Studies on the phenomena of valley bulging were reported in England in the early 20th century. Although many research and technical reports have been published since then in Britain, Europe and North America, publications on the subject are relatively new in Japan. One of the authors, Nozaki, reported one of the first cases of valley anticline that followed a river channel, describ-ing its occurrence mechanism as a type of valley bulging. In Britain, it is generally believed that valley bulging is initiated by val-ley rebound, resulting largely from freezing and thawing of deep permafrost which was one of the periglacial processes in glacier periods. In other countries however, the view that valley rebound due to gravitational creep causing buckling of rocks in the cen-ter of valleys is more prevalent. The authors basically take the latter viewpoint because there is no evidence of periglacial proc-esses in Japan except on Hokkaido Island and very mountainous area of Honshu Island. Apart from explanations on the physical phenomena, it is also believed that this kind of bulging is time-dependent phenomena that progresses over durations of geologic periods with no appreciable deformation caused by artificial means. During the excavation of the Jyoshin-etsu Express Highway in Central Japan, however, bulging in the direction of the excavation site crosscutting a high ridge was observed. The authors predicted this deformation and was able to verify this phenomenon by installing enough detection equipment and control points, along with detail drilling tests in advance of or during excavation works. As a result, the authors were able to conclude that this deformation was a case of artificially-induced valley bulging.
During the heavy rain on June 29, 1999, four slope failures occurred around the Taishi-do area in Zentoku landslide, Tokushima, Japan. Based on field investigation after these failures, and the monitored records of the three-dimensional shear displacement me-ters before the failures, it was made clear that 1) the failures were limited comparing to the rainfall ; 2) One of the failures showed precursory displacement of creeping failure. To clarify the failure mechanism, field investigations including one-meter depth of soil temperature survey, temperature measurements of spring water and groundwater in borehole were conducted, and pore water pressures generated at failure were estimated through back-analysis. Thereafter, the relationship between the location of failed slopes and flowing groundwater veins, and the relationship between groundwater vein and precursory displacement of failures were analyzed. It is found that: 1) Slope failure occurred above or near groundwater vein ; 2) There were two types of groundwater veins, one was surficial vein type with high water temperature, and the other was deep vein type originating from a depth between 49 and 70m with low water temperature ; 3) The precursory displacement of the creeping failure was associated with the groundwater vein.
This paper presents a numerical model based on the hydrodynamic shallow water equation, which is developed for simulations of landslide-generated waves in reservoirs and bays. The Galerkin finite element method is used to determine the amplitude of the waves, which is generated by accelerating the fluid due to bottom physical displacement, the bottom friction, and impact force due to landslide. The model is verified by the good agreement between the simulation and the theoretical analysis. In order to consider the case of complex topography and practical boundaries, auto-generation method of the modified Delaunay triangulation element is applied to the numerical model. In addition, the case of a landslide into reservoir is simulated and discussed. It shows the possibility to numerically analyze the waves caused by landslide into a reservoir with complicated topography.
Mitigation measure of rock fall was assessed for large unstable jointed rock blocks formed at 50m high steep rock slope. The site investigation of rock fall in1999indicates that the geometry of the rock blocks and slope have significant influences on the path, velocity, jump height, and travel distance of the falling blocks. Hence, the distinct element method (DEM) was applied to examine the effects of the geometry and also to estimate the path and dynamic behavior of rock fall.
Particles in slip surface clay is thought to align along slip surface. As the alignment direction can detect quickly, it gives us an important information to estimate the slip surface. Present study disclosed anisotropy of magnetic susceptibility (AMS) and micro-fabric of slip surface clay. The AMS is quick method to measure grain arrangement of slip surface clay.