TY - THES

T1 - Geological and geotechnical characterization and correlation of samples from El Misti (Peru)

AU - Winstel, Ruben Nicolas

N1 - no embargo

PY - 2024

Y1 - 2024

N2 - Recently, the interaction and influence of geological characteristics on geotechnical parameters has been increasingly investigated. In particular, the influence of porosity and the proportion of phenocrysts on the rock strength in volcanic rocks is of interest. As part of the UNSA II cooperation, volcanites from the El Misti stratovolcano in Peru were sampled and examined regarding the lithology, geological comparability and geological and geotechnical characterization. Furthermore, it was tested whether parameters influence or correlate with each other or not. For this purpose, the samples were analysed for uniaxial and triaxial compressive strength, tensile strength, P-wave velocity, porosity and density. Polarisation microscopy, scanning electron microscopy and total rock analysis using X-ray fluorescence analysis were carried out for geological characterization. In most parameters and properties, the samples, consisting of ignimbrites, rhyolites and andesites hardly differed from the Misti rocks described in the literature, and they are also similar to comparable geotechnical investigations on other stratovolcanoes. Mineralogically, no major differences are found between the ignimbrites and rhyolites. The samples also hardly differ geochemically. The main differences are only found in the phenocryst content, the porosity and the parameters influenced by this, such as the rock strength, consisting of tensile strength, uniaxial and triaxial compressive strength. Differences in composition and geochemistry are described in the andesites, particularly, between the andesites of Rio Chili and Rio Andamayo. The latter shows an increased K2O content and is trachyandesitic in composition. The correlation of the geotechnical and geological data prove the strong influence of porosity particularly on the stability and geotechnical properties of all samples. However, by subdividing the samples in pyroclastics and effusives, the pyroclastics show a clear positive correlation of the phenocryst content to most strength parameters, which contradicts to the negative correlation of porosity. A causal relationship has not been proven. Whereas in the effusives the matrix composition is decisive to rock strength in addition to the porosity. An increase in phenocryst content in the effusives leads to a reduction in tensile strength.

AB - Recently, the interaction and influence of geological characteristics on geotechnical parameters has been increasingly investigated. In particular, the influence of porosity and the proportion of phenocrysts on the rock strength in volcanic rocks is of interest. As part of the UNSA II cooperation, volcanites from the El Misti stratovolcano in Peru were sampled and examined regarding the lithology, geological comparability and geological and geotechnical characterization. Furthermore, it was tested whether parameters influence or correlate with each other or not. For this purpose, the samples were analysed for uniaxial and triaxial compressive strength, tensile strength, P-wave velocity, porosity and density. Polarisation microscopy, scanning electron microscopy and total rock analysis using X-ray fluorescence analysis were carried out for geological characterization. In most parameters and properties, the samples, consisting of ignimbrites, rhyolites and andesites hardly differed from the Misti rocks described in the literature, and they are also similar to comparable geotechnical investigations on other stratovolcanoes. Mineralogically, no major differences are found between the ignimbrites and rhyolites. The samples also hardly differ geochemically. The main differences are only found in the phenocryst content, the porosity and the parameters influenced by this, such as the rock strength, consisting of tensile strength, uniaxial and triaxial compressive strength. Differences in composition and geochemistry are described in the andesites, particularly, between the andesites of Rio Chili and Rio Andamayo. The latter shows an increased K2O content and is trachyandesitic in composition. The correlation of the geotechnical and geological data prove the strong influence of porosity particularly on the stability and geotechnical properties of all samples. However, by subdividing the samples in pyroclastics and effusives, the pyroclastics show a clear positive correlation of the phenocryst content to most strength parameters, which contradicts to the negative correlation of porosity. A causal relationship has not been proven. Whereas in the effusives the matrix composition is decisive to rock strength in addition to the porosity. An increase in phenocryst content in the effusives leads to a reduction in tensile strength.

KW - Vulkanite

KW - El Misti

KW - geologische Charakterisierung

KW - geotechnische Charakterisierung

KW - Korrelation von Gesteinseigenschaften

KW - Zentrale Vulkanzone der Anden

KW - Porosität

KW - Druckfestigkeit

KW - Zugfestigkeit

KW - Gesteinsfestigkeit

KW - XRF

KW - REM

KW - Mikroskopie

KW - Volcanites

KW - El Misti

KW - geological characterization

KW - geotechnical characterization

KW - rock parameter correlation

KW - central Andean volcanic zone

KW - porosity

KW - compressive strength

KW - tensile strength

KW - rock strength

KW - XRF

KW - SEM

KW - microscopy

U2 - 10.34901/mul.pub.2025.011

DO - 10.34901/mul.pub.2025.011

M3 - Master's Thesis

ER -