Tunnels under pavement shall not be permitted except by permission of the Water Commissioner and, if permitted, shall be adequately supported by timbering and backfilling under the direction of the Water Commissioner. Where gas pipe is to be tunneled or bored under a highway, except sidewalks, such pipe shall be driven through or bored in a casing of sufficient strength, which casing shall be left in place with the ends closed around the pipe. (Ord. 157 § 440, 1961)