A rock excavatability assessment for a basement excavation

James Dann, Vasantha Wijeyakulasuriya

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Engineering Geology and Rock Mechanics

ABSTRACT: xcavatability assessment for a basement excavation James Dann, B.Eng. (Hons), ACSM & Vasantha Wijeyakulasuriya, P.Eng. Coffey Geotechnics Inc., Toronto, Ontario, Canada ABSTRACT A series of ground investigations were completed within a study area to the west of Toronto, Ontario for a basement excavation at an existing commercial property. Compressive Strength and Point Load Index testing results are assessed in relation to rock mass discontinuity properties, comprising RQD and fracture indices, to develop a graphical and scaled Rock Excavatability ProfileUsing the body of knowledge generated by the investigation programs, strength and discontinuity characteristics of each rock type are characterized using statistical analysis. The results are compared to previous studies of similar geology undertaken by Gunsallus & Kulhawy, and also used as input to rock strength classification. A probabilistic approach, based on the RQD distributions, predicts the mean discontinuity spacings. This is input along with Is50 into the Pettifer & Fookes methodology to aid the assessment of the excavatability requirements. RESUME Une série de sol enquêtes ont été terminées au sein d'une zone d'étude à l'ouest de Toronto, en Ontario, pour un sous-évalués par rapport à discontinuité de roche de la masse proprieties, RQD et FI inclusif. En utilisant l'ensemble détaillé des connaissances développés concis de programmes d'enquête, caractéristiques de résistance de chacun des types 1 INTRODUCTION There is a significant assumption made by the majority of development-oriented companies in the Greater Toronto Area (herein GTA) in that the geology in the GTA is ripe for unhindered construction. However, past experiences have shown that excavations into shallow bedrock tend to present a number of issues during construction stages. As further development of the already well-established centers of the GTA development opportunities become less. With this come the uncertainties of ground conditions in virgin, or Together with this, an increase in investment towards transportation budgets and a foreseeable plan to transfer particularly road transport networks to underground networks, an sound understanding of bedrock behavior will become indispensable for rational design and to overcome major construction obstacles and issues. Significant advances in the understanding of engineering behaviour of the Georgian Bay Formation has been undertaken, especially at the Western University in London, Ontario under the leadership of Professor K.Y. Lo. 2 SITE DESCRIPTION The study area comprises a commercially operated property of approximately 250,000 m2 (25 hectares) plan area located to the west of Toronto in Ontario. The area is relatively flat-lying, and at a Geodetic elevation in the order of 155 m at its centre. There are locally variable ground elevations of between 3 m and 4 m across the site where basement access routes, pavement structure drainage falls and multiple construction phases to the existing property have been accommodated. 3 GEOLOGY The geological sequence underlying the study area is, in geological time, a measure of extremes, with Palaeozoic (Upper Ordovician) sedimentary deposits directly overlain by Quaternary (Pleistocene) superficial deposits. Some 450 million years ago, what is now southern Ontario was located along the northern coastline of the Iapetus Ocean, and a river network flowed southwards over the GTA via deltaic plains into the inland sea. Between 400 million and 350 million years ago, during the Acadian Orogeny, North America formed part of Pangea and southern Ontario was in an increasingly deeper, marine setting where abundant life was supported by the waters. Clay-rich sediments and lime-rich muds were deposited and eventually formed sequences of shales, siltstones and limestones up to approximately 250 m thick. These deposits, classified as the Georgian Bay Formation, are generally dipping towards the southwest at angles of generally between 5° and 10°. The seas eventually evaporated, and by 150 million years ago Pangea was breaking up. The resulting tectonic lead to the formation of the St. Lawrence valley, and ultimately the Atlantic Ocean. The continent of North America was finally formed. Approximately 3 million years ago, and for some half a million years, waters carved channels into the bedrock, ultimately creating the St. Lawrence River System. From 2.5 million years ago, and over the subsequent hundreds of thousands of years, the climate had sufficiently reduced in temperature to create Ages, exposing the GTA to a series of glacial, interglacial and periglacial periods. During this Ice Age, the Laurentide Ice Sheet would cover most of northern Canada and extend in part into what is now the United States. progressive movement

RÉSUMÉ: ck excavatability assessment for a basement excavation James Dann, B.Eng. (Hons), ACSM & Vasantha Wijeyakulasuriya, P.Eng. Coffey Geotechnics Inc., Toronto, Ontario, Canada ABSTRACT A series of ground investigations were completed within a study area to the west of Toronto, Ontario for a basement excavation at an existing commercial property. Compressive Strength and Point Load Index testing results are assessed in relation to rock mass discontinuity properties, comprising RQD and fracture indices, to develop a graphical and scaled

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Cite this article:
James Dann; Vasantha Wijeyakulasuriya (2014) A rock excavatability assessment for a basement excavation in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper381,author = James Dann; Vasantha Wijeyakulasuriya,title = A rock excavatability assessment for a basement excavation ,year = 2014}