Method of strengthening soil via chemical inducement

Abstract

Methods for increasing soil stabilization utilizing an anionic surfactant and a solution. Varying amounts of the anionic surfactant sodium dodecyl sulfate (“SDS”) is added to soils along with a solution of calcium chloride. A mixing procedure is then used to mix the SDS-soil matrix with the calcium chloride solution. The micelles surround the soil particles, creating a matrix, and then the calcium ions of the calcium chloride solution bonds the micelle complex together. The resulting calcium dodecyl sulfate (“CDS”) complex is very hard, relatively insoluble, and very strong. This process can be reversed by exposing the CDS complex to seawater. The sodium ions of the seawater exchange with the calcium ions of the CDS complex reforming the SDS surfactant.

Claims

1. A method of increasing strength of a soil, the method comprising: distributing an anionic surfactant to the soil; and distributing an alkaline earth metal solution consisting essentially of at least one alkaline earth metal and a carrier to the soil; wherein the anionic surfactant and the alkaline earth metal solution are distributed to the soil in the absence of an addition of bacteria or urea; wherein the strength of the soil is increased when the anionic surfactant and the alkaline earth metal solution are mixed thereby forming an anionic surfactant alkaline earth metal complex.

2. The method of claim 1, wherein the anionic surfactant is sodium dodecyl sulfate.

3. The method of claim 1, wherein the alkaline earth metal solution is aqueous calcium chloride.

4. The method of claim 1, wherein the anionic surfactant and the alkaline earth metal solution are distributed to the soil by spraying.

5. The method of claim 1, wherein the anionic surfactant and the alkaline earth metal solution are distributed to the soil by mixing into the soil.

6. The method of claim 1, wherein the anionic surfactant and the alkaline earth metal solution are stoichiometrically balanced.

7. The method of claim 1, wherein the alkaline earth metal solution further comprises two alkaline earth metals.

8. The method of claim 1, wherein the anionic surfactant is distributed to the soil in powdered form.

9. A method of increasing strength of a soil, the method comprising: distributing to the soil an anionic surfactant aqueous solution consisting essentially of sodium dodecyl sulfate and aqueous media wherein at least one micelle is formed in the aqueous media wherein upon exceeding critical micelle concentration the soil is absorbed into the at least one micelle to form an aqueous soil media; distributing an alkaline earth metal solution to the aqueous soil media wherein the alkaline earth metal solution consisting essentially of at least one alkaline earth metal and a carrier; and wherein the anionic surfactant aqueous solution is distributed to the soil in the absence of an addition of bacteria or urea; wherein the alkaline earth metal solution is distributed to the aqueous soil media in the absence of an addition of bacteria or urea; mixing the aqueous soil media and the alkaline earth metal solution to form an alkaline earth metal dodecyl sulfate complex; wherein the formation of the alkaline earth metal dodecyl sulfate complex strengthens the soil.

10. The method of claim 9, wherein the anionic surfactant aqueous solution and the alkaline earth metal solution are distributed to the soil by spraying.

11. The method of claim 9, wherein the anionic surfactant and the alkaline earth metal solution are distributed to the soil by injection into the soil.

12. The method of claim 9, wherein the anionic surfactant aqueous solution and the alkaline earth metal solution are stoichiometrically balanced.

13. The method of claim 9, wherein the alkaline earth metal solution is aqueous calcium chloride.

14. The method of claim 9, wherein the at least one alkaline metal in the alkaline earth metal solution are aqueous calcium chloride and aqueous magnesium chloride.

15. A method of increasing unconfined compression strength of a soil, the method comprising: mixing a first solution, the first solution consisting essentially of an amount of sodium dodecyl sulfate and an amount of water, wherein the sodium dodecyl sulfate dissociates when mixed with the water, such that a plurality of micelles are formed; mixing a second solution, the second solution comprises an amount of calcium chloride and an amount of water, wherein the calcium chloride dissociates into a plurality of calcium ions and a plurality of chloride ions when the calcium chloride is mixed with the water; distributing the first solution to the soil, such that the soil is capable of being absorbed within the plurality of micelles creating a plurality of micelle-soil complexes; and distributing the second solution to the soil including the micelle-soil complexes, such that one calcium ion of the plurality of calcium ions bonds with two micelle-soil complexes of the plurality of micelles-soil complexes forming a calcium dodecyl sulfate complex; wherein the first solution and the second solution are distributed to the soil in the absence of an addition of bacteria or urea; whereby the formation of the calcium dodecyl sulfate complex increases the strength of the soil.

16. The method of claim 15, further comprising distributing a sodium chloride solution to the calcium dodecyl sulfate complex, wherein the sodium chloride solution includes dissolved sodium ions, such that when the sodium chloride solution is distributed to the calcium dodecyl sulfate complex, the calcium ions of the calcium dodecyl sulfate complex exchanges with the dissolved sodium ions, thereby decreasing the strength of the soil.

17. The method of claim 15, wherein the first solution and the second solution are stoichiometrically balanced.

18. The method of claim 15, wherein the distribution of the first and the second solutions is by spraying.

19. The method of claim 15, wherein the distribution of the first and the second solutions is by mixing.

20. The method of claim 15, wherein the second solution further comprises an amount of magnesium chloride, such that the magnesium chloride dissociates into a plurality of magnesium ions and a plurality of chloride ions when the magnesium chloride is mixed in the second solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:

(2) FIG. 1 is a skeletal formula of the molecular structure of sodium dodecyl sulfate (“SDS”).

(3) FIG. 2A depicts an SDS micelle structure in aqueous solution.

(4) FIG. 2B depicts an SDS micelle structure in a hydrophobic solution.

(5) FIG. 2C depicts a calcium dodecyl sulfate complex with soil particles absorbed into the center of the micelles.

(6) FIG. 3 shows a skeletal formula of a calcium dodecyl sulfate complex.

(7) FIG. 4 shows UCS vs. percent SDS for various soil types.

(8) FIG. 5 shows clay 1 (left), Tennessee Ball clay (middle), and Ottawa sand (right) broken apart and analyzed qualitatively after being treated via surfactant-induced soil stabilization (SISS).

(9) FIG. 6 shows Tennessee ball clay after 48 hours mixed with water in a concrete tube.

(10) FIG. 7 shows SISS treatment results using soil with approximately 30% organic content.

(11) FIG. 8 shows grain size distribution for beach sand.

(12) FIG. 9A shows the UCS as a function of SDS mass.

(13) FIG. 9B shows the UCS as a function of SDS pore volume.

(14) FIG. 10 is a flow chart diagram of an embodiment of a method of increasing the strength of the soil.

(15) FIG. 11 is a flow chart diagram of an embodiment of the method of increasing the strength of the soil.

(16) FIG. 12 is a flow chart diagram of an embodiment of the method of increasing the strength of the soil.

DETAILED DESCRIPTION OF THE INVENTION

(17) In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part thereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized, and structural changes may be made without departing from the scope of the invention.

(18) As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the context clearly dictates otherwise.

(19) As illustrated in FIG. 1, sodium dodecyl sulfate (“SDS”) is a surfactant that contains a linear twelve-carbon chain tail and polar sulfate head. In solution, the sodium ion of the SDS disassociates from the dodecyl sulfate portion yielding a hydrophilic polar head and a neutrally charged hydrophobic tail. In an embodiment, the surfactant can be an anionic surfactant, organosulfate, and/or other compounds with similar chemical structures. In an embodiment, dications create a matrix of micelles from the combination of the dications and the negatively charged sulfate head/carbon tail portion of the SDS and bind the soil together.

(20) When the concentration of any substance passes its critical micelle concentration, the hydrophilic heads and the hydrophobic tails align with one another, creating micelles shown in FIGS. 2A-2C. Micelle shape may vary depending on interfacial conditions. Common micelle shapes include bilayers, spheres, rod-like structures, disc-like structures, vesicles, lamellae, and sponge-phase. Regardless of the shape of the micelle, they interact similarly with neutrally charged particles in solutions. When in solution, micelle formation results in interior hydrophobic pockets that can absorb neutrally charged particles coupled with hydrophilic exteriors capable of interacting with water or other polar solvents. In this way, soil particles can absorb into the interior of the micelle and effectively be solubilized into an aqueous media, as shown in FIG. 2C.

(21) FIG. 2B illustrates the structure of inverted micelles in hydrophobic solutions (e.g., liquid oils), or mixed hydrophobic/hydrophilic solutions, where the mixed solution is far more hydrophobic than hydrophilic. The inverted micelles also occur with an interior hydrophilic pocket containing the polar “heads” and non-polar exterior, where the hydrophobic “tails” point outward. This occurs to reduce the overall system entropy in hydrophobic media and to align “like” chemical properties.

(22) When added to treated soil water, molecules containing alkaline earth metals such as calcium chloride, magnesium chloride, etc., dissolve into positive ions (2.sup.+) and negatively charged ions (1.sup.−). Each positive ion bonds with two of the negatively charged dodecyl sulfate tails yielding an alkaline earth metal dodecyl sulfate complex. The formation of the calcium dodecyl complex prevents the micelle from achieving a hydrophilic exterior as the hydrophilic heads of the micelles are ionically bonded with Ca.sup.2+ ions resulting in the strength increase and insolubility of the treated soil.

(23) However, in additional embodiments, other alkaline earth metals, such as beryllium, magnesium, strontium, barium, and/or radium, can be substituted for calcium. In an embodiment, the solution may contain one or more combinations of alkaline earth metals. For example, a solution containing calcium chloride and magnesium chloride can be used in lieu of calcium chloride on its own. In an embodiment, chloride is used due to its ease of bonding with alkaline earth metals; however, other elements besides chloride can be substituted that permit the resulting compound to be dissolved in solution.

(24) In an embodiment, the SISS method can be used as a rapid response tool for protecting earthen shoreline structures from erosion. Calcium chloride is used as the “link” between dodecyl sulfate ions, as shown in FIG. 3. In the presence of seawater, the calcium ions exchange with dissolved sodium ions. As such, if used in a saltwater environment, after a few days, an earthen structure (beach dunes for example) would be back to “normal” (i.e., before a storm the dunes/beaches could be treated. After the storm, natural beach processes will return the beach to its untreated state).

(25) First Test Series

(26) During experimentation, several specimens were prepared using the surfactant SISS treatment technique whereby SDS was mixed with soil and an alkaline earth metal. Curing could occur both underwater and in the air. Subsequently, UCStesting was performed on the treated specimens that were generated using calcium as the alkaline earth metal.

(27) Further Testing with Various Soil Types

(28) In an embodiment, testing was expanded, concluding that the SISS method is an effective treatment method for a wide range of soil types. Testing was conducted using the SISS technique with 50/70 Ottawa sand, soil with 30% organic content, Tennessee ball clay (“TBC”), and another clay having an unknown origin that was available to the University of North Florida laboratory (“Clay 1”). Properties of the TBC and Clay 1 can be found in Table 1 below.

(29) TABLE-US-00001 TABLE 1 Tennessee Ball Clay Clay (TBC) Clay 1 Liquid Limit 57.9 30.4 Plastic Limit 26.2 22.9 Plasticity Index 31.7 7.5 USCS Classification CH CL Percent Clay 80% 65%

(30) These soils were mixed with SDS in 2-inch by 4-inch concrete molds. Then, 40-mL of 2.5 M calcium chloride solution was added to the specimens. The specimens were mixed until they were uniform. After mixing, the specimens were allowed to air dry for a minimum of 48 hours. However, hardening was usually observed within 20 minutes or less. After drying, the specimens were extracted using a Dremel® tool, and UCS testing was performed with results shown in FIG. 4. Specimens were broken apart and further qualitatively analyzed, as shown in FIG. 5.

(31) Similar results to soils with high organic content were found as these other soil types shown relationships between SDS concentration and maximum strength as determined by UCS. Ottawa sand showed a direct relationship between SDS and strength, while clays tended to show an inverse relationship, indicating that further optimization was needed as a function of soil-type (see FIG. 4).

(32) Control tests were prepared using the clays. The same procedure detailed above was repeated with the clays by mixing the clays with water only (i.e., no SDS or calcium). After 48 hours, the tubes were cut open. As pictured in FIG. 6, resulting specimens were not fully dry nor where the specimens fully hardened. Additionally, it was not possible to remove the specimen from its tube to finish drying. On-the-other-hand, the clays treated using the SISS technique were all sufficiently hardened after 48 hours allowing for “clean” specimen extraction.

(33) In an embodiment, a series of testing was conducted using the 30% organic-rich soil from Polk County, Fla. This soil was sieved through a #4 sieve so that soil particle distribution was more uniform. The SISS treatment components, calcium chloride, and SDS were stoichiometrically balanced and used to treat the sieved soil at various SDS percentages. Best-fit regression analysis was used to fit a curve to the data of the form y=ax.sup.3+bx.sup.2+cx+d. The results of the above experiments are shown in FIG. 7 depicting a clearly defined optimum SDS/soil ratio between 30% and 60% SDS. Between this optimum range, UCS was on the order of 50 psi.

(34) In an embodiment, a series of testing was conducted using beach sand obtained from Atlantic Beach, Fla. Grain size distribution for this soil is presented in FIG. 8. Specific gravity, void ratio, and porosity were 2.69, 0.36, and 0.26, respectively. The SISS components, calcium chloride, and SDS, were stoichiometrically balanced and used to treat the soil using varying quantities of SDS/calcium chloride. As depicted in FIGS. 9A and 9B, UCS data were plotted as a function of SDS percentage where SDS percentage was expressed both as a function of mass (see FIG. 9A) and as a percentage of pore volume (see FIG. 9B). Best-fit regression analysis was used to fit a curve of the form y=ax.sup.2+bx+c to the data. Results showed a clearly defined optimum SDS/soil ratio at approximately 13% SDS, which corresponded to approximately 75% of the pore volume filled with SDS. The corresponding UCS was approximately 50 psi.

(35) Application Techniques of SISS

(36) In an embodiment, the SDS can be sprayed onto the soil, and the calcium chloride solution subsequently sprayed or vice versa. In an embodiment, the SDS can be mixed into the soil, then the calcium chloride solution mixed in or vice versa. In an embodiment, the SDS, alkaline earth metal, and soil can be mixed similar to a grout mixing method, injecting, or any other mixing method that a person of ordinary skill in the art would appreciate to combine the SDS, alkaline earth metal, and soil together.

(37) Conclusion

(38) The SISS technique is a novel improvement for soil strengthening used to stabilize the soil. This novel technique is environmentally friendly and relatively inexpensive. To utilize this method, the surfactant and alkaline earth metal solutions can be mixed or added to the soil in a variety of ways. The calcium ions create a matrix of micelles from the combination of positive calcium ions (e.g., the dications) and the negatively charged sulfate head/carbon tail portion of the SDS (e.g., the surfactant), and hold the soil together.

(39) Referring now to FIGS. 10-12, in conjunction with FIGS. 1-9B, an exemplary process flow diagrams are provided, depicting embodiments of a method for increasing the strength of the soil. The steps delineated in the exemplary process flow diagrams of FIGS. 10-12 are merely exemplary of a preferred order of a method of increasing soil strength. The steps may be carried out in another order, with or without additional steps included therein. Additionally, the steps may be carried out with an alternative embodiment of the method of increasing soil strength, as contemplated in the description above.

(40) In FIG. 10, the method for increasing the strength of soil begins at step 100, by distributing an amount of an anionic surfactant to the soil. At steps 102, an amount of an alkaline earth metal solution is distributed to the soil. At step 104, the strength of the soil is increased when both the surfactant and alkaline earth metal solution are distributed to the soil by the formation of an alkaline earth metal dodecyl sulfate complex.

(41) In FIG. 11, an embodiment of the method for increasing the strength of the soils begins at step 200, by distributing to the soil a first aqueous solution including the anionic surfactant sodium dodecyl sulfate (SDS). The SDS dissociates into sodium ions and dodecyl sulfate ions when in the first aqueous solution. When the first aqueous solutions critical micelle concentration is exceeded, a plurality of micelles are formed. Each micelle includes an interior hydrophobic pocket that is capable of absorbing the soil, thereby solubilizing the soil into an aqueous soil media. At step 202, an alkaline earth metal solution is distributed to the aqueous soil media thereby mixing the alkaline earth metal solution and the aqueous soil media. In step 204, an alkaline earth metal dodecyl sulfate complex is formed that increases the strength of the soil.

(42) In FIG. 12, an embodiment of the method for increasing the strength of the soils begins at step 300 by mixing a first solution having an amount of an anionic surfactant, such as sodium dodecyl sulfate and an amount of water. When in solution, the sodium dodecyl sulfate dissociates and forms a plurality of micelles. At step 032, a second solution is mixed containing an amount of an alkaline earth metal, such as calcium chloride, and an amount of water. At step 304, the first solution is then distributed to the soil creating a plurality of micelle-soil complexes. When the second solution is distributed to the soil containing the micelle-soil complexes, one dication and two micelle-soil complexes bond at step 306. This bonding forms an alkaline earth metal dodecyl sulfate complex, which increases the UCS of the soil at step 308.

Glossary of Claim Terms

(43) Dication: is any cation, of general formula X.sup.2+, formed by the removal of two elections from a neutral species.

REFERENCES

(44) Crowley, R., Zimmerman, A. R., Hudyma, N. and Wasman, S. (2019). Application of microbial-induced calcite precipitation for the stabilization of high organic matter soil for roadway construction. FDOT Final Report No. BDV75 977-06, Florida Department of Transportation, Tallahassee, Fla. Davies, M., Crowley, R., Ellis, T., Hudyma, N., Ammons, P., Matemu, C., Wasman, S., Yahaya, M., Ford, J. and Zimmerman, A. (2019). Microbially induced calcite precipitation using surfactants for the improvement of organic soil. Geo-Congress 2019. DeJong, J. T., Fritzges, M. B., and Nüsslein, K. (2006). “Microbially Induced Cementation to Control Sand Response to Undrained Shear.” Journal of Geotechnical and Geoenvironmental Engineering, 132(11), 1381-1392. Gue S. S., Tan Y. C., and Liew S. S. (2002). “Cost Effective Geotechnical Solutions for Roads and Factories Over Soft Ground.” 20th Conference of the ASEAN Federation of Engineering Organizations, Cambodia, September 2-5. Huat, B. B. K., Prasad, A., Asadi, A., and Kazemian, S. (2014). Geotechnics of Organic Soils and Peat. CRC Press, Taylor and Francis Group, Boca Raton, Fla. Lukas, R. (1986). “Dynamic Compaction for Highway Construction, Design and Construction Guidelines, Volume 1.” Federal Highway Administration Report FHWARD-86-133. Mullins, G. and Gunaratne (2015). “Soil Mixing Design Methods and Construction Techniques for Use in High Organic Soils.” Florida Department of Transportation, Tallahassee, Fla.

(45) All referenced publications are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

(46) The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

(47) It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.