Abstract: To address the difficulty in point-by-point detection of the grouting effect of water-rich broken sand strata, we propose to evaluate the detailed water-sealing effect of grouting via inversion of permeability using acoustic logging. On the basis of Wyllie-Clemenceau's formula and Kozeny-Carman's formula, we established an acoustic velocity-permeability model for water-rich sandstone. With a foundation grouting project in Hunan as research object, we obtained the acoustic velocity and permeability of rock core and rock strata before and after grouting through core test, acoustic logging, and hydraulic fracturing test. By fitting the core test results with the model, we found a nonlinear negative correlation between acoustic velocity and permeability with an obvious cut-off point of change rate in the curve. Grouting affects the rock matrix acoustic velocity and the exponent to the matrix nature. By comparing the permeability calculated by logging acoustic velocity with the hydraulic fracturing test results, we verified the reliability of the model. In addition, we built a quantitative evaluation system for the grouting effect of water-rich sandstone on the basis of calculated permeability, and evaluated the case using this system.

Key words: water-rich sandstone, grouting effect, acoustic velocity, permeability, acoustic logging