Vibratory hammer compaction of granular materials

[摘要] ENGLISH ABSTRACT: Compaction is one of the key processes in the construction of road pavement layers. Not onlyis it significant in ensuring the structural integrity of the material in the road layers, but it alsohas an influence on the engineering properties and performance of the soil material. A poorlycompacted material is characterised by low density, high porosity and below standard shearstrength. This, as a result causes rutting, moisture susceptibility, potholing, corrugations andpassability problems on the road. Therefore, it is vitally important that field compaction isdone correctly. For this reason, laboratory compaction methods have been developed tosimulate the field compaction process in the laboratory.The Mod AASHTO test has long been used as the laboratory compaction method of choiceby virtue of its simplicity and the lack of bulky equipment required. However, previousstudies have established that the Modified AASHTO method does not adequately simulatefield compaction criteria especially for cohesionless materials. Two reasons have beenadvanced;The Mod AASHTO compaction method does not adequately simulate the compactiondone in the field when the granular mix is laid;The compaction method may cause disintegration of the material.Alternative tests have been considered and much research has focused upon the use of amodified demolition hammer (vibratory hammer) for laboratory compaction of granularmaterials.This study undertook to evaluate the influence of test factors pertinent to the vibratoryhammer compaction method. The influence of these test factors on compaction time andobtainable material density was assessed with the objective of developing a compactionmethod for granular materials. Vibratory hammer compaction tests were conducted on G3hornfels, G4 hornfels and G7 sandstone material types and to a lesser extent, reclaimedasphalt (RA). Densities obtained were referenced to Mod AASHTO compaction density.Findings of the study showed that, the mass of the tamping foot has a significant influence onthe obtainable compaction density. Other factors such as, moisture content, frequency andframe rigidity were also found to affect compaction with the vibratory hammer. In addition, itis shown that the surcharge load does not significantly influence the obtainable compaction density but does contribute to the confinement of the material and restricts the upward bounceof the hammer.On the basis of the results and findings, a compaction method was proposed, incorporatingtest parameters and factors that would provide ideal results for a set compaction time.Repeatability tests showed that, the developed vibratory hammer compaction method waseffective in compacting graded crushed stone material types (i.e. G3 and G4) and probablyRA. The test was not as effective on the G7 material. Further studies on this material (G7) arerequired.In addition to the previous testing regime, a comparative assessment of the developedvibratory hammer compaction method in relation to the vibratory table method was done. Theresults show that the vibratory hammer is capable of producing specimens of densitiescomparable to those of the vibratory table.A sieve analysis undertaken before and after compaction showed that compaction with thedeveloped vibratory hammer compaction method does not result in any significant materialdisintegration.Based on the results of this study, a specification for the determination of maximum drydensity and optimum moisture content of granular material using the vibratory hammer isrecommended.

[发布机构] Stellenbosch University