The detection of the plastic limit of clays is subject to human error. Several attempts have been made to correlate across studies the geotechnical properties of fine-grained soils (water content, liquidity index, shear strength, etc.). Based on the premise that the liquidity index and water content ratio can be correlated directly, an alternative method to obtain indirectly the plastic limit is suggested here. The present study investigated 40 natural clayey samples of various mineralogies and origins and other publicly available data, where Atterberg limits and undrained shear strength values obtained with the vane shear tests were given. The liquidity index and water-content ratio correlate very well for defined undrained shear strength values of the clays. Solving the liquidity index equation for the plastic limit, estimated plastic limit values obtained by the liquidity index/water-content ratio relationship were compared with laboratory plastic-limit values. Preliminary results based on 62 values show an exponential trend with a multiple regression coefficient of 0.79. The data need to be confirmed on a larger database, however.
In geotechnical engineering, the clogging of clay soils can lead to serious problems. For example, during mechanical tunnel driving with tunnel boring machines, the problem of clogging is due to the excavated material, which sticks to the metallic parts of the machine, requiring cleaning, which in turn causes delays and financial losses. This article suggests a method to reduce adhesion of the excavated material on a steel surface by means of electro-osmosis. The adhesion of different clay types to a metal surface was studied in tilted plate tests. Three different clay samples were compacted and cut into slices with a thickness of 1 cm. Afterwards, both a direct current (DC) and pulsating DC, which consisted of the positive half-cycle only, were applied to the samples in order to study the influence of electro-osmosis on adhesion. The application of electrical fields caused the detachment of the clays from the metal surface by slight shear forces. It is not currently possible to determine the influence of the pulsating DC or DC on the detachment behavior of the clays because of the complexity of the system. However, the use of the pulsating DC results in a lower electrical contact impedance. The reduced pulsating DC contact impedance results in higher electrical currents (for the same applied potential difference) and thus a higher electro-osmotic efficiency (i.e., the energy needed to detach a clay from a metal
The Extended Finite Element Method (XFEM) approach is applied to the coupled problem of fluid flow, solid deformation, and fracture propagation. The XFEM model description of hydraulic fracture propagation is part of a joint project in which the developed numerical model will be verified against large-scale laboratory experiments. XFEM forms an important basis towards future combination with heat and mass transport simulators and extension to more complex fracture systems. The crack is described implicitly using three level-sets to evaluate enrichment functions. Additionally, an explicit crack representation is used to update the crack during propagation. The level-set functions are computed exactly from the explicit representation. This explicit/implicit representation is applied to a fluid-filled crack in an impermeable, elastic solid and compared to the early-time solution of a plane-strain hydraulic fracture problem with a fluid lag.
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