Method for the preparation of a sealed structure based on stabilized soil

Abstract

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

Description

[0001] PROCESS FOR PREPARING A WATERPROOF STRUCTURE BASED ON STABILIZED SOIL

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] 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.

[0004] STATE OF THE ART

[0005] In the construction industry, a stable and rigid soil is required in certain applications, such as paving, construction, traffic structures, embankments, earthworks, subgrades, subgrades, roadbeds, construction tracks, and hydraulic structures such as canals, dams, retention basins, and tailings ponds. To achieve this, the soil in the construction area must be stabilized. This stabilization can be achieved by combining cement with the soil. Combinations of cement and soil are called, among other things, soil cement, cement-treated base, cement-stabilized soil, and cement-treated soil. Creating a cement-stabilized soil involves adding specific amounts of cement per unit of soil.The soil is then mixed, moistened if necessary, then remixed, leveled and compacted to meet the requirements specified in the site plans and drawings. Over time, the soils treated with cement harden and gain strength and rigidity.

[0006] When it is desired to ensure the waterproofing of the structure based on this stabilized soil, an additional waterproof layer is added. This surface layer is generally prepared using bentonite, a natural smectite-type clay with high swelling power which allows for perfect and lasting waterproofing of the soils.

[0007] Thus, a waterproof structure based on stabilized soil includes:

[0008] - a layer which provides the desired mechanical resistance, generally a mixture of soil, typically earth, and a mineral binder;

[0009] - a sealing layer which can be made up of:

[0010] - a mixture of soil, typically earth and bentonite, generally about 30 cm thick; or - a bituminous waterproof layer; or

[0011] - a waterproofing membrane; or

[0012] - a mixture of all of these solutions.

[0013] No requirements in terms of impermeability are expected from the stabilized soil layer. No requirements in terms of mechanical strength are expected from the waterproofing layer.

[0014] Such an approach is complex due to the fact that 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 hazards (such as moderate and / or intense rain), which makes the site potentially inaccessible for several days for construction machinery. Finally, membrane or bitumen solutions require the sequential implementation of two separate workshops: one for the soil treatment, then another for the waterproofing solution.

[0015] The present invention seeks to overcome these drawbacks by providing a stabilized soil having 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 device. The invention provides a structural waterproofing solution.

[0016] Depending on the application for which the waterproof structure based on stabilized soil is intended, it may be in contact with the outside air, water or even a top layer which may or may not be a surface layer. For example, these applications may be paving, construction, traffic structures, embankments, leveling or upper parts of earthworks, platforms, subgrades, road bases or even construction tracks, hydraulic structures such as canals, dams, retention basins, tailings basins.

[0017] The present invention has the following advantages:

[0018] - ease and simplicity of implementation;

[0019] - saving raw materials / land;

[0020] - reduction in construction costs due to one less processing operation;

[0021] - reduction in the number of layers of the final structure. SUMMARY OF THE INVENTION

[0022] The subject of the invention is a method for preparing a waterproof 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:

[0023] (i) mix, by weight relative to the total weight of the stabilized soil:

[0024] - from 70% to 99% of soil to be stabilized;

[0025] - from 1% to 30% by weight of a stabilizing composition; the stabilizing composition comprising:

[0026] - a hydraulic road binder as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014;

[0027] - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof;

[0028] - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent, and mixtures thereof;

[0029] (ii) compact the stabilized soil from step (i).

[0030] Advantageously, the layer of stabilized soil obtained has a compressive strength at 28 days, determined according to standard NF EN 13286-41:2003, greater than 0.3 MPa.

[0031] Advantageously, the layer of stabilized soil obtained has a permeability, determined according to standard NF EN ISO 17892-11:2019, of less than 2.10 9 ms 1 .

[0032] Advantageously, the composition comprises, as hydraulic road binder, a binder comprising at least 10% by weight of lime, relative to the total weight of the binder.

[0033] Advantageously, the composition comprises, as hydraulic road binder, a binder comprising at least 30% by weight of Portland clinker, relative to the total weight of the binder.

[0034] The soil to be stabilized can be selected from the group consisting of 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 - Pll-300 1992.

[0035] 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. 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

[0036] - from 0.5% to 8% of road hydraulic binder,

[0037] - from 0.005% to 1% of the water-repellent additive,

[0038] - from 0% to 1%, preferably from 0% to 0.8% of clay deflocculating additive,

[0039] - from 0 to 10%, preferably from 1% to 4% of bentonite,

[0040] - from 0 to 5%, preferably from 0.1% to 4% of a water reducing agent.

[0041] Advantageously, prior to step (i) the soil is moistened to reach a water content ranging from 2% to 40% by weight relative to the dry weight of the soil to be stabilized.

[0042] Advantageously, compaction step (ii) makes it possible to achieve a densification of more than 90% of the maximum dry density determined according to NF EN 13286-2:2010.

[0043] Advantageously, each layer of stabilized soil has a thickness of less than 45 cm, preferably ranging from 20 cm to 40 cm.

[0044] Advantageously, the structure is a coating layer or an embankment.

[0045] The invention also relates to the use of a composition comprising:

[0046] - a hydraulic road binder as defined in standard NF EN 13282-1:2014 or NF EN 13282-

[0047] 2:2014,

[0048] - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof;

[0049] - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent and their mixtures; for the preparation of a stabilized soil having both waterproofing properties and mechanical performance.

[0050] Stabilized soil is obtained by mixing the soil to be treated with the composition.

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] The various embodiments presented throughout the description may be used alone or in combination with each other, without limitation of combination. The present invention relates to a method for preparing a waterproof structure based on stabilized soil, in which the structure consists of one or more layers, advantageously one layer, of a stabilized soil, comprising the following steps:

[0053] (i) mix, by weight relative to the total weight of the stabilized dry soil:

[0054] - from 70% to 99% of soil to be stabilized;

[0055] - from 1% to 30% by weight of a stabilizing composition; the stabilizing composition comprising:

[0056] - a road hydraulic binder (LHR) as defined in standard NF EN 13282-1:2014 or NF EN 13282-2:2014;

[0057] - a water-repellent additive selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and mixtures thereof;

[0058] - optionally one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent and their mixtures;

[0059] (ii) compact the stabilized soil from step (i).

[0060] The term “soil to be stabilized” refers to the soil intended to be used to prepare the waterproof structure by bringing it into contact with the LHR, the water-repellent additive and possibly one or more optional additives.

[0061] The term "stabilized soil" refers to the soil constituting the waterproof structure which has been brought into contact with the LHR, the water-repellent additive and possibly one or more optional 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 layer of stabilized soil 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 2.10 -9 m.s' i

[0062] The expression "stabilized soil layer" means a layer comprising the mixture and / or the in situ reaction product of the various constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the various stages of preparation of the layer. Due to the improved mechanical and sealing properties of the stabilized soil layer, the upper sealing layer used in conventional methods is no longer necessary. 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, 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.

[0063] The stabilized soil layer according to the present invention typically has a permeability of less than 2.10' 9 ms -1 , preferably less than 1.10' 9 ms-1, preferably less than 5.1O 10 ms' 1 and preferably less than 1.0.10 10 ms-1. The permeability of the layer is measured according to the NF EN ISO 17892-11:2019 standard.

[0064] Soil to be stabilized

[0065] The soil to be stabilized can be any type of soil. The soil to be stabilized is generally composed of a mixture of natural, artificial, waste and recycled materials. Advantageously, the soil to be stabilized is selected from the group consisting of 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 - Pll-300 1992.

[0066] The process may include a step of moistening the soil to be stabilized. In fact, the soil generally has an optimal moisture content, evaluated using the normal Proctor test according to standard NF EN 13286-2:2010. The water content for implementation may differ from the optimal water content, in the order of -2% to +4% compared to the optimum water content, depending on the type of soil and the treatment binder expressed in relation to the dry weight of the material considered (soil alone or soil + cement).

[0067] Thus, advantageously, prior to step (i) the soil is moistened to reach a water content ranging from 2% to 40% by weight relative to the dry weight of the soil to be stabilized.

[0068] Preferably, during step (i), from 80% to 99% by weight, preferably from 85% to 98% by weight, more preferably from 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.

[0069] Thus, in the layer based on stabilized soil, the dry soil represents from 70% to 99% by weight relative to the weight of the waterproof layer, preferably from 80% to 99%, preferably from 85% to 98%, and preferably from 90% to 96% by weight relative to the total weight of the waterproof layer.

[0070] 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". However, it should be noted that the binder and the additive(s) may be added separately. Thus, the components of the stabilizing composition are not necessarily pre-mixed with their mixture with the soil to be stabilized.

[0071] Advantageously, the stabilizing composition, preferably in proportions adapted to the above proportions, may be in the form of a preparation kit with or without premixture of binder, water-repellent additive and possibly one or more optional additives.

[0072] Preferably, during step (i), from 1% to 20% by weight, preferably from 2% to 15% by weight, more preferably from 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.

[0073] Hydraulic road binder (also called binder or

[0074] An LHR is defined either in the standard NF EN 13282-1:2014, or in the standard NF EN 13282-2:2015.

[0075] An LHR comprises main constituents whose proportion exceeds 10% by weight and which are chosen from: a) the constituents described in the cement standard NF EN 197-1:2012 or the standard NF EN 197-5:2021; b) lime.

[0076] 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).

[0077] 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.

[0078] The lime may be calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide or mixtures thereof. Advantageously, the binder comprises at least 30% by weight of Portland clinker, based on the total weight of the binder. More advantageously, the binder comprises from 30% to 90% by weight of Portland clinker, more advantageously from 40% to 70% by weight based on the total weight of the binder.

[0079] The binder may also comprise 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.

[0080] The binder may also comprise fly ash, in particular siliceous fly ash, advantageously in a content ranging from 5% by weight to 40% by weight, preferably from 10% by weight to 25% by weight.

[0081] The binder may include secondary constituents, each not exceeding 10% by weight, as defined in standard NF EN 13282-1:2014.

[0082] As indicated in the standards, calcium sulfate can be added to these main and secondary constituents.

[0083] The main constituents described in the cement standard NF EN 197-1:2012 present in the binder are also called "cement".

[0084] 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 dry stabilized soil.

[0085] Water-repellent additive

[0086] The water repellent additive is selected from the group consisting of a silane, a polysiloxane, a fatty acid salt, and their mixtures.

[0087] The polysiloxanes may be polysiloxane derivatives represented by the following general formula (I) (R1SiO1n) in which n is an integer between 1 and 70; R, identical or different, is selected from the group consisting of: 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 thereof. Preferably, R is selected from the group consisting of C1-C12 alkyl, C1-C12 alkoxy, C1-C12 hydroxyalkyl, C1-C12 aminoalkyl, C1-C12 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, C1-C20 or C1-C20 alkyl means an alkyl having a carbon number between 1 and 20. The silane compound may be an alkoxysilane derivative represented by the following general formula (II): R 1 n If(OR 2 ) 4.nin which n is equal to 1, 2 or 3; R 1 , the same or different, is a C1-C20 alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C6-C20 aryl, C7-C20 aralkyl group or a derivative thereof, and the substituents R 1 in a molecule can be all the same or different; R 2 is a C1-C20 alkyl group, preferably a C1-C6 alkyl group. Preferably, R 1 is selected from the group consisting of C1-C12 alkyl, C1-C12 alkoxy, C1-C12 hydroxyalkyl, C1-C12 aminoalkyl, C1-C12 haloalkyl, C7-C14 aralkyl and C6-C12 aryl.

[0088] The silane compound may also be any compound carrying one or more silane functions of general formula (III) *- R 1 n If(OR 2 ) 4.n in which * represents the point of attachment to the compound and n, R 1 and R 2are as defined above for general formula (II). For example, tris(alkoxysilane)isocyanurate, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate, may be mentioned.

[0089] The silane and polysiloxane may be selected from the group consisting of isobutylmethoxysilane, polydimethylsiloxane, amino-functional polydimethylsiloxane, aminoethylaminopropyltrimethoxysilane, 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, the silane and the siloxane may be selected from the group consisting of polydimethylsiloxane, octyltriethoxysilane, iso-octyltriethoxysilane, octyltrimethoxysilane, iso-octyltrimethoxysilane, potassium methylsiliconate, tris(alkoxysilane)isocyanurate, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate and mixtures thereof.

[0090] The fatty acid salt may be a compound having the formula R 3 COOH in which R 3is a linear or branched alkyl comprising a carbon number ranging from C15 to C48, preferably from C18 to C45, preferably from C20 to C40, and more preferably from C24 to C36. Preferably, R 3 is a linear alkyl. Advantageously, the fatty acid is a zinc, sodium, calcium, magnesium, manganese, copper salt 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. Preferably, the water repellent additive is selected from the group consisting of calcium stearate, polydimethylsiloxane, octyltriethoxysilane, iso-octyltriethoxysilane, octyltrimethoxysilane, iso-octyltrimethoxysilane, potassium methylsiliconate, tris(alkoxysilane)isocyanurate, such as tris(3-(trimethoxysilyl)propoyl)isocyanurate and mixtures thereof.

[0091] Preferably, during step (i), the content of water-repellent additive added 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The water-repellent additive can be added in the dry state or in the liquid state. For the water-repellent additive in the liquid state, the content is expressed as % 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 the liquid state with a solid additive content of between 10 and 70% by weight, preferably between 30 and 60% by weight.

[0096] Optional additives

[0097] The stabilizing composition may also comprise one or more additive(s) selected from the group consisting of bentonite, a clay deflocculant, a water reducing agent, and mixtures thereof.

[0098] Preferably, the bentonite content ranges from 0% to 10% by weight, preferably from 1% to 4% by weight and more preferably from 2% to 4% by weight, relative to the total weight of stabilized dry soil.

[0099] The clay deflocculating additive may be selected from the group consisting of sodium or potassium phosphates, sodium or potassium silicates, and mixtures thereof. Preferably, the deflocculating additive is sodium hexametaphosphate. Preferably, the content of deflocculating additive 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.

[0100] The water reducing agent can be selected from the group consisting of a plasticizer, a superplasticizer and a mixture thereof.

[0101] The term "superplasticizer" as used in this specification and the accompanying claims is to be understood to include both water reducers and superplasticizers as described in the book entitled "Concrete Admixtures Handbook, Properties Science and Technology", VS Ramachandran, Noyes Publications, 1984.

[0102] Water reducers include, for example, lignosulfonates, hydroxycarboxylic acids, carbohydrates, and other specialized organic compounds, for example, glycerol, polyvinyl alcohol, sodium aluminomethylsiliconate, sulfanilic acid, and casein.

[0103] Superplasticizers belong to a new class of water reducers, chemically different from normal water reducers and capable of reducing water quantities by approximately 30%. Superplasticizers have been broadly classified into four groups: sulfonated naphthalene formaldehyde (SNF) condensates (usually a sodium salt); sulfonated melamine formaldehyde (SMF) condensates; modified lignosulfonates (MLS); and others. Newer superplasticizers include polycarboxylic compounds such as polycarboxylates, e.g., polyacrylates. A superplasticizer is preferably a new generation superplasticizer, e.g., a copolymer containing a polyethylene glycol as a graft chain and carboxylic functions 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.

[0104] Preferably, the water reducing agent is a polynaphthalene sulfonate polymer, a polycarboxylate, a polymelamine sulfonate or a mixture thereof.

[0105] Preferably, the content of water reducing agent ranges from 0% to 5% by weight, preferably from 0.1% to 4% by weight, more preferably from 0.2% to 3% by weight, relative to the total weight of stabilized dry soil. 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

[0106] - from 0.5% to 8% of road hydraulic binder,

[0107] - from 0.005% to 1% of the water-repellent additive,

[0108] - from 0% to 1%, preferably from 0% to 0.8% of clay deflocculating additive,

[0109] - from 0% to 10%, preferably from 1% to 4% of bentonite,

[0110] - from 0% to 5%, preferably from 0.1% to 4% of a water reducing agent.

[0111] Construction site process characteristics

[0112] The waterproof structure is prepared by a process comprising the following steps:

[0113] (i) mixing the soil to be stabilized and the stabilizing composition, which are as previously described; then

[0114] (ii) compact the stabilized soil from step (i).

[0115] 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 spread out over time. For the binder, it could be considered to add the cement and the lime separately.

[0116] The mixing step can be carried out by any method known to those skilled in the art that allows a homogeneous monolayer to be obtained. Advantageously, during step (i) the mixing is carried out using a pulvimixer type mixer. Advantageously, during step (i) the soil to be stabilized is treated in situ, i.e. directly on site without transportation.

[0117] In step (ii), compaction is advantageously mechanical compaction. Advantageously, compaction is also carried out directly on site.

[0118] The compaction may be carried out to reduce the thickness of the monolayer by at least 10%, preferably at least 15%, preferably at least 20% and most preferably 20 to 25%.

[0119] Compacting step (ii) advantageously makes it possible 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.

[0120] Water may be added during step (i) to achieve optimal soil compaction parameters and also to allow hydration of the cement. Advantageously, prior to step (i) the soil is moistened to achieve a water content ranging from -2% to +4% relative to the optimal water content of the soil to be stabilized.

[0121] The method may include the following steps:

[0122] (i-2) Addition of water to reach a target water content (in several stages if necessary)

[0123] (i-1) Spreading of the binder and additive(s), then

[0124] (i) mixing preferably using a pulvimixer type mixer,

[0125] (ii) mechanical compaction.

[0126] In step (i-2), the soil to be stabilized and the added water can be mixed to ensure better homogeneity.

[0127] In step (i-1), the binder and the additive(s) are spread directly onto the soil to be stabilized having the target water content.

[0128] The mixing step (i) allows the binder, the additive(s) and the soil to be stabilized to be mixed.

[0129] Step (ii) of mechanical compaction advantageously allows densification to be achieved: 97% of the MDD (Maximum Dry Density).

[0130] Step (ii) is advantageously carried out by carrying out the following steps:

[0131] (a) pre-adjustment of the surface with a grader for example then

[0132] (b) mechanical compaction, using various types of compactors (sheep's foot, pneumatic compactor and roller compactor);

[0133] (c) a final adjustment of the surface is generally necessary in order to achieve the final dimension and a satisfactory surface condition.

[0134] This process is advantageously implemented on ready-to-stabilize soil, i.e. soil from which the large elements have been removed and which has advantageously been scarified.

[0135] This process is particularly suitable when the waterproof structure is a sub-base.

[0136] The layer of stabilized soil obtained following step (ii) has a thickness of less than 45 cm, preferably ranging from 20 cm to 40 cm.

[0137] The waterproof structure is advantageously made up of one or two layers of stabilized soil. When the waterproof structure comprises more than one layer of stabilized soil, then, following step (ii), steps (i) and (ii) are repeated. The waterproof structure may then be in contact with the outside air, water or even an upper layer which may or may not be a surface layer. As an example, depending on these applications, such a structure may be intended for paving, construction, traffic structures, embankments, leveling courses or upper parts of earthworks, platforms, subgrades, road bases or construction site tracks, hydraulic structures such as canals, dams, retention basins, tailings basins.

[0138] 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.

[0139] Advantageously, the method does not include the step of adding a waterproofing layer of any kind. Indeed, the structure combines waterproofing and structural properties.

[0140] Thus, according to the invention, a composition is used comprising:

[0141] - a hydraulic road binder as defined previously;

[0142] - a water-repellent additive as defined above;

[0143] - optionally one or more additive(s) as defined above; for the preparation of a stabilized soil having both waterproofing properties and mechanical performance.

[0144] The stabilized soil can thus be used as the sole component of a structure's waterproofing system.

[0145] Advantageously, the sealing device consists of at least one layer of stabilized soil.

[0146] MEASUREMENT METHODS

[0147] Evaluation of mechanical resistance:

[0148] The compressive strength at 28 days is determined according to standard NF EN 13286-41 of July 2003.

[0149] The assessment is carried out according to the NF EN ISO 17892-11 standard. Two specimens from the same mixture are tested. Permeability is calculated according to the previous standard and expressed as flow velocity in ms-1. Water permeability is measured using an oedometer. The standard followed for laboratory tests is: NF EN ISO 17892-11:2019.

[0150] EXAMPLES

[0151] The following non-restrictive examples illustrate exemplary embodiments of the invention.

[0152] Materials

[0153] The soil to be stabilized is a silty soil classified A2 according to the GTR soil classification standard NF - Pll-3001992.

[0154] The hydraulic road binder (HRB) has the following formulation:

[0155] - 100 parts by weight of main and secondary constituents of the hydraulic road binder (LHR) within the meaning of standard NF EN 13282-1:2014 comprising by weight relative to the total weight of the main and secondary constituents:

[0156] - 39% Portland clinker (K)

[0157] - 15% blast furnace slag (S)

[0158] - 21% lime (limestone oxide) (CL)

[0159] - 15% siliceous fly ash (V or Va)

[0160] - 10% by weight of secondary constituents within the meaning of standard NF EN 13282-1:2014

[0161] - 2 parts by weight of calcium sulfate;

[0162] In addition to this LHR, the following is added to the soil to be stabilized:

[0163] - 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;

[0164] - sodium hexametaphosphate according to the quantities given in Table 1 below.

[0165] The comparative formulations are made with bentonite alone or mixed with hydrated lime (Ca(OH)) in the proportions given in Table 1 below.

[0166] Laboratory test methods

[0167] Successive stages of the test protocol:

[0168] 1. In a knife mixer, mix the soil to be stabilized.

[0169] 2. Moisten the soil to be stabilized by adding water to the mixer to achieve a water content of 19% by weight relative to the dry weight of the soil. Mix for 2 minutes.

[0170] 3. If necessary, add additives to the mixer. Mix for 3 minutes. 4. Compact 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.

[0171] For these tests, specimens are prepared for the evaluation of mechanical resistance and for permeability tests.

[0172] Thus, for permeability tests, the treated soil is compacted using a special mold into a small stainless steel ring (70 mm in diameter and 20 mm thick) using a press device in static compression mode. After compaction, the stainless steel ring with the treated soil is leveled on both sides using a metal ruler. Then, the sample is weighed and placed in a sealed plastic bag for 24 hours in a climate chamber regulated at 20°C and 95% relative humidity.

[0173] For the evaluation of mechanical resistance, the same protocol is followed but a standardized mold is used (standard NF EN 13286-53). The size of the samples is 50 mm in diameter and 100 mm in height. Then, the sample is weighed and placed in an airtight plastic bag for 28 days in a climatic chamber regulated at 20°C and 95% relative humidity.

[0174] Results

[0175] Different test tubes are prepared with the formulations presented in the table below.

[0176] FR: reference test piece comprising only the soil to be stabilized

[0177] FT: control specimen including the soil to be stabilized and the LHR

[0178] FC1: comparative test piece including the soil to be stabilized and bentonite

[0179] FC2: comparative test piece including the soil to be stabilized, bentonite and lime

[0180] FI4 wire: test pieces according to the invention [Table 1]

[0181] It has been found that only the combined use of LHR with a water-repellent additive can significantly improve the permeability and compressive strength of the soil to be stabilized. Adding bentonite directly, alone or mixed with lime, to the soil to be stabilized is not sufficient.

Claims

CLAIMS 1. Method for preparing a waterproof 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: - from 70% to 99% of soil to be stabilized; - from 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. Method according to claim 1, in which the layer of stabilized soil 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 2.10 -9 ms 1 .

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

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

5. Method according to any one of the preceding claims, in which 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 - P11-300 1992.

6. Method according to any one of the preceding claims, comprising, in step (i), mixing from 1% to 20% by weight, preferably from 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.

7. Method according to any one of the preceding claims, in which 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 - from 0.5% to 8% of road hydraulic binder, - from 0.005% to 1% of the water-repellent additive, - from 0% to 1%, preferably from 0% to 0.8% of clay deflocculating additive, - from 0 to 10%, preferably from 1% to 4% of bentonite, - from 0 to 5%, preferably from 0.1% to 4% of a water reducing agent.

8. Method according to any one of the preceding claims, in which prior to step (i) the soil is moistened to reach a water content ranging from 2% to 40% by weight relative to the dry weight of the soil to be stabilized.

9. Method according to any one of the preceding claims, in which the compacting step (ii) makes it possible to achieve a densification of more than 90% of the maximum dry density determined according to NF EN 13286-2:2010.

10. Method according to any one of the preceding claims, in which each layer of stabilized soil has a thickness of less than 45 cm, preferably ranging from 20 cm to 40 cm.

11. A method according to any preceding claim, wherein the structure is a revetment layer or an embankment.

12. 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, prepared by mixing the soil to be treated with the composition, the stabilized soil having both waterproofing properties and mechanical performance.

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