scope:

This method covers procedures for preparing and testing untreated subgrade soils and untreated base/subbase materials for determination of resilient modulus (Mr) under conditions representing a simulation of the physical conditions and stress states of materials beneath flexible pavements subjected to moving wheel loads.

The methods described are applicable to undisturbed samples of natural and compacted subgrade soils, and to disturbed samples of subgrade soils and untreated base/subbase prepared for testing by compaction in the laboratory.

In this method, stress levels used for testing specimens for resilient modulus are based on the location of the specimen within the pavement structure. Samples located within the base and subbase are subjected to different stress levels as compared to those specimens that are from the subgrade. Generally, specimen size for testing depends on the type of material based on the gradation and the plastic limit of the material as described in a later section.

The value of resilient modulus determined from this procedure is a measure of the elastic modulus of untreated base and subbase materials and subgrade soils recognizing certain nonlinear characteristics.

Resilient modulus values can be used with structural response analysis models to calculate the pavement structural response to wheel loads, and with pavement design procedures to design pavement structures.

This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Note 1-Test specimens and equipment described in this method may be used to obtain other useful and related information such as the Poisson's ratio and rutting characteristics of subgrade soils and base/subbase materials. Procedures for obtaining these are not covered in this standard.

The quality of the results produced by this standard are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of R 18 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with R 18 alone does not completely assure reliable results. Reliable results depend on many factors; following the suggestions of R 18 or some similar acceptable guideline provides a means of evaluating and controlling some of those factors.