Devising a procedure for assessing the subgrade compaction degree based on the propagation rate of elastic waves

V . K o v a l c h u k Doctor of Technical Sciences, Аssociate professor* E-mail: kovalchuk.diit@gmail.com I . K r a v e t s Postgraduate Student* Department of Bridges and Tunnels Dnipro National University of Railway Transport named after academician V. Lazaryan Lazaryan str., 2, Dnipro, Ukraine, 49010 E-mail: kravetsivan2017@gmail.com O . N a b o c h e n k o PhD, Associate Professor Department of "The rolling stock and track" Lviv Branch of Dnipro National University of Railway Transport named after Academician V. Lazaryan I. Blazhkevych str., 12a, Lviv, Ukraine, 79052 E-mail: olganabochenko@gmail.com A . O n y s h c h e n k o Doctor of Technical Sciences, Associate Professor* E-mail: onyshchenko.a.m.ntu@gmail.com O . F e d o r e n k o Acting General Director, Deputy General Director for Production Development Kyivavtodor Municipal Corporation Petra Bolbochana str., 6, Kyiv, Ukraine, 01014 E-mail: oleksandr.fedorenko.ntu@gmail.com A . P e n t s a k PhD, Associate Professor** E-mail: apentsak1963@gmail.com O . P e t r e n k o PhD, Associate Professor** E-mail: olexapetrenko@gmail.com N . H e m b a r a PhD Department of Engineering Ukrainian Academy of printing Pidholosko str., 19, Lviv, Ukraine, 79020 E-mail: gembara2011@gmail.com *Department of Bridges and Tunnels National Transport University M. Omelianovycha-Pavlenka str., 1, Kyiv, Ukraine, 01010 **Department of Construction industry National University Lviv Polytechnic S. Bandery str., 12, Lviv, Ukraine, 79013 This paper reports the analysis of the methods for estimating the technical condition of the subgrade underneath a constructed railroad track or road during its operation. The study results have proven that the issue related to monitoring and controlling high-quality compaction of a heterogeneous subgrade remains relevant and requires the construction of reliable experimental methods for assessing the subgrade degree of compaction. A procedure for determining the compaction of subgrade in the laboratory has been devised, based on inertial microcomputer technologies, which makes it possible to assess the degree of compaction of subgrade soils depending on the propagation rate of an impact's elastic waves. An experimental study has been performed into the propagation rate of elastic waves across a homogeneous subgrade made of coarse-grained sand and a heterogeneous subgrade made of coarse sand with a layer of clay in the middle of the prism. The study results established that the propagation rate of an elastic wave in a heterogeneous subgrade accepts a lower value than the rate of wave propagation in a homogeneous subgrade. Through the dynamic interpretation, by using a discriminant statistical analysis, the characteristic features have been defined in the distribution of accelerations in the body of the homogeneous and heterogeneous subgrade, depending on the degree of compaction, which would make it possible to monitor the state of the subgrade during operation. As the degree of the subgrade soil compaction affects the technical condition of roads