Abstract

Abstract

Compaction of Soil by Repeated Loading

Rouzbeh Roudgari

Construction of roads is usually made by stripping the top soil (600 to 1000 mm), which often contains organic materials, and replacing it with a layer of subgrade material (crushed stones, well-graded sand). One of the main design requirements is that the subgrade material must be compacted up to a minimum of 95% of the Proctor maximum dry density, as determined from laboratory test results (AASHTO T99). This requirement is usually specified as a norm in any contract document involving field compaction.
Soils can be compacted by repeated, systematic application of high energy using hammer. The imparted energy is transmitted from the ground surface to the deeper soil layer by propagating shear and compression waves types, which force the soil particles into a denser state (R. Massarsch, 1999)
Research in this field has been directed to establish relationships between the water content, the dry density and the compacting effort, the type of soils which allow a higher level of compaction, and to develop field equipment and techniques which would be more effective in performing field compaction. Nevertheless, there are reports to confirm that achieving 95 % of the Proctor maximum dry density in the field compaction is impossible in some cases. The role of the surrounding soils, in particular the underlying layer, in determining the level of compaction, is a paramount parameter in achieving high level of compaction.

This thesis presents a plane-strain numerical model using PLAXIS computer software to simulate shallow compaction of a subgrade layer underlain by a deep deposit of various stiffness levels. The compaction effort is applied by means of repeated loading on the ground and modeled as a static load applied to the soil through a rigid plate having similar properties of roller material. Based on the results obtained in this study, it can be stated that the level of compaction achieved in the field depends on the thickness of the subgrade layer, stiffness of the lower layer, the number of load cycles, and the magnitude of the load applied.
The results of this study are presented in the form of compression curves of the subgrade and lower layer, and accordingly, the level of compaction for a given soil/load/geometry conditions can be predicted. Design guidelines are presented for practitioners.