US3091935A - Rock treatment - Google Patents

Description

3,091,935 Patented June 4, 1963 3,091,935 ROCK TREATMENT Frank Brown, Summit, and John H. Prichard, Springfield,

N ..l., assignors, by mesne assignments, to American Cyanamid Company, Wayne, N.J., a corporation of Maine No Drawing. Filed Aug. 13, 1957, Ser. No. 677,824

8 Claims. (CI. 61-36) This invention relates to a method for reinforcing stratified rock against structural failure under load and particularly for reinforcing the roof of a subterranean cavity which is below a layer of stratified rock. The invention also relates to the reinforced Stratified rock produced by the aforesaid method.

In the excavation of subterranean cavity, such as a mine, tunnel or bomb shelter the layer of material immediately above the cavity is subjected to severe loading due to the weight of the layers above it and due to the lack of immediate vertical support beneath it. In order to prevent the roof of the cavity from caving in it is necessary to reinforce it or support it.

In the excavation of bituminous coal for example, where coal seams are found beneath layers of shale, it has been necessary to leave pillars of coal as supports for the shale as entry is made into the mine. After the coal around the pillars is mined by this method, retreat mining is carried out, wherein the coal pillars are systematically mined and the mine roof is deliberately caved in as the miners retreat.

Even with the use of pillars of coal for support, it is necessary to support the roof between pillars. Three methods of support are commonly used:

1. Timber props are used, both with and without cross beams.

2. Angle iron is used (H-beams or rail-iron) in a similar manner as the timber props or by grouting into the side walls.

3. Bolting is used wherein a hole is drilled into the ceiling 4 to 6 feet deep and a /2 inch bolt of appropriate length with an expansion shield at the top is inserted. On tightening the bolt the shield expands and grips the surrounding area.

The success of bolting is due to the fact that structural failure of a shale roof is caused by the layers of shale sliding over each other. Bolting prevents such sliding. The application of severe loading in a direction transverse to the horizontal layers of shale causes the shale to be deformed into an inverted arch and causes the outer (or lower) layers of lengthen in comparison with the inner (or upper) layers. When the layers slide over each other, all of the tension must be borne by the outermost layer of shale which ruptures easily since it is weak in tensile strength. On the other hand if the layers are prevented from sliding over each other the tension is borne by many thicknesses of shale and no one thickness has its tensile strength exceeded.

It is an object of this invention to provide a novel method for reinforcing the roof of a mine or other sub.- terranean cavity.

It is a further object of this invention to provide a novel method of bonding layers of shale or other stratified rock to each other top revent them sliding with respect to each other under load. It is a further object of this invention to produce a reinforced stratified rock.

These and other objects are obtained by preparing a structurally reinforced stratified rock having between its strata a reaction product of (a) a condensation product of an alpha, beta-ethylenically unsaturated dibasic acid with a dihydric alcohol and (b) an ethylenically unsaturated reactant with said condensation product which is capable of intimate admixture therewith. The reinforced stratified rock is prepared by applying a mixture of (a) and (b) between the strata of the rock and copolymerizing the same.

Preferably, the mixture of the condensation product and the ethylenically unsaturated reactant therewith is applied between the shale layers in a mine roof by pressure injection through holes in the shale drilled for the purpose. Preferably the mixture should be of relatively low viscosity to permit penetration between the layers and should be capable of curing in one hour or less at 70 F. in order to avoid delays in mining operations.

The condensation product of the alpha, beta-ethylenically unsaturated dibasic acid and the dihydric alcohol is an ethylenically unsaturated linear unsaturated polyester and may be made from a mixture of unsaturated dibasic acids and/or a mixture of dihydric alcohols. If desired, a portion of the unsaturated dicarboxylic acid may be substituted by a dicarboxylic acid Without ethylenic unsaturation as a condensation product with the dihydric alcohol.

Among the acids with alpha, beta-ethylenic unsaturation which may be used are maleic acid, fumaric acid, methyl maleic acid, methyl fumaric acid, itaconic acid, dimethylmaleic acid, glutaconic acid, chlormaleic acid. Anhydrides of the acids may be used when available and it is to be understood that the term acid as used herein also encompasses the anhydride.

Among the acids without ethylenic unsaturation which may be used are phthalic acid, isophthalic acid, terephthalic acid, adipic acid, sebacic acid, tetrachlorophthalic acid, succinic acid, azelaic acid, glutaric acid, pimelic acid, 3,3 dipropionic acid and mixtures thereof. These acids are preferably used in molar proportions up to about 96%, based on the total number of moles of diacid used.

Among the dihydric alcohols which may be used are 1,2-propylene glycol; ethylene glycol; diethylene glycol; triethylene glycol; 1,3-propy1ene glycol; dipropylene glycol (1,2); dipropylene glycol (1,3); 2,3-butylene glycol, and neopentyl glycol. Halogenated glycols such as 2,2 bis-chloromethyl 1,3-propanediol and 2,2 bis-bromomethyl 1,3-propanediol may also be used.

It is to be noted that dihydric alcohols containing ether linkages, such as diethylene glycol, may be used. It is also within the scope of this invention to use as a dihydric alcohol, a derivative of more highly hydroxylated compound, such as a monoether or a monoester of glycerm.

The molar proportions of total dicarboxylic acid to total dihydric alcohol may vary between about 1.0 to about 0.8.

In a preferred modification, an unsaturated polyester resin is prepared by reacting 50 mole percent of phthalic anhydride and 50 mole percent of maleic anhydride with a 10 percent molar excess of 1,2-propylene glycol until the resin has an acid number of about 50. The excem propylene glycol is distilled olf leaving a solid, hard, brittle unsaturated polyester resin which may be readily crushed and which is stable in storage.

Styrene is preferred as the ethylenically unsaturated reactant with the unsaturated polyester. Styrene is a solvent for the polyester and is thus capable of intimate admixture therewith. Among the other ethylenically unsaturated reactants with the unsaturated polyester which may be used are methyl methacrylate, vinyl acetate, ethyl aerylate and diallyl phthalate. These compounds 00- polymerize with the unsaturated polyester in situ to produce stable space polymers of high molecular weight. The styrene or equivalent is generally blended with the unsaturated polyester in amounts between 15% and 50% by weight, based on the weight of the polyester.

The blend of the unsaturated polyester and the styrene,

for example, copolymerizes when subjected to heat or to the action of an appropriate polymerization catalyst. When used to reinforce a mine roof. the application of heat is not practical and the action of a catalyst, particularly a catalyst which is effective at temperatures not higher than 90 F., is preferred. Among the catalysts suitable for such use are the organic peroxides and hydro peroxides such as benzoyl peroxide, lauroyl peroxide. In some cases, a polymerization accelerator, such as dimethylaniline or cobalt naphthenate may be required to activate the catalyst at the desired temperature. The peroxides are generally incorporated into the blend in amounts between about /z% and 2% by weight based on the total weight of the blend.

The Styrene or other reactant with the ethylenically unsaturated linear polyester copolymerizes therewith by linking a carbon atom at an ethylenic bond on one linear polyester molecule with a carbon atom at an ethylenic bond on another. in order to obtain a reaction, intimate admixture between the two components must be achieved. Generally, the polyester is soluble in the ethylenically unsaturated comonorner, such as styrene. In some cases, both components are soluble in a common solvent.

In a preferred embodiment, the aforementioned unsaturated polyester resin is dissolved in styrene. the styrene comprising 30% by weight of the entire blend.

Fifty parts by weight of the aforementioned blend is added to fifty parts by weight of a styrene solution of a polyester of ethylene glycol with 60 mole percent of adipic acid, 30 mole percent of phthalic acid and mole percent of maleic anhydride. The styrene solvent in the latter blend also comprises by weight of the entire blend.

The combined blend is then divided into two equal portions with two parts of benzoyl peroxide added to one portion and two parts of dimethylaniline added to the other. The portions are reblended and applied between the rock strata to cure Within a few hours at 90 F. to form an excellent bond between the strata.

In a qualitative bond strength test a bonded area be tween two slate tiles 2.8 inches square withstood more than 150 lbs. of weight in direct tension without rupturing the bond.

In another preferred embodiment, the aforementioned condensation product of l.2--propylene glycol with equimolar portions of phthalic anhydride and maleic anhydride is dissolved in styrene, as above, sulli-cient to produce a solution containing 30% of styrene. A small amount (0.05% by weight) of cobalt naphthenate is ineluded as an accelerator.

Seventy-five parts by weight of this colbalt naphthenatecontaining solution is blended with twenty-five parts by weight of the above described styrene solution of ethylene glycol condensation product with adipic acid. phthalic acid and maleic anhydride. The total blend is divided into two portions as above with two parts by weight of benzoyl peroxide added to one and two parts by weight of dimethylaniline added to the other. The portions are reblended and applied between rock strata for about a half hour at 90 F. to form an excellent bond between the strata.

In a bond strength test a bonded area between two slate tiles 2.8 inches square withstood more than 400 lbs. of direct tensions before the slate broke in shear without rupturing the bond.

In a flexural test of the identical polyester blend, but cured at 77 F. and applied between slate tiles one inch square, the bond withstood a flexural load of 500 pounds although the slate broke at that load. This test unequivocably shows the bond to be strong in both tension and shear.

in applying the last described polyester blend to the rock strata of a horizontal bed of shale, which is overhead in a mine roof, a series of holes /2 inch in diameter and 5 feet deep are drilled 6 feet apart in a freshly excavated area of square feet. The polyester blend, preferably having the catalyst added at the site is injected into the holes at a pressure of 600 pounds per square inch. The polyester is permitted to cure for about 1 hour at the mine temperature of 55 F. The roof is then safe enough to permit the excavation to advance.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. A method of reinforcing the roof of a subterranean cavity which is below a layer of Stratified rock which comprises drilling a series of spaced holes upwardly into said Stratified rock in a direction transverse to the direc tion of the strata of said rock and injecting through said holes, under pressure, between the strata of the rock a mixture of an ethylcnically unsaturated linear polyester and an ethylenically unsaturated reactant with said linear polyester which is capable of intimate admixture therewith and allowing said mixture to cure.

2.. The method of claim 1 wherein said polyester mixture is capable of curing at 70 F. within one hour.

3. A method of reinforcing the roof of a subterranean cavity which is below a layer of shale which comprises drilling a series of spaced holes upwardly into said shale in a direction transverse to the direction of the strata of said shale and injecting through said holes. under pressure, between the strata of the shale a mixture of a condensation product of an ethylenically unsaturated dibasic acid with a dihydrie alcohol and an ethylenically unsaturated reactant with said condensation product which is capable of intimate admixture therewith and allowing said mixture to cure.

4. A method of reinforcing the roof of a subterranean cavity which is below a layer of Stratified rock which comprises drilling a series of spaced holes upwardly into said stratified rock in a direction transverse to the direction of the strata of said rock and injecting through said holes, under pressure, between the strata of the rock a mixture of a condensation product of an cthylenically unsaturated linear polyester and an ethylenically unsaturaated reactant with said polyester which is capable of intimate admixture therewith, and an organic peroxide curing catalyst and allowing said mixture to cure.

5. A method of reinforcing the roof of a subterranean cavity which is below a layer of shale which comprises drilling a series of spaced holes upwardly into said shale in a direction transverse to the direction of the strata of said shale and injecting into said holes, under pressure, a mixture of a condensation product of an ethylenically unsaturated diba ic ac d with a dihydric alcohol. styrene and an organic peroxide curing catalyst and allowing raid mixture to cure.

6. A method of reinforcing the roof of a subterranean cavity which is below a layer of shale which comprises drilling a series of spaced holes upwardly into said shale in a direction transverse to the direction of the strata cf said shale and injecting into said holes, under pressure, a mixture of a condensation product of malcic anhydride and 1,2-propylene glycol, styrene and bcnzoyl peroxide as a curing catalyst and allowing said mixture to cure.

7. The method of claim 6 wherein said holes are approximately /2" in diameter and six feet apart and wherein said mixture is injected into said holes at a pressur: of about 600 pounds psi.

8. A method of stabilizing underground rock formations which form mine roofs which comprises: drilling a hole into a rock formation having zones of weakness and which is subject to failure in tension as well as shear, injecting under pressure into said hole and through said hole into the rock formation a formation adhesive rezin which is liquid and self-curing at ambient temperatures,

and which is selected from the group consisting of solutions of linear polyesters in liquid monomeric unsaturated polymerizable compounds containing an alphabets ethylenie iinkage, said solutions also containing a peroxide type catalyst and a cobalt promoter, whereby said resin flows into and filis said zones of weakness and cures in position, thereby adhesively uniting said formation at the zones of weakness, and stabilizing said rock formation against roof falls.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 8. A METHOD OF STABILIZING UNDERGROUND ROCK FORMATIONS WHICH FORM MINE ROOFS WHICH COMPRISES: DRILLING A HOLE INTO A ROCK FORMATION HAVING ZONES OF WEAKNESS AND WHICH IS SUBJECT TO FAILURE IN TENSION AS WELL AS SHEAR, INJECTING UNDER PRESSURE INTO SAID HOLE AND THROUGH SAID HOLE INTO THE ROCK FORMATION A FORMATION ADHESIVE RESIN WHICH IS LIQUID AND SELF-CURING AT AMBIENT TEMPERATURES, AND WHICH IS SELECTED FROM THE GROUP CONSISTING OF SOLUTIONS OF LINEAR POLYESTERS IN LIQUID MONOMERIC UNSATURATED POLYMERIZABLE COMPOUNDS CONTAINING AN ALPHA-BETA ETHYLENIC LINKAGE, SAID SOLUTIONS ALSO CONTAINING A PEROXIDE TYPE CATALYST AND A COBALT PROMOTER, WHEREBY SAID RESIN FLOWS INTO AND FILLS SAID ZONES OF WEAKNESS AND CURES IN POSITION, THEREBY ADHESIVELY UNITING SAID FORMATION AT THE ZONES OF WEAKNESS, AND STABILIZING SAID ROCK FORMATION AGAINST ROOF FALLS.