地すべりを反映する地下水,微生物,粘土の特徴(地盤工学会・技術者交流特別セッション)

抄録

The colorful microbial mats formed and caused stoppage in all drainage pipes at several landslide areas in Niigata Prefecture. The water catchments worked well for a short period such as within three years after the construction. In this study, samples from the damaged areas showing reddish brown microbial mats with iron bacteria, and green microbial mats with diatoms were observed by optical and electron microscopy, XRF and XRD analyses. The green microbial mats were more remarkable in areas mainly containing smectite clays versus sandstone areas rich in ferrihydrite. The green microbial mats formed in areas where the concentration of dissolved oxygen (DO) was more than 8mg/L, and the oxidation-reduction potential (Eh) was more than +300mV. On the other hand, the reddish-brown microbial mats formed in areas where the DO was less than 6.2mg/L, and Eh was less than +300mV. The reddish-brown microbial mats consisted of ferrihydrite formed by iron oxidizing bacteria at the outlets of the drainage pipes. In landslide areas, we pointed out the necessity of maintenance based on groundwater, microorganisms and geological features which contribute to the spread of clays. We propose two methods to prevent the formation of biomats in landslide fields, such as connected pipes and different materials used for drainage pipes.