No description available.

No description available.

The design of interface elements in geotechnical engineering traditionally involves empiricism and lacks a solid fundamental underpinning based on the controlling mechanisms. These design shortcomings exist due to deficiencies in the fundamental understanding of geotechnical interface behaviors and the lack of test methods and devices available to directly measure interface properties in situ. The current work strives to improve the state of geotechnical knowledge and design with regard to interface behavior through fundamental laboratory studies and the development and use of a new in situ testing device. The current investigations are focused across a range of scales from micromechanical interactions to full scale field implementation. A series of laboratory investigations at the micromechanical level have been performed, specifically aimed at investigating the mechanisms controlling granular interactions against conventional and textured friction sleeves, and hook and loop type interactions present within textured geomembrane - geotextile systems. Additionally, a new in situ testing device has been designed and developed, the Multi Piezo Friction Attachment (MPFA), to allow for the characterization of geotechnical interface properties in situ within the context of an effective stress framework. The MPFA simultaneously provides four independent measures of interface friction (f

A laboratory experimental programme was carried out to investigate the behaviour of the piezocone in lightly over consolidated clay. The clay samples were prepared from reconstituted kaolin. The powdered form of this clay was mixed with water to form a slurry at a moisture content of approximately 120% under vacuum. The clay slurry was consolidated and then allowed to swell in chambers which were well instrumented. Penetration tests were carried out with two sizes of piezocones. The smaller piezocone had a cross sectional area of 1cm² with pore pressure measurement at the cone shoulder. The larger piezocone with a cross sectional area of 5cm² had pore pressure measurements at four locations. In addition to penetration testing, further information on the strength and consolidation characteristics of the test chamber samples was obtained form shear vane, restricted flow consolidation, flow pump permeability and consolidated undrained triaxial tests. The horizontal effective stress and the vertical stress ratio were found to influence the generated excess pore pressure at all four different locations on the piezocone shaft and the net tip resistance. This led to the establishment of direct correlations for the tip resistance factor Q with the coefficient for lateral earth pressure at rest Ko and the vertical effective stress ratio (OCR). Direct correlations for the excess pore pressure ratio at all four measuring positions with Ko and OCR were also established. Several methods of estimating over consolidation ratio were examined. One of the factors examined was Bq which was found to correlate poorly with OCR before tending asymptotically to a value of approximately 0.4. Other examples of factors which showed promising results as estimators of OCR were Bmi, the excess pore pressure ratio, and Q, the tip resistance factor. The excess pore pressures well behind the cone shoulder, which are partly generated by the shear stress in the area, showed promising correlations with the undrained shear strength. However, because correlations with pore pressure on the piezocone are dependent upon the position of the filter element, the particular results from this series may only be used for piezocones whose filter elements are at equivalent positions. The undrained strength ratio was also correlated with the tip resistance factor Q and the result was very promising for future interpretation of piezocone data.

The quasi-static penetration of a cone penetrometer into clay can be formulated as a steady state problem by considering a steady flow of soil past a stationary cone. The soil velocities are estimated from the flow field of an inviscid fluid, and the incompressibility condition is achieved by adopting a stream function formulation. Emphasis is placed on obtaining an accurate velocity estimate and this is accomplished by a solution of the Navier-Stokes equations. The strain rates are evaluated from the flow field using a finite difference scheme. The clay is modelled as a homogeneous incompressible elastic-perfectly plastic material and the soil stresses are computed by integrating along streamlines from some initial stress state in the upstream region. These stresses do not in general obey the equilibrium equations, although one of the two equations can be satisfied by an appropriate choice of the mean stress. Several attempts have been made to use the remaining equilibrium equation to obtain an improved velocity estimate and three plausible iterative methods are detailed in this thesis. In a second study, a series of finite element calculations on the cone penetration problem is performed. In modelling the penetration process, the cone is introduced in a pre-formed hole and some initial stresses assumed in the soil, incremental displacements are then applied to the cone until a failure condition is reached. Although the equilibrium condition is satisfied very closely in the finite element calculations, it is extremely difficult to achieve a steady state solution. In a third series of computations, the stresses evaluated by the strain path method are used as the starting condition for the finite element analysis. This is believed to give the most realistic solution of the cone penetration problem because both the steady state and equilibrium conditions are approximately satisfied. Numerically derived cone factors are presented and these are found to depend on the rigidity index of the soil and the in situ stresses. The pore pressure distribution in the soil around the penetrometer is estimated using Henkel's empirical equation. The dissipation analysis is based on Terzaghi's uncoupled consolidation theory. The governing equation is formulated in the Alternating-Direction-Implicit finite difference scheme. This formulation is unconditionally stable and variable time steps are used to optimise the solution procedure. The dissipation curves are found to be significantly affected by the rigidity index of the soil and a dimensionless time factor is proposed to account for this effect.

The research was intended to enhance the understanding of penetrometer behaviour in normally consolidated clay. The effects of varying penetration rate and clay shear strength were studies and the distribution of pore pressures determined. The meet these objectives laboratory testing was undertaken. Penetration tests were to be performed in tanks of clay consolidated from slurry and maintained under known stresses. An initial series of tests examined the effect of stiff tank walls. These showed unexpectedly high radial boundary stresses were generated with tank to probe diameter ratios of 50:1. This finding dictated laboratory tests with small scale penetrometers in the largest practical size of tank. Field tests with small scale and full size penetrometers demonstrated an absence of scale effect in the penetrometer pore pressures and total stress data. Two consolidation tanks of 580mm diameter and one of 1000mm diameter were built with the facility for maintaining constant stresses on top of the sample during penetration. Piezocone penetrometers of 5cm2 and 1cm2 cross-section were built. Penetration tests were performed from 2cm/s to 3m/s with hydraulic insertion equipment. At lower rates the total cone resistance factor Nkt was shown to be 10.3±0.9 in normally consolidated kaolin. The corresponding pore pressure factor NΔu was 8.25±1.0 at the cone shoulder. A hundredfold increase in the penetration rate increased the Nkt factor by 40% but the NΔu factor was unchanged. Various subsidiary points emerged. The type of strength test used for comparison with penetrometer data is significant. Major strength reductions occur on sample depressurization. These were demonstrated with vane and triaxial tests. Baligh and Levadoux’s method for determining ch from pore pressure dissipation around penetrometers matched experimental data. Ratios of excess pore pressures on the cone face and shoulder show some promise in the evaluation of OCR.

Today mines produce metals which are used for everyday products by people worldwide. When metals are produced, waste products known as tailings are generated. These tailings are commonly stored in impoundments, surrounded by embankment dams. The demands from the society are constantly increasing regarding the quality and safety of dams. One step in development towards a better control regarding safety and quality of tailing dams, could be to compact the beach. Today there is a lack of methods to easy check the dry densities over large areas for a compacted material. Since these dams can be large structures with embankment lengths of several kilometers, it is necessary to be able to check the density with a fast method. In this thesis it was investigated if the dry density, and correspondingly the compaction, can be checked with a Dynamic Cone Penetrometer (DCP). In the thesis the dry density of tailings was compared with penetration rate of the DCP. A laboratory setup was made with a test box filled with tailings provided by Boliden AB from the Aitik mine. Six different box tests were performed, each test with different compaction. From the tests a trend was observed, for which the tailings increased in density as the DCP indexes showed an increased resistance. A relationship between DCP index and dry densities was found. Though a relationship was found, it is important to emphasize that the tests were carried out in an environment that was easy to control. One test with high water content showed that water was influencing the DCP index results. Therefore it was concluded that if the DCP will be used in field, the water content also has to be checked.

No description available.

No description available.

No description available.