Introduction. The introduction to the paper highlights the methods of standard geotechnical tests for in situ measurements of subgrade strength or strength estimation.
Problem statement. The issue of the paper concerns the interpretation and the application of the results of testing of the subgrades or granular layers of a road pavement by the dynamic cone penetrometer.
Purpose. The goal of the paper consists of the analysis of practices of the subgrade strength evaluation by the conversion of the dynamic cone penetration test (DCPT) results to the nominal values of the California bearing ratio (CBR) or by plotting the subgrade profile and also of practices for the layer thickness evaluation and compaction control.
Results. The main principles of DCPT were reviewed with performing the analysis of factors affecting the test results. The equations of the dependence of the nominal CBR values on the penetration index as the main result of DCPT was analyzed. The assumption was made that the difference in such equations may be determined by the differed confinement conditions under testing in accordance with which the calculated values provided by the results of testing under the triaxial confinement are higher. Also the stair-stepping effect appeared when performing DCPT on cohesive soils was reviewed.
The main provisions relating the evaluation of thickness and the control of compaction for subgrades and the road pavement granular layers after the results of DCPT were reviewed as well.
Conclusions. It was concluded that as the critical affecting factor of DCPT the conditions of the confinement should be recognized which depend on the presence of a paved surface on the location and which, in case of its absence, should be characterized as the conditions of partial confinement, under which false increasing of the estimate values of the subgrade strength may be obtained due to the entering of a cone penetrometer in a subsurface layer.
It was pointed out that in case of testing during the design stage the DCPT results are applied mainly to accept the representative values of the subgrade strength as the CBR values in the recognized interval of (75 – 85) % of a nominal value. During the road pavement survey the DCPT results are applied for the identification of weak areas of an object by plotting the subgrade profiles.
