Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
  • E02D3/11—Improving or preserving soil or rock, e.g. preserving permafrost soil by thermal, electrical or electro-chemical means

Definitions

• the present invention relates to a method for the stabilisation of soils and the restoration of any collapses, with particular reference to foundation soils.
• Clay soils have a particular and complex crystalline structure which makes them unique from the standpoint of their reaction to loading in relation to the presence of water.
• Clay minerals are hydrated phyllosilicates with structures having superposed and linked sheets, based in turn on the two-dimensional repetition of tetrahedral units (T) having at their centre a silica atom, or multiple octahedral units (O) having at their centre an aluminium atom.
• the cohesive energy between the packets of the layers is not sufficient to contrast the hydration force of the ions so that, by way of compensation, the packets surround themselves with a high and variable number of layers of water and of cations, appearing as lenticular shaped structures contained in sacks of pellicular water molecules and positive ions, having an average diameter of less than 2 ⁇ m.
• the pellicular water no longer held, tends to escape, increasing the values of the geo-technical characteristics of the soil and reducing its volume (consolidation).
• the aim of the present invention is to eliminate the aforesaid drawbacks by making available a method that acts on the causes and not on the effects of the collapses, retains its effectiveness unaltered over time, does not get altered and insofar as possible restores the original conditions of the soil, is not highly invasive and not at all destructive and also has reduced costs.
• Said method unlike those of the prior art, takes place in the absence of a draining cathodic pit, and it is further characterised by the content of the claims set out below and in particular in that it entails the use of electrosmosis to obtain the cessation of drainage and the superficial link, and/or inside the crystal of the clay mineral of the water (present naturally and/or supplied artificially) and of the ions (present naturally and/or supplied artificially), stabilising soil behaviour by stopping collapses and possibly obtaining a partial restoration thereof.
• the power supply provides a difference in potential that is opposite to the one caused by the outflow of the water.
• the negative electrodes are normally positioned in the soil immediately underlying the foundations, preferably at the centre of the pressure bulb, whilst the positive electrodes are normally positioned in the soil surrounding the walls a few meters away therefrom and at a distance of about 4-10d from the corresponding negative electrodes, where d is the thickness of the foundation wall overlying the negative electrode.
• the present method originally provides for the application of electrosmosis technology not to dry or dehumidify but rather to restore to its place the stratum that had moved farther away or had lowered, or the constitution of a humid environment (at least 85% saturation).
• the soil as a whole is electrically neutral, in its interior the interstitial water is in the condition of having an electrical potential exceeding that of the surface of the lenticules so that the application of an external electric field induces its migration towards the negative electrodes.
• the soil surrounding the masonry does not contain sufficient water because of an excessive removal of the water-bearing stratum, the latter will be created artificially by means of an external sources that injects water directly in proximity to the positive electrodes (anodic wells), which will migrate towards the negative electrodes.
• Electrosmosis technology has the advantage of being economical, non invasive and reversible, so that it allows to place the building in a safe condition for a nearly indefinite time interval, thereby allowing sufficient space, should it be deemed necessary, for the study and planning of restorations and possible consolidation of a different kind.
• Another advantage of the electrosmosis technique of the present invention is given by the increased resistance which may be produced in the soil through a change in the grain size of the fine claim (about 2 ⁇ m) existing near the anodes.
• the cost of an intervention using the electrosmosis technology is smaller by about an order of magnitude than the cost of a classic stabilisation intervention by means of micro-posts or jet-grouting.
• the water requirement through the anode wells amounts to a few tens of litres for each cubic metre of foundation.
• the present method comprises the following phases:
• the crystalline grid of clays is constituted by sheets of phyllosilicates and ionic layers.
• the water recall obtained by the present method there is a transfer of Al, Mg, Ca ions which enter between the sheets and replace pre-existing ions (Na and K ions). Since Al, Mg, Ca ions have greater diameter than Na and K ions, they surprisingly cause the clays to expand, which allows to restore collapses.
• the pressure bulb extends significantly below said wall for about 4d in depth and 2d in width.
• the negative electrode is normally positioned as close as possible to the centre of the pressure bulb (for instance with an oblique hole into which is introduced a metal tip serving as an electrode), whilst the positive electrode is positioned at a distance of4 - 10 d from the negative electrode.
• Electrosmosis consists of the movement of a liquid through a capillary (or through the innumerable capillaries of a porous diaphragm) by effect of the application of a difference in electrical potential.
• the quantity of liquid transferred through the porous septum is proportional to the intensity of the current that traversed the septum and is independent from the area and thickness thereof.
• the free cations of the solution tend to crowd in proximity to the surface of the solid phase, initially forming a second, rather orderly, layer of positive charges and progressively towards the interior of the solution a third diffuse layer of cations.
• the set of the first two layers is called Helmoltz compact double layer and its behaviour is similar to that of a planar capacitor whose negative plate coincides with the glass surface and whose positive plate has a diffuse shape starting from the partially orderly layer of cations.
• the thickness of the compact double layer is in the order of about 10 -8 m, i.e. a length equal to the diameter of some cations whilst if the diffuse area is also included a value of 10 -7 m is obtained.
• the cavity of interest are the innumerable small channels which are present in the most common lithoid materials, which, being made up almost exclusively of silicates, have the same adsorption selectivity as glass.
• Electrokinetic Potential (generally, it is a value ranging between 10 mV and 100 mV).
• the positive ions contained in the diffuse area create a region of solution with a non-zero average charge density which, under the influence of an external electrical field, is able to move because of the viscous driving force exerted by the migrating cations.
• thermodynamic considerations one can also reach a relationship that links electro-kinetic potential to the concentration of salts in the solution but experimental evidence shows that the electro-kinetic potential is scarcely influenced by small saline concentrations whilst it can even switch signs at high concentrations, causing the oft-observed phenomenon of field inversion.
• the problem can be easily solved by controlling electrode polarity with a power supply station.
• Masonry is subject to the phenomenon of successive concentration whilst, on the contrary, the more superficial water-bearing strata are subject to periodic dilution due to water filtering as a consequence of atmospheric precipitation.

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• Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Paleontology (AREA)
• Soil Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Agronomy & Crop Science (AREA)
• Civil Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Processing Of Solid Wastes (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)
• Soil Conditioners And Soil-Stabilizing Materials (AREA)
• Building Environments (AREA)

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• 1999
  • 1999-12-17 IT IT1999PR000093A patent/IT1308583B1/it active
• 2000
  • 2000-12-14 EP EP00830821A patent/EP1108817A3/de not_active Withdrawn

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