US 3354656 A
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. FAHNESTOCK Nov. 28, 1967 METHOD OF FORMING AN UNDERGROUND STORAGE CHAMBER 2 Sheets-Sheet Filed May 1-, 1964 INVENTOR FfankCfb/znes/ac/r QMW/ ATT'OR EY Nov. 28, 1967 c. FAHNESTOCK METHOD OF FORMING AN UNDERGROUND STORAGE CHAMBER Filed May 1, 1964 l NVE NTOR Fran/r CFahnesfac/r United States Patent 3,354,656 METHOD OF FORMING AN UNDERGROUND STORAGE CHAMBER Frank C. Fahnestock, Roslyn Harbor, N.Y., assignor to Mobil Oil Corporation, a corporation of New York Filed May 1, 1964, Ser. No. 364,180 12 Claims. (61--36) This invention relates to underground storage of liquids and gases in excavated chambers. In particular, the present invention relates to underground chambers suitable for low-temperature storage of liquified gases at substantially atmospheric pressure, and to improved methods of their excavation, in which the walls of said chambers essentially are stabilized by a soil-stabilizing material.
Excavated or natural underground storage chambers have been found particularly well suited for low-temperature storage of volatile hydrocarbons, such as natural gas, propane, butane, and the like, whose vapor pressures are high at atmospheric temperatures. The cost of comparable surface storage chambers, such as steel tanks, becomes excessive when highly volatile materials are to be stored in large quantities. Provision must be made either for pressure resistant construction at normal temperature storage or for insulation at low temperature storage. For surface storage in either case, great expense together with practical quantity limitations are incurred. Thus, extensive surface storage of highly volatile hydrocarbons, as required during elf-season, has not been found economically feasible.
Low temperature underground storage of highly volatile hydrocarbons has been found preferable to surface storage in certain locations, particularly where existing caves or favorable soil conditions have permitted uncomplicated excavation and construction of underground chambers. The earth walls of such chambers provide excellent insulation, particularly when equilibrium conditions of storage are approached and the walls have become frozen for a substantial thickness. Under equilibrium conditions, low temperatures may be readily maintained by asmall refrigeration system. Generally, it has been found that adequate cooling may be provided by surface evaporation of the stored hydrocarbon, which vapors are compressed in a refrigeration unit, condensed and recycled to the chamber. In this manner, the evaporation loss of the product is minimized at little expense. Additionally, large quantities of storage may be provided at low maintenance expense without costly pressure equipment or insualtion.
The benefits of low temperature underground storage, however, are not without practical limitations. Understandably, soil conditions favoring readily constructed underground chambers are limited. Tight walls are a practical necessity; permeable walls, for example, would allow product loss or contamination from leakage. Moreover, unstable or weak earth walls would present the hazard of imminent crumbling or collapse, and of destruction of the chamber during or after excavation. The hazard of a collapsed chamber containing large quantities of volatile, highly flammable hydrocarbons, capable of forming an explosive mixture with air, is easily recognized.
The above limitations of underground chambers are largely obviated by freezing the walls thereof. Construc tion of underground storage chambers, accordingly, has generally been accomplished by driving tubes into wet soil in a circle around the circumference of the proposed excavation, circulating a refrigerant in the tubes to freeze an earth ring to the required depth of the chamber, and excavating the soil within the frozen circumference 3 ,354,656 Patented Nov. 28, 1967 which comprises the solidified walls of the excavated chamber. See Oil and Gas Journal 60, No. 30, pp. 1 (July 23, 1963). Materials ranging from liquified natural gas (normal boiling point, 285 F.) to liquified propane (normal boiling point, 44 F.) have been stored in such chambers.
Frozen walls have been found substantially impermeable and can efiiciently enclose liquiiied hydrocarbons with little loss from product seepage. Furthermore, frozen walls exhibit strength superior to earth or sand Walls per se. However, although the permeability and weakness of underground walls may be overcome by freezing, additional problems are encountered in that the ground must be frozen prior to excavation and maintained frozen during and after excavation. Thus, if the frozen walls were allowed to thraw during construction, the hazard of collapse would again exist. Moreover, construction time and expense are high, since a delay is required during freezing prior to and throughout excavation and independent refrigeration must be maintained until the product is stored. A period of a year or vmore typically is required to construct an underground chamber. In addition to the delay and expense of constructing such chambers, a further limitation exists: frozen earth occasionally exhibits plastic flow at temperatures in excess of about -50 F. Consequently, underground storage in frozen chambers is practically limited in temperature range to a maximum of about 50 F.
It is a major object of the present invention to provide a method of excavating underground storage chambers, which method obviates the above-mentioned limitations of delay and expense incurred by present methods of excavation.
An underground chamber, able to store large quantities of liquids at extremely low temperatures or at substantially atmospheric temperatures, or in the temperature range between about -423 F. and about 100 F., is a major result of the present method.
The expedition of the construction of underground chambers is a further result and object of the invention.
Moreover, a primary objective of the present invention is to permit excavation of storage chambers in locations where soil conditions heretofore have precluded or discouraged such endeavor, or where expense or delay have dictated alternative methods of storage at great expense or inconvenience. I
Other objects and advantages of the present invention will become manifest to those skilled in the art from the following detailed description and illustrations thereof.
In one embodiment the present invention comprises an underground chamber for the storage of liquids, the soil walls of which are consolidated by injected soil-stabilizing material.
In another embodiment the present invention comprises a method of excavating an underground chamber, serviceable for the storage and insulation of liquids over a wide range of temperature, which comprises defining a soil core to be excavated and thereby to provide said chamber, injecting, prior to excavation of a soil core into soil immediately adjacent and surrounding said soil core a soil-stabilizing material, allowing said material to set and to consolidate said immediately adjacent soil, excavating said soil core within said immediately adjacent consolidated soil, which consolidated soil comprises walls for said underground chamber.
Soil stabilizing materials suitable for use in the method of the present invention are broadly known in the art as grouting materials and the like. As employed herein and in the claims, soil-stabilizing material may be defined as a substance which can be injected into soil and which,
- upon'setting, consolidates the soil in a region substantially stronger than the soil per se, and such materials include chemical grouts, Portland cement, slag-cement, resin gypsum cements, clays, bentonites, pozzolans and the like, and mixtures and products thereof. Essentially, for the present invention, these materials must be capable offluid transfer and of permeating the specific soil injected therewith in order to stabilize a substantially continuous region underground, which region comprises the walls of a chamber after excavation. With an understanding of the teaching of the present invention, the man skilled in the art will immediately recognize its adaptability to numerous specific problems arising from variations in soil conditions, service requirements, and storage products. Thus, although this disclosure by implication recites the available soil-stabilizing materials, the appended claims and their purview fairly should not be limited to the specific materials disclosed, but should include as well the practice of the present invention utilizing all soil-stabilizing materials anticipated by this disclosure.
The broad area of grouting has been covered in a symposium under the authority of the American Society of Civil Engineers, see Symposium on Grouting, Journal of the Soil'Mechanics and Foundations Division. Proceedings of the American Society of Civil Engineers, April 1961, pp. 1148, incorporated herein by reference.
As disclosed by the above reference, cement products, such are Portland cement, slag-cement, resin gypsum cement and the like, are well suited as soil-stabilizing materials in coarse to medium sand. For the purposes of the present invention, cement products may be injected into such sand and form upon standing a stabilized region as discussed in suggested methods and embodiments hereinafter. Clays, bentonites, pozzolans or mixtures thereof, alone or in combination with cement products, are also suitable soil-stabilizers over a wide range of soil conditions.
Chemical grouting is even wider in its scope of application, and a suitable composition may be found to stabilize soil in virtually any condition to any degree of stability. Moreover, chemicals may be used in combination or with cements, clays, and other materials. A highly fluid chemical may .be employed to stabilize a difficulty permeated soil or a viscous chemical may be preferred to stabilize a coarse soil. By a proper choice of materials, chemical soil stabilizers may be utilized to effect a stabilized soil having a wide range of properties, such as strength, setting time, chemical inertness, permeability, or insulation.
The most common chemical grouts are combinations of sodium silicate with a soluble alkaline earth salt, a soluble metallic salt, an acid, or an alkali salt of an amphoteric metal. These and other grouts are commercially available under various tradenames. See also US. Patent No. 2,968,572, C. E. Peeler, Jr., assigned to Diamond Alkali Co., issued Jan. 17, 1961, for disclosure of a soil-stabilizing material comprising an aqueous alkali metal silicate, water and an amide. Other chemical grouts, suitable as soil-stabilizing materials for use in the present invention, such as chrome lignins or organic polymerizers, are well known to those skilled in the art.
In the construction of an underground chamber, according to the method of the present invention, the selection of a soil-stabilizing material from the wide variety available will depend largely upon the conditions of the soil of the designated area, the properties desired for the chamber and the economics of the method. A number of materials may be employed in combination by multiple injection in areas where stratification presents regions of diverse conditions. Drilling and soil sampling, of course, are suggested expediencies to determine most suitable materials,
The advantages over the prior art-and therefore the distinction therefromof the present invention are-clear.
Although soil stabilizers have long been available, the
procedures for constructing underground storage facilities practiced by those skilled in the art have been limited:
a recent chamber has been excavated inside walls that were frozen by a time-consuming and expensive process; others have been constructed by sealing the walls of existing chambers. Adverse soil conditions often have practically precluded construction by prior art methods. The present method knows no such limitations; in fact, its applicability is manifest where conditions are diverse or adverse. The present method makes possible the excavation of chambers in locations where heretobefore such endeavor was impossible, and makes more economical where heretofore possible.
Essentially, the present invention contemplates underground injection of a soil-stabilizing material to form a wall-defining region of solidified soil, preferably annular. After excavation of the earth core within the defined region, the solidified soil comprises the walls of an underground chamber. The walls may be made substantially impermeable if so desired and of a strength adequate to prevent collapse. Thus, by the method of the present invention the shortcomings of delayed construction, product leakage and potential collapse, inherent with prior methods, substantially are overcome; the present method ofiers a significant improvement over the prior art.
The principles and the advantages of the present invention will be more fully understood by consideration of preferred methods and embodiments shown in the attached drawings, wherein:
FIGURE 1 is a cross-sectional view of an injector in place in an underground well, by means of which a soilstabilizing material is dispersed into surrounding soil in a method suitable for the present invention.
FIGURE 2 is a top view of the excavation area showing a typical scheme of injection.
FIGURE 3 is a cross-sectional diagrammatic view, taken along 3-3 of FIGURE 2, showing the depth and effect of the injection-stabilization process.
FIGURE 4 is a diagrammatic cross-sectional view, similar to FIGURE 3, showing an excavated and covered underground chamber, suitable for the storage of material not requiring refrigeration or extensive insulation.
FIGURE 5 is a diagrammatic cross-sectional view-of an excavated and covered underground chamber, provided with supplemental insulation and refrigeration, suitable for low temperature storage of volatile hydrocarbons and the like.
FIGURE 6 is a diagrammatic cross-sectional view of a region characterized by zones of diverse soil conditions, which illustrates techniques of the present invention particularly Well-suited for such conditions.
FIGURE 7 is a diagrammatic cross-sectional view of a chamber characterized by multiple injection and excavation where specific soil conditions so require.
With reference now particularly to FIGURE 1 by way of example there is shown a suggested method of injecting a soil-stabilizing material into a region to be stabilized. Injection well 10 is drilled to the depth desired. Injection tube 12 fitted with cap 14 is inserted into the well. The annular space between tube 12 and the wall of well 10, desirably is small so that vertical leakage of soil-stabilizing material is not excessive. Soil-stabilizing material is pumped downwardly from the surface by means not shown through injection tube 12, leaves tube 12 by outlets '16 spaced in the tube at the region where injection is to take place, and is dispersed and permeates adjacent soil 18 into a stabilization region 20, diagrammatically represented by the darkened area of FIGURE 1. Injection tube '12 is then withdrawn and the soil-stabilizing material is allowed to solidify in the injection region 20. Injection tube 12 may then be relocated in a different location in well 10 or in another well to impregnate other regions.
FIGURE 2 shows by way of illustration a typical distribution of injection wells 10 to provide a substantially continuous solidfied zone consisting of the stabilization region 20 about the wells. Consequently, this solidified zone comprises an approximate cylinder into the soil which after excavation becomes the substantially continuous, strengthened walls of the excavated chamber. A cross-sectional view of the solidified zone is shown by FIGURE 3.
With reference to FIGURE 4 by way of example there is diagrammatically shown a simple embodiment of the present invention, an excavated underground chamber suitable for the storage of a variety of liquids in large volume. The chamber comprises stabilized soil walls and floor 20 and a cover 22 to protect the contents thereof from the elements. The cylindrical walls of the chamber have been stabilized by an injection of soil-stabilizing material through now-abandoned injection Wells 10. The floor of the chamber may be stabilized after excavation to prevent product leakage or to increase chamber strength if desired. The stabilized soil walls and floor of the chamber of FIGURE 4 may provide adequate strength and insulation for the storage of liquids at low temperatures, at atmospheric temperatures or higher. Under low-temperature storage, freezing of the wall may occur to provide supplementary insulation and strength. Frozen walls are not required for the present method, however, and storage may be provided at temperatures above freezing; herein lies an important distinction and advantage over the frozen-wall method of the art described above.
Upon occasion, however, the simple and inexpensive underground chamber illustrated in FIGURE 4 may prove uneconomical for the storage of certain volatile materials liquifiable only at extremely low temperatures; product loss by boil-off may be substantial. Thus, as a preferred embodiment of the present invention, supplemental insulation or refrigeration may be provided as shown by way of example in FIGURE 5. The storage chamber illustrated in FIGURE 5 comprises the basic elements of stabilized soil walls and floor 20 and cover 22. To provide insulation to supplement that provided by the stabilized soil, insulating material 24 is applied on the inner surfaces of the chamber. Insulation may be applied in any suitable manner, such as by spraying the surfaces with urethane foam or the like. 'In addition to providing an excellent insulation, a layer of urethane foam or the like on the inner surfaces of an underground chamber effectively seals the soil walls thereof to prevent leakage, drying out, or other deterioration. Such an effect is particularly desirable where soil conditions preclude practically the realization of impermeable solidified walls and where sealing may be effected more readily after excavation by spraying the surfaces.
Autorefrigeration is provided by evaporation and condensation of the liquid being stored. Evaporated vapors of the stored volatile liquid 26 pass from the chamber via conduit 28 to a refrigeration and compressor unit 30, wherein the vapors are condensed and cooled. The condensed liquid is returned to the chamber via conduit 32. By this method, a large quantity of volatile liquid may be stored at a low temperature at or below its normal boiling point, and the temperature may be readily maintained by the cooling effect of evaporation.
As hereinabove mentioned, the method of the present invention finds beneficial employment in numerous situations: where soil conditions are such that unsupported underground chamber is unfeasi'ble due to the weakness of the walls, expense, or delay of construction. In such situations, the stabilization of the soil before excavation is generally simple and avoids the above shortcomings inherent to prior art practices. The advantage of the present method is especially apparent where diverse soil conditions exist, one or more of which makes unsuitable other methods of underground chamber excavation. For example, where a layer of dry sand exists, the freezing method of the prior art described above may not be suitable, for during or after excavation the sand possibly would present a serious cave-in hazard. And where oer tain diverse soil conditions exist, freezing may even pro- 6 mote shifting of cracking, and collapse of the walls may become an imminent hazard.
FIGURE 6 illustrates a method of soil stabilization by injection in areas of diverse soil conditions, where the present method is preferred and well suited. Zones A, B, and C are areas of different soil conditions, such as sand, shale, limes-tone, quicksand, and the like. One or more zones may be such as to make the area impractical for underground storage utilizing the methods of the prior art. Utilizing the present method, however, different soilstabilizing materials particularly suited therefor may be injected separately into each zone, and the soil therein may be effectively stabilized. For example, Zone C may be substantially impermeable and a chemical grout of low viscosity may be particularly suitable therein as a stabilizer, while Zone B may be a coarse Wet material requiring a more viscous stabilizer and" Zone A may be a fine sand preferring still another material. Thus, by multiple injection of different stabilizers at various depths or locations, effective stabilization may be realized in each zone, a result heretofore unattainable :by the prior art method. It may be necessary to inject different stabilizers above and below the water table 34, another result readily achieved by the present method.
The method of the present invention is particularly advantageous in excavation to provide the novel underground chamber in an area where, because soil conditions may be adverse to excavation readily by methods known to the art, or otherwise, an application of the present method is particularly well-suited.
It is desired, as an example of the application of the present invention, to construct an underground storage chamber for the storage of about 17,500 barrels of a liquid mixture essentially of butane and propane, which mixture has a normal boiling point of about -25 F. A circular chamber measuring 50 feet across and 50 feet deep is sufficient for the above storage requirements.
The soil conditions at the desired location for excavation, exclusive of a few feet of topsoil as determined by random drilling and sampling, are as follows: a top zone of 17 feet of coarse sand, having an average grain size of about 0.9-1.3 millimeters, and a bottom zone of greater than 8 feet of a substantially impermeable shale. Clearly, a 50-foot by 50-foot pit could not be excavated at such a location without a hazard of collapse. Since the temperature of the liquid to be stored is above 50 F., and potential danger of plastic flow of frozen soil exists, mere freezing of walls should not sutfice, Consequently, it is highly desirable to stabilize an annular region about the excavation zone in order to provide stable walls for the excavated chamber.
Those skilled in the art of grouting will recognize that the choice of soil-stabilizing material depends upon several factors, among them the characteristics of the soil to be stabilized. Thus, customarily where diverse soil conditions exist in strata, it is preferable to vary the composition and consistency of the soil-stabilizing material to suit the characteristics of the individual strata. Accordingly, for the top zone of coarse sand, very fine grind Type III Portland cement is selected; the middle zone of fine-medium sand requires a more permeative material, and a silicate stabilizer is selected, consisting of 70 parts by volume of an aqueous sodium silicate (1Na O:3.22SiO 40.0-4l.5 B, av. solids 37.5%), 5 parts of formamide, 5 parts of a solution (62.5 grams per liter) of sodium aluminate, and 20 parts of water; soil stabilization is unnecessary for the impermeable bottom zone of shale.
A reasonably flat, workable area is selected at the location for the excavation of the chamber and a 50-foot diameter circle is staked out. Injection holes of a 1-inch diameter are drilled about the circle to the level of the shale zone. The spacing of the holes is about three feet, making a total number of 54 l-inch holes, varying in depth from 40 to 45 feet.
The injection pipes are 1-inch pipes comprising 2-foot connectingsections, the bottom section is provided with 92 7 holes, 23 rows of 4 holes each, about circumferences spaced one inch along the section. The pipe, as designed, injects a bulb of soil-stabilizing material approximating a sphere of about a 3-foot diameter. Each injection, depending upon the porosity of the soil, requires from about 30 gallons of injection fluid (for fine-medium sand zone, porosity=.284) to about 32 gallons (for coarse sand zone, porosity==.303). The silicate stabilizer injection material is made in batches, one batch of 65 gallons being sufficient for two injection bulbs. Type III Portland cement is prepared according to standard procedure in larger batches.
The batch preparation of silicate stabilizer is contemporaneous with its injection and proceeds as follows. The following materials are required per batch: 45.5 gallons of the silicate solution, 3.25 gallons of formamide, 3.25 gallons of the sodium aluminate solution, and 13.0 gallons of water. The sodium aluminate solution and water are mixedin a IOU-gallon tank. The formamide is added thereto and mixed thoroughly. The silicate solution is added to a separate 100-gallon mixing tank and agitated continuously, while the contents of the first tank are added to the second tank. Upon complete mixing, the solution is ready for injection.
The injection procedure is accomplished by two work groups, one injecting the silicate solution initially from injection well to well, while the other group follows, injecting the portland cement. Each group has injection equipment comprising a pump, lines, 2-foot sections of pipe and the 2-foot injection section. They proceed at each well as follows: The injection pipe is lowered by the first work group in the well to the impermeable shale, the bottom section being the injection section. A halfbatch of silicate stabilizer is pumped through the injection pipe into the fine-medium sand. A high initial pressure is required, but the material flows more easily thereafter. After each injection, a 2-foot section is removed and the injection pipe is raised two feet, whereupon a further injection is made. The procedure is repeated at 2-f0ot intervals through the fine-medium sand zone. Then the silicate stabilizer group removes its injection pipe to another well, and the portland cement group takes over at the well and follows a similar procedure.
The above process requires about 650 injections or 21,000 gallons of silicate stabilizer and about 460 injections or 15,000 gallons (2000 ft.) of Type III Portland cement. The material is allowed to set for one week and to consolidate the soil about the 50-foot excavation zone.
Thereafter, the sand and shale within the consolidated region is excavated to form a pit of the desired dimensions. The walls of the pit are then inspected and, where required, are further reinforced with cement, A circular cover is constructed and placed atop the pit to protect the stored product from the elements. A circulatory refrigeration unit is added to condense and recycle the stored product. The excavated chamber is now capable of storing the propane-butane liquid.
The scope of the present invention as illustrated by the above-suggested methods and embodiments should not be limited thereby. Thus, other than cylindrical chambers may be better suited in some applications and would, of course, be within the purview of the present invention. If deep penetration is desirably avoided, stabilization and excavation may readily be done in stages, as illustrated by FIGURE 7, each being excavated within the one above. The multistage method may find particular utility where soil conditions are very adverse. In such a method, soil stabilization and excavation for the first stage is effected to a safe depth. After excavation, the soil walls may be further stabilized or reinforced and the next stage then may be excavated within the prior stage. The number of stages required will, of course, depend upon the depth of excavation achievable with safety and the de- 3 sired capacity of the chambers. Multistage excavation is also particularly well-suited in areas of soil stratification. One stratum may be suitably stabilized and excavated, and thereafter other strata may be stabilized and excavated in successive stages, each within the one immediately above.
Essentially, however, the present invention comprises the construction of underground chambers by stabilization of the walls thereof by injection of a suitable soilstabilizing material prior to excavation, as Well as the chamber constructed according to the present method.
1. A method for forming an underground chamber serviceable for the storage and insulation of liquids over a wide temperature range which comprises, forming a plurality of injection wells of desirable depth in the ground, said wells arranged to define the approximate perimeter of an underground chamber, inserting in each of said wells a hollow injection tube of a diameter such as to minimize the space between the outside wall of the tube and the well wall and to prevent vertical leakage of liquid soil-stabilizing material to be passed through said tube, said injection tube being closed at its lowest end within said wells and said tube having a plurality of holes in the lower portion of the walls thereof, injecting a liquid soil stabilizing material through said tube to premeate the soil adjacent said plurality of wells beginning at the deepest portion in each of said wells in an amount suiiicient to stabilize the soil, repeating said injection of soil stabilizing material at progressively higher portions of each of said wells until the adjacent soil surrounding the vertical length of each of said wells has been injected with said liquid, permitting the soil stabilizing liquid to set and consolidate said adjacent soil, and excavating unstabilized soil enclosed by said consolidated adjacent soil to form an excavated underground chamber.
2. The method of claim 1 wherein said liquid soil stabilizing material is a member selected from the group consisting of chemical grouts, portland cement, slag cement, resin gpysum cement, clays, bentonite, pozzolans and mixtures thereof.
3. The method of claim 1 wherein said liquid soil stabilizing material comprises sodium silicate and a reagent selected from the group consisting of a soluble alkaline earth salt, a soluble metallic salt, an acid, and an alkali salt of an amphoteric metal.
4. The method of claim 1 wherein said wells are formed in Stratified diverse soil conditions and a plurality of liquid soil stabilizing materials are separately injected depending upon the soil conditions at a given stratum.
5. The method of claim 1 wherein thefloor and walls of said excavated underground chamber are coated with a substantially impermeable and insulating layer of sealing material.
6. The method of claim 5 wherein said insulating layer comprises polyurethane foam.
7. The method for forming a multistage underground chamber serviceable for the storage and insulation of liquids over a wide temperature range which comprises, forming a plurality of injecting wells of desirable depth in the ground for a first stage to be excavated, said wells arranged to define the approximate perimeter of the first stage of said underground chamber, inserting in each of said wells a hollow injection tube of a diameter such as to minimize the space between the outer wall of the tube and the well well and to prevent vertical leakage of liquid soil-stabilizing material to be passed through said tube, said injection tube being closed at its lowest end within said wells and said tube having a plurality of holes in the lower portion of the walls thereof, injecting a liquid soil stabilizing material through said tube to permeate the soil adjacent said plurality of wells beginning at the deepest portion in each of said wells in an amount sufficient to stabilize the soil, repeating said injection of soil stabilizing material at progressively higher portions of each of said wells until the adjacent soil surrounding the vertical length of each of said wells has been injected with said liquid, permitting the coil stabilizing liquid to set and consolidate said adjacent soil, excavating unstabilized soil enclosed by said consolidated adjacent soil to form the first stage of an excavated underground chamber and repeating the above procedure for at least one stage below said first stage excavation wherein the injection Wells for a given stage are formed beginning at the soil floor of the adjacent upper stage excavation.
8. The method of claim 7 wherein said liquid soil stabilizing material is a member selected from the group consisting of chemical grouts, portland cement, slag cement, resin gypsum cement, clays, bentonite, pozzolans, and mixtures thereof.
9. The method of claim 7 wherein said liquid soil stabilizing material comprises sodium silicate and a reagent selected from the group consisting of a soluble alkaline earth salt, a soluble metallic salt, an acid, and an alkali salt of an amphoteric metal.
10. The method of claim 7 wherein said wells are formed in stratified diverse soil conditions and a plurality of liquid soil stabilizing materials are separately injected depending upon the soil condition at a given stratum.
10 11. The method of claim 7 wherein the floor and wall of said excavated underground chamber is coated with a substantially impermeable and insulating layer of sealing material.
12. The method of claimll wherein said insulating layer comprises polyurethane foam.
References Cited UNITED STATES PATENTS 768,774 8/ 1904 Schmidt 6136 2,159,954 5/1939 Powell 6130 X 2,914,923 12/1959 Harrison 61.5 2,961,840 11/1960 Goldtrap 61-.5 X 2,968,572 1/ 1961 Peeler.
3,159,006 12/1964 Sliepvich 61.5 X 3,175,370 3/1965 Schlumberger et al. 61.5 X
FOREIGN PATENTS 1,278,379 10/ 1961 France.
28,541 1907 Great Britain. 921,844 3/1963 Great Britain. 111,569 3/ 1962 Pakistan.
EARL I. WITMER, Primary Examiner.