Method for preparing a watertight structure based on stabilized soil

Abstract

The present invention relates to a method of stabilizing and waterproofing soil by preparing a waterproof structure based on stabilized soil, in which the structure consists of one or more layers of stabilized soil.

Description

Title of the invention: Method for preparing a watertight structure based on stabilized soil TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method of stabilizing and waterproofing soil by preparing a waterproof structure based on stabilized soil, in which the structure consists of one or more layers of stabilized soil. STATE OF THE ART

[0002] In the field of construction, a stable and rigid soil is necessary in certain applications, such as paving, building construction, traffic structures, embankments, subgrades or upper parts of earthworks, platforms, subgrade layers, road bases or construction site access roads, and hydraulic structures such as canals, dams, retention basins, and tailings ponds. To achieve this, it is necessary to stabilize the soil at the construction site. This stabilization can be carried out by combining cement with the soil. Cement-soil combinations are called, among other things, cement-stabilized soil, cement-treated base, cement-stabilized soil, and cement-treated soil. The creation of cement-stabilized soil involves adding specific quantities of cement per unit of soil.The soil is then mixed, moistened if necessary, then re-mixed, leveled and compacted to meet the requirements specified in the site plans and drawings. Over time, the soils treated with cement thus harden and gain in strength and rigidity.

[0003] When it is desired to ensure the watertightness of the structure based on this stabilized soil, an additional waterproof layer is added. This surface layer is generally prepared using bentonite, a natural clay of the smectite type with high swelling capacity, which allows for perfect and permanent soil waterproofing.

[0004] Thus, a watertight structure based on stabilized soil comprises: - a layer that provides the desired mechanical resistance, generally a mixture of soil, typically earth, and a mineral binder; - a waterproofing layer which can be made of: - a mixture of soil, typically earth and bentonite, generally about 30 cm thick; or - a bituminous waterproof layer; or - a waterproofing membrane; or - a mixture of all these solutions.

[0005] No impermeability requirements are expected of the soil layer Stabilized. No specific mechanical resistance requirements are expected of the waterproofing layer.

[0006] Such an approach is complex because two layers are required for the complete waterproofing system. Furthermore, the soil and bentonite mixture is often sticky, difficult to handle and compact. It is also very sensitive to weather conditions (such as moderate and / or heavy rain), which can make the site potentially inaccessible to construction equipment for several days. Finally, membrane or bitumen solutions require the sequential implementation of two separate operations: one for soil treatment, then another for the waterproofing solution.

[0007] The present invention seeks to overcome these drawbacks by providing a stabilized soil that has both waterproofing properties and mechanical performance. These performances are advantageously obtained in the short, medium, and long term. The invention provides a simple method of soil stabilization, in which a stabilized soil can be used as the sole component of a waterproofing system. The invention provides a structural waterproofing solution.

[0008] Depending on the application for which the stabilized soil-based watertight structure is intended, it may be in contact with outside air, water, or a top layer, which may or may not be a surface layer. Examples of such applications include paving, construction, traffic structures, embankments, top courses or upper parts of earthworks, platforms, subgrades, road bases or construction site access roads, and hydraulic structures such as canals, dams, retention basins, and tailings ponds.

[0009] The present invention has the following advantages: - ease and simplicity of implementation; - economy of raw materials / soils; - reduced construction cost due to one less processing operation; - reduction in the number of layers in the final structure. Summary of the invention

[0010] The invention relates to a method for preparing a watertight structure, having mechanical resistance, based on stabilized soil, in which the structure consists of one or more layers, advantageously one layer, of stabilized soil, comprising the following steps: (i) mix, by weight relative to the total weight of the stabilized soil: - 70% to 99% of soil to be stabilized; - from 1% to 30% by weight of a stabilizing composition; the stabilizing composition comprising: - a road hydraulic binder as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014; - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof; - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent, and mixtures thereof; (ii) compact the stabilized soil from step (i).

[0011] Advantageously, the stabilized soil layer obtained has a compressive strength at 28 days, determined according to standard NF EN 13286-41:2003, greater than 0.3 MPa.

[0012] Advantageously, the stabilized soil layer obtained has a permeability, determined according to standard NF EN ISO 17892-11:2019, of less than 2.109 ms 1.

[0013] Advantageously, the composition comprises, as a road hydraulic binder, a binder comprising at least 10% by weight of lime, relative to the total weight of the binder.

[0014] Advantageously, the composition comprises, as a road hydraulic binder, a binder comprising at least 30% by weight of Portland clinker, relative to the total weight of the binder.

[0015] The soil to be stabilized can be selected from the group consisting of a soil of class Al, A2, A3, A4, Bl, B2, B3, B4, B5, B6, ClAi, CIBi, C2Ai, C2Bi, Dl, D2, D3 and one of their mixtures according to the GTR soil classification standard NF - PI 1-300 1992.

[0016] Advantageously, during step (i), the mixture of 1% to 20% by weight, preferably 2% to 10% by weight, relative to the total weight of the stabilized dry soil, of the stabilizing composition with the soil to be stabilized.

[0017] Advantageously, the stabilized soil obtained comprises, in addition to the components of the starting soil, by weight relative to the total weight of the stabilized dry soil - 0.5% to 8% hydraulic road binder, - from 0.005% to 1% of the water-repellent additive, - 0% to 1%, preferably 0% to 0.8%, of clay deflocculating additive, - 0 to 10%, preferably 1% to 4% bentonite, - 0 to 5%, preferably 0.1% to 4% of a water reducing agent.

[0018] Advantageously, prior to step (i) the soil is moistened to achieve a water content ranging from 2% to 40% by weight relative to the dry weight of the soil to be stabilized.

[0019] Advantageously, the compaction step (ii) allows a densification of more than 90% of the maximum dry density determined according to NF EN 13286-2:2010 to be achieved.

[0020] Advantageously, each layer of stabilized soil has a thickness of less than 45 cm, preferably ranging from 20 cm to 40 cm.

[0021] Advantageously, the structure is a coating layer or an embankment.

[0022] The invention also relates to the use of a composition comprising: - a hydraulic road binder as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014, - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof; - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent and mixtures thereof; for the preparation of a stabilized soil having both waterproofing properties and mechanical performance. DETAILED DESCRIPTION OF THE INVENTION

[0023] The various embodiments presented throughout the description can be used alone or in combination with each other, without limitation of combination.

[0024] The present invention relates to a method for preparing a watertight structure based on stabilized soil, in which the structure consists of one or more layers, advantageously one layer, of stabilized soil, comprising the following steps: (i) mix, by weight in relation to the total weight of the stabilized dry soil: - from 70% to 99% of soil to be stabilized; - from 1% to 30% by weight of a stabilizing composition; the stabilizing composition comprising: - a road hydraulic binder (RHB) as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014; - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof; - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent and mixtures thereof; (ii) compact the stabilized soil from step (i).

[0025] The term "soil to be stabilized" refers to the soil intended to be used to prepare the watertight structure by bringing it into contact with the LHR, the water-repellent additive and possibly one or more optional additives.

[0026] The term "stabilized soil" refers to the soil constituting the waterproof structure that has been brought into contact with the LHR, the water-repellent additive, and optionally one or more additional additives. The stabilized soil according to the invention has improved compressive strength and waterproofing compared to the soil to be stabilized. By way of illustration, the stabilized soil layer obtained has a compressive strength at 28 days, determined according to standard NF EN 13286-41:2003, greater than 0.3 MPa and a permeability, determined according to standard NF EN ISO 17892-11:2019, less than 2 x 10⁹ ms⁻¹.

[0027] The expression "stabilized soil layer" should be understood as a layer comprising the The mixture and / or the in-situ reaction product of the various constituents used, some of which may react and / or are intended to react with each other, at least partially, during the different stages of layer preparation. Due to the improved mechanical and waterproofing properties of the stabilized soil layer, the top waterproofing layer used in conventional methods is no longer necessary.

[0028] The stabilized soil layer according to the present invention advantageously has a compressive strength at 28 days greater than 0.5 MPa, preferably greater than 1.0 MPa, preferably greater than 1.2 MPa, preferably greater than 1.4 MPa, preferably greater than 1.6 MPa, most preferably greater than 1.8 MPa, and preferably greater than 2.0 MPa. The compressive strength of the layer is measured according to standard NF EN 13286-41:2003.

[0029] The stabilized soil layer according to the present invention typically has a permeability of less than 2 x 10⁹ ms⁻¹*, preferably less than 1 x 10⁹ ms⁻¹, preferably less than 5 x 10⁻¹⁰ ms⁻¹, and preferably less than 1.0 x 10⁻¹⁰ ms⁻¹. The permeability of the layer is measured according to standard NF EN ISO 17892-11:2019. Soil to be stabilized

[0030] The soil to be stabilized can be any type of soil. The soil to be stabilized is generally composed of a mixture of natural materials, artificial materials, waste, and recycled materials. Advantageously, the soil to be stabilized is selected from the group consisting of a soil of class Al, A2, A3, A4, Bl, B2, B3, B4, B5, B6, ClAi, CIBi, C2Ai, C2Bi, Dl, D2, D3 and one of their mixtures according to the GTR soil classification standard NF-PI 1-300 1992.

[0031] The process may include a step of moistening the soil to be stabilized. Indeed, the soil generally has an optimal moisture content, evaluated using the standard Proctor test according to standard NF EN 13286-2:2010. The application water content may differ from the optimal water content, by approximately -2% to +4% compared to the optimal water content, depending on the type of soil and the treatment binder expressed relative to the dry weight of the material considered (soil alone or soil + cement).

[0032] Thus, advantageously, prior to step (i) the soil is moistened to achieve a water content ranging from 2% to 40% by weight relative to the dry weight of the soil to be stabilized.

[0033] Preferably, during step (i), 80% to 99% by weight, preferably 85% to 98% by weight, preferably 90% to 96% by weight, relative to the total weight of the stabilized dry soil, of soil to be stabilized is mixed with the stabilizing composition.

[0034] Thus, in the stabilized soil-based layer, the dry soil represents 70% to 99% by weight relative to the weight of the waterproof layer, preferably 80% to 99%, preferably 85% to 98%, and preferably 90% to 96% by weight relative to to the total weight of the waterproof layer. Stabilizing composition

[0035] In the invention, a combination of a hydraulic road binder and at least one water-repellent additive is used. This combination is called the "stabilizing composition." It should be noted, however, that the binder and the additive(s) can be added separately. Thus, the components of the stabilizing composition are not necessarily pre-mixed with the soil to be stabilized.

[0036] Advantageously, the stabilizing composition, preferably in proportions adapted to the proportions above, can be in the form of a preparation kit with or without premix of binder, water-repellent additive and possibly one or more optional additives.

[0037] Preferably, during step (i), 1% to 20% by weight, preferably 2% to 15% by weight, preferably 4% to 10% by weight, relative to the total weight of the stabilized dry soil, of the stabilizing composition is mixed with the soil to be stabilized.

[0038] Road hydraulic binder (also called binder or RHL)

[0039] An LHR is defined either in standard NF EN 13282-1:2014, or in standard NF EN 13282-2:2015.

[0040] An LHR comprises main constituents whose proportion exceeds 10% by weight and which are selected from:

[0041] a) the constituents described in the cement standard NF EN 197-1:2012 or the standard NF EN 197-5:2021; b) lime.

[0042] A binder according to the invention is also any binder obtained by mixing Portland clinker with any of the components described in the standard on hydraulic road binders (NF EN 13282-1 and NF EN 13282-2).

[0043] Optionally, the binder comprises at least 10% by weight of lime, relative to the total weight of the binder. More advantageously, the binder comprises from 10% to 40% by weight of lime, relative to the total weight of the binder.

[0044] Lime can be calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide or mixtures thereof.

[0045] Advantageously, the binder comprises at least 30% by weight of Portland clinker, relative to the total weight of the binder. More advantageously, the binder comprises from 30% to 90% by weight of Portland clinker, and more advantageously from 40% to 70% by weight relative to the total weight of the binder.

[0046] The binder may also include blast furnace slag, advantageously in a content ranging from 10% by weight to 50% by weight, and preferably from 10% by weight to 30% by weight.

[0047] The binder may also include fly ash, in particular fly ash siliceous fly slurries, advantageously in a content ranging from 5% by weight to 40% by weight, preferably from 10% by weight to 25% by weight.

[0048] The binder may include secondary constituents, each not exceeding 10% by weight, as defined in standard NF EN 13282-1:2014.

[0049] As indicated in the standards, calcium sulfate may be added to these main and secondary constituents.

[0050] The main constituents described in the cement standard NF EN 197-1:2012 present in the binder are also called "cement".

[0051] Preferably, the binder content in the stabilized soil, i.e., at the end of step (i), ranges from 1% to 29.95% by weight, preferably from 1% to 20% by weight, and more preferably from 2% to 10% by weight relative to the weight of the dry stabilized soil. Water-repellent additive

[0052] The water-repellent additive is selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof.

[0053] Polysiloxanes can be polysiloxane derivatives represented by the following general formula (I) (R2SiO)n, where n is an integer between 1 and 70; R, identical or different, is selected from the group consisting of the following groups: C1-C20 alkyl, C1-C20 alkoxy, C1-C20 hydroxyalkyl, C1-C20 aminoalkyl, C1-C20 haloalkyl, C7-C20 aralkyl, C6-C20 aryl groups, or a derivative of these groups. Preferably, R is chosen from the group consisting of the Cl-Cl2 alkyl, Cl-Cl2 alkoxy, Cl-Cl2 hydroxyalkyl, Cl-Cl2 aminoalkyl, Cl-Cl2 haloalkyl, C7-C14 aralkyl, and C6-C12 aryl groups. In the invention, the number of carbons is denoted CXX to CYY or CXX-CYY. For example, a C1-C20 alkyl or a C20 Cl alkyl means an alkyl having a carbon number between 1 and 20.

[0054] The silane-type compound may be an alkoxysilane derivative represented by the following general formula (II): RkSiCOR2)^ in which n is equal to 1, 2 or 3; R1, identical or different, is a C1-C20 alkyl group, C1-C20 alkoxy, C2-C20 alkenyl, C6-C20 aryl, C7-C20 aralkyl or a derivative of these groups, and the R1 substituents in a molecule may all be identical or different; R2 is a C1-C20 alkyl group, preferably a C1-C6 alkyl group. Preferably, R1 is chosen from the group consisting of the alkyl groups in C1-C12, alkoxy in Cl-Cl2, hydroxyalkyl in Cl-Cl2, aminoalkyl in Cl-Cl2, haloalkyl in Cl-Cl2, aralkyl in C7-C14 and aryl in C6-C12.

[0055] The silane-type compound can also be any compound bearing one or more silane functions of general formula (III) *-R'nSi(OR2)4 n in which * represents the bonding point to the compound and n, R1 and R2 are as defined previously for general formula (II). By way of example, tris(alkoxysilane)isocyanurate may be cited, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate.

[0056] Silane and polysiloxane may be selected from the group consisting of isobutylmethoxysilane, polydimethylsiloxane, amino-function polydimethylsiloxane, raminoethylaminopropyltrimethoxysilane, octyltriethoxysilane, iso-octyltriethoxysilane, octyltrimethoxysilane, iso-octyltrimethoxysilane, potassium silicone, sodium silicone, potassium methylsiliconate, tris(alkoxysilane)isocyanurate, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate and mixtures thereof. Preferably, silane and siloxane may be selected from the group consisting of polydimethylsiloxane, octyltriethoxysilane, iso-octyltriethoxysilane, roctyltrimethoxysilane, iso-octyltrimethoxysilane, potassium methylsiliconate, tris(alkoxysilane)isocyanurate, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate and mixtures thereof.

[0057] The fatty acid salt may be a compound having the formula R3COOH, in which R3 is a linear or branched alkyl group comprising a carbon number from C15 to C48, preferably from C8 to C45, preferably from C20 to C40, and more preferably from C24 to C36. Preferably, R3 is a linear alkyl group. Advantageously, the fatty acid is a salt of zinc, sodium, calcium, magnesium, manganese, copper, or a mixture thereof. In a preferred embodiment, the fatty acid salt is selected from the group consisting of a stearate salt, preferably selected from the group consisting of sodium stearate, calcium stearate, and a mixture thereof.

[0058] Preferably, the water-repellent additive is selected from the group consisting of calcium stearate, polydimethylsiloxane, octyltriethoxysilane, iso-octyltriethoxysilane, roctyltrimethoxysilane, iso-octyltrimethoxysilane, potassium methylsiliconate, tris(alkoxysilane)isocyanurate, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate and mixtures thereof.

[0059] Preferably, during step (i), the content of added water-repellent additive ranges from 0.05% to 10% by weight, preferably from 0.1% to 6% by weight and more preferably from 0.2% to 5% by weight relative to the weight of cement.

[0060] Advantageously, the water-repellent additive is a silane, which is added in a content ranging from 0.1% to 5% by weight relative to the weight of cement.

[0061] Advantageously, the water-repellent additive is a polysiloxane, which is added in a content ranging from 0.1% to 5% by weight relative to the weight of cement.

[0062] Advantageously, the water-repellent additive is a fatty acid salt, which is added in a content ranging from 0.1% to 7% by weight relative to the weight of cement.

[0063] The water-repellent additive can be added in dry or liquid form. For the water-repellent additive in liquid form, the content is expressed as a percentage by weight of the solid content in the liquid mixture relative to the total weight of the cement. Preferably, the water-repellent additive is in liquid form with a solid additive content between 10 and 70 % by weight, preferably between 30 and 60% by weight. Optional Add-ons

[0064] The stabilizing composition may also include one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent, and mixtures thereof.

[0065] Preferably, the bentonite content ranges from 0% to 10% by weight, preferably from 1% to 4% by weight and preferably from 2% to 4% by weight, relative to the total weight of stabilized dry soil.

[0066] The clay deflocculant additive can be selected from the group consisting of sodium or potassium phosphates, sodium or potassium silicates, and mixtures thereof. Preferably, the deflocculant additive is sodium hexametaphosphate. Preferably, the deflocculant additive content ranges from 0% to 1% by weight, preferably from 0.01% to 1% by weight, and most preferably from 0.01% to 0.8% by weight, relative to the total weight of the stabilized dry soil.

[0067] The water-reducing agent can be selected from the group consisting of a plasticizer, a superplasticizer and a mixture of theirs.

[0068] The term “superplasticizer” as used in this description and the accompanying claims is to be understood as including both water reducers and superplasticizers as described in the book entitled “Concrete Ad-mixtures Handbook, Properties Science and Technology”, VS Ramachandran, Noyés Publications, 1984.

[0069] Water reducers include, for example, lignosulfonates, hydroxycarboxylic acids, carbohydrates and other specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium aluminomethyl siliconate, sulfanilic acid and casein.

[0070] Superplasticizers belong to a new class of water reducers, chemically different from normal water reducers and capable of reducing water content by about 30%. Superplasticizers have been broadly classified into four groups: naphthalene formaldehyde (SNF) sulfonated condensates (usually a sodium salt); melamine formaldehyde (SMF) sulfonated condensates; modified lignosulfonates (MLS); and others. More recent superplasticizers include polycarboxylic compounds such as polycarboxylates, for example, polyacrylates. A superplasticizer is preferably a next-generation superplasticizer, for example, a copolymer containing polyethylene glycol as a grafted chain and carboxylic groups in the main chain such as a polycarboxylic ether. Sodium polycarboxylate-polysulfonates and sodium polyacrylates can also be used.Phosphonic acid derivatives can also be used.

[0071] Preferably, the water-reducing agent is a polynaphthalene sulfonate polymer, a polycarboxylate, a polymelamine sulfonate or a mixture thereof.

[0072] Preferably, the water reducing agent content ranges from 0% to 5% by weight, preferably from 0.1% to 4% by weight, preferably from 0.2% to 3% by weight, relative to the total weight of stabilized dry soil.

[0073] Advantageously, the stabilized soil obtained comprises, in addition to the components of the starting soil, by weight relative to the total weight of the stabilized dry soil - 0.5% to 8% hydraulic road binder, - from 0.005% to 1% of the water-repellent additive, - 0% to 1%, preferably 0% to 0.8%, of clay deflocculating additive, - 0% to 10%, preferably 1% to 4% bentonite, - 0% to 5%, preferably 0.1% to 4% of a water reducing agent. Construction process characteristics

[0074] The watertight structure is prepared by a process comprising the following steps: (i) mixing the soil to be stabilized and the stabilizing composition, which are as previously described; then (ii) compact the stabilized soil from step (i).

[0075] As already indicated, in step (i) a composition comprising the binder and the pre-mixed additive(s) can be added, or each constituent of the stabilizing composition can be added separately, simultaneously or over time. For the binder, it would be possible to add the cement and lime separately.

[0076] The mixing step can be carried out by any method known to those skilled in the art that produces a homogeneous monolayer. Advantageously, during step (i) the mixing is carried out using a pulvimixer-type mixer.

[0077] During step (ii), the compaction is advantageously mechanical compaction.

[0078] Compaction can be carried out to reduce the thickness of the monolayer of minus 10%, preferably at least 15%, preferably at least 20% and preferably 20 to 25%.

[0079] Step (ii) of compaction advantageously allows to achieve a densification of more than 90% of the maximum dry density determined according to NF P 94-093:2014 or NF EN 13286-2:2010.

[0080] Water can be added during step (i) to achieve optimal soil compaction parameters and also to allow cement hydration. Advantageously, prior to step (i), the soil is moistened to achieve a water content ranging from -2% to +4% relative to the optimum water content of the soil to be stabilized.

[0081] The process may include the following steps: (i-2) Adding water to achieve a target moisture content (in several stages if necessary) (i-1) Spreading of the binder and additive(s), then (i) mixing preferably using a pulvimixer type mixer, (ii) mechanical compaction.

[0082] Step (ii) of mechanical compaction advantageously allows the densification to be achieved: 97% of the MDD (Maximum Dry Density).

[0083] Step (ii) is advantageously carried out by carrying out the following steps: (a) pre-setting of the surface with a grader for example then (b) mechanical compaction, using various types of compactors (sheep's foot, pneumatic compactor and roller compactor); (c) a final adjustment of the surface is usually required in order to achieve the final dimension and a satisfactory surface condition.

[0084] This process is advantageously implemented on a soil to be stabilized ready, that is to say a soil in which the large elements have been removed and which has advantageously been scarified.

[0085] This method is particularly suitable when the waterproof structure is a form layer.

[0086] The stabilized soil layer obtained following step (ii) has a thickness of less than 45 cm, preferably ranging from 20 cm to 40 cm.

[0087] The watertight structure advantageously consists of one or two layers of stabilized soil. When the watertight structure comprises more than one layer of stabilized soil, then, following step (ii), steps (i) and (ii) are repeated.

[0088] The watertight structure can then be in contact with outside air, water, or a top layer, which may or may not be a surface layer. By way of example, depending on these applications, such a structure could be used for paving, construction, traffic structures, embankments, top courses or upper parts of earthworks, platforms, subgrade layers, road or construction site track foundations, and hydraulic structures such as canals, dams, retention basins, and tailings ponds.

[0089] The invention also relates to the use of a stabilized soil according to the invention for a construction structure, preferably the construction of roads, buildings, hydraulic works such as canals, dams, retention basins, tailings basins.

[0090] Advantageously, the process does not include a step of adding a sealing layer of any kind. Indeed, the structure combines waterproofing and structural properties.

[0091] Thus, according to the invention, a composition comprising is used: - a hydraulic road binder as defined previously; - a water-repellent additive as defined above; - optionally one or more additive(s) as defined above; for the preparation of a stabilized soil having both waterproofing properties and mechanical performance.

[0092] Stabilized soil can thus be used as the sole component of a sealing device for a structure.

[0093] Advantageously, the sealing device consists of at least one layer of stabilized soil. MEASUREMENT METHODS Evaluation of mechanical resistance:

[0094] The 28-day compressive strength is determined according to standard NF EN 13286-41 of July 2003. Permeability assessment:

[0095] The evaluation is carried out according to standard NF EN ISO 17892-11. Two test specimens from the same mixture are tested. Permeability is calculated according to the previous standard and expressed as flow velocity in ms-1.

[0096] Water permeability is measured using an oedometer. The standard followed for laboratory tests is: NF EN ISO 17892-11:2019. EXAMPLES

[0097] The following non-restrictive examples illustrate examples of implementation of the invention. Materials

[0098] The soil to be stabilized is a silty soil classified A2 according to the GTR soil classification standard NF-PI 1-300 1992.

[0099] The road hydraulic binder (RHB) has the following formulation: - 100 parts by weight of main and secondary constituents of the road hydraulic binder (RHB) as defined in standard NF EN 13282-1:2014, comprising by weight relative to the total weight of the main and secondary constituents: - 39% Portland clinker (K) - 15% blast furnace slag (S) - 21% lime (calcium oxide) (CL) - 15% siliceous fly ash (V or Va) - 10% by weight of secondary constituents as defined in standard NF EN 13282-1:2014 - 2 parts by weight of calcium sulfate;

[0100] In addition to this LHR, the following are added to the ground to be stabilized: - water-repellent additive chosen from calcium stearate and silane (Silquest® A-Link 597 supplied by Momentive) according to the quantities given in Table 1 below; - sodium hexametaphosphate according to the quantities given in Table 1 below After.

[0101] Comparative formulations are made with bentonite alone or mixed with hydrated lime (Ca(OH)2) in the proportions given in Table 1 below. Laboratory testing methods

[0102] Successive steps of the test protocol: 1. In a knife mixer, mix the soil to be stabilized. 2. Moisten the soil to be stabilized by adding water to the mixer to reach a water content of 19% by weight relative to the dry weight of the soil. Mix for 2 minutes. 3. If necessary, add additives to the mixer. Mix for 3 minutes. 4. compaction to achieve a densification of 97% of the maximum dry density determined according to NF EN 13286-2:2010 or NF P 94-093:2014.

[0103] For these tests, test specimens are prepared for the evaluation of mechanical resistances and for permeability tests.

[0104] Thus, for permeability tests, the treated soil is compacted using a special mold in a small stainless steel ring (70 mm in diameter and 20 mm thick) with a press device in static compression mode. After compaction, the stainless steel ring containing the treated soil is leveled on both sides using a metal straightedge. The sample is then weighed and placed in a sealed plastic bag for 24 hours in a climate chamber controlled at 20°C and 95% relative humidity.

[0105] For the evaluation of mechanical resistance, the same protocol is followed, but a standardized mold is used (NF EN 13286-53 standard). The sample size is 50 mm in diameter and 100 mm in height. The sample is then weighed and placed in a sealed plastic bag for 28 days in a climate chamber regulated at 20°C and 95% relative humidity. Results

[0106] Different test tubes are prepared with the formulations shown in the table below.

[0107] FR: reference test specimen comprising only the soil to be stabilized

[0108] FT: control test specimen comprising the soil to be stabilized and the LHR

[0109] FC1: comparative test specimen comprising the soil to be stabilized and bentonite

[0110] FC2: comparative test specimen comprising the soil to be stabilized, bentonite and the lime

[0111] FI4 wire: test tubes according to the invention

[0112] [Tables 1] Formulation (% weight of stabilized soil) FR FT FC1 FC2 Fil FI2 FI3 FI4 Soil to be stabilized 100 96.15 96.15 95.24 96.15 96.15 96.15 96.15 LHR - 3.85 - - 3.73 3.62 3.81 3.81 Bentonite - 3.85 3.81 - - - - Hydrated lime - - 0.95 - - - - Calcium stearate - - - 0.12 0.24 - - Silane - - - - - 0.04 - Sodium Hexametaphosphate - - - - - - 0.04 Permeability (ms-1) 1.7 x 10⁹ 2.9 x 10⁹ 3.9 x 10¹⁰ 1.6 x 10⁹ 8 2.2 x 10¹⁰ 9.4 x 10¹⁰ 5 x 10¹¹ 1.5 x 10⁰° Compressive strength at 28 days (MPa) 0.06 1.65 0.15 0.32 2.18 2.12 2.12 1.72

[0113] It is observed that only the combined use of LHR with a water-repellent additive significantly improves the permeability and compressive strength of the soil to be stabilized. The direct addition of bentonite, alone or mixed with lime, to the soil to be stabilized is insufficient.

Claims

Demands

1. A method for preparing a watertight structure, having mechanical resistance, based on stabilized soil, in which the structure consists of one or more layers, advantageously one layer, of stabilized soil, comprising the following steps: (i) mixing, by weight relative to the total weight of the stabilized soil: - 70% to 99% of the soil to be stabilized; - 1% to 30% by weight of a stabilizing composition; the stabilizing composition comprising: - a hydraulic road binder as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014; - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof; - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent, and mixtures thereof; (ii) compact the stabilized soil from step (i).

2. A method according to claim 1, wherein the stabilized soil layer obtained has a compressive strength at 28 days, determined according to standard NF EN 13286-41:2003, greater than 0.3 MPa and a permeability, determined according to standard NF EN ISO 17892-11:2019, less than 2.109 ms 1.

3. A method according to claim 1 or 2, wherein the composition comprises, as a road hydraulic binder, a binder comprising at least 10% by weight of lime, relative to the total weight of the binder.

4. A method according to any one of the preceding claims, wherein the composition comprises, as a road hydraulic binder, a binder comprising at least 30% by weight of Portland clinker, relative to the total weight of the binder.

5. A method according to any one of the preceding claims, wherein the soil to be stabilized is selected from the group consisting of a soil of class Al, A2, A3, A4, Bl, B2, B3, B4, B5, B6, ClAi, CIBi, C2Ai, C2Bi, Dl, D2, D3 and one of their mixtures according to the GTR soil classification standard NF - PI 1-300 1992.

6. A method according to any one of the preceding claims, comprising, in step (i), mixing 1% to 20% by weight, preferably 2% to 10% by weight, relative to the total weight of the dry soil stabilized, from the stabilizing composition with the soil to be stabilized.

7. A process according to any one of the preceding claims, wherein the stabilized soil obtained comprises, in addition to the components of the starting soil, by weight relative to the total weight of the dry stabilized soil: - 0.5% to 8% of road hydraulic binder, - 0.005% to 1% of water-repellent additive, - 0% to 1%, preferably 0% to 0.8% of clay deflocculating additive, - 0% to 10%, preferably 1% to 4% of bentonite, - 0% to 5%, preferably 0.1% to 4% of a water-reducing agent.

8. A method according to any one of the preceding claims, wherein prior to step (i) the soil is moistened to achieve a water content of 2% to 40% by weight relative to the dry weight of the soil to be stabilized.

9. A process according to any one of the preceding claims, wherein the compaction step (ii) enables a densification of more than 90% of the maximum dry density determined according to NF EN 13286-2:2010 to be achieved.

10. A method according to any one of the preceding claims, wherein each layer of stabilized soil has a thickness of less than 45 cm, preferably from 20 cm to 40 cm.

11. A method according to any one of the preceding claims, wherein the structure is a coating layer or an embankment.

12. Use of a composition comprising: - a road hydraulic binder as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014, - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof; - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water-reducing agent, and mixtures thereof; for the preparation of a stabilized soil having both waterproofing properties and mechanical performance, the preparation of a stabilized soil is carried out by mixing the soil and the composition.