Deep Foundations

Pipe Pile Points

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Pipe has been (and probably always will be) pushed off trucks and allowed to fall into a pile. This is dangerous and may damage the pipe. Any labor one might think he has saved by “unloading” in this manner is lost later in straightening bent, bowed or damaged pipe lengths.

Pipe for piling frequently will come to the job with cutting shoes, conical points or flat-plate closures already attached. Sometimes a splicer sleeve will also be welded on. Local work rules may sometimes require that such attachments be made at the job site. If pipe arrives at the jobsite with points and/or splices already attached, check to see that required material certificates or test reports for all materials (welding as well as the accessory) are supplied.

When pipe piles are installed with a closed end, 1/2′ to 3/4′ inch thick flat plates are sometimes used as a form of tip protection. The suggested diameter of this plate is generally 1/2 inch larger than the actual O.D. of the pipe. Flat plates usually are permitted to extend 1/4 in. outside the periphery of the pipe and are welded for attachment. When plates are required to be kept flush accurate beveling of the pipe and skillful welding are required.

Where plate is used around the pipe as reinforcement it should be heat-treated steel. Consult experienced welding authorities on how this should be welded and inspected as driving is in shear on the welds.

conical-insideEnd closure may be flat plates or conical points. Conical points have sixty degree configurations and are available with either an inside flange or outside flange. This angle parts the soil and preserves friction along the walls rather than just beating a path through it. Use of conical points keeps soil disturbance to a minimum and permits development of maximum friction support. Where boulders or sloping rock are encountered, they distribute the reaction stresses to the entire periphery of the pipe, rather than just a segment. On boulders or uneven rock, the point distributes the hammer impact load around the periphery of the pipe rather than concentrating it as occurs with a flat plate closure.

Conical points are also used as end-closures for pipe piles although they generally cost more than plate type protection. Conical points should be cast steel meeting the requirements of ASTM a-27 65/35; for tougher conditions A-148 80/40 is preferred. Plates may be A-36 steel and should be thick enough to resist all driving stresses, plates should not extend more than 1/4 in. outside the pipe for exterior welding.

insideInside-flanged conical points for pipe attach with just a simple weld as driving is in compression on a ledge. For advance preparation pipe can be laid on supports and rolled slowly while hand or machine welding is conveniently done.

Outside-flanged conical points can be made for a drive fit so no welding is required. Minor water leaks can be controlled, by swabbing roofing mastic around the joint. Both inside and outside flange types have a level ledge on which the pipe seats and drives.

It should be noted that the inside type have a limitation on the pipe thickness they can accommodate, normally 1/2 inch for popular sizes. When a large quantity is required, and should time be permitting a pattern can be made for almost anything. In the case of the outside flange type, these shoes can be welded or tapered for a drive fit. Pipe wall thickness of outside flange type pipe is generally not of concern as heavier wall pipe will increase in wall thickness inward, while the outside diameter will remain constant. Points should be inside ribbed for strength with no metal less than 1/2 inch. This thickness should increase for larger diameter pipe.

taperWeld beads on spiral (or other) pipe that protrude outside the surface must be ground smooth at ends where drive-fit end-closures or splicers might be adversely affected. (The pipe manufacturers will remove protrusions, if requested).

Pipe in any nominal size has the same outside diameter. Outside flanged points and splicers can be made to one size and splicers can be made to one size and tapered for a drive-fit for all wall thicknesses. Such points and splicers can be attached by friction driving the pipe into them against a square should without welding.

Inside diameter of pipe varies with the wall thickness. Fittings are made to match and accommodate about a 1/2 in. wall thickness; they are welded for attachment. This strengthens the pipe against stretching and splitting from driving over the fitting. The inside flange type does not extend beyond the pipe; this may be an advantage in some soils, especially permafrost where soils do not readily reform after driving.