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
  • E02D3/12—Consolidating by placing solidifying or pore-filling substances in the soil

Definitions

• the present invention relates to a method for mitigating the risk of liquefaction of ground which includes the production of at least one hole in the ground and the injection of an expanding resin into the hole and an associated kit which operates according to that method.
• the equilibrium between friction force and interstitial pressure can change differently over time both as a result of natural actions (for example, variations of the conditions of a layer present in the ground of interest, mechanical actions of radical plant equipment, climate variations, etc.) and as a result of anthropic actions (for example, carrying out excavations in pieces of ground adjacent to the constructions, vibrations, loss of fluid in the ground, etc.). All these actions can increase or give rise to, for example, occurrences of subsidence and/or of subsequent structural collapse of the constructions erected above the ground mentioned, produce physical depressions in the ground and the structures in contact therewith, such as, for example, vertical structures (walls) or horizontal structures (pavements) and which can also occur in ground with momentary and/or periodic good mechanical properties.
• These phenomena of instability are technically defined as differential settlements and occur partially and locally in pieces of ground positioned below a foundation of a building leading the foundation to subsequently collapse and fail with subsequent lowering.
• the document EP0851064 relates to injections of chemical products which expand rapidly, such as polyurethane foams which react by substantially increasing the initial volume thereof and which harden in the ground until hardened columns of ground mixed with the resin are produced, at injection locations which are pre- established and arranged in accordance with a grid-like distribution which is predefined and three-dimensionally regular.
• That technique has some disadvantages which are correlated with the fact of using resins which expand up to a final volume which is also equal to twenty times the initial volume thereof. Consistently with the teachings of this document, in fact, there is encountered the risk of excessively expanding the structure of the ground, fracturing it internally and producing a weak conglomeration of the granular components.
• this document makes provision for the injected resin to be so expanding as to involve the raising of the ground itself and the building structures or the bonding structures above.
• the Applicant has established in practice that, by modifying the hydraulic conditions of the pieces of ground, as a result of a high level of mechanical compression which is really obtained with the great expansion of resin which is injected with free diffusion in the ground, it is possible to obtain new concentrations and different distributions of water in the same pieces of ground processed, even after a few kilograms of expanding products have been injected. Consequently, by applying the known teachings, it is possible to obtain, even rapidly, a false increase of load-bearing capacity of the ground, which may be encountered outside the ground with the misleading lifting, sometimes instantaneous lifting (precisely as in the case of sands) of the structures erected thereabove.
• volume of mortar grout introduced may vary by from 3 to 20% of the volume of ground processed, this process is very invasive and sometimes destructive as a result of great occurrences of lifting of the pieces of ground, including in the order of several tens of centimetres, which reveal resultant limitations of applicability especially in ground which is already built on.
• the technical problem addressed by the present invention is to provide a method and a kit for mitigating the risk of liquefaction of ground which are structurally and functionally configured to overcome, at least partially, one or more of the limitations set out above with reference to the prior art cited.
• a main object of the invention is to provide a method and a kit for mitigating the risk of liquefaction of ground by producing a consolidation of the ground itself by means of expanding resin.
• the method and the kit according to the present invention advantageously allow the production of a mitigation of the risk of the phenomena of liquefaction in varied types of ground, both built-up and free from building structures.
• Another advantage is that the method according to the present invention can be readily and effectively monitored.
• Figure 1 is a schematic illustration of a section of a piece of ground to be consolidated and an injection kit which can be associated therewith
• Figure 2 is a schematic illustration of the flow chart of the claimed method.
• the method for mitigating the risk of liquefaction of ground according to the present invention can be carried out by using an injection kit which is schematically illustrated therein.
• the injection kit comprises an injection device 1 including supply tubes 4.
• the supply tubes 4 can be inserted in at least one hole 2 which is formed in the ground T to be consolidated.
• the injection device 1 is capable of injecting an expanding resin 3 into the at least one hole 2 produced in the ground T.
• a person skilled in the art will be capable of identifying, modifying and adapting various types of tubes which are known in the same sector of the technique in order to optimize the connection to the injection device 1, the supply of the expanding resin 3 and reaching the portions of ground T involved in the process for mitigating the risk of liquefaction.
• the injection device 1 comprises at least one tank 5, for containing the components of the resin to be injected, a pumping device 7 and at least one pipe 8 which can be inserted inside the hole 2 for reaching the zone involved in the injection.
• the expanding resin 3 has an expansion relationship R between a final volume Vfin and an initial volume Vin less than 5. Even more preferably, the expanding resin 3 has an expansion relationship R between a final free volume Vfin and an initial free volume Vin less than 5.
• the final free volume Vfin and the initial free volume Vin relative to the expansion of the expanding resin 3 are calculated from final and initial density values (for the same mass) measured by means of ISO 845 (defined in regulations as "apparent density").
• the calculation in relation to the final free volume Vfin and initial free volume Vin is carried out by means of ISO 845 or similar standards of a national or international type which can readily be identified by the person skilled in the art. It will be commonplace for the person skilled in the art to calculate, from those values obtained in accordance with regulations, the value of the relationship R between the final free volume Vfin and the initial free volume Vin of the expanding resin 3. It is important to note that these measures are carried out under conditions of free expansion of the expanding resin 3 and in a manner substantially without any application of additional pressures or pressures different from the one provided for under standard conditions.
• This type of expanding resin 3 has inside the ground T to be consolidated characteristics of permeation which are advantageously slow and with an initial triggering time of the chemical reaction which is at least greater than 15 seconds, technically defined as “pot life” and which can be measured in accordance with the criteria of the pr EN 14319-1 : 2007 Annex D "Determination of the reaction profile and free rise density”.
• types of expanding resins 3 such as polyurethane resins, are capable of being used in an injection device 1 according to the claims of the present invention.
• the expanding polyurethane resins used are of the closed-cell type.
• the polyurethane resin has a content of closed cells greater than 50% of the total volume.
• the closed-cell polyurethane resins have an expansion relationship R between 1 and 4.8.
• the expanding resins 3 which can be used in the injection device 1 preferably have a free density between approximately 230 and 600 kg/m 3 .
• the expanding resins 3 which can be used under conditions involving high external loads which are or can be applied in a point-like manner have a free density between approximately 255 and 600 kg/m 3 , benefitting from mechanical characteristics of rigidity and breaking load resistance greater than those of expanding resins having free densities less than 200 kg/m 3 .
• the above-mentioned injection kit further comprises at least one investigation means 6 which can be associated with the ground T for monitoring at least one predetermined investigation parameter I.
• the monitoring is brought about by means of electrical resistivity tomography of the ground being processed combined with penetrometer tests.
• the tomography is used to detect the presence, the concentration and the distribution in a spatial environment of water in the ground T and the penetrometer tests serve to verify the reduction of the risk of liquefaction of the above-mentioned ground T.
• the penetrometer tests which have an intrinsic point-like nature are correlated with the measurements of tomography in order to obtain provision of behaviour of the ground T in zones adjacent to the ones measured by means of penetrometer techniques.
• this monitoring is carried out before, during and after the step of injecting the expanding resin 3 in the ground T.
• the monitoring may alternatively be carried out during a single one of those steps.
• the operating methods of the injection kit which define the method for mitigating the risk of liquefaction of a piece of ground T of the present invention comprise the steps described below with reference to the flow chart of Figure 2.
• a user identifies the ground T to be consolidated having an upper surface S and provides for an injection device 1, which can be operationally associated with the ground T (step 402). Subsequently, the user produces at least one hole 2 in the ground T to be reached or towards volumes of the ground T to be processed (step 404).
• the at least one hole 2 in the ground T is produced by means of the known techniques which are most advantageous for a person skilled in the art and may advantageously be produced in a direction perpendicular or transverse with respect to the upper surface S of the ground T.
• different types of holes for example, vertical, inclined, superimposed or multiple holes
• holes for example, vertical, inclined, superimposed or multiple holes
• the method provides for injection of an expanding resin 3, by means of the injection device 1, in the at least one hole 2 (step 406).
• the resin used in the method according to the present invention is capable of reacting chemically, producing an expansion reaction changing from an initial free volume Vin to a final free volume Vfin at the end of the expansion reaction.
• the method provides for activation of the expanding resin 3 (step 408).
• this activation reaction can be produced spontaneously by the components of the resin itself, by the humidity in the air contained in the tubes and in the ground T or by other factors which are known in this technical field.
• the expansion reaction is activated during or after the injection step of the expanding resin 3 in the at least one hole 2 of the ground T.
• the expanding resin 3 is a multi-component polymer material .
• the activation step of the above-mentioned multi-component polymer material allows time-based differentiation of a polymerization process of the expanding resin 3 and a cross-linking process of the resin itself by producing, for example, an improvement of the cross-linking step in a cross- linking time Tr which is substantially greater than a polymerization time Tp.
• That condition involves the additional advantage of being able to permeate the ground T in a more extensive manner over time and more efficiently before the definitive cross-linking occurs, which involves the end of the permeation and the achievement of the final mechanical and physical characteristics of the expanding resin 3.
• the method provides for the conglomeration of the ground T by means of the expanding resin 3, binding to each other portions of the ground T (step 410).
• the action of binding together portions of the ground is carried out by increasing the heterogeneous interactions of the adhesive type between granules and the expanding resin 3 by forming a macro-system which is fixedly conglomerated and capable of better counteracting the deformations induced in the system (for example, deformations induced by the increase of the interstitial pressure during the occurrence of seismic phenomena).
• the expanding resin 3 advantageously has an expansion relationship R between a final free volume Vfin and an initial free volume Vin less than five.
• the above-mentioned method comprises the monitoring, by means of at least one investigation means 6 which can be associated with the ground T, of at least one predetermined investigation parameter I.
• the user activates the at least one investigation means 6 (step 403) and activates the acquisition of the values of the at least one predetermined investigation parameter I (step 414).
• the activation step of the investigation means 6 can be carried out at any time between the step of providing an injection device 1 which can be associated with the ground T (step 402) and the step of ending the injection of the expanding resin 3 (step 412).
• the monitoring of the at least one predetermined investigation parameter I is carried out during the step of injecting the expanding resin 3 so as to verify that the final safety factor Fs_fin is complied with.
• the above-mentioned method comprises the step of interrupting the step of injecting the expanding resin 3 in the ground T when the final safety factor Fs_fin is complied with.
• the spatial formation of the upper surface S of the ground T remains unchanged and continuous even following the expansion of the expanding resin 3 except for minor geometric temporary fluctuations which are then recovered by the ground (for example, fluctuations of the upper surface S of a few millimetres for times in the order of minutes or hours).
• the use of the at least one investigation means 6 is therefore advantageous in order to evaluate the state and/or the variations in terms of composition and behaviour of the ground T in a mechanical and/or tribological sense.
• the at least one investigation means 6 can be used during each step which is provided for by the present method.
• the above- mentioned at least one investigation means 6 is an analysis technology which is capable of detecting significant variations of parameters in order to monitor the development over time of the mitigation of the risk of liquefaction of the ground T.
• the at least one investigation means 6 can be activated before, during or after any step which is correlated with the step of injecting the expanding resin 3 in the ground T.
• the activation of the at least one investigation means 6 allows adequate periodic verification of the final safety factor Fs_fin.
• the above-mentioned method comprises the step of interrupting the injection of the expanding resin 3 in the ground T once the conditions required in relation to the final safety factor Fs_fin are complied with from the at least one predetermined investigation parameter I.
• the user after activating the at least one investigation device 6 at the desired time (step 403, 405, 407, 409 or 411) carries out the acquisition and updating, according to known and preferred methodologies, of the at least one predetermined investigation parameter I (step 414).
• the at least one predetermined investigation parameter I is preferably used to calculate a current safety factor Fs_corr (step 415) which is subsequently intended to be compared with the final safety factor Fs_fin (step 416).
• this calculation and/or comparison operation may be carried out by the user himself, by a processing unit or by similar solutions which can readily be identified by the person skilled in the art.
• the method continues with the step following the last one carried out: this means, for example, that if the last action carried out before the activation of the investigation means 6 and the result Fs_corr ⁇ Fs_fin was the production of the at least one hole 2 in the ground T (step 404), then the method continues with the injection of the resin in the at least one hole 2 (step 406).
• the method continues with the injection step of the expanding resin 3 in the at least one hole 2 of the ground T (step 412) being stopped.
• an iterative cycle CI which comprises the steps from 404 to 417 (excluding the steps 412 and 413) in which the at least one predetermined investigation parameter I is acquired and updated (according to step 414) a number n of times (with n being equal to any whole number).
• This iterative cycle CI allows a calculation of n values of the current safety factor Fs_corr to be compared, in accordance with preferred methods, with the final safety factor Fs_fin so as to be able to monitor the development of the safety condition of the ground T as a function of time or predetermined time intervals.
• the user will acquire the at least one predetermined investigation parameter I in accordance with a given frequency of sampling, or spot sampling or random sampling or in accordance with another advantageous identified sampling methodology.
• the user also to selectively define as a function of which and how many values of the at least one predetermined investigation parameter I the corresponding current safety factor Fs_corr is calculated (for example, via a mean, via a weighted mean, etc.).
• investigation methodologies such as penetrometer tests SPT, CPT, CPTU, SCPTU or DPM and geophysical investigations.
• Exemplary and non-limiting cases of predetermined investigation parameters I and the corresponding current safety factor Fs_corr can be the ones indicated by the conventional calculation methodologies of the potential liquefaction, such as: Robertson and Wride, Andrus and Stokoe, Eurocode 8 (ENV 1998-5) while the final safety factor Fs_fin can advantageously be established with the verification of the safety factor which is technically expressed by the following equation [1]
• CRR indicates the resistance of the ground to the cyclical shearing forces (Cyclic Resistance Ratio) while CSR indicates the maximum shearing stress induced by the system (Cyclic Stress Ratio).
• the final safety factor Fs_fin is less than or equal to 1.25 and is established by means of Eurocode 8.
• the at least one investigation means 6 is electrical resistivity tomography (capable of producing geoelectrical monitoring of the ground T) or a penetrometer test, or both .
• the at least one predetermined investigation parameter I is the resistivity measured in the ground T during the geoelectrical monitoring step of the ground T.
• the at least one investigation means 6 is electrical resistivity tomography of the three-dimensional type (3D).
• the geoelectrical monitoring step is carried out by acquiring data by means of transmitting/receiving electrodes at the surface and/or at depth in the ground, which are connected to a georesistivity meter.
• the monitoring of the at least one predetermined investigation parameter I can be carried out before, during or after the injection of the expanding resin 3 in the ground T.
• the expanding resin 3 includes closed-cell expanded polyurethane.
• the above-mentioned method comprises a step of carrying out at least one penetrometer test for defining the local correlation of the site and the characteristics in terms of composition or physical characteristics thereof with the tomography of electrical resistivity.
• the injections are carried out both in surface layers and in deep-lying layers of the ground T even in the absence of a building structure erected above, for examining or counteracting the expansion of the expanding resin 3.
• the ground T described in all the steps of the present method is a sandy ground.
• the characteristics of the resin are particularly advantageous because the resin is prevented from producing an excessive pressure on the ground.

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• Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Soil Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Agronomy & Crop Science (AREA)
• Mining & Mineral Resources (AREA)
• Paleontology (AREA)
• Civil Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Consolidation Of Soil By Introduction Of Solidifying Substances Into Soil (AREA)
• Foundations (AREA)

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Cited By (1)

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• 2016
  • 2016-04-18 IT ITUA2016A002691A patent/ITUA20162691A1/it unknown
• 2017
  • 2017-04-18 EP EP17727696.1A patent/EP3445915B1/de active Active
  • 2017-04-18 WO PCT/IB2017/052203 patent/WO2017182939A1/en active Application Filing
  • 2017-04-18 PT PT177276961T patent/PT3445915T/pt unknown

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