Abstract:

Aiming at the difficulty of engineering survey of the boulder in the Hengqin Submarine Shield Tunnel in Zhuhai, seismic scattering technique is selected which has high resolution feature. Seismic scattering technique utilizes small-scale and dense data collection methods, of which data collection grid is up to 2 m×1 m. Three-dimensional velocity structure and geological interface distribution with axial spacing of 1 m, lateral 2 m, and vertical 0. 5 m are obtained. The elevation distribution of bedrock and boulders are distinguished whose velocity is greater than 2 400 m/ s. The horizontal, vertical and lateral slices of three-dimensional velocity structure illustrate the distribution of bedrock and boulder. Exploration revealed 26 boulder stones, 9 of which are more than 3 m in diameter. The results demonstrate that geophysical prospecting coincides to drilling exploration, and its average depth error is less than 1 m. The features of easy data collection and high resolution make seismic scattering profile technology suitable for boulder exploration.

Key words: boulder exploration, prospecting in sea area, seismic scattering, submarine tunnel, multiple wave, velocity scanning, migration imaging, shield tunnel