The retaining wall must be strong enough to hold back the pressure of a great weight of soil, and yet porous enough to allow drainage.



The most popular types of walls are built of stone, either dressed or rubble. In using stone for a retaining wall, there are two basic types of construction: dry-wall, which uses earth as a filler between the stones, and mortar, which uses cement as a bonding agent.

The base of any retaining wall must be sunk below the frost line. This is about 6 inches in the northern half of the United States.

For a flat wall (one without buttresses or projections), the width of the base should equal one-fourth the height of the wall. The wall can taper to a width of about one-fourth of the width of the base.

For buttressed walls, the base should be one-fourth as wide as the wall is to be high. This refers to the widest points, where buttressing is to be used. In the narrower areas, the base may be of slimmer proportions.

At intervals of about 24 inches, and about 6 inches from the lower ground level of the retaining wall, drainage pipes should be imbedded in the wall.

In some walls, if the wall itself is porous enough, it is possible to eliminate these drains. But in any construction using mortar as a bonding agent, these drainage pipes are essential.

In dry-wall construction it is possible (although not advisable) to start at ground level, and not sink the wall below the frost line.

The most inexpensive way of constructing a dry wall is to choose local stone, picking large ones for the main stones and smaller ones for the chinks. The largest stones should form the base of the wall with the smaller ones leading to the top.

The side of the wall which faces out should be as level as possible, with obstructions and edges of outside stones facing inward.

This not only gives the wall a better purchase on the soil it retains, but also insures a good appearance. Stones with round surfaces should be discarded since they do not form a good wall.

Stones should be placed in a good bond. This simply means that edges of stones on one course should overlap spaces in the lower courses.

Where a stone on an upper course is crooked or does not fit firmly, earth and small stones can be packed in to improve the bond. No vertical crevices should be left.

The wall itself should slope back against the soil it is retaining. This gives it greater strength. The width of the base of the wall should be, again - as a rule of thumb - one-third of the height.

It is the practice in many areas to slope the wall as much as 5 or 6 inches for each vertical foot, although this degree of slope is not essential. Soil should be firmly packed in all pockets in the wall and should be continued back into the earth being retained.