Economy of Piles

CEMP-E

EI 02G001

01 July 1997

encountering changed conditions. Avoidance of such a situation requires professional judgment and

customer education. A waiver requirement by higher authority to the pile testing procedures for verifying

design is described in chapter 6 of TM 5-809-7.

(b) Data from the exploration program should be made available to designers and prospective

bidders and contractors and should include complete boring logs showing all encountered strata, locations

of changes in strata, and locations of groundwater including perched and artesian pressures.

(c) Cobbles and boulders should be indicated because they may interfere with the driving of

piles.

(d) Landfills often contain poorly compacted materials and may not provide soils that will

provide adequate pile capacity.

(e) The soil actually encountered during installation of the piles may not provide the

penetration resistance that was expected from results of the soil exploration program. A variety of problems

can be encountered leading to unexpected behavior of the driven pile as discussed in paragraph 4-3. Costly

delays from unexpected pile behavior can be minimized by driving indicator piles with PDA equipment and by

performing load tests as discussed in paragraphs 2-2b, 2-2c, and 2-2d below.

(f) Refer to TM 5-818-1 and TM 5-809-7 for guidance on the exploration program.

(2) Economy of Piles. The most economical piles will usually be those that can be obtained and

manufactured locally.

(a) Cost estimates should be prepared and a comparison made of alternative pile materials

and construction methods.

(b) The least cost alternative capable of providing acceptable pile capacity should be selected

depending on the skills of the local construction force, availability of materials, and availability of equipment

to install the piles.

(c) Alternative piles where costs are within 15 percent of each other should be included in the

contract documents.

b. Indicator Piles. Indicator piles are the same as the actual production piles used to support the

structure. These piles are driven at the start of construction to provide information on the behavior of the

piles during their installation and to provide an assessment of the actual capacity of the piles. Indicator piles

are usually designed to be part of the production piles that support the structure.

(1) Driving of Indicator Piles. Depending on the job size of the production piles, 2 to 5 percent is

typically driven as indicator piles at locations specified by the design engineer or at locations that may have

inadequate pile capacity.

(a) Locations where indicator piles should be driven include the corners, edges, and center of

the site where piles are to be installed.

(b) Indicator piles should be driven at locations where the soil exploration program indicated

relatively low standard penetration resistances, loose sands, or soft clays.

(c) The driving of indicator piles in loose sands or some clay soils may indicate penetration

resistances that are too low to provide adequate pile capacity. Driving the piles may also cause pore water

pressures to increase and further reduce the penetration resistance. Dissipation of pore water pressures

over time will cause the penetration resistance to increase and lead to a pile with greater capacity. This is

soil freeze.

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