Assessment Of Geotechnical Features Of Miocene Volcaniclastics Using Integrated Logging

This paper describes that integrated logging evaluates geotechnical conditions of fractures in Miocene<br>volcaniclastics, where the damsites are for proposed. The purpose of this study was to detect fractures for<br>seepage contols along borehole wall and characterize its geotechnical features by integrated logging. It is<br>first step to evaluate the continuity and permeability of fractures.<br>Integrated logging comprises of caliper, acoustic borehole televiewer, full-wave sonic, temperature,<br>borehole video logging, natural gamma spectrum, and magnetic loggings. Natural gamma spectrum and<br>magnetic logs would characterize litholofacies. Caliper, acoustic borehole televiewer and borehole video<br>loggings would identify the depth, the dip and the azimuth of fractures. Besides temperature logging would<br>determine the groudwater flow and suggest the permeable fracture.<br>Integrated loggings were performed at damsites for proposed in northern Kanto district, middle part<br>of Japan, where Miocene volcaniclastics are widely exposed. In Yunishigawa site, thermal jump was<br>remarkaby observed at 84 meters in depth from temperature logging. Its thermal gradient, differntiation of<br>temperature, was 30 “C/m. The farcture causing it was recognized by the borehole enlargemnts from caliper<br>logging, and had low slowness of full-wave sonic logging.<br>Integrated logging enabled us to identify the fractures in the order of a dozen centimeters along a<br>borehole wall. The identification would be useful for the geotechnical evaluation. Especially Differentiation<br>of temperature revealed the fracture for seepage controls and classified the fractures into three types, which<br>are (1) the permeable fracture circulating the runoff, (2) the permeable one controlling the groundwater<br>from the deep, (3) the non-permeable fracture. As the first and the second are fractures for the seepage<br>controls, they would involve the geotechnical problems.