Examination of evaluation criteria for the possibility of fallen trees by pull-down test for roadside trees

Abstract

The purpose of this study was to verify the feasibility of formulating evaluation criteria based on the results of pull-down tests for actual street trees. Four Japanese pagoda trees (Maackia amurensis) planted in roadside in Tokyo were investigated. Three are damaged trees, another is a healthy tree. PiCUS TreeQinetic (manufactured by IML) was used for the measurement to determine the inclination angle and moment of the trunk. From the relationship between the root tilt angle and the moment, the damaged trees were suggested that tilts earlier as the moment increases. Two damaged trees were thought that there was a possibility that the trees would fall, because the wind speed obtained from the maximum moment of the damaged trees were smaller than the wind speed observed in the past 10 years. On the other hand, root-bearing capacity to withstand wind speed 30m was obtained even when the roots were damaged by Bekko-mushroom. Arbostat evaluated “Safety Factor < 1” for all target trees including healthy trees. From comparing the estimated wind speed calculated from the overturning load using the theory used in the arbostat and the moment measured in this test, different results were found. It was considered necessary to study the theory and calculation process used in arbostat and to examine the operation method in Japan.