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 E_u50 was determined from each test. The E_u50 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 E_u50 modules or other geotechnical parameters (e.g., c_u) were observed. This work presents the concept of normalization of E_u50 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 c_u 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 E_u50 of consolidated 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.

In the paper the results of laboratory investigations of structure of layered soil are presented. They focus on varved clay that is a soil composed of two alternately arranged varves with different texture and mechanical properties. An effect of such structure is an anisotropy of the material. Due to varying conditions during its formation process the soil exhibits some irregularities in composition and structure. Due to that modelling of mechanical behavior, like strength, may not provide satisfactory results. Main purpose of the examinations is an investigation of internal structure of layered soil – varved clay – in relation to its strength anisotropy and evaluation of the suitability of the use of two different techniques to assess the soil structure. Investigated material have been taken from area near city of Bełchatów in central Poland. The examinations included investigation of particle size distribution of soil and its components, identification of lamination with use of scanning electron microscope (SEM) and computed microtomography technique (μCT). First, the texture of each varve and varved clay as a composite have been estimated. Next, the investigation of surface perpendicular to the lamination have been carried out with SEM. Pictures of varves with different magnifications are presented. Also the varves arrangement and details of layers contact area are shown. Finally, investigation of internal structure of the soil have been performed by using microtomograph. The outcome is a series of radiographic images and reconstructed 3D model of tested soil. Presented results show complexity of the structure of varved clay that affect the mechanical behavior. Determination of the structure with use of presented techniques may be helpful in examination of strength properties and proper modeling of such soil.

The paper presents results of laboratory unconfined and confined shear tests. Tests were conducted on samples of clays taken from depth 100-300 meters below ground level. All confined tests were performed in triaxial apparatus following TXCIU procedure. Selected samples were tested in overconsolidation state. The OCR ratio values ranged from 3 to 28. Values of uniaxial compressive strength qu and undrained shear strength cu were established for each OCR ratio. The normalization procedure was done and the normalized ratio cu/σ’vc and qu/σ’vc were obtained. The results were compared with SHANSEP equation. The analysis shows that SHANSEP equation can be used for natural clayey soils in heavily overconsolidated state

Varved clay is a sedimentary soil formed in glacier lakes. It consists of two alternating thin layers with different granulometric composition and mechanical properties. The result of layered structure is strength anisotropy of the material. Such soil requires special attention and design approach in geotechnical engineering. In this paper, the findings of laboratory examinations are presented. The investigations are focused on varved clay found in Poland, near city Bełchatów. In order to evaluate mechanical behavior of tested material, series of conventional triaxial tests have been conducted. Tests have been made on intact cylindrical samples taken from opencast mine, about 30 m below origin ground level. The cores have been cut out at seven various orientations of laminations relative to transverse axis of the specimen, i.e. 0°, 15°, 30°, 45°, 60°, 75°, 90°. Tests have been performed under five different confining pressures, i.e. 200kPa, 400kPa, 600kPa, 800kPa and 1000kPa. Main outcomes of the investigations are directional failure characteristics of the soil. They were plotted by marking the value of peak deviatory stress from each test in dependence to value of orientation angle. Obtained laboratory data have been used for calibration of the selected mathematical model of strength anisotropy, i.e. Pariseau criterion. Comparison of the laboratory data with considered criterion shows a good qualitative agreement

The paper demonstrates the applicability of X-ray microtomography (ìCT) to analysis of the results of shear strength examinations of clayey soils. The method of X-ray three-dimensional imaging offers new possibilities in soil testing. The work focuses on a non-destructive method of evaluation of specimen quality used in shear tests and mechanical behavior of soil. The paper presents the results of examination of 4 selected clayey soils. Specimens prepared for the triaxial test have been scanned using ìCT before and after the triaxial compression tests. The shear strength parameters of the soils have been estimated. Changes in soil structure caused by compression and shear failure have been presented as visualizations of the samples tested. This allowed for improved interpretation and evaluation of soil strength parameters and recognition of pre-existing fissures and the exact mode of failure. Basic geometrical parameters have been determined for selected cross-sections of specimens after failure. The test results indicate the utility of the method applied in soil testing.

In this paper, a qualitative safety analysis of the Żelazny Most tailings pond is addressed. This object is one of the largest facilities of this type in the world being a crucial element in the technological line of copper production in KGHM Polska Miedź S.A. The assessment of the effectiveness of two types of preventive measures, i.e., relief wells and loading berms, is investigated based on displacement and stability analysis of two 2D cross-sections in a technical section of the dam. The study shows that the considered preventive measures generally have a positive impact on increasing the safety level of the structure during its further raise. In particular, their effectiveness is most evident when they are applied simultaneously. It is eventually suggested that the selection of final solutions to be applied on the facility should be based on the quantitative 3D analysis.