ASTM D6758-18e1 PDF Download

ASTM D6758-18e1 is a standard test method that describes the measurement of the stiffness and apparent modulus of soil and soil-aggregate mixtures in their in-place state using an electro-mechanical method. The purpose of this method is to determine the Young's modulus of the materials based on certain assumptions. The test is conducted by applying low strain cyclic loading to the surface of the ground while measuring the resulting surface velocity. The stiffness is then calculated based on the measured data over a frequency range and averaged.

This test method is particularly useful for monitoring and controlling compaction during construction to avoid under-compaction or over-compaction. It can provide a means of measuring stiffness that is related to the percentage compaction and density of the material. The method is applicable to silty and clayey materials containing more than 20% fines, and the relationship between stiffness and dry density is sensitive to water content, which should be determined separately using specific test methods. The non-destructive nature of this method makes it suitable for production testing without interfering with or delaying construction.

The standard also highlights the suitability of this method for mitigating the risk of pavement failure by ensuring the relative uniformity of stiffness in highway subbases, subgrades, and bases, which distributes stresses more uniformly and extends pavement life. Additionally, it can be used to determine the load-bearing capacity of a soil or soil-aggregate structure, particularly in stabilized fills where the material gradually hardens over time without significant changes in density or moisture content.

It is important to note that the stiffness measured using this method depends on factors such as boundary conditions (support from underlying layers) and the thickness and modulus of the layer being tested. The precision of the test method also relies on the competence of the personnel, equipment, and facilities used. Compliance with relevant practices is necessary but does not guarantee reliable testing.