TECHNICAL FIELD

The present disclosure relates to a sealing device adapted for mounting around a rock bolt protruding from a surface, which sealing device serves to provide corrosion protection. The disclosure further relates to a method for filling a space between a surface and a domed bearing plate mounted around a portion of a rock bolt protruding from said surface with a wet cement or mortar material.

BACKGROUND

Rock bolts are used for rock support in tunnels and caverns underground as well as on slopes above ground. By anchoring in deeply located stable rock, the rock bolts prevent superficial rock fragments resulting from natural cracks or blasting induced fissures from coming off as a result of gravitation, possibly combined with water/ice pressure, drying, temperature variations, vibrations or suction from traffic. A typical rock bolt consists of a steel rod (a rebar) with a mechanical or chemical anchor at one end or chemical anchor along its whole length and a bearing plate and nut at the other end. Commonly, the rock bolt is anchored in a cementitious grout. In that case, a drilled borehole is filled from its bottom with a stiff wet cement or mortar paste. Another way to achieve the anchoring is by loading water exposed cement cartridges in the borehole. This method is preferably used when only a few bolts are to be mounted.

To ensure strengthening of thin rock fragments, rock bolts can be completed with threads on the exposed end and a domed bearing plate fitted with a half sphere and an internally threaded nut. The half sphere is especially useful when the rock surface is not perpendicular to an axial direction of the bolt. The method is also used to secure rock anchored sprayed concrete lining. On one hand, the hardened cement results in a very strong anchoring of the rock bolt. On the other hand, it also protects the steel rock bolt from corrosion due to the high pH-value of cement. This is very important, as durability demands are essential in tunneling.

Ground water can be corrosive to steel due to chlorides, but ground water chemistry can also be changed during operating time caused by ground water flow after tunneling which can result in acid conditions. In Sweden, the demands on design lifetime for infrastructure tunnels is generally 120 years. To meet these demands, bolts with strengthened corrosive protection consisting of combined zinc and epoxy layers often are used. Outer parts of the rock bolts must be protected in the same way.

Tunnel environment is extremely tough for steel bolts and corrosion protection must be accurate, not leaving any parts of the bolt unprotected. Therefore, outer parts of the anchor must be covered by cementitious products to meet durability demands, even when industrial protection is used. This is usually achieved by filling the space between the rock bolt and the domed bearing plate with mortar (also referred to as cladding). After completed installation, the bearing plate is covered with sprayed concrete. To be sure that all parts are sufficiently protected, it is essential that no cavities or cracks resulting in local corrosion are provided. Defective installation may severely affect the durability and the load bearing capacity of the construction.

However, while inspecting rock bolting, it has been found that defective installation occurs frequently. In particular, this applies to the mortar cladding between the rock bolt, the rock surface and the domed bearing plate. To achieve a proper installation, the cementitious mortar must have the correct consistence, the amount of mortar must be sufficient and spanning of the bearing plate must be carefully performed so that mortar fills all voids perfectly. The installation consists of several steps, the work is heavy and the process is repeated many times. When the installation is not properly performed, the construction will possibly not meet the demands on durability. Cladding is typically achieved by a process where all steps are carried out in the installation area after mounting the rock bolt. The process may comprise:

a) manual dosing of dry cement and water;

b) mixing using e.g. a hand held drill mixer or a small concrete mixer;

c) applying the wet cement within the domed bearing plates using hand tools or hand directly; d) mounting the bearing plate on the protruding rock bolt;

e) mounting and tightening a half sphere and a hex nut, using an electric or pneumatic spanner; and

f) removing excess wet cement by hand, and adding any missing wet cement.

Incorrect dosing, too short mixing time, too small volume, wrong consistence resulting in outrunning mortar, to little tied up are a few faults that can be done. The mixing procedure typically has to be repeated once per ten or twenty rock bolts, which is inconvenient in larger constructions. It is difficult and time consuming to ensure correct processing and there may be large variations in the final quality.

The cladding process is also very heavy, and the cement paste is hazardous to skin and eyes if proper means of protection are lacking. The cladding is typically carried out standing on a lift or platform, and the ergonomic conditions are often not optimal.

SUMMARY

It is an object of the present invention to overcome or at least alleviate the above mentioned problems, or to provide a useful alternative. In particular, the present invention aims at facilitating the application of a wet cement or mortar material such that it fills the space between a surface from which a rock bolt protrudes and a domed bearing plate mounted around the rock bolt, thereby protecting the rock bolt from corroding. It further aims at improving the quality and durability of rock bolt installations. To better address these concerns, a sealing device according to claim 1 , a package according to claim 8, and a method according to claim 13 are provided. Embodiments are set forth in the appended dependent claims.

According to a first aspect, the present invention relates to a sealing device adapted to be positioned within a domed bearing plate and mounted around a portion of a rock bolt protruding from a surface, the sealing device comprising:

a body consisting of a dry cement or mortar material; and

a casing of a water permeable material surrounding the body and holding the body together; wherein the sealing device is ring shaped or essentially ring shaped and extends around a through hole centred on a central axis of the sealing device.

According to a second aspect, the present invention relates to a package comprising:

- a watertight bag having a top end and a bottom end;

- a plurality of the proposed sealing devices positioned within the watertight bag.

According to a third aspect, the present invention relates to a method for filling a space between a surface and a domed bearing plate mounted around a portion of a rock bolt protruding from said surface with a wet cement or mortar material the method comprising:

providing the proposed sealing device;

- soaking the sealing device in water to form the wet cement or mortar material; positioning the soaked sealing device within the domed bearing plate; mounting the domed bearing plate and the soaked sealing device positioned therein around the protruding portion of the rock bolt;

applying a pressure on the domed bearing plate mounted around the protruding portion of the rock bolt such that the domed bearing plate is pressed toward the surface and the casing of the sealing device breaks, thereby filling the space with the wet cement or mortar material.

By means of the proposed sealing device, package and method, it is possible to facilitate the application of cementitious paste, i.e. wet cement or mortar material, in the space between the protruding portion of the already installed rock bolt, the surface from which the rock bolt protrudes (hereinafter referred to as the rock surface, although it is to be understood that it may also be e.g. a concrete surface or similar), and the domed bearing plate. The part of the rock bolt extending inside the rock surface is herein already anchored by means of cement or mortar deep down in stable rock.

The casing of water permeable material allows the body of the sealing device, consisting of dry cement or mortar material in powder form, to absorb water to activate the cement or mortar material, and it also holds the wet body together as the sealing device is mounted around the rock bolt. It can thereby be ensured that an accurate amount of cementitious paste is applied, thereby improving the quality of the sealing. Moreover, the time consuming and heavy step of dosing and mixing dry cement or mortar powder with water on the construction site can be eliminated, since the sealing devices are simply immersed in water in order to wet the dry cement or mortar material. The working environment as well as the time efficiency of the installation of the rock bolts may thereby be improved.

Since the soaked sealing devices are according to the proposed method positioned within the domed bearing plates (i.e. on the concave surface of the bearing plate adapted to be directed toward the rock surface), no manual cladding of the wet cementitious paste within the bearing plate is necessary. Instead, the wet cement or mortar material of the sealing device fills out the space between the bearing plate and the rock surface as a pressure is applied to the domed bearing plate after mounting around the rock bolt, e.g. as a fastening member is mounted and secured on the rock bolt using a torque tool.

With the prefabricated sealing devices and with the proposed method, the risk of forming voids in the cement or mortar material after setting is reduced since the consistency and amount of wet cement or mortar can be better controlled than in a manual cladding process. The quality and durability of the installation may thereby be improved, with reduced maintenance costs as a result.

Further advantages of the present disclosure and advantageous embodiments appear from the following detailed description and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended drawings, wherein:

Fig. 1 is a sectional view of a prior art rock bolt;

Fig. 2 is a top view of a sealing device according to a first embodiment;

Fig. 3 is a perspective view of a sealing device according to a second

embodiment;

Fig. 4 is a top view of the sealing device in fig. 3;

Fig. 5a-d show sections along the line Ill-Ill in fig. 4 for various embodiments;

Fig. 6 shows a package according to an embodiment; and Fig. 7 is a flow chart illustrating a method according to an embodiment of the invention.

It should be noted that the appended drawings are schematic and that individual components are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION

A prior art rock bolt 1 of the type referred to in this application is schematically shown in fig. 1. The rock bolt 1 is in the form of a steel bar extending along a longitudinal axis A and having a threaded end portion (threading not shown). In fig. 1 , the rock bolt 1 is installed in a rock (e.g. anchored deep down in the rock by means of cement or mortar) and a portion 2 of the rock bolt 1 protrudes from a rock surface 3. A domed bearing plate 4 is mounted around the protruding portion 2 and a half sphere 5 and a fastening member 6 in the form of a nut is mounted around the protruding portion 2 of the rock bolt 1 , outside of the domed bearing plate 4. The domed bearing plate 4 thus presses against the rock surface 3.

A sealing device 10 according to a first embodiment of the invention is shown in fig. 2 and a sealing device 10' according to a second embodiment is shown in figs. 3-4. The sealing device 10, 10' is adapted to be positioned within a domed bearing plate 4 as shown in fig. 1 and mounted around the portion 2 of the rock bolt 1 protruding from the rock surface 3. The sealing device 10, 10' comprises a body consisting of a dry cement or mortar material. It further comprises a casing of a water permeable material surrounding the body and holding the body together, i.e. tightly encapsulating the body. The sealing device 10, 10' is ring shaped, or essentially ring shaped, and extends around a through hole centred on a central axis C of the sealing device 10, 10'.

The sealing device 10 may be formed as a device having two connected ends 1 1 , 12, such as shown in fig. 2. In this embodiment, the sealing device 10 is formed from a cylinder with rounded ends, wherein the rounded ends have been connected to form a ring shape. In the second embodiment shown in figs. 3-4, the sealing device 10' may have a toroidal shape, i.e. the shape of the sealing device can be obtained by rotating a section of the sealing device 10', taken in a plane parallel with the central axis C, around the central axis C. In this embodiment, the sealing device thus has an even thickness and is rotationally symmetric. A section 14 of the sealing device 10' may in this case have a variety of different shapes, e.g. such as illustrated in figs. 5a-d wherein the section 14 is elliptic (fig. 5a), rectangular (fig. 5b), rectangular with rounded corners (fig. 5c) and trapezoidal (fig. 5d), respectively. The sealing device 10' may be tapered along the central axis C by providing the sealing device with a trapezoidal section 14 such as shown in fig. 5d or in any other suitable way. In this case, the sealing device 10' fits well into the domed bearing plate 4 and is easy to apply. The body of the sealing device 10, 10' may consist of a dry mortar material comprising cement and at least one filler material. The filler material may e.g. consist of fly ash, slag, lime stone filler or fine graded sand. For example, the body may consist of cement and one filler material. Mixing the cement with one or more filler materials to provide a mortar reduces the environmental impact of the material. To ensure sufficient corrosion protection, the dry mortar material may preferably comprise at least 50 percent by weight of cement, the remainder being the filler material. The body may alternatively consist of a dry cement material, i.e. a cement material without any filler material.

The water permeable material of the casing may preferably be a fibrous material such as a paper material. This type of material easily breaks when a pressure is applied to the domed bearing plate. The paper material should be selected to be strong in a wet condition, since the sealing devices are to be handled when wet. Since the wet paper becomes impregnated by the alkaline cement or mortar, it will not harm the final construction. An alternative to a paper material is a textile material or a non-woven material.

A package 15 according to an embodiment of the invention is schematically illustrated in fig. 6. The package 15 comprises a watertight bag 16 having a top end 17 and a bottom end 18, and a plurality of sealing devices 10' (shown with dashed lines) positioned within the watertight bag 16. The watertight bag 16 may be adapted to be opened at the top 17 end and filled with water. The bag 16 may be configured to be free-standing or hanging while being filled with water, e.g. by providing the bag with one or more handles for hanging or by making the bag from a material which is sufficiently stiff to allow the bag to be free-standing, or by providing the bag with reinforcing structures that allow the bag to be free-standing. The bag 16 may e.g. be provided with a marking to show where it may be cut open to be filled with water, or it may comprise a breakable seal. Of course, the sealing members of the package may be of any type described herein.

In the shown embodiment, the watertight bag 16 comprises an openable tap 19 at its bottom end for draining water from the watertight bag 16. This facilitates the process of draining water from the bag 16 when the sealing devices 10' contained therein have been soaked. If no tap 19 is provided, the bag may e.g. be drained by cutting the bag open.

The watertight bag 16 may further comprise a control device (not shown) configured to open the tap 19 after a predetermined time period subsequently to filling the watertight bag 16 with water. Thus, a suitable time period for soaking the sealing devices 10' may be pre-set, and the bag 16 is automatically drained after this time period, thus ensuring that the sealing devices 10' are soaked for an appropriate time period and that a suitable consistency of the wet cement or mortar material is achieved. A method for filling a space between a surface 3 and a domed bearing plate 4 mounted around a portion 2 of a rock bolt 1 protruding from said surface 3 with a wet cement or mortar material is illustrated in the flow chart in fig. 7.

In a first step 101 , a sealing device 10, 10' as described above is provided. The sealing device 10, 10' may e.g. be provided in a package 15 as described above.

In a second step 102, the sealing device 10, 10' is soaked in water to form the wet cement or mortar material, preferably for a predetermined time period. Soaking in water is preferably carried out in the watertight bag 16, in which case soaking the sealing device 10' comprises filling the watertight bag 16 with water such that it covers the sealing device(s) 10' and subsequently draining the water from the watertight bag 16.

In a third step 103, the soaked sealing device 10, 10' is positioned within the domed bearing plate 4. The domed bearing plate 4 comprises a central opening configured to receive the rock bolt 1 , and the soaked sealing device 10, 10' is placed so that its central through hole overlaps the opening.

In a fourth step 104, the domed bearing plate 4 and the soaked sealing device 10, 10' positioned therein are mounted around the protruding portion 2 of the rock bolt 1 , so that the rock bolt 1 extends through the central through hole of the sealing device 10, 10'.

In a fifth step 105, a pressure is applied on the domed bearing plate 4 mounted around the protruding portion 2 of the rock bolt 1 such that the domed bearing plate 4 is pressed toward the surface 3 and the casing of the sealing device 10, 10' breaks, thereby filling the space with the wet cement or mortar material. The pressure is preferably applied by mounting a fastening member 6 around the protruding portion of the rock bolt. Typically, this may be an internally threaded hex nut combined with a half sphere 5, which is mounted between the fastening member 6 and the domed bearing plate 4.

Surplus material may after mounting be removed using an appropriate tool or using gloved hands.

The sealing device 10 shown in fig. 2 may be manufactured by providing a pre-made tube of the water permeable material configured to form the casing of the device, filling the pre- made tube with the dry cement or mortar material, sealing and cutting the filled pre-made tube into desired lengths, bending the resulting sealed and cut filled tube into a ring shape, and connecting its ends to form the sealing device 10. The sealing device 10' shown in figs. 3-4 may be manufactured by means of the following steps:

providing a pre-fabricated mould having a mould cavity;

- covering the mould cavity with the water permeable material configured to form the casing of the sealing device;

- filling the covered mould cavity with the dry cement or mortar material;

- wrapping and subsequently sealing the water permeable material around the dry cement or mortar material within the mould cavity to form the sealing device 10'. Further modifications of the invention within the scope of the appended claims are feasible. As such, the present invention should not be considered as limited by the embodiments and figures described herein. Rather, the full scope of the invention should be determined by the appended claims, with reference to the description and drawings.