Civil Engineering Association

In-situ penetration tests have been widely used in geotechnical and foundation engineering for site investigation in support of analysis and design. The standard penetration test (SPT) and the cone penetration test (CPT) are two typical in-situ penetration tests. The dynamic cone penetration test shows features of both the CPT and the SPT. The DCPT is similar to the SPT in test. It is performed by dropping a hammer from a certain fall height and measuring a penetration depth per blow for each tested depth. The shape of the dynamic cone is similar to that of the penetrometer used in the CPT. In road construction, there is a need to assess the adequacy of the subgrade to behave satisfactorily beneath a pavement. A recently completed Joint Transportation Research Program project showed that the DCPT can be used to evaluate the mechanical properties of compacted subgrade soils. In the present implementation project, the application of the DCPT is further investigated.

Present practice in determining the adequacy of a compacted subgrade is to determine the dry density and water content by the sand-cone method or with a nuclear gauge. However, the use of the resilient modulus (Mr) has become mandatory for pavement design. To find the Mr, a time consuming testing procedure is required which demands significant effort. Therefore a faster and easier alternative for compaction control in road construction practice is desired. To this end, the present project aimed to take a first step in the generation of data to create appropriate correlations among subgrade parameters and DCPT results.

The present research project consists of field testing, laboratory testing, and analysis of the results. The field testing includes the DCPT and nuclear gauge tests. In the planning stage, several road construction sites were selected for the field testing. For the selected road construction sites, both the DCPT and nuclear tests were performed at the same location, allowing a comparison between DCPT and nuclear test results. Soil samples for the selected project sites were also obtained for the laboratory testing program.