Brick Foundations. Foundations of brick have fre quently been used under brick pavements. The pave ment in such cases consists of two layers of brick, with sand between, and is known as double-layer pavement. These foundations are usually formed by placing upon the road-bed a layer of sand or gravel 3 or 4 inches thick, which is rolled thoroughly to a uniform surface, and then receives a layer of brick, commonly laid flat and with the greatest dimension lengthwise of the street. These bricks are laid as closely as possible with broken joints. The joints are filled with sand care fully swept in, and the bricks are rammed to a firm bearing.
Upon this course of brick is placed a cushion layer of sand, and then the surface layer. The bricks of the lower layer may be of a cheaper grade than the sur face paving brick, as they are not required to resist the attrition of travel.
Care must be used to thoroughly fill the joints in the foundation layer of brick in order that the sand in the cushion layer may not work downward and allow the surface bricks to settle.
These foundations were formerly quite extensively used for brick pavements, but have for the most part been superseded by concrete or macadam bases. They have, in many instances, given good results in use when resting upon a firm road-bed, but lack the strength of the concrete foundation and are not usually economical.
Sand and Plank Foundation. Under many wood pavements, and sometimes under brick surfaces, foun dations formed of sand and planks have been used. These foundations differ somewhat in construction in various localities, but are essentially a bed of sand or gravel, upon which is 'placed a layer of tarred boards which support the surface layer.
It is common to use a layer of sand 3 or 4 inches thick, which is 'compacted by rolling, after which the boards are laid lengthwise of the street close together, so as to form a floor upon which the blocks may be set. With a brick surface a cushion coat of sand is used under the surface layer.
Sometimes two layers of one-inch tarred boards are employed, the lower being laid crosswise of the street and the upper lengthwise of it. In other cases the boards of a single thickness are nailed to scantling laid across the street and bedded in the sand. The boards must in all cases press evenly upon the layer of sand that covers the road-bed.
These foundations were used under the round block wood pavement, at one time quite extensively. They are employed only where low cost of construction is necessary, and are not economical when a durable road surface is to be constructed.
Sand Foundations. Brick pavements have frequently been constructed with only a cushion coat of sand upon the earth road-bed. In some instances, where the road-bed is firm and well drained, forming a natural foundation, this method of construction has been successful under light traffic, but the failures have been numerous, and it is only under exceptional circum stances that such construction will prove economical. The same method has been applied to wood-block and stone-block pavements, stone blocks being usually set in a bed of sand or gravel 4 to 8 inches deep.