Abstract:
A multi-purpose anchor bolt, which performs two principle functions: (1) it acts as an active reinforcement for the ground when it is installed and tensioned, and (2) it is used to excavate and advance the face in steps. The invention also includes the method of the multi-purpose anchor bolt&#39;s use. This invention is a hybrid of traditional and mechanized excavation techniques.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to anchor bolts used in ground excavation, and in particular, to an anchor bolt assembly for simultaneous support and excavation of weak ground.  
           [0002]    When an excavation is made in weak ground, i.e., ground that cannot support itself for a reasonable period of time and for a reasonable size of excavation, stabilizing the excavation face, i.e., the front of the advancing excavation, becomes necessary. This is true for both surface and underground excavations.  
           [0003]    The current practice addressing the problem of face stability may be discussed with reference to the two principal excavation approaches, i.e., conventional excavation and mechanized excavation.  
           [0004]    In the conventional excavational approach, the following techniques are used:  
           [0005]    (a) The entire face is divided into a number of smaller, self-supporting (or self-supporting with the assistance of a layer of sprayed concrete) faces for step-wise excavation (one smaller face at each step), and the excavation is advanced to a pre-determined location of the face. See FIGS. 1A and 1B where reference numerals  1  through  9  represent the smaller faces and  12  represents the entire face. FIG. 1A illustrates the initial excavation sequence with primary support. FIG. 1B represents the final sequence with final lining. The example shown in FIGS. 1A and 1B is for an approximate twenty-seven meter wide tunnel having a height of approximately eighteen meters. The principal shortcomings of this technique are that the advance is slow and there is an added expense of supporting the smaller faces and their peripheries.  
           [0006]    (b) The face is pre-supported by using the technique of “forepoling” which comprises the installation of grouted anchors  10  (or dowels) normal to the face. See FIG. 2, illustrating a forepoled tunnel in coal, said tunnel having a roof  11 , face  12 , boreholes  13 , seam  14 , and resin  15  about the dowels  10 . In the case of an underground excavation, the forepoles  10  are often installed at an upward-inclined angle at the crown of the opening. The disadvantages of this technique are that extra time is involved for the grout to harden; there is only the one-time use of the dowels; the hole for the dowel may be unstable; and the dowel only provides a “passive” reinforcement (or stabilizing force). The passive reinforcement results from the outward (toward the excavated space) deformation of the ground which, in turn, is resisted by the dowel, thus producing tension in the dowel and, as a reaction, producing confinement (or stabilizing force) to the face. In contrast, the “active” reinforcement is achieved by pre-tensioning the dowel (or bolt), which restricts the outward deformation of the ground.  
           [0007]    (c) The face is supported by modifying the characteristics of the ground by means of jet grouting. This technique creates grouted columns (horizontally) which help to stabilize the face. The disadvantages of this technique are that: specialized equipment is needed, an exceptionally large amount of time is required for the operation, and the cost of the technique increases with depth because the jet grouting equipment has to be removed after each advance of the face.  
           [0008]    In the mechanized excavation approach, a tunnel boring machine (TBM), normally a shielded TBM, is used. The following techniques are used for supporting the face:  
           [0009]    (a) A physical shield is used to protect the workers and the equipment while the face is stabilized with compressed air or by ground freezing.  
           [0010]    (b) A slurry or earth-pressure balance support is used at the face, ahead of the cutter head of the TBM.  
           [0011]    The disadvantages of this technique include the questionable reliability of the technique, safety aspects, and slow advance of the excavation face. Furthermore, there is a large initial investment, inflexibility with regard to alignment of (tunnel) excavation, huge and expensive back-up system, and requirement of very skilled labor.  
         SUMMARY OF THE INVENTION  
         [0012]    In view of the foregoing disadvantages inherent in the known types of devices now present in the prior art, the present invention provides both passive and active reinforcement, thus making it possible to control the outward deformation of the face, which is the critical aspect of ground control in design of excavations of weak ground.  
           [0013]    The main objectives of the invention are to: provide continuous support and reinforcement to the front (or face) of an advancing excavation in weak ground; advance the face at a higher rate compared to the results of the current methods by performing simultaneous reinforcement and excavation; reduce the cost of advancing the excavation by eliminating the need for renewed reinforcement of the face after each advance; improve the reliability of the face reinforcement and, consequently, the safety of the workers; and eliminate the constraint of not exceeding a threshold for the radius of curvature of the tunnel axis, as in the case of excavating by a TBM.  
           [0014]    To attain this, the present invention provides a multi-purpose anchor bolt, which performs two principal functions: (1) it acts as an active reinforcement for the ground when it is installed and tensioned, and (2) it is used to excavate and advance the face in steps. The invention helps to advance the face at a higher rate compared to the results of the current methods by performing simultaneous reinforcement and excavation functions. The invention reduces the cost of advancing the excavation by eliminating the need for installing new reinforcement at the face after each advance. The invention is a hybrid of traditional and mechanized (such as a full-faced TBM) excavation techniques.  
           [0015]    These together with other objects of the invention, along with various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1A illustrates the initial excavation sequence with primary support for step-wise excavation and support of a tunnel in weak ground.  
         [0017]    [0017]FIG. 1B illustrates the final excavation sequence with final lining for step-wise excavation and support of a tunnel in weak ground.  
         [0018]    [0018]FIG. 2 illustrates forepoling in coal using dowels.  
         [0019]    [0019]FIG. 3 is a longitudinal section view of the invention.  
         [0020]    [0020]FIG. 4A is an end view the invention bearing plate.  
         [0021]    [0021]FIG. 4B is a cross-sectional view along the line A-A′ of FIG. 4A.  
         [0022]    [0022]FIG. 5A is an end view the invention excavation head.  
         [0023]    [0023]FIG. 5B is a cross-sectional view along the line Y-Y′ of FIG. 5A.  
         [0024]    [0024]FIG. 5C is a view along the line X-X′ of FIG. 5B.  
         [0025]    [0025]FIG. 6 illustrates a typical application of the invention to tunneling.  
         [0026]    [0026]FIG. 7 is a longitudinal sectional view along the center line L-L′ in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring to the drawings in detail wherein like elements are indicated by like numerals, there is shown, especially in FIGS.  3 - 5 C, and  7 , a multi-purpose anchor bolt assembly  19  comprised of an elongated anchoring element  20 , a bearing plate  50  attachable to said anchoring element  20 , and an excavation head  60  attachable to said anchoring element  20 .  
         [0028]    The anchoring element  20  is an elongated, generally cylindrical element with a variable diameter. The anchoring element  20  has a forward end  21  terminating in a conical tip  22 , sometimes terminated “head”, and a rearward end  23 . The longitudinal axis of the anchoring element  20  is defined by the forward end  21  and the rearward end  23 . The anchoring element  20  has an internal, central, longitudinal aperture  24  along its central longitudinal axis. The anchoring element  20  may be divided longitudinally into three main portions, a forward portion  25 , a middle portion  30 , and a rearward portion  40 .  
         [0029]    The forward portion  25  begins at the anchoring element forward end  21  and extends rearwardly toward the rearward end  23  a predetermined distance. The forward portion  25  comprises a tapered anchoring screw having a diameter increasing from a minimum diameter at the anchoring element forward end  21  to a maximum diameter at the tapered anchoring screw rearmost end  26 . The forward portion  25  has a helical external surface  27  suggesting a screw thread. The forward portion  25  has a plurality of radial holes  28  extending from the external surface  27  and opening into the anchoring element central aperture  24 .  
         [0030]    The middle portion  30  extends rearwardly along the anchoring element longitudinal axis from the forward portion rearmost end  26  a predetermined distance toward the anchoring element rearward end  23 . The middle portion  30  comprises a drill bit which facilitates the reach of the tapered anchoring screw  25  a desired depth. The middle portion  30  has an external surface  31  shaped with cutting drill teeth  32 . The middle portion  30  terminates rearwardly in a gradually increasing, tapered, radial, flange-like, plate element  33 . The middle portion flange plate  33  has a tapered front surface  34  and a flat rear surface  35 . The flange plate front surface  34  faces the anchoring element forward end  21  and the flange plate rear surface  35  faces the anchoring element rearward end  23 . The flange plate  33  provides a means for drilling as well as providing confinement to the material expelled by the drill bit  30 . In this embodiment of the invention the flange plate rear surface has four key holes  36  formed therein. Other embodiments may have more or less key holes. The key holes  36  accommodate bearing plate keys and excavation head keys as are discussed below.  
         [0031]    The rearward portion  40  extends rearwardly along the anchoring element longitudinal axis from the flange plate rear surface  35  to and terminating at the anchoring element rearward end  23 . The rearward portion  40  comprises a bearing plate  50  and excavation head  60  anchoring element engagement portion as described in more detail below. The rearward portion  40  may be divided along the anchoring element longitudinal axis into two segments, a forward segment  41  and a rearward segment  42 . The forward segment  41  begins at the middle portion flange plate rear surface  35  and extends toward the anchoring element rearward end  23  a predetermined distance. The forward segment  41  has a smooth external surface  43  and a diameter less than the diameter of the drill bit  30 . The rearward segment  42  begins where the forward segment  41  rearwardly ends and extends to the anchoring element rearward end  23 . The rearward segment  42  has a threaded external surface  44  and a diameter approximately equal to the diameter of the forward segment  41 .  
         [0032]    Referring more particularly to FIGS. 4 a  and  4   b , as well as FIGS. 3, 6 and  7 , the invention is further comprised of a bearing plate  50  attachable to said anchoring element  20 . The bearing plate  50  is a round, plate-like element with a diameter several times greater than the diameter of the anchoring element, middle portion, flange plate  33 . The bearing plate  50  has a central hole  51  with a diameter slightly greater than the diameter of the anchoring element rearward portion  40 . The bearing plate  50  has a front surface  52  and a rear surface  53 . The bearing plate  50  is adapted to having its central hole  51  slid onto and positioned coincidentally about the anchoring element rearward portion  40  and having the bearing plate front surface  52  abut the anchoring element middle portion flange plate rearward surface  35 . The bearing plate front surface  52  has four keys  54  adapted to engaging the anchoring element flange plate keyholes  36 . The bearing plate rear surface  53  has a hexagonal sleeve flange  55  about the central hole  51  protruding rearwardly from the bearing plate rear surface  53  a predetermined distance.  
         [0033]    The bearing plate sleeve flange  55  and rear surface  53  are adapted to be engaged by a drilling jumbo, i.e., a large drilling machine, (not shown). The anchoring element tip  22  is positioned perpendicular to an excavation face  12  and pointing at the identified point of initiation of advance into the ground  16 . The anchoring element  20  is driven into the ground  16  until the bearing plate front surface  52  touches the face  12  of the excavation. The screw part  27  of the anchoring element  20  compacts the surrounding material as it advances. This process is similar to the process of driving a displacement pile into the ground for increasing the load-bearing capacity of the ground. The anchoring element forward portion radial holes  28  provide a means for releasing excess pore water pressure that is developed due to the process of compaction. The drill bit  30  acts as an auger and removes the material through which it is advancing.  
         [0034]    The drilling arm of the jumbo is then detached from the bearing plate  50  and is retracted. The invention is further provided with a locking nut  57 . See FIG. 3. The locking nut  57  is adapted to engage the anchoring element rearward portion, rearward segment threaded surface  44 . The locking nut  57  is attached to the anchoring element rearward segment threaded surface  44  and is tightened against the bearing plate sleeve flange  55  using the drilling arm of the jumbo. The tightening of the nut  57  creates tension in the anchoring element  20 , which is made possible by the shear resistance of the contact surface between the tapered anchoring screw  25  and the ground  16 . The bearing plate  50  restrains the potential extrusion of the anchored ground  16  and, as a counter reaction, imparts a confining pressure on the face  12 .  
         [0035]    Referring more particularly to FIGS. 5 a  and  5   b,  as well as FIGS. 3, 6 and  7 , the invention is further comprised of an excavation head  60  attachable to said anchoring element  20 . In operation, the excavation head  60  replaces the bearing plate  50 . The excavation head  60  and bearing plate  50  are never used at the same time on the same anchoring element  20 . The excavation head  60  has a round, torque-transmission plate-like element  70  with a diameter several times greater than the diameter of the anchoring element, middle portion, flange plate  33 . The torque plate  70  has a central hole  61  with a diameter slightly greater than the diameter of the anchoring element rearward portion  40 . The torque plate  70  has a front surface  62  and a rear surface  63 . The torque plate  70  is adapted to having its central hole  61  slid onto and positioned coincidentally about the anchoring element rearward portion  40  and having the torque plate  70  front surface  62  abut the anchoring element middle portion flange plate rearward surface  35 . The torque plate  70  front surface  62  has four keys  64  adapted to engaging the anchoring element flange plate keyholes  36 . The torque plate  70  rear surface  63  has a hexagonal sleeve flange  65  about the central hole  61  protruding rearwardly from the bearing plate rear surface  63  a predetermined distance.  
         [0036]    The torque plate  70  has four excavation arms  66  fixedly attached to its perimeter  71 , lying in the same plane as the torque plate  70  and extending radially out from said perimeter  71 . Each arm  66  is positioned 90° from each adjacent arm. Each arm  66  has a front surface  67  and a rear surface  68 . A plurality of excavation picks  72 , i.e., excavation teeth, are attached to the front surface  67  of each arm  66 . The number of picks as well as the number of arms are a function of ground conditions. A continuous stiffening ring  73  is attached to the excavation arms&#39; free ends  69 , said ring  73  lying in the same plane as the torque plate  70 .  
         [0037]    In operation, the locking nut  57  is unscrewed using the drilling arm of the jumbo. The bearing plate  50  is detached from the anchoring element  20 . The excavation head  60  is then attached to the anchoring element  20  as described above. The excavation head  60  is then activated to excavate material and to simultaneously drive the anchoring element  20  forward. The excavated material, i.e., the muck  17 , can be removed from the face  12  by any available technique (such as letting the muck fall to the ground by gravity or by sucking it directly from the excavation head).  
         [0038]    Referring more particularly to FIG. 6, there is shown a transitional configuration of the multi-purpose anchor bolts in a tunnel face which otherwise may experience face-stability problems. After advancing to a desired location, a number of anchor bolt assemblies  19  of the present invention are required and are installed in a pre-defined pattern. At a given time, most of these anchor bolts will be performing an anchoring function with bearing plates  50 , with only a limited number of the anchor bolt assemblies  19  performing the simultaneous excavation-and-advance function with excavation heads  60 . The actual number of the anchor bolt assemblies  19  performing excavation-and-advance functions will depend on the dimension of the face, the type of ground, and the available number of drilling arms. In any case, it will be possible to assure that the influence of the anchor bolt assemblies are performing excavation-and-advance functions is both temporary and localized and, therefore, the overall stability of the face is not be affected. The theoretical excavation boundary is indicated at  80 . The theoretical limits of material removed by the excavation head  60  is indicated at  81 . The bottom portion  82  of the excavation is normally accomplished by conventional methods, either manual or mechanical.  
         [0039]    In general, the components of the present invention are expected to be made of high-strength steel or a steel alloy. However, the surface of the tip  22  and picks  72  will need to be treated with a film of wear-resistant material, such as tungsten carbide or diamond.  
         [0040]    The integrated, group effect of the installed invention has several critically important and unique features. The invention provides a high degree of compaction of the ground  16 , in and around the face  12 , not only helping to preserve the peak strength (the maximum resistance to the applied loads before yielding begins) of the ground, but also increasing it. The mechanical characteristics (strength and deformability) of the ground  16  are also enhanced by the transformation of the ground into a composite material (ground plus the steel bolts). The potential for extrusion of the excavation face  12  is practically eliminated due to the resistance provided by the interaction among the anchor bolts in the group. Under conditions of squeezing (movement of the ground toward the excavated space) and swelling (expansion of the ground after addition of water), it is possible to control the deformation of the face by withdrawing a small, selected number of bolts  19  or, alternatively, by advancing them to a sufficient depth ahead of the face  12 . In either case, a cylindrical slot (or slots) is (are) created to allow the surrounding ground to deform radially into the slot(s), thus reducing the amount of supporting pressure that might otherwise be required for stabilizing the periphery of the excavation.  
         [0041]    For the very first installation of the anchor bolt assemblies  19  in the excavation face  12 , reference is made to the example pattern in FIG. 6. An example sequence of installation of the anchor bolts and excavation of the ground is illustrated in FIG. 7 which is the longitudinal section along the center line of the excavation face L-L′ in FIG. 6, showing a typical application of the invention to tunneling with the order of advancing the anchor bolts established by considering the need of both maintaining a concave face and the ease of muck removal. As shown in FIG. 7, the anchor bolts  19 ′ have temporarily stopped advancing, but are performing their anchoring function. The top anchor bolt  19  is performing simultaneously its excavating-advancing and anchoring function. In order to produce a slightly concave and, therefore, a more stable face, the anchor bolts (b, c, and d) in the central portion of the face are advanced further than the peripheral anchor bolts a and e. This pattern of relative, or offset, advance would be maintained, if required by the nature of the ground. However, to facilitate the removal of muck  17  (or debris) resulting from the excavation, it may be necessary to advance the bottom anchor bolt (e) slightly more than the upper anchor bolt (a). The sequence of advance of the central anchor bolts (b, c, and d) may also follow the rule of starting from the center (c) and progressing outward (to d and b). The excavated boundary (or walls and roof—in the case of a tunnel) will need to be supported by some means after the face has been advanced for a pre-determined “round” length (in conventional excavation) or a “stroke” length (in TBM excavation). The support of the excavated boundary is shown in FIG. 7. The figure indicates that the primary support is provided by a combination of steel ribs  83 , sprayed concrete  84 , and conventional rock bolts  85 . It is noted that the conventional rock bolts can be replaced by the invention (using anchor bolts of a smaller diameter than that required for the face support) through the performance of its anchoring function with the advantages of providing immediate support and reinforcement and support to the excavation boundary and eliminating the need for stabilizing the bolt hole, with a casing, in loose ground, and the need for grouting the hole in all circumstances. As the excavation progresses a permanent concrete lining  86  is formed.  
         [0042]    The method of the present invention comprises the following steps. The invention has two principal operations, or functions, which are described below as Functions A and B of the individual, multi-purpose anchor bolts. Function A provides active anchoring of the face of an excavation. Function B involves the excavation-and-advance of the face.  
         [0043]    The sequence of operations used for achieving function A is as follows. A drilling jumbo (a large drilling machine) is positioned in front of the excavation face. The bearing plate  50  is coupled with the anchor bolt  20  by inserting the keys  54  into the keyholes  36 . The assembly  19  is attached to the drilling arm of the drilling jumbo. The drilling arm is now positioned such that the tip  22  of the anchor bolt  19  is perpendicular to the face  12  and is pointing at the identified point of initiation of advance into the ground  16 . The anchor bolt  19  is driven into the ground  16  until the bearing plate face  52  touches the face  12  of the excavation. The screw part  27  of the anchor bolt is compacting the surrounding material as it advances. The side holes  28  in the tapered anchoring screw  25  provide a means for releasing the excess pore water pressure that is developed due to the process of compaction. The drill bit  30  acts as an auger and removes the material through which it is advancing. The drilling arm of the jumbo is detached from the bearing plate  50  and is retracted. The locking nut  57  is attached to the threaded portion  44  of the anchor bolt and is tightened against the bearing plate  55  using the drilling arm of the jumbo. The tightening of the nut  57  creates tension in the anchor bolt  19 , which is made possible by the shear resistance of the contact surface between the tapered anchoring screw  20  and the ground  16 . The bearing plate  50  restrains the potential extrusion of the anchored ground  16  and, as a counter reaction, imparts a confining pressure on the face  12 .  
         [0044]    The sequence of operations used for achieving function B is as follows. The locking nut  57  is unscrewed using the drilling arm of the jumbo. The bearing plate  50  is detached from the anchor-bolt assembly  19 . The excavation head  60  is attached to the anchor-bolt assembly  19 , using the arm of the jumbo, by inserting the keys  64  into the keyholes  36 . The excavation head  60  is activated to excavate the material and to simultaneously drive the anchor bolt  19  forward. After advancing to a desired location, the excavation head  60  is removed and the bearing plate  50  is re-attached to the anchor-bolt assembly  19  and is re-tensioned with the locking nut  57 . At this point, the invention returns to its anchoring function (Function A).  
         [0045]    The integrated, group effect of the installed invention has several critically important and unique features. A high degree of compaction of the ground, in and around the face, is provided not only helping to preserve the peak strength of the ground, but is also increasing it. The mechanical characteristics (strength and deformability) of the ground are also enhanced by the transformation of the ground into a composite material (ground plus the steel bolts). The potential for extrusion of the excavation face is practically eliminated due to the resistance provided by the interaction among the anchor bolts in the group. Under conditions of squeezing (movement of the ground toward the excavated space) and swelling (expansion of the ground after addition of water), it is possible to control the deformation of the face by withdrawing a small, selected number of bolts or, alternatively, by advancing them to a sufficient depth ahead of the face. In either case, a cylindrical slot (or slots) is (are) created to allow the surrounding ground to deform radially into the slot(s), thus reducing the amount of supporting pressure that might otherwise be required for stabilizing the periphery of the excavation. The support of the excavated boundary (or walls and roof—in the case of a tunnel) can be provided by the invention (using anchor bolts of a smaller diameter than that required for the face support) through the performance of its Function A with the advantages of providing immediate support and reinforcement and support to the excavation boundary and eliminating the need for stabilizing the bolt hole, with a casing, in loose ground, and the need for grouting the hole in all circumstances.  
         [0046]    Therefore, the main aspects of the invention are to: (a) provide continuous support and reinforcement to the front (or face) of an advancing excavation in weak ground, (b) advance the face at a higher rate compared to the results of the current methods by performing simultaneous reinforcement and excavation, (c) reduce the cost of advancing the excavation by eliminating the need for renewed reinforcement of the face after each advance, (d) improve the reliability of the face reinforcement and, consequently, the safety of the workers, and (d) eliminate the constraint of not exceeding a threshold for the radius of curvature of the tunnel axis, as in the case of excavating by a TBM.  
         [0047]    The invention provides an active reinforcement (or stabilizing force) to a part of the excavation face in weak ground. A group of these devices is used to stabilize the entire face whose area may be many times larger than the area of the device. The invention provides both passive and active reinforcement, thus making it possible to control the outward deformation of the face, which is the critical aspect of ground control in design of excavations in weak ground.  
         [0048]    It is understood that the above-described embodiment is merely illustrative of the application. Other embodiments may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.