Engineering characteristic of Georgian Bay Formation in Toronto

L.F. Cao, S.M. Peaker, S. Ahmad, A. Sirati

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

Session: Engineering Geology and Rock Mechanics

ABSTRACT: A series of laboratory and in-situ testing on the bedrock of Georgian Bay Formation has been carried out in relation to a rock tunnel project in Toronto, Ontario. This paper presents the laboratory and in-situ test results. The rock strengths obtained from various laboratory tests are compared and discussed. The deformation moduli of rock mass obtained from in-situ pressuremeter tests are compared with the moduli of the intact rock samples measured from laboratory unconfined and triaxial compression tests. It is found that the deformation moduli of shaly rock mass measured from in-situ tests are generally higher than those measured on the rock samples in laboratory. The use of modulus obtained from unconfined compression testing on the intact shaly rock sample will lead to a conservative approach in geotechnical design for the shaly rock. RÉSUMÉ A effectué une série de tests sur le substratum rocheux de la baie Georgienne Formation in situ et de laboratoire en ce qui concerne un projet de tunnel de rock à Toronto, en Ontario. Cet article présente les résultats des tests en laboratoire et in situ. Les points forts de roche provenant de différents tests de laboratoire sont comparés et discutés. Les modules de déformation de roche masse provenant d'essais pressiométriques in situ sont comparés avec les modules des échantillons de roche intacte mesurées de laboratoire non confiné et triaxiales tests de compression. Il est constaté que les modules de déformation des roches schisteuses masse mesurée à partir d'essais in-situ sont généralement plus élevées que celles mesurées sur les échantillons de roche en laboratoire. L'utilisation du module obtenu à partir d'essais compression non confinés sur l'échantillon de roche schisteux intacte conduira à une approche prudente dans la conception géotechnique pour le rocher schisteux. 1 INTRODUCTION The bedrock underlying the Greater Toronto area consists of the three shale-dominated units of the Ordovician age: the Blue Mountain (Whitby), Georgian Bay and Queenston Formations. The highest member, the Queenston Formation, is generally found west of Toronto, while the Georgian Bay Formation underlies most of Metro Toronto, with the lowest member, Blue Mountain (Whitby) Formation east of Toronto. The Georgian Bay Formation consists of massive shale interbedded with limestone and siltstone/sandstone with widely spaced jointing and sub-horizontal bedding planes. A series of laboratory and in-situ testing on the bedrock of Georgian Bay Formation has been carried out in relation with a rock tunnel project in Toronto. This paper presents the laboratory and in-situ test results. The rock strengths obtained from point load test, unconfined compression test and triaxial compression tests are compared and discussed. The use of the empirical relationship between unconfined compressive strength and point load index is also discussed. The rock mass moduli obtained from in-situ pressuremeter tests are compared with the moduli of intact rock samples measured in laboratory unconfined compression tests and triaxial compression tests. The difference between rock mass and rock sample moduli is discussed. The free swelling test results are present and compared with published data. 2 SITE CONDITION AND REGIONAL GEOLOGY The site is situated at Lakeshore Boulevard East, approximately 200 m west of Coxwell Avenue, in the City of Toronto, Canada. The lands on both sides of Lakeshore Boulevard at this site include facilities associated with the Ashbridges Bay Water Treatment Plant, as well as parkland. The existing site grade lies between Elev. 76.8 m to 79.4 m, which is approximately 1.8 m to 4.4 m above Lake Ontario level. Lake Ontario lies some 50 m to the south of this site. Based on Sharpe (1980), the Quaternary deposits of the Toronto region consist predominantly of glacial till, glaciolacustrine and glaciofluvial sand, silt, and clay deposits and beach sands and gravels. These deposits were laid down by glaciers and associated glacial rivers and lakes. Recent deposits of alluvium are found in river and stream valleys and their flood plains. The Quarternary soil deposits overlie the Ordovician age bedrock of the Georgian Bay Formation which consists predominantly of shale with interbeds of limestone and siltstone. This bedrock formation has a regional dip to the southeast of about 5 m/km. 3 FIELD INVESTIGATION AND LABORATORY TEST PROGRAMS Field investigation consisted of borehole drilling and rock coring at periodic intervals along the proposed tunnel

RÉSUMÉ: eering characteristic of Georgian Bay Formation in Toronto L.F. Cao, S.M. Peaker, S. Ahmad & A. Sirati

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Cite this article:
L.F. Cao; S.M. Peaker; S. Ahmad; A. Sirati (2014) Engineering characteristic of Georgian Bay Formation in Toronto in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper110,author = L.F. Cao; S.M. Peaker; S. Ahmad; A. Sirati,title = Engineering characteristic of Georgian Bay Formation in Toronto,year = 2014}