Vibratory surface compaction

Various types of equipment are available single-drum vibratory rollers, towed single-drum vibratory rollers, vibratory tandem rollers, hand-held tampers and vibratory plate compactors. Most of the vibratory rollers have a smooth drum and are suitable for granular material only. Vibratory rollers have weights that typically range between 4 and 25 tonnes and generally move at speeds not exceeding 6 km/hr. 

The influence depth of vibratory rollers is limited and varies between 0.30 m and 0.80 m, depending on the type of soil to be compacted and the equipment used. In practice vibratory rollers are only used for fill layers of limited thickness. However, discharge capacities of modem dredgers result in layer thicknesses not less than 2-3 m. This implies that the use of vibratory rollers is limited to the uppermost layer only. 

Depth compaction trials with the polygonal drum roller (Weingart et al, 2003) indicated an increase of density to a degree of compaction of 95% MDD at a depth of more than 1.30 to 1.50 m. Compaction performance was reported as 500-1500 m /hr. As a result of the special drum shape, the roller is suitable for granular, mixed and cohesive soils. 

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Rollers, compactors, and vibratory compactors. Compacting material, whether soil below the road surface or the road surface itself, was quickly seen as important. Basic rollers used only their weight. Later compactors often have complex feet designed into the roller. Finally, modem compactors vibrate to give up to double the level of compaction, depending on soil characteristics (Wixom, 1975 148). 

Field procedures to decrease the void volume include static and dynamic compaction, pile driving and the use of surface and deep vibratory equipment. Explosives have also been used for this purpose. 

Vibrating rollers are widely used in all asphalt compaction works because they are very versatile and effective, especially when thick mats are to be compacted. They consist of two smooth-surface steel drums equipped with a vibratory system. They compact through a combination of static and dynamic loading. Modern vibrating rollers are capable of varying both frequency and amplitude. Figure 8.17 shows a double-drum vibrating roller. 

Roller-compacted concrete is developed and extensively applied to construct concrete dams in Japan. In order to control the consistency of fresh concrete, the VC test is carried out. The test is illustrated in Fig. 10.1. Fresh concrete after mixed is placed in the mold on the vibratory table, which vibrates vertically with 1mm stroke and 10 gal acceleration. The surcharge weight is 20 kg. During the vibration, time is measured by second, which is named VC value , until breeding water is observed at the surface of the mold. 

Densify the loose, liquefiable soil layer. Stone column is often satisfactory if the loose layer is mostly sand. Other approaches, such as jet grouting, deep soil mixing with cementing agents and in situ vibratory densification can all be used. If the liquefiable soil layer is close to the ground surface, a complete excavation and replacement with compacted engineering fill is sometimes also feasible. 

Vibratory tamper method a rigid steel plate (tamper) attached to a vibrator at the surface of the ground to compact the surface soil. 

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