USE OF CBR MOULD FOR EVALUATION OF CONSTRAINED MODULUS-BULK STRESS RELATIONS OF PAVEMENT STRUCTURE MATERIALS
Keywords:Pavement Structure Materials, Constrained Modulus, Resilient Modulus, Coefficient of Lateral Earth Pressure, Bedding Error
One of important parameters used in the mechanistic pavement engineering design is resilient
modulus (MR) of pavement structure materials. In general, MR is evaluated in a complicated and thus expensive
triaxial compression test in that a number of repeated loads are applied at various stress states. This research
presents an alternative method to determine the constrained modulus (M) of a dried sand, a lateritic soil and a
crushed rock, under one-dimensional compression. At various vertical stress levels, M values were determined
by applying small strain-amplitude cyclic loadings to the compacted soil specimens prepared in a CBR mould.
In the present study, the CBR mould was made special in that it can measure the lateral stress confining to the
specimen during a test. Hence the bulk stress () can then be determined, and M- relations for the tested
materials were presented. In addition, an analytical method for eliminating the effects of bedding error was
attempted so as to obtain the true M value. It is found that M is not constant but increases with , similar to
MR- relations found with the resilient modulus test. In addition, the bedding error is important and can result
in a significant underestimation of the true M value.