Effect of slip, spacing and moisture content on lug forces in Bangkok clay soil

This study was conducted to investigate the effect of low slip, lug spacing and moisture content on forces producted by cage wheel lugs. Experiments were conducted in a laboratory soil bin having Bangkok clay soil to measure the forces under model cage wheel lugs. A special transducers were fabricated to measure the soil perpendicular and radial reactions on the lugs. The slips were varied from 5 %, 10 %, 15 %, 20 % to 25 %. The force measurements on both lugs were done at 6.3 %, 27.4 % and 50.9 % soil moisture content. The lug spacings were varied to 20 and 30 and 40 deg. The measured perpendicular and radial forces were converted to lug pull and lift forces. The perpendicular and radial as well as pull and lift forces acting on the first lug were higher than the forces on the second lug. The perpendicular, pull and lift forces increased after lug entry into the soil and after attaining a certain peak value they decreased and obtained a zero value at lug exit. The radial force increased initially as lug enter the soil and after attaining a positive peak value it decreased continuously attaining a negative peak and then become zero at lug exit. The radial force was much smaller than the perpendicular but calculated lift force was higher than pull force. The increase of the slip up to 25 % caused increase in lug forces on both lugs. The increase in the soil moisture content from 6.3 % to 27.4 % caused increase in lug forces on both lugs but further increase in moisture content to 50.9 % decreased the lug forces. The lug spacing did not show any effect on the first lug forces, but it showed significant effect on the second lug forces. The increase in lug spacing increased lug forces at all slips and moisture contents. The ratio of forces produced under the second lug to the forces under the first lug decreased as the lug slip increased. Increase in lug slip also increased the lug forces at any given spacing and moisture content. The pull and lift forces under multiple lugs were predicted and it was found that these forces vary in cyclic nature. The variation of the output forces can be reduced significantly by using inclined lugs. At the same lug spacing, slip and soil moisture contents, the variation of lift can be reduced by 40 %, the variation of pull can be reduced by 240 %.