The invention concerns a method of injecting pri¬ marily rock or concrete by pumping into holes previously drilled into the rock or the concrete, a liquid sealing agent of a kind that solidifies after a predetermined period of time. The pressure exerted on the sealing agent forces the sealing agent into the fissures in the rock or the concrete, which fissures are sealed by the sealing agent as the latter solidifies.

This method has been in use for quite some time in order to seal crevisses and fissures in rock. As sealing agents various suspensions have been used, such as cement and water and solutions of various chemical agents. There is also a considerable need for methods allowing various types of concrete structures to be sealed off against seepage, from the exterior, of subsoil water or even of rain water. Injection is also sometimes used for ground- reinforcement purposes. As a rule, the injection step is carried out up to the point when the amount of sealing agent that penetrates into the crevisses becomes so small that the injection pressure reaches a predetermined value. Among the available types of cement, ordinary

Portland cement or rapid-hardening cement are those most commonly used, since they are comparatively cheap. Finer- grain types of cement, known as micro-grain cement, are also available, allowing deeper and easier penetration into narrow crevisses. As examples of chemical agents may be mentioned isocyanates which transform into poly- urethane. Chemical agents are used because their ability to penetrate into narrow and fine crevisses surpasses that of cement, and because their gelling progress may be controlled. These agents may be made to react and solidify within the minute. The depth of penetration into the material to be injected thus may be reduced and con-

sequently also the costs with respect to the injection agent. In addition, polyurethanes are able to swell considerably, thus allowing also very wide fissures to be sealed off, even in the case of running subsoil water. It is, however, necessary to bear in mind that the cost differences between the cheapest and the most expensive sealing agents are considerable. The cost relations between cement/micro-grain cement/isocyanates are approximately 1:10:100. Consequently, considerable economical gains may be made by using the cheaper types of cement to the largest possible extent. The large costs of material in the case of chemical substances tend to restrict their use, despite the favourable technological properties that these substances possess. A considerable proportion of the costs of material relates to the sub¬ stances that remain inside the bore holes after completion of the injection. As one example may be mentioned that in the pre-in ection of an ordinary tunnel front, about 15 holes having a diameter of 51 mm and a length of up to 15 m are drilled. The volume of the injected material alone, which fills the injection holes after the completed injection, amounts to about 450 liters. In other words, the volume of the cavities created from the drilling may be considerably larger than the volume of the cracks in the rock to be sealed. Consequently, there are economical grounds for emptying the drilled holes of expensive injection material that could be replaced by some other, cheaper material.

The subject invention provides a method by means of which the above-mentioned task may be performed in a con¬ siderably more economical manner. The characteristic features of the method in accordance with the invention reside therein that a sealing agent, while still in liquid form inside the injection hole, is forced to flow out of said hole in a controlled manner to be re-used, which is effected by pumping a second, different >agent into said hole. In this manner it becomes possible to choose in each

instance precisely the sealing agent that is the most suitable one considering the prevailing circumstances. The invention likewise makes it possible to empty an injection hole of the sealing agent, once the injectio process is completed. In this manner the hole may be re¬ used for purposes of subsequent injection or for later checks to verify the efficiency of the injection. This ma be advantageous when working with long and consequently expensive injection holes, as is the case for instance in the injection of dams, or when the requirements precise location of the holes are high, for instance in the case of bridge-pillars.

The invention also concerns a device for performing the method. The features characterizing this device are defined in the appended claim 6.

The invention will be described in closer detail in the following with reference to the accompanying drawings, wherein

Fig. 1 schematically illustrates three drill holes, each one fitted with a device and each representing one injection stage,

Fig. 2 illustrates on an enlarged scale the device in accordance with the invention in a broken lateral view, Figs. 3 and 4 show in a horizontal view and a front view, respectively, a rock which is pre-drilled for tunnel excavation purposed, and

Fig. 5 is a vertical sectional view through a bridge- pillar.

Fig. 1 illustrates a mass of rock 1 divided into three sections. In each section an injection hole 2, 3 and 4, respectively has been drilled. The rock exhibits several fissures 5 that are to be sealed.

In accordance with the invention a sleeve 6 is applied in each pre-drilled hole 2, 3, and 4. The sleeves 6 penetrate into the associated hole 2, 3, 4 over a small distance only. Over this distance, into the space between the external walls of the sleeve 6 and the wall of the

associated one of holes 2, 3 or 4, is forced a volume of a hardenable compound 7, forming a plug sealing off the respective hole 2, 3, 4. In accordance with the embodimen illustrated, the sleeve 6 is also formed with a transvers inlet/outlet 8 on which a valve 9 is mounted.

A pipe 10 extends through the sleeve 6 inside the injection hole 2, 3, 4, approximately up to bottom 11, 12, and 14 of the associated hole. The pipe 10 is formed externally of the sleeve 6 with an inlet/outlet 15 fitted with a valve 14.

As appears from Fig. 2, the sleeve 6 is connected with the pipe 10 at its outer end and at the same time it is closed in a liquid-tight manner by means of a con¬ ventional screw coupling 16. An inspection valve 17, the function of which will be explained in further details in the following, is mounted between the screw coupling 16 and the valve 14.

The device also comprises a first supply 18 of a chemical agent 19 of a kind that is able to swell heavily, for instance isocyanates. With the aid of a pump 20 the agent 19 may be pumped into any one of the injection holes 2, 3, 4 by way of a hose 21, the latter being connected to either the inlet/outlet 8 of the sleeve 6 or to the inlet/outlet 15 of the pipe 10. A second container 22 holds cement mortar 23. In a similar manner, the cement mortar may be pumped into any one of the injection holes 2, 3, 4 by means of a pump via a hose 25. Finally, the device comprises a conduit 26 which may be coupled so as to interconnect, for instance as illustrated, the inlet/outlet 15 of pipe 10 in the injection hole 3 with the inlet/outlet 15 of pipe 10 in the adjacent injection hole 4.

In order to ensure that a compact and impervious plug forms about the sleeve 6, an annular groove 27 may be formed at the inner end of the sleeve for reception therein of a sealing ring 28. In addition, the sleeve 6 may be fitted with a tube 29 extending some distance

along the sleeve wall inside the injection hole 2, 3 or 4 At its outer end, the pipe 29 supports a nipple 30. The function of the pipe 29 is to facilitate supply of the hardenable compound 7 into the space between the sleeve 6 and the walls of the injection hole 2, 3, 4.

In the following description of the method in accordance with the invention, reference is made to Fig. 1, with respect to which it is assumed that the hose 21 has already been connected to either the inlet/outlet 8 or to the inlet/outlet 15 of injection hole 3 and that the pump 20 has pumped the injection agent 19 into this injection hole 3. The agent 19 has penetrated up and into the crevisses 5 while heavily expanding and swelling inside the latter, and in time it has gelled. In accordance with prior-art technology, it was necessary in this situation to pump the injection agent 19 still remaining inside the hole 3 into the rock 1 by changing- over to another injection agent which gradually replaced the first injection agent 19 inside the hole 3. This may be a time-consuming procedure, also involving the risk that the injection agents will gel before the procedure is completed. This method also is dependent on exact determination as to when the injection step is to be stopped, i.e. it is necessary to know when penetration of injection agent can no longer occur. The injection hole was then left in its thus state filled with the second injection agent, which also formed a solidifying mass.

According to the teachings of the subject invention, on the other hand, one proceeds in the following manner. The hose 21 is disconnected from the inlet/outlet 8 or the inlet/outlet 15. The hose 25 is then connected to the inlet/outlet 8 and with the aid of the pump 24, the second injection agent 23, which contrary to the first injection agent 19 preferably consists of cheap cement mortar, is forced into the injection hole 3 before the first, injection agent 19 has had time to gel inside this hole

3, whereby the second injection agent 23 forces the first mentioned injection agent 19 out of the hole. In this manner, the cheaper agent 23 will fill up the injection hole 3 and also partly the fissures 5 in which the agent 19 has not yet had time to gel. The more expensive material 19 may be recovered outside the device to be use again in another position.

It may be practical and suitable to transfer, as illustrated in Fig. 1, the agent 19 direct from one injection hole 3 to the next hole 4 with the aid of the conduit 26. This method is both rapid and functional. By briefly opening the inspection valve 17 (see Fig. 2) on a few occasions it is possible to check when the hole 3 is emptied of agent 19 and has instead been filled with agent 23.

Under several circumstances it may be appropriate to expand the method by a third step. This is illustrated with respect to injection hole 2 in Fig. 1. In this case, a further hose has been connected to any one of inlet/outlet 8 or inlet/outlet 15 and with the aid of water the second injection agent 23 has been forced out of the injection hole 2 before having had time to harden inside the hole. One advantage gained by this third method step is that when the water has been pumped out of the hole 2, the latter may be inspected. It likewise becomes possible, should new fissures form later, or should one or several fissures 5 not have been sealed off sufficiently, to again inject the hole 2 at a later date.

The primary advantage gained by the method in accord- ance with the invention is that it allows rapid and convenient changes from one sealing agent to another. For instance, it is quite possible first to inject one hole with a cheap cement mortar 23. Then, should one find that the consumption of cement mortar is considerable due to the fact that the fissures are too large to be sealed by means of cement mortar, a change-over is made to inject the more expensive sealing agent 19. This agent

possesses extremely good sealing properties because of its ability to swell and to gel comparatively quickly. Next, as described in the aforegoing, the agent 19 is again forced out of the injection hole because it is expensive, and non-used amounts thereof, i.e. those inside the injection hole proper, therefore should be recovered.

A third method step is also possible, involving gas, such as air, instead of water being pumped into the hole and maintaining a pressure inside the injection hole during the gelling time. With the aid of a manometer 31 which is connected to the inlet/outlet 8 or to the inlet/outlet 115, the pressure inside the injection hole may be controlled during tests of the pressure therein. The majority of the equipment is re-useable i.e.in one injection hole after the other. Only the sleeve 6 which is anchored in the hole by means of the sealing compound 7, is expandable equipment.

Figs. 3 and 4 show the arrangement of a number of injection holes 32 drilled into rock prior to blasting to excavate a tunnel in a rock. Fig. 3 also illustrates the manner in which a sleeve 6 and a pipe 10 have been inserted in each one of the holes 32 and how tubes 26 extend from one sleeve 6 to the next. The containers 18, 22 holding different sealing agents, are placed in readiness and one of the containers 18 is connected to one of the sleeves 6. This embodiment intends to illustrate the complexity of the work involved in pre- drilling a large number of injection holes 32 in order to seal off many fissures in rock. The method in accordance with the invention therefore provides considerable gains, allowing this work to be accelerated and recovery of the more expensive sealing agent or agents that are used. Fig. 5 shows a bridge-pillar 33 in which is precision-drilled an injection hole 34 reaching all the way down to the bridge-pillar base 35. This embodiment

intends to illustrate the advantage to be gained by the possibility allowing the injection hole 34 to be emptied for later inspection. Should fissures 36 arise when the bridge-pillar 33 has been in use for a couple of years, post-injection of the hole 34 is easily performed at this later date, which is a much more convenient procedure tha having to precision-drill new injection holes 34. As a more simple alternative to precision-drilling it is possible, when the bridge-pillar 33 is cast, to embed a perforated pipe in the concrete, which pipe is used for injection at a later stage.

Neither the method nor the device in accordance with the invention are restricted to the features illustrated and described in the accompanying drawings but may be varied in several ways within the scope of the appended claims. Consequently, the method offers possibilities of changing the type of sealing agent used according to need. It is easily understood that the device may be varied in many different ways without departure from the inventive idea. For instance, either one of the inlets/outlets 8 and 15 may be arranged in other positions than those shown.