Note 80 — PART I SPECIFICATIONS FOR STREET ROADWAY PAVEMENTS (continued 2)

It is customary in many cities to require that the drainage course under the concrete shall have a depth of twelve or more inches. This deep-drainage is designed to prevent the heaving of the sidewalk by freezing. Experience seems to prove that this is not necessary, particularly if tile drains are provided to carry off the water from the drainage course, as specified. Comparatively dry material, even earth, does not heave with freezing; on the other hand, if the material and the trench in which it is placed is wholly or partly filled with water, heaving is liable to occur in severe freezing weather, whatever the depth of the drainage course. Experience has proven, however, that four inches of drainage material is sufficient if the water is drained out of it, while if allowed to stand saturated with water, deeper drainage will give little if any better results. Where the soil is sandy or the natural drainage is otherwise good, no drainage course is necessary.