Application of Electro-Osmosis to Reduce the Adhesion of Clay during Mechanical Tunnel Driving

Abstract

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

Nano- to Millimeter Scale Morphology of Connected and Isolated Porosity in the Permo-Triassic Khuff Formation of Oman

“…For this, we assume, that the frequency dependence of the sample resistivity can be neglected but consider the influence of the sample permittivity. More information regarding the influence of the contact impedance on such measurements can be found, e.g., in Spagnoli et al [32].…”

Electro-osmotic flow in clays and its potential for reducing clogging in mechanical tunnel driving

“…Several authors have already carried out laboratory studies on electro-osmosis as a possible alternative solution to the problem of clogging during tunnel driving or oil drilling (Roy and Cooper 1993;van Baalen 1999;Thewes 1999;Spagnoli 2011). However, this technique is yet to be used in in situ conditions.…”

“…Whereas current and potential are constant for direct currents, they vary over time for alternating currents; this must be considered for the calculation of the effective AC power (Spagnoli et al 2011): For the signal (Fig. 3) consisting of the positive half cycle, i.e.…”

Semi-analytical solutions to one-dimensional electro-osmotic consolidation in unsaturated soils

“…Based on the assumption that the pore water flow resulting from the hydraulic gradient and the electrical gradient can be superimposed linearly, the governing equation for electro-osmotic consolidation was developed, and many analytical solutions were derived based on different conditions to analyze the development of pore water pressure and the degree of consolidation [22][23][24][25][26][27][28][29][30]. Esrig [22] first proposed a 1D theoretical model and derived the solution for the excess pore water pressure under different boundary conditions.…”