Large-diameter piles socketed into bedrock support the abutments and piers of several large railway and highway bridges across the approach cuts of a tunnel near Welland, Ontario. The design of these piles was governed by the following considerations: (a) the large vertical and lateral loads involved, (b) the low shear strengths of the overburden and the low design factor of safety of the slopes of the approach cuts, (c) the effect of the construction of piers and abutments on the stability of the slopes, (d) the development of negative skin friction on the piles at the abutments and some piers, (e) chemical and micro-biological attack on steel, and sulfate attack on concrete by the constituents of the groundwater, (f) the low shear strength of the gypsum in the bedrock and its tendency to creep, and (g) the possibility that gypsum might be leached out of the bedrock as the groundwater regime changes.The piles used varied from 24 in. (61 cm) and 30 in. (76 cm) in diameter for the highway bridges to 48 in. (122 cm) in diameter for the railway bridges. Where settlement of the overburden was expected to occur, only groups of vertical piles were used and these were coated with coal tar to limit the maximum value of negative skin friction. As these piles also were required to resist large lateral loads, the steel casings used in construction were designed to contribute to the structural strength of the piles and were protected from chemical and microbiological attack by a coat of an epoxy resin beneath the coal tar. The design took into account the lateral resistance of the overburden and, where it was insufficient, that of the bedrock. This type of pile was installed in an overexcavated hole and the casing was concreted several feet into bedrock; where bedrock conditions warranted it, the vertical load on the pile was transferred to the rock by the wedge action of a tapered socket.Where negative skin friction was not a problem, combinations of raked and vertical piles were used. The contribution of the casing to the strength of the piles was ignored and the casings were not protected. Tapered sockets were used on some of these piles where rock conditions were unsatisfactory.All concrete was sulfate-resistant, and for casings socketed into bedrock a method of installation was used that ensured intimate contact of concrete with the casings and the surrounding bedrock.