design or designs shown on the plans. They shall consist of concrete cast in drilled holes or in steel shells or pipes driven to the required bearing. Concrete shall conform to the requirements of section 601.

(b) Drilled holes.-All holes for concrete piles cast in drilled holes shall be drilled dry to the tip elevations shown on the plans. All holes will be examined for straightness and any hole which on visual inspection from the top shows less than one-half the diameter of the hole at the bottom of the hole will be rejected. Suitable casings shall be furnished and placed when required to prevent caving of the hole before concrete is placed.

All loose material existing at the bottom of the hole after drilling operations have been completed shall be removed before placing concrete.

The use of water for drilling operations or for any other purpose where it may enter the hole will not be permitted. All necessary action shall be taken to prevent surface water from entering the hole and all water which may have infiltrated into the hole shall be removed before placing concrete.

Concrete shall be placed by means of suitable tubes. Prior to the initial concrete set, the top 10 feet of the concretefilled pile or the depth of any reinforcing cage, whichever is greater, shall be consolidated by acceptable vibratory equipment.

Casing, if used in drilling operations, shall be removed from the hole as concrete is placed. The bottom of the casing shall be maintained not more than 5 feet nor less than 1 foot below the top of the concrete during withdrawal and placing operations unless otherwise permitted by the Engineer. Separation of the concrete during withdrawal operations shall be avoided by hammering or otherwise vibrating the casing.

(c) Steel shells and pipes.-The inside of shells and pipes shall be cleaned and all loose material removed before concrete is placed. The concrete shall be placed in one continuous operation from tip to cut-off elevation and shall be carried on in such a manner as to avoid segregation. The top one-third of concrete-filled shells shall be consolidated by acceptable vibratory equipment.

No shell or pipe shall be filled with concrete until all adjacent shells, pipes, or piles within a radius of 5 feet or 41⁄2 times the average pile diameter, whichever is greater, have been driven to the required resistance.

After a shell or pipe has been filled with concrete no shell, pipe, or pile shall be driven within 20 feet thereof until at least 7 days have elapsed.

600A.11 Extensions. Extensions, when permitted or di

rected by the Engineer, shall be made as shown on the plans and in accordance with this subsection.

(a) Precast concrete piles.-Extensions of precast concrete piles shall be made by cutting away the concrete at the end of the pile, leaving the reinforcement steel exposed for a length of 40 diameters. The final cut of the concrete shall be perpendicular to the axis of the pile. Reinforcement of the same size as that used in the pile shall be fastened securely to the projecting steel and the necessary form work shall be placed. Care shall be taken to prevent leakage along the pile. The concrete shall be of the same quality as that used in the pile. Just prior to placing concrete, the top of the pile shall be wetted thoroughly and covered with a thin coating of neat cement, retempered mortar, or other suitable bonding material. The forms shall remain in place not less than 7 days. Curing and finishing operations shall be in accordance with the requirements of sections 601 or 601A.

(b) Prestressed piles.-Extensions of prestressed precast piles will generally not be permitted, but when permitted they shall be made in accordance with (a) above, but only after driving has been completed. Reinforcement bars shall be included in the pile head for splicing to the extension bars. No additional driving will be permitted. The Contractor, at his option, may submit alternative plans of extensions for consideration by the Engineer.

(c) Steel piles, pipes, and shells.-If the ordered length of a steel pile, pipe, or shell is insufficient to obtain the specified bearing value, an extension of the same cross section shall be spliced to it. Unless otherwise shown on the plans, splices shall be made by butt-welding the entire cross section using the electric arc method when available. Buttwelded surfaces shall preferably be flat or concave. Reinforcement on the welds exceeding 1/16 inch in thickness shall be ground off.

600A.12 Pile Bents. Piles for any one bent shall be carefully selected as to size, to avoid undue bending or distortion of the sway bracing. However, care shall be exercised in the distribution of piles of various sizes to obtain uniform strength and rigidity in the bents of any given structure.

Cut-offs shall be made accurately to insure full bearing between the caps and piles of bents.

600A.13 Driving Piles. All piles shall be driven as shown on the plans or as ordered in writing by the Engineer. They shall be driven within an allowed variation of 4 inch per foot of pile length from the vertical or batter shown on the plans. The maximum allowable variation at the butt end of the pile shall be 3 inches in any direction from the location shown on the plans or as directed by the Engineer.

When water jets are used, the number of jets and the nozzle volume and pressure shall be sufficient to freely erode the material adjacent to the piling. The plant shall have sufficient capacity to deliver at all times a pressure equivalent to at least 100 pounds per square inch at two 4-inch jet nozzles. Unless otherwise indicated, jets shall be cut off before the required penetration is reached and the piles shall be driven by hammers to final penetration.

Except when the pile head is fitted into a steel head block, every timber pile shall be provided with a metal collar or wire wrapping. When the nature of driving is such that piles may be unduly injured, the heads of all piles shall be protected by caps of approved design, preferably having a rope or other suitable cushion next to the pile head and fitting into a casting which in turn supports a timber shock block.

For special types of piling, driving heads, mandrels, or other devices in accordance with the manufacturers' recommendations shall be provided so that the pile may be driven without injury.

For steel piling the heads shall be cut squarely and a driving cap shall be provided to hold the axis of the pile in line with the axis of the hammer. Where shown on the plans, steel piles shall be capped with steel plates or other acceptable devices.

Full-length piles shall be used where practicable. In exceptional circumstances, the splicing of piles may be permitted. The method of splicing shall be in accordance with the provisions of subsection 600A.11.

Metal shoes of the design shown on the plans shall be used as indicated on the plans or ordered in writing.

Piles may be driven with steam, air, gravity, or diesel hammers, or a combination of hammers with water jets. When diesel hammers or any other types requiring calibration are used, they shall be calibrated with load tests in accordance with the requirements of subsection 600A.03.

Vibratory or other pile driving methods may be used whenever permitted by special provisions.

The plant and equipment furnished for steam and air hammers shall have sufficient capacity to maintain, under working conditions, the pressure at the hammer specified by the manufacturer. The boiler or tank shall be equipped with an accurate pressure gage, and another gage shall be supplied at the hammer intake to determine the drop in pressure between the gages.

Any gravity hammer permitted shall weigh not less than the combined weight of the driving head and pile and not less than 3,000 pounds. The fall should be regulated so as to avoid injury to the pile and in no case shall exceed 15 feet for

timber and steel piles. When gravity hammers are permitted for driving concrete piles, the drop of the hammer shall not exceed 8 feet.

Pile hammers, except drop hammers, shall be approved steam, air or diesel hammers that develop sufficient energy to drive the piles at a penetration rate of not less than % inch per blow at the required bearing value. When steam, air or diesel hammers are used, the total energy developed by the hammer shall be not less than 7,000 foot pounds per blow, except as specified below for concrete piles.

Diesel hammers shall be operated with wide open throttles when blows are being counted for determination of penetration to use in the safe load formula, except that in the case of diesel hammers with enclosed rams, the throttle settings shall be just short of the settings that would cause nonstriking parts of the hammers to rise off the piles as the ram-piston travels upward.

Piles shall be supported in line and position with leads while being driven. Pile driver leads shall be constructed in such a manner as to afford freedom of movement of the hammer, and they shall be held in position by guys or steel braces to insure rigid lateral support to the pile during driving. Except where piles are driven through water, the leads in general shall be of sufficient length to make the use of a follower unnecessary, and shall be so designed as to permit proper placing of batter piles. The driving of piling with followers shall be avoided if practicable and shall be done only under written permission from the Engineer.

Steam, diesel, or air hammers used for driving concrete piles shall develop an energy per blow at each full stroke of the piston of not less than 3,500 foot-pounds per cubic yard of concrete in the pile driven. No driving of piles shall be done within 20 feet of concrete less than 7 days old.

600A.14 Defective Piles. The method used in driving piles shall not subject them to excessive and undue abuse producing crushing and spalling of concrete, injurious splitting, splintering, and brooming of the wood, or deformation of the steel. Manipulation of piles to force them into proper position, if considered by the Enigneer to be excessive, will not be permitted. Any pile damaged in driving by reason of internal defects, or by improper driving, or driven out of its proper location, or driven below the elevation fixed by the plans or by the Engineer shall be corrected by the Contractor without added compensation by one of the following methods approved by the Engineer for the pile in question:

(1) The pile shall be withdrawn and replaced by a new and, when necessary, longer pile.

(2) A second pile shall be driven adjacent to the defective pile.

(3) The pile shall be spliced or built up as otherwise provided herein or a sufficient portion of the footing extended to properly embed the pile. Timber piles shall not be spliced without specific permission of the Engineer. All piles pushed up by the driving of adjacent piles or by any other cause shall be driven down again.

A concrete pile will be considered defective if it has a visible crack, or cracks, extending around the entire periphery of the pile, or any defect which, as determined by the Engineer, affects the strength or life of the pile.

600A.15 Cutting Off and Capping Piles. Tops of foundation piles shall be embedded in the concrete footing at least 1 foot except where seals of concrete deposited in water are used piles shall project at least 6 inches above the top of the seal concrete. Piles shall be cut off level at the elevation indicated on the plans. The length of pile cut-off shall be sufficient to permit the removal of all injured material. The distance from the side of any pile to the nearest edge of the footing shall be a minimum of 9 inches. When the cut-off elevation for a precast concrete pile or for the steel shell or concrete casing for a cast-in-place concrete pile is below the elevation of the bottom of the cap, the pile shall be built up from the butt of the pile to the elevation of the bottom of the cap by means of a reinforced concrete extension constructed as shown on the plans. Steel shells or concrete casings for cast-in-place concrete piles shall be cut off at the designated elevation before being filled with concrete.

Cut-offs of steel bearing piles shall be made at right angles to the axis of the pile. The cuts shall be made in clean, straight lines.

Unless otherwise specified, pile cut-off lengths shall become the property of the Contractor and shall be disposed of beyond Government property limits and outside the limits of view from the roadway.

600A.16 Protecting Untreated Timber Trestle Piles. The heads of untreated piles shall be given one of the following treatments, type A being used unless otherwise provided on the plans or in the special provisions:

Type A treatment.-The sawed surface shall be heavily coated with red lead paint, after which it shall be covered with cotton duck of at least 8-ounce weight, which shall be folded down over the sides of the pile and firmly secured thereto with largeheaded roofing nails. The edges of the duck shall be trimmed to give a neat appearance. The duck shall then be waterproofed by being thoroughly saturated and coated with one or more applications of red lead paint.