Rock bolt

A rock bolt comprising a bolt body, a bag member directly surrounding an outer periphery of the bolt body adjacent to one end thereof, retainer means from securely fixing the bag member direct to the bolt body, a first tube means for feeding packing material into the bag member and extending through the bag member and toward the other end of the bolt body. The packing material filled into the bag member acts to lid or plug the hole into which the rock bolt has been inserted.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The rock bolts used in tunneling work to support the natural ground at the 
inner periphery of the tunnel are classified broadly into the tightening 
type and the overall adhesion type. The present invention relates to an 
improvement in the overall adhesion type rock bolt. 
(2) Description of the Prior Art 
In order to settle a rock bolt in a hole bored in the inner periphery of a 
tunnel, the rock bolt used in conventional practice is provided with a 
tubular resilient element or the like securely fitted on one end of the 
bolt body to fix the bolt body in the interior of the hole and to plug the 
mouth of the hole. The rock bolt is inserted into the hole and is fixed 
therein by means of the resilient element or the like, and at the same 
time the mouth of the hole is plugged by the resilient element or the 
like. Thereafter packing material such as mortar or cement paste is 
directly fed into the hole to fill its interior. However, this structure 
involves a troublesome insertion of the rock bolt into the hole in that 
the resilient element is fitted on the bolt body. Furthermore, there is a 
disadvantage of imperfect plugging of the mouth of the hole when the hole 
has uneven inner wall surfaces adjacent to the mouth. More particularly, 
while the resilient element which is a manufactured product having a 
certain outer shape is used to plug the hole, the mouth of the hole may 
have a larger diameter than expected or may become rugged because it 
crumbles depending on the nature of the soil or due to vibrations of the 
boring work. Therefore, the resilient element having a predetermined shape 
is not always effective to plug the mouth of the hole. Consequently, the 
packing material injected into the hole will flow out through the gap 
between the resilient element and the opposed soil. 
Besides the tubular resilient element, varied structures have been 
practised as means for plugging such holes but most of them are 
complicated or involve many components. 
SUMMARY OF THE INVENTION 
Having regard to the above state of the art, the object of the present 
invention is to provide a rock bolt which is easy to insert into the hole 
and yet effective to completely plug its mouth. 
In order to achieve the above object, a rock bolt according to the pesent 
invention comprises a bolt body, a bag member directly surrounding an 
outer periphery of the bolt body adjacent to one end thereof, retainer 
means for securely fixing the bag member direct to the bolt body, and a 
first tube means extending from adjacent the one end of the bolt body 
through the bag member toward the other end of the bolt body and having 
openings to communicate with interior of the bag member. 
This rock bolt is inserted into the hole formed in the natural ground 
without any packing material in the bag member, and its insertion is 
therefore carried out with ease. The mouth of the hole is plugged by 
filling the bag member with packing material. This assures a reliable 
plugging of the mouth of the hole even if the inner wall surfaces adjacent 
thereto are rugged. This plugging is also more reliable than the 
conventional plugging by the resilient element where the mouth of the hole 
has a somewhat large diameter after crumbling of adjacent soil. Thus the 
invention provides a rock bolt of desired strength by preventing the 
packing material from flowing out of the hole. 
Other objects and advantages of the present invention will be apparent from 
the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a rock bolt 1 is shown settled in a hole 3 bored in an 
upwardly inclined direction in the ground 2 at the inner periphery of a 
tunnel. The rock bolt 1 comprises a bolt body 4 made of steel bar or the 
like and having one end screw threaded. The bolt body 4 is directly 
covered adjacent the one end thereof by a bag member 5 comprising a cloth 
such as of cotton or polyester or a sheet of synthetic resin (polyester, 
nylon, or vinyl), rubber or the like. Instead of being screw threaded at 
one end or the base end, the bolt body 4 may have a helical projection 
over its entire length. The bag member 5 used in this embodiment comprises 
a tubular cloth fitted on the bolt body 4 adjacent to one end thereof, 
with the longitudinal ends 5a and 5b affixed to the peripheral surface of 
the bolt body 4 by retainer means 17 comprising adhesive tapes. The bag 
member 5 is filled with packing material 6 such as mortar or cement paste, 
and is in tight contact with the inner wall surfaces of the hole 3 except 
at the longitudinal ends 5a and 5b. Where the bag member 5 comprises a 
permeable cloth, the packing material 6 filled into the bag member 5 
exudes therefrom onto the inner wall of the hole 3 thereby to reinforce 
the contact between the bag member 4 and the inner wall of the hole 3. The 
retainer means 17 may comprise an adhesive agent or a combination of 
adhesive tapes 20 and rubber bands or the like which is described later. 
The bolt body 4 has three tubes attached to the outer periphery thereof by 
means of adhesive tapes 20, which are a third tube 7 extending from one 
end of the bolt body 4 through the bag member 5 to a vicinity of the other 
end of the bolt body 4, a first tube 8 extending from the one end of the 
bolt body 4 toward the other end thereof and penetrating the bag member 5 
to open into the interior of the bag member 5 as at 8a, and a second tube 
9 having one end thereof opening into the interior of the bag member 5 as 
at 9a and extending through the bag member 5 to slightly protrude 
therefrom toward the other end of the bolt body 4. These tubes 7, 8 and 9 
are made of synthetic resin. The first and second tubes 8 and 9 constitute 
a first tube means 15, and the third tube 7 constitutes a second tube 
means 16. 
Number 21 indicates a protector cone securely attached to the extreme end 
of the bolt body 4 to prevent a forward end of the third tube 7 from 
getting plugged with earth at the time of inserting the bolt body 4 into 
the hole 3. The packing material 6 such as mortar or cement paste is 
present also in the hole 3 beyond the bag member 5. When the rock bolt 
shown in FIG. 1 is used in a downwardly bored hole, the second tube 9 may 
be shortened such that it slightly protrude from the bag member 5 toward 
the protector cone 21. 
FIG. 2 is an enlarged perspective view of the portion of the rock bolt 
including the bag member 5, and shows the bag member 5 inflated with the 
packing material 6. 
When the rock bolt 1 of the above described construction is inserted into 
the hole 3 bored in an upwardly inclined direction in the ground 2 at the 
inner periphery of the tunnel, the rock bolt 1 is inserted into the hole 3 
with one end of the bolt body 4 forward, until the end of the bag member 5 
at the other end of the bolt body 4 reaches the mouth of the hole 3. This 
insertion of the rock bolt 1 into the hole 3 is carried out easily since 
the bag member 5 is not filled with the packing member 6 at this stage. 
Then the packing material 6 is injected through the first tube 8. The 
packing material 6 pours out of the opening 8a of the first tube 8 into 
the interior of the bag member 5, whereby the bag member 5 is pressed 
against the inner wall of the hole 3 except at the ends thereof axially of 
the bolt body 4. Since the packing material is fluid, the bag member 5 is 
positively pressed against the inner wall of the hole 3 even if the hole 3 
has a rugged wall surface adjacent its mouth. Therefore, once the packing 
material 6 has been filled into the bag member 5, the rock bolt 1 is fixed 
in the hole 3 and the gap between the wall surface of the hole 3 adjacent 
its mouth and the outer periphery of the bolt body 4 is positively closed 
by the bag member 5 inflated by the packing material. Then, on further 
injection of the packing material from the end of the first tube 8 at one 
end of the bolt body 4, the packing material 6 proceeds by way of the 
second tube 9 into the interior space of the hole 3 beyond the bag member 
5 because the bag member 5 is already filled. At this time there is no 
possibility of the packing material 6 flowing out through the mouth of the 
hole 3 since the gap between the inner wall of the hole 3 adjacent its 
mouth and the outer periphery of the bolt body 4 is positively closed by 
the bag member 5. In other words, the bag member 5 acts as plug of the 
hole 3. The air inside the hole 3 which is driven to the depth of the hole 
3 by the incoming packing material is smoothly let out of the hole by the 
third tube 7. When the packing material fills the hole 3 to its deep end, 
the packing material flows out of the hole 3 by the third tube 7, by which 
completion of the filling work is confirmed. Thereafter the rock bolt 1 is 
firmly settled in the hole 3 by the curing of the packing material in the 
bag member 5 and in the depth of the hole 3 beyond the bag member 5. Then 
a plate is mounted on the base end of the bolt body 4 for supporting the 
natural ground, and a nut is attached and tightened to the base end which 
has a screw thread. 
As described, since the bag member 5 is not filled with the packing 
material 6 at the time of inserting the rock bolt into the hole 3, the 
rock bolt 1 is easily inserted into the hole 3. Further, the rock bolt 1 
is firmly settled in the hole 3 since there is no possibility of the 
packing material 6 filled into the depth of the hole 3 beyond the bag 
member 5 flowing out through the mouth of the hole 3. 
It is to be understood that the rock bolt 1 may be settled in the hole in 
the described order of operation where the hole 3 is bored in a vertically 
upward direction in the ground 2. 
It is possible to substitute a tube 10 extending axially along the periphey 
of the bolt body 4 for the first tube 8 and the second tube 9, as shown in 
FIG. 3. The tube 10 extends from one end of the bolt body 4 through the 
bag member 5 to slightly protrude from the member 5 toward the other end 
of the bolt body 4, and includes a cut-out 10a at a position inside the 
bag member 5. 
FIG. 4 shows a modified rock bolt 1 which is used where the hole 3 is bored 
in a downwardly inclined direction in the ground 2 as shown, or in a 
vertically downward direction or in a horizontal direction. This rock bolt 
1 has a third tube 12 extending from one end of the bolt body 4 through 
the bag member 5 to slightly protrude from the bag member 5 toward the 
other end of the bolt body 4, a first tube 8 extending from the one end 
toward the other end of the bolt body 4 and penetrating the bag member 5 
to open into its interior as at 8a, and a second tube 13 having one end 
thereof opening into the bag member 5 as at 13a and extending through the 
bag member 5 to a vicinity of the other end of the bolt body 4. These 
tubes 12, 8 and 13 are secured to the outer periphery of the bolt body 4 
to extend axially thereof. This rock bolt is settled in the hole in the 
same manner as the foregoing embodiment. The packing material 6 is filled 
through the first and second tubes 8 and 13, and the air inside the hole 3 
is evacuated by the third tube 12. The same effect is produced in this 
instance as in the foregoing embodiment. To summarize the difference 
between the foregoing embodiment and the embodiment of FIG. 4, the latter 
has the second tube 3 for filling the depth of the hole 3 with the packing 
material 6 extending to the extreme end of the bolt body 4, and the third 
tube 12 for letting out the air as short as to slightly protrude from the 
bag member 5 into the depth of the hole 3. The embodiment of FIG. 4 may be 
modified to include a tube only for filling the packing material 6 into 
the bag member 5 independently of a tube only for filling the packing 
material 6 into the depth of the hole 3, or the tube 10 having a cut out 
10a as shown in FIG. 3, or the first tube 8 and the second tube 9 as shown 
in FIG. 1. 
FIGS. 5 and 6 show a modified retainer means 17 for fixing the bag member 5 
to the bolt body 4 more positively and in fluid-tight condition. The 
retainer means 17 of this embodiment comprises rings 18 and 18 of adhesive 
elastic material such as butyl rubber, silicon rubber or epoxy rubber 
fitted on the bolt body 4, leaves 19, 19, 19 and 19 of the same material 
as the rings 18 and 18 to secure the first, second and third tubes 8, 9 
and 7 placed on the rings 18 and 18, and adhesive tapes 20 and 20 wound 
about the ends of the bag member 5 placed over the leaves 19, 19, 19 and 
19 and the rings 18 and 18. As seen from FIG. 5, the bag member 5 is 
formed by first fitting a tubular sheet about the bolt body 4 and fixing 
to the bolt body 4 the end of the sheet opposed to the protector cone 21 
at the extreme end of the bolt body 4, then turning back and pulling the 
other end of the sheet toward the base end of the bolt body 4 and fixing 
it to the bolt body 4. It will be understood that the end of the bag 
member 5 opposed to the protector cone 21 is tucked inside the bag member 
5. 
FIG. 7 shows a modified bag member 5' which differs from the described bag 
member 5 in itself having inner and outer peripheral walls 22 and 23. The 
bag member 5' provides a tubular space S for containing the packing 
material 6 when in use. The first tube 8 is connected to one end of the 
bag member 5' so as to open into the tubular space S. The second tube 9 
has one end thereof inside the bag member 5' and the other end protruding 
from the bag member 5'. And the third tube 7 is fixed to the bag member 5' 
so as to penetrate the tubular space S. This unitary construction of the 
bag member 5' has the advantage of easiness in mounting on to the bolt 
body 4. Since the bag member 5' and the bolt body 4 are contacting each 
other across the inner peripheral wall 22, there is no possibility of the 
packing material 6 leaking therethrough. 
FIG. 8 shows a further modification of the bag member 5. The bag member 5" 
here is the same as the bag member 5' in having itself inner and outer 
walls and providing a space S' for containing the packing material 6. The 
bag member 5" differs from the bag member 5' of FIG. 7 in that the bag 
member 5" is not in the tubular form but in a strip form. This bag member 
5" is wrapped about the bolt body so that its lateral edges overlap each 
other peripherally of the bolt body 4 and this overlapping extend over the 
entire length of the bolt body 4. In the other respects the two bag 
members 5' and 5" are substantially the same. The bag member 5" has 
advantages over the bag member 5' having the tubular space S in that the 
former is less expensive to manufacture and easier to mount on and 
dismount from the bolt body 4.