Economy - Influence on the Selection of Deep Foundations.

(1) Driven piles. Costs will depend on driving rig rental, local labor rates, fuel, tools, supplies, cost and freight of pile materials, driving resistance, handling, cutoffs, caps, splicing, and jetting.  Jetting is the injection of water under pressure, usually from jets located on opposite sides of the pile, to preexcavate a hole and to assist pile penetration.  Costs are also influenced  by downtime for maintenance and repairs, insurance, overhead, and profit margin.  An economic study should  be made to determine the cost/capacity ratio of the various types of piles.  Consideration should be given to including alternative designs in contract documents where practical.

(2) Drilled shafts. Drilled shafts are usually cost effective in soil above the water table and installation in cohesive soil, dense sand, rock, or other bearing soil overlaid by cohesive soil that will not cave when the hole is bored.  Drilled shafts, mparticularly auger-placed, pressure-grouted shafts, are often most economical if the hole can be bored without slurry or casing.