Abstract:
The use of the trenchless plough drainage implement has increased in the
past few years due to its efficiency and cost advantages over other
methods. However, the performance of these machines when working in fields
with irregular soil conditions is not yet satisfactory. It is important
therefore to study the soil parameters and conditions which could affect
the implement behaviour under these circumstances.
Therefore, a detailed investigation of the soil reaction forces acting
upon a scale model of the trenchless plough was conducted under
controlled conditions in a soil laboratory. The model was tested first
under restricted conditions of movement, in order to observe and determine
all the possible soil reaction forces.
The tine, due to its geometric characteristics, was classified as a very
narrow tine, and an existing model to predict the soil reaction force
acting on the front face of these tines was extended to predict the forces
on the sides. Since the length of the failure plane ahead of the tine is
often required in the investigation of the soil reaction forces, a
mathematical solution based on the Coulomb principle of Passive Earth
Pressure was presented to estimate the soil failure pattern. There was
good agreement between the values of the angle of the shear plane
predicted by this method and the experimental data obtained from the
glass sided tank tests.
Dynamic tests were conducted with the implement assembled with a long
floating beam arrangement assisted by a small link (free-link), used
between the hitch-point and the pivoted end of the beam. These tests
revealed that, when working over irregular soil conditions a better grade
control can be obtained if the hitch-point is kept at constant level in
reference to a desired line. In the case where field irregularities
persist for long (step inputs), corrections in the hitch-point height
might be necessary. These tests show that the implement depth changes in
different proportion in relation to the hitch-point height. Where no
control is imposed on the hitch-point, the path of the implement is
attenuated in relation to the hitch-point position, where better results
are obtained for high frequency of the hitch-point.
A mathematical solution based on these findings and on the dynamic balance
of the forces acting on the system was presented. Since it is an
interactive method and requires long and repetitive calculations, a
computer programme was developed and used to predict the response of the
implement under these uneven conditions. Good agreement between data and
estimated values suggested that the method is acceptable.