Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Reexamination Certificate
2002-01-24
2004-09-21
Shackelford, Heather (Department: 3673)
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
C405S259100, C405S288000, C405S302100, C405S303000
Reexamination Certificate
active
06793445
ABSTRACT:
BACKGROUND
The present invention relates to insertion of rock bolts used in applications such as but not limited to underground mining. More particularly, the invention relates to an automatic drilling and injection head and a method of use thereof for automatic installation of self drilling rock bolts thereafter secured by preselected anchoring compounds.
Rock bolts are commonly used as anchors for securing rock strata to prevent unwanted collapse during mining operations such as excavation and the like. They are a proven means of securing rock masses in underground excavations and road tunnelling which might otherwise be in danger of collapse. Efficient installation of rock bolts is a critical facet of mining operations and it is desirable that this non productive part of mining activities be done as speedily as possible.
The concept of rock bolting involves the installation of a bolt in a predrilled hole in rock whose length is longer and whose diameter is slightly larger than the diameter of the rock bolt inserted therein.
PRIOR ART
There are in existance a wide variety of rock bolts and drilling machines for insertion of said bolts. The drilling machines employ drill rods with a cutting tip or drill bit on the leading end of the drill rod. The drill bit is usually larger in diameter than the drill rod to ensure a hole diameter at least slightly larger than the diameter of the drill rod. In order to drill a hole, the drill rod is rotated and urged against the rock face to initiate penetration.
In accordance with conventional methodology, most drill rods use air or water as a flushing fluid to flush rock cuttings from the drill hole during drilling. The flushing fluid is normally pumped through a central hole in the drill rod exiting the cutting tip then flowing out of the drill hole between the sides of the drill rod and the rock bolt hole thereby removing the rock cuttings from the hole during the drilling operation. The hole flushing clears the hole to accommodate the anchoring compound which is normally inserted manually after drilling. Whilst all drills employ rotation and axial thrust some additionally use impact drilling for very hard rock. Drilling into softer rocks such as sandstone will generally only require rotation and thrust. Hole drilling speed is a function of the type of rock, drill bit material and configuration and axial force applied during drilling. After drilling is complete, rock bolts are inserted once the drill rod has been withdrawn. There are two broad categories of rock bolts which are differentiated by the manner of engagement between bolt and rock. Bolts in the first category rely on frictional engagement between the bolt and at least a portion of the wall of the pre-drilled bolt hole. Bolts in the second category rely for their anchorage on grouting between the rock wall and bolt. The grouting compound will either be chemical or cement based.
Friction bolts rely on expansion of an associated member such as a sleeve which is engaged for example by rotation of a nut after insertion of the bolt in its hole, whereupon the sleeve engages the wall tightly to resist unwanted withdrawal. Bolts of this type include expansion shell bolts, inflating bolts and split set bolts.
Grouted rock bolts rely entirely on the integrity of the grouting compound which is inserted into the bolt hole once the hole is drilled. Maximum engaging strength is not achieved until the grout has set and has formed a solid anchor around the rock. A typical grouting compound is polyester resin although other compounds are used.
The coal industry commonly uses grouted rock bolts using resin anchors. The resin is held in cartridges which are inserted into predrilled bolt holes prior to insertion of the bolt. The resin cartridges are filled with resin mastic and resin catalyst and are typically 500 mm to 1500 mm in length. They must be of a diameter smaller than the bolt hole to enable insertion.
According to conventional methodology the steps involved in insertion of a resin anchored rock bolt are as follows:
a) drilling a hole of a diameter which is larger than the diameter of a bolt to be inserted;
b) withdrawing the drill rod from the hole;
c) manually inserting the resin cartridge;
d) inserting the bolt into the hole such that the bolt engages the resin cartridge and urges it to the back of the hole;
e) rotating and advancing the rock bolt such that the bolt penetrates the cartridge causing mixing of the cartridge contents (mastic and catalyst);
f) urging the bolt to full penetration whilst continuing rotation of the bolt;
g) allowing resin to cure and harden; and
h) tightening a nut on the proximal exposed end of the bolt to securely engage said bolt.
Whilst the above described method, used in various forms over the past twenty years, results in effective anchorage of rock bolts in underground mining applications, the process described is labour intensive, time consuming and therefore costly and is susceptible to poor quality control. There has been a long felt want in the mining industry for more efficient installation of bolts of the type which rely on grouting for anchorage, to reduce the time and labour component disadvantages of the present methodology.
Attempts have been made to address the aforesaid problems in resin anchored bolt installations by using self drilling rock bolts of the type described in patent application PCT/A91/00503. One such attempt involved the use of self drilling hollow rock bolts to the obviate the step of pre-drilling followed by withdrawal of the drill prior to insertion of the bolt. The self drilling bit functions as a combined drill and bolt. During self drilling, the hole is flushed with water to expel rock debris until the bolt has reached maximum depth whereupon the fluid is turned off. A grouting compound is then inserted into the space between the bolt and hole wall until the available space is occupied by the anchoring compound which could be resin or cement grout. Cement grout has major advantages over resin in that it can be mixed in a machine then pumped into the rock bolt hole. As the curing time for the cement grout is typically several hours, it is proceedurally simple to mix and pump cement grout and flush hoses and the machine before curing. The major disadvantage of cement grouting is that the cement takes several hours to cure which is unacceptable in the coal industry. Resin anchored bolts have the advantage that the resin cures in about 20 seconds but this fast setting may cause problems of clogging in the resin a delivery and mixing system once the mastic and catalyst, which are initially separated, have thoroughly mixed.
INVENTION
The present invention seeks to ameliorate the aforesaid prior art disadvantages by providing a method and associated apparatus for installing and anchoring self drilling rock bolts using an improved resin delivery and mixing system. The present invention also seeks to provide a system for installation of self drilling bolts, quickly and efficiently without clogging of the reson and delivery system. According to one embodiment of the invention there is porvided a drilling head for attachment to a drilling machine wherein the drilling head has means for rotation thrust and feed of a rock bolt, means for water injection and an apparatus for resin injection.
More particularly, according to one embodiment, the invention comprises a drill head adapted for releasable attachment to a drilling apparatus, wherein the drill head includes means to receive a proximal end of a self drilling rock bolt having an internal cavity and further comprising means to enable injection through said internal cavity of resin grout such as a mastic and a catalyst, wherein said mastic and said catalyst whilst present in said drill head are separated until co injection into said internal cavity of said bolt, whereupon mixing of said mastic and catalyst occurs to form a resin in which said bolt anchors; wherein the resin is injected into said cavity until it exits an opening in a distal end of said bolt and fills a space betwe
Charlton Paul
Flynn Daniel
Saldano Lisa M.
Saltamar Innovations
Shackelford Heather
Wertsberger Shalom
LandOfFree
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