In order to understand the hydrological process of expansive soil slopes, simulated rainfall experiments were conducted to study the effects of slope gradient and initial soil moisture content on runoff and infiltration for expansive soil slopes located in south China. The field program consisted of four neighboring slopes (70%, 47%, 32%, and 21%) instrumented by a runoff collection system and moisture content sensors (EC-5). Results from the monitored tests indicate that there was delay in the response of surface runoff. The runoff initiation time decreased with initial soil water content and increasing slope gradient. After the generation of runoff, the cumulative runoff per unit area and the runoff rate increased linearly and logarithmically with time, respectively. The greater the initial soil moisture content was, the smaller the influence of slope gradient on runoff. A rainfall may contribute from 39% to about 100% of its total rainfall as infiltration, indicating that infiltration remained an important component of the rainwater falling on the slope, despite the high initial soil water content. The larger the initial sealing degree of slope surface was the smaller the cumulative infiltration per unit area of the slope. However, the soil moisture reaction was more obvious. The influence of inclination is no longer discernible at high initial moisture levels. The greater the initial soil moisture content and the smaller the slope gradient, the weaker was the change of soil water content caused by simulated rainfall. The influence of initial soil moisture content and slope gradient on the processes of flow and changes of soil water content identified in this study may be helpful in the surface water control for expansive soil slopes.

This study investigates the dynamic analysis of parametrically excited marine riser under simultaneous stochastic waves and vortex. A general analysis considers the parametric excitation resulting from platform motion, ocean wave loading directly on the rise, and vortex-shedding excitation due to flow bypassing the risers. Stochastic wave force and vortex excitation acting on the riser in the time domain is formulated by the stochastic phase spectrum method and derived by the linear-wave theory using a Pierson–Moskowitz wave spectrum to simulate real sea conditions. A derived parametrically excited top tensioned riser model subjected to simultaneous stochastic waves and vortex excitations is proposed. The efficacy of the present method is assessed by solutions obtained from other existing methods and experimental data of two test models. The present method is evaluated by solutions computed from existing methods and experimental data of two test models, and a general good agreement of the analyses between the proposed approach and other methods is observed. The availability of resonance, parametric stability, energy distribution and transfer, and the sensitivity of key parameters estimated by single-frequency and multi-frequency excitation are compared and discussed. Comparing with the results obtained from the harmonic excitation method, the present method can be used to make more reasonable and accurate calculations of the dynamic response of risers operating in real sea conditions.

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