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.

Description

BACKGROUND OF THE INVENTION

[0001] The Erodible Soil Bulkhead (ESB) is applicable to the fields of geotechnical engineering, general construction as well as marine engineering and construction pertaining to coastal erosion. Wave erosion occurs on an ongoing basis at most unprotected shorelines and in many cases the stability of near-beach development becomes threatened over time by undermining due to progressive beach erosion. In the past conventional “hard” beach protection (e.g., rock, concrete or steel structures) have been used to provide protection from further wave erosion, however “hard” protection is no longer acceptable to some local, state and federal regulatory agencies because they have determined that the soil added to the near-shore environment from ongoing beach erosion is essential to sustaining natural habitat for marine life (and in particular some endangered species) and “hard” structures stop the natural flow of eroded soil to the beach. The ESB is intended to solve the existing problem of protecting coastal shorelines and development from the effects of wave erosion while at the same time providing controlled erosion of soil to the beach to help sustain the natural marine habitat.

[0002] Existing information which is utilized in this invention include the procedures for design, mixing and placing soil-cement mixtures (see Portland Cement Association documents pertaining to soil-cement) and the manufactures brochures and technical specifications for the numerous geotextiles currently available through local and regional sales representatives.

BRIEF SUMMARY OF THE INVENTION

[0003] The Erodible Soil Bulkhead (ESB) is a coastal beach protection system that protects existing coastal bluffs and shorelines from wave erosion for a period of time 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 beach/bluff 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.

[0004] The ESB solves the existing problem of protecting existing coastal shorelines and development from the effects of wave erosion while at the same time providing controlled release of soil to the beach to help sustain the natural marine habitat. 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 degradable reinforcing and/or by mixing the soil with a cementing agent to provide additional strength. The degree of erosion resistance is controlled by the nature and amount of reinforcing provided and/or by the amount of cementing agent mixed with the soils. Untreated soils are placed on top of the treated erosion resistant soils to provide additional volume of erodible soils to the beach as controlled recession of the treated soils of the ESB occurs.

BRIEF DESCRIPTION OF FIGURES

[0005] FIG. 1:

[0006] Presents a side view, partial top view and partial end view of a the general concept of the Erodible Soil Bulkhead.

[0007] FIG. 2:

[0008] Presents a side view, partial top view and partial end view of a Erodible Soil Bulkhead constructed using layered geotextile reinforcing.

[0009] FIG. 3:

[0010] Presents a side view, partial top view and partial end view of a Erodible Soil Bulkhead constructed using soil tube geotextile reinforcing.

[0011] FIG. 4:

[0012] Presents a side view, partial top view and partial end view of a Erodible Soil Bulkhead constructed using soil-cement mixture.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The Erodible Soil Bulkhead (ESB) is a coastal beach protection system that provides wave erosion protection to existing coastal bluffs and shorelines from wave erosion while at the same time providing controlled release of soil to the beach to help sustain natural habitat for marine life (see FIG. 1). The ESB is intended to provide protection to coastal beach/bluff 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. 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 developed shoreline and/or structures.

[0014] The ESB is constructed on the beach, normally seaward of the existing eroded shoreline. 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 is limited only by site geometry and stability of the overall ESB.

[0015] The ESB is constructed with natural soils which are strengthened via reinforcing an/or cementation to have much greater erosion resistance than conventional fill soil while remaining, to a controlled degree, erodible. Erosion resistance is provided by environmentally-degradable reinforcing (reinforcing which degrades when exposed to natural sunlight and/or natural organisms) and/or by mixing the soil with a cementing agent such as portland cement to provide cementation. The degree of erosion resistance is controlled by the amount and degredation characteristics of the reinforcing material and/or by the amount of cementing agent mixed with the soils. Untreated soils are placed on top of the treated erosion resistant soils to provide additional volume of erodible soils to the beach as controlled recession of the treated soils occurs.

[0016] Where reinforcing is used to provide erosion resistance, the primary reinforcing is normally commercially available ultraviolet-degradable geotextile products (see FIGS. 2 and 3) although other types of degradable reinforcing can be used. Geotextiles have previously been used as soil reinforcing in the design and construction of reinforced soil retaining structures and slopes, as well as filters for subsurface water flow and surface stabilization to prevent erosion. The unique difference of the use of geotextiles in the ESB is that to my knowledge geotextiles have never been used to allow erosion to occur at a controlled rate as they are in the ESB. In addition to my knowledge the geotextile wrapped soil tubes configuration of the ESB reinforcement has not been previously used.

[0017] Where cementation is used to provide erosion resistance (see FIG. 4), a cementing agent such as portland cement is mixed with the soil to provide sufficient unconfined compressive strength to control erosion to the desired rate. The concept of mixing a cementing agent with soil to increase soil strength has been used for many years. The unique difference of the use of cemented soil in the ESB is that the cemented soil mixture is intended to allow erosion of the soil at a controlled rate.

[0018] ESB Construction Using Geotextile

[0019] Geotextile is placed within compacted granular soil fill to form a reinforced soil mass by layering geotextile and soil (see FIG. 2) or by forming geotextile wrapped soil tubes (see FIG. 3). 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.

[0020] ESB construction using layered geotextile reinforcing (see FIG. 2) is similar to that of a conventional reinforced soil structure except that the geotextile layers may be more closely spaced than normal reinforced soil structures. A geotextile layer is placed on a prepared soil surface and a layer of soil is placed over it and compacted to a specified density. Construction proceeds to the design height of the ESB by placing a new layer of geotextile over the previously compacted soil layer and subsequently placing and compacting another layer of soil.

[0021] ESB construction using soil filled geotextile tubes (see FIG. 3) is accomplished by using a form which is lined with geotextile and then filled with soil. The top seam of the tubes are fastened using biodegradable pins and/or twine. Tubes constructed using the form are constructed about one tube diameter apart and the intermediate tubes are constructed to fill the space between the formed tubes. The tubes are oriented with the long dimension approximately perpendicular to the beach line in general as shown in FIG. 2, but can be oriented at different angles as required for existing site conditions and end protection. Each layer of tubes are laid side-by-side across the length of the beach to be protected. Subsequent layers of the soil tubes are formed in the same manner and are stacked vertically to the design height of the ESB. Diameter of the tubes and the ultra-violet degradation rate of the geo-textile is varied to control the rate of erosion. Supplemental biological reinforcement can be provided by planting trees, shrubs, etc. on the ESB.

[0022] ESB Construction Using Portland Cement-Soil Mixture

[0023] A typical soil-cement ESB is shown on FIG. 4. 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. The amount of portland cement required to control erosion will vary from site to site and possibly from point to point within the ESB at a particular site. Typically the cement to soil ratio will range from about 1% to 10% by weight depending on site conditions.

[0024] On-Site Mixed Soil-Cement

[0025] A temporary form such as stackable concrete blocks (commonly called “ecology blocks” in the Puget Sound Region) or other suitable system is placed along the seaward limit of the ESB. Natural soil material is placed behind the form in controlled thickness layers, cement is spread on the surface at the proper ratio, water is added as necessary and the soil and cement are mixed with a traveling mixing machine. Alternatively a on-site batch mixer could be used and the mixed soil-cement batch material would be transported and placed in layers. The mixed soil-cement layer is then compacted to a specified dry density using conventional soil compaction equipment. The process is repeated to construct the ESB and the temporary forms are removed to allow the erosion process to begin.

[0026] Off-Site Mixed Soil-Cement

[0027] Limited size temporary forms are used to support the off-site mixed soil cement when it is delivered to the site. The size and shape of the forms volume will vary depending upon the ESB design, logistical constraints of soil-cement delivery to the site and the time constraints of tidal water level fluctuations at the site. The soil-cement mixture is placed into the temporary form and densified as required to achieve design density. After the soil-cement mixture has gained sufficient strength, the form is removed. The process is repeated incrementally to create the seaward face of the ESB. After completion of the initial seaward face of the ESB, placement of the remaining soil-cement material between the seaward face and the existing shoreline is performed with or without forming depending upon the site specific design.

Claims

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.