PADFOOT ROLLERS WITH AND WITHOUT VIBRATION:

Conventional single drum rollers with pad foot drum in weight range from 6 to 25t are used for the compaction of cohesive soils, stony mixed soils and solid rock of variable strength. They have proved worthwhile because of their implicational versatility and their compaction performance.

               The drums are normally fitted with 100mm trapezoidal pad foot elements (studs) with flat side faces and scrapers for cleaning. In connection with the vibration these studs produce a kneading and pushing effect, which leads to the reduction of air void volume and to a pulverisation of lumps and rock fragments. Due to the shape of the pad feet the contact surface increases with the penetration depth. The compaction effect adapts to the stiffness of the soil to be compacted via the penetration depth of the studs. The compaction effect depends substantially on the areal pressure of the ground contact area. Foot shape and covering rate of the studs on the drum shell have a tremendous effect. This effect is enforced by the increase of pad foot pressure, the increase of the clay proportion and the reduction of the water content in the soil.

               On clayey soil these pad foot rollers compact most effectively at water contents below the optimum, whereby this influence of the water content diminishes with increasing silt and sand fractions in the soil. The compaction effect increases strongly with the number of passes, but also in this case this influence is reduced by rising water content.

               The number of required passes is also influenced by the degree of coverage the pad foot elements. The more clayey and less moist the soil, the higher the compaction that can be achieved with increasing pad foot pressure. Compaction is even possible at a high water content, as long as the pad foot elements have a kneading effect and do not sink in completely. The surface structure that changes strongly with the water content. The thickness of the loose soil ripped up by the profile of the drum is reduced with dropping water content, whereby small or tapered pad feet generally have a higher loosening effect than large area pad feet. Raising the rolling speed results in a sub linear increase in the number of rolled passes.