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To address the problem of bench mark stability on levelling operations, the deep bench mark designed by the National Research Council was introduced. It consisted in an inner galvanized steel rod pushed to refusal, protected by an outer galvanized steel pipe. The space between the two was filled with heavy oil. Freeze and thaw would affect only the outer pipe, leaving the inner rod intact. Installation was done by hydraulic drill rig mounted on a truck. During the summer of 1967, a total of 67 of these were installed at eight-mile intervals (13 km) between Toronto and Quebec City with an average depth of 40 feet (12 m), with the maximum depth being 180 feet (55 m) near Sorel.
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