Toshiaki Tasaka

The ability of a carriages developed for a mobile tower yarder: A comparison of the hauling force and walking time in a line pulling out process

The ability of a newly developed carriage equipped with a remote control lock and self line extraction system manufactured by Oikawa motors Co., Ltd. was analyzed. The study investigated the reduction of the work load of the choker setter in the haul line-pulling out process of a cable logging system by a mobile tower yarder. The main objective was to compare the walking time, pulling out time, and the tension force using the three types of cable setting method, a running skyline with a simple carriage, a fixed skyline with a simple carriage and a fixed skyline with a newly developed carriage. The measuring of haul line pulling out was conducted on different slope gradients at different distances from the tower spar by four choker setters. The study showed that choker setters could reduce the force exerted by about 33%, and a decrease in the heart beat rate of 12%, when using the fixed skyline with the newly developed carriage as opposed to the running skyline with the simple carriage. The fixed skyline with the newly developed carriage resulted in more pulling speed than the running skyline with the simple carriage on the slope gradient of over 2° and the fixed skyline with simple carriage on the slope gradient of over 7°. With the newly developed carriage the pulling tension, time and heart rate are lower, when the haul line is pulled out. Thus it can be concluded that the new carriage is more productive than the simple carriage in the line pulling out process.

Re-Estimation Method of Landslide-Triggering Rainfall Thresholds After an Earthquake with the Two Conceptual Models

This study used two conceptual models to examine the effects of rainstorms on post-earthquake landslides: a tank model to calculate the soil water index and a process-based model employing a digital terrain model with 10-m resolution to calculate the regional potential for shallow landslides, based on the distribution of shallow infiltration water, Darcy’s law, and a safety factor estimated by infinite-slope stability analysis. The two models were applied to the Funyu Experimental Forest of Utsunomiya University, Tochigi Prefecture, Japan. In August 1998, a heavy rainfall event caused many shallow landslides in the study area, whereas other heavy rainfall events in 1994–2003 did not cause severe landslides. The two indices were closely correlated, confirming the validity of both approaches for the estimation of rainfall properties. Response analysis of the effect of earthquakes on soil strength parameters indicated that landslide-triggering rainfall thresholds varied with decreasing effective soil cohesion, implying that the relationships between effective soil cohesion and the soil water index derived from the two conceptual models were valid for the re-estimation of the influence of rainfall properties on post-earthquake landslide occurrence.