ИСТИНА

Transformations of volcanic rocks within thermal fields lead to the formation of a near-surface horizon of hydrothermal clay soils up to several meters thick. The base of the clay stratum represented by fractured and brecciated, intensely argilized andesite lavas, which can be classified as metasomatic breccias. Below occur the andesites, which have undergone transformations to varying degrees. Studies have shown that hydrothermal exposure firstly results to transformation of volcanic glass, and then secondary changes develop in phenocrysts in the following order: plagioclases, pyroxenes, amphiboles, potassium feldspar. For hydrothermal clay soils, the content of clay minerals is more than 50%, in some samples it reaches 95%. Clay minerals are represented by kaolinite, mixed-layer kaolinite-smectites and smectite group minerals, mainly montmorillonite. Despite the complete transformation of the mineral composition of the original volcanic rocks, pseudomorphs, due to the inherited structure, are characteristic of the formed clay soils. Such a structure determines the nature of deformation and destruction during the strength and deformation tests of clay soils. Iron and silica minerals precipitated from the solution through cracks form a “framework”, due to which these soils do not become fluid, despite full water saturation. Particles and aggregates with a size of less than 0.005 mm prevail in the particle size distribution; their content for most samples is about 60-70%. In this case, up to 60% may fall on particles whose size does not exceed 0.001 mm. At the same time, in the microaggregate composition, aggregates with a size of 0.01-0.1 mm prevail, the content of which can reach 80% The soils that were formed as a result of hydrothermal transformations are characterized by extremely low indicators of strength and deformation properties. At that time, as the initial rocks are characterized by the values of the strength for uniaxial compression up to 120 MPa, the hydrothermal formed clay soils are characterized by values not exceeding 180 kPa. To study the deformation properties of clay soils were carried out compression tests. They can be characterized as highly compressible: the compressibility coefficient reaches 10 MPa-1. In the natural state of the soil are at temperatures up to 100 °C, which affects their properties. However, the effect of temperature on the strength and deformation properties is ambiguous. On the one hand, a decrease in the viscosity of cohesive water leads to a decrease in the strength of coagulation contacts, on the other hand, as a result of a decrease in the thickness of electrical double layer, the number of particles directly in contact with each other increases. Thus, the overall effect of temperature on properties may be different.