Testing Technology

LEADING THE WAY

WITH RTK-GPS TECHNOLOGY

The Question often arises: Just how accurate is Drainage installation done with the modern “Tile­plow” (Trenchless Plough)? After such a discus­sion at a recent contractor’s meeting in the USA Dr Jim Fouss (Ph.D P.E, (well respected, retired re­search engineer at Ohio State University and USDA) did a study to determine the actual accura­cy of drainage installation by modern “Tileplow” (Trenchless Plough), equipped with RTK-GPS. 

First, they would develop a process to identify the potential differences between elevations recorded based on the cutting blade position of the drain plow and the position where the pipe is in-stalled.Secondly, they would locus on the devia­tions between the RTK-GPS drainage system design data and the RTK-GPS data recorded during installation. 

DIGGING INTO THE DETAILS

Most drainage ploughs are fitted with two RTK-GPS receivers: one on the tractor for steer¬ing and one above the cutting-edge of the plough blade for grade control. The general idea is that the blade will act as a rudder, pitching up and down into the soil to cut a trench bottom at the correct elevation while this is taking place three other things are happening.

A groover forms the appropriate trench bottom for the pipe type and size that is being installed. 

A ramp or angle lifts and grates the soil to create finely milled initial backfill. 

The pipe boot floats behind the plow blade in order to lay the pipe in the desired location at the bottom-centre of the grooved trench. 

The design and especially that of the boot differs quite a bit between ploughs. For one the freedom of movement between the boot and the blade is crucial as It allows the boot to stay in place on the bottom of the ploughed-trench as the blade articulates during grading. Configuration and shape of the boot are critical to correct installation.

Fouss and Clark questioned: Is the back of the boot always on the bottom of the trench? Is the trench bottom always at the same elevation as the plough blade was when It made the trench-bottom cut In front of the blade?

In order to answer these questions, they deployed a third RTK-GPS receiver mounted directly above the pipe chute on the pipe boot. They recorded real time RTK-GPS data during installation on drains for the cutting blade position and the pipe chute position and then graphed and subjected the data to statisti¬cal analysis in order to evaluate the significance of any deviations between the blade and boot eleva¬tions.

SAMPLE DATA

FIGURE 1

Here we can see the drain Installation accuracy on a scale of hundredths of a foot. This signifies exceptionally accurate and precise RTK-GPS sensing equipment, coupled with extremely pre­cise machine control, grading and boot place­ment. 

FIGURE 2

Here we can see the plough blade and boot posi­tion data for a segment of changing grade drain Installation. The graph shows the elevation of the pipe boot and plough blade for a number of posi­tions along the drain line to be very precisely In synch. 

ASSESSING THE DATA

In conclusion, after data collection and analysis, Fouss and Clark were amazed and pleased with the con­sistency and the accuracy of the RTK-GPS equipment, as well as the precision and ability of the plough boot to maintain an appropriate location at the bottom of the cut and formed trench during pipe. 

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