A Seismic Refraction Survey Conducted In The Artificial Lake Of Working Dam

Abstract

This paper presents that a seismic refraction survey conducted in the artificial lake is a useful non-destructive testing to determine the velocity structure around the working dam in Japan. All seismic data were collected using air gun and 144 channel hydrophones laid on the water bottom in the river and the lake. They enable us to determine crystalline bedrock depth and velocity structure around the working dam. The velocity ranged from 600 to 4300 m/s. Velocity structure was divided into four layers. The first and the second correspond to river deposits, sand and gravel over the Mesozoic crystalline bedrock. The depth to bedrock varied from 10 to 13 meters in the lake. On the other hand, the third and the fourth in velocity structure were crystalline bedrock, which ranged from 3000 to 4300 m/s. It depends on the occurrence of fracturing and weathering. Introduction This seismic refraction survey conducted in the artificial lake is a useful nondestructive test to determine the velocity structure around the working dam. It was necessary to collect bedrock strength and overburden thickness in designing the overlaid dam for water resource redevelopment. The working dam was a concrete gravity structure, which was 11 meters high and 71.5 meters wide (see Figure 1). It was built in 1937 and founded on the Mesozoic crystalline bedrock, which is composed of sandstone and mudstone. We collected seismic refraction data along six lines (see Figure 2). Four of them are parallel to the river, the others traverses across the river and the artificial lake.