, the rock was seldom unsupported for more than 16 to 20 hours.

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