Effect of heterogeneity scale on chemical grouting in porous media

Abstract

Performance of chemical grouting as a containment technology is investigated through a numerical modeling study. A new grouting model that couples MODFLOW [1] and RT3D [2] combined new modules for the gelling process is presented. The present study is aimed at understanding the role of heterogeneity on grout curtain performance. The paper addresses two important issues related to heterogeneity and grid resolution: (1) relative influence of small-scale heterogeneity and large-scale heterogeneity, and (2) effect of numerical grid resolution on predicted curtain performance. Monte-Carlo simulations with statistically equivalent heterogeneous hydraulic conductivity ( K ) fields are conducted to assess the uncertainty of the grout performance. Grid resolution adequacy is determined by generation of heterogeneous K -fields at a coarse resolution and completing simulations using grid resolution equal to the K -field resolution and then refining that grid up to five times. Comparison of results at different grid resolution provides estimates of increased error associated with grid coarsening. Using the optimal grid resolution, effect of large-scale and small-scale heterogeneity is explored using simulations that incorporate primary and secondary heterogeneity each with different correlation lengths and variability and comparing to simulations having only large-scale heterogeneity. Grout curtain performance is assessed by simulation of grout injection, determinatin of post-grouted conductivity field, and assessment of overall grout curtain hydraulic conductivity using a flow model.