The influence of clay minerals on the physical properties of fine-grained soils from the Zagreb Podsljeme area : doctoral thesis

Veliki dio površine podsljemenske zone u gradu Zagrebu prekriven je sedimentima pliokvartarne (PLQ) i gornjomiocenske (GM) stratigrafske pripadnosti. U inženjerskogeološkom smislu to su uglavnom sitnozrnasta tla, karakterističnih fizičko-mehaničkih svojstava i inženjerskog ponašanja. Mehanička svojstva tla prvenstveno ovise o osnovnim fizičko – kemijskim svojstvima tla te faktorima koji na njih utječu. Vrlo veliki utjecaj na navedena svojstva ima udjel glinovite frakcije u tlu te vrste i relativni udjel minerala glina. Cijelo istraživanje temeljeno je na pretpostavci da mehanička svojstva sitnozrnastih tala u podsljemenskoj zoni ovise o količini glinovite frakcije i njezinom mineralnom sastavu te vrsti i relativnom udjelu minerala glina. Cilj istraživanja bio je analizirati i kvantificirati detaljni mineralni sastav spomenutih naslaga te kvantificirati njihova osnovna fizička svojstva kako bi se mogli definirati njihovi statistički odnosi na temelju kojih bi se dobio uvid kako i na koji način utječe mineralni sastav na fizička svojstva sitnozrnastih vrsta tla. Istraživanje je provedeno na ukupno 59 uzoraka sitnozrnastih tala (39 uzoraka PLQ) i (20 uzoraka GM) prikupljenih iz istražnih bušotina na kojima je određen detaljni mineralni sastav, kapacitet kationske izmjene (CEC), granulometrijski sastav, Atterbergove granice i indeks plastičnosti te je izračunata vanjska specifična površina cjelovitih uzoraka (SSA). S obzirom na veliki broj dobivenih podataka za opis i interpretaciju rezultata korišteni su jednostavni statistički testovi (t-test i analiza varijance), multivarijatna diskriminantna analiza te jednostavna korelacijska analiza. Dobiveni rezultati pokazali su kako se PLQ i GM tla razlikuju u vrstama tla prema geomehaničkoj klasifikaciji, fizičkim svojstvima tala, mineralnom sastavu te zastupljenosti i udjelima minerala glina. Isto tako, korelacijskom analizom pokazalo se kako i na koji način pojedine vrste minerala glina utječu na određena fizička svojstva sitnozrnastih tala podsljemenske zone grada Zagreba.About 70% of the Zagreb Podsljeme area is occupied with sediments of Plioquaternary and Upper Miocene age. From an engineering geological point of view, their are mostly fine-grained soils (clays and muds of low and high plasticity) with characteristic properties and engineering geological conditions. Their physical and mechanical properties primarily depend on the basic physico-chemical properties of soil particles and factors that affect them. One of these basic factors that have greatest influence on the main properties of fine-grained soils is the proportion of the clay fraction as well as type and relative proportion of clay minerals. Based on preliminary investigations it has been found that between Plioquaternary and Upper Miocene fine-grained soils in Podsljeme area occurred some differences in particle size distribution, Atterberg limits and plasticity index. It is assumed that these differences are present due to different lithological and mineral composition, especially in amount of clay minerals, because of two different environmental regimes that prevailed at the time of deposition; Upper Miocene lake environment and Plioquaternary alluvial and continental sedimentation environment. Which type of clay minerals and how they affect the physical properties of fine-grained soils was interpreted on the basis of obtained statistical relationships with the Atterberg limits, plasticity index, soil surface area (SSA) and cation exchange capacity (CEC). According to this, it have been set the four research hypotheses: 1. The relative presence of certain types of clay minerals in the Plioquaternary and Upper Miocene fine-grained soils of Zagreb Podsljeme area is different 2. The greatest influence on the Atterberg limits and specific surface area of Plioquaternary fine-grained soils have vermiculites and in Upper Miocene fine-grained soils smectites. 3. Fine-grained soils that do not contain expandable types of clay minerals can also have a large specific surface area and high values of the Atterberg limits. 4. The dependence of the physical properties on the amount and mineral composition of the clay fraction can be described by statistical models. According to these, the main research objectives were to analyze and quantify mineral composition of fine-grained soils, as well as their physical properties and to define statistical relationships between physical properties of soil and relative proportions of clay minerals. For this purpose, 59 samples (39 Plioquaternary fine-grained soils and 20 Upper Miocene fine-grained soils) were collected and laboratory tested. The first step, before laboratory testing, was to classify the samples according to relative geological age and litostratigraphic affiliation. The first phase of laboratory testing involved determining of the particle size distribution and Atterberg limits. Results of these tests served as input data for geomechanical classification according to USCS method and for calculating of specific surface area. The second phase of laboratory testing involved determining the mineral composition of samples by X-ray powder diffraction and measuring of cation exchange capacity by Cu-trien method. In order to find differences in clay mineralogy between two stratigraphic different sets of samples (PLQ and GM), a t-test and analysis of variance (ANOVA) was performed. The next step in the analysis of the obtained data was to define the difference in mineral composition and physical properties between four a priori defined soil classes based on geomechanical classification and stratigraphic affiliation. For this purpose it was used a multivariate discriminant analysis based on the calculations of a series of linear combinations of the observed variable that represent physical properties and mineralogical composition. In order to find whether clay minerals affect the physical properties of fine-grained soils and in which way, it was used a simple linear correlation analysis. The analysis was performed on several soil groups classified based on relative geological age and geomechanical classification. An original scientific contribution of this research lies in a definition and detail knowledge of the mineral composition of Plioquaternary and Upper Miocene fine-grained soils of the Zagreb Podsljeme area. In addition, the scientific contribution is reflected in interpretation of the influence of clay minerals and their proportions in clay fraction on the main physical properties of observed fine-grained soils. And the last, the certain scientific contribution lies in the development of a method for defining the dependence of physical properties and mineral composition of fine-grained soils of Podsljeme area