A large number of laboratory triaxial experiments were performed to evaluate the likely cumulative settlement of a low embankment road on soft subsoil due to the traffic loads, for the purpose of determining the undrained cumulative strain and cumulative pore-water pressure for different loading conditions. A cumulative settlement model of soft subsoil was then derived with the provision for dynamic stress, confining pressure, initial static deviatoric stress, number of load cycles, and loading frequency. Based on a particular vehicle-road-ground coupling model, the dynamic stress induced by traffic loads, which has a great influence on the cumulative settlement of soft subsoil, is given in explicit form. The cumulative settlement of a road with a low embankment was evaluated, and the results were compared with the field data. The calculated results agreed well with those from the field, which implies that the method proposed in this paper can give precise predictions of the likely cumulative settlement of low embankment roads on soft subsoils due to traffic loads. Moreover, a parametric study was conducted using numerical computation, and the results show that the vehicle types and the pavement unevenness parameters have a major influence on the settlement caused by traffic loads. The influences of the pavement and embankment properties on the cumulative settlement also are significant.

A new procedure is developed for rapidly determining the water retention curves of unsaturated fine-grained soils based on the nuclear magnetic resonance (NMR) technique. From a well-defined pore-size distribution function, a distribution function of NMR transverse relaxation time ($T_2$ ) is derived for fully-saturated soils, by virtue of the Young-Laplace equation and the linear relationship between pore radius and $T_2$ . By fitting the measured $T_2$ distribution curve with the proposed $T_2$ distribution function, the key parameters characterizing the soil-water retention characteristics can be determined. To validate the proposed method, a series of the NMR measurements was performed for two types of fully-saturated fine-grained soils. The proposed procedure is then used to obtain the soil-water retention curves of the tested soils from the NMR measurements; the obtained soil-water retention curves are compared with those determined independently by the pressure-plate method. It is shown that the proposed procedure can be effectively used to determine the soil-water retention curves of fine-grained soils in a capillary regime. Compared to conventional methods, which are generally time-consuming, the proposed procedure can save a significant amount of time in determining the soil-water retention curves.

A soil-water retention curve (SWRC) is one of the important constitutive laws for soil-water distribution and shear-strength assessment in unsaturated soil. A SWRC commonly shows the hysteretic behavior under drying and wetting conditions. Several mathematical models have been developed to describe hysteresis, including a model commonly presented in the literature and implemented into HYDRUS software. Recently, the authors developed a new hydraulic hysteresis model for which only one additional parameter was introduced to capture the effects of capillary and air-entrapment hysteresis. To confirm the capabilities of the two models in analyzing the unsaturated flow, the authors’ model was implemented with a numerical code using the FORTRAN language. The numerical codes including the authors’ model and the model in HYDRUS for hysteresis assessment were used to analyze the same transient unsaturated flow problems under drying and wetting conditions. By comparing the measured data to curves predicted by the two models, the results show that the hysteretic SWRC cannot be described correctly when the effects of hydraulic hysteresis are ignored under drying and wetting conditions. Moreover, the comparison between the results predicted by the two models shows that the authors’ model gave a robust performance for capturing hydraulic hysteresis behavior in unsaturated flow.