US3222872A - Method of strengthening and sealing rock - Google Patents

Description

Dec. 14, 1965 Filed May 2. 1961 U. M. LANGEFORS ET AL METHOD OF STRENGTHENING AND SEALING BOOK 2 Sheets-Sheet 1 Dec. 14, 1965 u. M. LANGEFORS ETAL 3,

METHOD OF STRENGTHENING AND SEALING ROCK Filed May 2, 1961 2 Sheets-Sheet 2 United States Patent l 3,222,872 METHGD 0F STRENGTHENHNG AND SEAHNG RUCK Ulf Marten Langefors, Stoekhoim, and Sten Harald Brannfors, Lidingo, Sweden, assignors to Nitrogiycerin Aktiebolaget, Gyttorp, Sweden Filed May 2, 1961, Ser. No. 107,175 Claims priority, application Sweden, May 5, 1960, 4,474/60 9 Claims. ((11. 61-36) The present invention relates to the strengthening and/ or tightening, or sealing of rock by so-called injection or spreading of a binding or sealing medium either in cracks or faults inside the rock or over parts of a rock surface uncovered by blasting.

In all rock-working by blasting it is important to ensure that only the intended parts of the rock are detached by the blasts. For various reasons, such as natural crack formations and other local weaknesses in the rock, there is often a risk, however, of unintended subsequent slips of material and furthermore in tunnel work, for example, the blasting operations may create open communications to veins of water present in the rock so that the progress of the work is hindered by a heavy outflow of water.

In order to avoid such disturbances it is well known to strengthen and/or tighten the weak parts of the rock by injecting a binding or sealing medium and to improve the tightness and strength of an uncovered rock surface by applying a covering layer of a rapidly solidifying sealing medium to the same by spraying for example.

The injection of a binding or sealing medium is usually effected by pumping in some hydraulic cement composition, such as Portland cement slurry or concrete through drill holes, especially prepared for that purpose. Preparatory to such injection it has also been suggested to establish an improved communication between the drill hole and the adjoining natural cracks and faults in the rock by firing a limited blasting charge in the hole to thereby provide for a locally increased artificial crack formation and hence facilitate the distribution of the injection medium. After its injection the injection medium is, of course, allowed to bind before further work is done on the rock.

In many cases, however, it is not possible to strengthen the rock to a desired extent by injections made in advance of blasting, or such injections may for some other reason he insufiicient to avoid complications and disturbances during the subsequent rock blasting work. Under such circumstances some sort of surface-strengthening or sealing measures must be resorted to, and it is of great importance that such measures are then effected as rapidly as ever possible after the blasting so that the rock cannot start moving or the water cannot gush out in such quantities that the cracks are washed clean and will be difficult to seal.

Obviously this is a demand which is very difficult, and sometimes risky, to fulfill when the sealing or strengthening of the surface is to be effected by spraying the recently uncovered rock surface with concrete for example.

The present invention has for its main object to con siderably improve the possibilities for effectively spreading injection or sealing materials in order to strengthen and/or seal the rock. According to the invention this improvement is achieved by utilizing the gas pressure from a detonating blasting charge for spreading the binding or sealing medium. Secondarily the temperature rise occurring at the detonation of the explosive can be used to facilitate the distribution of the binding or sealing medium.

According to the invention, not only can the injection or spreading of the binding or sealing medium be carried 3,222,872 Patented Dec. 14, 1965 out without the help of any special equipments in the form of pumps or the like but, at the same time, improved spreading is achieved both as a result of the high pressure available and also owing to the fact that the cracks in the vicinity of a detonating change at the actual moment of blasting are expanded by the gas pressure so that the penetration of the medium will be facilitated.

The invention can be applied both for the injection of a binding or sealing medium in advance and for spreading the medium in direct connection with such blasts which have for their purpose to uncover fresh rock surfaces. In the later case the invention supplements or replaces in a very favorable manner the subsequent application of a covering layer mentioned in the introduction, since according to the invention the binding or sealing medium is driven into the cracks in the remaining rock surface with considerable force and thus effectively binds the latter to a considerable depth. Therefore, also in this case, the treatment may be referred to as a kind of injection although a part of the binding or sealing agent will then, of course, 'be lost because some of the agent will become distributed over the surfaces of such blocks or pieces of the rock which are removed by the blast.

The application of the invention in direct connection with the removal of rock by blasting may in certain cases advantageously replace the strengthening of the rock by injection before the blasting work is started. When undertaking such preparatory injection there is, namely, a considerable risk that the bond formed between the parts of the rock will be again broken apart at the momentary expansion of the cracks during the subsequent blasting. In contradistinction thereto, by injecting a binding or sealing medium in connection with the blasting away of the rock according to the present invention the adhesion of the medium first begins when the cracks are subjected to the pressure of the gases of explosion and are thus expanded, and the subsequent hardening or solidification of the medium generally occurs first when the blasting process has already taken place and the cracks have contracted again. This, however, requires that the hardening or solidifying process take place rapidly.

Obviously the basic inventive idea may be applied in many different ways. For example, the binding or sealing medium and the blasting charge, respectively, may each be introduced as separate units into a drill hole, whereupon the blasting charge is caused to detonate, or the binding or sealing medium and the blasting charge may be introduced together into a drill hole as a single unit prepared in advance.

The magnitude of the blasting charge must, of course, be adapted to the desired effect, which in case of a preparatory injection may consist solely of the spreading or blowing in of the medium into existing holes and cracks, but it may also include the blasting of communicating cracks between a drill hole and the natural crack formations in the rock, so that the need for a separate blast in the hole before the injection proper is entirely eliminated. In addition, as already mentioned, the blasting charge can be utilized for positively detaching material from a rock surface while, at the: same time, it causes a spreading of the binding or sealing medium not only over considerable parts of the rock surface exposed by blasting but also into cracks and faults in such surface.

The invention may, of course, very well be applied in its primary form together with a fluid injection medium e.g. in the form of a cement slurry or concrete, which should then preferably be of the rapid hardening type. In view of the new technical aspects offered by the invention, however, it is also possible to employ other types of binding or sealing media than just suspensions of this kind. Thus, it is possible by means of a blasting charge to spread a hydraulic binding medium such as cement also in a pulverulent form. In such a case the medium may, if desired, be compressed beforehand into a solid body or briquette which is pulverized during the explosion in the blasting. A hydraulic binding medium of this kind can then be caused to bind and harden rapidly in the cracks and holes of the rock by the addition of water produced by the detonation of the explosive, or deriving from the natural supply of water which can be counted on from the water veins in the rock itself. If this supply of water should be insufiicient, the charge itself may be supplemented either by the addition of a water capsule which is split up by the explosion, or by submerging the charge in water before it is inserted into the hole, the water then suitably being absorbed in an ample quantity in a porous paper wrapping, for example, surrounding the binding medium unit itself. The water may, of course, be replaced by some other additional liquid agent which causes binding and hardening. By way of a further example it may be mentioned that the hydraulic binding medium may be substituted by a partially polymerized synthetic resin composition and the water by a hardener or accelerator to rapidly cause complete polymerization of the same.

In place of media of the type just mentioned, there may also be used sealing media in the form of particular, hydrophilized asphalt compositions, thermo-plastics or similar materials, the viscosity of which may be reduced by the heat produced during the explosion, so that the material can easily flow into thin cracks, etc. under the pressure exerted by the gases of explosion. These latter media may, of course, also be shaped into briquettes or solid bodies which are disintegrated by the detonation.

To further elucidate the invention some applications of the process as well as some forms of charges to be used have been illustrated in the accompanying drawings, in which FIG. 1 is a sectional elevation taken through part of a rock in which a tunnel is in course of construction by blasting; I

FIG. 2 shows to an enlarged scale a vertical section through a fragment of a tunnel back or root;

FIG. 3 is a longitudinal section through a drill hole containing a charge which consists of an explosive and a binding or sealing medium, and

FIG. 4 shows a cross-section through another drill hole having inserted thereinto a charge comprising both a dry binding medium, a liquid capsule and a central blasting charge.

FIG. 1 shows, on the top lefthand side, a typical example of an injection drill hole 1, through which a binding or sealing medium for local tightening or strengthening of the rock can be injected into a rock portion containing numerous cracks as indicated, in the Vicinity of the lower end of the drill hole. In a downwardly directed injection hole of this kind one may advantageously use the most simple form of application of the inventive process which consists in first pouring a certain quantity of fluid concrete or cement slurry into the hole and then submerging into the fluid contents of the hole a blasting charge, which is subsequently fired, so as to both blast apart the walls of the drill hole to establish communication between the hole and the adjacent natural cracks in the rock, and also spread the concrete or cement slurry into the cavities and cracks in the weak part of the rock with considerable force.

It will be apparent that a fluid medium, such as the cement slurry or concrete mass mentioned, is not so handy to use where the drill holes extend horizontally or upwardly from below as may frequently be the case. In such cases, injection may more suitably be carried out with sealing media in solid or at least plastic form so that the medium may be introduced into the drill hole in pieces of suitable shape to surround the blasting charge proper. Such ,a procedure as well as charging the drill hole with a prefabricated composite charge containing both an explosive and a suitable quantity of sealing mass, as will be referred to hereinafter, may, of course, always be used for injection irrespective of the location of the drill hole.

The tunnel 2 indicated in FIG. 1 is in course of being extended in an upward direction and a series of substantially horizontal drill holes 3 have therefore been provided in that part of the rock which forms the back or roof of the tunnel. According to the invention, charging units preferably prepared in advance and of a type which will be more particularly described hereinafter with reference to FIGS. 3 and 4 are inserted into these drill holes 3. The purpose of these charges is not only to detach material from the tunnel back, but at the same time they should produce a strengthening of the new roof surface in the tunnel uncovered by the blast, by spreading a binding or sealing medium both over considerable parts of the fresh rock surface to be exposed and also into such cracks and cavities in said fresh surface which already exist or are produced as a result of the blast.

FIG. 2 shows in an enlarged scale a fragment of a tunnel roof surface newly uncovered by blasting. In this figure the thickened radiating lines and contours 4 indicate the surfaces and cracks over which the binding or sealing medium is spread by the charge 5, indicated by dash-and-dot lines. It should be immediately obvious that by a suitable distribution of the drill holes and the charges a practically continuous spreading of the binding or sealing medium over the entire uncovered surface may be obtained, this being, however, not always necessary or even desirable. When calculating the intermediate distances between the drill holes it should also be borne in mind that the spreading of the binding or sealing medium over the exposed rock surface is always appreciably greater than the penetration of the medium into the racks, etc. It should also be noted that the explosive charge even in the last-mentioned type of blasting may to a considerable extent assist in producing new communications between the drill holes and the natural cracks in the rock so that spreading of the binding or sealing medium is facilitated.

In FIG. 3 there is shown in shortened longitudinal section a drill hole 6 with a sealing charge intended for simultaneous blasting away of the rock. This composite charge which is inserted into the hole in the usual manner inside a stemming 7, is in the form of a rod which may, if desired, be assembled from a number of sections, and which consists of an outer tubular casing 8 formed by a binding or sealing medium and an inner core of an explosive substance 9. The two parts 8 and 9 of the charge may, of course, be stored and transported to the working site separately to be assembled to a unit first when inserted into the drill hole, but the parts of the charge may also be combined in a single unit already at the factory producing the explosive.

In FIG. 3 the tubular casing 8 may be moulded from a quick-setting hydraulic cement in a dry, powdered state, for example, but compressed to form a kind of briquet (of course without any addition of water). Alternatively the casing 8 may be moulded of a thermo-plastic resin or a similar composition, such as hydrophilized asphalt.

On the other hand, it should be understood that the binding or sealing medium may also be introduced into the drill hole at the working site without being preshaped to tubular bodies. Thus the sealing medium, if in the form of a dry cement powder, may be blown or stamped into the drill hole and the filling or plug formed thereby be hollowed to receive the explosive charge. Stamping and hollowing may, of course, also be used in connection with binding or sealing media in plastic form, and is sometimes the most convenient method, the more since it is not absolutely necessary to locate the explosive substance 9 centrally in the filling or tube of the sealing agent. In certain cases an eccentric location of the explosive may even be advantageous in order to produce a more controlled distribution of the binding or sealing material in certain predetermined directions.

Far more important from the point of view dealing with best possible utilization of the blasting charge for spreading the binding or sealing medium in the most favorable manner over a maximum rock surface area is the distribution of the medium in the longitudinal direction of the drill hole. As a general rule, the seal forming material to be spread out should be distributed as evenly as possible longitudinally of that part of the drill hole which is intended to receive the explosive. This is the reason why a substantially tubular body of sealing medium is preferred but on the other hand, if such moulding of the medium is not desirable, for instance because it would be rather expensive, one may equally well use an explosive charge divided into several pieces and place the sealing medium between such pieces spaced in the drill hole.

FIG. 4 shows a slightly modified type of composite charge in a drill hole 10, this latter charge consisting of a central core 11 of an explosive substance surrounded by a capsule 12 containing a liquid such as water and a tubular outer casing 13 of a binding medium, such as a hydraulic cement in dry form. The liquid capsule 12 may be constructed of a plastic material or the like for example, and it is, of course, intended to burst at the blast so that the liquid therein mixes with the dry cement derived from the outer casing 13 disintegrated by the explosion.

The invention must, of course, in no way be considered limited to the examples shown herein, because such examples have only been given to facilitate understanding of the general idea. by those skilled in the art that the basic inventive principle can be applied in many different ways in order to attain the desired result, and that particularly the choice of the binding or sealing medium to be used in the various cases is dependent upon the special requirements that are considered of importance at each particular working site.

What we claim is:

1. A method of creating a layer of sealing material across a broad area of an earth formation, comprising:

(a) drilling a plurality of spaced holes in said formation;

(b) said holes being spaced a predetermined distance from one another;

(0) depositing a sealing material and an explosive material in each of said holes; and

(d) detonating said explosive material;

(c) said predetermined distance between said holes being such that the pressure created by detonation of said explosive material is sufiicient to form interconnecting fractures between said holes and distribute said sealing material throughout said fractures between said holes, whereby a practically continuous layer is formed across the earth formation by said sealing material.

2. A method in accordance with claim 1 wherein the sealing material is distributed along substantially the entire length of the holes.

3. A method in accordance with claim 1 wherein the formation contains water and said water, together with dry, hydraulic cement, forms the sealing material.

4. A method in accordance with claim 1 wherein water is distributed in a dry, hydraulic cement by detonation of the explosive to form the sealing material.

Instead it should be readily understood 5. A method in accordance with claim 4 wherein the water is contained in a frangible container deposited in the hole.

6. A method in accordance with claim 1 wherein the holes have deposited therein elongated cartridges having the sealing material and the explosive material distributed along their entire length.

7. A method in accordance with claim 6 wherein water in a frangible container is also located in the cartridge.

8. A method of blasting to expose a broad area of earth formation and simultaneously seal the surface thereof, comprising:

(a) drilling a plurality of holes into the formation at a level at which the formation is to be removed;

(b) said holes being spaced a predetermined distance apart;

(c) depositing in each of said holes a cementitious material and an explosive material;

(d) detonating the explosive material;

(e) said predetermined distance between said holes being such that the pressure created by the detonation of the explosive material is sufficient to break away the unwanted formation and distribute a practically continuous layer of sealing material on the face of the formation between the holes, whereby the exposed surface of the formation is sealed by said sealing material.

9. A method of blasting to expose a broad area of rock formation and simultaneously strengthen the surface thereof, comprising:

(a) drilling a plurality of holes into the formation at a level at which the formation is to be removed;

(b) said holes being spaced a predetermined distance apart;

(c) depositing in each of said holes a strengthening medium and an explosive material;

((1) detonating the explosive material;

(e) said predetermined distance between said holes being such that the pressure created by the detonation of the explosive material is sufiicient to break away the unwanted formation and distribute said strengthening medium into cracks adjoining the remaining face between the holes, whereby the exposed surface of the formation is strengthened by said sealing material.

References Cited by the Examiner UNITED STATES PATENTS 442,678 12/1890 Hartley 102-23 748,935 1/1904 Durham 102-24 1,480,674 1/1924 Diescher 16623 1,592,104 7/1926 Hallvarson 166-23 1,734,670 11/1929 Greene 166117 X 1,934,701 11/1933 Edwards 166-23 1,987,958 1/1935 Klie 61-36 2,229,264 1/ 1941 Wertz 1172 2,627,169 2/ 1953 Poulter 61-35 2,689,008 9/1954 Allen et al 16623 2,718,264 9/1955 Allen 166--36 X 2,911,046 11/1959 Yahn 10223 X 3,108,443 10/1963 Schuermann et a1. 61-450 CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, EARL I. WITMER,

Examiners.

Claims (1)

1. A METHOD OF CREATING A LAYER OF SEALING MATERIAL ACROSS A BROAD AREA OF AN EARTH FORMATION, COMPRISING: (A) DRILLING A PLURALITY OF SPACED HOLES IN SAID FORMATION; (B) SAID HOLES BEING SPACED A PREDETERMINED DISTANCE FROM ONE ANOTHER; (C) DEPOSITING A SEALING MATERIAL AND AN EXPLOSIVE MATERIAL IN EACH OF SAID HOLES; AND (D) DETONATING SAID EXPLOSIVE MATERIAL; (E) SAID PREDETERMINED DISTANCE BETWEEN SAID HOLES BEING SUCH THAT THE PRESSURE CREATED BY DETONATION OF SAID EXPLOSIVE MATERIAL IS SUFFFICIENT TO FORM INTERCONNECTING FRACTURES BETWEEN SAID HOLES AND DISTRIBUTE SAID SEALING MATERIAL THROUGHOUT SAID FRACTURES BETWEEN SAID HOLES, WHEREBY A PRACTICALLY CONTINUOUS LAYER IS FORMED ACROSS THE EARTH FORMATION BY SAID SEALING MATERIAL.

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