The october 17, 1989 loma prieta earthquake provided an ideal time and situation to perform for the first time, at no installation cost, a full scale lateral load test on a group of driven piles in typical bridge footings at the cypress street viaduct. Since these foundations were no longer going to be used, we were able to load them laterally to failure and record load versus deflection. Testing was performed at two different locations. Location .1 Consisted of 60 ftlong piles in a clayey (bay mud) material, and location .2 Consisted of 15 ft long piles in sandy silt. Preliminary results were very encouraging. Lateral pile capacities were observed at 1/4 in. Deflection, which greatly exceed the bridge design specifications criteria.Reduced data produced a range from 17 kips to approximately 26 kipsper pile in these two soil types. Considering that we use 5 kips/pile in today's design criteria for this type of pile, one can readilysee that if this number were increased to just 10 kips, the number of piles required for lateral forces would be significantly reduced, thereby achieving an appreciable reduction in cost for foundations of this type. Pile capacities are correlated with appropriate soil parameters for the two soil types. Bridge design specifications are being proposed to take advantage of the increased lateral load capacities obtained in this research project. This paper appears in transportation research record no. 1290, Third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 2.
Abstract