16 research outputs found
Economic Sampling and Extraction of Undisturbed, High Quality Samples in Normally Consolidated Lacustrine Clays Using a Large Diameter Tube
No full textThis paper describes the development, design and use of a large diameter sampling tube. High quality test specimens are essential for the investigation of mechanical properties of a soil for high risk projects and when complex and expensive testing methods are to be used. Block sampling is recommended to give the highest sample quality for clayey soils, however, extracting blocks of normally consolidated lacustrine silty clay without excessive disturbance was challenging due to the inherent structure of the soft varved silty clay and difficulty in maintaining Ko conditions, as well as no vertical strain, in the sample. A new sample tube, with an inner diameter of 196mm, an area ratio of 4% and an outer cutting-edge angle of 11° was designed to offer a larger cross sectional area than conventional thin walled sampling tubes, to provide the necessary side support and to prevent water ingress at the sides of the sample. The length-diameter aspect ratio was 1.275 to optimise the amount of clay sampled for subsequent testing and in an attempt to minimize the pressure in front of the tube. Samples were taken in initially newly excavated trenches at a depth of c. 1m with this new sampler and with conventionally sampled soil specimens, prior to the main testing programme with samples from 6m depth. A comparative study was then performed including preliminary unconsolidated unconfined compression tests followed by anisotropically consolidated undrained triaxial compression tests. It was important to establish whether this approach had led to an improvement in sample quality prior to embarking on an extensive triaxial stress path testing programme on this varved soil (Messerklinger, Non-linearity and small strain behaviour in lacustrine clay, 2006; Messerklinger and Springman, Geotech Test J 30(6), 2007; Messerklinger and Springman, Geotech Geol J, 2008). The results showed that the undrained shear strength of the specimens from the new sampler was consistently around 20% higher than that of specimens extruded from conventional thin walled tube samplers. This confirmed that samples with a significantly higher quality could be extracted from normally consolidated, fine grained, varved lacustrine deposits with this large diameter ‘block' sampling tub
Non-Linear Elasto-Plastic Behaviour of Lacustrine Clay
No full textThe paper presents the experimental investigation and analysis of the non-linear elasto-plastic stress-strain behaviour of normally consolidated lacustrine clay. Drained triaxial stress path tests were performed on natural block samples of Swiss lacustrine clay. Data were analysed using plasticity theory and the shape and extent of kinematic yield and bounding surfaces were determined and found to be elliptical but not congruent. Cross-anisotropic elasticity was used to quantify elastic strains to permit plastic strain increment vectors and hence a plastic potential surface to be define
CLINICAL AND EPIDEMIOLOGICAL FEATURES OF INTRACRANIAL COMPLICATIONS OF INFLAMMATORY DISEASES OF THE ENT ORGANS IN CONDITIONS OF THE EAST-SIBERIAN REGION OF RUSSIAN FEDERATION
No full textThe authors investigated the epidemiological and clinical features of otogenic and rhinosinusogenic intracranial complications in East-Siberian region of Russian Federation. The rate of intracranial complications consisted of 0,2±0,1% in patients of ENT hospitals in Sakha- Yakutia, Krasnoyarsk Territory, Irkutsk Region, Republic of Tuva. The intracranial inflammatory pathology of otogenic nature was diagnosed two times more frequent than rhinosinusogenic. Meningitis was revealed at the same rate as lesions of brain substance (encephalitis, epi- and subdural abscesses). The high clinical efficacy was shown in surgical treatment of purulent polysinusitis using W. Messerklinger method of functional endoscopic rhinosinusosurgery (FESS). The method of transtemporal incision and drainage of otogenic abscess of the brain temporal lobe has a number of essential defects, because of them, the indications for application of this method should be considered and specified. It is necessary to have an interdisciplinary approach and use the modern achievements of medical science in order to develop the efficacy of treatment of given category of patients
Micromechanical analysis of kinematic hardening in natural clay
No full textThis paper presents a micromechanical analysis of the macroscopic behaviour of natural clay. A microstructural stress-strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. Numerical simulations of multistage drained triaxial stress paths on Otaniemi clay have been performed and compared the numerical results to the experimental ones in order to validate the modelling approach. Then, the numerical results obtained at the microscopic level were analysed in order to explain the induced anisotropy observed in the clay behaviour at the macroscopic level. The evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material
The investigation of tube sampling disturbance using transparent soil and particle image velocimetry
No full textA small-scale physical modelling system was developed and employed to investigate the effects of tube sampling. Amorphous silica and an oil blend of matching refractive index were mixed to form a transparent soil. Black glass beads were embedded within the soil body on the vertical central plane. After consolidation in a Perspex box, a glass model sampler was pushed into the transparent soil. Movements within the soil body were recorded using digital photography; these images were later analysed by Particle Image Velocimetry.
The centreline strain path (CSP) of the sample during tube penetration was calculated and compared to existing analytical and numerical models’ strain predictions, and some degree of correlation was observed. However, it is shown that the CSP is not constant throughout the sample, but varies with depth below the base of the borehole. It was also noticed that after tube penetration, significant residual extensive strains remain for soil on the centreline of the specimen. Different tube geometries were tested and a correlation was found between strain magnitudes and the Area Ratio, Inside Clearance Ratio and the Outer Cutting Edge Taper Angle. It was also found that samples taken in normally consolidated soils were more heavily disturbed than those in lightly overconsolidated soils. After removal from the soil model, samples were stored for six months and volumetric strains within them, set up by a redistribution of pore fluid pressures, were found to be small, typically less than 1%. Soil at the edge of the sampler wall reduced in volume, while the centre swelled. Specimens were thereafter extruded from the sampling tube and the strain path created by this step was quantified. It was found that extrusion compresses the soil while still inside the tube, with soil closest to the extruder more significantly affected. All of these parts of the sampling process contribute to the overall sample disturbance and can therefore have an effect on the sample’s measured properties
