Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
Results of studies of natural conditions and engineering-geological structure of the valley of the river Bolshaya Aleksandrovka (Sakhalin island)
Abstract
The relevance of the discussed issue is caused by the need of precise ideas about the structure of the upper part of geological section, based on understanding of sediments genesis for use as engineering geological support of construction in the study area. The main aim of the study is to identify engineering-geological conditions in the valley of river Bolshaya Aleksandrovka according to the results of engineering surveys and determination of features of formation of the Neogene-Quaternary deposits of the territory. The methods used in the study: methods of engineering-geological researches: surface observation, drilling; complex laboratory methods for determining physic-mechanical properties of rocks: determination of granulometric composition of cohesive and non-cohesive sedimentary rocks, density and bulk density calculation of porosity, moisture content and the maximum molecular moisture capacity, plasticity, stickiness, swelling and other; methods for determining petrophysical properties of igneous rocks: density, bulk density, water saturation, water absorption, humidity, capillary rise, porosity, strength and elastic properties; geophysical methods of vertical electrical sounding and seismic exploration by the method of refracted waves; direct methods of correlation of ground sections, based on the study of cores and the mapping of columns in different wells; stratigraphic method. The results: As a result of geological engineering survey the authors have compiled geological section of seven kilometers to the bottom of the valley of the river Bolshaya Aleksandrovka, located in the central part of Sakhalin island. The conditions of formation of the upper part of the section were identified and engineering-geological elements and their spatial position were selected. The authors zoned the valley territory by the totality of sediments characteristics and variability of the individual parameters in different parts of the section. It was ascertained that since the Upper Pliocene time the bottom of the valley of river Bol. Aleksandrovka was subjected to sustainable lift. The authors determined the break in the alluvium between stations 31-47, which is caused by the washing of a new straightened river channel at the runoff from higher terraces, with edge level on the height of 12 m, to a lower one, with the surface level of 4-6 m above sea level. The formation of the lowest marine terraces of abrasion-accumulative genesis is associated with post-glacial transgression, occurred near 7-9 ka BP, when the sea went inward into the valley of Bol. Aleksandrovka on 5-7 km. Formation of terraces with surface level of 12-15 m can be explained by the ocean level rise at significant glacioeustatic transgressions in Late Pleistocene.
