CA2281164A1

CA2281164A1 - Method for stabilizing soil using a cationic surfactant, soil stabilizing agent and stabilized soil

Info

Publication number: CA2281164A1
Application number: CA 2281164
Authority: CA
Inventors: Zhihong Zhou; Gerry Kehler
Original assignee: Nilex Inc
Current assignee: Nilex Inc
Priority date: 1999-08-27
Filing date: 1999-08-27
Publication date: 2001-02-27

Abstract

A soil stabilizing agent is comprised of an amount of a cationic surfactant, a stabilized soil is formed by the mixing of the soil and the stabilizing agent and a method for stabilizing soil is comprised of the steps of providing an amount of the cationic surfactant and applying the cationic surfactant to the soil.
Preferably, the cationic surfactant has the following structural formula:
(see formula I) wherein R is selected from the group consisting of CH3, C6H5 and CH2-C6H5;
wherein R' is selected from the group consisting of CH3, C6H5, CH2-C6H5, an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; wherein R" is selected from the group consisting of an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; and wherein X- is an anion.

Description

METHOD FOR STABILIZING SOIL USING A CATIONIC SURFACTANT SOIL
STABILIZING AGENT AND STABILIZED SOIL
FIELD OF INVENTION
The present invention relates to the chemical stabilization of soil, preferably for road and foundation construction and maintenance. Specifically, the chemical stabilization of the soil preferably enhances or improves the characteristics of compacted soil. More particularly, the present invention relates to a soil stabilizing agent comprised of an amount of a cationic surfactant, a stabilized soil formed from mixing soil and the stabilizing agent and a method for stabilizing soil using the cationic surfactant.
BACKGROUND OF INVENTION
Construction and maintenance of roads and foundations typically constitutes a relatively large expense both publicly and privately. The magnitude of this expense is dependent, at least in part, on the type of soil present. For instance, difficulties with road and foundation construction are often encountered in the presence of finely divided soils, being fine grained soils and coarse grained soils including a substantial portion of fines, which difficulties result in an increase in the associated expenses.
Finely divided soils, especially those containing swelling clays, tend to experience volume changes in a dry-wet cycle. During rainfall, water is soaked or imbibed into the soil which weakens its structure and decreases its stability.
Capillary suction force can also imbibe groundwater into surface soil. In colder regions, frost damage presents a problem, particularly during spring melt. Excess water is released during the thawing period which causes a loss of soil strength.
As well, soil minerals tend to be hydrophilic in nature. Thus, compacted soils have a strong tendency to imbibe water through capillary suction because of the hydrophilic nature of the soil minerals. In imbibing water into the soil, the soil tends to become soft and the bearing capacity of the road or foundation decreases. The resulting instability causes damage to unpaved roads as well as to the sub-bases or foundations of paved roads.
One approach to stabilizing soils has been the incorporation of "borrow"
materials, such as gravel and other granular materials, into the soil. The borrow materials tend to provide some support and drainage to such soils. However, these materials may be impractical to use or may not be readily available. For instance, difficulties may be encountered in transporting these materials to the construction site with a resulting increase in the overall costs.
A further approach to enhancing soil stability is the addition of conventional compounds such as lime, lime-fly ash compositions, cement and asphalt.
However, these compounds have limited applications and must often be used in combination with borrow materials. In addition, these compounds tend to be relatively expensive and difficult to apply in the quantities required to enhance soil stability.
More recently, a number of chemical soil stabilizers have become available on the market. Specifically, the chemical stabilizers are provided to alter the soil chemistry to improve its stability. However, these chemical soil stabilizers tend to be anionic in nature.
It has been found that anionic chemicals are not fully satisfactory or suitable for stabilizing soil, and more particularly, for modifying the hydrophilic nature of the soil.
Specifically, it has been found that these anionic chemicals may not be readily attracted to the negatively charged soil minerals.
Thus, none of the approaches thus far has provided a fully satisfactory or suitable solution to enhancing soil stability and more particularly, to modifying the hydrophilic nature of soils.

Several examples of previous approaches taken to enhancing soil stability are provided below. For instance, United States of America Patent No. 5,827,568 issued October 27, 1998 to Wickett describes an asphalt modifying emulsion, containing natural rubber and crumb rubber from used vehicle tires, which is mixed with an asphalt paving material mix and applied to a surface for soil stabilization.
United States of America Patent No. 3,854,968 issued December 17, 1974 to Minnick et. al. describes a modified lime-fly ash cementitious mixture comprised of a lime-sulfate material which is used as a subsurface base material or a soil stabilization agent.
The lime-sulfate material is preferably made by the addition of a sulfuric acid solution to quicklime in a modified lime hydration process. Alternately, the lime-sulfate material may comprise lime and a separate sulfate compound such as gypsum.
United States of America Patent No. 5,336,022 issued August 9, 1994 to McKennon et. al. describes a method for stabilizing clay bearing soils including incorporating a silica compound into the soil and applying lime to promote a pozzolanic reaction in the soil. United States of America Patent No. 5,354,787 issued October 11, 1994 to Shimoda et. al. describes a soil stabilizing agent comprising a mixture of a material including quick lime and/or calcined dolomite and fibrillatable polytetraflouroethylene resin.
United States of America Patent No. 5,795,104 issued August 18, 1998 to Schanze describes a material for soil stabilization consisting of an alkali silicate waterglass component and a hardener component. The hardener component is comprised of a fast-acting hardening agent, preferably an ester, lactone, lactam, inorganic or organic acid, anhydride, nitrite, amide or acid chloride, and a slower-acting hardening agent to function as a hardening retarder, preferably butylene carbonate or a mixture of different dialkyl carboxylates.

United States of America Patent No. 4,276,077 issued June 30, 1981 to Zaslavsky et. al. describes reagents applied to soil for improving the soil structure by stabilizing the aggregates therein. The reagents are graft polymers obtained from crude lignosulfonate and a monomer selected from the group consisting of vinyl cyanide (acrylonitrile), vinyl acetate, hydrolyzed vinyl acetate and acrylamide in the presence of an initiator. United States of America Patent No. 4,277,203 issued July 7, 1981 to Reed, ]fr. et.
al. describes a method for stabilizing soil wherein a liquid is applied to the soil and allowed to polymerize to form an elastomeric resin which bonds the soil particles together.
The liquid is selected from the group consisting of (1) a mixture of dimer diisocyanate and dimer diamine and (2) a mixture of dimer diisocyanate and a ketamine derivative of dimer diamine.
United States of America Patent No. 5,770,639 issued June 23, 1998 to Bitter et. al. describes the use of a stabilizer for increasing the water resistance of soil impregnations based on polyvinyl acetate and comparable esters of polyvinyl alcohol with lower monocarboxylic acids. The stabilizer includes fatty acids or fatty alcohols and/or at least substantially water-insoluble esters, ethers and/or salts thereof.' United States of America Patent No. 3,980,490 issued September 14, 1976 to Schneider describes a soil stabilizing agent consisting of a source of calcium, such as calcium carbonate, and a spent sulfuric acid in a water solution. United States of America Patent No. 5,000,789 issued march 19, 1991 to Merritt describes a method for chemically stabilizing cohesive soils wherein sulfuric acid, citrus stripper oil and water are admixed to the soil.
Thus, there remains a need in the industry for a soil stabilizing agent, a stabilized soil formed from the agent and a method for stabilizing soil, all of which improve or enhance the characteristics of soil, preferably compacted soil, to facilitate road and foundation construction and maintenance.

SUMMARY OF INVENTION
The within invention is directed at a soil stabilizing agent, a stabilized soil formed from the agent and a method for stabilizing soil which improve or enhance the characteristics of the soil. Preferably, the agent, the soil and the method of the within invention all provide for the chemical stabilization of the soil. In addition, preferably, the agent, the soil and the method of the within invention all particularly improve or enhance the characteristics of compacted soils.
Further, the present invention relates to a soil stabilizing agent comprised of an amount of a cationic surfactant, a stabilized soil formed from mixing soil and the stabilizing agent and a method for stabilizing soil using the cationic surfactant. The minerals within the soil tend to have a negative surface charge and a predominantly hydrophilic nature. The hydrophilic nature results in a tendency of the soil to attract water and a tendency of the soil to imbibe water through capillary suction.
The cationic surfactant is attracted to the soil minerals and modifies the hydrophilic nature of the soil.
Specifically, the cationic surfactant renders the soil somewhat hydrophobic, or relatively more hydrophobic as compared with untreated or unmodified soil. In particular, the attraction of water to the soil is reduced and the imbibition of water into the soil is also reduced. Accordingly, the stability of the soil is enhanced.
As stated, in a first aspect of the within invention, the invention is comprised of a stabilizing agent for soil. The stabilizing agent is comprised of an amount of a cationic surfactant. In a second aspect of the invention, the invention is comprised of a stabilized soil. The stabilized soil is formed by the mixing of soil and the stabilizing agent. In a third aspect of the invention, the invention is comprised of a method for stabilizing soil. The method is comprised of the steps of providing an amount of a cationic surfactant and applying the cationic surfactant to the soil.

The cationic surfactant may be comprised of any cationic surfactant capable of, and suitable for, modifying the predominantly hydrophilic nature of the soil to render it relatively more hydrophobic, as compared with untreated soil, such that the soil has a lesser tendency to attract water and a reduced tendency to imbibe water. The modification of the naturally hydrophilic nature of the soil results in an enhancement of the stability of the soil or contributes to the stabilization of the soil. More particularly, the attraction of water to the soil and the imbibition of water into the soil tend to weaken its structural integrity. Thus, the lessened attraction of water to the soil and the reduction in the imbibition of water into the soil stabilizes the soil by lessening the negative effect of the exposure of the soil to water on its structural integrity.
Preferably, the cationic surfactant is comprised of at least one hydrophobic group attached to a cationic (N+) hydrophilic group. More preferably, the cationic surfactant is comprised of two hydrophobic groups attached to a cationic (N+) hydrophilic group.
More preferably, the cationic surfactant has the following structural formula:

R,-( R X_ -R"' wherein R is selected from the group consisting of H and (CHz)nCHs, wherein n=0, 1, 2 or 3;
wherein R' is selected from the group consisting of H, (CHz)"CH3, C6H5 and CHz-C6H5, wherein n=0, 1, 2 or 3;
wherein R" is selected from the group consisting of H, (CHz)nCH3, C6H5, CHz-C6H5, an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl, wherein n=0, 1, 2 or 3;

wherein R"' is selected from the group consisting of an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; and wherein X- is an anion.
Within the context of the structural formula provided above, the cationic surfactant is preferably comprised of one of the following:
(a) at least one hydrogenated tallowalkyl;
(b) two hydrogenated tallowalkyls;
(c) two alkyl chains with at least 12 carbons on each chain;
(d) a benzyl group and a hydrogenated tallowalkyl; and (e) a benzyl group and an alkyl chain with at least 12 carbons.
In the preferred embodiment, the cationic surfactant is comprised of at least one of dimethyl di(hydrogenated tallow)alkyl ammonium chloride (DM2HT), dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB), methyl di(hydrogenated tallow)alkyl benzyl ammonium chloride (M2HTB), alkyl dimethyl benzyl ammonium chloride (ADMB), dialkyl dimethyl ammonium chloride (DADM) and dialkyl methyl benzyl ammonium chloride (DAMB).
Further, the within invention may be used for any type or class of soil.
Preferably, the soil is comprised of a finely divided soil. A finely divided soil is defined to include a fine grained soil and a coarse grained soil including a substantial or significant amount or percentage of fines therein. Specifically, the coarse grained soil preferably includes at least 35 % fines.
As well, in the first and second aspects of the within invention, the stabilizing agent is further comprised of an amount of water to provide an aqueous mixture. Thus, the stabilizing agent is comprised of the amount of the cationic surfactant distributed within the water, through dissolution, dispersion or both, to form the aqueous mixture.
The cationic surfactant may be distributed within the water to any degree, however, preferably, the aqueous mixture is substantially homogeneous. Thus, the cationic surfactant is substantially homogeneously distributed within the water.
In addition, in the second aspect of the invention, the soil may be mixed with the stabilizing agent, and thus the cationic surfactant, in any proportions or amounts providing for or permitting the stabilization of the soil in the manner described herein.
Thus, any amount of cationic surfactant may be mixed with the soil which is capable of stabilizing the soil, and more particularly, which is capable of modifying the hydrophilic nature of the soil. However, preferably, the cationic surfactant is mixed with the soil in an amount of at least 0.005 % by weight of dry soil mass. In the preferred embodiment, the cationic surfactant is mixed with the soil in an amount of between about 0.01 % and about 1.0 % by weight of dry soil mass.
As indicated, in the third aspect of the invention, the method is comprised of the steps of providing the amount of the cationic surfactant and applying the cationic surfactant to the soil. In addition, the method is preferably comprised of the step of compacting the soil to a desired density. The compacting step may be performed in any manner and by any mechanism, apparatus or process capable of compacting the soil to the desired density.
In a preferred embodiment of the method, the compacting step is performed following the applying step. In an alternate embodiment of the method, the compacting step is performed prior to the applying step to provide a compacted soil. In this instance, the applying step is comprised of applying the cationic surfactant to the compacted soil.
As indicated, in the preferred embodiment of the method, the compacting step is performed following the applying step. The applying step may be performed in any manner and by any mechanism, apparatus or process capable of applying the cationic surfactant to the soil. For instance, the applying step may be performed in any manner and by any mechanism, apparatus or process able to bring the cationic surfactant and the _g_ soil into physical contact with each other such as by laying, spreading, mixing or spraying the cationic surfactant on or in the soil.
Preferably, the applying step is comprised of the steps of: (a) contacting the cationic surfactant with the soil; and (b) mixing the soil in order to distribute the cationic surfactant substantially throughout the soil. The contacting step may be performed in any manner and by any mechanism, apparatus or process capable of contacting the cationic surfactant with the soil or adding the cationic surfactant to the soil such that the cationic surfactant and the soil are brought into physical contact with each other.
The mixing step may be performed in any manner and by any mechanism, apparatus or process capable of mixing or combining the cationic surfactant with the soil or otherwise putting them together such that the cationic surfactant is distributed within the soil. Although the cationic surfactant may be distributed within the soil to any degree, preferably, the cationic surfactant is distributed substantially throughout the soil. More preferably, the cationic surfactant is distributed substantially evenly or uniformly throughout the soil.
The cationic surfactant may be applied to the soil in any proportion or amount providing for or permitting the stabilization of the soil in the manner described herein. Thus, any amount of cationic surfactant may be applied to the soil which is capable of stabilizing the soil, and more particularly, which is capable of modifying the hydrophilic nature of the soil. However, in the preferred embodiment of the method in which the compacting step is performed following the applying step, the cationic surfactant is preferably applied to the soil in an amount of at least 0.005 %
by weight of dry soil mass. More preferably, the cationic surfactant is applied to the soil in an amount of between about 0.01 % and about 1.0 % by weight of dry soil mass.
Further, the compacting step may be performed at any moisture content of the soil compatible with compacting the soil to a desired density. However, the soil has an optimum moisture content for compacting. Preferably, the moisture content of the soil following the applying step is between about 4 % less than the optimum moisture content and about 4 % greater than the optimum moisture content. More preferably, the moisture content of the soil following the applying step is between about 2 % less than the optimum moisture content and about 2 % greater than the optimum moisture content.
In the alternate embodiment of the method, the compacting step is performed prior to the applying step to provide a compacted soil. Thus, the applying step is comprised of applying the cationic surfactant to the compacted soil. The applying step may be performed in any manner and by any mechanism, apparatus or process capable of applying the cationic surfactant to the compacted soil. For instance, the applying step may be performed in any manner and by any mechanism, apparatus or process able to bring the cationic surfactant and the compacted soil into physical contact with each other such as by laying, spreading or spraying the cationic surfactant on the compacted soil.
The cationic surfactant may be applied to the compacted soil in any proportion or amount providing for or permitting the stabilization of the soil in the manner described herein. Thus, any amount of cationic surfactant may be applied to the compacted soil which is capable of stabilizing the soil, and more particularly, which is capable of modifying the hydrophilic nature of the soil.
Further, in the alternate embodiment, the compacting step may be performed at any moisture content of the soil compatible with compacting the soil to the desired density. However, preferably, the moisture content of the soil prior to the compacting step is between about 4 °/o less than the optimum moisture content and about 4 % greater than the optimum moisture content. More preferably, the moisture content of the soil prior to the compacting step is between about 2 % less than the optimum moisture content and about 2 % greater than the optimum moisture content.

In both the preferred and alternate embodiments of the method of the within invention, the method is preferably further comprised of the step of combining the cationic surfactant with an amount of water to produce an aqueous mixture. In the preferred embodiment, the applying step is thus comprised of applying the aqueous mixture to the soil. In the alternate embodiment, the applying step is comprised of applying the aqueous mixture to the compacted soil.
The cationic surfactant may be combined with the water in any amount or percentage compatible with the particular method of stabilizing the soil or compacted soil.
However, in the alternate embodiment of the method, the aqueous mixture is preferably comprised of the cationic surfactant in an amount of at least about 0.01 % by weight of the aqueous mixture. More preferably, the aqueous mixture is comprised of the cationic surfactant in an amount of between about 0.1 % and about 10.0 % by weight of the aqueous mixture.
The combining step may be performed in any manner and by any mechanism, apparatus or process capable of adding or uniting the cationic surfactant with the water or otherwise bringing or contacting them together such that the cationic surfactant is distributed within the water to provide the aqueous mixture.
Thus, the combining step results in the dissolution, dispersion or both the dissolution and dispersion of the cationic surfactant within the water.
Further, in both the preferred and alternate embodiments of the method of the within invention, the method is preferably further comprised of the step of mixing the aqueous mixture so that it is substantially homogeneous. Although the cationic surfactant may be distributed within the water to any degree, the aqueous mixture is preferably substantially homogeneous. The step of mixing the aqueous mixture may be performed in any manner and by any mechanism, apparatus or process capable of mixing or combining the cationic surfactant within the water or otherwise distributing the cationic surfactant throughout the water, preferably substantially homogeneously.

As well, in order to enhance or facilitate the applying step in either the preferred or alternate embodiments, the water combined with the cationic surfactant to produce the aqueous mixture preferably has a temperature of between about 5° Celsius and 90° Celsius. More preferably, the water has a temperature of between about 20°
Celsius and 60° Celsius. Thus, where necessary in order to achieve the desired temperature, the method may be further comprised of the step of heating, or alternatively cooling, the water to the desired temperature prior to the combining step. The water may be heated or cooled in any manner and by any mechanism, apparatus or process capable of and suitable for heating or cooling the water to the desired temperature prior to the combining step such that the combining step combines the cationic surfactant and the water having the desired temperature.
Finally, in the alternate embodiment of the method in which the compacting step is performed prior to the applying step, the method may be further comprised of the step, prior to the applying step, of drying the compacted soil such that the moisture content of the compacted soil is equal to or less than about the optimum moisture content of the soil at the commencement of the applying step. Further, the applying step may be performed repeatedly. In this instance, the drying step is preferably performed prior to each applying step such that the moisture content of the compacted soil at the commencement of each applying step is equal to or less than the optimum moisture content of the soil.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a method described herein for comparing the capillary suction between a control soil sample and a stabilized soil sample prepared in accordance with the within invention; and Figure 2 is a representation of the results of a slaking test comparing a control soil sample and a stabilized soil sample at the commencement of the slaking test, at 3 hours and at 48 hours.
DETAILED DESCRIPTION
The within invention is directed at a soil stabilizing agent, a stabilized soil formed from the agent and a method for stabilizing soil, all of which improve or enhance the characteristics of soil. The invention may be used for any application requiring the stabilization of soil. However, the within invention is particularly applicable to the construction and maintenance of roads, parking lots, airfields and building foundations generally.
Specifically, the agent, the soil and the method all provide for the chemical stabilization of soil in order to improve or enhance the stability of the soil, particularly compacted soils as described further below. More particularly, the soil stabilizing agent is comprised of an amount of a cationic surfactant. The stabilized soil is formed by the mixing of soil and the stabilizing agent. The method for stabilizing soil is comprised of the steps of providing an amount of a cationic surfactant and applying the cationic surfactant to the soil.
The minerals within the soil tend to have a negative surface charge and a predominantly hydrophilic nature. The hydrophilic nature results in the attraction of water to the soil and the imbibition of water into the soil through capillary suction. The cationic surfactant has a positive hydrophilic head and a hydrophobic tail.
The positive hydrophilic head is attracted to the negatively charged soil minerals and the hydrophobic tail modifies the predominantly hydrophilic nature of the soil minerals.
Specifically, the hydrophilic nature of the soil minerals is modified by rendering the soil minerals somewhat hydrophobic, or relatively more hydrophobic as compared with untreated or unmodified soil. As a result, the attraction of water to the soil is lessened and the imbibition of water into the soil through capillary suction is reduced.
As a result, the stability of the treated or stabilized soil is enhanced.
Specifically, the modification of the naturally hydrophilic nature of the soil results in an enhancement of the stability of the soil or contributes to the stabilization of the soil. More particularly, as stated, the attraction of water to the soil and the imbibition of water into the soil tends to weaken its structural integrity. Thus, the lessened attraction of water and the reduction in the imbibition of water act to stabilize the soil by lessening the negative effect of the exposure of the soil to water on its structural integrity.
Generally speaking, the term surfactant refers to any surface active agent which acts or functions to reduce surface tension, particularly of a liquid, or interfacial tension, being the surface tension at the interface of two liquids. Surface tension tends to minimize the area of the surface and is manifested in capillarity. Surfactant classification depends upon the charge of the surface active moiety, typically the larger part of the molecule. In cationic surfactants, the charge is positive. Further, the solubilizing group of the cationic surfactant carries a positive charge when dissolved in an aqueous medium, which positive charge is provided by an amino or quaternary nitrogen.
Preferably, the cationic surfactant is comprised of at least one hydrophobic group attached to a cationic (N+) hydrophilic group. More preferably, the cationic surfactant is comprised of two hydrophobic groups attached to a cationic (N+) hydrophilic group. Hydrophobic groups tend to be comprised of either long hydrocarbon chains or shorter aromatic (or cyclo) rings. An example of a long hydrocarbon chain is an alkyl chain with at least 8 carbons, while an example of a shorter aromatic ring is a benzyl ring.

More particularly, the cationic surfactant has the following structural formula:

' R N- R X
-R"' wherein R is selected from the group consisting of H and (CH2)nCH3 (wherein n=0, 1, 2 or 3); wherein R' is selected from the group consisting of H, (CH2)"CHs, C6Hs and CH2-C6Hs (wherein n=0, 1, 2 or 3); wherein R" is selected from the group consisting of H, (CHz)nCH3, C6H5, CH2-C6H5, an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl (wherein n=0, 1, 2 or 3); wherein R"' is selected from the group consisting of an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; and wherein X-is an anion.
Further, it has been found that the more preferred cationic surfactants are comprised of: (1) at least one hydrogenated tallowalkyl; (2) two hydrogenated tallowalkyls; (3) two alkyl chains with at least 12 carbons on each chain; (4) a benzyl group and a hydrogenated tallowalkyl; or (5) a benzyl group and an alkyl chain with at least 12 carbons.
Thus, referring to the preferred structural formula above, where the cationic surfactant is comprised of one or two hydrogenated tallowalkyls, one or both of R" and R"' is preferably a hydrogenated tallowalkyl. Where the cationic surfactant is comprised of two alkyl chains with at least 12 carbons on each chain, R" and R"' are each preferably an alkyl chain with at least 12 carbons. Where the cationic surfactant is comprised of a benzyl group and a hydrogenated tallowalkyl, at least one of R' and R" is preferably a benzyl group and at least one of R" and R"' is preferably a hydrogenated tallowalkyl.
Finally, where the cationic surfactant is comprised of a benzyl group and an alkyl chain with at least 12 carbons, at least one of R' and R" is preferably a benzyl group and at least one of R" and R"' is preferably an alkyl chain with at least 12 carbons.
In the preferred embodiment, the cationic surfactant is comprised of at least one of dimethyl di(hydrogenated tallow)alkyl ammonium chloride (DM2HT), dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB), methyl di(hydrogenated tallow)alkyl benzyl ammonium chloride (M2HTB), alkyl dimethyl benzyl ammonium chloride (ADMB), dialkyl dimethyl ammonium chloride (DADM) and dialkyl methyl benzyl ammonium chloride (DAMB). Thus, the cationic surfactant may be comprised of one of DM2HT, DMHTB, M2HTB, ADMB, DADM and DAMB or may be comprised of a mixture or combination of two or more of DM2HT, DMHTB, M2HTB, ADMB, DADM and DAME.
Further, the within invention may be used for the stabilization of any type or class of soil having a predominantly hydrophilic nature such that it tends to attract water and tends to imbibe water through capillary suction. However, preferably, the soil is comprised of a finely divided soil. A finely divided soil includes fine grained soils and coarse grained soils including a substantial or significant amount or percentage of fines therein. Preferably, the coarse grained soil includes at least 35 % fines.
More particularly, fine grained soils include those soils falling within the definition of "fine-grained soils" provided by the Unified Soil Classification System including both silts and clays. In addition, fine grained soils also includes the general class of "silt-clay materials" provided by the American Association of State Highway and Transportation Officials ("AASHTO") System, including those described as silty soils and clayey soils. In the preferred embodiment, the fine grained soils fall within CL Group, CH
Group, ML Group or MH Group pursuant to the Unified Soil Classification System and within A-6 Group or A-7 Group, being clayey soils, pursuant to the AASHTO
System.

Coarse grained soils include those soils falling within the definition of "coarse-grained soils" provided by the Unified Soil Classification System, preferably coarse grained soils including a substantial or appreciable amount of fines such as "sands with fines" and "gravels with fines." In addition, coarse grained soils also include the general class of "granular materials" provided by the AASHTO System, preferably those granular materials described as silty or clayey gravel and sand. In the preferred embodiment, the coarse grained soils fall within SC Group or SM Group pursuant to the Unified Soil Classification System and within A-2 Group pursuant to the AASHTO
System.
In the preferred embodiment, the stabilizing agent is also further comprised of an amount of water to provide an aqueous mixture. The stabilized soil is thus formed by the mixing of the stabilizing agent, comprised of the aqueous mixture of cationic surfactant, and the soil. In addition, the method is preferably further comprised of the step of combining the cationic surfactant with an amount of water to produce the aqueous mixture.
The amount of the cationic surfactant is distributed within the water, either through dissolution, dispersion or both, to produce the aqueous mixture.
Specifically, the cationic surfactant may be dissolved within the water, dispersed within the water or a combination of both. In any event, the cationic surfactant may be distributed within the water to any degree, however, preferably, the aqueous mixture is substantially homogeneous. Thus, the cationic surfactant is substantially uniformly or homogeneously distributed within the water. The aqueous mixture may be formed with any type of water so long as the water does not significantly alter the cationic nature of the cationic surfactant. Fresh-water, surface water, ground water or a combination thereof may all be used to produce the aqueous mixture. In addition, the aqueous mixture may be formed with any proportion or percentage of water to cationic surfactant. The desired proportion or percentage may vary depending upon such factors as the amount of cationic surfactant desired to be applied to the soil, the manner of application of the aqueous mixture to the soil, the desired moisture content of the soil and the soil composition.
In addition, in the preferred embodiment of the stabilized soil, the soil may be mixed with the stabilizing agent, and thus the cationic surfactant, in any proportions or amounts providing for or permitting the stabilization of the soil in the manner described herein. Thus, any amount of cationic surfactant may be mixed with the soil which is capable of stabilizing the soil, and more particularly, which is capable of modifying the hydrophilic nature of the soil.
However, preferably, the cationic surfactant is mixed with the soil in an amount of at least 0.005 % by weight of dry soil mass. Conversely, the maximum desired amount to be mixed with the soil is determined by the cation exchange capacity of the soil.
Specifically, the cations provided by the cationic surfactant preferably do not exceed the canon exchange capacity of the soil.
As indicated previously, the soil minerals have a negative surface charge.
This results in attempts to balance the charges by cation attraction which is in proportion to the surface charge deficiency of the soil minerals. The cation exchange capacity ("CEC") of the soil minerals represents the equivalent negative surface charge on the soil minerals, which will vary with the type of minerals found within the soil and is often measured by a methylene blue method. Thus, the cationic exchange capacity of the soil represents the maximum canon exchange that may occur. Accordingly, although the amount of the cationic surfactant may exceed the cationic exchange capacity, no further canon exchange will occur. In other words, the excess cationic surfactant above the cationic exchange capacity will essentially have no effect on the soil properties.
In the preferred embodiment, the cationic surfactant is mixed with the soil in an amount of between about 0.01 % and about 1.0 % by weight of dry soil mass.
However, the preferred minimum and maximum amounts will vary depending upon factors such as the desired effect of the cationic surfactant, the desired properties of the stabilized soil, the type of cationic surfactant and the soil type or composition.
The method of the within invention is comprised of the steps of providing the amount of the cationic surfactant and applying the cationic surfactant to the soil. In addition, the method is preferably comprised of the step of compacting the soil to a desired density. Compaction is the densification of the soil by the application of mechanical energy. The compacting step may be performed in any manner and by any mechanism, apparatus or process capable of compacting the soil to the desired density.
Thus, the soil mass of the compacted soil is equal to total depth of the compacted soil multiplied by the surface area of the compacted soil. Further, where either required or otherwise desirable to achieve the desired density of the soil, the soil may be compacted in a series or plurality of lifts, steps or layers. In this case, the combined depths of each lift provides the total depth of the compacted soil. Thus, the compacted soil mass of each lift will be equal to the depth of the lift multiplied by the surface area of the lift.
In a preferred embodiment of the method, the compacting step is performed following the application of the cationic surfactant to the soil. In an alternate embodiment of the method, the compacting step is performed prior to the application of the cationic surfactant to the soil to provide a compacted soil. In this instance, the applying step is comprised of applying the cationic surfactant to the compacted soil. Where the soil is compacted in lifts, the cationic surfactant may be applied to each compacted lift in turn.
Thus, in the preferred embodiment of the method, the method is comprised of the steps of providing an amount of the cationic surfactant, applying the cationic surfactant to the soil and compacting the soil to the desired density. In addition, in the preferred embodiment, the method is further comprised of the step of combining the cationic surfactant with an amount of water to produce an aqueous mixture, as discussed above. Thus, the applying step is comprised of applying the aqueous mixture, including the cationic surfactant, to the soil.

The combining step may be performed in any manner and by any mechanism, apparatus or process capable of adding or uniting the cationic surfactant with the water or otherwise bringing or contacting them together such that the cationic surfactant is distributed within the water to provide the aqueous mixture.
Thus, the combining step results in the distribution of the cationic surfactant within the water. The cationic surfactant may be distributed within the water through dissolution, dispersion or both dissolution and dispersion to produce the aqueous mixture.
As discussed above, the cationic surfactant may be combined with any type of water so long as the water does not significantly alter the cationic nature of the cationic surfactant. Fresh-water, surface water, ground water or a combination thereof may all be combined with the cationic surfactant. In addition, the cationic surfactant may be combined with any proportion or percentage of water to produce the aqueous mixture.
The desired proportion or percentage of water to cationic surfactant may vary depending upon such factors as the amount of cationic surfactant desired to be applied to the soil, the manner of application of the aqueous mixture to the soil, the desired moisture content of the soil and the soil composition.
Further, the cationic surfactant may be distributed within the water to any degree, however, preferably, the aqueous mixture is substantially homogeneous.
Thus, the cationic surfactant is substantially uniformly or homogeneously distributed within the water. As a result, the method is preferably further comprised of the step of mixing the aqueous mixture so that it is substantially homogeneous. The mixing step may be performed in any manner and by any mechanism, apparatus or process capable of mixing or combining the cationic surfactant within the water or otherwise distributing the cationic surfactant throughout the water, preferably substantially homogeneously.
As well, in order to facilitate or enhance the combining step, a solvent may be added to the aqueous mixture to assist with the dissolution or dispersion of the cationic surfactant in the water. Although any solvent compatible with the aqueous mixture may be used, the solvent is preferably comprised of an alcohol. As indicated, the alcohol aides the dissolution or dispersion of the cationic surfactant, but preferably does not alter or affect the effectiveness of the cationic surfactant. Any type or appropriate amount of alcohol capable of and suitable for performing this function may be used. For instance, the appropriate amount of alcohol is typically less than about 20 % by weight of the cationic surfactant. Further, the alcohol is preferably comprised of isopropyl alcohol.
The water to be combined with the surfactant by the combining step to produce the aqueous mixture preferably has a temperature which facilitates or enhances the later application of the aqueous mixture to the soil. Preferably, in order to enhance or facilitate the applying step, the water combined with the cationic surfactant has a temperature of between about 5° Celsius and 90° Celsius. In the preferred embodiment, the water has a temperature of between about 20° Celsius and 60°
Celsius. Thus, where necessary to achieve the desired temperature, the method may be further comprised of the step of heating, or alternatively cooling, the water to the desired temperature prior to the combining step. The water may be heated or cooled to the desired temperature in any manner and by any mechanism, apparatus or process capable of and suitable for heating or cooling the water to the desired temperature as indicated above.
In the preferred embodiment, the applying step may be performed in any manner and by any mechanism, apparatus or process capable of applying the cationic surfactant, and preferably the aqueous mixture, to the uncompacted soil. For instance, the applying step may be performed in any manner and by any mechanism, apparatus or process able to bring the aqueous mixture, including the cationic surfactant, and the soil into physical contact with each other, such as by laying, spreading, mixing or spraying the aqueous mixture on or in the soil.
Preferably, the applying step is comprised of the steps of contacting the aqueous mixture with the soil and mixing the soil in order to distribute the aqueous mixture, and thus the cationic surfactant, substantially throughout the soil.
The contacting step may be performed in any manner and by any mechanism, apparatus or process capable of contacting the aqueous mixture with the soil or adding the aqueous mixture to the soil such that the aqueous mixture and the soil are brought into physical contact with each other. Preferably, the aqueous mixture is sprayed onto the soil in any manner and by any mechanism, apparatus or process for spraying an aqueous mixture.
The mixing step may be performed in any manner and by any mechanism, apparatus or process capable of mixing or combining the aqueous mixture with the soil or otherwise putting them together such that the aqueous mixture is distributed within the soil. Although the aqueous mixture, and thus the cationic surfactant, may be distributed within the soil to any degree, preferably, the aqueous mixture is distributed substantially throughout the soil. More preferably, the aqueous mixture is distributed substantially evenly or uniformly throughout the soil.
In the preferred embodiment in a road application, the road surface is first scarified. The aqueous mixture of the cationic surfactant is then sprayed onto the soil of the scarified road surface. Repeated grading and discing are then performed to mix the aqueous mixture into the soil until the aqueous mixture is distributed throughout the soil.
Any compaction method may then be performed to compact the soil to the desired density.
In the preferred embodiment, the cationic surfactant may be applied to the soil in any proportion or amount providing for or permitting the stabilization of the soil in the manner described herein. Thus, any amount of cationic surfactant may be applied to the soil which is capable of stabilizing the soil, and more particularly, which is capable of modifying the hydrophilic nature of the soil. However, preferably, the cationic surfactant is applied to the soil in an amount of at least 0.005 % by weight of dry soil mass.
Conversely, as described above, the maximum desired amount to be mixed with the soil is preferably less than or equal to the canon exchange capacity of the soil.

More preferably, the cationic surfactant is applied to the soil in an amount of between about 0.01 % and about 1.0 % by weight of dry soil mass. However, the preferred minimum and maximum amounts will vary depending upon such factors as the desired effect of the cationic surfactant, the desired properties of the stabilized soil, the type of cationic surfactant and the soil type or composition.
Finally, the compacting step may be performed at any moisture content of the soil compatible with compacting the soil to the desired density. However, the soil has an optimum moisture content ("OMC") for compacting the soil which permits the soil to be compacted to its maximum or highest density. The OMC is expressed as a percentage of moisture by weight of dry soil mass. Preferably, in the preferred embodiment, the moisture content of the soil following the applying step is between about 4 %
less than the optimum moisture content and about 4 % greater than the optimum moisture content. In other words, the moisture content is between about OMC-4 and about OMC+4. More preferably, the moisture content of the soil following the applying step is between about 2 less than the optimum moisture content and about 2 % greater than the optimum moisture content. In other words, the moisture content is between about OMC-2 and about OMC+2.
In the alternate embodiment of the method, the method is comprised of the steps of providing an amount of the cationic surfactant, compacting the soil to a desired density to provide a compacted soil and applying the cationic surfactant to the compacted soil. In addition, preferably, in the alternate embodiment, the method is further comprised of the step of combining the cationic surfactant with an amount of water to produce an aqueous mixture. Thus, in the alternate embodiment, the applying step is preferably comprised of applying the aqueous mixture, including the cationic surfactant, to the compacted soil.

The combining step may be performed in any manner and by any mechanism, apparatus or process capable of adding or uniting the cationic surfactant with the water or otherwise bringing or contacting them together such that the cationic surfactant is distributed within the water to provide the aqueous mixture.
Thus, the combining step results in the dissolution, dispersion or both the dissolution and dispersion of the cationic surfactant within the water.
As discussed previously, the cationic surfactant may be combined with any type of water so long as the water does not significantly alter the cationic nature of the cationic surfactant. However, preferably fresh-water, surface water, ground water or a combination thereof is combined with the cationic surfactant. In addition, the cationic surfactant may be combined with any proportion or percentage of water to produce the aqueous mixture. The desired proportion or percentage of water to cationic surfactant may vary depending upon such factors as the amount of cationic surfactant desired to be applied to the compacted soil, the manner of application of the aqueous mixture to the compacted soil, the desired moisture content of the compacted soil and the soil composition.
Further, the cationic surfactant may be distributed within the water to any degree, however, preferably, the aqueous mixture is substantially homogeneous.
Thus, in the alternate embodiment, the cationic surfactant is also substantially uniformly or homogeneously distributed within the water. As a result, the alternate method is preferably further comprised of the step of mixing the aqueous mixture so that it is substantially homogeneous. The mixing step may be performed in any manner and by any mechanism, apparatus or process capable of mixing or combining the cationic surfactant within the water or otherwise distributing the cationic surfactant throughout the water, preferably substantially homogeneously.
As well, as in the preferred embodiment of the method, in order to facilitate or enhance the combining step, a solvent may be added to the aqueous mixture to assist with the dissolution or dispersion of the cationic surfactant in the water.
Although any solvent compatible with the aqueous mixture may be used, the solvent is preferably comprised of an alcohol such as isopropyl alcohol. In addition, although any appropriate amount of alcohol may be used, the amount of alcohol used is typically less than about 20 % by weight of the cationic surfactant.
Further, as in the preferred embodiment, the water to be combined with the surfactant by the combining step to produce the aqueous mixture preferably has a temperature which facilitates or enhances the later application of the aqueous mixture to the compacted soil. Preferably, in order to enhance or facilitate the applying step, the water combined with the cationic surfactant has a temperature of between about 5° Celsius and 90° Celsius. In the preferred embodiment, the water has a temperature of between about 20° Celsius and 60° Celsius. Thus, where necessary to achieve the desired temperature, the method may be further comprised of the step of heating, or alternatively cooling, the water to the desired temperature prior to the combining step.
Again, the water may be heated or cooled to the desired temperature in any manner and by any mechanism, apparatus or process capable of and suitable for heating or cooling the water to the desired temperature as indicated above.
In the alternate embodiment, the applying step may be performed in any manner and by any mechanism, apparatus or process capable of distributing the cationic surfactant, and preferably the aqueous mixture, onto or upon the compacted soil. For instance, the applying step may be performed in any manner and by any mechanism, apparatus or process able to bring the aqueous mixture, including the cationic surfactant, and the compacted soil into physical contact with each other such as by laying, spreading or spraying the cationic surfactant on the compacted soil. Further, the aqueous mixture may be applied to the compacted soil such that it is distributed upon the compacted soil in any manner and to any degree. However, preferably, the aqueous mixture is distributed substantially evenly or uniformly upon the compacted soil.

Preferably, in the alternate embodiment, the applying step is comprised of spraying the aqueous mixture on the compacted soil. The spraying step may be performed in any manner and by any mechanism, apparatus or process compatible with and suitable for spraying an aqueous mixture. Preferably, the spraying step is performed such that the aqueous mixture is substantially evenly or uniformly contacted with or distributed upon the compacted surface.
In the alternate embodiment in a road application, the road surface is first scarified, graded and disced. The soil is then compacted to provide the compacted soil surface using any method of compaction. The aqueous mixture is then sprayed onto the compacted soil of the road surface. Where the road surface is prepared by compacting the soil in a series or number of lifts, the aqueous mixture is preferably applied only to the upper compacted surface of the uppermost or top lift comprising the road surface in order to stabilize the uppermost surface of the soil and provide protection primarily against damage caused by rainfall. However, where desired such as where damage is also caused by groundwater, the aqueous mixture may be applied to each lift in turn.
In the alternate embodiment, the cationic surfactant may be applied to the compacted soil in any proportion or amount providing for or permitting the stabilization of the soil in the manner described herein. Thus, any amount of cationic surfactant may be applied to the compacted soil which is capable of stabilizing the soil, and more particularly, which is capable of modifying the hydrophilic nature of the soil. However, as described above, the maximum desired amount to be applied to the soil is preferably less than or equal to the canon exchange capacity of the soil.
More particularly, in the alternate embodiment of the method, the aqueous mixture is applied to the compacted soil. Preferably, the aqueous mixture is comprised of the cationic surfactant in an amount of at least about 0.01 % by weight of the aqueous mixture. More preferably, the aqueous mixture is comprised of the cationic surfactant in an amount of between about 0.1 % and about 10.0 % by weight of the aqueous mixture.

However, the preferred minimum and maximum amounts of the cationic surfactant will vary depending upon factors such as the desired effect of the cationic surfactant, the desired properties of the stabilized soil, the type of cationic surfactant and the soil type or composition.
In addition, where the soil is compacted prior to applying the cationic surfactant thereto, it has been found that the amount of cationic surfactant or the concentration of the cationic surfactant within the aqueous mixture required to be applied to achieve the desired result is typically greater than that required where the soil is compacted after applying the cationic surfactant to the soil. Where the cationic surfactant is applied prior to compacting to the soil, the cationic surfactant within the aqueous mixture is preferably mixed with the soil such that it is uniformly distributed throughout the entire depth or thickness of the soil. However, where the soil is compacted prior to applying the aqueous mixture, the aqueous mixture only contacts the upper surface or very top crust of the compacted soil. As a result, there is a tendency for the aqueous mixture to run off the compacted soil surface. Accordingly, to compensate for this run off, a greater amount of cationic surfactant or a greater concentration of the cationic surfactant within the aqueous mixture may be required to permit the desired amount of the cationic surfactant to soak into or permeate the soil and achieve the same results.
Further, in the alternate embodiment, the compacting step may similarly be performed at any moisture content of the soil compatible with compacting the soil to the desired density. However, preferably, in the alternate embodiment, the moisture content of the soil prior to the compacting step is between about 4 % less than the optimum moisture content and about 4 % greater than the optimum moisture content. In other words, the moisture content is between about OMC-4 and about OMC+4. More preferably, the moisture content of the soil prior to the compacting step is between about 2 less than the optimum moisture content and about 2 % greater than the optimum moisture content. In other words, the moisture content is between about OMC-2 and about OMC+2.

In addition, the alternate embodiment of the method may be further comprised of the step, prior to the applying step, of drying the compacted soil such that the moisture content of the compacted soil is equal to or less than about the optimum moisture content of the soil at the commencement of the applying step. It is believed that drying the soil following the compacting step and prior to the applying step to a moisture content of less than or equal to the OMC may be facilitate or enhance the application of the aqueous mixture. Specifically, the aqueous mixture may more readily soak into or permeate the compacted soil.
The drying step may be performed in any manner and by any mechanism, apparatus or process compatible with and suitable for drying the compacted soil to the desired moisture content. However, preferably, the compacted soil is air dried.
Similarly, after the aqueous mixture is applied to the compacted soil, the aqueous mixture is preferably permitted to soak into the compacted soil and the compacted soil is preferably dried. When the moisture content of the compacted soil is less than or equal to the optimum moisture content, the aqueous mixture may be reapplied. In other words, the applying step may be repeated once the compacted soil is dried to a moisture content of less than or equal to the OMC.
Accordingly, the applying step may be performed repeatedly. In this instance, the drying step is preferably performed prior to each applying step such that the moisture content of the compacted soil at the commencement of each applying step is equal to or less than the optimum moisture content of the soil. The applying step may be repeated any number of times as desired or required to provide the desired results.
The following examples serve more fully to illustrate the invention.

EXAMPLE A
Example A shows the effect of cationic surfactants in reducing capillary suction of soil. As discussed above, capillary suction is largely responsible for the weakening of soil. Thus, a reduction in capillary suction will enhance the stability of the soil.
Two soil samples were used in Example A, Devon silt soil from Devon, Alberta, Canada and Drayton Valley soil from Drayton Valley, Alberta, Canada.
The Devon silt soil is silty clay material with a low plasticity, being classified under A-6 Group in the AASHTO Classification System and under CL Group in the Unified Soil Classification System. The Drayton Valley soil contains relatively more sands and clay but less silt than the Devon silt soil. The Drayton Valley soil is thus poorly sorted. It has a high plasticity, being classified under A-7-6 Group in the AASHTO
Classification System.
In the Unified Soil Classification System, the Drayton Valley soil is also classified under CL
Group but it is at the boundary with CH Group.
In the tests, aqueous mixtures comprised of the cationic surfactant were first mixed with the soil. Two specific cationic surfactants were tested: "Phob 1"
being dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB); and "Phob 3" being methyl di(hydrogenated tallow)alkyl benzyl ammonium chloride (M2HTB).
In addition, each of the specific cationic surfactants was mixed with the soil in an amount of 0.375 % by weight of dry soil mass and in an amount of 0.094 % by weight of dry soil mass.
Following mixing, the soil was dried, either in air or in an oven at 60 °C, and passed through an 18-mesh sieve to produce the stabilized soil to be tested in Example A.
The set-up for the test of Example A is shown in Figure 1. Thus, referring to Figure 1, a fixed amount of a control or untreated soil (10) was lightly packed into a first plastic tube (12). Similarly, a fixed amount of the stabilized soil (14) was lightly packed into a second plastic tube (16). The bottom tips (18) of each of the plastic tubes (12, 16) was then cut and dipped into water (20) within a container (22). As expected, the water (20) was imbibed into both the control and stabilized soils (10, 14) such that a wetting front (24) of the control soil (10) and a wetting front (26) of the stabilized soil (14) moved upward along the first and second tubes (12, 16) respectively. The force responsible for moving the water (20) upwards is the capillary suction of the soils (10, 14), which draws the water upwards against gravity. During the test process, the control soil sample (10) and the stabilized soil sample (14) were weighed to quantify the amount of water (20) imbibed into the soils (10, 14).
Table 1 and Table 2 show the effect of the cationic surfactant, Phob 1 and Phob 3, on water imbibition by Devon silt soil and Drayton Valley soil respectively. The untreated control Devon silt soil sample imbibed 0.368 grams of water per gram of soil.
The untreated control Drayton Valley soil sample imbibed 0.261 grams of water per gram of soil. In comparison, after the treatment by Phob 1 and Phob 3 in an amount of 0.375 wt% of dry soil mass, both soils imbibed a very small amount of water (less than 5% of that in the control samples). After the treatment by Phob 1 and Phob 3 in an amount of 0.094 wt% of dry soil mass, the amount of water imbibed into both soils was about 2/3 of that imbibed into the control soil samples. Thus, these imbibition tests demonstrate the effect of the cationic surfactants in reducing capillary suction of water. Reduced capillary suction means less moisture into the soil and thus, greater strength for the soil or enhanced stability of the soil.
Table 1- Effect of Soil Stabilizing Agent on Water Imbibition by Devon Silt Soil Sample Wsoil Wimbibed waterWimbibed WSample after 270 water /W~ontrol min. /gram of soil Control 10.15 g 3.74 g 0.368 g 100%

Phob 1, 0.375 10.17 g 0.10 g 0.010 g 3%
wt%

Phob 1, 0.094 10.24 g 2.55 g 0.249 g 68%
wt%

Phob 3, 0.375 10.25 g 0.09 g 0.009 g 2%
wt%

Phob 3, 0.094 10.33 g 2.55 g 0.247 g 67%
wt%

Table 2 - Effect of Soil Stabilizing Agent on Water Imbibition b~yton Valley Soil Sample Wsil Wimbibed waterWimbibed WSample after 270 water /W~ntrI
min. /gram of soil Control 10.29 g 2.685 g 0.261 g 100%

Phob 1, 0.375 10.16 g 0.116 g 0.011 g 4%
wt%

Phob 1, 0.094 10.11 g 0.547 g 0.054 g 21 wt%

Phob 3, 0.375 10.22 g 0.138 g 0.014 g 5%
wt%

Phob 3, 0.094 10.17 g 1.980 g 0.195 g 75%
wt%

EXAMPLE B
Example B shows the effect of cationic surfactants in maintaining the strength of a compacted soil when the soil is contacted by water. As discussed previously, an important objective for soil stabilization is to reduce the soil's ability to imbibe water and be softened thereby.
To demonstrate the effectiveness of cationic surfactants as a soil stabilizer, Devon silt soil, as described above, was compacted at optimum moisture content without a cationic surfactant and with a cationic surfactant. Specifically, the control soil sample was prepared without the use of any chemicals. The stabilized soil sample was prepared using a cationic surfactant. The cationic surfactant used to prepare the stabilized soil sample was "Phob 1 ", being dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB). Phob 1 was mixed with the soil in an amount of 0.225 % by weight of dry soil mass.

Referring to Figure 2, the compacted control soil sample (28) and the compacted stabilized soil sample (30) were placed in a glass cylinders (32).
Water (20) was added into the cylinders (32) to contact the compacted soil samples (28, 30).
Due to capillary suction force, the compacted soil samples (28, 30) imbibed water into their structures, causing crumbling of the soil core. Figure 2 shows the results of the slaking tests for the Devon silt soil in fresh water at the commencement of the test, at an interval of 3 hours and at an interval of 48 hours. As can be seen in Figure 2, the control soil sample (28) quickly disintegrated, falling apart and settling to the bottom of the cylinder (32). In contrast, the stabilized soil sample (30) remained intact.
In addition, Unconfined Compressive Strength ("UCS") tests were performed in accordance with ASTM D2166 to assess the shear strength of the soil samples (28, 30) before soaking and after soaking for 48 hours. Table 3 shows the relative UCS
of the control soil sample (28) and the stabilized soil sample (30), being Devon silt soil mixed with Phob 1 at 0.225 wt% of dry soil mass. After 48 hours of soaking, the control soil sample (28) disintegrated. The stabilized soil sample (30) retained about 25%
of its original strength.
Finally, the soil samples (28, 30) were wrapped by a latex membrane before being immersed into the water (20). As a result, water (20) could only be soaked from the top and bottom of each soil sample (28, 30). Table 3 also shows the relative UCS of the control soil sample (28) with a latex membrane and the stabilized soil sample (30) with a latex membrane before soaking and after soaking for 48 hours. After 48 hours, both ends of the control soil sample (28) were so soft that they had to be trimmed off before an UCS
measurement could be performed. For the stabilized soil sample (30), the ends were still stiff after soaking and they were not trimmed. The control soil sample (28) retained about 5% of its original strength, while the stabilized soil sample (30) retained about 44% of its original strength. It is believed that the greater strength of the stabilized soil sample (30) as compared with the control soil sample (28) indicates that the cationic surfactants reduce the attraction of water to the soil and minimize the strength loss during a wetting cycle.

Table 3 - Unconfined Compressive Strength of Devon Silt Soil No Latex With Latex Membrane Membrane Sample Before After Before After Soaking Soaking Soaking Soaking UCS (kPa) UCS (kPa) UCS (kPa) UCS (kPa) Control 360 -- 258 14 Phob 1, 0.225 297 ~ 74 261 114 wt%

Claims

1. A stabilizing agent for soil comprised of an amount of a cationic surfactant, wherein the cationic surfactant is comprised of at least one hydrophobic group attached to a cationic (N+) hydrophilic group.

2. The soil stabilizing agent as claimed in claim 1 wherein the cationic surfactant has the following structural formula:
wherein R is selected from the group consisting of H and (CH2)n CH3, wherein n=0,1, 2 or 3;
wherein R' is selected from the group consisting of H, (CH2)n CH3, C6H5 and CH2-C6H5, wherein n=0, 1, 2 or 3;
wherein R" is selected from the group consisting of H, (CH2)n CH3, C6H5, CH2-C6H5, an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl, wherein n=0, 1, 2 or 3;
wherein R"' is selected from the group consisting of an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; and wherein X- is an anion.

3. The soil stabilizing agent as claimed in claim 2 wherein the cationic surfactant is comprised of at least one hydrogenated tallowalkyl.

4. The soil stabilizing agent as claimed in claim 3 wherein the cationic surfactant is comprised of two hydrogenated tallowalkyls.

5. The soil stabilizing agent as claimed in claim 2 wherein the cationic surfactant is comprised of two alkyl chains with at least 12 carbons on each chain.

6. The soil stabilizing agent as claimed in claim 2 wherein the cationic surfactant is comprised of a benzyl group and a hydrogenated tallowalkyl.

7. The soil stabilizing agent as claimed in claim 2 wherein the cationic surfactant is comprised of a benzyl group and an alkyl chain with at least 12 carbons.

8. The soil stabilizing agent as claimed in claim 2 wherein the cationic surfactant is comprised of at least one of dimethyl di(hydrogenated tallow)alkyl ammonium chloride (DM2HT), dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB), methyl di(hydrogenated tallow)alkyl benzyl ammonium chloride (M2HTB), alkyl dimethyl benzyl ammonium chloride (ADMB), dialkyl dimethyl ammonium chloride (DADM) and dialkyl methyl benzyl ammonium chloride (DAMB).

9. The soil stabilizing agent as claimed in claim 8 wherein the soil stabilizing agent is further comprised of an amount of water to provide an aqueous mixture.

10. The soil stabilizing agent as claimed in claim 9 wherein the aqueous mixture is substantially homogeneous.

11. A stabilized soil formed by the mixing of:
(a) a soil; and (b) a stabilizing agent comprised of an amount of a cationic surfactant, wherein the cationic surfactant is comprised of at least one hydrophobic group attached to a cationic (N+) hydrophilic group.

12. The stabilized soil as claimed in claim 11 wherein the cationic surfactant has the following structural formula:
wherein R is selected from the group consisting of H and (CH2)n CH3, wherein n = 0, 1, 2 or 3;
wherein R' is selected from the group consisting of H, (CH2)n CH3, C6H5 and CH2-C6H5, wherein n=0, 1, 2 or 3;
wherein R" is selected from the group consisting of H, (CH2)n CH3, C6H5, CH2-C6H5, an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl, wherein n=0, 1, 2 or 3;
wherein R"' is selected from the group consisting of an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; and wherein X- is an anion.

13. The stabilized soil as claimed in claim 12 wherein the cationic surfactant is mixed with the soil in an amount of at least 0.005 % by weight of dry soil mass.

14. The stabilized soil as claimed in claim 13 wherein the cationic surfactant is mixed with the soil in an amount of between about 0.01 % and about 1.0 % by weight of dry soil mass.

15. The stabilized soil as claimed in claim 12 wherein the soil is comprised of a finely divided soil.

16. The stabilized soil as claimed in claim 12 wherein the cationic surfactant is comprised of at least one hydrogenated tallowalkyl.

17. The stabilized soil as claimed in claim 16 wherein the cationic surfactant is comprised of two hydrogenated tallowalkyls.

18. The stabilized soil as claimed in claim 12 wherein the cationic surfactant is comprised of two alkyl chains with at least 12 carbons on each chain.

19. The stabilized soil as claimed in claim 12 wherein the cationic surfactant is comprised of a benzyl group and a hydrogenated tallowalkyl.

20. The stabilized soil as claimed in claim 12 wherein the cationic surfactant is comprised of a benzyl group and an alkyl chain with at least 12 carbons.

21. The stabilized soil as claimed in claim 12 wherein the cationic surfactant is comprised of at least one of dimethyl di(hydrogenated tallow)alkyl ammonium chloride (DM2HT), dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB), methyl di(hydrogenated tallow)alkyl benzyl ammonium chloride (M2HTB), alkyl dimethyl benzyl ammonium chloride (ADMB), dialkyl dimethyl ammonium chloride (DADM) and dialkyl methyl benzyl ammonium chloride (DAMB).

22. The stabilized soil as claimed in claim 13 wherein the stabilizing agent is further comprised of an amount of water to provide an aqueous mixture.

23. The stabilized soil as claimed in claim 22 wherein the aqueous mixture is substantially homogeneous.

24. A method for stabilizing soil comprising the steps of:

(a) providing an amount of a cationic surfactant, wherein the cationic surfactant is comprised of at least one hydrophobic group attached to a cationic (N+) hydrophilic group; and (b) applying the cationic surfactant to the soil.

25. The method as claimed in claim 24 wherein the cationic surfactant has the following structural formula:
wherein R is selected from the group consisting of H and (CH2)n CH3, wherein n=0,1, 2 or 3;
wherein R' is selected from the group consisting of H, (CH2)n CH3, C6H5 and CH2-C6H5, wherein n=0, 1, 2 or 3;
wherein R" is selected from the group consisting of H, (CH2)n CH3, C6H5, CH2-C6H5, an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl, wherein n=0,1, 2 or 3;
wherein R"' is selected from the group consisting of an alkyl chain with at least 8 carbons and a hydrogenated tallowalkyl; and wherein X- is an anion.

26. The method as claimed in claim 25 wherein the cationic surfactant is comprised of at least one hydrogenated tallowalkyl.

27. The method as claimed in claim 26 wherein the cationic surfactant is comprised of two hydrogenated tallowalkyls.

28. The method as claimed in claim 25 wherein the cationic surfactant is comprised of two alkyl chains with at least 12 carbons on each chain.

29. The method as claimed in claim 25 wherein the cationic surfactant is comprised of a benzyl group and a hydrogenated tallowalkyl.

30. The method as claimed in claim 25 wherein the cationic surfactant is comprised of a benzyl group and an alkyl chain with at least 12 carbons.

31. The method as claimed in claim 25 wherein the cationic surfactant is comprised of at least one of dimethyl di(hydrogenated tallow)alkyl ammonium chloride (DM2HT), dimethyl (hydrogenated tallow)alkayl benzyl ammonium chloride (DMHTB), methyl di(hydrogenated tallow)alkyl benzyl ammonium chloride (M2HTB), alkyl dimethyl benzyl ammonium chloride (ADMB), dialkyl dimethyl ammonium chloride (DADM) and dialkyl methyl benzyl ammonium chloride (DAMB).

32. The method as claimed in claim 25 wherein the applying step is comprised of the steps of:
(a) contacting the cationic surfactant with the soil; and (b) mixing the soil in order to distribute the cationic surfactant substantially throughout the soil.

33. The method as claimed in claim 32 wherein the cationic surfactant is applied to the soil in an amount of at least 0.005 % by weight of dry soil mass.

34. The method as claimed in claim 33 wherein the cationic surfactant is applied to the soil in an amount of between about 0.01 % and about 1.0 % by weight of dry soil mass.

35. The method as claimed in claim 33 wherein the soil is comprised of a finely divided soil.

36. The method as claimed in claim 33 wherein the soil has an optimum moisture content and wherein the moisture content of the soil following the applying step is between about 4 % less than the optimum moisture content and about 4 % greater than the optimum moisture content.

37. The method as claimed in claim 36 wherein the moisture content of the soil following the applying step is between about 2 % less than the optimum moisture content and about 2 % greater than the optimum moisture content.

38. The method as claimed in claim 36 further comprising the step, following the applying step, of compacting the soil to a desired density.

39. The method as claimed in claim 38 further comprising the step of combining the cationic surfactant with an amount of water to produce an aqueous mixture and wherein the applying step is comprised of applying the aqueous mixture to the soil.

40. The method as claimed in claim 39 further comprising the step of mixing the aqueous mixture so that it is substantially homogeneous.

41. The method as claimed in claim 39 wherein the water combined with the cationic surfactant has a temperature of between about 5° Celsius and 90° Celsius.

42. The method as claimed in claim 41 wherein the water has a temperature of between about 20° Celsius and 60° Celsius.

43. The method as claimed in claim 25 further comprising the step, prior to the applying step, of compacting the soil to provide a compacted soil and wherein the applying step is comprised of applying the cationic surfactant to the compacted soil.

44. The method as claimed in claim 43 wherein the soil is comprised of a finely divided soil.

45. The method as claimed in claim 43 wherein the soil has an optimum moisture content and wherein the moisture content of the soil prior to the compacting step is between about 4 % less than the optimum moisture content and about 4 % greater than the optimum moisture content.

46. The method as claimed in claim 45 wherein the moisture content of the soil prior to the compacting step is between about 2 % less than the optimum moisture content and about 2 % greater than the optimum moisture content.

47. The method as claimed in claim 45 further comprising the step of combining the cationic surfactant with an amount of water to produce an aqueous mixture and wherein the applying step is comprised of applying the aqueous mixture to the compacted soil.

48. The method as claimed in claim 47 further comprising the step of mixing the aqueous mixture so that it is substantially homogeneous.

49. The method as claimed in claim 47 wherein the aqueous mixture is comprised of the cationic surfactant in an amount of at least about 0.01 % by weight of the aqueous mixture.

50. The method as claimed in claim 49 wherein the aqueous mixture is comprised of the cationic surfactant in an amount of between about 0.1 % and about 10.0 % by weight of the aqueous mixture.

51. The method as claimed in claim 49 wherein the water combined with the cationic surfactant has a temperature of between about 5° Celsius and 90° Celsius.

52. The method as claimed in claim 51 wherein the water has a temperature of between about 20° Celsius and 60° Celsius.

53. The method as claimed in claim 49 further comprising the step, prior to the applying step, of drying the compacted soil such that the moisture content of the compacted soil is equal to or less than about the optimum moisture content of the soil at the commencement of the applying step.

54. The method as claimed in claim 53 wherein the applying step is performed repeatedly and wherein the drying step is performed prior to each applying step such that the moisture content of the compacted soil at the commencement of each applying step is equal to or less than the optimum moisture content of the soil.