Contractor at Work
By James L. Fouss Ph.D. P.E.
Accountability for depth and grade-control accuracy
By James L. Fouss Ph.D. P.E.
Since the mid-1970s, the province of Ontario has had a plow testing and certification program and is currently updating the program. With the significant increase in plow-installed subsurface drainage over the last several years in both the U.S. and Canada, it seems that it is time that a drainage plow testing and certification program be considered for development in the United States. Corrugated plastic (HDPE) subsurface drain tubing installed with plow-type equipment has increased dramatically since the early 1970s, in both Canada and the United States. All of the early drainage plows were equipped with laser-based automatic depth and grade-control systems. Older systems have now been upgraded on many plows, and some trenchers, with the modern satellite-based 3-D GPS depth and grade-control system.
More recently, innovative designs for self-contained drainage plows have become available and their acceptance by contractors has significantly increased in the U.S. and Canada. Most of the modern plows are very powerful and capable of operating at greater depths, and can install drainage pipe faster than earlier plows. However, current regulations in Canada do not set limits on the maximum speed the plows should be operated at in order to ensure drain tubes are installed accurately at design depth and grade. Although the U.S. has current subsurface drainage design and installation specifications and standards though the American Society of Agricultural and Biological Engineers, the American Society of Civil Engineers, and the Natural Resources Conservation Service of the United States Department of Agriculture, there are no drainage plow performance regulations in place in the U.S.
Ontario’s program is based on specifications and standards stated in the Agricultural Tile Drainage Installation Act originally passed in 1973. The act includes a provision for training and licensing of drainage contractors that is administered by the Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs. A similar testing and certification program is not available in the United States.
The advanced features provided by the GPS-RTK systems, including automatic steering of the plow or trencher, should be considered and included in the plow-testing standard. The GPS-RTK system now available may allow higher ground speeds with modern plows, if the machine hydraulics responds quickly enough to the control system feedback signals at the higher speeds to maintain design drain depth and grade. Mounting a second satellite GPS-RTK receiver directly above the drainage tube feeder boot attached to the plow blade may provide the enhanced accuracy needed to establish guidelines for a plow-testing program. The second receiver would monitor and record the GPS co-ordinates (X, Y, and Z-h, where “h” is the height at which the second receiver is mounted above the bottom of the tube feeder boot) at the bottom of the drain tube as it emerges from the tube feeder boot and is installed in the soil channel created by the plow. The co-ordinate data recorded by the second receiver would more accurately define the final X, Y, and Z-h locations along the line of the installed drain tube than a recording of co-ordinates from the controlling receiver mounted on a forward reaching cantilever arm attached to the plow blade. For advanced drainage plows, the Z-h data versus ground travel could be displayed graphically to the plow operator, along with other performance information.
Without regulated programs, it is the contractor’s responsibility to find solutions ensuring accuracy and quality of installation.