Compacted Fill

Abstract

As a construction material soil has been used since antiq- uity with both success and failure. The widespread avail- ability and relative economy of earth material continue to make it attractive for use in foundations, embankments, and as backfill. It has long been recognized, first empiri- cally and then scientifically, that compaction changes the physical properties of soils-in some cases tremendously. For example, a properly compacted, well-graded gravel may be 15 times as resistant to deformation under a bearing load than the same material in the loose state. To be used effectively, compaction must be tailored to the soil type, moisture condition, and subsequent environ· ment of the compacted product. Thus the ability of the engineer or job superintendent to identify the soil type accurately takes on prime importance. Wasted effort, such as that in attempting to compact clean sands with sheeps· foot rollers, Can result from inattention to the recognition of soil type. The fallacy of making twice as many passes of the roller in an attempt to compensate for overly thick layM ers or overly wet soil can be avoided by an understanding of the compaction process in cohesive soils. In section 7.2 the elements of soil compaction for coheH sive and noncohesive soils are discussed, their respective compaction characteristics are described, and the effect of compaction on soil physical properties important in engiM neered construction is explained. In section 7.3 we discuss the various types of compaction equipment and indicate what to expect from their use with different soil types. The procedures by which quality control of compaction can be achieved are covered in section 7.4. Miscellaneous problems of compacted fills such as expansive clays, frost action, and slopes are treated in section 7.5.