Construction and exploitation of a buildings at loess foundations is the significant problem for southern regions of Russia and Kazakhstan. There are many methods for loess subsidence removal. The most common of them is preconstruction compaction by pinning. However, when the loess thickness is more than 4-6 meters or an exploiting building foundation improvement is required the chemical grouting by sodium silicate solutions is preferable way. Efficiency of such soil improvement will depend on the chemical composition and structure of loesses.From the author's viewpoint loesses are divided at three groups: the high active loesses, the moderate active ones and the inactive ones. This loess classification is caused by some geochemical criteria. The main ones are: absorption alkali capacity (AAC), gypsum content, water-soluble salts content, pH value and carbonate content (table 1).Grouting and Deep Mixing 2012 Downloaded from ascelibrary.org by New York University on 08/02/15.

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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 ...

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The effectiveness of methods of rock stabilization by injecting grouts and, in particular, the gelling time of the grout, the stabilization radius, and the strength and uniformity of the stabilized rock, depend on the nature and intensity of the changes in the properties of the gel-forming grouts when moving along the injection path.The transformation of the injected grouts when moving through porous or jointed media and the changes in the physical state and related physicochemical properties are the result of the action of complex and little-investigated processes which take place during the interaction between the flouts and the containing rock. However, experience with the construction of impervious curtains, including those in alluvial deposits, indicates that for important problems, such as determination of the distance between the grout holes, evaluation of the effect of the seepage flow on the pumped flout, and others, Use can be made of a simplified approach to their solution, taking into account the effect of only two factors: dilution of the grouts by the pore water and variation of their temperature during the process of heat exchange with the rock.To evaluate the effect of the above-mentioned phenomena on the nature of the changes in the properties of gel-forming flouts, it is necessary to establish laws governing the concentration and temperature along the injection radius. According to theoretical concepts, the variation in the concentration of an indicator solution introduced into an isotropic soil is determined by a phenomenon which is called hydrodynamic dispersion or hydrodispersion. This phenomenon is characterized by the absence of a clearly defined boundary between the two liquids being mixed and by formation of a continuously expanding transition Zone. Hydrodispersion is determined by molecular and convective diffusion.The type of mixing called convective diffusion (microdispersion) is caused by movement of the liquid and the pore system. The complex nature of the system of interrelated pores leads to continuous disinteflation of the indicator mass. In addition, nonuniform distribution of the indicator in the flow region results in variation of the velocity of the elementary jets both in magnitude and direction.In a heterogeneous medium, the process of grout spreading is complicated not only by hydrodynamic dispers'ion but also by a phenomenon known as macrodispersion. This phenomenon characterizes the flout mixing determined by the seepage macroheterogeneity of the rock. The degree of occurrence of the above-mentioned phenomena is determined by the properties of the medium in which movement of the indicator takes place.In the general form, the nature of the dilution of the grout along the injection radius is described by the equationin which m is the layer thickness; Q is the grout discharge; r is the distance along the radius of flout spreading; n is a measure of the porosity; C is the flout concentration; t is the movement time of the flout; D is the effective coefficient of dispersion; D...