The invention relates to earth strata bolts or anchorages used, for example, in the stabilisation and reinforcement of earth strata such for example, as rock in quarrying, and for roof support in underground mines and tunnels for example. For convenience we will hereinafter and in the claims refer simply to "strata bolts".

Strata bolts according to this invention are primarily for use in competent strata but can be used in friable and unconsolidated stratas or ground.

More specifically they can be used in underground mines (coal and metalliferous), road and water tunnels, underground rock chambers, quarrying and for ground engineering such as stabilisation of slopes for example.

Reference will be made hereinafter and in the claims to "inner end" and "outer end" of a strata bolt and it is to be understood that these terms respectively mean "the leading end of the strata bolt in terms of the insertion of the latter into a drill, or otherwise formed, hole in the strata" and "the trailing end of the strata bolt in terms of such insertion" .

According to the present invention a strata bolt comprises an axially-split tube capable of peripheral expansion, and open at its outer end, and an expander slug for insertion into and passage along the tube to effect said peripheral expansion and effect a positive location between the bolt and the surrounding strata to provide a primary anchorage therebetween.

Preferably, the tube at its inner end is axially split at a plurality of angularly-spaced locations at

its inner -end;-aiid .is of -r duced inner cross-sectional area at its inner end whereby the primary anchorage due to the action of the expander slug is effected at the inner end of the strata bolt.

Preferably, the tube is fitted internally at its inner end with a tapered insert adapted to be acted upon by the expander slug which is of tapered configuration.

Preferably, the inner end of the tube is formed as a return bend and is peripherally inwardly compressed.

Preferably _r ----- ^' trie ^' -ι outser end of-; -the tube is outwardly flanged.

Preferably, a resilient indicator plate of dished construction is provided and is adapted to be slid onto the tube for location between the earth or rock strata and the outer end flanging, which tube is adapted to be flattened upon pre-tensioning of the strata bolt on its insertion into a hole in the strata to .provide a visual indication of correct aτ_cr_orage- ΌΪ 4:he; stra a÷lsol ,.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which;-

Fig. 1 is a longitudinal cross-sectional view of a preferred form of strata bolt with an anchorage slug aτ_ a pr ssure ^' sl g^ located ^■ within -the strata bolt;

Fig. 2 is a detail view of an alternative outer end locating configuration;

Fig. 3 is an end view of the inner end of the strata bolt;

Figs. 4 and 5 are respectively a fragmentary sectional view and a fragmentary perspective view of the outer end of the strata bolt with an associated

pre-tension and/or load indicator plate;

Fig. 6 is a perspective part-sectional view of an alternative form of strata bolt with associated indicator plate;

Fig. 7 is a sectional detail view of the inner end of the strata bolt of Fig. 6;

Figs. 8 and 8A are perspective views of alternative forms of slug;

Fig. 9 is a detail view of a modification of the slugs of Figs. 8 and 8A; and

Fig. 10 illustrates the sequence of fixing a strata bolt in position.

Referring firstly to Figs. 1 and 3, the strata bolt 20 comprises a metal, say a steel, tube 21 axially split along its whole length as indicated at 22. The tube 21 may be tack welded at one or more locations along the length of the split 22 or the split 22 may be of interrupted construction (any sequence of split, non-split). The bore 21A of the tube 21 is parallel from the outer end 21B to the inner end 21C.

The inner end 21C of the tube 21 has fitted therein a Morse taper insert 23 (No. 2 Morse for example), which is welded inside the tube 21 as indicated at 24. The inner end 21C of the tube 21 and the Morse taper insert 23 are, after welding of the latter in position, axially slit at four equi-angularly spaced locations 25 (see Fig. 3).

The inner end 21C of the strata bolt 20, therefore, due to the slits 25 is thus readily peripherally or circumferentially expandible.

The outer end 21B of the tube 21 is outwardly flanged as indicated at 27 by turning over the extremity of said outer end 21B as shown.

An alternative outer end construction (Fig. 2)

is provided by welding, as indicated at 28, -arσund the outer end a collar 29 which is externally screw-threaded as indicated at 30. Due to the provision of this collar 29 the tube 21, in this example is wider at its outer end 21B to facilitate entry of expander slugs referred to hereafter. The major length of the tube bore 21A after a short tapered length at the outer end is of parallel configuration.

Expander slugs are used with the strata bolt 20 and in Fig. 1 is shown an anchorage slug 31 and a pressure, slug, 32. -These slugs ^31, : 32 -are tapers- (for example No. 2 Morse) and differ in their cross-sectional area dimension, the pressure slug 32 having a greater cross-sectional area dimension than the anchorage slug 31.

A number of pressure slugs 32 of increasing cross-sectional area dimesnion may be provided. It is considered that three sizes of pressure slugs 32 will probably be sufficient _t eac .size .larger than the other -but this number is- ot ^' limitative.

The tapered expander slugs, whether anchorage or pressure, may alternatively be constructed in accordance with Figs. 8, 8A and 9.

The tapered expander slug 33 of Fig. 8 has circumfexentiall -spaced ..fins 3.4 extending its -full length while that of Fig. 8A has circumferentially- spaced fins 35 terminating at a bullet-shaped nose 36. The fins 34 and 35 may be indented or of toothed configuration as shown in Fig. 9.

It is to be noted that the outer surface of the -tube 21 or an area -of area-s- thereof maybe roughened, indented or fletched as indicated at 37 to improve anchoring of the strata bolt 20 to the earth strata or rock (see Figs. 6 and 10).

An indicator or "tell-tale" plate 39 (Figs. 4, 5 and 10) is provided for use with the strata bolt 20 when necessary. It will more often not be used than used.

The indicator plate 39 is a spring disc 40 of generally dished configuration with a central hole 41, and, in use, it is slid onto the tube 21 and is disposed between the outer end flange 27 or 29 and the earth and/or rock strata 42 with a resilient washer 43 located between the flange 27 or 29 and the indicator plate 39.

Anchoring of the strata bolt 20 in the earth and/or rock strata 42 will now be described with reference to the sequence illustrations of Fig. 10. In this description, the anchoring is described using the indicator plate 39 but, as aforesaid, the use of this indicator plate 39 is optional.

The first step is to drill a hole 44 in the strata 42, which hole 44 is slightly over-size relative to the outside diameter of the strata bolt 20.

The second step is to insert the strata bolt 20 with the indicator plate 39 and the resilient washer 43 fitted thereon into the hole 44.

The third step (preferred but not strictly essential) involves pre-tensioning or loading the strata bolt 20 using a pressure (usually hydraulic) cylinder 45 of tubular configuration applied against the flange 27 or 29, washer 43 and indicator plate 39.

The fourth step comprises driving, by means of a plunger rod 46, an anchorage slug 31 up through the pressure cylinder bore and tapered bore 21A of the tube 21 of the strata bolt 20 into the inner end 21C whereof the coacting Morse tapers of the slug 31 and the insert 23 and the slits 25 and holes 26 cause

said inner - end 21-C to expand circumferentially outwardly to create an end anchorage between the strata bolt 20 and the strata 42. In competent strata such, for example, as rock such end anchoring may be sufficient. If not, or if the strata is soft or friable, one or more pressure slugs 32 are driven, in the same way, into the tube 21 of the strata bolt 20. These pressure slugs 32 of the required or desired size or sizes are driven into the tube 21 to an appropriate location.

The fifth step comprises releasing the pressure applied by the-? pressure cylinder 45. If the spring disc indicator plate 39, which would be flattened from its dished shape when the pressure was applied, returns to its dished shape then this indicates that the anchorage between the strata bolt 20 and the strata 43 has not been fully developed. In this circumstance, pressure is once again applied and one or more additional pressure slugs 32 is or are driven into the- tube 21 _* .This ..is _* done until.-, ..upon pressure release,- the indicator plate ^' 39 remains flat.

If, after a period of time, the anchorage of a strata bolt 20 fails and the latter falls wholly, or more likely partially out of the hole 44, then the anchorage can be readily re-established by pre-tensioning .or -loading the strata bol 20 into the hole 44 and driving in one or more pressure slugs 32 of appropriate size.

If a strata bolt 20 drops partly out of the hole 44 its anchorage can be re-established (without pushing it back into the hole 44 which might be difficult- or not possible) simply by driving in one or more pressure slugs to a convenient location or locations, say, for example, one pressure slug up to the anchorage slug and .another to .a , location just

above the bottom of the hole 44.

It will be manifest to those skilled in the art that a multiplicity of such strata bolts 20 will be anchored in an area of strata, and that such strata bolts, again in accordance with customary practice, can be linked by appropriate beam strapping. The externally screw-threaded collar 29 facilitates fixing of such strapping.

If it is desired to increase the expandibility of the strata bolt 20, the length of the slits 25 can be increased.

The strata bolt may be formed of two lengths of tube welded together, the length which includes the inner end being formed internally, say, by boring to provide the taper equivalent to the taper insert 23. Reference is now made to Figs. 6 and 7. The strata bolt 50 comprises an axially-split tube 51, a pre-tensioning and/or load indicator plate 52, and one or more expander slugs 31, 32, 33.

The tube 51 is formed by, for example, cold rolling steel plate, the axial slit being indicated at 53. Indents 37 or holes 38 are preferably formed on the outer surface of the tube 51 to provide keying formations and so improve anchoring.

The length of the tube 51 is made to suit customer requirements, for example between six and twelve feet. This applies equally to the embodiment of Fig. 1.

The tube 51 is tack welded adjacent each end say, for example, three inches from the inner end as indicated at 54, and one inch from the outer end as indicated at 55.

Six, for example, equi-angularly spaced axial slits 56, one of which is on the axial split 53, are formed in the wall of the tube 51 at the inner end

for a length- which stops short, of the tack welding 54 say for example a length of two and three quarter inches.

The tube 51 at its outer end is rolled back to provide an external circumferential flange 57, and, at its inner end, is rolled back for a distance say of one inch to form a return bend and is inwardly compressed to form a bullet head 58 with indents 59. The diameter of the bullet head 58 does not exceed the diameter of the tube 51 as can be seen.

The optional indicator plate 52 is a spring steel disc of dished shape as indicated at 60. .It has a hole 61 for passage of the tube 51 but not the flange 57 and is cut at a number (only one shown) of locations inwardly from its periphery as indicated at 62 to facilitate flattening thereof.

The anchoring of this strata bolt 50 in earth or rock strata is as described with reference to Fig. 10.

Compared with existing strata bolts, which are long established and well-known to those skilled in ihe art, and- -which .comprise, .inter . ^ali , cement grouted bolts, pre-tensioned resin grouted bolts, expansion bolts, cement grouted wedge type bolts and friction bolts, the strata bolts according to the present invention have the following advantages:-

1. It has a positive point, usually within the length of the taper at the inner end, anchor resistance which can be developed to provide (by use of pressure slugs) a partial or full column anchor resistance to take into consideration variable rock or ground strata conditions as encountered.

2. ; Full i or partial failure of- the anchorage resistance load of a strata bolt due to creep or strata relaxation is easily and readily rectifiable.

3. The strata bolt is provided with a

pre-tensioning facilitity to ensure application of a predetermined load to the bolt during installation, which facility automatically and clearly shows its anchorage state or condition without recourse to instrumentation.

4. The strata bolt substantially fills the hole drilled in the earth or rock strata and, as a result, it accommodates lateral movement and forces.

5. No chemicals or cement are used.

6. The length of the strata bolt and its performance is designed to customer specification.

7. The strata bolt is quickly and easily installed by hand or machine, and is easy to handle and transport.

8. Where corrosion is a problem, the strata bolt can be made of, or treated with, corrosion resistant material.