Method and device for anchoring electric conductive bolts in a solid matrix

The present invention concerns a method for anchoring electric conductive bolts in a solid matrix and a device for performing said method.

Background

In connection with road cutting and tunnels it is a a significant safety problem that rocks and loose parts of the matrix sometimes fall down from over a road surface and injure or kill road-users and severely damage vehicles, while the traffic is significantly delayed with accompanying consequences.

In other connections it can be of relevance to stabilize entire mountain sides in order to prevent avalanches over roads, buildings or into fjords.

Temperature variations, moisture variations and the nature of the mountain itself will lead to continuous loosening of new masses from a mountain surface as time passes by.

Different attempts have been made to overcome this problem, hereunder using plates of different kinds that are bolted to the mountain to hold small and larger rocks in place and to prevent solid parts of the mountain to come loose over time and fall down.

Plates attached with bolts have proven successful with respect to significantly reducing the problem, but it is still a challenge to attach the bolts good enough and rapid enough to be economically desirable.

In the following the term "matrix" is used as a common denomination for such mountain or ground formations to which it is relevant to attach bolts of said type, independent of whether the surface between the formation and the surroundings is natural or the result of a road-cut or drilling, independent on whether it is inside a tunnel or out in the open and independent of the orientation of the surface (horizontal, vertical, inclined).

Objective

It is an object of the present invention to provide e method for rapid, inexpensive and safe anchoring of bolts in a matrix in a safe and durable manner.

Hereunder it is an object to establish a quick, simple and safe method for attaching, in an internal or external mountain wall (matrix), bolts that are to serve as anchoring means for different types of elements such as fire retardant plates, rock-fall preventing plates,

moisture barrier plates, cladding plates etc. in tunnels and road-cuts. The term "plates" refers to any kind of substantially plane building elements independent of their dimensions in directions perpendicular to their thickness.

The invention

The above mentioned objects are fulfilled by the method as defined by claim 1.

According to a different aspect the invention concerns a device as claimed by claim 16.

Preferred embodiments are disclosed by dependent claims.

It is convenient that the present invention is performed with a settable mass that during heating by current is able to be transformed from a fluid to a solid mass in a very short time, preferably a time that for a defined layer of a settable mass receiving an appropriate current intensity, sets in a matter of seconds rather than minutes. The term "solid mass" refers to a mass having a strength sufficient to hold a bolt under influence of the bolts own weight. With a suitably chosen settable mass as further described below, it will be feasible to achieve a well developed strength in a matter of minutes so that subsequent attachment to the bolts may follow with no practical time of delay.

With regard to supply of electric voltage, this may take place directly to the back end of the bolt through an electrode attached to the bolt. The electrode or electrodes attached to the bush member receives electric voltage via suitable cable attached to, but electrically insulated from, the bush member. The bush member can for instance be equipped with a recessed groove or the like in which the electric cable is placed to ensure that it is not subjected to mechanical tensions from the solid matrix or from the settable mass during use. The voltage supplied can be alternating current or direct current and practical limitations may determine whether AC or DC is used in each case.

It may be convenient, but it is not a requirement, that the cementing (setting) is conducted immediately after drilling completion of the relevant hole, e.g. by using a common equipment in the form of combines drilling rig and cementing rig which does not need to be moved (with the possible exception of being rotated) between drilling and cementing. The present invention does however not concern the drilling as such which may be conducted in any suitable manner.

Detailed about the invention

Below the invention is illustrated more in detail in the form of a discussion of a certain, non-limiting embodiment with reference to the enclosed drawings, where:

Figure 1 is a side sectional view of an assemble comprising a rig for cementing according to the present invention.

Figure 2a is a side sectional view of an early stage of the cementing process according to the present invention.

Figure 2b is a side sectional view of a later stage of the cementing process also shown in Figure 2a.

Figure 1 shows a mountain wall (matrix) 1 with a drilled hole 2. A rig 3 positioned in front of the hole 2 has a pivot arm 4 with telescopic joints 5 and a jig or attachment device 6. The rig 3 is shown with wheels 7 placed in a position by which penetrating elements 8 attached to the lower part of the rig 3 are forced into the surface below and thereby stabilize the rig 3. On top of the rig a container 9 for the settable mass 12 is shown. The settable mass is transferred from the container 9 to the cementing point by means of a pump 10 and a hose 11. Details regarding the cementing are shown more clearly by Figure 2. The container also contributes with its weight to hold the rig 3 immovable when exerted to forces. The hose 11 must be able to adapt to length change of the arm 4 with the telescopic joints 5. In this connection it is a possibility to arrange the container 9 pivotally on top of the rig 3 so that the attachment point of hose 11 to container 9 may be turned away from the hole 2 when the telescopic joints are being contracted and correspondingly be turned in the direction of the hole 2 when the telescopic joints 5 are being extracted.

It is possible to use a rig like the one shown in Figure 1 and which comprises more than one pivot arm 4 and which, with drilling equipment attached to one arm (not shown) to first drill the hole 2 and thereafter - without moving the rig on the ground surface to perform the cementing as generally described by Figure 1. For this purpose the rig may e.g. comprise a body which rests pivotally on a chassis, one arm (e.g. an arm holding the drilling equipment) being extended from the rig body in one direction, while another arm (e.g. an arm provided with cementing equipment) being extended in a direction from the rig body in a direction different from the direction of the first arm.

In Figure 2a and 2b a borehole 2 is shown in a mountain wall 1. The borehole is shown as vertically downwards but is principally equal to borehole 2 in Figure 1. In general the boreholes can have any orientation and will often in practice be directed inclined upwards or even vertically upwards. A person skilled in the art will understand that the direction is not decisive, but that the orientation of the borehole may require some practical arrangements as described below, since the gravity will influence a still fluid cement composition differently dependent on the equipment used and dependent upon the orientation of the borehole.

Figure 2a and 2b furthermore show a bolt 13 surrounded by a bush member 14. Near the front end of the bush member 14 an electrode 15 is attached thereto. The electrode 15 can have the shape of at least a part of a cylinder body with a radius larger than the radius of the bush member 14 and preferably arranged substantially concentric with the bush member. The electrode(s) 15 may however also have the forms of a number of smaller electrodes distributed around the circumference of the bush member 14 at a certain distance therefrom. The front edge or end of the electrodes 15, i.e. the end or edge furthermost into the borehole, may be in line with the inner end of the bush member 14 but may also extend longer or shorter into the borehole than does bush member 14.

In Figure 2a there is as a symbol for supplied current a "plus" sign and a broken line to the bolt (13) and a "minus" sign with a broken line to the electrode(s) 15, but the current may as well be reversed or be supplied as an alternating current.

A settable mass 12 is supplied from the back (in Figure 2 upper) end of the bush member 14, surrounds a certain length of the bolt 13 and flows out at the end of the borehole 2 so that the settable mass 12 contacts the electrode 15.

The electrode or electrodes 15 is/are attached to the bush member 14 with attachment brackets 16 arranged at a distance from one another around the circumference of the bush member 14 so that the attachment brackets 16 to just a minor extent shall influence on the flow of settable mass around the bush member 14.

The bush member 14 shall be provided with or comprise a sealing cap 17 that prevents settable mass from escaping when cementing sideways or upwards. In the sealing cap 17 there is an opening for a hose 11 through which the settable mass may be pumped to the (front) end of the bush member 14 beyond the sealing cap 17.

The bush member 14 can also comprise guide members 18 which are interspaced in the length direction of the bush member and with intervals around the inner circumference of the bush member 14, e.g. with an angular space of 90 or 120 degrees between each guide member, the guide members extending towards the bolt 13 and ensuring that the bush member at any time is concentric with the bolt 13. The guide members may be arranged in a manner ensuring that the bolt is tightly squeezed when the bush member is moved in a forward direction (into the hole 2 to be cemented) but such that the guide members only drag along the bolt 13 with a light squeeze when the bush member 14 is withdrawn from the hole 2. There may be guide members both at the front end of the bush member, arranged to hold the settable mass and in the back part of the bush member 14 outside the sealing cap 17.

The difference between Figure 2a and 2b is that the cementing process has progressed further in Fig. 2b; the bush member 14 and the equipment attached thereto having been pulled partly out of the hole 2 while additional settable mass 12 has been supplied. A person skilled in the art will understand that the rate at which the bush member is withdrawn, is adapted to the volume rate of supply of settable mass and the rate at which the settable mass in question sets when using the apparatus in question and the actual current intensity. The convenient volume rate for supply of settable mass can partly be calculated, partly be found by empirical testing.

It is required to use a settable mass that is able to set very quickly under the described conditions and it is also convenient to use settable masses that develops high tensile strength and exhibits little shrinkage during setting. In accordance therewith it is in some embodiments preferred to use a settable mass that contains more than 25 % by weight of aplite calculated on the basis of all bonding material in the settable mass, preferably more than 50 %. In some embodiments it may be desirable to use a settable mass that contains more than 75 % by weight of aplite calculated on the entire amount of bonding material in the settable mass.

To obtain a best possible distribution of the electric current through the settable mass during setting, it is convenient to use at least one electrode that extends around the substantial part of the circumference of the front end of the bush member.

The electric voltage applied is adjusted typically in dependence of the moisture content of the settable mass to obtain a current that corresponds to a desired temperature increase in the settable mass. Such adjustment can be made by empirical test using real time temperature increase to ensure a desired temperature development, optionally with automatic control of the voltage by use of a computer, in dependence of the actually measured temperature development.

By the method according to the present invention it is possible and often convenient to conduct the cementing process for a bolt in a time period of maximum 5 minutes or even within maximum 3 minutes.

In some embodiments it is preferred to drill to a depth of about 6 meters. In other embodiments it may be more convenient to drill to a depth in the range from 0.5 to 5 meters or to a depth in the range l to 3 meters. The rate of withdrawal of the bush member during cementing can typically be of order from 30 centimeters per minute to 6 meters per minute and often in the higher end of this interval, such as from 3 to 5 meters per minute.

To further improve the properties of the settable mass, either as fresh mass, as finished set mass or both, carbon fibers and nanometric carbon spheres may be added. Other additives that can contribute to increased strength or affect the settable mass' electrical conductivity may also be used. It should be noted, however, that many known additives for conventional cements, lead to properties that are desirable in a short perspective but which are undesirable since they may shorten the lifetime of the settable mass.

It is convenient that drilling and cementing is performed in sequence in a manner as rational as possible, for instance by using the same rig for drilling and for cementing. It should be emphasized, though, that drilling as such is not part of the present invention and may be performed in any suitable manner.

It is evident that steel bolts or bolts in other metals may be used in the method according to the present invention, but bolts that partly or wholly comprise carbon and/or basalt may also be used in dependence of the embodiment in question.