Bulkheads

Bulkheads are flexible soil retaining walls which derive their stability from the structural members and the strength of the soil. The soil as well as providing stability , creates loads upon the system which must be resisted. The principle component of the system is the sheet pile. Horizontal stresses exerted by the soil on the backfill side of the wall tend to move the piles outward. The resistance of this outward movement is prevented by the pile embedment in the subgrade. If insufficient embedment in subgrade occurs, failure is likely.

Horizontal stresses on the pile cause bending, making the pile function as a beam. Therefore pile design is two fold, the pile must be long enough to prevent toe failure, it must be stout enough to resist flexural stresses induced by bending.

The sheet piles are tied together by whales. These members are designed to resist bending and are fastened to the piles with bolts and nails. At various points the whales require spilces that must resist the same loads as the whales.

The resistance to outward movment can be enhanced by employing a tierod and anchorage. Since a portion of the horizontal load is transmitted to the anchorage through the tierod, the tierod must be suitably designed. The anchorage must also must adequately dimensioned and properly positioned. If the anchorage is located to close to the wall, it will be located within the failure wede, and will be of no use.

Sheet piles are normally made of steel, concrete, aluminum, vinyl or wood. The actual thickness is determined by the structural needs computed by the structural engineer.

The most basis type of bulkhead is the cantilevered wall. Typically the sheeting is extended in length to overcome the loss of the anchorage. Quite often this will reduce costs in areas where the installation of anchorage and tierod would be extremely difficult or costly.

The Navy Bulkhead is another variation of the anchored wall that incorporates 8" fender piles being driven in front of the bulkhead. The presence of fender piles adds considerable rigidity to the wall system and is quite usefull where there are considerable external loads on the wall.

One of the most critical aspects of the bulkhead site is the type of soil present. In general there are to types of soil that the designer must contend with, cohesionless soils referred to as sand, cohesive soils which can be referred to as clay. The behavior of sand is quite predictable and reliable designs can be rendered with relative certainty. Clay on the other hand is complex soils. Their strength varies considerably from point to point and their behavior depends upon a wide range of conditions, such as mineralogy, soil structure, and stress history.

The key element in the design of bulkhead is a sound computational procedure. Such a procedure depends largely upon the adequacy of the mathmatical model chosen to represent the behavior of the system. Basicly hire an engineer that has extensive experience in this type of design or a contractor with extensive experience in your local region.

Please contact Michigan Shoreline Construction And Permitting for your free consultation and quote.

By: Daniel Pierson

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