To repairor replace a bulkhead: that is the question

1 To repair or replace a bulkhead: that is the question New steel sheet pile bulkhead under construction, Grove Harbor Marina (Dinner Key Boatyard Marina) Miami, Florida By: Timothy K. Blankenship tial economic impact on marina opera- coastal storm events. Some localized tions. Underwater bulkhead deterioration waterfront properties may be subject to T he most common form of shoreline stabilization at marinas is a bulkhead. The bulkhead provides an economical or other problems such as undermining due to propeller scour are not visible above water and cannot be monitored on a significant wave activity, even though they are not exposed to ocean waves. The rule of thumb in bulkhead design is to shoreline interface between the upland regular basis.

2 Account for wave impacts if the significant marina area and wet slips. For some mari- This article will explain the difference wave height at a project site is expected to nas, the bulkhead also serves as a source between a seawall and bulkhead, intro- be in excess of three feet (1 meter). of revenue, whether it be parallel docking duce elements of bulkhead design, present or perpendicular mooring. Marina man- bulkhead materials of construction, and Elements of bulkhead design agement is faced with the maintenance of discuss bulkhead evaluation methodology. The following design considerations marine structures, and a proper assess- need to be addressed to properly assess ment of the bulkhead with estimated Seawall vs.

3 Bulkhead? the condition of a bulkhead. remaining service life is essential for Many people refer to all vertical shoreline Topography: elevations, grading, etc. budgeting repairs and/or replacement. In structures as seawalls, but there is a dif- Soil Properties: unit weight of soil, clay addition, there are safety concerns relative ference between a seawall and a bulkhead: vs. sand, etc. to loads behind the bulkhead such as fork- Seawall: structure that provides shore- Embedment/Stability: depth of bulk- lifts, vehicles, and marina customers. line protection from waves but also retains head Assessing the condition of bulkheads on soil. for stability a regular basis can extend the service life Bulkhead: vertical shoreline stabiliza- Water Table: differential water levels of a structure.

4 Performing preventative tion structure that primarily retains soil, behind and in front of walls can intro maintenance or minor repairs as a result of and provides minimal protection from duce additional loading on the wall a bulkhead condition study can be com- waves. Exposure: climate and saltwater vs. pleted before they become major con- Seawalls are typically located on the freshwater cerns. Often times, bulkhead problems do coast fronting beaches, and are subject to Material Properties: strength and not "surface" until it is too late. Sinkholes storm surges with pounding surf, eroding performance in the marine environment or bulkhead failure can a have a substan- shorelines and wave overtopping from Surcharge: live loads behind the wall 22 MARINA DOCK AGE, APRIL 2004.

5 Properly identified during the assessing. The condition. The following table pres- This is a relatively new, economical prod- ents common wall construction materials uct with service life of 50+ years (based with comments regarding availability, on manufacturer warrenties) It's available construction issues, and general perform- in different colors. Strength characteris- ance in the marine environment: tics are limited for high wall heights. It is difficult to install in hard substrates. Concrete Pile/panel and sheet piling configurations Structural evaluation provide a service life of 30+ years if cor- The American Society of Civil Engineers rect mix design and proper marine struc- (ASCE) Underwater Investigations tural design implemented.

6 Sheet piling can Standard Practice Manual was released in be difficult to install in hard substrates, 2001 and provides guidance for the evalu- and concrete pile/panel walls can be sub- ation of marine structures including bulk- ject to undermining. head. The following topics are covered related Steel to structural bulkhead evaluation: Steel sheet piling commonly used for Qualifications of inspection personnel bulkheads . The material provides excel- Types and methods of inspections lent strength characteristics for high wall Typical forms of deterioration exposure applications. has an interlocking Condition Rating seal, and is generally easy to install, even Frequency of Inspection Replacement steel sheet pile bulkhead under in harder substrate.

7 It must be properly Marina management should retain the construction, Bahia Mar Yachting Center, Ft. coated and maintained for long service life services of a consulting engineering firm Lauderdale , Florida of 25+ years. that provides above/below water inspec- tion services. Aluminum A comprehensive report is essential to such as vehicles Sheet piling provides good corrosion document a proper bulkhead evaluation. Ice Loads: in northern climates resistance, but lighter sections allow for The report should reference procedures Prior Maintinance minimal exposed wall height. It is impor- and guildlines from the associate manual. Changes in use tant to recognize corrosion potential of All of the above items should be included Original or as-built plans can provide dissimilar metal hardware, do not use in along with photographs and sketches of a wealth of information including the age waters with low backfill with clay-mucky the observed configuration with notes of the structure and many of the design soils.

8 It is difficult to install in hard sub- regarding deterioration. Comparison of elements listed in the above paragraphs. strates. previous reports provides an indication of The deteriorated condition of a bulkhead the rate of deterioration. be an indication that the bulkhead is either Timber Repair recommendations, along with in need of maintenance, or that it has ful- A timber pile/wale/sheet system is a com- construction cost estimates, should be filled its service life. In some cases, the mon structural configuration. It is general- included to provide marina management bulkhead may be damaged due to loads in ly economical material, but has limited with sound engineering advice so they can excess of loads it was designed to with- strength characteristics for high wall plan of maintenance/repairs as necessary.

9 Stand. heights. Preservative treatment is essential Even though a bulkhead is deteriorated, it for marine life is gener- may not require immediate replacement. Materials of construction ally less than 25 years. It is difficult to The report should be sealed by a regis- The material of the bulkhead must be install in hard substrates. tered professional engineer experienced in Two examples of typical concrete bulkheads : Eleuthera, Bahamas MARINA DOCK AGE, APRIL 2004 23. Who can build a bulkhead? bulkheads are specialized structures, often requiring water-based construction equipment and techniques. The costs for waterfront construction are generally higher than for upland structures such as buildings.

10 Bulkhead or seawall work should be reserved for a qualified and experienced marine contractor. How much does Bulkhead construction cost? Depending on the local construction market and bulkhead design requirements, repairs may cost $100-$400 per linear foot of wall. Bulkhead replacement may cost Deteriorated concrete pile/panel bulkhead. Note the storm sewer outfall through the bulkhead. $500-$1,000 per linear foot. the evaluation of in-service marine struc- subjective. An experienced marine struc- tures. The engineer is required by law to tural engineer can also provide an indica- Conclusions provide independent un-biased advice. tion of material performance.