Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1967. Department of Agricultural Engineering.
The objectives of this investigation concerning the use of open end drain tile on steep slopes were:
To determine the effect of misalignment and velocity on pressures in a two dimensional model tile line.
To predict the mechanisms of failure in open end tile lines flowing full on steep slopes.
An analysis of the pressure data showed that negative pressures were statistically influenced by misalignment, but not by velocity. Positive pressures in the test joint were significantly dependent on both velocity and misalignment.A velocity times misalignment interaction was significant for all piezometers in the test section.
A general prediction of pressure trends within the test joint on the basis of joint geometry and the principles of fluid mechanics was accurate.Pressure trends could be predicted for joint geometries other than the one of this investigation, using these same principles.
The development of negative pressures for the joint geometry studied was dependent on full pipe flow.Observations on the tile model using soil above and below the test section indicated that full pipe flow is not likely to develop in a tile line.This is because of the flow separation occurring at misaligned joints, and because of the ease of air entry through the soil at these points.Full pipe flow would be possible only for a highly cohesive, saturated soil, and a high head on the tile line.
Observations on the two dimensional model, coupled with the study of pressures within the misaligned joint indicated that several theoretically possible failure mechanisms are not likely to develop in a field installation.These are:
eddying action erosion at the joints,
circumferential flow erosion within a joint,
“blowouts” to the ground surface, and
negative pressures drawing soil into the line.
The failure mechanisms most likely to occur in a tile line with misalignments are:
piping erosion from one joint to another along the bottom of the tile section
jetting action at the joints where misalignment occurs, and
full pipe flow forcing water out at the joints as a result of extremely high heads or a restricted outlet.
Advisor:H. D. Wittmuss