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Preliminary investigations of creep strain of Neogene clay from Warsaw in drained triaxial tests assisted by computed microtomography

Kaczmarek Ł. D., Dobak P. J., Kiełbasiński K.

Studia Geotechnica et Mechanica

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2017

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Vol. 39, nr 2

35--49

EN

The study concerns soil creep deformation in multistage triaxial stress tests under drained conditions. High resolution X-ray computed microtomography (XμCT) was involved in structure recognition before and after triaxial tests. Undisturbed Neogene clay samples, which are widespread in central Poland, were used in this study. XμCT was used to identify representative sample series and informed the detection and rejection of unreliable ones. Maximum deviatoric stress for in situ stress confining condition was equal 95.1 kPa. This result helped in the design of further multistage investigations. The study identified the rheological strain course, which can be broken down into three characterizations: decreasing creep strain rate, transitional constant creep velocity, and accelerating creep deformation. The study found that due to multistage creep loading, the samples were strengthened. Furthermore, there is a visibly “brittle” character of failure, which may be the consequence of the microstructure transformation as a function of time as well as collapse of voids. Due to the glacial tectonic history of the analyzed samples, the reactivation of microcracks might also serve as an explanation. The number of the various sizes of shear planes after failure is confirmed by XμCT overexposure.

2

Numerical approach in recognition of selected features of rock structure from hybrid hydrocarbon reservoir samples based on microtomography

Kaczmarek Ł. D., Zhao Y., Konietzky H., Wejrzanowski T., Maksimczuk M.

Studia Geotechnica et Mechanica

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2017

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Vol. 39, nr 1

13--26

EN

The study employs numerical calculations in the characterization of reservoir sandstone samples based on high-resolution X-ray computed microtomography. The major goals were to determine porosity through pore size distribution, permeability characterization through pressure field, and structure impact on rock strength by simulation of a uniaxial compression test. Two Miocene samples were taken from well S-3, located in the eastern part of the Carpathian Foredeep. Due to the relation between sample size and image resolution, two X-ray irradiation series with two different sample sizes were performed. In the first approach, the voxel side was 27 µm and in the second it was up to 2 µm. Two samples from different depths have been studied here. Sample 1 has petrophysical features of conventional reservoir deposits, in contrast to sample 2. The approximate grain size of sample 1 is in the range 0.1–1.0 mm, whereas for sample 2 it is 0.01–0.1 mm with clear sedimentation lamination and heterogenic structure. The porosity, as determined by µCT, of sample 1 is twice (10.3%) that of sample 2 (5.3%). The equivalent diameter of a majority of pores is less than 0.027 mm and their pore size distribution is unimodal right-hand asymmetrical in the case of both samples. In relations to numerical permeability tests, the flow paths are in the few privileged directions where the pressure is uniformly decreasing. Nevertheless, there are visible connections in sample 1, as is confirmed by the homogenous distribution of particles in the pore space of the sample and demonstrated in the particle flow simulations. The estimated permeability of the first sample is approximately four times higher than that of the second one. The uniaxial compression test demonstrated the huge impact of even minimal heterogeneity of samples in terms of micropores: 4–5 times loss of strength compared to the undisturbed sample. The procedure presented shows the promising combination of microstructural analysis and numerical simulations. More specific calculations of lab tests with analysis of variable boundary conditions should be performed in the future.

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Zastosowanie numerycznych obliczeń stateczności zboczy dla oceny potencjalnych stref przemieszczeń zwietrzelin i koluwiów rozwiniętych na podłożu fliszowym

Dobak P., Gawriuczenkow I., Kaczmarek Ł. D., Kiełbasiński K., Wójcik E.

Przegląd Geologiczny

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2016

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Vol. 64, nr 9

683--693

EN

This study concerns the modeling potential of slopes development with use of numerical stability calculations. Boundary conditions of performed numerical simulations are according to morphological and geological engineering conditions of the flysch slope shaped by weathering and surface mass movements. The multilaminate material model was used in order to imitate shale spatial variation in weathering zones. Furthermore, X-ray computed microtomography technique enabled for visualization of varied condition of shear surface extortion, which cause physical and strength parameters diversity. Calculation outputs show that geometry and location of deformation zones are affected by a model input strength parameter. The presented results confirm utility of numerical modeling as important aspect in the investigation and verification of spatiotemporal slope development cycle.

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Porównanie wyników analiz zawartości części organicznych w iłach mioplioceńskich z podłoża stacji Centrum Nauki Kopernik II linii metra w Warszawie

Kaczmarek Ł. D., Gawriuczenkow I.

Przegląd Geologiczny

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2016

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Vol. 64, nr 7

489--494

EN

The paper attempts to answer the question which method provides an accurate assessment of organic matter content in the study of Mio-Pliocene clay. Samples were taken from the excavation of Copernicus Science Centre metro station. The soil was tested by three most common techniques: ignition loss method, reaction with hydrogen peroxide, and Tiurin method. Furthermore, thermal method (DTA) was used as a complex method for mineral composition (including organic matter) verification. Results of Tiurin and DTA methods provided information about the residual presence of organic matter in the Mio-Pliocene clay. Nonetheless, because of their simplicity, the commonly used methods are ignition loss and reaction with hydrogen peroxide. The results of ignition loss method were ~7 times higher than those of the other methods. The reaction with hydrogen peroxide method, revealed a negative result ~ –0.89%, due to oxidation of iron and hydration of its compounds. Based on these observations, it can be concluded that the Tiurin method is the recommended technique for the assessment of organic matter content in cohesive soils. However, for studies requiring high accuracy and reliability, the thermal method is recommended. It is important to pay special attention in organic matter evaluation particularly for commercial projects, because organic matter evaluation can result in a large increase in the cost of investment.

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Wpływ wybranych aspektów symulacji numerycznych na wyniki obliczeń stateczności Skarpy Warszawskiej w obszarze Południowej Obwodnicy Warszawy

Kaczmarek Ł. D., Popielski P.

Inżynieria Morska i Geotechnika

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2016

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nr 4

210--215

PL

Opis i interpretacja wyników obliczeń numerycznych metod równowagi granicznej oraz MES w dwóch przekrojach. Analiza wpływu różnych form dyskretyzacji modelu geotechnicznego na wskaźnik stateczności F. Porównanie wyników obliczeń MES z wykorzystaniem dwóch programów (Z_Soil i PLAXIS). Analiza przeprowadzona dla przypadku Skarpy Warszawskiej w dwóch prostopadłych do rozciągłości skarpy, sąsiadujących przekrojach w obszarze projektowanej Południowej Obwodnicy Warszawy (POW).

EN

Description and interpretation calculation results of limit equilibrium methods and FEM in two cross-sections. The impact analysis of different forms of mesh discretization on slope stability factor F. Comparison of FEM simulations results of two calculation programs (Z_Soil and PLAXIS). Analysis conducted for the Warsaw Slope in two cross-section perpendicular to extent of the slope, in proximity to the Warsaw Southern Ring Road.