- Détails du magazine
- Format
- Magazine
- eISSN
- 2083-831X
- Première publication
- 09 Nov 2012
- Période de publication
- 4 fois par an
- Langues
- Anglais

#### Chercher

- Accès libre

The Evaluation of the Initial Shear Modulus of Selected Cohesive Soils

Pages: 3 - 9

#### Résumé

The paper concerns the evaluation of the initial stiffness of selected cohesive soils based on laboratory tests. The research materials used in this study were clayey soils taken from the area of the road embankment No. WD-18, on the 464th km of the S2 express-way, Konotopa-Airport route, Warsaw. The initial stiffness is represented here by the shear modulus (G_{max}) determined during resonant column tests. In the article, a number of literature empirical formulas for defining initial value of the shear modulus of soils being examined were adopted from the literature in order to analyze the data set. However, a large discrepancy between laboratory test results and the values of G_{max} calculated from empirical relationships resulted in the rejection of these proposals. They are inaccurate and do not allow for an exact evaluation of soil stiffness for selected cohesive soils. Hence, the authors proposed their own empirical formula that enables the evaluation of the test soils’ G_{max} in an easy and uncomplicated way. This unique formula describes mathematically the effect of certain soil parameters, namely mean effective stress ( p′) and void ratio (e), on the initial soil stiffness.

#### Mots clés

- initial soil stiffness
- cohesive soils
- resonant column tests

- Accès libre

Repeated Loading of Cohesive Soil – Shakedown Theory in Undrained Conditions

Pages: 11 - 16

#### Résumé

The development of industry and application of new production techniques could bring about extraordinary problems that have been neglected. One of these challenges in terms of soil mechanics is high frequency cyclic loading. Well constructed foundation may reduce this troublesome phenomenon but excluding it is usually uneconomic.

In this paper, shakedown theory assumptions were studied. Cyclically loaded soils behave in various ways depending on the applied stress rate. Common cohesive soils in Poland, i.e., sandy-silty clays are problematic and understanding of their behaviour in various conditions is desired. In order to study repeated loading of this material, cyclic triaxial test were carried out. Cyclic loading tests were conducted also in one way compression. These methods in small strain regime allow permanent strain increment analysis with resilient response after numerous cycles. This behaviour was subsequently exploited in the study of shakedown theory. This paper contains some conclusions concerning the above-mentioned theory.

#### Mots clés

- cyclic
- triaxial test
- clay
- shakedown
- undrained
- resilient modulus

- Accès libre

On Some Methods in Safety Evaluation in Geotechnics

Pages: 17 - 32

#### Résumé

The paper demonstrates how the reliability methods can be utilised in order to evaluate safety in geotechnics. Special attention is paid to the so-called reliability based design that can play a useful and complementary role to Eurocode 7. In the first part, a brief review of first- and second-order reliability methods is given. Next, two examples of reliability-based design are demonstrated. The first one is focussed on bearing capacity calculation and is dedicated to comparison with EC7 requirements. The second one analyses a rigid pile subjected to lateral load and is oriented towards working stress design method. In the second part, applications of random field to safety evaluations in geotechnics are addressed. After a short review of the theory a Random Finite Element algorithm to reliability based design of shallow strip foundation is given. Finally, two illustrative examples for cohesive and cohesionless soils are demonstrated.

#### Mots clés

- reliability index
- random field
- Eurocode 7

- Accès libre

Theoretical Analysis of Model Seabed Behavior under Water Wave Excitation

Pages: 33 - 37

#### Résumé

Theoretical analysis of the behavior of a model seabed subjected to water wave excitation is presented. The experiments were performed in the wave flume at the Danish Technological University in Lyngby. Such experiments are unique in engineering sciences and therefore provide unique empirical data for testing various models of the seabed. A controversial explanation of the experiments is presented in the literature. The goal of this research was to study pore pressure changes caused by water waves and the subsequent liquefaction of the seabed. The authors of the present contribution offer their own theoretical explanation of the wave flume experiments and discuss errors found in the literature cited. The analysis is based on the classical soil mechanics, including the Biot type approach

#### Mots clés

- seabed
- liquefaction
- wave-flume experiments
- saturated soil

- Accès libre

Liquefaction of Saturated Soil and the Diffusion Equation

Pages: 39 - 44

#### Résumé

The paper deals with the diffusion equation for pore water pressures with the source term, which is widely promoted in the marine engineering literature. It is shown that such an equation cannot be derived in a consistent way from the mass balance and the Darcy law. The shortcomings of the artificial source term are pointed out, including inconsistencies with experimental data. It is concluded that liquefaction and the preceding process of pore pressure generation and the weakening of the soil skeleton should be described by constitutive equations within the well-known framework of applied mechanics. Relevant references are provided

#### Mots clés

- liquefaction
- diffusion equation
- saturated soil
- seabed

- Accès libre

Scale Effect in Direct Shear Tests on Recycled Concrete Aggregate

Pages: 45 - 49

#### Résumé

The depletion of natural resources is forcing researchers to explore the possibilities of new aggregates, such as recycled concrete aggregate (RCA). In this article, the mechanical properties and the influence of the size of the direct shear box on the obtained parameters were examined. The study was conducted in two apparatus: medium (120 × 120 mm) and large (250 × 250 mm). In each of these devices, a total of 6 tests were performed: 3 for dry sample and 3 at optimum moisture content. From the results, the conclusions described below have been drawn

#### Mots clés

- direct shear test
- recycled concrete aggregate
- scale effect
- box size

#### Résumé

The article presents a comparison of shear strength values in silty soils from the area of Poznań, determined based on selected N_{kt} values recommended in literature, with values of shear strength established on the basis of N_{kt} values recommended by the author. Analysed silty soils are characterized by the carbonate cementation zone, which made it possible to compare selected empirical coefficients both in normally consolidated and overconsolidated soils

#### Mots clés

- shear strength
- cone factor Nkt
- silty soils

- Accès libre

Influence of Strain Rate on Tensile Strength of Woven Geotextile in the Selected Range of Temperature

Pages: 57 - 60

#### Résumé

Investigation of geosynthetics behaviour has been carried out for many years. Before using geosynthetics in practice, the standard laboratory tests had been carried out to determine basic mechanical parameters. In order to examine the tensile strength of the sample which extends at a constant strain rate, one should measure the value of the tensile force and strain. Note that geosynthetics work under different conditions of stretching and temperatures, which significantly reduce the strength of these materials. The paper presents results of the tensile test of geotextile at different strain rates and temperatures from 20 °C to 100 °C. The aim of this study was to determine the effect of temperature and strain rate on tensile strength and strain of the woven geotextile. The article presents the method of investigation and the results. The data obtained allowed us to assess the parameters of material which should be considered in the design of the load-bearing structures that work at temperatures up to 100 °C.

#### Mots clés

- geotextile
- tensile strength
- strain rate
- temperature

- Accès libre

Improved Formulation of the Hardening Soil Model in the Context of Modeling the Undrained Behavior of Cohesive Soils

Pages: 61 - 68

#### Résumé

The analysis of an important drawback of the well known Hardening Soil model (HSM) is the main purpose of this paper. A special emphasis is put on modifying the HSM to enable an appropriate prediction of the undrained shear strength using a nonzero dilatancy angle. In this light, the paper demonstrates an advanced numerical finite element modeling addressed to practical geotechnical problems. The main focus is put on serviceability limit state analysis of a twin-tunnel excavation in London clay. The two-phase formulation for partially saturated medium, after Aubry and Ozanam, is used to describe interaction between soil skeleton and pore water pressure.

#### Mots clés

- soil constitutive modeling
- undrained shear strength
- deep excavations

- Accès libre

Testing of Undrained Shear Strength in a Hollow Cylinder Apparatus

Pages: 69 - 73

#### Résumé

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

#### Mots clés

- Keywords undrained shear strength
- cohesive soils
- principal stress directions
- hollow cylinder tests

- Accès libre

Remediation of Acid Generating Colliery Spoil Using Steel Slag – Case Studies

Pages: 75 - 84

#### Résumé

One of the legacies of the coal mining industry is the existence of numerous colliery spoil mounds. Run-off waters from some of these mounds result in oxidation of sulphur compounds causing pH to drop to perhaps as low as 2.5. At this pH, mobility for metals increases and it results in destruction of both flora and fauna. In order to reduce acidity, a number of solutions have been investigated with varying degree of success. A recent study to reduce acidity in spoil run-off water included the use of Basic Oxygen Steel slag. Its slow release of lime resulted in longer term remediation compared with other techniques. In addition to this, steel slag contains elements which are essential for plant growth and can be regarded as a weak fertiliser. This was substantiated in two field trials, which had the aim of not only remediating acidity from two different types of colliery spoils, but also to develop a composition that supports grass growth. The objectives were achieved at both sites and some of the results of over 5000 chemical tests conducted during these studies are reported in this paper.

#### Mots clés

- Keywords colliery spoil
- steel slag
- limestone quarry fines
- remediation of acidity

- Accès libre

Evaluation of the Impact of Hydrostatic Pressure and Lode Angle on the Strength of the Rock Mass Based on the Hoek–Brown Criterion

Pages: 85 - 91

#### Résumé

Determination of the global uniaxial compressive strength of rock mass on the basis of the Hoek-Brown failure criterion requires knowledge of the strength parameters: cohesion and the angle of internal friction. In the conventional method for the determination of these parameters given by Balmer, they are expressed by the minimum principal stress. Thus, this method does not allow for the assessment of an impact of hydrostatic pressure and stress path on the value of cohesion, friction angle and global uniaxial compression of rock mass. This problem can be eliminated by using the Hoek-Brown criterion expressed by the invariants of the stress state. The influence of hydrostatic pressure and the Lode angle on the strength parameters of the rock mass was analysed.

#### Mots clés

- generalized Hoek-Brown failure criterion
- equivalent cohesion
- equivalent friction angle
- the global strength
- invariant stress

- Accès libre

Slope Stability Estimation of the Kościuszko Mound in Cracow

Pages: 93 - 101

#### Résumé

In the paper, the slope stability problem of the Kościuszko Mound in Cracow, Poland is considered. The slope stability analysis was performed using Plaxis FEM program. The outer surface of the mound has complex geometry. The slope of the cone is not uniform in all directions, on the surface of the cone are pedestrian paths. Due to its complicated geometry it was impossible to do computing by Plaxis input pre-procesor. The initial element mesh was generated using Autodesk Autocad 3D and next it was updated by Plaxis program. The soil parameters were adopted in accordance with the detailed geological soil testing performed in 2012. Calculating model includes geogrids. The upper part was covered by MacMat geogrid, while the lower part of the Mound was reinforced using Terramesh Matt geogrid. The slope analysis was performed by successives reduction of φ /c parameters. The total multiplayer ΣM_{sf} is used to define the value of the soil strength parameters. The article presents the results of slope stability before and after the rainfall during 33 days of precipitation in flood of 2010.

#### Mots clés

- soil analysis by FEM
- slope stability analysis of soil mound
- numerical analysis by PLAXIS program