The increments in compressive displacement and the stress increase of a sandy slope due to the growth of subsurface flow during rainfall were theoretically examined. Both the stress variation and the displacement equations were derived based on the assumption that the slope was a compressible continuum, which was in proportion with the power of stress. These equations provided schematically their distribution patterns of stress and compressive displacement in a slope at a certain time. The model simulation under a constant rainfall intensity indicated that the compressive displacement drew a rise curve, but the increment decreased with time, and the stress became constant gradually from the top of slope with time since the steady zone of the subsurface flow expanded from the top of the slope. The equilibrium of the compressive force and the critical passive earth pressure at the foot of the slope enable both the prediction of failure time and the evaluation of compressive displacement preceding the slope failure. Finally the transition point from the above compression stage to the initiation of slope failure was discussed on the basis of the characteristics of compressive displacement and its velocity curves.
Landslide mass flowing into a reservoir causes a giant wave that runs up until high altitude on the steep slope and generates water breaking of high wave height with high speed. This giant wave brings greatly serious disasters and the establishment of prediction method of water wave is expected. This paper discusses a numerical method which is the guarantee of mass conservation and is the restrain of numerical oscillation due to the discretization of convection term for shallow water equations by using stabilized finite element method. The presented scheme uses the mass conservation equation expressing directly the water altitude for governing equation. Analytical scheme introduces the retainment of mass conservation by using the integrated CIVA method and the shock-capturing term resulting from the securement of second-order accuracy. The presented analysis method is applicable for water waves analysis containing the moving boundary on the steep slope and confirms the utility in comparison with model analysis.
This paper discusses the characteristics of cross section of slide and c'-tanφ' diagram of the landslides observed in the area of Shimajiri-mudstone of Okinawa, Japan. In addition, the pre-slide conditions of unstable slopes were given due consideration and an attempt was made to propose an advanced typological classification of first-activated type landslides. Obtained results are as follows: 1. Length and displacement of Shimajiri-mudstone landslides were found to increase with decreasing average gradient of the slip-surface. The values of tanφ'-intercept of the c'-tanφ' diagrams of the slides showed a tendency to increase as the average gradient of the slip-surface increases and vice-versa. 2. The occurrence of first-activated type landslide is influenced by the release of in situ stress, which is brought about by the displacement of a previous landslide or human-induced land alteration, such as cutting away at slope toes. The displacement of a landslide became larger when the slip-surface of a previous slide transformed into being a part of the slip-surface of a succeeding slide. 3. Pre-sliding slopes of first-activated landslides were classified into three types based on the land features and the geotechnical conditions: unstable slopes with a previous slide located in the lower part of slope, unstable slopes with a previous slide located in the middle part of slope and, thirdly, unstable slopes with cut away portions.
In order to predict the initiation of shallow landslide due to rainfall, it is important to establish the method to determine the constants in Soil and water characteristic function (SWCF) , which is the relation between volumetric water content θ and matric potential φ, only from the in-situ observed data of water content or matric suction, without indoor test on undisturbed sample. In this article, some methods were applied and examined using in-situ observed data of Aratani observation slope at Hiroshima. Firstly, in order to compare the reliability of the trial and error method which inversely solutes the constants in van Genuhten equation using only the measurement data of volumetric water content, and that of in-situ θ-φ method which combines the measured volumetric water content and measured matric potential directly, simulation of the time variation of volumetric water at certain rainfall event were carried out. It revealed that both methods have almost same reliability. Secondly, in order to reflect the variation of SWCF along the vertical depth, not only α, n in van Genuchiten equation, but also θs which corresponds to saturated water volumetric content, should be also identified by in situ θ-φ method for approximating SWCF better especially in a region of low matric potential.