SE2150229A1 - Method for stabilizing grounds - Google Patents

Abstract

The invention relates to a method for stabilizing ground by using a device which creates a disturbed column in the ground to be stabilized. The method is comprises the following steps:i) drilling a column in the ground, and injecting an aqueous solution of sodium and/or potassium silicates into the ground during the downward drilling,ii) mixing the ground in the column, andiii ) infusing dry powdered calcinated carbonate rocks into the ground, by blowing the chemicals into the column by means of a propellant gas, during the upwards drilling.

Description

Process for stabilizing grounds The invention relates to a process for stabilizing and consolidating grounds, especially soft and sensitive clay grounds, to improve their mechanical strength. Stabilisation of such grounds may be useful for the construction of roads, railways, airports, buildings, etc., but also preventive to reduce risks for landslides and the similar.

Soft and sensitive grounds may include marine "quick clays" and other sensitive marine clays; and by "sensitive marine clays" and "quick clays", it is here meant clays mainly found in the glaciated areas of Canada and Scandinavia. They were deposited in marine environments during the retreat of the inland glaciers 10 to 13 thousand years ago. The fine material in these marine sediments is dominated by phyllo-silicates, i.e. mica and clay minerals. Small distortions of "quick clays" may cause collapse of the particle aggregates, resulting in a complete loss of sediment shear strength, which can lead to large landslides. This phenomenon has caused several quick clay slides in the lowlands of Norway, often with catastrophic consequences. These types of clays are more thoroughly described in Rosenqvist, I.T. (1978), "A general theory for the sensitivity of clays". Proceeding of the interdisciplinary conference held at the University of Luleå. Permont Press.

Soft grounds such as clay deposits often need to be stabilized before they can carry any additional load such as applied during filling and construction activities, and thus, several chemical stabilization schemes have been tried for such clays. Stabilization of quick clays has mainly been performed in two ways; mixing and remoulding the clay with the chemicals, or the chemicals have been allowed to diffuse into the undisturbed quick clay. The disadvantage of the diffusion method is the time; it may take long time to reach the required stabilization.

A method according to prior art, for stabilization deep into the ground, is the infusion of unslaked lime (CaO). Lime is an old stabilizing agent that has been used for centuries as construction material. The deep stabilization method involves mixing and moulding the lime with the clay to form a series of piles which extend down into the clay. These piles provide stabilization to the clay deposit.

The use of hydroxy-aluminium alone and/or in combination with chemicals such as potassium chloride (KCl) is disclosed as a clay stabilizing agent in US patent 4,360,599. The same patent further describes the need for proper admixing of the stabilizing agent into the clay in order to achieve the desired results.

Another method for infusing chemicals such as hydroxy-aluminium mixture, into a quick clay formation, and an in-situ mixing device is described in Norwegian patent NO 168124. The method comprises the steps of: (a) rotating a hollow torque tube with a helical blade having convolutions of at least one revolution attached thereto down into the formation, said convolutions having substantial thickness adjacent said torque tube and tapering to an outer edge; (b) creating a disturbed column in the formation and flowing the hydroxy-aluminium down the torque tube to the helical blade and into the formation; (c) rotating said torque tube and helical blade thereby mixing the hydroxy-aluminium into the formation; (d) rotating out said helical blade from the formation and allowing the formation to stabilize; and (e) permitting backflow through bypass channels in the convolutions of said helical blade.

Yet another method for stabilizing clay deposits (particularly quick clay) by creating a disturbed column and infusing stabilizing chemicals by means of an in-situ mixing device, is for instance described in a brochure published by NORCEM in collaboration with NGI, 2006: "Grunnforsterkning med kalksement", and G. Holm, 2006: "Svensk Djupstabilisering FoU 1995-2006", Report 18. According to this method, large drill rigs are used for carrying out this consolidation jobs, by drilling down to e.g.25 meters depth (or deeper if needed). A "wing" or bucket with nozzles is mounted onto the drill string (close to the drill bit) where the cementing substances are blown out with a propellant gas at 4 to 9 bar pressure. The high pressure is necessary to overcome the pore pressure in the ground, and at depths of 15 to 25 meters commonly applied pressures are 7-9 bar. This takes place while the drill is rotated upwards in the bore hole. The diameter of the treated zone is determined by selecting "wings" of different sizes, but has a maximum diameter of about one meter.

By these known methods one achieves a stabilisation of the ground, but it takes time before the added chemicals are completely cured. Therefore, the stabilisation must take place in sufficient time before the ground may be used. Traditionally the aim has been to achieve a shear strength of at least 500 kPa after one year of curing In order to stabilize the ground with the method above, one traditionally uses engines with combustion motors, and CO2 will be released to the environment during the operation. This might cause environmental problems and should be avoided. In NO 339059 it is described a method whereby the propellant gas used to blow out cementing substances, contains more CO2 than the air surrounding the air intake of the pump. The CO2 may originate from an environmentally unfriendly process, and thus some of the environmental problems may be accounted for.

The object of the present invention is to develop a method for stabilizing ground fast, and that sufficient shear strength of the ground is established within hours rather than weeks. This will enable an operator to move the drill rig forward into the sensitive region, without the need for temporary enforcement of the ground. Another object of the present invention is to achieve a shear strength greater than 200 kPa within a day.

Another object of the invention is to reduce the energy consumption and the time it takes to carry out the consolidation work.

Yet another object of the invention is to reduce the use of cement, such as Portland cement and/or Multicem (CKD). Cement is expensive, but more important, the manufacture of cement releases about 800 kg CO2 to the environment per 1000 kg of cement produced SUMMARY OF THE INVENTION The present invention concerns a method for stabilizing clay deposits, according to the characterizing part of the independent patent claim. Further features are stated in the independent claims.

The method for stabilizing ground comprises infusing powdered calcinated carbonate rocks into the ground, using a device which creates a disturbed column in the ground to be stabilized. The method further comprises the following steps: i) drilling a column in the ground, and injecting an aqueous solution of sodium and/or potassium silicates into the ground during the downward drilling, ii) mixing the clay in the column, and iii ) infusing dry powdered calcinated carbonate rocks into the ground, by blowing the chemicals into the column by means of a propellant gas, during the upwards drilling. The method is especially suitable for stabilizing clay deposits (particularly quick clay) by creating a disturbed column and infusing stabilizing chemicals by means of an insitu mixing device, for instance corresponding to the process described in NO168124 or NO339059 as mentioned above. As this process is known to a person skilled of the art we will not describe all features and technical details of the known parts of this process.

The invention relates to a method for stabilizing ground by infusing powdered calcinated carbonate rocks, into the ground during upward drilling, while an aqueous solution of sodium and/or potassium silicates is injected into the ground during downward drilling. The aqueous solutions of sodium and/or potassium silicates mixed into the ground during the downward drilling is a strong dispersant, thus, creating a low viscosity "slurry" of the stirred ground in the column. The subsequent injection of the dry powdered calcinated carbonate rocks during the upwards drilling is hence faster and less energy consuming, and the low viscous slurry ensures a more homogeneous mixture of the dry powdered cementitious compounds and the stirred ground.

Further, the more homogeneous soft slurry constitutes an easier escape route for the propellant gas that is used for the injection of the dry powdered cementing chemicals. This easier escape route of the propellant gas will reduce the building up of high pore pressures in the borehole, that commonly displaces porewater away from the borehole; porewater that is needed for the hydration of the dry cementitious materials. Thereby, not only will the injection process during downwards and upwards drilling be improved, but even the hardening process will be faster and better.

Finally, by adding the aqueous solutions of sodium and/or potassium silicates during the downward drilling, the friction and tear on the drill string will be reduced, which makes the drilling less demanding regarding the energy used for the drilling process.

The aqueous solutions of sodium and/or potassium silicates mixed into the ground during the downwards drilling, are a liquid hydrous solution of strongly alkaline alkalisilicates, preferably sodium silicate, commonly referred to as "water-glass", e.g. Na2OxSiO2 H2O with x > 3,2.

The powdered calcinated carbonate rocks to be infused into the ground, may comprise e.g. portland cement, Multicem (CKD) or quick lime, to form cementing calcium-silicates that is consolidating the sensitive geological formation.

The interaction between cement and water includes two main processes: 1) Dissolution of anhydrous compounds in the cement, to form hydrated ions in solution, followed by eventual precipitation of hydrates due their low solubility. 2) Solid-state hydration; i.e. hydration reactions at the surface of anhydrous cement particles, without going into solution.

The major oxides in Portland cement are four clinker minerals, denoted in shorthand: C3S (52-54%), C2S (30-32%), C3A (7-17%) and C4AF (0-4%). In addition, some gypsum may be added. These shorthand formulas denote C=CaO; S=SiO2; A=Al2O3; and F=Fe2O3. However, these mineral formulas are not completely fixed, because clinker "minerals" are not pure, and thus, the shorthand formulas represent "average" compositions.

The main component in portland cement; the C3S (tricalcium silicate) phase, has fast hydration rate and hardens rapidly. This phase is responsible for an early strength build-up in concrete and reaches a significant compressive strength after a few days curing.

Calcium silicate hydrate (shown as C-S-H) is a result of the reaction between the calcium-silicate phases of Portland cement and water. This reaction typically is expressed as: 2Ca3SiO5 7H2O → 3CaO · 2SiO2 · 4H2O 3Ca(OH)2 heat The stoichiometry of C-S-H in cement paste is variable and the state of chemically and physically bound water in its structure is difficult to estimate.

Synthetic C-S-H can be prepared from the reaction of CaO and SiO2 in water or through the double precipitation method using various salts. These methods provide the flexibility of producing C-S-H at specific C/S ratios. Based on this, sodium silicate ("water-glass") can be added to hydrated cement paste, to precipitate calcium silicate in the pore system, thus, obtaining a more water-resistant concrete, i.e. in swimming pools.

This means that the "water-glass" can also react with the calcined cements and precipitate cementing calcium-silicate, as indicated by the equation: 3Ca(OH)2 Na2Si2O3 → 3CaO*2SiO3 2NaOH ;;The mineral structure of C-S-H is highly variable and ranges from poorly crystalline to amorphous. It occupies 50-60% of the volume of solids in the hydrated cement paste, with a large surface area of 100-700 m2/g. Mechanical strength is due to ionic and van der Waals bonding. ;The calcium hydroxide (Ca(OH)2) crystals are varying from large prisms to thin, elongated crystals, depending on available space. These crystals (portlandite) occupies 20-25% of the volume of solids in the hydrated cement paste. Portlandite does not contribute much to the strength of concrete but keeps the pH of the pore water strongly alkaline. Therefore, it is beneficial to convert most of the calcium hydroxide in the cement to calcium-silicates, by adding "water-glass", which is also strongly alkaline. ;;The reactions involving the "water-glass" are very fast (in the order of minutes) and allows the heavy drilling equipment to move forward on newly consolidated ground in relatively short time; much faster than with the conventional method of cement stabilization. This means that the consolidation work can be done faster, safer and more efficient. ;;The chemistry of cement, water glass and the hardening process as described above, is well known to a skilled person. ;;In a preferred embodiment of the present invention, calcium-bearing compounds; e.g. unslaked lime, fly-ash, calcium salts or preferably chalk-containing ash for instance a from paper-mills, is added in addition to the calcinated carbonate rocks in step III of the method described above. Sodium-silicate ("water-glass") will react with the calcium-bearing compounds to establish calcium-silicate cement in the soft clays. The calcium-bearing compounds is preferably injected into the clay as a mixture with the calcinated carbonate rocks such as Portland cement, CKD, and/or quicklime, depending on the conditions at each specific drilling site. When adding calciumbearing compounds, the amount of calcinated carbonate rocks may be reduced, and in an even more preferred embodiment, the amount of calcinated carbonate rocks may be reduced substantially . ;By "cementitious compounds or chemicals" it is herein meant both calcinated carbonate rocks, and calcium-bearing compounds such as chalk-rich ash from paper mills, calcium salts e.g. calcium-chloride. ;;The method according to the invention is performed by a device which creates a disturbed column in a sensitive ground formation and the aqueous solution of sodium and/or potassium silicates are injected during the downward drilling, while the powdered calcinated carbonate rocks are infused during upwards drilling, both preferably during mixing of the ground in the column. In a preferred embodiment, several holes are drilled in the same area to achieve columns of stabilized material into the area of soft ground, and by making a sufficient number of such columns, the whole area will be stabilized. The column should be as deep as necessary, such as 40 m, or even more, preferably 5-25, most preferred about 15 m. The upper part of the column, such as the upper 1-5 m, is normally a mechanically firmer ground, but the stabilization is commonly continued nearly to the surface, e.g. one meter below the surface. ;;In a further preferred embodiment, a drilling rig is used to create the column into the ground, and the chemicals, both the aqueous solutions of sodium and/or potassium silicates, and the powdered calcinated carbonate rocks, are pumped through a drill string of the rig and out of a lower end of the drill string and into the surrounding ground, while the drill string is moved vertically. ;;In a preferred embodiment the drill string is provided with wings creating a whisk to mix the clay during downwards and upwards drilling, and to create the disturbed column. In this way, the mixing of the ground in the column will be performed simultaneously as the injection of the aqueous solutions and the infusion of the powdered calcinated carbonate rocks, rather than as a separate step. ;;The injection of an aqueous solution of sodium and/or potassium silicates is preferably performed by pumping the solution out through nozzles arranged at the lower end of the drill pipe/drill string, or arranged on or below the wings, whatever most convenient. The solutions are thus mixed into the ground during the downwards drilling by the wings. At the bottom of the column the injection of the solution stops and the infusion of the calcinated carbonate rocks begins. A propellant gas preferably at pressures between 4 and 9 bar is infusing the dry powdered rocks into the drill hole during the upwards drilling, through the nozzles. The powdered rocks are thus mixed into the ground by fast rotation of the drill string, during the upwards movement of the drill string. This process is continued upwards to near the surface. ;;The propellant gas may be any suitable gas supplied at sufficient pressure. The compressor compressing the gas should be strong enough to release the propellant gas with sufficient pressure to transport the chemicals into the desired depth of the borehole, and still overcome the pore pressure. As said above, the injection of an aqueous solution of sodium and/or potassium silicates during the downward drilling is reducing the shear strength of the stirred column of clay. This will facilitate upward migration of compressed air, and therefore reduce the build-up of pore pressure in the clay, and thus the pressure of the propellant gas may be reduced correspondingly. ;;As mentioned above, it is an objective of the invention to establish a fast stabilization of the ground. According to methods of prior art, it takes weeks before the full impact of concrete mineralization is expressed from Portland cement. Formation of calcium hydroxide (Ca(OH)2) is relatively fast, but gives a relatively weak cementing mineral. It is therefore desirable to replace calcium hydroxide by the stronger calcium silicate minerals. This will be the case by the inmixing of "water-glass", where a very fast reaction takes place between the "water-glass" and the reactive calcium bearing compounds. ;;The present invention differs from prior art by injecting liquid solutions of "waterglass" into the formation during the downward drilling phase. During the upwards drilling operation, the dry and powdered calcium bearing compounds are injected by the propellant gas and mixed into the already low viscous stirred ground in the bore hole. ;;A preferred process according to the present invention which may be used for stabilizing a ground such as quick clay, is to create a disturbed column in the ground with lowered viscosity by injecting and stirring liquid "water-glass" solutions into the formation. "Water-glass" is a strong dispersant in clays. This must be done during the downwards drilling process. The mixing device is rotated through the upper soil and down to the bottom of the soft ground, or as far down as it is desired to stabilize. ;;Vertical travel speed, rotational speed and direction of the mixing device may be varied to optimize mixing. Means for applying and controlling vertical and rotational motion are supplied from a surface equipment. Such surface equipment is for instance available from Linden-Alimak AB, 5-93103 Skelleftea, Sweden. ;;When infusing the cementitious compounds while the mixing device is moving upwards through the formation, the stabilizing processes, which start immediately once the chemicals are infused, will not be disturbed significantly by the mixing. This is particularly important when stabilizing clay formations with "water-glass" and calcium-bearing compounds, like Portland cement, Multicem (CKD), ash from paper mills, as the chemical reaction is almost immediate. ;;Experiments with quick clay under controlled conditions show that up to 50% of the pore water is displaced by compressed air at 7 bar pressure. This is critical for the hydration of the calcinated compounds, e.g. Portland cement. However, the new invention includes the inmixing of "water-glass" during the downwards drilling; a process that will liquefy most clays to a low viscosity and more homogenous slurries. Thus, the propellant gas (air) will more easily escape up through the bore hole, without building up high pore pressures in the underground that can displace pore water. ;This inmixing of "water-glass" during the downward drilling phase will produce a low viscosity and homogenous clay suspension in the bore hole that have several beneficial consequences: ;• It will assure a more homogenous inmixing of the injected chemicals and cementitious compounds. ;• There will be less friction on the drill string and rotating equipment, which will reduce the applied force on the drilling equipment; i.e. reduce the energy consumption (e.g. diesel) used for drilling. ;• The use of propellant gas during the subsequent upwards drilling will more easily escape upwards through the low viscosity clay column, and the building up of high pore pressures is reduced. ;• As the propellant gas is more easily escaping, the pressure of the gas may be reduced, and thus any displacement of the water in the ground close to the bore hole will be reduced, more water will be available to the hydration of the cement, and thus the process will be faster. ;;Example ;The invention will in the following be described by an example of stabilizing ground. The following detailed description is for illustrative purposes only, and not meant or intended to limit the invention. ;;Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. ;;I prior art, calcinated carbonate rocks used as stabilizing chemicals to stabilize the ground, are generally standard Portland cement mixed 1:1 with quicklime or "Multicem" (CKD). Recommended quantities of stabilizing chemicals, that is recommended quantities of Multicem (CKD) and Portland cement mixtures, for the stabilization of soft clay grounds, are 80 to 120 kg per m<3>. In "quick clays" it has become common practice to inject 100 kg cement per cubic meter of clay (in the bore hole) and to use a mix of 50% Multicem (CKD) and 50% Portland cement. ;Multicem (CKD) may be exchanged with quicklime. ;;According to a preferred embodiment of the present invention, aqueous solutions of sodium and/or potassium silicates, are injected during downward drilling, and calcium-bearing compounds such as chalk-rich ash from paper mills, fly-ash, calcium salts; e.g. calcium-chloride are added in addition to the calcinated carbonate rocks, and are infused during the upwards drilling. When using papermill ash, this allows a reduction of the mixture Portland cement and Multicem (CKD) (or quicklime) substantially, while still obtaining the same shear strength of the stabilized clay. This is very favourable regarding the reduced emissions of CO2 from the calcination of carbonaceous rocks to produce Portland cement and Multicem (CKD). The sum of the added amount of cementitious compounds must not add up to 100 kg per cubic meter ground to be stabilized, neither must the sum of added amount of cementitious compounds and aqueous solutions of sodium and/or potassium silicates. ;;Sodium-silicate may be produced with various concentrations of alkalis (sodium) and the formula for sodium-silicates may be written Na2O*xSiO2, where x denotes the molar ratios between Na2O and SiO2. Thus, x may vary between 1.6 and 3.5 depending on the producer. These sodium-silicates are dissolved in water at concentrations from 25 to 55%, and the densities of these solutions may vary from 1.26 to 1.7 kg/L. Commercial available "water-glass" are commonly found in the molar ratio range of 3.2-3.5; concentration range 35-40%; and density range 1.35 -1.40 kg/L.

The water-glass solution used in the stabilizing clay experiments below, have a molar ratio of 3.3; a concentration between 36 and 40 weight-%; the density of the solution is 1.32 kg/m3; and the pH of the solution is 11. This is a convenient solution to work with, because according to OECD-testing, sodium-silicate solutions having a molar ratio > 3,2 and a dry weight of the sodium silicate < 40 weight-% need no hazard labelling.

Conventional stabilisation of sensitive clays in Norway is performed by blowing dry powdered cementitious compounds into the clay through nozzles situated below an upper "wing" mounted on the drill string. This is taking place during the upward drilling phase, with a controlled elevation of the drill string and high rotation velocities of the mixing "wings" mounted on the lower part of the drill string. During this operation 100 kg of a 50/50 mixture of Portland cement and Multicem (CKD) is mixed into each cubic meter of clay in the borehole. This recipe was used to produce the reference samples.

In a method according to an embodiment of the present invention, the amount of cement was reduced by 50%; i.e. a reduction from 100 kg to 50 kg. cement. Instead 12 kg sodium silicate was added as a water-based 40% solution with a density of 1.32 g/cc while the rig was drilling downwards in the column, and 25 kg carbonate ash was mixed with the cement and infused during upwards drilling. The carbonate ash is a waste product from papermills; e.g. Norske Skog ASA in Mid-Norway. This ash is a residue from the combustion of organic matter and chalk in an oven at temperatures well below the calcination temperature of chalk (<950 degree C). The mixture of ash and cement is reacting vigorously (exothermic) with the "water-glass", to produce cementing calcium-silicates. The results after 7 days curing is given in the table 1 below, as series 1 and 5.

Further studies were performed to study the shear strengths obtained with various mixtures of papermill ash, sodium silicate, and cement. Desired mixtures must be determined according to the shear strengths needed; the geological conditions, including water saturations and contents of organic material; and operational restrictions. Actual mixtures may include 5 kg to 100 kg cement (Portland cement and Multicem (CKD), either blended or individual); 5 kg to 50 kg papermill ash; and 5 kg to 50 kg sodium silicate (40% solution with density 1.32 g/cc). Other calcium containing compounds that reacts readily with sodium silicate may also be included; e.g. calcium chloride.

Table 1. Series of clay stabilized by portland cement blended with Multicem (1:1), papermill ash and sodium silicate (waterglass) were tested. In the laboratory experiments 9% extra water (i.e. weight increased from 2200 kg to 2400 kg) was added to the clay to ease the mixing in the laboratory. The temperature during curing was about 10 degree C, which is lower than in a column in the ground. Nevertheless, the tests shows a clear tendency.

Image available on "Original document" Further examples were performed to study any differences between portland cement and CKD (Multicem); series 6 and 7, while series 8 shows a mixture of Portland, Ash and Sodium Silicate.

Table 2. Experiments performed to study the differences between portland cement and CKD (Multicem); Series 6 and 7. Series 8 shows the high shear strengts obtained with only 36 kg cement added (36%). Curing temperature 22 degree C.

Image available on "Original document" Series 8 shows the high shear strengts obtained with only 36 kg cement added (36%).

Testing of the shear strengths of the samples are carried out at the Norwegian Geotechnical Institute (NGI) in Oslo.

These experiments demonstrate the fast and strong consolidation potential of the present invention. If higher shear strength are needed, e.g. higher shear strength than achieved with 100 kg of cement per cubic meter of clay, this can be achieved by adding more "water glass" and paper mill ash and/or more cement.

According to the present invention, strongly alkaline sodium and/or potassium silicate, (water-glass) should be added in combination with dry powdered reactive calcium bearing compounds. Both Portland cement, Multicem (CKD), calcinated carbonates and other reactive calcium bearing compounds are applicable, including ash from paper-mills, and other calcium-containing compounds that react readily with "water-glass". If higher shear strength is desired, in the short or longer term, this can easily be achieved by adding more "water glass" and paper mill ash.

Limits for the addition of cementitious compounds The example described above is relevant for the most common applications of clay stabilization. But the need to establish a certain shear strength in the clay formation depends on the purpose of stabilization, e.g. a moderate stabilization to protect against landslides, or to consolidate the clay formation for building heavier constructions, like buildings or roads. The dosage of injected components cement will vary accordingly, having a preferred range of 5 to 100 kg cement, 5 - 50 kg papermill ash and 5 - 50 kg sodium silicate solution (at 40% concentration) pr cubic meter ground to be stabilized. Depending on the need for shear strength, any combination of the amount of chemicals, within these limits may be used. All numbers given above are referring to the weight of cementitious compounds added to each cubic-meter clay in the borehole.

The example above is given to illustrate the invention and should not be used to interpret the following claims limiting. The scope of the invention is not limited by the example given above, but the following claims. Modifications and amendments of the invention, being obvious to a person skilled of the art, should also be included in the scope of the invention.

Claims (6)

Patent claims 1. Method for stabilizing ground by using a device which creates a disturbed column in the ground to be stabilized, the method is characterized by comprising the following steps: i) drilling a column in the ground, and injecting an aqueous solution of sodium and/or potassium silicates into the ground during the downward drilling, ii) mixing the ground in the column, and iii ) infusing dry powdered calcinated carbonate rocks into the ground, by blowing the chemicals into the column by means of a propellant gas, during the upwards drilling. 2. Method according to claim 1, characterized in that step ii) is performed at the same time as both step i) and iii). 3. Method according to claim 1 and 2, characterized by further comprising a step for infusing calcium-bearing compounds such as chalk-rich ash from paper mills, fly-ash, calcium salts; e.g. calcium-chloride. 4. Method according to claim 3, characterized in that the amount of calcium-bearing compounds is 5 - 50 kg, the amount of dry powdered calcinated carbonate rocks is 5 - 100 kg, and the amount of aqueous solution of sodium and/or potassium silicate is 5 - 50 kg per cubic meter ground to be stabilized. 5. Method according to any of the proceeding claims, characterized in that the aqueous solution of sodium and/or potassium silicates is sodium silicate. 6. Method according to claim 5, characterized in that the sodium silicate has a molar ratio range of 3.2-3.5; concentration range 35-40%; and density range 1.35 -1.40 kg/L. Patentkrav

1. Framgangsmåte for stabilisering av grunn ved bruk av en anordning som danner en omrørt kolonne i grunnen som skal stabiliseres, framgangsmåten er karakterisert ved å omfatte følgende trinn: i) bore en kolonne i grunnen, og injisere en vandig løsning av natrium- og/eller kalium-silikater i grunnen under boring nedover, ii) blande grunnen i kolonne, og iii) infusere tørr, pulverisert, kalsinert karbonatbergart i grunnen, ved å blåse kjemikaliene inn i kolonnen ved hjelp av en drivgass, under boring oppover.

2. Framgangsmåte i samsvar med krav 1, karakterisert ved at trinn ii) utføres samtidig som både trinn i) og iii).

3. Framgangsmåte i samsvar med krav 1 og 2, karakterisert ved å ytterligere omfatte et trinn for å infusere kalsiumholdige forbindelser så som kritt-rik aske fra papirfabrikker, flygeaske, kalsiumsalter,f.eks. kalsiumklorid.

4. Framgangsmåte i samsvar med krav 3, karakterisert ved at mengden kalsiumholdige forbindelser er 5 - 50 kg, mengden tørr, pulverisert, kalsinert karbonatbergart er 5 - 100 kg, og at mengden vandig løsning av natrium- og/eller kalium-silikat er 5 - 50 kg per kubikkmeter grunn som skal stabiliseres.

5. Framgangsmåte i samsvar med et av de foregående krav, karakterisert ved at den vandige løsningen av natrium- og/eller kalium-silikat er natriumsilikat.

6. Framgangsmåte i samsvar med krav 5, karakterisert ved at natriumsilikatet har et molart forhold i området 3,2-3,5; konsentrasjon i området 35-40%; og tetthet i området 1,35 - 1,40 kg/L.