1,720,987 research outputs found
Analytical solutions for piles subjected to a passive load
No full textThe paper analyses a single free-head flexible passive pile embedded in a soil profile consisting of an unstable layer overlying a stable one. The pile segment in the unstable layer is subjected to a linear distribution of the load, whereas the pile response is evaluated by assuming a uniform modulus of subgrade reaction in the stable layer. Closed-form expressions are derived for the pile head deflection and tabulated values are provided to evaluate the maximum bending moment as a function of dimensionless length of the pile segment in the unstable and stable layers. Analytical solutions for infinitely flexible and rigid piles have been obtained as special cases of the general solution. A novel rational rigidity criterion for passive piles is also proposed. A numerical example is finally presented to illustrate the application of the derived solution
Investigating the Semi-Permeable Membrane Behavior of Geosynthetic Clay Liners by Means of a Novel Apparatus
Full text linkThe paper presents a recently developed rigid-wall diffusion cell and the experimental setup that allows the determination of the coefficient omega, which quantifies the degree of solute restriction in clays or GCLs that exhibit semi-permeable membrane behaviour. In addition, the apparatus allows the monitoring of the total vertical stress acting on the specimen during a chemico-osmotic diffusion test while keeping the vertical deformations at a negligible level (<1%). This improvement of the traditional testing approach allows for the determination of the chemical-osmotic efficiency coefficient, omega, and of the swelling coefficient omega, the main parameters that characterize the chemico-osmotic behaviour of clays and GCLs on the same specimen. The paper also reports on the results of some tests carried out on conventional and enhanced GCLs, with the main purpose of comparing the results obtained by means of the new testing apparatus with literature data. A first application of an advanced existing theoretical model for the description of chemical-osmotic phenomena to the results obtained is also illustrated
Sorption and hydraulic performance of cement-bentonite cutoffs in saline sulphatic solutions
Full text linkThe paper discusses the results of an experimental research on the short and long term hydraulic performance and sorption of cement-bentonite mixtures in saline sulphate solutions. Batch tests at different curing times and permeation tests were performed on three cement-bentonite mixtures with solutions of K2SO4. The results show that permeation can adversely affect the hydraulic performance of cement-bentonite mixtures depending on the sulphate concentration and mixture composition and that the choice of a very low permeable mixture is essential to limit adverse effects of interaction with SO42- on the hydraulic performance. Sorption of K+ was found to be significant, well described by a linear isotherm in a wide range of concentration and nearly constant with curing. Sorption of SO42 was found to decreases with mixture porosity. Since sorption of SO42- means negative interaction, batch tests were found to be useful for a rapid estimation of possible negative effect of SO42- on the hydraulic behaviour in the long term, when selecting a mixture in the design phase. All the results point out the importance of selecting a mixture to be used for cut-off walls with a low hydraulic conductivity already at brief curing and of carefully considering interaction with solute pollutants and sorption capacit
Critical issues in the determination of the bentonite cation exchange capacity
Full text linkThe swelling pressure and transport properties of bentonites are controlled by the electric charge density of solid particles, which is commonly estimated from the laboratory measurement of the cation exchange capacity (CEC). However, the standard ammonium displacement method for CEC determination does not take into account the fabric changes that occur in bentonites under exposure to high salt concentration solutions. A series of laboratory tests was conducted to assess the relevance of such a critical issue, by varying the concentration of the extracting KCl solution with respect to that of the standard test. The obtained results show that the release of the adsorbed ammonium cations depends on the bentonite fabric, which is controlled by the KCl concentration. As a consequence, the ammonium displacement method may provide an unrepresentative estimate of the CEC of bentonites. The methylene blue titration method, despite its apparently more limited accuracy, instead seems to provide a more reliable estimation of the CEC, as the bentonite fabric is maintained dispersed during the test
- …
