WO2011079829A2

WO2011079829A2 - Expansion rock anchor

Info

Publication number: WO2011079829A2
Application number: PCT/CZ2010/000133
Authority: WO
Inventors: Ujka ZDENĚK
Original assignee: Geofinal, S.R.O.
Priority date: 2009-12-28
Filing date: 2010-12-21
Publication date: 2011-07-07
Also published as: CZ2009885A3; CZ305105B6; WO2011079829A3

Abstract

An expansion rock anchor comprise an expansion body of a circular diameter and having at least two pressed section in the form of deep groves on the entire lenght, the said expansion body being closed at one end by a filling end piece (7) having a channel for supplying a hydraulic medium in interior to the expansion body and at the other end by a closing end piece (8) and further, the said expansion body being installed in a friction casing; wherein the friction casing is formed by at least two tubular sleeves (3, 4) inserted one into the other, the said tubular sleeves having a longitudinal cutting (5) or a longitudinal burstable seam (6) and further the said tubular sleeves being firmly attached to the filling endpiece and the closing end piece by a surface connection.

Description

Expansion Rock Anchor

Field of the Invention

The invention relates to an expansion rock anchor which is used for securing and consolidating rock as well as for its strengthening by grouting when building underground constructions, especially in the construction of tunnels, mine drifts and chambers, in the stabilisation of rock walls, slopes and consolidation of dam bodies and other technological applications in coal mining and ore mining.

Prior State of the Art

Different types of anchors are used today for' securing and consolidating rock when constructing mine drifts, tunnels and chambers, stabilising rock walls, slopes* consolidating dam bodies, etc. One specific group of rock anchors are hydraulically expandable anchors, the so-called expansion anchors, that are driven into boreholes iri the rock to secure the rock cohesion by exerting frictional force of the expansion anchor body on the borehole wall. The most popular of these are the expansion anchors of Swellex and Boltex types. These two well-known rock anchors share one particular feature, which is the technical solution of their expansion body. The body lias the form of a thin- walled pipe of a circular cross-section made of high ductility steel, where the circular cross-section is deformed in several lines usually in the form of deep grooves. The expansion body has cylindrical end pieces on both sides > that is a filling end piece for the supply of a high-pressure medium into the anchor expansion body and a closing end piece which is often designed as a flow coupling for the connection of several anchors into a string or fitted with an opening with a burstable or flow element for the grouting of the rock to be consolidated. Both the end pieces are fitted on the cross-sections of the expansion body reduced by pressing and they are welded to the expansion body in the interior cylindrical space of the expansion body, thus creating a pressure vessel of it. The anchoring effect of these anchors is achieved by the frictional force exerted on the circumferential surface of the expansion body, i.e. on the non-deformed surface of the thin- walled pipe. The frictional force is generated by the residual prestress of the expansion body after the partial restraightening of the deformed, originally circular cross-section. The restratghtening of the deformed circular cross-section in the rock borehole causes the anchoring of the frictional anchor in its entire length. The reliability and stability of the anchoring of these known anchors also depends on the hardness of the rock to be consolidated or secured by anchoring. In case of hard rock, where the expansion body can achieve the required frictional force, the anchors of this type are capable of maximum transmission of tensile force which results in full utilisation of their rated load. Nevertheless, the frictional forces required for proper and stable anchorage of frictional anchors cannot be achieved in soft rock due to unstable and yielding contact of the frictional surface of the anchor expansion body with the borehole wail surface. Apart from that, these anchors do not cover the entire range of tolerances in the rock borehole diameter occurring in practice. This results in a significant decrease in the anchor rated load and sheai strength required in case of potential shift of laminar rock layers. This problem is solved quite satisfactorily by a rock expansion anchor with the expansion body having a friction casing with one or two longitudinal expansible joints. The friction casing is either welded to the filling end piece, as it is documented for instance by the utility design document CZ 8988, or it is used as an additional anchor element into which the anchor expansion body is inserted, which is described, for instance, in the European patent documentation,

The disadvantage of all the currently known expansion anchors is the fact that meeting the requirements regarding their maximum tensile strength and shear strength depends on the strength of the steel of the anchor expansion body and the strength of the steel of its friction casing as Well as on the size of their cross-section areas. Nevertheless, the application of maximum values of these two variables is limited, mainly due to the following requirements. It is the availability of the equipment for the demanding production of the anchor expansion body, i.e. the capability of producing a cross-sectionally deformed pipe made of high strength and ductility steel and the use of high-pressure hydraulic medium necessary for achieving the maximum expansion of the anchor and its prestress in the borehole. The aforementioned expansion rock anchors are fastened in the borehole hydraulically by a pressure medium, usually water with the pressure of approx. 30 MPa Which requires absolute tightness in order to eliminate the high-pressure medium leakage when installing the anchor in the rock. Under these conditions, handling and, in particular, fastening expansion anchors in the rock boreholes and checking their anchoring poses significant hazard to operators. This hazard results from the current design and the way of fastening of the filling end piece. It has a cylindrical shape and it is welded to the deformed end of the expansion body with pressed groove sections and deformed into a smaller diameter. For this reason the weld in this area where the material structure is impaired by pressing is uncontrollable and unsatisfactory in view of the prerequisites for pressure vessels. The high-pressure medium is supplied to the expansion body through a channel drilled in radial direction in the filling end piece after the welding joint. This solution results in the fact that the filling head of the high-pressure equipment has the form of a cylindrical sleeve which has inconvenient rugged shape and high weight due to the design of the filling end piece and the pressure of the hydraulic medium. The way of filling the anchor expansion body through the radial channel is also disadvantageous. This design requires sealing of the filling head by two pieces of packing where unbalanced hydrostatic load cannot be excluded,. This can result, in case of the packing leakage after the radial channel and the packing overload before the radial channel, in the filling head being ejected from the filling end piece towards the operators which poses serious safety hazard for the operators. The current design of the filling; head of cylindrical shape with radial filling channel also causes significant problems with, the check of strength and the check of the anchoring of the expansion anchor in the rock. This is done by means of a collet which is attached to the cylindrical surface of the filling end piece with which it mutually clamps by means of the collet clamp bushing of high conicalness ensuring the clamp self-locking. The collet must then be released by blows on the collet which often results in its damage. Another problem is the maintenance of high cleanliness of conical surfaces of the clamp bushing in the environment of building underground constructions which is vital for reliable checks of strength and quality of the anchorage of the expansion anchors in the rock. An undisputed drawback of current expansion anchors is the fact that they are exposed to combined stress when installed. This undesirable axial force and transverse stress results from the asymmetry of the expansion body cross-section and that of his friction casing. This stress results in uneven distribution of stress on their circumference and, subsequently, to the reduced load-bearing capacity of the expansion anchor. Therefore, the aim of this invention is to make an expansion rock anchor with a thin-walled expansion body and a thin-walled friction casing jacket enabling the required anchor expansion while maintaining its maximum centricity and significantly lower hydraulic medium pressure. Subsequently, the aim of the invention is also to enable the manufacture of the anchors of different rated load and shear strength according to the character of the rock mass for which the anchor is intended. Nature. of the Invention

The aforementioned disadvantages are eliminated by the expansion rock anchor according to this invention. Its design comprises the already known expansion body of circular cross- section. This cross-section is in the entire length of the expansion body formed centrically with at least two pressed sections in the form of deep grooves. The expansion body is closed by a filling end piece with a filling opening which leads into its interior area at one end and by a closing end piece at the other. In this design the expansion body is inserted into the friction casing with the longitudinal expansible joint, the friction casing being welded to the expansion body filling end piece. The new solution according to this invention is based on the fact that the friction casing is formed by at least two tubular sleeves with a longitudinal expansible, joint or longitudinal burstable seam inserted one into the other. The tubular sleeves are firmly connected to the filling end piece and the closing end piece by a surface connection so that the positions of the joints or seams are distributed along the circumference of the expansion body. The design of the expansion rock anchor according to this invention is also based on the following variants: The filling end piece and the closing and piece are fitted with threaded couplings at their external ends used for the coririection of all kinds of assembly, measuring and technological equipment on the filling end piece and for the connection of a number of expansion rock anchors into a string on the closing end piece. The filling end piece has an axial supply channel while the closing end piece has a flow opening which is blinded with a plug or a burstable membrane. The filling end piece is equipped with a check valve. The surface of the friction casing tubular sleeves is roughened or galvanised. The pressed sections of the expansion body are made in the form of a helix. An advantage of the expansion rock anchor according to this invention is its versatile use, i.e. it can only be used for direct stabilisation of a rock mass without grouting, or it can also be used, along with this function, for grouting purposes or for grouting itself. A significant advantage is also its design making use of a thin-walled expansion body and its thin-walled jacket enabling the required centric expansion of the anchor at the filling pressure significantly lower than today, decreased up to the value of 10 MPa. The design of the expansion rock anchor provides for the manufacture of these anchors of different rated load and shear strength according to the character of the rock mass for which the anchor is intended. All these advantages will have a significantly positive impact on the efficiency of the consolidation and stabilization of the rock mass and safety at work. Overview of figures included in the drawing

The attached drawing represents a schematic depiction of an example design of the expansion rock anchor according to this invention with six pressed sections in the centric circular cross- section of its expansion body that is fitted with a friction casing made of two tubular sleeves. Fig. 1 shows the anchor in the front view and longitudinal section while Fig. 2 represents its cross section.

Examples of the Invention

The expansion rock anchor comprises an expansion body 1 made of a thin-walled pipe of a circular cross-section in which six pressed sections 17 are formed by rolling centrically and in the: entire length of the expansion body 1_, as it is shown in Fig. 2. At one of its ends - the front end - the expansion body 1 is closed by the filling end piece 7. The filling end piece is then fitted on the through neck 16 of the expansion body 1_ which is formed on it by forge welding of its end into a smaller diameter and the tilling end piece 7 is then firmly fitted to the neck Id by soldering. In the filling end piece 7 a supply channel 12 of the high-pressure hydraulic medium, water in this case, is made by its axial drilling., The axial supply channel 12 is connected to the interior of the expansion body 1 which is at its other end - back end - designed as the front end, closed by a closing end piece 8 with the flbw opening 11 blinded with a plug 13. The expansion body 1. is situated in the friction casing 2 which consists of two tubular sleeves 3 and 4 inserted one into the: other, These are extensible into a bigger diameter due to the longitudinal cutting creating an expandable joint 5. The friction casing 2, or its tubular sleeves 3 and 4, are welded to the filling end piece 7 and the closing end piece 8 by means of a surface connection 15, a welded j oint in this case, so that their expandable joints 5 are situated in the opposed position on the expansion body 1. Instead of the expandable joint 5, longitudinal burstable seams 6 may be formed on the tubular sleeves 3 and 4 by pressing, thus thinning the walls of the tubular sleeves 3 and 4 to the maximum extent. The filling end piece 7 and the closing end piece 8 are fitted on their external ends with the threaded couplings 10 used, in case of the filling end piece 7, mainly for the connection of the anchor support (not depicted) and the pressurising equipment of the expansion body 1 by pressurised water. The coupling 10 is also used for the connection of the equipment checking the fastening of the anchor in the borehole, for fitting some required technological equipment, for fitting hitches, etc. As the closing end piece 8 is concerned, the threaded coupling 10 is used for the connection of another expansion anchor making part of a string. In this case, the plug 13. will be removed from the flow opening 11. of the closing end piece 8. The expansion rock anchor in the described design is used as a friction reinforcing rock mass pin. Apart from this function, it can also be used simultaneously or separately for the grouting of the rock borehole area. For this purpose the flow opening11. of the closing end piece 8 will be closed by a burstable membrane 14, the pressure of the grouting material causing the expansion of the expansion body 1. A check valve 9 may be installed in the supply channel 12 of the filling end piece 7. It is used for locking the high-pressure medium in the expansion body 1 and, in this way, maintaining the prestress of the expansion anchor fitted in the borehole and increasing the resistance against its loosening when loaded. For this purpose the surface of the tubular sleeves 3, 4 of the friction casing 2 can be roughened and also galvanised to ensure its protection against corrosion. The pressed sections 17 of the expansion body 1 can be made in the form of a helix ih order to increase the frictional effect when in contact with the friction casing 2.

industrial Application

The expansion rock anchor according to. this invention can be used for the consolidation of the compactness of the rock mass and for its grouting by consolidation material in mining, construction of tunnels and ducts, as well as in building industry.

List of reference characters

1- expansion body

2- friction casing

3- pipe sleeve

4- pipe sleeve

5- expandable joint

6- burstable seam

7- filling end piece

8- closing end piece

9- check valve

10- threaded coupling

11- flow opening

12- axial supply channel

13- plug

14 - burstable membrane

15- surface connection

16- neck

17- pressed section

Claims

PATENT CLAIMS

I . An expansion rock anchor comprising an expansion body of a circular diameter formed centrically in the entire length of the expansion body with at least two pressed sections in the form of deep grooves which is closed by a filling end piece with a hydraulic. medium supply channel connected to the interior of the expansion body at one end and a closing end piece on the other, where the expansion body is installed in a friction casing with a longitudinal expandable joint which is welded to a filling end piece, characterised in that the friction casing (2) of the expansion body (1) is formed by at least two tubular, sleeves (3, 4), inserted one into the other, with a longitudinal expandable joint (5) or with a longitudinal burstable seam (6) the position of which is distributed along the circumference of the expansion body (1), with the tubular sleeves (3, 4) with joints (5) or seams (6) being firmly attached at these positions to the filling end piece (7) and the closing end piece (8) by a surface connection (15).

2. An expansion rock anchor according to Claim 1, characterised in that the filling end piece (7) and the. closing end piece (8) have a threaded coupling (10) on the outer side, where the filling end piece (7) has an axial supply channel (12) and the closing end piece (8) has a flow opening (11 ) blinded with a plug ( 13 ) or a burstable membrane (14).

3. An expansion rock anchor according to Claim 1 or Claims 1 and 2, characterised in that the filling end piece (7) is equipped with a check valve (9).

4. An expansion rock anchor according to Claim 1 or Claims 1 to 3, characterised in that the surface of the tubular sleeves (3, 4) of the friction casing (2) is roughened or galvanized;

5. An expansion rock anchor according to Claim 1 or Claims 1 to 4, characterised in that the pressed sections (17) in the expansion body (1) are made in the form of a helix.