Using Polyacrylamide Grouts for Permeability Control in Sand

Abstract

Chemical grouting of permeable soils with highly concentrated low-molecular-weight polymeric solutions greatly reduces the permeability. However, a toxicity problem arose from these chemicals. A new process of treating soil with low-concentration cationic and anionic poly-acrylamides with cross-linking aluminum citrate in a cyclic way with particular sequencing is introduced. The new process provides effective control of permeability and eliminates the risk of toxicity. A total of 25 one-dimensional flow laboratory tests were carried out on sand. The effect of three anionic-type polyacrylamides having different molecular weights on the number of cycles required to attain a significant reduction in permeability was investigated. Controlled volumes of chemical flood solutions having four levels of concentration were injected to inspect the impact of concentration on the gel distribution. The effects of water flow and time factor on gel stability were studied. The results of these runs demonstrate the effectiveness of the aluminum citrate cross-linking process between cationic and anionic polyacrylamides in controlling permeability. Partial control of permeability as well as significant seepage cutoff was achieved as a result of gel formation. The spreadability of the gel improved upon increasing the amount of chemical solutions injected. The gel formed endured water pressure of 3 bars for 28 days. Injection with large volumes and low concentrations was found to be equivalent to injection with smaller volumes and higher concentrations. As the molecular weight of the anionic-type polyacrylamide increased, the amount that was required to be injected decreased and, accordingly, the number of cycles needed for blockage under the same conditions also decreased. Toxicological tests run on the solutions used in this research revealed no toxicity to cesarian-originated, barrier-sustained albino rats.