Dam

A structure constructed to obstruct the flow or to impound water.

Dancing

The term "dancing" or "bouncing" is used to describe a vibratory pile driver/extractor's behavior when driving a pile that has hit a rock layer or some other obstruction causing the vibro to jump up and down in an erratic pattern of amplitude. The vibro suppressor housing "dances" due to its lack of capacity to absorb the unwanted erratic amplitude, thus transferring unwanted vibration into the housing and crane line. This, of course, will overheat and damage or destroy the rubber elastomers in the suppressor housing or destroy the bearings in the gearbox or both. Do not operate a vibratory pile driver/extractor in this manner. Should the contractor wish to allow the vibratory pile driver to “dance” then the machine should be shut down at once and an agreement should be made where the contractor agrees to accept all responsibility for damages. Those damages could be to the vibratory suppressor, gearbox, clamp attachment, bolts and fasteners as well to the crane line and boom. In some cases, such as when the pile lands on a buried wood pile or a layer of hard soil, the vibratory pile driver/extractor may experience “dancing” for a second or two before breaking through the obstacle. It is up to the judgment of the pile crew to determine if the “dancing” is minor or harmful. In any case, “dancing” will cause excessive wear on all components involved including the crane line and boom. Driving piles is an art and a skill. Rookie pile drivers should shut the machine down the moment the hammer is dancing. A skilled pile driver may attempt to slow the machine down by lowering the engine rpm (which slows down the machine because the slower rpms of the engine will reduce hydraulic flow). Slowing the machine down may reduce or eliminate the “dancing” problem. Lifting up on the suppressor housing may also prevent “dancing”. Hard layers may require pre-drilling or the use of an impact hammer or a combination of both. In permafrost soil conditions a combination of predrilled holes and hot water or even steam jetting has been used. Consult the factory and asked to speak with an experienced person regarding what to do in case of “dancing”.

Dap

Incision or notch cut in timber into which the head of a pile or other timber is fitted.

Dead Load

Weight of the structure only.

Deadman

A pile, cluster of piles or buried timber or a wall driven to withstand a horizontal force as through a tie rod fastened to a retaining wall. See Anchor Pile.

Death Zone Area

Area around the pile as it is being driven. This Death Zone Area includes all area around the pile driving rig that is subject to danger should the crane and leads tip over. Only the trained pile drivng crew should be allowed to work in this area during pile driving operations. Never stand next to the pile while it is in the act of being driven. Never check plumbness by placing level on a pile that is in the act of being driven. Do not stand anywhere under the pile as it is being driven due to the possibility of the pile breaking or parts or pieces falling from the pile hammer or leads or any other support structure. Please note that mis-placed tools, shackles, and any other items placed on the leads or hammer have been known to fall and cause injury. Please stand clear and up wind.

Decrementation

Removal of a load in steps at completion of test loading. See incremental loading.

Density

The weight or mass per unit of vilume. In reference to soil, the term usually indicates weight per unit volume and is synonymous with unit weight.

Depth of Fixity

Distance from the ground surface to the depth at which a pile is held firmly by the soil.

Desanding Plant

Equipment used to filter or desand contaminated bentonite slurry prior to its reuse.

Design Engineering Firm

The professional organization responsible for the design, plans and specifications to fulfill the cope of work to be performed to sucessfully complete the design of a project. The firm may also monitor and observe the construction of the project. See A/E.

Design Load

The load which the pile is intended to carry without excessive movement and with an acceptable factor of safety against plunging failure.

Deviation

Variation from the designated plan location or elevation.

Dewatering

1. The procedure utilized to remove water from a construction area such as pumping from an excavation or location where water covers the planned surface.
2. The procedure used to lower the groundwater table in order to obtain a "dry" area in the vicinity of an excavation which would otherwise fill with water.

DFI

Deep Foundations Institute.

Diaper

Term used for a woven burlap type fabric tacked over a cut wood piling to hold the bear shit in place for protection against deterioration. Also a term for an absorbant material or pad used to contain and clean up spilled liquids such as oil, hydraulic fluid, gas, etc.

Diaphragm wall

See Slurry Trench Wall.

Diaphragm-Type Cellular Cofferdam

A structure made of steel sheet piles with each of the inner and outer walls consisting of a series of arc segments, which are connected at their intersections with diaphragms that exctend through the cofferdam to form a series of cells. The cells are filled with earth, sand, gravel or rock. See circular-type cofferdam.

Diesel Hammer

A pile hammer, which carries its own diesel fuel to generate power internally.

Diesel Hammer, Closed-End

A diesel pile hammer in which the upward flight of the ram is arrested by compressing air, above the ram to form an "air spring." Also called Double-Acting Diesel Hammer.

Diesel Hammer, Open-End

A diesel pile hammer in which the upward flight of the ram is arrested by gravity. Also called Single-Acting Diesel Hammer.

Diesel I Program

TItle of a proprietary computer program for solving wave equations for diesel hammers.

Dieseling

Undesirable precombustion of the fuel in a diesel pile hammer (usually due to overheating or improper fuel). Also called Prefiring, Preignition.

Differential-Acting Hammer

A fluid-powered hammer in which fluid lifts the ram un the op stroke and is exhausted into and combined with addition fluid entering over the piston to take advantage of differential piston areas to accelerate the ram and to act in concert with gravity on the down stroke.

Dike

An impervious barrier to control movement of water.

Dip

Angle of inclination a fault stratum makes with the horizontal plane. See Strike.

Direct Circulation

See Reverse Circulation.

Displacement Pile

A solid pile, or hollow pile, driven with the lower end closed, which displaces an equivalent soil volume by compaction or by lateral or vertical displacement of the soil, such as timber, closed-end pipe or precast concrete piles. A Franki pile.

Disturbed Sample

A sample of soil taken without effectively minimizing disturbance of the soil mass.