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nited States contractors engaged in doing similarwork will be interested in a continuous slip-form-ing rig which Au s t ralian engineers have deve l-oped for lining irrigation channels. Named from

the front of the unit backwards, the slip-form is made up ofa skid pan, a partitioned hopper, a vibrating pad and a floatpad and pressure blade.

Riding on the subgrade, the skid pan virtually steers theform. Its length is important as it affects the distribution ofthe weight of the form and the way the curves are negotiat-ed. Partitioned into eight compartments, the hopper makespossible the even distribution of the concre t e, a head ofc o n c rete above the feed being a necessary feature of theslip-form design.

The vibrating section consists of a quadrant of 4 inchesradius along which the vibrators (either 6 or 8) are spaced.To avoid the dissipation of vibration to the stru c t ure as a

whole, and particularly to the float pan and pressure plate,the vibrating pad is insulated from adjoining sections byrubber packing.

For the successful operation of the float pan and pressureplate it is essential for the form to travel exactly parallel tothe bed. The pressure plate is adjustable by means of turn-buckles.

Initial earthworks involved the construction of the com-pacted banks and the completion of all lead by excavatingwith a dozer and scoop to a depth determined by the scoopwidth. This was followed by the excavation of the remaining

section of channel and trimming of the channel section bya Briscoe ditcher towed by two tractors. Later the spoil wasspread evenly over the banks on either side.

Hand trimming is essential in the sections of channel to

be concrete lined. It is important that this work be kept suf-ficiently ahead of the slipform to permit the latters unin-terrupted operation, but not so far ahead as to make the ex-c a vation subject to storm damage. Because the slip-formrides on the excavation, line and level must be closely con-trolled during excavation.

For best results with the continuous slip-form, concretewith a water/cement ratio of about 0.65 is used, with a sandcontent of approximately 45 percent and a slump of 112inches to 2 inches. A cement content of five bags per cubicyard is considered adequate.

The slip-form is advanced by means of a winch mountedon an anchoring device which automatically digs into the

ground when the pull is applied. About 300 feet of travel ispossible before the anchor must be shifted.Moving at an average speed of 20 inches per minute, the

Australians best 8-hour day output with this slip-form hasbeen 780 linear feet of channel having 1,360 square yardsof surf ac e. Average daily pro g ress is just under 500 linearfe et.

Continuous sl ip-for mfor ir r igation channels

Irrigation channel in Australia is lined with concrete by slip-form unit developed by Australian engineers. An average of 500linear feet of channel can be placed in a day. Best 8-hour day performance has been 780 feet.

PUBLICATION #C610281

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