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Mini-Piles

 

Location:
North Western Pennsylvania

Project:
Structure Construction for Parking Deck, Chiller Plant and Multi-Story Academic Building

Situation:
The project site is located in an area of karstic geological formations consisting of pillared limestone with voids or soil filled solution cavities. The seams of hard limestone underlain by voids or clay prevent driving piling to competent rock.

The project was fast-tracked by the construction manager, which required 823 mini-piles totaling approximately 50,000 lineal feet in length to be installed in less than three months.

Coastal Drilling East, a division of Shaft Drillers International, was selected as the mini-pile specialty contractor.

Solution:
Mini-piles are defined as small diameter, grouted in-place, drilled piles incorporating a steel core and an outer casing shell to resist the applied loads. The mini-pile casing can be drilled through the seams of limestone by utilizing rotary percussive eccentric drilling methods. The mini-pile is advanced until the required depth of competent rock (rock socket) is obtained. The mini-pile consists of a 7" OD x 0.500" wall outer casing and a core steel used to transfer the tension and compression loads into the rock.

Results:

Parking Deck and Chiller Piles: 150 Ton Capacity
Academic Building: 100 Ton Capacity
Designated tension piles required an uplift load of 125 Tons.

Pile Testing:
A total of four pile load tests were performed in accordance with ASTM D1143. Each pile was tested to a minimum of 200 percent of the design load. To verify the pile design, one of the 100-Ton piles was loaded to its ultimate capacity of 300 percent of the design load. The load testing setup, consisting of the test beam, test jack, and load cell, have a total capacity of 500 Tons.

By working a fleet of five drills, Coastal Drilling East recovered three weeks of schedule lost during the site and utility work.

 

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