Application of Jet Grouting for Development of Underground Areas in St. Petersburg
Jet grouting technology, which has been tested under the geotechnical conditions of St. Petersburg, provides effective solutions for a number of relevant geotechnical problems, including deepening of foundations of historical buildings, making soil-cement discs to fix fences of deep pits, construction of box soil-cement structures to organize underground spaces under the existing buildings. Studies show that in sandy and clayey soils jet grouting helps to make soil-cement with acceptable mechanical properties. When designing soil-cement structures, it is proposed to treat soil-cement as fine concrete of a low grade. When developing such megapolis as Saint-Petersburg, there is an urgent need for controlled transformation of properties of foundation soils and giving them the necessary properties (increase in strength and deformation modulus, reduction in water permeability). Jet grouting of soils is a technological process which, for creation of geo-massif with required properties, includes a complex of special works, for example, pilot well-drilling with washing of drill cuttings with water or solution, mixing of the site soils, as a rule, with cement solutions containing chemical additives and then reinforcement of the well. Jet technology is being introduced in Saint-Petersburg over 20 years, at first as a one-component, then - as two-component. Examples of calculations of soil-cement structures of different types are presented and examples of realization of project solutions at the sites in the historic center of St. Petersburg are considered.