Foundation Specifications 0151

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Slurry Displacement Piles

CALTRANS FOUNDATION MANUAL

be adjusted to account for some of these conditions, or chemical additives may be necessary.

Because most drilling slurries are difficult and expensive to dispose of, most drilling

contractors will want to reuse the drilling slurries. Occasionally, contractors will want to

reuse the drilling slurry on another pile after completion of the previous pile. Some con-

tractors may want to reuse the drilling slurry on another contract.

The contract specifications do not prohibit the reuse of drilling slurry. However, the drilling

slurry must meet the physical property requirements of the contract specifications. Drilling

slurries will degrade over time (usually measured in months). If a Contractor proposes to

reuse a drilling slurry from a different contract, the Structure Representative may want to

have the physical properties of the drilling slurry tested prior to placement in the drilled

The reuse of drilling slurries requires careful planning on the Contractor's part. Drilling

slurries must be cleaned before they are reused. For mineral slurries, this is accomplished

through the use of desanding units and chemical additives. For polymer slurries, this is

accomplished by allowing the contaminants to settle out.

The types of drilling slurries that are permitted for use by Caltrans (as of 1994) are detailed

in the following sections. Three types of drilling slurries are permitted: water, mineral, and

Water may be a suitable drilling slurry under the right conditions. Most drilling contractors

will try to use water as a drilling slurry if the ground conditions are right because it is

inexpensive. However, use of water as a drilling slurry is limited to ground formations that

are strong enough not to deform significantly during drilling. The water level in the drilled

hole must be maintained at least 5 feet above the groundwater level in order to maintain

positive effective stress on the sides of the drilled hole. This is the only means of stabiliza-

tion provided to the sides of the drilled hole since water does not control filtration.

The contract specifications state that water may only be used as a drilling slurry when

temporary casing is used for the entire length of the drilled hole. Although water was

permitted to be used as a drilling slurry in the recent past by the contract specifications,

history has shown that water was inappropriately chosen as a drilling slurry for use in holes

drilled in unstable ground formations by some contractors for economic reasons. This

resulted in many defective piles that required repair.