Changes in the physical properties of gel-forming grouts during injection

Abstract

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...