An Experimental Study on the Estimation of Field Compaction States and Stress-Strain Properties of Unbound Granular Materials from Laboratory Test Results

Field fill materials often contain gravel particles larger than the allowable limit for standard laboratory compaction tests. In such cases, the maximum dry density (ρd)max of a material containing large gravels is obtained by correcting laboratory test results for specimens without large gravels. Usually, the Walker–Holtz (WH) method is used for this correction, but there are many materials whose gravel ratio (P) is 0.3 − 0.4, which is usually considered to be the application limit. Moreover, accurate stress-strain properties under field compaction conditions are necessary for relevant stability analysis of soil structures including embankments. However, with unbound granular materials, it is difficult to obtain undisturbed samples for laboratory tests or to carry out field shear tests. Also, large-scale triaxial compression tests on specimens containing large gravels are difficult to perform in ordinary engineering practices. In this study, a series of laboratory compaction tests were performed changing the maximum particle size (Dmax), compaction energy level (CEL) and P to examine the validity of the WH method and a series of drained triaxial compression tests were performed varying the Dmax and the degree of compaction. Based on the test results, a method to modify the WH method is proposed to properly estimate the (ρd)max value after adding or removing gravel particles when compacted at a certain CEL. Also, a method is proposed to correct the strength for a given gravel ratio to estimate the in-situ strength from the strength obtained from laboratory tests.