Erodible soil bulkhead

Abstract

The Erodible Soil Bulkhead (ESB) is a coastal beach protection system that protects existing coastal bluffs and shorelines from wave erosion while at the same time providing controlled time release of soil to the beach to help sustain natural habitat for marine life. The ESB is intended to provide protection to coastal shoreline areas where conventional “hard” beach protection (e.g., rock, concrete or steel structures) is not preferred or allowed by regulatory agencies due to detrimental effects on the coastal marine environment. The ESB is constructed with natural soils which are strengthened via degradable reinforcing an/or cementing agents to have a greater erosion resistance than untreated fill soil while remaining, to a controlled degree, erodible. By its nature the ESB is disposable and must be re-constructed at the end of its useful life to continue providing protection to the shoreline and/or structures. The ESB is constructed on the beach, normally seaward of the existing eroded shoreline. The ESB is constructed with natural soils which are strengthened via reinforcing an/or cementation to have a greater erosion resistance than conventional fill soil while remaining, to a controlled degree, erodible. Erosion resistance is provided by biodegradable reinforcing and/or by mixing the soil with portland cement or other agent to provide cementation. The degree of erosion resistance is controlled by the nature and amount of reinforcing provided and/or by the amount of cementing agent and admixtures mixed with the soils. Untreated soils may be placed on top of the treated erosion resistant soils to provide additional volume of erodible soils to the beach as controlled recession of the ESB occurs. The ESB extends as far as practical seaward of the existing shoreline (as limited by physical beach conditions and/or regulatory agencies). Typically the width of the ESB will be about 10 to 30 feet but could be larger. Height of the erosion resistant portion of the ESB will depend on the local tidal range, wave action and site specific geotechnical conditions but generally ranges from about 6 to 8 feet above the beach level. Additional height of untreated soils above the erosion resistant lower portion can range from none to maximum heights limited only by site geometry and stability of the overall ESB. Where reinforcing is used to provide erosion resistance, the reinforcing is normally commercially manufactured, ultraviolet-degradable geotextile products. The geotextile is placed within compacted granular soil fill to form a reinforced soil mass by layering geotextile and soil or by forming geotextile wrapped soil tubes. The seaward side of the geotextile ESB is initially closed by wrapping the geotextile back into the reinforced soil. As degradation of the geotextile occurs due to daily exposure to natural elements (including ultraviolet light), the soil of the ESB is exposed to wave action and erosion occurs. As soil erosion occurs, the geotextile reinforcing is undermined and the newly exposed fabric droops down, covering the seaward face of the ESB which reduces the erosion rate of the soils. The process is repeated as the newly exposed geotextile degrades and additional soil erosion occurs. Where cementation is used to provide erosion resistance, the cementing agent is mixed with the soil to provide sufficient unconfined compressive strength to control erosion to the desired rate. The amount of cemention required to control erosion varies from site to site and possibly from point to point within the ESB at a particular site. Typically the ratio of portland cement to soil will range from about 1% to 10% by weight depending on site conditions. The soil-cement mixture can be mixed and placed on-site, provided conditions will allow, or the soil-cement can be mixed off-site and delivered to the site for placement.

1 . I claim as my invention the concept of an Erodible Soil Bulkhead (ESB) system that can provide significant erosion protection of shoreline (greater protection than a untreated fill soil mass) while at the same time eroding at a controlled rate to provide an ongoing flow of soil to the near-shore marine environment.  
     
     
         2 . I claim as my invention the use of geotextile to allow a controlled rate of erosion of a soil mass.  
     
     
         3 . I claim as my invention the use of cementing agents such as portland cement to provide a controlled rate of erosion of a soil mass.