ABSTRACT

This paper is based on a case study of cathodic protection of building foundation piles for several buildings installed on top of a landfill in the San Francisco Bay Area.

Ground settlement, methane discharge from the landfill, chlorine generation from the anodes, a high density of bare steel piles, requiring several hundred amperes of cathodic protection current, and the City's requirements of a shallow clay cap for methane blockage [5 feet (1.52 meter) below grade], were some of the technical challenges that were faced during the design stage. The original cathodic protection systems, consisting of anodes under the foot print of the building, failed in a few buildings, due to cable breaks from soil settlement. The replacement systems were designed and installed with anodes on the periphery of the buildings and have been operating successfully for many years. This paper describes the design process where a scale model of one of the building’s piles and a cathodic protection system was constructed and operated for several months to determine the polarizing characteristics of the piles, especially on the piles in the middle of the building footprint.

INTRODUCTION

During the construction boom in the San Francisco Bay Area in the 1990s, several high-rise buildings with steel H-pile foundations were constructed on top of old landfill sites. Due to severely corrosive soils, the City required cathodic protection of the steel H-piles. The original cathodic protection systems, consisting of a few hundred cast iron anodes placed under the foot print of each building, ensured good polarization of the hundreds of steel H-piles, each reaching depths of approximately 200 feet (60.96 meter). The original systems failed after several years of successful operation due to cable breaks because of major soil settlement under the buildings, which was up to 2-3 feet (0.60-0.91 meter) in some areas. The replacement systems were designed to be installed around the periphery of the building. There were two technical challenges for this approach: (a) chlorine generation at the anodes & (b) venting issues and shielding of cathodic protection current at inner piles.

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