Quaternary sediments in central Edmonton, Alberta, Canada: Stratigraphy, distribution and geotechnical implications

Abstract

Borehole logs were used to determine the stratigraphy and distribution of sedimentary units in central Edmonton. The Quaternary sediments overlying Upper Cretaceous sedimentary bedrock consist of preglacial fluvial sand and some gravel, glaciofluvial sand and gravel, a glacial diamicton complex composed of melt-out and flow diamictons, glaciofluvial sand and silt, glaciolacustrine silt and clay, and minor deposits of postglacial fluvial sand. The glacial sediments represent deposition during one major glaciation in the Late Wisconsinan. The diamicton complex has an intermediate stratigraphic position in the Quaternary sequence, is generally thick and laterally continuous, and serves as a satisfactory substrate for many deep foundations and tunnels, including part of the Light Rail Transit system. Seepage and block failures during tunnelling in the diamicton complex are mainly due to abundant saturated sand lenses in the upper part of the complex. The lateral continuity of the diamicton complex is interrupted by sand infilling a meltwater channel incised into bedrock. Tunnelling is difficult and costly within the sand, due to seepage and collapse. Mapping of the meltwater channel and associated outwash deposits allowed adjustment of the tunnel alignment to avoid intersection with the channel. Over the meltwater channel, deposits of outwash sediments and flow diamictons form a broad surface ridge.