Zbigniew Lechowicz

Influence of the rotation of principal stress directions on undrained shear strength

Abstract Influence of the rotation of principal stress directions on undrained shear strength. The paper presents the results of research on natural cohesive soil carried out in the Hollow Cylinder Apparatus (HCA). The main goal of this study was to determine the values of undrained shear strength at different angle of the rotation of principal stress directions. The research were carried out with anisotropic consolidation and shearing in undrained conditions (CAU) on cohesive soil with overconsolidation ratio (OCR) equals 4 and plasticity index (Ip) about 77%. The results of laboratory tests allow to assess the influence of the rotation of principal stress directions on undrained shear strength

Chapter 3 Laboratory investigations

Publisher Summary This chapter discusses the laboratory investigations. The common laboratory tests and equipments used for soft mineral soils can also be used for most organic soils. One condition for laboratory tests to be relevant to the field conditions for which the results are applied is that undisturbed and representative samples can be brought into the laboratory and mounted in the testing equipment. Particularly for peats, special samplers have to be used, as well as special trimming and mounting techniques. For fibrous and pseudo fibrous peats many of the common laboratory tests are not relevant. These soil types also often require larger specimens than usual to be tested and special apparatus, such as the compressiometer, to be used rather than ordinary oedometers. The initial ocular inspection and the very simple tests, with alkali extraction and lowering of samples into hydrochloric acid, required for preliminary soil classification, may be carried out in the field. In the laboratory, further quantitative analyses are carried out to enable a more precise classification and to give additional basic data.

Testing of Undrained Shear Strength in a Hollow Cylinder Apparatus

Abstract The paper presents the results of tests performed in a Torsional Shear Hollow Cylinder Apparatus on undisturbed cohesive soils. The tests were performed on lightly overconsolidated clay (Cl) and sandy silty clay (sasiCl). The main objective of the tests was to determine the undrained shear strength at different angles of rotation of the principal stress directions. The results of laboratory tests allow assessing the influence of rotation of the principal stress directions on the value of undrained shear strength that should be used during designing structure foundations

Concept of hybrid embankment

Abstract An innovative technique which is similar to a natural process, i.e., biogeochemical (carbonate) diagenesis, is proposed to construct a hybrid embankment. In this study, the hybrid embankment is defined as a soil embankment which has a microbially induced framework structure of sand sheets and columns in the soft soil matrix. The sand materials are cemented with magnesium-calcite or dolomite, induced by ureolytic microbes. To design and construct hybrid embankments, fundamental problems, such as feasibility in terms of stability, geoenvironmental engineering practices, etc., are examined and discussed. It was shown that the hybrid embankment can be environmentally friendly and also can contribute solving technical and financial problems encountered in actual practice.

Settlement evaluation of spread foundations on heavily preconsolidated cohesive soils

Settlement evaluation of spread foundations on heavily preconsolidated cohesive soils The paper presents the results of field and laboratory tests performed on the heavily preconsolidated boulder clays which prevail on the campus of the Warsaw University of Life Sciences - SGGW as foundation layers. Based on the results of field and laboratory tests a problem of spatial variability assessment of the thickness of foundation layers and the soil parameters is discussed. Special attention is drawn to the selection of the design values of oedometer moduli and the suitability of calculation methods for settlement evaluation. Calculated settlements were approved by the field measurements performed during building construction. Ocena osiadań fundamentów bezpośrednich posadowionych na prekonsolidowanych gruntach spoistych Projektowanie budynków z użytkową częścią podziemną stwarza często warunki bezpośredniego posadowienia fundamentów na występujących w podłożu silnie prekonsolidowanych gruntach spoistych. Duże wartości parametrów wytrzymałościowych prekonsolidowanych gruntów spoistych powodują, że decydujące znaczenie ma zapewnienie nieprzekroczenia stanu granicznego użytkowalności. Zróżnicowanie obciążenia przy zmiennej miąższości występujących warstw, charakteryzujących się najczęściej różną ściśliwością, wymaga od projektanta bardziej precyzyjnej prognozy osiadań. Poprawna prognoza osiadań, oprócz oceny obciążeń i dobrego rozpoznania warunków geotechnicznych posadowienia, wymaga właściwego doboru parametrów geotechnicznych do obliczeń. W artykule przeprowadzono ocenę przemieszczeń pionowych fundamentów bezpośrednich posadowionych na silnie prekonsolidowanych glinach zwałowych. Moduły ściśliwości wyznaczono na podstawie badań dylatometrycznych wykorzystując w interpretacji zależność podaną przez Marchettiego oraz zależność opracowaną dla gruntów spoistych z rejonu Warszawy. Obliczenia przemieszczeń pionowych pozwoliły na ocenę doboru modułów ściśliwości z badań dylatometrycznych oraz porównanie obliczonych przemieszczeń pionowych na podstawie wyznaczonych modułów oraz analizy numerycznej z wartościami pomierzonymi.

Determination of undrained shear strength and constrained modulus from DMT for stiff overconsolidated clays

Abstract The paper presents the results of dilatometer and laboratory tests performed on heavily preconsolidated boulder clays and Pliocene clays prevailing in the Warsaw region. Several different correlations available for evaluating undrained shear strength and constrained modulus from dilatometer tests are discussed. Empirical coefficients for multi-factor correlation to obtain undrained shear strength from dilatometer tests for boulder clays and Pliocene clays were determined. The relationship between factor RM and horizontal stress index (KD) for boulder clays was proposed for the evaluation of constrained modulus from dilatometer tests.

Wyznaczanie wybranych parametrów geotechnicznych prekonsolidowanych gruntów spoistych na podstawie sondowań SDMT

The paper presents seismic flat dilatometer tests (SDMT) results carried out at selected test sites located in Warsaw. The primary focus has been given to analysis of preconsolidated cohesive soils. Both, in situ, as well as, laboratory test results are presented and discussed. The paper briefly presents soil conditions at each test site, and describes the test carried out. Based on the comparison of the results of laboratory tests with the results of the SDMT, an assessment of the use of the Marchetti and Crapps nomogram was made to determine the type and state of the tested cohesive soils. Analysis of the results of the SDMT allowed to develop for the investigated cohesive soils the empirical relationship between the G0/ED ratio and the material index ID.

Chapter 4 Stability analysis

Publisher Summary This chapter discusses the stability analysis. For embankments and dikes on organic soils, an evaluation of the stability during construction is of major importance. Stability analyses may also have to be carried out for other particular loading situations, such as: (a) steady seepage conditions, (b) sudden drawdown of the water level, and (c) application of additional load. In estimation of stability of embankments on organic soils, two particular cases may be identified: single-stage loading—when the initial shear strength of the soil is sufficient to support safely the maximum embankment load—and multi-stage loading—which requires evaluation of the shear strength increase with load and time for the design of a safe loading rate. In evaluation of the stability of embankments on organic soils, more attention should be paid to the appropriate selection of initial values of soil parameters and their changes due to consolidation than to the application of more complex methods of stability calculation.