Compacted high-gravel-content subgrade materials

Gravelly subgrade materials are frequently evaluated on the basis of laboratory testing on material passing the number 4 sieve size due to difficulties in obtaining representative samples and because laboratory testing of soils containing rock is more difficult or expensive. When the large aggregate is not considered in the evaluation process, it is quite possible to discard a material as being inappropriate as subgrade material when in fact it may be quite suitable. For example, the presence of rock or gravel materials may have an ameliorating effect for clayey soils having potential for expansion upon wetting. The effect of large aggregate on the moisture sensitivity of subgrade materials are reviewed. It is more difficult to establish field specifications and to conduct field inspections for compaction of subgrades containing large aggregate. The potential pitfalls in obtaining the desired relative compaction in the field are discussed. The various comonly used techniques in writing field specifications for compaction of materials containing rock or gravel are reviewed.