Method of anchoring a bolt in a hole

Abstract

 ® A grouting composition for anchoring a reinforcing member in a hole is delivered into the hole in uncartridged, unmixed form. In the hole the reactive components of the grout are present in stable, minimally interpenetrated adjacent columns (3, 4) of fluent material adapted to remain in position in a vertical, overhead hole. When convenient, the reinforcing member is inserted into the columns of material and rotated, whereby the mixed material hardens. The stability of the grout after delivery to the hole frees the user from tight time constraints on the placement of the reinforcing member therein.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a method of anchoring a reinforcing member in a hole, e.g., a rock bolt in a hole in a mine roof, and, more particularly, to a method wherein a grouting composition is introduced into a hole in uncartridged form and allowed to harden around a bolt subsequently embedded therein.

2. Description of the Prior Art

[0002] The types of bolt systems that have been used for mine roof support include tensioned mechanical steel bolts and resin-anchored bolts. In the latter system, a cured resin is used to anchor the bolt to the surrounding strata, preferably over the entire length of the bolt. Cartridges containing a polymerizable resin formulation and, separated therefrom, a catalyst which catalyzes the curing of the resin are introduced into a hole, and are penetrated and ruptured by the bolt, whereupon the package contents are mixed by rotation of the bolt. The resin hardens around the bolt so as to anchor it in place. The use of inorganic cements to anchor rock bolts, e.g., as described in U.S. Patent 4,126,005, also has been proposed. Cement grouts are less expensive than resin grouts while still providing the advantages of a grouted bolt.

[0003] In an effort to eliminate the cost of packaging the grout components, whether they be resin/catalyst or cement/water components, grout pumping or injection techniques have been investigated. In one method, described in U.S. Patents 3,861,155 and 3,930,639, two components of a curable resin system are premixed and then injected into a hole together with a flexible glass roving and a metal tube which supports the roving while it is fed into the hole and also provides venting. The roving and tube are then cut off and left in the hole. Some of the resin mixture extends out of the hole, forming a hardened plug which is cut off and inserted into another hole as a precursor. This technique requires pumping the two components of the resin system through a mixer and into a bolting head assembly, which is moved into contact with the mine roof. The hardening time of the mixture has to be long enough, and the pumping rate high enough, that the mixture does not harden in the bolting head assembly, thereby precluding its delivery into the hole in the mine roof, or in the hole, preventing bolt insertion. In any case, the apparatus may be rendered nonfunctional owing to the hardening of the mixture therein as a result of a temporary failure of some part or the accumulation of residual mixture which has escaped the purging operation.

[0004] The U.S. Bureau of Mines has described the injection of a mixed slurry into a hole, followed by insertion of a bolt before the setting of the slurry (Simpson, R.E., et al., Bureau of Mines Report of Investigations 8494, Inorganic Cement for Mine Roof-Bolt Grouting, 1980). This system requires a machine that contains a cylindrical mixing-extruding chamber from which the slurry is extruded into the bolt hole through a hose. The hose and cylinder, being filled with reactive material, are susceptible of becoming clogged with prematurely hardened grout, which is difficult to remove.

[0005] According to U.S. Patent 3,283,513, a plastic, settable, form-retaining material, e.g., a mixture of an epoxy or polyester resin, a hardening agent, and a solid filler, is formed in a cylindrical mixing vessel and transferred to an open-ended tube having one end seated in an annular transfer piston slidably mounted in the mixing vessel. The tube contains a free-sliding imperforate piston which moves in advance of the plastic material as it is forced to flow through the tube by the pressure exerted on the annular piston when downward pressure is applied to the tube. After all of the material has been transferred to the tube, the latter is removed from the mixing vessel and annular piston, and inserted into a borehole, open end first. The tube is withdrawn while pressure is applied to the free-sliding piston, whereby the plastic material is extruded into the hole. After removal of the tube from the hole, the rockbolt is inserted in the column of plastic material. The required assemblage of mixing vessel, transfer tube, and pistons, and the disengagement of the transfer tube from the mixing vessel, prior to the introduction of the filled tube in the hole are procedures which can result in protracted operations for the installation of bolts in numerous holes in a mine roof. In addition to the costs associated with the slow installation method, the technique involves the ever-present risk that the grout may harden prematurely and prevent bolt insertion, or at least make it difficult. In any case, the bolt must be installed immediately after the grout or mortar has been introduced, so that it is not feasible with this method to fill a large number of holes with the grout first and subsequently to introduce the bolts, a more efficient procedure.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method of anchoring a reinforcing member in a hole comprising

(a) delivering into the hole, through separate feeding conduits, e.g., separate hoses or the separate chambers of a multi-chambered hose, multiple, and usually two, uncartridged, discrete masses of fluent material at least one of which is of different composition from another, these masses, as fully delivered, being in the form of stable, minimally interpenetrated adjacent columns having sufficient viscosity, or being adapted by some other means, to remain in position in a vertical, overhead hole;

(b) inserting a reinforcing member, e.g., a bolt, into the adjacent columns, whereby the fluent material therein is forced into an annulus formed between the reinforcing member and the wall of the hole; and

(c) rotating the reinforcing member whereby the resultant mixing of the fluent material in the annulus causes it to harden as a result of a reaction between at least two of the masses with one another, or the activation of at least one by another, thereby anchoring the reinforcing member.

[0007] Also provided by this invention is an uncartridged grout, in position in a hole and ready to receive, and be mixed by, a reinforcing member, which is to be anchored in the hole by the hardening of the mixed grout. In the hole the grout of the invention is in the form of multiple, and usually two, stable, minimally interpenetrated adjacent columns of fluent material at least one of which is of different composition from another, which columns have sufficient viscosity, or are adapted by some other means, to remain in position in a vertical, overhead hole, and at least two of the columns, when the columns are mixed with one another, being reactive with one another, or activated one by another.

[0008] The present method and product offer the economic advantage of uncartridged grout systems while at the same time overcoming the disadvantages of previous pumped systems wherein rapid-setting resin mixtures were introduced into holes. The present uncartridged grout is stable after delivery to the hole and consequently places no tight time constraints on the placement of the bolt therein. Thus, in a preferred method of the invention, the multi-columnar grout is placed in a group of holes, and after all of the holes have been loaded, the bolts are installed therein. This is a more efficient procedure than the completion of one hole at a time.

BRIEF DESCRIPTION OF THE DRAWING

[0009] In the accompanying drawing, which illustrates specific embodiments of the bolt-anchoring method and grout of the invention,

FIG. 1 is a schematic representation of the step of delivering two masses of fluent material into a hole through a dual-chambered filling hose;

FIG. 1A is a section of the filling hose taken through line A-A of FIG. 1;

FIG. 2 is a schematic representation of a bicolumnar grout of the invention after having been fully delivered into a hole by the step depicted in FIG. 1; and

FIG. 3 is a schematic representation of the grout shown in FIG. 2 after a rock bolt has been inserted and rotated therein according to the method of the invention.

DETAILED DESCRIPTION

[0010] In the method of the invention, the reactive components of a rock bolt grout, e.g., a fluent composition containing a crosslinkable polymer and a fluent composition containing a catalyst which initiates the crosslinking polymerization of the polymer, are delivered into a hole as separate, unmixed masses, being deposited therein in a manner such that interpenetration or mixing of the masses is minimized. Mixing on a macro, or gross, scale is avoided, thereby keeping the area of the interface between the two masses to a minimum. This is accomplished by pumping or extruding the fluent materials (which preferably are pasty and thick enough to be retained in the hole even when the latter is vertical and downward-directed) into the hole in a substantially laminar flow configuration, produced by the proper selection of their flow rates and viscosities. Although a small amount of mixing may occur to cause a shallow interpenetration of adjacent columns of fluent material, the interface is essentially straight on a macro scale, and this small interfacial area gives stability to the uncartridged grout so that a widespread hardening reaction does not occur between the reactive components that might make subsequent bolt penetration difficult or impossible. A self-terminating reaction confined to this interface, such as is stated to occur in the cartridged products of U.S. Patent 3,731,791, does not destroy the stability of the present grout inasmuch as the depth of interpenetration is shallow because of the lack of mixing, and any reaction that occurs is confined to this zone of interpenetration.

[0011] The present invention now offers the user of grouted rock bolts the economic advantage of a pumped grout, and the stability advantage of a cartridged grout before bolt installation. Because the grout is unmixed before bolt insertion, there is no risk of equipment breakdown due to the hardening of grout therein, and the grout pumping and bolt insertion operations can be carried out without the threat that a delay could result in the grout's becoming hardened before the bolt has been inserted.

[0012] Furthermore, as was stated above, it now becomes possible to install a number of bolts in rapid succession in a number of "prepared" holes, i.e., holes containing the stable, multi-columnar grout.

[0013] Referring to FIG. 1, 1 is a hole in a solid formation such as a mine roof 2, which is to be reinforced by means of grouted rock bolts. The two reactive components of the grout, e.g., a fluent material containing a crosslinkable polymer and a fluent material containing a catalyst which initiates the crosslinking polymerization of the polymer, are shown being pumped into hole 1 as a pair of discrete masses 3 and 4 which, in the hole, are in contact with one another along interface 5. Masses 3 and 4 are pumped through a pair of filling hoses 6 and 7, respectively, which are united in their nozzle portions so as to become the dual chambers of a single hose. Thus, masses 3 and 4 remain separated until they emerge from the leading ends of chambers 6 and 7. Ring 8, made of a material such as poly(tetrafluoroethylene), is a guide member which keeps the hose centered in hole 1. As masses 3 and 4 emerge from dual chambers 6 and 7, the hose is retracted, and masses 3 and 4 become two columns, best seen in FIG. 2. When the columns are of the required length, the filling hose is removed from hole 1. In the case shown, the fluent materials which form adjacent columns 3 and 4 are sufficiently viscous that they remain in position in hole 1, a vertical, overhead hole, without mechanical assistance. Suitable viscosities generally are in the range of about from 10,000 to 1,000,000 centipoises. If necessary, however, retention in hole I can be accomplished by end-capping the grout with a retaining means which either can be penetrated by the bolt or removed when the bolt is to be inserted.

[0014] In FIG. 3, a rock bolt 9 has been pushed upward into the hole shown in FIG. 2 and rotated to mix masses 3 and 4. After mixing, the reactive components rapidly react to form a hardened grout 10, whereby bolt 9 is anchored to the surrounding rock.

[0015] In the drawing, interface 5 is shown as a line having some shallow interpenetrations between discrete masses 3 and 4. Such a small degree of interpenetration might result as the hose is retracted, for example.

[0016] The columns of fluent material which form the uncartridged grout of the invention comprise at least two separate components of a bolt-grouting composition, i.e., one of the columns contains a first reactive component and another column a component which reacts with, or activates, the first reactive component. As a matter of convenience, all of the ingredients of the grout will be present in the two inter-reactive columns, although additional columns may be used to introduce other ingredients if desired.

[0017] In one embodiment of the invention, the reactive components of the grout, e.g., a resin component and a catalyst component, are divided into multiple columns, e.g., two or more resin columns and/or two or more catalyst columns. This division of the components into multiple columnar units affords greater efficiency in obtaining a homogeneously mixed, and therefore more completely reacted, grout.

[0018] The present invention can be used with any reactive grouting system which can be provided in an extrudable or pumpable form. Typical of such systems are the two-component resin compositions described in U.S. Patents 3,324,662, 3,324,663, and 3,302,410, all granted to D. C. McLean, and the improved resin/catalyst system described in U.S. Patent 4,280,943, granted to J. R. Bivens et al. Inorganic systems such as the cement/water system described in U.S. Patent 4,126,005, issued to D. L. Coursen, and the phosphate system described in U.S. Patent 4,174,227, issued to E. A. Tomic also are suitable for use in the present method. The selected system will be formulated so as to provide the required ratios of components in the column diameters to be employed.

Example

[0019] Grouting compositions having a resin component (A) and a catalyst component (B) in A/B percentage ratios of 40/60 to 60/40 were prepared as described in Example 2 of U.S. Patent 4,280,943. Components (A) and (B) were pumped into 1.2-meter-and 0.6-meter-long, 2.5-cm-diameter steel pipes (simulated boreholes), whereby two adjacent columns of about equal diameter were formed therein, as shown in FIG. 2. Bolts were inserted into the grouts at time intervals varying from 5 minutes to 48 hours after pumping. All bolts were inserted, and grouts mixed, with no difficulty, and pull strengths were satisfactory. In approximately 20 bolt insertion tests using a 13 kN thrust, the insertion times were in the range of 7 to 10 seconds. Approximately 10 measurements were made of pull strength in the 0.6-meter pipes by applying a pull force to the bolt, and determining the load at which the bolt pulled out completely. The pull strengths ranged from 125 to 151 kN.

Claims

1. A method of anchoring a reinforcing member in a hole comprising

(a) delivering into said hole, through separate feeding conduits, multiple uncartridged, discrete masses of fluent material at least one of which is of different composition from another, said masses, as fully delivered, being in the form of stable, minimally interpenetrated adjacent columns sufficiently viscous, or otherwise adapted, to remain in position in a vertical, overhead hole;

(b) inserting a reinforcing member into said adjacent columns, whereby said fluent material therein is forced into an annulus formed between said reinforcing member and the wall of said hole; and

(c) rotating said reinforcing member whereby the resultant mixing of the fluent material in said annulus causes it to harden as a result of a reaction between at least two of said masses with one another, or the activation of at least one by another, thereby anchoring said reinforcing member.

2. A method of Claim 1 wherein said columns of fluent material are adapted to remain in position in a vertical, overhead hole by virtue of their viscosity.

3. A method of Claim 1 wherein said masses of fluent material are delivered to each of a group of holes, and, at some convenient time thereafter, reinforcing members are introduced into the columns of fluent material in the group of holes and rotated.

4. A method of Claim 1 wherein said masses of fluent material are delivered into the hole by inserting multiple filling hoses, or a multi-chambered filling hose, into the hole for practically the entire length thereof, and pumping a preselected volume of fluent material through each hose or chamber whereby the masses of fluent material emerge from the forward ends of the filling hoses or chambers and are deposited in the hole adjacent one another with minimal interpenetration, said hose(s) retracting as the masses emerge from the ends of said hoses or chambers; and said hose(s) are removed from the hole leaving said masses in the form of adjacent columns.

5. In a hole, an uncartridged grout in the form of multiple stable, minimally interpenetrated adjacent columns of fluent material of different composition and sufficiently viscous, or otherwise adapted, to remain in position in a vertical, overhead hole, the compositions of at least two of said columns, when the columns are mixed with one another, being reactive with one another, or activated one by another, to form a hardened product.

6. The grout of Claim 5 wherein said columns of fluent material are adapted to remain in position in a vertical, overhead hole by virtue of their viscosity.

7. The grout of Claim 5 wherein one of said columns contains a crosslinkable unsaturated polyester resin formulation, and the other a peroxide catalyst.

8. In a mine roof, a plurality of holes containing the grout of Claim 5.

9. The grout of Claim 5 wherein multiple columns of a first composition are interspersed with multiple columns of a second composition reactive with, or activated by, the first.

Drawing