Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D35/00—Straightening, lifting, or lowering of foundation structures or of constructions erected on foundations
• • 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
  • E02D3/12—Consolidating by placing solidifying or pore-filling substances in the soil
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D2250/00—Production methods
  • E02D2250/003—Injection of material

Definitions

• the present invention relates to a method for consolidating foundation soils or for lifting very heavy or large structures requiring the application of a pressure of more than 500 kPa.
• Background Art In the field of interventions for consolidating foundation soils for buildings, aimed at increasing the bearing capacity of the soil before and after building a structure, and in the field of interventions for obviating the subsidence of flooring or paving, it is known to use substances which expand as a consequence of a chemical reaction, of the type comprising a mixture of polyols and an MDI isOcyanate, or a similar expandable substance, which after expansion solidifies and makes said expansion permanent.
• European Patent no. 851,064 by same Applicant discloses a method for increasing the bearing capacity of foundation soils that substantially consists in forming a plurality of spaced deep holes in the soil and in injecting through these holes an expandable substance of this type, which expands as a consequence of a chemical reaction of its components, utilizing an expansion power which, at atmospheric pressure, causes a volume increase of at least five times its initial volume. The expansion of the substance produces a compaction of the contiguous soil until. it reaches the intended bearing capacity.
• the level of the soil or of the structure overlying the region of the soil that is subjected to intervention is monitored constantly in order to detect the beginning of its lifting, which means that the foundation soil has achieved a bearing capacity suitable to support the overlying structure or simply, if there is no structure, that the layer of soil between the ground and the injection region has been compacted.
• the structure can be lifted only if the pressure generated by the expansion of the substances involved is greater than the pressure applied to the soil affected by the expansion, by the static and dynamic weight of the structure plus the weight of any soil overlying, the injection point and the friction forces within the soil.
• the edometric modulus of a soil is in fact inversely proportional to the subsidence.
• a high compression of the soil above 500 kPa would increase the edometric module and accordingly reduce subsidence even in these kinds of soil.
• the aim of the present invention is to provide a method that allows to utilize the force generated by the expansion of these substances to consolidate foundation soils and to lift, particularly for repair after subsidence, very large or very heavy structures, such as for example skyscrapers, large mundane buildings, bridges, highway structures, silos, dams, large infrastructures etcetera, which can be lifted only by overcoming a pressure thereof on the soil of far more than 500 kPa, i.e., for interventions that up to now were not even imaginable by using substances that expand as a consequence of a chemical reaction, or in any case to obtain effects of overconsolidation in some kinds of soil underlying even not very heavy structures, since sometimes this is the only way to prevent subsidences and ensure, over time, the stability of the structure.
• very large or very heavy structures such as for example skyscrapers, large mundane buildings, bridges, highway structures, silos, dams, large infrastructures etcetera, which can be lifted only by overcoming a pressure thereof on the soil of far more than 500 kPa
• an object of the present invention is to provide a method that allows to perform prevention or repair after subsidences of very large or very heavy structures with considerably lower costs than required by known kinds of intervention.
• a method for consolidating foundation soils or for lifting very heavy or very large structures requiring the application of a pressure of more than 500 kPa characterized in that it consists in injecting into the soil to be consolidated or into the soil below the foundations of the structure to be lifted substances which expand as a consequence of a chemical reaction and are suitable to generate, during expansion, a pressure of more than 500 kPa.
• the method according to the invention consists in:
• Figures 1-3 are graphs which show the swelling pressure variation as a function of several injection factors
• Figures 4 and 5 are comparative diagrams showing results of penetrometric tests carried out on treated foundation soils, under heavy structures.
• the method according to the invention conveniently comprises a first step of producing a plurality of holes in the soil, said holes being mutually spaced and lying below the lower front or underside of the foundations of the structure.
• the number of holes to be produced, their dimensions and their mutual distance are calculated according to the force to be overcome in order to lift the structure, i.e., according to the weight of the structure and to the distribution of said weight on the soil being treated.
• the holes can run vertically or can be inclined with respect to the vertical, according to requirements.
• a substance which expands as a consequence of a chemical reaction among its components is injected into the soil, said substance comprising a mixture of polyols and an MDI isocyanate, or a similar expandable substance, with an expansion start time between 2 and 25 sec, preferably between 2 and 7 sec, and with a potential volume increase of at least five times the volume of the substance before expansion.
• the expression "potential volume increase” relates to the volume increase of the substance as a consequence of an expansion occurring unhindered at atmospheric pressure.
• Said substance is constituted by a closed-cell polyurethane foam which, after expansion, gradually hardens and permanently maintains its expansion.
• the components of the expandable substance are mixed inside a mixing apparatus with a pump, which is connected to the tubes inserted in the holes formed in the soil.
• the expandable substance is preferably constituted by two components, respectively a first component constituted by a mixture of polyols comprising a polyether polyol and/or a polyester polyol, a catalyst and water, for example such as URETEK GEOPLUS A produced by the Dutch company Resina Chemie, and a second composed constituted by an MDI isocyanate, for example such as URETEK GEOPLUS B produced by the same company, which has an expansion start time of approximately 3 seconds and in particular can generate the maximum measured expansion force, as described in greater detail hereinafter.
• a first component constituted by a mixture of polyols comprising a polyether polyol and/or a polyester polyol, a catalyst and water
• URETEK GEOPLUS A produced by the Dutch company Resina Chemie
• a second composed constituted by an MDI isocyanate for example such as URETEK GEOPLUS B produced by the same company, which has an expansion start time of approximately 3 seconds and in particular can
• the pressure that the substance transmits to the adjacent soil is also proportional to the density and therefore to the resistance opposed by the soil into which the substance is injected.
• the abbreviation signs are P (weight), D (diameter), H (height), V (volume), ⁇ (swelling pressure), t (testing time), and represent features of the tests samples.
• the tests were carried out at, and with an instrumentation available at the specialized Laboratory of the University of Padova, based substantially on creating in controlled pressure environments pressure conditions similar to those at which the expanding substance is subjected during injection/expansion in heavy loaded foundation soils, and eventually measuring the swelling pressure of the various test samples obtained.
• the accompanying figures 1-3 plot, respectively, the pressure generated by the expansion of said substance as a function of the density of the substance at the end of expansion, which as mentioned is proportional to the density of the soil into which the injection is performed, of the swelling time, and of the volume-weight.
• the pressure actually generated by the expansion of said substance can reach and exceed 10,000 kPa.
• the pressure generated by the expansion also varies as a function of the temperature of the substance.
• the illustrated chart plots two curves of the pressure at two different temperatures, respectively 80 °C and 238.6 °C.
• the expansion start time can be changed by varying the ratio between the two components of the substance according to requirements. More particularly, preference is given to a shorter time for injection into soils that can cause dispersions of the substance and to longer times (in any case preferably between 2 and 7 seconds) for more uniform and compact soils. Times above 7 seconds can be suitable or useful under very extensive foundations.
• the substance can be injected into the holes formed in the soil in a single injection step, making the injection point rise gradually and therefore retracting upward the tubes inserted in the holes formed in the soil, or it can be injected in a plurality of steps by causing the intermittent rise of the injection point, i.e., by retracting upward the tubes inserted in the holes with intermediate pauses.
• the expandable substance is injected simultaneously into a plurality of holes, optionally using a plurality of pumps.
• the expandable substance, during injection is very fluid and therefore penetrates more easily in the less dense regions of the soil.
• the subsequent expansion of the substance then compacts more intensely the less dense regions of the soil, further improving the uniformity of the density of the soil.
• the swiftness of the expansion of the injected substance in any case avoids unwanted dispersions of the substance, delimiting the region affected by the expansion rather accurately and therefore obtaining an excellent effectiveness in the compaction of the soil and in the lifting of the structure.
• the thrust effect on the soil produced by the substance during expansion arises from the chemical reaction of its components, not from hydraulic pressure.
• the depth of the holes formed in the soil may vary according to the method for compacting the soil beneath the structure on which one wishes to act.
• the expression "foundation soil” is used to designate an area covered by the pressure bulb, i.e., the entire portion of soil, below the foundations, that dissipates almost all the tensions and stresses induced by the static and dynamic load, and calculated for each specific case; it generally corresponds to a depth, below the bottom plane, of approximately 2-3 times the width of said foundation.
• a first method consists in treating the entire thickness of the pressure bulb and any further thickness of the compressible or low-bearing layers so as to perform the consolidation, to the solid horizon, of the sufficiently bearing layers, whatever their depth.
• the solid horizon can be identified by means of geotechnical soil analysis.
• the second method instead consists in treating a layer of soil (at least equal to the pressure bulb) which, for reasons of technical and/or financial convenience, does not reach the identified solid horizon, which might be located at an excessive depth, but in any case has a thickness that is sufficient to dissipate the overlying weight on a wider surface.
• the intervention is aimed at lifting the structure located above the injection region, during the injection of the expandable substance, the level of the structure above the treated soil area is monitored constantly by means of laser levels or another system in order to detect with high accuracy the beginning of the lifting of the structure.
• the beginning of the lifting of the structure means that the compaction performed on the soil in that point is sufficient to support the structure and that the further expansion of the substance will lift the structure.
• the intervention is aimed at consolidating the foundation soil without lifting the structure, for example because its rigidity or weight do not allow to lift it, or simply because this is not the effect being sought
• achievement of the required degree of consolidation can be determined by measuring the amount of injected expandable substance, as an alternative to monitoring the beginning of the lifting of the structure. It is in fact possible to determine in advance, by way of appropriate calculations, how much expandable substance to inject in order to obtain the intended consolidation.
• the pressure that can be generated by the substance during expansion can reach and exceed 10,000 kPa.
• Penetrometric tests were carried out in foundation soils (as shown in Figures 4 and 5), treated with the method according to the present invention, under very heavy buildings located in Paris (loads generating soil pressures) well in excess of 500 kPa.
• the injections were carried out at 1, 2 and 4, 5m under the foundation and the area treated had a linear extension of about 9m.
• the penetrometric tests showed dynamic resistances improved up to 10 times and more with respect to the initial values, perfectly suitable to provide lifting of the structures and reliable consolidation of the foundation soil.
• the method according to the invention fully achieves the intended aim and objects, since by utilizing hitherto unknown properties of expandable substances of the above cited type it allows to perform consolidation interventions for foundation soils with optional lifting, particularly for preventing or repairing subsidences, for very large or very heavy structures, and also allows a great increase in the degree of consolidation (overconsolidation) in scarcely, loaded fine-grain soils.

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• Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Civil Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Paleontology (AREA)
• General Engineering & Computer Science (AREA)
• Soil Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Agronomy & Crop Science (AREA)
• Consolidation Of Soil By Introduction Of Solidifying Substances Into Soil (AREA)
• Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
• Polyurethanes Or Polyureas (AREA)
• Revetment (AREA)

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Applications Claiming Priority (2)

Publications (2)

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Citations (3)

• 2001
  • 2001-11-27 IT IT2001MI002496A patent/ITMI20012496A1/it unknown
• 2002
  • 2002-11-26 HU HU0402308A patent/HU228156B1/hu not_active IP Right Cessation
  • 2002-11-26 JP JP2003547717A patent/JP4071716B2/ja not_active Expired - Fee Related
  • 2002-11-26 KR KR10-2004-7008081A patent/KR20040053376A/ko not_active Application Discontinuation
  • 2002-11-26 SI SI200231017T patent/SI1314824T1/sl unknown
  • 2002-11-26 CN CNA028233654A patent/CN1592809A/zh active Pending
  • 2002-11-26 EP EP02026410A patent/EP1314824B1/en not_active Expired - Lifetime
  • 2002-11-26 DK DK02026410.7T patent/DK1314824T3/da active
  • 2002-11-26 CA CA002467630A patent/CA2467630A1/en not_active Abandoned
  • 2002-11-26 AU AU2002352158A patent/AU2002352158B2/en not_active Expired
  • 2002-11-26 US US10/495,659 patent/US20050158128A1/en not_active Abandoned
  • 2002-11-26 WO PCT/EP2002/013325 patent/WO2003046296A1/en active IP Right Grant
  • 2002-11-26 RU RU2004119433/03A patent/RU2293818C2/ru not_active IP Right Cessation
  • 2002-11-26 PT PT2026410T patent/PT1314824E/pt unknown
  • 2002-11-26 PL PL368418A patent/PL218227B1/pl unknown
  • 2002-11-26 BR BR0214435-2A patent/BR0214435A/pt not_active Application Discontinuation
  • 2002-11-26 ES ES02026410T patent/ES2394415T3/es not_active Expired - Lifetime
  • 2002-11-26 NZ NZ533093A patent/NZ533093A/en not_active IP Right Cessation
• 2004
  • 2004-06-24 NO NO20042665A patent/NO20042665L/no not_active Application Discontinuation
• 2007
  • 2007-08-29 JP JP2007222817A patent/JP2007332771A/ja active Pending

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