As a rule, wooden bulkheads are used for temporary structures because of their economy, whereas reinforced concrete, metal bin-type, or other types of retaining walls are used for permanent structures. Wooden bulkheads are generally used on streets that are not improved to their ultimate width (half streets) or in unimproved, undeveloped areas. In the latter case, as the abutting property is developed and ingress and egress (driveways, walks, steps, etc.) are provided, bulkhead removal becomes necessary.
Some of the retaining wall design problems caused by space limitations are as follows: Additional right of way may be necessary to construct the footing (or even the entire wall) on private property. A footing may be designed for the dual purpose of supporting the wall and acting as a sidewalk. In other situations, enough vertical clearance may have to be provided between the buried footings and the sidewalk to permit installation of utility lines.
Consideration must be given to other factors, such as the construction costs of cut and fill and additional right-of-way costs. These costs must be compared with the cost of the retaining wall construction and with other connected costs, such as excavation and backfilling.
On hillside streets with steep side slopes, the low side of the street may require a retaining wall to retain part of the street and/or sidewalk. The portion of wall used for retaining purposes may require a height of only 1 or 2 feet. However, to provide adequate protection for pedestrians and vehicles, the use of a higher wall is advisable. In these cases, to economize on construction, the wall may be made of a combination of masonry and concrete blocks, or of masonry and chain link fence.
Drainage problems are sometimes encountered because of the total or partial blockage of natural watercourses by retaining walls. In other cases, weep holes in the walls may permit undesirable drainage channels to form because of the pressure created from dry-weather flow.
To make a comprehensive design study, the designer must consider all of the above factors. In addition, plans, profiles, and cross-sections showing the relationship of the proposed street grade and alignment to the existing or future ones must be included
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