**Abstract**

In this chapter, two karst protection methods are analyzed: the structural karst protection method, when designed structures of the underground part prevent the development of the bearing structures strains while karst deformations occur; the geotechnical karst protection method, when the design of a foundation includes a protection geotechnical screen in the base, which excludes or essentially decreases the negative influence of karst development on the bearing structures of the building. The results of numerical calculations are analyzed for different types of foundations. The advantages of the model of the variable coefficient of subgrade reaction are discussed. It is proposed to determine the coefficients of subgrade reaction (stiffness of the piles) around the karst cavity by decreasing these coefficients in relation to the same coefficients, calculated using standard methods (i.e., without karst deformations). Analytical solutions for different types of foundations are presented. Analytical solutions for designing bridge support pile foundations in karst areas are proposed. The correct design model and criteria for stability evaluation of the arch over the cavity are selected and the method for estimating the thickness of an effective karst protection geotechnical screen is proposed.

**Keywords:** structural karst protection, geotechnical karst protection, numerical modeling, foundations, analytical solutions
