A group of five closed-end steel pipe piles were driven into a sandy hydraulic fill at Hun...

A group of five closed-end steel pipe piles were driven into a sandy hydraulic fill at Hunter’s Point in San Francisco, California (DiMillio, et al., 1987a). A single isolated pile also was driven nearby. Each pile had an outside diameter of 10.75 in and a length of 30 ft. The group piles were placed 3 to 4 ft on-center, and their pile cap was elevated above the ground surface.

The upper 4.5 ft of the soil was predrilled to a diameter larger than the piles, and the top of the completed piles extended 5 ft above the ground surface. Therefore, only 20.5 ft of each pile was in contact with the soil. No other predrilling or jetting was done.

An extensive subsurface investigation was conducted before these piles were installed. This included SPT, CPT, DMT and other tests. The CPT results are shown in Figure 15.14.

a. Using this CPT data, compute the ultimate downward load capacity of the single pile.

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b. Based on a pile load test, the ultimate downward load capacity of the single pile was 80 k (based on Davisson’s method). Other methods of reducing the load test data gave ultimate load capacities of 80 to 117 k. How accurate was your prediction?

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c. Using this CPT-based static load analysis, compute the ultimate downward load capacity of the pile group.

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d. Based on a group pile load test, the ultimate downward load capacity of the pile group was 432 to 573 k, depending on the method of reducing the load test data. How accurate was your prediction?

Figure CPT results and soil profile.