Melvin I. Esrig
Presented by: Melvin I. Esrig, Ph.D. P.E., Consulting Geotechnical & GeoEnvironmental Engineering
The Geotechnical Group held its first lecture of the 2007/2008 season in a new venue for the Group at the General Society for Mechanics and Tradesmen in Manhattan on October 23, 2007. The lecture focused on the corrosion potential and engineering design of steel piles buried in the ground and in the marine environment. Dr. Esrig began the lecture by describing the various environments that may lead to the corrosion of buried and partially buried steel. Such environments of the ground include the electrical resistivity, the quantity of available free oxygen, the pH concentration, the quantity of salt and sulfate ions, the biological (bacterial) conditions, and possible stray currents due to outside electrical sources. Oxygen is problematic only in partially saturated conditions near the groundwater level and tends to diminish significantly below. Sulfates, which may act in anaerobic conditions, tend to be more problematic.

Dr. Esrig then discussed commonly seen corrosion rates for various environments based on oxygen content and water conditions. The rates, from low to high, are typically quoted in millimeters per year in the published literature. The published rates vary between 0.015 mm/yr to 0.075 mm/yr. Based on the rates presented, it was estimated that it may require between 90 and 200 years for 1/8-inch of corrosion to take place for piles in water and in the ground, respectively, to occur. Based on these findings, the common engineering solution for sizing piles is to simply add this 1/8 inch to the thickness of the pile wall.

It was also found that the rate of corrosion may not be constant over the lifetime of the structure. The corrosion process often results in an oxidized protective layer that prevents further exposure to oxygen and decreases the corrosion rate. In mechanically active environments, such as marine wave action conditions, the mechanical action causes the protective layer to be removed and can maintain or increase the corrosion rate.

A case study by M. Romanoff of the National Bureau of Standards was presented wherein 40 piles were driven into various soil conditions and were allowed to corrode for as much as 40 years. It was found that the predominant form of corrosion was pitting, which was concluded not to be of engineering significance.

Dr. Esrig then went on to present various other case studies to illustrate the effects of low acid environments (US Steel Research Laboratory), high salinity environments (LNG facility in Cove Point, MD), stray electric current (Jacob K. Javits Center, Manhattan, NY), and H-piles near waterfront conditions (North Hudson Hospital & Watermark High Rise, North Bergen, NJ).

The preferred engineering solution is to avoid the problem if possible. This is usually not a viable solution and the most common solutions include the use of concrete piles or adding protective coatings. Jacketing piles in concrete can be a solution if the conditions allow. Cathodic protection often results in high initial project costs and the need to be maintained. The most common solution is to add 1/8 inch of steel to the thickness of the piles. This may add costs to the project if it has not already been accounted for through driveability analyses or lateral capacity requirements. A brief discussion on the New York City Building Code requirement for all pile steel to be designed assuming a yield strength of 36 ksi or less, regardless of the true material strength, often results in piles that may have reserve capacity to account for 1/8 inch corrosion.

Dr. Esrig concluded the lecture by stating that corrosion of piling is not a concern when driven into "undisturbed ground", but that there are various means of designing around and with it when the possibility exists. Following a number of questions from the audience, Dr. Esrig was presented a Golden Apple from Geotechnical Group Chairman Terry Holman, Ph.D., P.E. in appreciation for the lecture.