Construction of impervious curtains with experimental use of a new chemical grout

Abstract

In hydraulic construction chemical grouting methods are applied to create impervious curtains in order to make watertight slightly pervious rock and semirocky soilr when suspended grouts cannot be used because of their relatively low penetrating capacity. The methods of chemical soil stabilization proposed until now exhibit the following unfavorable properties: a) high gel-formation rate and development of intermediate products of the reaction in the form of suspensions preventing penetration of the grout into the soil (hydrofluorosilicic acid formula); corn paratively weak mobilization of the silica(aluminosilicate formula); c) sensitivity to certain components of the solid and liquid phases of the soil (carbamide formula); and d) toxicity of the starting reagents and reaction products (chrome lignin and phenol formulas). For this reason, the improvement and development of new chemical grouting methods continues to be a topical problem of modern technical soil reclamation. A new injected grout was developed with the cooperation of the Problems Laboratory of the Geology D epartm ent of Moscow State University.The proposed oxalic-aluminosilicate grout formula is based on the use of a complex hardener to obtain a silicate gel from a commercial sodium silicate (water glass). The complex hardener is an aluminum sulfate solution in an oxalic acid solution. As a result of neutralization of the alkaline component of the sodium silicate by the oxalic acid, a silicic acid salt is produced, and a certain decrease in the pH gives rise to hydrolysis of the aluminum sulfate with formation of aluminosilicate complexes. When the buffer capacity of the hardener is fully expended, continuing hydrolysis of the aluminum sulfate leads to polycondensation of the resulting complexes, with formation of aluminosilicate gel. The general equation of the reaction between the sodium silicate and the hardener can be written in the following form:The working oxalic-aluminosilicate grout is prepared from two components: solution A, which is a sodium silicate solution 1.19-1.13 g/cm 3 in density and 2.6-2.9 in silicate modulus; and solution B, which is a complex hardener in the form of a solution containing 4-5 kg of aluminum sulfate powder and 4-5 kg of oxalic acid powder per I00 liters of water. D epending on the content of A and B, the u~.,isity of the working grout may vary within the range I.Ii-I.15 g/cm a and the initial viscosity may vary from 1.5 to 1.7 ep. Forfine and medium sand stabilized with oxalic-aluminosilicate grout, the uniaxial strength is equal to 2-4 kg/cm z. The gel time varies from a few minutes to several hours depending on the ratio between the components A and B (Fig. i). From the construction viewpoint the relation between gel time and temperature is a favorable property of the formula here considered: In the range I0-30~ the gel time practically does not vary; a temperature drop from i0 to 0*C leads to a decrease in the gel time. Since the peripheral part of the pumped mass takes the soil temperature under the above ...