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Laboratory research on stiffness of unsaturated soil in very small and small strain region
Mohyla, Tomáš ; Boháč, Jan (advisor) ; Herle, Ivo (referee) ; Panuška, Jakub (referee)
Unsaturated soils have come into focus of the geotechnical community in recent decades. They are commonly found in the interaction of structures with the geological environment. Laboratory tests are important to provide information on the behaviour of unsaturated soils and as a fundamental input for the design of engineering structures. Laboratory tests can also be used to design and calibrate numerical models describing the behaviour of unsaturated soils. One of the important input parameters of such models is the initial stiffness of the soil and its decrease with increasing strain. This thesis deals with a laboratory investigation of the stiffness of unsaturated soil in the regions of very small and small strains. The tested soil was a loess from the quarry near the village of Horky nad Jizerou, Central Bohemia, which represents a typical soil found in engineering practice. The soil was reconstituted for the purpose of laboratory tests. The maximum (initial) stiffness of the soil was determined from measurements using piezoelectric bender elements and the stiffness decay curves were measured using local strain transducers (LVDTs). The laboratory tests were carried out in a double-walled triaxial cell for unsaturated soils, mounted with a high air-entry value ceramic disc (HAEV). The triaxial...
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Contributions to the experimental investigation and numerical description of soil cyclic behavior
Duque Felfle, Jose Alejandro ; Mašín, David (advisor) ; Herle, Ivo (referee) ; Wichtmann, Torsten (referee)
A wide range of geotechnical structures are subjected to episodes of cyclic loading. Among them, we can for example mention onshore and offshore foundations subjected to environmental loadings, pavements subjected to traffic loading, filling-emptying cycles on silos and water tanks, among many others. In order to develop constitutive models or numerical tools that accurately reproduce the soil behavior on the aforementioned geotechnical problems, a deep understanding on how soil behaves under cyclic loading is necessary. This behavior is, however, not trivial since non-linearity, small strain stiffness, stiffness degradation, cyclic hysteresis and recent stress history play a significant role. This dissertation presents some contributions to the experimental evidence and numerical description of soil cyclic behavior. It begins with comprehensive experimental databases on Malaysian kaolin and Zbraslav sand. In each database, several monotonic and cyclic tests were performed and analyzed considering a wide range of initial conditions and loading characteristics. In particular, the influence of the deviatoric stress amplitude, soil plasticity, initial stress ratio, drained cyclic preloading and sequence of packages of cycles with different deviatoric stress amplitudes was investigated on Malaysian...
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Mechanical behaviour of cemented fine-grained soils - simulation of undisturbed samples
Trhlíková, Jana ; Boháč, Jan (advisor) ; Herle, Ivo (referee) ; Miča, Lumír (referee)
The mechanical behaviour of natural clays is influenced by the degradation of the structure developed during and after deposition. In order to model the influence of structure artificially cemented specimens have been prepared. A series of one-dimensional compression tests of cement treated kaolin specimens were analysed. The effect of bonding and debonding on compression of the specimens was observed. The compression of cemented specimens was not monotonic, depending on disturbance of the structure. Cement content and curing period were found the main factors influencing the compressibility of cement treated kaolin clay. The possibility of using cement treated kaolin to model naturally cemented soil was confirmed. For the purpose of the research described in this dissertation, artificial cementation bonds were created in a model clayey material by adding 4% of Portland cement to kaolin clay. The mechanical behaviour of the model material at compression and shearing was compared with the behaviour of the pure reconstituted kaolin clay. Triaxial CIUP tests were carried out in determining the shear strength. Submersible LVDT's and bender elements were used for measuring of the shear modulus to identify the destructuration of the specimens. The experimental behaviour was successfully simulated by the...
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Modelling of lumpy clay fills
Najser, Jan ; Boháč, Jan (advisor) ; Herle, Ivo (referee) ; Doležalová, Marta (referee)
of the dissertation An extensive open cast mining of brown coal has been taking place in NW Bohemia since 1940's. During the mining process, overburden clay is placed in the form of irregularly shaped lumps of typical dimensions up to 500 mm into large spoil heaps. The total thickness of the lumpy clay landfills is usually 20-50 m. Their material has a double porosity structure: the porosity of intact clay (intragranular porosity) and the voids between clay lumps (intergranular porosity). The total porosity of the fresh fill can be up to 70%. This soil presents special challenges for geotechnical design, primarily because of its high and non-uniform settlement. Further, the progressive tranformation from the "granular" to "fine-grained" material makes the lumpy clay difficult to characterise and model. The aim of the presented thesis is to describe the behaviour of the landfill and the change of its structure by means of field measurements, the centrifuge and numerical modelling. During site investigation for a motorway over a 20-30 years old landfill, two trial embankments were built and 1 monitored over the period of 3 and 6 years respectively. The subsoil of the embankments was instrumented by hydrostatic levelling profiles, pore pressure transducers and depth reference points installed in...
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