Mechanisms of amendment transport in low-permeability contaminated sites enhanced by hydraulic fracturing
Due to the low permeability characteristics of contaminated clay sites,the injection and migration of amendments are significantly hindered,leading to a reduced efficiency of traditional remediation methods.Hydraulic fracturing,as an effective means of enhancing mass transfer,has been widely recognized.Hence,in conjunction with the injection-extraction technique,this study developed a numerical model for the enhanced transport of amendments in low-permeability contaminated sites by hydraulic fracturing that considers the convection,diffusion,adsorption,and degradation mechanisms and investigates the enhancing role of hydraulic fractures in the transport of amendments in low-permeability environments.Based on geostatistical methods,a random permeability field was generated to study the influence of heterogeneity on the transport and distribution of amendments.The results indicate that hydraulic fractures can effectively promote the migration of amendments by forming preferential flow paths and intensifying pressure transmission.Compared to low-permeability sites,the influence range of amendments in fractured sites increased by at least 50％.The heterogeneity of the site leads to significant fluctuations in the concentration of amendments and localized concentration accumulations and the degree of fluctuation increases with the increase in heterogeneity.As a result,this results in a location-specific amendment missing rate of around 7.14％for weakly heterogeneous sites and up to 28.57％for strongly heterogeneous sites.
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