ALBERT

Description: Deposits of the Quaternary Period in the Edmonton area consist of a lower and an upper till, in places separated stratigraphically by a sand, with lacustrine clays, silts, and sands overlying this sequence. Detailed field investigations suggest the possible existence of complexities that have not been fully integrated into an understanding of the Quaternary history of the Edmonton area.The lower till is a moderately stony sandy silt till. In places the upper portion has been reworked or sheared by the ice that deposited the upper till producing a thin zone of slightly lower strength. The upper till is a moderately stony sand till. Regionally it appears to be quite variable lithologically and contains inclusions of sand and gravel; therefore it is more reasonable to think in terms of an upper till unit composed of till and genetically related material. In some localities this upper unit is one single bed of till; in other places, however, it is a layered sequence of paratills, sands, and silts resulting probably from deposition in standing water. The lenses of sand and gravel associated with this unit have caused problems in tunnelling operations and other construction as they contain water, which can cause flooding when encountered during excavation. The paratills known from the examination of outcrops consist of sequences of interbedded till-like material and sands. These sequences are probably the result of turbidite deposition in an ice-marginal lake. These materials would resemble till when encountered in drilling operations.Problems associated with the Quaternary deposits of the Edmonton area include borehole interpretation to develop site stratigraphy, and the determination of geotechnical properties of the deposits and an assessment of their local variation over a specific site. Also of concern are the joints and fractures in the deposits, which affect slope stability and permeability of the soil mass.An understanding of the Quaternary history and the intrinsic variability of the deposits formed predominantly under the influence of ice is necessary for an understanding of potential sources of variability in geotechnical properties. Interaction between the geologist and the geotechnical engineer can only enhance their mutual comprehension of potential problems and their solutions.