Novel method to estimate the stiffness of compacted granular geomaterials

Transport infrastructure involves the use of large volumes of compacted geomaterials, leading to significant economic and environmental impacts that need to be addressed in all stages of the project. A new laboratory procedure to estimate the stiffness of embankments, subgrades, granular bases and subbases is proposed. The utilization of well-established and simple equipment results in an easy-to-conduct and cost-effective method that combines the compaction procedure of a Modified Proctor test with the loading scheme of a repetitive static plate load test, adapted to the reduced geometry of this new ‘miniature plate load test’ (mPLT). This enables the estimation of the compaction characteristics and the vertical strain modulus in a single test. Subsequently, the elastic modulus needed for analytical design is derived through back-calculation using a numerical model. Soil specimens were tested using different gradations, compaction energies and moisture contents to generate various regression surfaces that correlate the variables of interest. Furthermore, the laboratory strain modulus obtained from this test was compared with full-scale static plate load tests conducted in the field. The results show that this methodology could become a valuable reference test to aid in the design and quality control of compacted fills for civil infrastructures.