Use of CPT for design, monitoring, and performance verification of compaction projects

Soil compaction projects can potentially offer significant savings in terms of cost and time. However, they require the active participation of the geotechnical engineer throughout the project. An important requirement of many compaction projects is to control total and differential settlement. The definition of project- specific compaction criteria is a key task, the importance of which is not often recognized. A reliable and transparent method of calculating settlement in granular soils is the tangent modulus method. By assessing soil compressibility prior to the compaction work it is possible to determine whether, and to which degree, soil compaction will be required. A method is presented by which the modulus number can be determined from CPT results adjusted for mean confining stress. The compactability of soils can be assessed, based on the cone stress and sleeve friction records. An important aspect of soil compaction is the increase in horizontal stress, which results from the compaction-induced overconsolidation of the soil. A method is described which makes it possible to take this preconsolidation effect into account. The proposed concepts are illustrated by examples.