WATER STABILIZATION USING MICROPARTICLES

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to co-pending U.S. Provisional Application Serial Number 60/963,761, filed August 7, 2007, entitled "WATER STABILIZATION USING MICROPARTICLES," which is hereby incorporated by reference as if set forth herein.

FIELD OF THE INVENTION The present invention relates to the avoidance of soil liquefaction. More specifically, the present invention relates to a new, useful and non-obvious water stabilization particle and its use in preventing soil liquefaction, and other uses.

BACKGROUND OF THE INVENTION Liquefaction results in large ground displacements, causing major building distress and loss of life and property. This effect is well documented and has been investigated for decades. The huge liquefaction slide associated with the 1964 Prince William Sound, Alaska earthquake (discussed in Updike et al. (1987), Geologic and Geotechnical Conditions Adjacent to the Turnagain Heights Landslide, Anchorage, Alaska, United States Geological Bulletin 1817); and Lemke (1966), Effects of the Earthquake of March 27, 1964 at Seaward, Alaska, U.S. Geol. Survey Prof. Paper 542-E, p. 43) was one of the first to draw significant attention to the profession. Liquefaction associated with the 1964 Nigaata, Japan earthquake had the same effect. The event and analysis are discussed in several references (Ohsaki (1966), Nigaata Earthquakes, 1864 Building Damage and Soil Condition, Soils and Foundations, v.VI, no.2; Seed and Idriss (1967), Analysis of Soil Liquefaction: Nigaata Earthquake, Journal of the Soil Mechanics and Foundations Division, ASCE, v59, no. SM3, p83- 108; and Kawasumi (1968), Historical Earthquakes in the Disturbed Area and Vicinity, General Report on the Nigaata Earthquake of 1964, Electrical Engineering College Press, University of Tokyo).

The 1987 San Fernando, CA earthquake, which caused liquefaction failure of the Lower San Fernando Dam was analyzed by many (Seed et al. (1975), The Slides in the San Fernando Dams During the Earthquake of February 9, 1971, ASCE Journal of the Geotechnical Engineering Division, Vol. 101, No. 7, pp. 651-688; Ming and Li

(2003), Fully Coupled Analysis of Failure and Remediation of Lower San Fernando Dam Journal of Geotechnical and Geoenvironmental Engineering, Vol. 129, No. 4, April 2003, pp. 336-349) and resulted in information and design procedures for predicting liquefaction susceptibility. An overview evaluating liquefaction resistance is provided by Youd and Idriss (2001), Liquefaction Resistance of Soils: Summary report from the 1996 NCEER and 1998 NCEER/NSF workshops on evaluation of liquefaction resistance of soils, Journal of Geotechnical and Geoenvironmental Engineering, v 127, n. 4, p 297-313, ASCE.

Maps of liquefaction susceptibility for metropolitan areas have been drawn by researchers in the U.S. and abroad (e.g., Kavazanjian et al. (1985), Liquefaction

Potential Mapping for San Francisco, Journal of Geotechnical Engineering, v 1 11, n. 1, p 54-76; Elton and Hadj-Hamou (1990), Liquefaction Potential Map for Charleston, South Carolina, ASCE Journal of Geotechnical Engineering, v 116, n. 2, p 244-265; and Youd and Perkins (1987), Mapping of Liquefaction Severity Index, Journal of Geotechnical Engineering, v 113, n. 11, Nov. 1987, p 1374-1392). These maps show the areas most in need of remediation and assist in land development.

Some buildings are already sited on liquefiable soil (loose, saturated sand). This soil could liquefy during an earthquake, causing considerable damage. These buildings need protection from liquefaction. It is difficult, expensive and potentially dangerous to perform conventional, in-situ soil modification to reduce liquefaction susceptibility underneath a building without damaging the building, adjacent buildings and/or utilities.

Remediation procedures have been proposed and executed for high liquefaction susceptibility sites. Several of these methods are discussed in Mitchell et al. (1995), Performance of Improved Ground During Earthquakes, in Soil

Improvement for Earthquake Hazard Mitigation, Hryciw, R. ed., Geotechnical Special Publication no. 49, ASCE, Reston, VA, 141pp.; and Mitchell et al. (1998), Design Considerations in Ground Improvement for Seismic Risk Mitigation, Geotechnical Special Publication, v 1, 1998, p580-613, in Conference: Proceedings of the 1998 Conference on Geotechnical Earthquake and Soil Dynamics III. Part 1 (of 2), Aug 3-6 1998, Seattle, WA, USA, ASCE. Current remediation efforts mostly consist of treating the soil before construction or treating soil outside the building footprint after construction. Current solutions focus on keeping the soil particles stationary during earthquakes. This strategy reduces pore pressure buildup and, therefore, liquefaction

susceptibility. Some current liquefaction amelioration schemes include grouting, soil compaction, dewatering, and drainage.

Grouting requires skill to perform and usually requires the invasion of the overlying building, with concomitant loss of functionality. It is expensive and can displace soil, causing heave or building/utility damage. Also, the placement of the grout is uncertain and there is a risk of rupturing utilities with pressurized grout. Furthermore, grouting typically involves the creation of a hard layer, which may result in differential settlement if settlement occurs, especially if the grout is nonuniform in strength or distribution. Additionally, grout is brittle and can break during an earthquake, resulting in uneven settlement and reduced resistance during the next earthquake (shown with colloidal silica grout in Gallagher and Mitchell (2002), Influence of Colloidal Silica Grout on Liquefaction Potential and Cyclic Undrained Behavior of Loose Sand, Soil Dynamics and Earthquake Engineering, v22, pi 017- 1026). Soil compaction requires a great deal of skill to perform and is hard to do under existing buildings. Furthermore, it is likely to cause settlement of and damage to the overlying building, adjacent buildings and underground facilities, and may interrupt building service.

Dewatering causes settlement and is expensive to maintain. Drainage is difficult to do under existing structures, with the main problems being installation of gravel or geosynthetic drains and the disturbance of the building.

SUMMARY OF THE INVENTION

The present invention uses hydrophilic particles, such as hydrogel (a polymer), to immobilize pore water. Although the description below often refers to the use of "hydrogels" specifically, it is contemplated that other hydrophilic particles can alternatively or additionally be used. Hydrogel turns pore water into an immobile, soft gel. Hydrogel doesn't flow or liquefy or break the way grout does when shaken. This solution performed very well in preliminary laboratory tests and represents a blend of high technology nanoscale chemistry, chemical engineering and civil engineering. Hydrogels absorb huge amounts of water (up to 240 times by weight), but do not dissolve in water. The absorbed water becomes immobile and acts as a very flexible solid (soft gel). Hydrogels do not change volume when hydrated and are environmentally benign, inexpensive, and readily available. Hydrogels are widely

used in baby diapers, contact lenses, and wound dressings for this purpose. Existing soil applications are waterproofing and water retention for agricultural purposes. However, current hydrogels have not addressed nor have they been made suitable for addressing the immobilization of porewater to avoid soil liquefaction. Installing hydrogel under the water table (e.g., under a building) will require special hydrogel microparticles. Bare hydrogels activate immediately in contact with groundwater due to their strong hydrophilic nature. This immediate activation reduces soil permeability drastically and prevents further hydrogel placement. Therefore, a special hydrogel is needed that exhibits time-delayed activation so that all the hydrogels are in place before activation (water absorption).

In one aspect of the present invention, a water stabilization particle is disclosed. The water stabilization particle comprises at least one hydrophilic core and a hydrophobic shell covering the at least one hydrophilic core. The hydrophobic shell is configured to degrade over a period of time, thereby delaying exposure of the at least one hydrophilic core to any liquid that is external to the hydrophobic shell. It is contemplated that the hydrophilic core and the hydrophobic shell can comprise a variety of different compositions.

In some embodiments, the at least one hydrophilic core comprises a plurality of hydrophilic cores. In some embodiments, each one of the hydrophilic cores is a hydrogel. In some embodiments, each one of the hydrophilic cores comprises or consists of a polyacrylamide. In some embodiments, each one of the hydrophilic cores is dry.

In some embodiments, the hydrophobic shell comprises or consists of a polymer, including, but not limited to, polypropylene and polyethylene. In some embodiments, the polymer has a density of less than 997 kg/m ³ . In some embodiments, the hydrophobic shell has an outer diameter that is less than or equal to 10 micrometers. In some embodiments, the hydrophobic shell has an outer diameter that is less than or equal to 1 micrometer.

In another aspect of the present invention, a method of making a water stabilization particle is disclosed. The method comprises providing at least one hydrophilic core and coating the at least one hydrophilic core with a hydrophobic shell. The hydrophobic shell is configured to degrade over a period of time, thereby delaying exposure of the at least one hydrophilic core to any liquid that is external to the hydrophobic shell.

In some embodiments, the step of providing the at least one hydrophilic core comprises emulsifying monomer droplets and crosslinker droplets in water to form an emulsion. An initiator is introduced into the emulsion to carry out polymerization, thereby producing at least one hydrophilic particle. The water is then removed from the at least one hydrophilic particle, thereby producing the at least one hydrophilic core. It is contemplated that the monomer, the crosslinker and the initiator can comprise a variety of different compositions. In some embodiments, the monomer comprises or consists of acrylamide. In some embodiments, the crosslinker comprises or consists of N,N'-methylene-bis-acrylamide. In some embodiments, the initiator comprises or consists of ammonium persulfate. It is contemplated that the step of removing the water from the at least one hydrophilic particle can be carried out in a variety of ways. In some embodiments, the removal of the water comprises a vacuum evaporation process or a freeze-drying process.

It is contemplated that the hydrophilic cores can be coated in a variety of ways. In some embodiments, the step of coating the at least one hydrophilic core with the hydrophobic shell comprises suspending the at least one hydrophilic core in toluene to form a suspension. A coating polymer is added to the suspension, thereby forming a mixture of the at least one hydrophilic core, the toluene and the coating polymer. The coating polymer is configured to dissolve in toluene. The toluene is then removed from the mixture under supercritical conditions. Under these supercritical conditions, the coating polymer precipitates to form the hydrophobic shell coated around the at least one hydrophilic core.

It is contemplated that the removal of the toluene can be carried out in a variety of ways. In some embodiments, the step of removing the toluene from the mixture comprises injecting the mixture into supercritical carbon dioxide and mixing the mixture with the supercritical dioxide using an ultrasonic field.

In yet another aspect of the present invention, a method of preventing soil liquefaction is disclosed. The method comprises providing a plurality of water stabilization particles, wherein each water stabilization particle comprises at least one hydrophilic core coated with a hydrophobic shell, and depositing the plurality of water stabilization particles into a target soil. The hydrophobic shells of the deposited particles degrade over a period of time, thereby delaying exposure of the at least one hydrophilic core to water in the target soil. An opening forms in the hydrophobic shells of the deposited particles after the period of time, thereby exposing the at least

one hydrophilic core to water in the target soil. The exposed hydrophilic cores then absorb water in the target soil, thereby immobilizing the absorbed water. It is contemplated that the target soil can be located in a variety of different locations. In some embodiments, the target soil is located underneath a building. In some embodiments, the step of depositing the plurality of water stabilization particles into the target soil comprises inserting the water stabilization particles into an injection well at a location upstream from the target soil. The injection well comprises a flow of groundwater. The flow of groundwater then carries the inserted water stabilization particles to the target soil. In some embodiments, the target soil is blocked off from an exterior using a slurry wall, thereby forming an exterior side and a target side and the step of depositing the plurality of water stabilization particles into the target soil comprises inserting the particles into a conduit at a location on the exterior side of the slurry wall. The conduit passes from the exterior side through the slurry wall to the target side and into the target soil. The plurality of water stabilization particles flow through the conduit, from the exterior side of the slurry wall to the target side, where they flow out of the conduit and into the target soil.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates one embodiment of different stages of a water stabilization particle in accordance with the principles of the present invention.

FIG. 2 is a table illustrating particle settling velocities and Brownian displacement for water stabilization particles of various diameters in accordance with the principles of the present invention. FIG. 3 is a flowchart illustrating one embodiment of a method of making a water stabilization particle in accordance with the principles of the present invention.

FIG. 4 is a graph illustrating the mean lysozyme particle size versus power supply to the ultrasonic horn in the Supercritical Antisolvent with Enhanced Mass transfer process for coating hydrophilic particles in accordance with the principles of the present invention.

FIG. 5 is a flowchart illustrating one embodiment of a method of using a water stabilization particle in accordance with the principles of the present invention.

FIG. 6 illustrates one way of delivering the water stabilization particles to target soil underneath a building in accordance with the principles of the present invention.

FIG. 7 illustrates another way of delivering the water stabilization particles to target soil underneath a building in accordance with the principles of the present invention.

FIG. 8 is a table illustrating the permeability of sand at different hydrogel treatment concentrations in accordance with the principles of the present invention.

FIG. 9 is a graph illustrating the effect of hydrogel on the permeability of sand at different concentrations in accordance with the principles of the present invention.

FIG. 10 illustrates the reaction of sand at different hydrogel concentrations to shaking in accordance with the principles of the present invention.

FIG. 11 is a graph illustrating static triaxial test results for treated and untreated soil in accordance with the principles of the present invention. FIG. 12 is a graph illustrating 0% hydrogel cyclic triaxial test results in accordance with the principles of the present invention.

FIG. 13 is a graph illustrating 0.16% hydrogel cyclic triaxial test results in accordance in accordance with the principles of the present invention.

FIG. 14 is a graph illustrating 0.33% hydrogel cyclic triaxial test results in accordance in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein. This disclosure provides several embodiments of the present invention. It is contemplated that any features from any embodiment can be combined with any features from any other embodiment. In this fashion, hybrid configurations of the illustrated embodiments are well within the scope of the present invention.

The present invention provides a special, coated particle having a hydrophilic core and a degradable, waterproof (e.g., hydrophobic) shell. In some embodiments, the particle is a microparticle and the core is a hydrogel. The shell allows placement of the hydrogel underwater without hydrogel hydration. First, the special particles are placed in the ground. Then, the shell degrades slowly in a time-release fashion.

Eventually, the hydrogel core hydrates, immobilizing the water (e.g., making it a gel). Shell thickness and polymer type are controlled so that the shell remains intact only for a predetermined time in groundwater, hence providing the "time-release" nature of the particle. After this time, the shell opens due to its degradation in the groundwater. Finally, hydrogel hydration takes place and the gel forms, immobilizing the water in the soil pores. In some embodiments, FDA-approved biocide molecules in the shell are used to resist the microbial attack on the hydrogel.

FIG. 1 illustrates one embodiment of different stages of a water stabilization particle 100 in accordance with the principles of the present invention. Here, a plurality of hydrophilic (e.g., hydrogel) nanoparticles 110, each with a 100 nm diameter, with a polymeric coating or casing 120 form a 1000 nm diameter microparticle 100. The casing 120 keeps hydrogel nanoparticles 110 dry until they reach the soil pores, where the casing 120 degrades and the hydrogel nanoparticles 110 will be exposed to water. The water is immediately absorbed by the hydrogel nanoparticles 1 10, causing these nanoparticles 110 to expand, form soft gel particles 110', and get locked in the pores. Hydrogel absorbs up to 240 times its weight in water. It is important to note that the excess volume of absorption is zero. Therefore, there is no net volume increase. The hydrogel-volume-increase equals the water- volume-decrease. It is contemplated that the size of the hydrophilic particles is able to vary. In some embodiments, the diameter of each hydrophilic particle is less than 10 micrometers in size in order to fit in soil pores. In some embodiments, a hydrophilic particle size of 1 micrometer will be used for ease of transport into the tortuous soil pores. It should be noted that it is not critical that all pores in the soil be filled with hydrogel since hydrogel absorbs up to 240 times its weight in water. Only a tiny percentage of pores need to contain the unhydrated particles (e.g., 0.34 wt.%).

Regarding the coating, in some embodiments, a group of hydrogel molecules are surrounded by a layer of hydrophobic polymer in order to prevent premature hydrogel hydration during placement. After the particles have been transported to the

voids in the soil, the coating must degrade, exposing the hydrogel to the pore water for hydration. Coating thickness and material are varied in order to adjust the degradation time.

Particle density is not necessarily crucial because the small particle size allows the particles to remain suspended in groundwater. They can be moved into place either by (a) existing groundwater flow, or (b) a small hydraulic gradient induced by pumping to create groundwater flow. The general subsurface placement schemes are shown in FIGS. 6 and 7 discussed below. Particle settling velocity, v, is given by

Stokes' law as v = — °-Ei — EL- _S where g is gravitational acceleration (9.8 m/s ² at sea

18// _/ level), p _/ is liquid density (997 kg/m ³ for water), μ _/ is dynamic viscosity (0.00089 Pa-s for water). Settling velocities for various particle diameters (d) are shown in FIG. 2 for hydrogel (solid density, p _s , 1700 kg/m ³ ). Thermal (Brownian) fluctuations resist particle settlement. According to Einstein's fluctuation-dissipation theory, average

12k Tt

Brownian displacement x in time t is x = I — - — , where kg is Boltzman's constant

\ πμd (1.38 x 10 ^~23 J K ^"1 ) and T is temperature in Kelvin. FIG. 2 also shows displacements for particles of varying sizes in water at 15°C (typical groundwater temperature).

The Brownian displacement of 1000 nanometer-size particles in water is 1,687 nm/s, which is more than the settling velocity of 430 nm/s. Therefore, these particles are too small to settle by themselves and are not likely to float merely due to Brownian motion, thereby imparting an important property to small particles: they can be easily kept suspended in groundwater at any solid density.

Therefore, in some embodiments, the water stabilization particle size is kept at

1000 nanometers or lower so that density matching of solids to groundwater is not a concern. The particles will stay where they are placed, suspended in the water. FIG. 3 is a flowchart illustrating one embodiment of a method 300 of making a water stabilization particle in accordance with the principles of the present invention.

At step 310, a plurality of hydrophilic cores is provided. As discussed above, in some embodiments, each hydrophilic core can comprise or consist of a hydrogel. It is contemplated that the hydrophilic cores can be provided in a variety of ways. In some embodiments, hydrogel nanoparticles are produced by the emulsion

polymerization method already developed by W. Cai and R.B. Gupta (described in 2002, Fast-Responding Bulk Hydrogels with Microstructure, Journal of Applied Polymer Science, 83(1), pi 69- 178; and 2002, Hydrogel, in Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, New York, http://www.mrw.interscience.wiley.com/kirk/articles/hydrgupt .a01/frame.html) and hereby incorporated by reference as if set forth herein. Here, a monomer (acrylamide) and crosslinker (N,N'-methylene-bis-acrylamide) nanodroplets are emulsified in water at the step 312. The polymerization is carried out at the step 314 by introducing an initiator (e.g., ammonium persulfate), thereby producing hydrogel nanoparticles. Finally, at the step 316, water is removed from the hydrogel nanoparticles, thereby producing the dry hydrogel nanoparticles. The water can be removed in a variety of ways, including, but not limited to, vacuum evaporation and freeze-drying.

At the step 320, the hydrophilic cores are coated with a hydrophobic shell. The hydrophobic shell is configured to degrade over a period of time, thereby delaying exposure of the plurality of hydrophobic cores to any liquid that is external to the hydrophobic shell.

It is contemplated that the hydrophilic cores can be coated in a variety of ways. In some embodiments, the hydrogel particles are coated with a toluene soluble polymer. At the step 322, the hydrophilic nanoparticles are suspended in toluene, using a small amount of surfactant if needed (e.g., food grade dioctyl sodium sulfosuccinate). At the step 324, the coating polymer, dissolved in toluene, is added to the suspension. At the step 326, the toluene is rapidly removed under supercritical conditions, precipitating the coating onto the hydrophilic cores and forming a degradable hydrophobic shell around the plurality of hydrophilic cores. In some embodiments, the toluene is removed using the Supercritical Antisolvent with

Enhanced Mass transfer process (SAS-EM), developed and patented by the co-PI at Auburn Universuty (Gupta and Chattopadhyay, U.S. Patent No. 6,620,351, issued September 16, 2003, entitled "Method of Forming Nanoparticles and Microparticles of Controllable Size Using Supercritical Fluids with Enhanced Mass Transfer, which is hereby incorporated by reference as if set forth herein). Details are in

Chattopadhyay and Gupta for the production of protein, antibiotic and polymer nano- and micro-particles.

In SAS-EM, the liquid/solid suspension is injected, using a fine nozzle, into supercritical carbon dioxide at 4O ⁰ C and 100 bar. The liquid/solid jet is mixed with

carbon dioxide using an ultrasonic field, thereby creating microdroplets. Toluene is readily soluble in supercritical carbon dioxide, whereas hydrogel and the coating polymer are not. Due to the high diffusivity in the supercritical conditions, all the toluene very rapidly leaves the droplets, precipitating the coating onto the hydrogel nanoparticles. Microparticles (hydrogel nanoparticles now enclosed into a shell) are precipitated.

In SAS-EM, particle size is easily controlled by regulating the mass transfer rate of toluene, achieved by adjusting the ultrasonic vibration in the precipitation vessel. Polymer particles of desirable size in the range 200 to 2,000 nm can be easily obtained. For example, size control of the lysozyme particles is shown in FIG. 4, using SAS-EM process. FIG. 4 is a graph illustrating the mean lysozyme particle size versus power supply to the ultrasonic horn in the Supercritical Antisolvent with Enhanced Mass transfer process for coating hydrophilic particles.

In order to protect the hydrogel from microbial degradation in the soil, an FDA approved antimicrobial agent will be selected and covalently bonded to the hydrogel network while making hydrogel microparticles in emulsion polymerization. This addition of an antimicrobial agent yields a hydrogel nanoparticle with a long soil-stabilizing life.

The coating on the composite hydrogel nanoparticles must degrade in order to allow the hydrogel to access the groundwater. The degradation rate depends on the temperature (T). Thus, Degradation rate = A e ^{( £/λr)} , where A (molecular collision frequency), E (activation energy), and R (gas constant) are constants. A coating that degrades in 4 months at 15°C is expected to take only 15 days to degrade at 45°C. In some embodiments, standard FDA-approved biocides are included in the hydrogel coating to delay biological degradation. Furthermore, in some embodiments, adjustments to the manufacturing process are needed. Optimization is achievable by varying several factors including, but not limited to, the size of hydrogel nanoparticles, the thickness of the polymer micro-coating, and the amount of antimicrobial agent needed in the hydrogel. FIG. 5 is a flowchart illustrating one embodiment of a method 500 of using a water stabilization particle in accordance with the principles of the present invention. At the step 510, a plurality of water stabilization particles are provided and deposited into a target soil. Each water stabilization particle comprises a plurality of hydrophilic cores coated with a hydrophobic shell. At the step 520, the hydrophobic

shell degrades over a period of time, thereby delaying exposure of the hydrophilic cores to the water in the target soil. At the step 530, an opening forms in the hydrophobic shell, thereby exposing the hydrophilic cores to the water in the target soil. At the step 540, the hydrophilic cores absorb the water in the target soil, thereby immobilizing the absorbed water.

The water stabilization particles can be deposited into the target soil in a variety of ways. In some embodiments, such as the embodiment illustrated in FIG. 6, the water stabilization particles are suspended in water and placed into injection wells (e.g., via conduits 610) upstream from the target soil under very low head at the step 512a. At the step 514a, the inserted particles are moved under the building 620 in the direction of groundwater flow by the flow of the groundwater. The particles travel under the whole building 620 before the protective coating dissolves, releasing hydrogel, which immediately hydrates and immobilizes the groundwater. The coating's dissolution time is chosen based on the velocity of groundwater flow and the coating material dissolution rate.

If distribution time is long (e.g., due to low groundwater velocity), minor wellpoint dewatering may be performed opposite the injection side in order to assist horizontal groundwater flow. In some embodiments, this operation is performed by installing small wellpoints and extracting small amounts of groundwater. Gallagher and Lin's work (2005, Column Testing to Determine Colloidal Silica Transport

Mechanisms, Geotechnical Special Publication, Proceedings of GeoFrontiers, ASCE, p 130- 142) suggests that this operation is feasible and that the hydrogel would be evenly distributed.

In some embodiments, such as the embodiment illustrated in FIG. 7, the target site is blocked off with a slurry wall 715. Directional drilling is used to get under the building 720 and release the particles through porous pipes. For example, a conduit 710 passes through the slurry wall 715, which blocks of the target soil. At the step 512b, the water stabilization particles are inserted into the conduit 710. At the step 514b, the inserted particles flow through the conduit 710, traveling from a location outside of the boundaries of the slurry wall 715 to a location within the boundaries of the slurry wall 715. At the step 516b, the particles flow out of the conduit 710 and into the target soil (e.g., underneath the building 720), moving upwards with a small hydraulic gradient created by mild dewatering. The particles are retained laterally by the slurry wall 715. The coating eventually dissolves. The first breach of the coating

allows for complete hydrogel hydration, where the gel forms, thereby immobilizing the water in the target soil.

Laboratory evaluation of the effectiveness of the hydrogel in reducing permeability, liquefaction susceptibility and cyclic mobility of Ottawa sand has been performed. Three series of tests were run: (1) permeability, (2) static and cyclic triaxial, and (3) flow table tests.

ASTM D-5084 flexible wall permeability tests were run on Ottawa sand to evaluate the effect of hydrogel treatment. Low density samples (<102 pounds per cubic foot) were frozen at about -34°C (-30 ⁰ F) before deaired water was added with a hypodermic needle. The samples were tested in a flexible wall permeameter with B- values greater than 0.97. Samples without hydrogel had average permeabilities of 2.17χ lO ^"3 cm/sec. Treated sample permeabilities ranged from 2.06χ l0 ^"3 cm/sec to 4.14x 10 ^"9 cm/sec, depending on hydrogel concentration. FIG. 8 is a table illustrating the permeability of sand at different hydrogel treatment concentrations. FIG. 9 is a graph illustrating the effect of hydrogel on the permeability of sand at different concentrations.

Hydrogel reduced permeability in all cases. A very low permeability was reached at a hydrogel concentration of only 0.34 wt.%. This is less than the volume of the soil voids. Additional hydrogel did not significantly reduce the permeability. A sufficient amount of hydrogel blocks and isolates pores and produces a minimum permeability.

Static triaxial tests were run with different hydrogel concentrations. The static triaxial tests show hydrogel does not significantly affect the peak pore pressures, as seen in FIG. 11, which is a graph illustrating static triaxial test results for treated and untreated soil. At high hydrogel concentrations, the soil ceases to dilate and pore pressures do not decrease. The variation in peak pore pressures seems to be within the scatter of the data. High pore pressures during shear suggest liquefaction susceptibility was not reduced. This is refuted completely by the cyclic triaxial and flow table tests discussed below. It should be noted that this is not just soil anymore. Rather, it is soil with hydrogel and does not behave like soil alone. The soil does not dilate or contract because the water is gelled.

Constant stress cyclic triaxial tests were performed on untreated and treated samples of Ottawa sand. One hertz, sinusoidal loading was used. Hydrogel

concentrations by weight were 0%, 0.16% and 0.33%. The results are shown in FIGS. 12, 13, and 14.

FIG. 12 is a graph illustrating 0% hydrogel cyclic triaxial test results. Samples were considered liquefied when they had significant strength loss (a cyclic mobility). The 0% sample liquefied after only about 6 cycles, at ± 40 pounds, as shown by the increase in pore pressure and the decrease in force needed to deform the sample. The force decreased from ± 40 pounds to less than ± 10 pounds.

FIG. 13 is a graph illustrating 0.16% hydrogel cyclic triaxial test results. The 0.16% hydrogel would not fail at ± 40 pounds. The sample failed at ± 100 pounds after about 40 cycles. It did not liquefy (fluidize), but did exhibit strength loss. 40 cycles represents an earthquake much, much stronger than any earthquake ever experienced on earth. A M8.5 event suggests only 26 cycles (Seed and Idriss (1982), Ground Motions and Soil Liquefaction During Earthquakes, EERI, UCB, Berkeley, CA). FIG. 14 is a graph illustrating 0.33% hydrogel cyclic triaxial test results. The

0.33% hydrogel would not fail at ± 40 pounds. The sample failed at ± 60 pounds after about 80 cycles. It did not liquefy. 80 cycles represents a monstrous earthquake. Each concentration was tested three times, with very similar results each time. To summarize the cyclic triaxial test results, hydrogel soil does not liquefy and is stronger (requires larger cyclic force to fail) than untreated soil.

Castro and Poulos define cyclic mobility as "the progressive softening of a saturated sand specimen when subjected to cyclic loading at constant water content" (Castro et al. (1977), Factors Affecting Liquefaction and Cyclic Mobility, Journal of the Geotechnical Engineering Division, Vol. 103, No. 6, pp. 501-506). Hydrogel greatly reduced the cyclic mobility by immobilizing the pore water.

ASTM C 230 (Standard Specification for Flow Table for Use in Tests of Hydraulic Cement) evaluated cyclic mobility. The test uses a ten inch diameter table that is lifted and dropped 0.5 inches, 100 times per minute. FIG. 10 illustrates the reaction of sand (at different hydrogel concentrations) to the agitation of the table. Nearly saturated, untreated Ottawa sand samples liquefied and flowed almost immediately, as seen in the top row of FIG. 10. Saturated hydrogel treated samples did not flow at all, as seen in the bottom row of FIG. 10, but broke apart in large chunks. The treated samples broke apart only because they were unconfined. Water never left these treated samples. No signs of liquefaction or cyclic mobility were

present. This reduction in cyclic mobility is vividly illustrated in the bottom row of FIG. 10. While the untreated sample flowed before 25 drops, the hydrogel treated samples never flowed and remained largely intact after 25 drops. This is a dramatic illustration of the effect of hydrogel on reducing liquefaction and cyclic mobility, the effect being that the gelled soil does not liquefy.

The present invention reduces liquefaction susceptibility by immobilizing porewater. The result stops liquefaction under existing buildings and on new sites, thereby saving money and lives. The advantages of using hydrogel to absorb porewater are that it can be installed without interrupting building service and that it can be placed with a very low amount of pressure, thereby minimizing the chance of breaking any utilities. Furthermore, hydrogel is flexible, which means that it does not crack and will survive any number of earthquakes. Additionally, hydrogel is inexpensive and has low permeability. Among the disadvantages of using hydrogel in the proposed fashion is that it is a new technology and people are typically resistant to change. Also, installation of the hydrogel can be slow, quite often taking a few months. Furthermore, installation techniques can be limited and injection drilling suffers from a risk of puncturing utilities.

The present invention can immediately prevent liquefaction under existing buildings in extreme events. Currently, it is expensive and risky to ameliorate soils for liquefaction abatement under existing buildings. The present invention makes it possible, effective, and inexpensive.

The impact of the present invention on infrastructure is huge. Liquefaction susceptibility under existing buildings, pipes, dams, and roads can be reduced or even eliminated. Insurance costs will go down. Liquefaction-prone sites, formerly undevelopable, will become available. The method of the present invention is much easier to use and less risky to structures than existing methods.

There are also dozens of other civil engineering projects where immobilizing pore water will reduce the cost of construction and speed the work, thereby reducing costs. In fact, hydrogels of the present invention have applications in groundwater remediation, contaminant isolation, dam rehabilitation, foundation remediation, canal lining, dewatering, and landfill isolation.

Medical, agricultural and chemical engineering applications are envisioned for the developed coating technology. Construction of new, custom microparticles may

impact medical delivery technologies and coating technologies such as painting and manufacturing. Time-release coated energy capsules for space travel can be made. The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be readily apparent to one skilled in the art that other various modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention as defined by the claims.