EFFECT OF TINE RAKE ANGLE AND ASPECT RATIO ON SOIL FAILURE PATTERNS IN DRY LOAM SOIL

Studies were conducted in a laboratory glass-sided soil bin with dry c ompact loam soil (c = 0.02 kPa, phi = 20 degrees and cone index 210 kP a) with the specific objective of observing the effect of flat tine ra ke angle and aspect ratio on soil failure patterns. The tine was moved in the soil in a quasi-static condition and soil failure patterns wer e observed through a glass window. Tine rake angles of 50 degrees, 90 degrees and 130 degrees were used while aspect ratio effects were stud ied by varying both width and depth of the tine. Individual effects of width and depth were investigated by maintaining a constant aspect ra tio of 2.0 but varying width and depth. Results obtained indicated tha t soil failure patterns are affected by tine design parameters. Soil f ailure patterns were observed to be of progressive shear type in all c ases. For 50 degrees rake angle tines, the patterns consisted of incli ned shear lines starting from the tine tip and gradually moving upward s towards the horizontal soil surface, intersecting it at an average f ailure angle of 32 degrees. In the case of 90 degrees rake angle tines , the inclined shear surface was at a distance from the tine tip where as, for 130 degrees rake angle tines, prismatic-shaped stationary soil wedges were formed adjacent to the tine. Failure angles for the 90 de grees and 130 degrees rake angle tines were almost the same as those f or 50 degrees rake angle tines. The results of this study also indicat ed that aspect ratio alone cannot account for changes in soil failure patterns, their corresponding soil reactions, forward rupture or surch arge profiles. The effects are mainly due to the individual changes in width and depth. There were no distinct zones as described in the pas sive soil pressure theory. Soil failures were in regular cycles result ing in corresponding Variations in the soil reactions on the tines. (C ) 1997 ISTVS.