Estimation of stress state-dependent elastic modulus of pavement structure materials using one-dimensional loading test

Abstract

An important key parameter used in mechanistic pavement engineering design is the resilient modulus (Mr ) or elastic modulus (E) of pavement structure materials. Although the Mr value can be estimated from the California Bearing Ratio (CBR) value by various empirical equations, it is rather inaccurate, and importantly, its dependency on the bulk stress (θ) cannot be taken into account. This paper presents an alternative method for evaluating the E value by a one-dimensional (1D) compression test performed on the sample prepared as usual in the CBR mould. The materials studied consist of sand, lateritic soil, and crushed rock. The CBR mould was modified such that the mobilized θ value can be measured. The nominal constrained modulus (M o) was determined with a 1D compression test using this mould. Another series of triaxial compression (TC) tests was performed to determine the quasi-elastic Young’s modulus (E eq). Then, the E eq value was converted to the corresponding constrained modulus (M TC). It was found that bedding errors are responsible for the constrained modulus difference (ΔM = M TC − M o), which consists of (i) the independent part of θ (ΔM 1) and (ii) the dependent part of θ (ΔM 2). By performing a 1D compression test as described above, both the M o and θ values can be determined, and the ΔM value can be obtained from the ΔM − θ relationship. Then, the true constrained modulus (M 1D) can be determined. This M 1D can then be converted to the E value for use in a pavement engineering design.