Journal of the Japan Society of Erosion Control Engineering, Vol.60,No.2,2007
Evaluating method of durability of small wooden crib dams with considering
the deterioration rate
Quoc Dung DANG, Yoshiharu ISHIKAWA, Hiroyuki NAKAMURA and@Katsushige SHIRAKI
Abstract
In Japan, small wooden dams were built to prevent soil erosion and control sediment
discharge. However, the wooden materials deteriorate under the actions of fungi
that are controlled by temperature, oxygen and humidity, which cause the durability
(service time) of wooden dam shorter than that of concrete and steel crib dam.
Therefore, it is very important to evaluate the durability of dam in order to
serve effectively for designing and maintenance works. The purpose of this study
is to develop a new design method with considering the deterioration rate that
allows evaluating the durability of crib dam. We defined a new term of the deterioration
rate and have conducted the field measurement of actual deterioration rates of
Cryptomeria japonica D.DoN and Chamaecyparis obtusa ENDL. at four wooden dams
in Kyoto Prefecture. The actual deterioration rates of Cryptomeria japonica D.DoN
and Chamaecyparis obtusa ENDL. were obtained. The diameter and cross sectional
area of the sound part of deteriorated log were calculated using the deterioration
rate and the time after completion of dam. Then the maximum bending, shear and
tensile stresses acting on deteriorated log were calculated using the diameter
and the cross sectional area of the sound part. We proposed three formulas for
evaluating the durability considering the maximum stresses equal to allowable
stresses of wood. The parameters in three formulas showed that the durability
of small wooden crib dam depended upon the deterioration rate, log diameter, log
length, dam height, and overflow depth. To increase the durability, the log diameter
needs to be increased, and the dam height, overflow depth, as well as the log
length need to be decreased. In an application of the new design method, a new
diagram was also developed to show the durability of crib dam built with Cryptomeria
japonica D.DoN.
Key wordsFdurability, design method, wooden crib dam, deterioration rate, field
measurement
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