Development and Procedure for Constrained Modulus of Crushed Rock Test

A one-dimensional compression test procedure to measure the constrained modulus (M_s) of coarse-grained soils, such as crushed rock and clean gravel, has been developed to fulfill practical application purposes. To date, M_s could be measured in the laboratory by two testing methods, i.e. one-dimensional compression or triaxial compression tests. However these conventional methods are typically limited to fine-grained soils primarily because cumbersome large-scale testing is needed for materials with gravel-size particles. For this newly developed method, a test specimen is placed in a 17½-inch diameter Teflon^TM lined steel or aluminum pipe operating as a floating ring. Steel or aluminum platens above and below the sample are used to apply a series of increasingly greater axial loads creating axial stresses from approximately 1-lb/in² to a maximum of 150-lb/in². Axial deformation is measured following the application of each incremental pressure and cessation of axial displacement. M_s is then calculated for each incremental pressure. Samples may be tested at low, medium, and high densities at varying saturation. Proper testing procedures and equipment, including friction and scale effects adjustment factors, were developed. Establishing the M_s of coarse grained soils enables determination of the load displacement behavior of this material for many engineering applications.