GB2199105A

GB2199105A - Yieldable anchor plate system for rock bolts

Info

Publication number: GB2199105A
Application number: GB08728048A
Authority: GB
Inventors: Peter Stephan
Original assignee: Bergwerksverband GmbH
Current assignee: Bergwerksverband GmbH
Priority date: 1986-12-09
Filing date: 1987-12-01
Publication date: 1988-06-29
Anticipated expiration: 2007-12-01
Also published as: GB2199105B; ZA879204B; DE3641951C1; GB8728048D0

Abstract

A rock bolt used for securing lagging or lagging reinforcements in mining and tunnel construction, comprises a bolt (1) fixed by means of adhesive in a drill hole and projecting from the drill hole for engagement by a convex anchor plate (5) for clamping the lagging, and by a base plate (8) engaged by a nut (7) and fixed to a yieldable stirrup member (9) which engages a washer (10), the base plate (8) being rectangular so that it can pass through a rectangular opening (6) in the convex anchor plate (5) for rotation through 90 DEG into holding engagement. Increased tension in the bolt (1) due rock movement is accommodated by yielding of the stirrup member (9). <IMAGE>

Description

yieldable anchor plate system for rock bolts The invention relates to a rock bolt for securing galleries and openings in mining and tunnel construction, in particular as compound lagging roof bolting, the bolt bar of which can be secured at least in the drill hole bottom by means of an adhesive and the end of which projecting out of the drill hole opening can be braced with respect to the rock by means of an anchor plate at least partially clamping the lagging and a screw means.

Rock bolts with anchor plates of different form in conjunction with lagging mats are used mainly in coal mining, in particular for supporting the lining. The plates have square, circular, planar or also dome-shaped forms of different dimensions and material qualities. The dome-shaped plates are each arranged with the concave side towards the rock.

The plates provided with corresponding bores are screwed solely with the aid of nuts to the air-side bolt end until they - clamping the lagging therebetween - come to bear against the frequently irregular drift walls. Since hemispherical equalizing elements for correcting an irregularly angled assembly situation are used only in very rare cases, shortly after setting the bolt bending of the bolt end projecting from the drill hole frequently occurs and thus also undesired notch loads in this bolt region. Moreover, anchor plates installed askew lead to a high degree to edge crushing in the lagging and thus considerably reduce the loadbearing capacity of the latter.

A further disadvantage of the rock bolts provided with conventional anchor plates resides in the force transmission of the bolt tensile force to the rock and to the lagging because the collar nuts ensuring the bracing are pulled even by small forces through the anchor plate. In the overlapping region of the lagging mats when using dome-shaped or concave anchor plates firstly small circular anchor plates are mounted with a nut over which thereafter for holding the overlapping lagging mat a larger concave anchor plate is placed. However, this type of double fixing prevents the actual yieldability of the concave or dome-shaped anchor plate.

Compared therewith the problem underlying the invention is to provide a rock bolt for securing galleries, drifts and openings in mining and tunnel construction, in particular for joining lagging networks or mats, which avoids the disadvantages referred to, is simple to assemble, permits additionally assembly of lagging reinforcing elements and ensures optimum force transmission.

This problem is solved according to the invention in that the anchor plate consists of a shell-shaped plate provided with a rectangular cutout, surrounding the bolt bar end and directed with the convex side toward the rock in conjunction with a rectangular base plate which is disposed above the screw means and which is connected to a stirrup member engaging through the cutout and is formed as yielding element, the abutment of which is formed by a spacer washer.

A particular advantage of the yieldable anchor plate system resides in that the shell-shaped plate can be placed by means of the cutout over the base plate formed in conjunction with the stirrup member as yielding element onto the end of the braced bolt and can be secured in form-locking manner by rotation through 900. When the tensile force in the bolt increases, due for example to increasing cleavage or fracturing in the gallery wall, the yielding element initially acts in such a manner that the base plate undergoes a sagging and the stirrup arrangement trapezoidal in crosssection undergoes a bending up towards the sides, i.e.

into the shell-shaped plate. The stirrup member is thus pressed apart until it bears completely within the shellshaped plate and presses the latter with greater force against the rock. When the force taken up by such a rock anchor connected to a yieldable anchor plate system increases a yield travel of about 100 mm is available, the yielding of the entire structure being governed by the material quality and the material thickness of the individual components.

Since in advantageous further development of the invention additional lagging reinforcements in the form of circular rods or cables can be pulled through the plate system, it is important for the opening of the stirrup member to be directed after assembly in the peripheral direction of the drift. On assembly of an adjoining lagging mat the construction of the anchor plate system enables said mat to be pushed over the stirrup member already fitted with the base plate before for example lagging reinforcements and the shell-shaped plate are installed. To facilitate assembly of lagging mats or meshes welds between longitudinal and transverse wires in the edge regions of the lagging mats or meshes should be dispensed with, this enabling simultaneously overloading of individual wires to be avoided.

It is further found particularly advantageous within the scope of the invent'ion for the plate -to be possibly provided with burls on the surface convex towards the rock, preventing a slipping down of the flexible mat or mesh regions.

An example of embodiment of the invention is illustrated in the drawings and will be explained in detail hereinafter.

In the drawings: Fig. 1 is a section through a rock anchor equipped with the anchor plate system according to the invention in the peripheral direction of the drift, Fig. 2 is a plan view of the anchor plate system seen from the rock, Fig. 3 is a section through the anchor plate system accord ing to the invention transversely of the peripheral direction and Fig. 4 is a partial representation of the shell-shaped anchor plate.

As apparent from the section shown in Fig. 1, on the bolt bar 1 introduced within a drill hole in the rock 3, on the end 2 thereof, one type of anchor plate system 4 is fitted which consists of a shell-shaped plate 5 provided with a rectangular cutout 6, surrounding the rock bolt end 2 and facing the rock 3 with the convex side, in conjunction with a rectangular base plate 8 disposed beneath the screw means 7. The base plate 8 is provided with a stirrup member which projects through the cutout 6 and together with said member forms a yielding element, the abutment for the yielding element being constituted by a rotatable spacer washer or disc 10. As apparent from the plan view of the anchor plate system according to Fig. 2, the cutout 6 within the shellshaped or dish-shaped plate 5 is made slightly larger than the base plate 8. The stirrup member 9 is fixedly attached, for example by welding, to the narrow sides 12 of the base plate 8 and as apparent from Fig. 1 is made trapezoidal.

The stirrup member 9 bears with the shorter side 13 on the rotatable spacer disc 10. In the assembly of the entire anchor plate 4 firstly the yielding element consisting of the stirrup member 9 and the base plate 8 in conjunction with the spacer washer 10 is pushed onto the bolt end and tightened by means of the nut 7. Between the base plate 8 and nut 7 a washer 11 may be inserted. Thereafter the plate 5 is pushed by way of the rectangular cutout 6 over the base plate 8 and turned through 900 so that it is firmly fitted in form-locking manner on the stirrup 9 or the inclined extending outer sides thereof. The plate 5 is directed with its convex surface towards the rock 3. To facilitate turning of the plate 5 on fitting or after fitting onto the yielding element said plate 5 is provided at the outer edge with assembly aids 18, for example notches, permitting the use of a hand hammer. To prevent slipping down of the flexible lagging or mat regions, in particular in the overlapping area, the surface of the plates 5 facing the rock may additionally be provided with burls 17.

Claims

Yieldable anchor plate system for rock bolts

Claims: 1. Rock bolt for securing galleries and openings in mining and tunnel construction, in particular as compound lagging roof bolting, the bolt bar of which can be secured at least in the drill hole bottom by means of an adhesive and the end of which projecting out of the drill hole opening can be braced with respect to the rock by means of an anchor plate at least partially clamping the lagging and a screw means, characterized in that the anchor plate (4) consists of a shell-shaped plate (5) provided with a rectangular cutout (6), surround ing the bolt bar end (2) and directed with the convex side toward the rock (3) in conjunction with a rectangu lar base plate (8) which is disposed above the screw means (7) and which is connected to a stirrup member (9) engaging through the cutout (6) and is formed as yield ing element, the abutment of which is formed by a spacer washer (10).
2. Rock bolt according to claim 1, characterized in that the cutout (6) within the shell-shaped plate (5) is made with slightly greater dimensions than the base plate (8).
3. Rock bolt according to claim 1, characterized in that the stirrup member (9) connected via the narrow sides (12) to the base plate (8) is made trapezoidal in longi tudinal section through the base plate (8) and the shorter of the parallel sides (13) of the trapezium bears on the spacer washer (10).
4. Rock bolt according to claim 1, characterized in that the shell-shaped plate (5) can be fitted by means of the cutout (6) over the base plate (8), formed as yield ing element in conjunction with the stirrup member (9), of the tensioned rock bolt (1) andean be fixed on the stirrup member (9) in form-locking manner by rotation through 900.
5. Rock bolt according to claim 1, characterized in that the cutout (6) within the plate (5) comprises at the narrow sides (14) a depth (15) such that an additional lagging reinforcement (16) consisting of circular rods or cables can be inserted extending through the cutout (6).
6. Rock bolt according to claim 1, characterized in that the plate (5) is provided with burls (17) on the convex surface directed towards the rock (3).
7. Rock bolt according to claim 4, characterized in that the outer edge of the shell-shaped plate (5) is provided with assembly aids (18), for example in the form of notches.
8. Rock bolt according to claim 1, characterized in that the yieldability of the yielding element can be defined by the choice of material and material thickness.
9. Rock bolt according to claims 1 and 4, characterized in that to compensate the inclined position of the shell shaped plate (5) a corresponding clearance is provided between the stirrup member cross-section and the cutout (6).