Wpływ struktury gruntów spoistych facji powodziowej na przebieg filtracyjnych deformacji w aluwiach dolnej Wisły

Abstract

EFFECT OF STRUCTURE OF COHESIVE FLOOD FACIES DEPOSITS ON THE COURSE OF THEIR FILTRATIONAL DEFORMATION IN ALLUVIAL DEPOSITS OF THE LOWER VISTULA RIVER Summary The studies on engineering-geological properties of flood and channel fades deposits showed remarkable differences in susceptibility of the deposits of the same genesis to filtrational deformations. Deposits of river valleys are characterized by remarkable changes in structure and texture proceeding over a very short distance. Moreover, markedly increased hydraulic gradients persist for some periods in the area of river valleys. This, together with distinct granulometric differentiation marked at the contacts of layers, and particularly at the contact of channel and flood facies deposits, facilitate development of negative farms related to water filtration, proceeding parallely to the bedding. Intensity of the development of filtrational deformations highly depends on structure and texture, and particularly on the type and amount of water-resistant aggregates of flood facies. In order to examine the mechanism of the origin of negative forms at the contact of channel and flood facies deposits, laboratory model of one of the types of such contacts was formed. It is a model of contact of sandy (channel) and cohesive (flood facies) deposits (Fig. 1). This model was subjected to water flow under the conditions of steadily increasing hydraulic gradient. In the course of the experiment, three zones of formation of these characteristic forms were found (Fig. 2). The studies showed that mechanical contact suffusion is the initial process in the course of formation of filtrational deformations. This process determines development of inter-bed suffusion. Although hydraulic gradient equalled I = 6, water-resistant aggregates of flood facies occurred in amounts sufficient to prevent complete destruction of soil structure, i.e., to prevent liquefaction resulting from the process of inter-bed suffosion.