Method for reinforcing a masonry wall

Background of the Invention

This invention relates to a technique developed for coring masonry walls or the like, with less optimal, but adequate ability to core concrete and steel. In areas of the country that are susceptible to seismic shock caused by earthquakes it has become necessary to reinforce masonry buildings which, when constructed, were not built to withstand substantial seismic vibration. The method of reinforcement has generally been a technique which involves drilling long vertical holes through the masonry walls, inserting steel reinforcement bars, and grouting the bars in place with resin grout to provide the necessary reinforcement against seismic destruction. Because of the peculiar nature of drilling in an urban environment in what are often historic buildings and the final use of resin in the drill holes, there are several constraints placed upon such techniques.

The first constraint is that the holes which are to be drilled for long distances, which can be up to 30,48 m (100 feet) in depth, must be straight so that they do not exit the side of the wall while drilling and further, that they are well-centered for structural optimization. Secondly, since the friction of the drilling process is substantial, an adequate method of cooling the bit is necessary.

The use of water for cooling the drill bit has proven to be unacceptable because the resultant leakage has a tendency to break and wash away mortar between the bricks.

Also, the leakage results in an unsightly staining of the face of the masonry wall. Further, the dampness in the wall is a serious problem for the resin grouting formulation. Therefore, dry drilling is necessary not only to eliminate these problems but it is also advantageous because the resin grout can be used immediately. Wet drilling requires that the brick work first be allowed to dry so that the resin grout will cure and bond to the brick. However, dry drilling itself can create the problem of excessive dust. The excessive dust causes a problem of not only settling around the exterior as well as the interior of the building, but collects in the drill hole which plugs the hole and can cause the drill bit to bind up.

Another concern that must be dealt with in the coring of masonry walls is that present core bits which drill a cylindrical hole may leave a core in the hole which must be removed. Present methods for removing such cores have been to cut a series of holes in the face of the masonry wall to extract sections of the core. This technique obviously is undesirable because it requires each hole placed in the face of the masonry wall to be repaired. These repaired holes detract from the beauty of these buildings, many of which have historical and cultural values.

FR-A-2 635 550 discloses a method for reinforcing a masonry wall for supplemental floors of an existing building, this method, which is also suitable for reinforcing walls against seismic destruction, comprising the steps of rotating a drill bit on a drill shaft and coring a hole in the masonry wall producing a limited amount of drilling dust, placing a reinforcing steel bar in the hole and filling this hole with resin grout.

US-A-3 655 001 discloses a system for producing large-diameter, air-drilled holes through rock comprising a hollow, rotatable drill stem having a large bit at its lower end, and surrounded by a pipe which is relatively narrow compared to the hole diameter, which forms between itself and the drill stem, an annular passage. Air is blown downwardly through the drill stem, emerges at an opening at the location of the bit, and carries cuttings through the annular passage to the surface. A vacuum is drawn in a dust diverter immediately above the bit to insure that the cuttings enter the annular passage. Air descending through the drill stem under pressure operates a piston which imparts a hammering action to the bit. Drill stem sections and outer pipe sections may be added as required.

Thus, there exists an urgent need for a masonry coring technique which has the capabilities of drilling long, straight holes, utilizes a dry drilling technique which can control the extraction of the dust, keeps the drill bit cool, and provides for removing the core without having to damage the face of a masonry wall.

Summary of the invention

The present invention provides a substantially improved masonry coring technique which eliminates the problems associated with the coring of masonry walls. The system comprises a drill bit, which is simply a tube of steel with carbide and/or diamond teeth mounted at its lower end for cutting a core in the masonry. The steel tube can be from about 76,2 bis 305 mm (3 to 12 inches) in diameter. Inside the steel tube is a core breaker which conveniently can be a small version of a rotary cone rock bit which pulverizes the core. The bit and the core breaker are driven by a rotatable steel shaft threaded into a driver plate located at the top of the drill bit. The core breaker and the bit are also threaded onto the driver plate.

The shaft is rotated at a controlled speed by hydraulic motors. Controlled downward force is hand-controlled or may be automated. The bit can be kept in alignment since the shaft is quite stiff and the downward force and rotational speeds are kept low. Compressed air is forced down a small diameter axial hole in the steel shaft and exits through and around the core breaker. Air from inside the core drill flows past the teeth at the bottom and up the annulus between the core drill and the side of the hole being drilled. Air cools the teeth and carries out the ground masonry dust.

The system further includes a plastic pipe which has an interior diameter slightly larger than the steel shaft and is placed around the steel shaft. The plastic pipe does not rotate but simply rides on top of the driver plate. The annulus between the top of the plastic pipe and the hole being drilled is closed with a low-friction collar, or a packing. Air from the annulus around the plastic pipe enters the annulus between the inside of the pipe and the steel shaft through a series of holes located near the bottom of the plastic pipe.

Again, at the top of the hole, the annulus between the plastic pipe and the steel shaft is closed with a packing. This annulus is connected to the suction side of an ejector to draw a suction on the annulus. The ejector output goes into a dust collector.

By combining compressed air through the driver shaft and suction on a small area annulus within the bore hole, sufficient air flow is obtained to keep the cutting teeth of the bit cool and carry dust out of the hole. Material too heavy to be carried out is reground by the bit until small enough to be carried out. It is essential to use suction so that flow rate is enhanced over what could be obtained by air pressure applied to a relatively small diameter hole through the driver shaft.

The suction also is of great assistance in providing dust control. Additionally, it lowers the pressure around the drill bit, and particularly around the plastic pipe. This reduces air leakage through cracks or the like in the wall being drilled.

Such cracks are, however, detected by this technique since pressure in the hole near the bit is above atmospheric pressure and puffs of dust can be seen. This detection technique permits sealing before the resin grout is put in the hole. This is important since any resin grout that leaks through a crack detracts from the appearance of the building or causes a clean-up problem.

These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings.

Brief Description of the Drawings

• FIG. 1 is a front view of a masonry coring system according to principles of the present invention;
• FIG. 2 is a front cross-sectional view of a drill bit of the coring system of FIG. 1; and
• FIG. 3 is a bottom view of the drill bit of FIG. 2.

Detailed Description of the Drawings

FIG. 1 is a diagrammatical illustration of a masonry coring system 10 in operation. The coring system is comprised of a drill bit 12, which is a tube of steel with carbide and/or diamond teeth 14 mounted at its lower end for cutting a core in the masonry. Depending upon the particular wall to be drilled, the drill bit can range in size from about 76,2 to 304,8 mm (3 to 12 inches) in diameter. A 101,6 mm (four-inch) diameter is typical for most wall reinforcements. The steel tube preferably has a 9,6 mm (3/8 inch) wall thickness. The length of the steel tube is several times the diameter of the tube which enables the drill bit to act as a stabilizer and maintain a straight hole while cutting. As previously mentioned, located along the lower perimeter of the steel tube are a plurality of cemented tungsten carbide and/or diamond teeth. As can be seen in FIG. 2, the teeth are wider than the wall thickness of the steel tube and have a beveled cutting surface 16 which extends beyond the lower surface of the steel tube. The teeth can be mounted on the steel tube at various angles depending upon their intended use. Typically, the teeth are at a rake angle of from 5 to 15°.

The upper end of the steel tube is threaded onto a steel driver plate 18. The threads are standard Acme square thread. Located within the steel tube is the core breaker 26 which is discussed in more detail later.

The drill bit and the core breaker are driven by a rotatable steel driver shaft 20 which is approximately 47,6 mm (1-7/8 inch) in diameter. A driver shaft comes in 1,22 m (4-foot) sections with each section weighing approximately 13,6 kg (30 lbs). On opposite ends of each driver shaft are a male and a female thread so that the driver shafts can be threaded together as the drill bit works its way down the wall. The initial driver shaft is threaded into the driver plate. As can be seen in FIG. 2, located within the driver shaft is a small diameter axial hole 22, approximately 6,35 bis 12,7 mm (1/4 to 1/2 inch). The hole exists so that compressed air can be forced through the driver shaft. Another reason for the axial hole being of a small diameter is so that the driver shaft can maintain a thick wall for added weight and rigidity so that it can withstand the torque applied to it and remain straight in the hole.

The shaft is rotated at a controlled variable speed and with controlled downward force by a conventional hydraulic motor 24 of the same type previously used for wet drilling. The drill core is also capable of being maintained true and straight by keeping the downward force and the rotational speeds at a low level. A slow rotational speed is also necessary when using carbide teeth for dust control. A hydraulic motor is an ideal power source for controlling the amount of torque applied to the driver shaft. The actual speeds and downward force used depend on the type of material being drilled (concrete, soft brick, hard-fired brick, etc.) and the depth of the hole. Speeds range from 650 rpm for soft brick down to 350 rpm for hard brick. No additional force is applied to the drill bit beyond the weight of the bit and the drive shaft.

Referring now to FIGS. 2 and 3, located within the steel tube of the drill bit is a core breaker 26. The upper end of the core breaker is threaded into and driven by the driver plate. The core breaker conveniently may be a small version of a conventional three rotary cone rock bit which pulverizes the core as the bit cuts the hole. Such milled tooth, air cooled rock bits are commonly used for drilling blast holes in mining and quarrying operations.

A plastic pipe 28 with inner diameter just larger than the shaft is placed around the steel driver shaft. This creates approximately a 3,2 mm (1/8-inch) annulus between the plastic pipe and the driver shaft through which the pulverized masonry is removed. The plastic pipe does not rotate but simply rides on top of the driver plate. However, a Teflon ring 30 is placed between the driver plate and the bottom of the plastic pipe so that the plastic pipe will not be worn down due to the rotating driver plate.

To allow the pulverized core and the drilling dust to be removed through the annulus between the plastic pipe and the driver shaft there are a series of holes 32 approximately 16,5 mm (5/8-inch) in diameter located at the lower end of the plastic pipe and near the driver plate. A coupling 34 with similarly located holes is placed over the end of the plastic pipe for added structural integrity. The plastic pipe is preferably made of a schedule 80 PVC.

At the top of the wall, the annulus between the plastic pipe and the steel shaft is closed with a packing. This annulus is connected to the suction side of a Venturi ejector 36 to draw a suction on the annulus. The pulverized core and the drilling dust is drawn through the annulus by the ejector and into a dust collector 38 which normally is a bag located within a 55 gallon drum 40. Also located at the top of the hole is an air compressor 42 used to force compressed air through the small axial hole in the drive shaft as well as operate the ejector.

In operation, the hydraulic motor rotates the drive shaft which, in turn, rotates the driver plate and the drill bit. The carbide and/or diamond teeth cut a cylindrical hole through the brick. The core thus created by the drill bit is pulverized by the three rotary cone rock bit.

Compressed air is forced down the small axial hole in the steel drive shaft and exits through and around the core breaker. Air from inside the core drill flows past the teeth at the bottom of the drill bit and up the annulus between the core drill and the side of the hole being drilled. This air cools the teeth and carries out the ground masonry. The amount of compressed air that is forced down the hole in the drive shaft must be sufficient to carry out the ground masonry but not too excessive such that it would dislodge the mortar between the bricks. Applicant has found that between 620,5 bis 724 x 10³ N/m² (90 and 105 psi) of air pressure at the top of the wall is sufficient for drilling about the first 12,2 m (40 feet), and then the pressure is slightly increased beyond that level.

The annulus between the top of the plastic pipe and the hole being drilled is closed with a packing. The compressed air that has now exited around the drill bit and into the annulus between the drill bit and the hole being drilled then enters into the annulus between the plastic pipe and the drive shaft through the series of holes near the bottom of the plastic pipe. Again, at the top of the hole, the annulus between the plastic pipe and the steel drive shaft is sealed with a packing. This annulus is connected to the Venturi ejector which draws the dust laden air out of the hole through the annulus and into the dust collector. By combining compressed air through the driver shaft and suction on a small area annulus of the bore hole, sufficient air flow is obtained for keeping the cutting teeth of the drill bit cool as well as sufficient air flow for carrying the dust out of the hole. Pieces of the pulverized core which are too heavy to be carried out by this air flow, are reground by the bit until small enough to be carried out.

It is necessary to use suction so that the air flow rate is enhanced over that obtainable by air pressure alone applied to the relatively small diameter hole through the drive shaft. Furthermore, the suction is of great assistance in providing dust control. It also lowers the pressure around the drill bit and particularly around the plastic pipe. This reduces air leakage through cracks or the like in the wall being drilled.

Such cracks are, however, detected by this technique since pressure in the hole near the bit is above atmospheric pressure and puffs of dust can be seen through any existing cracks. This detection technique is important because it permits the sealing of these cracks before resin is put in the hole.

Once the hole has been completely drilled, the drill string is removed from the hole. A steel reinforcement rod is placed in the hole and resin grout is used to fill the hole to provide the wall with the necessary reinforcement against seismic destruction.

Although the present invention has been described and illustrated with respect to a preferred embodiment thereof, it is to be understood that it is not to be so limited, since changes and modifications may be made therein which are within the full intended scope of this invention as hereinafter claimed.