Experimental research of stress-strain properties of sandy soil when strengthened with polyurethane compounds

In a number of cases during construction and operation of engineering facilities, development of mineral deposits it is necessary to improve the properties of sandy soils by strengthening them with polymer compounds. Analysis of current research shows that the effect of flow rate and method of treatment with polyurethanes on the acquired properties of loose rocks is poorly understood. The paper presents the results of laboratory research of chemical strengthening of sandy soil with polyurethane compounds. Geomaterials typically produced by strengthening loose rock with highly elastic polymers have low strength properties and are stable under only minor loads. To improve the strength, a two-binder sandy soil treatment process is proposed, which includes sequential mixing of the soil with a two-component highly elastic slow-reacting compound and a small volume of a fast-curing one-component resin. The aim of the work is to experimentally investigate the dependence of strain and strength properties of sandy soil on the method of mixing with polyurethane compounds and the polymer volume flow rate. A standard one-component method of mixing samples with highly elastic resin at the resin-to-sand volume ratio from 0.05 to 0.4 and a two-component method including additional treatment with fast-curing one-component resin in the volume of 5 % of the strengthened soil were experimentally tested. The effect of polyurethane resins on rock properties was evaluated by triaxial compression strength tests. Electron scanning microscopy was used to determine the content and distribution of cured polymers in the loose rock structure. It was found that the addition of a fast-curing polyurethane compound in the two-component mixing method leads to the formation of aggregates of cured polymer, binding mineral grains without continuous filling of intergranular voids. The presence of such aggregates improves the strength characteristics of sand up to 5 times that is 1.3–3 times more than at the standard one-component mixing with highly elastic resin at a resin-to-rock to be strengthened volume ratio up to 0.3. It was found that under triaxial compression conditions, the geomaterial obtained by the two-component mixing method withstands higher axial stresses. In case the volume ratio of resin to rock is more than 0.3, the strength of the produced geomaterial does not depend on the addition of the fast-curing compound. The study findings practical significance consists in increasing the strength of a sandy soil due to its low-volume strengthening with highly elastic polyurethanes.