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Reliability of Methods for Determination of Stress History Parameters in Soils

Wdowska Małgorzata, Lipiński Mirosław J.

Studia Geotechnica et Mechanica

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2023

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Vol. 45, nr s1

350--361

EN

Stress history acquired by any cohesive soil influences, to a large extent, three groups of fundamental properties indispensable in geotechnical design i.e. state of soil, shear strength, and stiffness characteristics. The basic stress history parameter (from which other parameters are derived) determined directly from laboratory tests is a pre consolidation stress σ′p. Since the first method proposed by Casagrande in 1936, value σ′p is determined in the oedometer test as a border between over consolidated (OC) and normally consolidated (NC) zones. Approach based on division between predominantly elastic, (recoverable) strain, and plastic (irrecoverable) strain is a main principle of several methods of σ′p determination, which have been proposed over the past eighty-six years. Accumulated experiences have revealed that any laboratory procedure based on the oedometer test does not provide realistic value of pre consolidation stress, especially in heavy pre consolidated soils. The major reason for that results from the fact that the mechanism responsible for natural over consolidation is more complicated than mechanical preloading. Therefore, there is a necessity to reevaluate effectiveness of standard methods and look for another solution of evaluation yield stress σ′Y in natural soils. This article presents the comparison between σ′Y determined for various soils with use of standard methods based on conventional oedometer test and yield stress determined on the basis of alternative procedures. The latter are represented by various approaches as e.g. based on SHANSEP procedure or initial shear modulus and others. The most promising among these alternative methods is a new concept based on dilatancy phenomenon that takes place during shearing of a dense soil. The parameter reflecting stress history is derived from pore pressure response and is based on characteristic values of Skempton's parameter A record. Consistency of data concerning stress history parameters profile obtained for deep subsoil on the basis of various methods is shown for comparison.

2

Numerical analysis of the deep drawing process including the history of stress and strain

Kaldunski P.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 3

781--792

EN

This paper discusses the results of a numerical study of circular cup drawing of steel sheets using ﬁnite element method. The drawing process is considered as a geometrical and physical nonlinear problem with unknown boundary conditions in the contact area of the system, such as the tool and the workpiece. The updated Lagrangian description is used to characterize these nonlinear phenomena on a typical incremental step time. Numerical results are obtained using an explicit method in Ansys/Ls-Dyna program. The constitutive Cowper-Symonds material model with linear hardening strain to predict material plasticity is used. The results of implementation of stresses and strains from a blanking operation ﬂat disc of a sheet of metal for deep-drawing process are presented. After the blanking process simulation, an implicit springback analysis is performed. Then a numerical analysis of cup forming from this ﬂat disc plate was carried out. The analysis results are compared with one another through reading of the sheet thickness in several characteristic points and the overall height of the product.

3

The elastic undrained modulus Eu50 for stiff consolidated clays related to the concept of stress history and normalized soil properties

Stróżyk J., Tankiewicz M.

Studia Geotechnica et Mechanica

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2016

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Vol. 38, nr 3

67--72

EN

The paper presents the results of a triaxial test conducted on stiff, consolidated clays. The standard TXCIU procedure (isotropic consolidation and undrained shearing) was applied in the laboratory soil tests. The undrained elastic modulus Eu50 was de- termined from each test. The Eu50 values were determined for soil samples cut out from different depths and tested under different confining pressures. There was a significant scatter of values with depth, and no relationships between Eu50 modules or other geotechnical parameters (e.g., cu) were observed. This work presents the concept of normalization of Eu50 modulus values using modified normalization SHANSEP (Stress History And Normalized Soil Engineering Properties). This method was first proposed for estimating the value of the undrained shear strength cu normalizing the parameter relative to the in situ effective vertical stress σ vo and loading history (overconsolidation stress σ p and overconsolidation ratio OCR) of the soil. The study demonstrated that the concept of normalization of soil properties can also be used for testing elastic modulus Eu50 of con- solidated natural clays and normalized values of geotechnical parameters taking into account the state of stress and load history can be correlated with the value of the overburden pressure.

4

Grunty – przykład materiałów z pamięcią

Rabarijoely S., Garbulewski K.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2012

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Vol. 21, No. 3

182--194

PL

W artykule przedstawiono genezę i ogólną charakterystykę gruntów występujących w Polsce oraz metody badań laboratoryjnych i terenowych (CPT/DMT) wykonywanych w celu określenia naprężenia prekonsolidacji (σ’p) i współczynnika prekonsolidacji (OCR). Ponadto artykuł zawiera wyniki badań warunków geotechnicznych posadowienia obiektów kampusu SGGW. Analiza genezy i właściwości gruntów występujących w Polsce i wyniki badań podłoża obiektów na Kampusie SGGW uzasadniają propozycję włączenia gruntów do grupy materiałów z pamięcią.

EN

The paper focus on the genesis and general characteristics of the soils distinguished in Poland, laboratory and field methods (CPT/DMT tests) used for determination of preconsolidation stress (σ' p) and overconsolidation ratio (OCR). Moreover, the tests results obtained for geotechnical conditions in subsoils of design buildings at the SGGW Campus were presented. Analysis of the formations of soils in Poland and the results of the research justify the proposal to include soils to a group of smart materials, this mains materials with the memory of the history of stress.

5

A new approach to define surface/sub-surface transition in gravel beds

Haynes H., Ockelford A.-M., Vignaga E., Holmes W.

Acta Geophysica

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2012

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Vol. 60, no. 6

1589-1606

EN

The vertical structure of river beds varies temporally and spatially in response to hydraulic regime, sediment mobility, grain size distribution and faunal interaction. Implicit are changes to the active layer depth and bed porosity, both critical in describing processes such as armour layer development, surface-subsurface exchange processes and siltation/sealing. Whilst measurements of the bed surface are increasingly informed by quantitative and spatial measurement techniques (e.g., laser displacement scanning), material opacity has precluded the full 3D bed structure analysis required to accurately define the surface-subsurface transition. To overcome this problem, this paper provides magnetic resonance imaging (MRI) data of vertical bed porosity profiles. Uniform and bimodal (σg = 2.1) sand-gravel beds are considered following restructuring under sub-threshold flow durations of 60 and 960 minutes. MRI data are compared to traditional 2.5D laser displacement scans and six robust definitions of the surface-subsurface transition are provided; these form the focus of discussion.

6

Analysis of changes in overconsolidation ratio in selected profiles of non-lithified deposits

Wierzbicki J.

Architecture Civil Engineering Environment

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2009

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Vol. 2, no. 3

77-84

EN

The changes in overconsolidation ratio OCR under different geological conditions are analyzed in the paper. The application of modern subsoil testing methods, dilatometer tests (DMT) and cone penetration test (CPTU), made possible almost continuous observation of changes in overconsolidation ratio with depth. This fact allowed observing regularities and irregularities in stress history of investigated deposits. Some of these changes in stress were interpreted as consecutive stages of sedimentation and erosion, which made possible to find different stages of sedimentation and stratigraphic gaps along tested profiles. The paper points out the potential application of DMT and CPTU tests in geological analyses, particularly those connected with the analysis of stratigraphy of Cainozoic sediments.

PL

W artykule przedstawiono analizę zmian wartości wskaźnika prekonsolidacji (OCR) gruntu, w zależności od geologicznych warunków występowania. Zastosowanie w badaniach nowoczesnych technik in-situ, sondowania statycznego CPTU i badania dylatometrem płaskim (DMT), umożliwiło niemal ciągłą identyfikację wartości OCR wzdłuż analizowanych profili. Możliwość ta pozwoliła na obserwację pewnych nieregularności w przebiegu historii obciążenia podłoża. Niektóre z tych nieregularności zostały zinterpretowane jako przejaw następujących po sobie procesów sedymentacji i erozji. Takie spostrzeżenie pozwoliło na bardziej pełne odtworzenie stratygrafii badanych osadów. W pracy podkreślono możliwości jakie daje zastosowanie nowoczesnych badań in-situ (CPTU i DMT) w analizie historii geologicznej podłoża zbudowanego z kenozoicznych gruntów nieskalistych.

7

Czynniki warunkujące zmienność modułu odkształcenia gruntów spoistych

Wdowska M. K., Wudzka A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2006

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Vol. 15, No. 1

64--74

EN

The paper presents analysis of factors that subject a value o f Young's m odulus of cohesive soils. This parameter is indispensable in a design process of all soil structures and any engineering structure founded on soil. According to Polish practice expressed in Polish Standard PN-81/B-03020, value of Young’s modulus is uniquely related to soil kind and liquidity index. The paper presents considerably larger number of factors that influences deformation of soils with particular reference to strain range, State of stress and its history. From this results that Young's modulus should be perceived rather as deformation characteristic dependent on many factors and not material constant. The theses presented in the paper are exemplified by experimental data.

8

Soft Soil Overconsolidation and CPTU Dissipation Test

Bałachowski L.

Archives of Hydro-Engineering and Environmental Mechanics

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2006

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Vol. 53, nr 2

155-180

EN

Stress state and stress history of subsoil under the flood embankment was evaluated with CPTU and DMT tests. The CPTU dissipation tests in soft soils under the central part of the embankment and on the upstream and downstream sides were performed. The shape of pore water dissipation curve reflects stress state and stress history. Monotonic decay of water pore pressure was found for normally consolidated soils. Dilatory pore pressure response is typical for overconsolidated soils. Methods for the flow characteristics determination (coefficient of consolidation and hydraulic conductivity) were presented.