Abstract:
An auger bit is provided for a foundation pile system including a drilling rig adapted for mounting and rotating a grout pipe connected to the auger bit to form an auger. The auger bit includes a stem with lower and upper sections, which taper towards a transition whereat the stem has a maximum diameter. A pile foundation forming method includes the steps of providing a drilling rig, forming an auger with a grout pipe coupled to an auger bit, rotating the auger wit the rig, forming a borehole with laterally displaced soil, pumping pressurized grout through the auger and into the borehole, placing a reinforcing cage in the wet grout and curing same.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to pressure-grouted foundation pile forming equipment, and in particular to an auger bit adapted for substantially fully displacing soil while drilling a borehole, and a corresponding pile forming method using same. 
   2. Description of the Related Art 
   In the field of foundation construction, pile-type foundation systems are commonly used to support a wide variety of structures. Typical structural applications include commercial buildings, institutional buildings, industrial facilities, power plants, transportation and other structures involving relatively heavy static loads. Moreover, dynamic loads associated with operating equipment can be accommodated by pile-type foundation systems. 
   The piles comprising such foundation systems can be formed with poured-in-place concrete, which is generally poured into predrilled boreholes around steel reinforcing bar cages, which have been preset in the boreholes. Auger pressure grouting (“APG”) represents another type of pile forming technique wherein grout (generally comprising cement, fine aggregate, such as sand, and appropriate admixtures) is injected under pressure through the auger bit into the borehole, for example, during the extraction of the auger bit. APG foundations generally offer advantages of relatively high bearing capacities and relatively fast, cost-effective construction. Moreover, significant material savings can often be achieved, as compared to comparable poured-in-place pile foundation systems. 
   Auger pressure grouting with displacement (“APGD”) methods can offer further advantages, particularly with respect to the elimination of excessive spoilage extracted from the boreholes, which presents a disposal problem. Spoilage disposal can be particularly expensive and problematical when hazardous wastes are encountered in the subsurface soil being drilled, for example in environmental remediation projects and on project sites containing buried hazardous wastes. An APGD pile forming apparatus is shown in U.S. Pat. No. 6,033,152. The auger bit shown therein includes a lower section with constant-diameter, right-hand flighting on a downwardly-tapered core and an upper section with reverse (left-hand) flighting on an upwardly-tapered core. The tapered configuration of the lower section tends to displace and compact the soil laterally. The reverse flighting of the upper section pushes the spoilage brought up by the lower section back downwardly and outwardly for compaction. 
   Several benefits can be achieved with such displacement. The lateral displacement tends to “improve” the soil. Specifically, the borehole is thus lined with compacted soil, which tends to contain the grout and prevent its dispersal into loose, uncompacted surrounding soil. Another benefit relates to minimizing the quantity of spoilage exiting the borehole at grade. As compared to conventional, full-flight augers, displacement-type auger bits tend to displace soil capable of displacement. Displacement also avoids the extraction of soft, sloppy, water-laden soil. Another disadvantage associated with conventional, full-flight augers relates to over-excavation whereby excessive quantities of softer soil are extracted from certain portions of boreholes. The resulting over-excavated boreholes often have hourglass-shaped configurations with enlarged portions, which tend to require excessive quantities of grout or concrete, as compared to cylindrical, straight-walled boreholes. Such extra material can be relatively expensive, particularly when multiple and relatively deep boreholes are affected. 
   Lateral soil displacement can be accomplished with auger bits having tapered stems, which tend to force the displaced soil laterally outwardly. An example is shown in U.S. Pat. No. 6,033,152, which discloses a “full” displacement auger bit with a tapered stem and bidirectional flighting. The stem expands upwardly from a minimum diameter at its lower end to a maximum diameter at a transition section where the flighting reverses, and contracts back to a reduced diameter at an upper end of the auger bit. The flighting has a relatively constant diameter, which is approximately equal to the maximum diameter of the stem at the transition section whereby substantially “full” displacement occurs at the transition section. The fully-expanded stem and the bidirectional flighting of this auger bit cooperate to force substantially all of the displaced soil to the transition section of the bit, which “displaces” and compacts it laterally into the borehole periphery. The borehole periphery is thereby “improved”, with greater grout-retaining capacity. 
   Pile forming operations can extend to considerable depths, as required by project structural design criteria and depending upon the load-bearing capacity of the soil conditions encountered at different depths. For example, APGD piles can extend 50 feet or more into the earth. Pile diameters of two feet or more are relatively common. The various combinations of soil, rock and buried concrete (e.g., from previous projects) encountered in such borings tend to affect the materials and configurations of different cutting tips mounted on the augers. For example, soils with high rock content require bits with special cutting teeth and hardened (e.g., heat-treated) steel construction. Soils comprising primarily clay and/or sand, on the other hand, can be drilled with bits having other tip constructions and configurations. 
   Wear-resistance is a relatively important aspect of APGD bit design. Costs associated with bit wear and replacement tend to be relatively high. Therefore, minimizing wear and the attendant costs of same are important criteria. The present invention addresses these design criteria. Heretofore there has not been available a full-displacement APGD system and method with the advantages and features of the present invention. 
   SUMMARY OF THE INVENTION 
   In the practice of an aspect of the present invention, a full displacement system is provided for forming an auger pressure grouted displacement (APGD) foundation pile. The system includes a rig adapted for hoisting and rotating an auger for drilling a subsurface borehole. The auger includes an auger bit with bidirectional flighting and a tapered stem, which cooperate to laterally displace and compact soil on the borehole periphery. The auger bit includes anti-wear protrusions, comprising stepped edges of the stem plates and blocks extending transversely across the flighting upper faces. The protrusions trap soil in protective positions on the stem and flighting for protecting same from wear. Another anti-wear feature comprises a double layer of flighting at the auger bit lower end. In the practice of the method of the present invention, the auger is hoisted and rotated by the rig, which is also adapted for exerting a downward “crowding” force for boring. Upon reaching a desired depth, as determined by soil bearing conditions, the auger is extracted simultaneously with pumping grouting material therethrough and into the borehole. The rig can optionally be utilized for placing a reinforcing cage in the grout material for curing in-place to provide a reinforced pile. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an APGD system for constructing subsurface foundation piles embodying the present invention. 
       FIG. 2  is an enlarged, fragmentary, cross-sectional view of a full-displacement type auger bit boring the upper part of a borehole. 
       FIG. 3  is a side elevational view of the full displacement auger bit. 
       FIG. 4  is a horizontal, cross-sectional view of the auger bit, taken generally along line  4 — 4  in  FIG. 3 . 
       FIG. 5  is an enlarged, fragmentary, horizontal, cross-sectional view of the auger bit, showing soil compacted on and deflected by same. 
       FIG. 6  is an enlarged, fragmentary, side elevational view of the auger bit, showing soil compacted on and passing along the flighting of same. 
       FIG. 7  is a side elevational view of a first bit tip and cutting tool, particularly configured for medium to hard clay, weathered shale and similar soil conditions. 
       FIG. 8  is a side elevational view of a second bit tip and cutting tool, particularly configured for loam and similar soils. 
       FIG. 9  is a side elevational view of a third bit tip and cutting tool, particularly configured for rock, concrete and similar soil conditions. 
       FIG. 10  is a side elevational view of the system, shown installing a reinforcing cage in the borehole. 
       FIG. 11  in an enlarged, fragmentary, side elevational view of the completed foundation pile, showing the reinforcing cage in place. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   I. Introduction and Environment 
   As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
   Certain terminology will be used in the following description for convenience in reference only and will not be limiting. For example, up, down, front, back, right and left refer to the invention as oriented in the view being referred to. The words “inwardly” and “outwardly” refer to directions toward and away from, respectively, the geometric center of the embodiment being described and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof and words of similar meaning. 
   II. Preferred Embodiment APGD System  2   
   Referring to the drawings in more detail, the reference numeral  2  generally designates a pile-forming system embodying the present invention and including a rig  4  with a tracked transport vehicle and power source  6  mounting a mast  8  with a generally vertical, drilling position ( FIG. 1 ) and a generally horizontal transport position (not shown). The mast  8  includes a support column  9 , which slidably mounts a rotary drive  10  adapted for raising and lowering by a cable network  15 . A grout pump  12  is provided for pumping grout through a grout supply hose  14  to the rotary drive  10 . An auger  19  includes a grout pipe  18  drivingly connected to the rotary drive  10  and rotating in a lower guide  17 . 
   In performing a boring operation, the vehicle  6  traverses a job site ground surface  11  to locate the auger  19  over the desired location of a borehole  13 . The rig  4  can include manual or automatic fine adjustment controls for relatively precisely positioning the auger  19  and plumbing the mast  8 . The auger  19  includes an auger bit  20 , which is mounted on the lower end of the grout pipe  18  by a splined coupling  21  and is adapted for boring the borehole  13  when rotated by the rotary drive  10 . The auger  19  is urged downwardly (i.e. “crowded”) by a crowd winch  16  operating through the cable network  15 . Grout is pumped from the grout pump  12  through a swivel connection in the rotary drive  10 , through the grout pipe  18  and into the auger bit  20  for discharge from the lower end thereof during extraction of the auger bit  20  whereby the borehole  13  is filled with cementous grout below the extracting auger bit  20 . 
   The system  2  and the method described thus far are generally similar to known prior art systems. For example, U.S. Pat. No. 6,033,152 for Pile Forming Apparatus shows such a system and is incorporated herein by reference. 
   III. Auger Bit  20   
   The auger bit  20  includes a stem  22  with lower and upper sections  24 ,  26  terminating at stem lower and upper ends  28 ,  30  respectively. The stem lower section  24  is tapered with a downwardly-converging configuration and the stem upper section  26  is oppositely tapered with an upwardly-converging configuration. The maximum diameter of the stem  22  occurs at a transition  32  whereat the stem diameter is approximately equal to the overall diameter of the auger bit  20 . The bit  20  is thus a “full” displacement type. “Partial” displacement augers, on the other hand, have stem diameters that are less than their overall flighting diameters. 
   As shown in  FIG. 4 , the stem  22  includes an outer pipe core  34  and an inner pipe core  35 , which are coaxial with a rotational axis of the auger  11 . The inner pipe core  35  communicates with the grout pipe  18  for pumping grout  36  through the auger  20  for discharge into the borehole  13  via a discharge opening  38  located in proximity to the stem lower end  28 . The grout-carrying, inner pipe core  35  extends substantially full-length with respect to the bit  20 . The outer pipe core  34  is located within the expanded-diameter, upper, displacement portion of the stem  22  and terminates short of the constant-diameter, lower portion. The stem  22  also includes a generally helical, outer shell  40  comprising multiple, juxtaposed plates  42  mounted on the pipe core  34  by spacers  44 . Each plate  42  has leading and trailing edges  46 ,  48  respectively, which are staggered as shown in  FIGS. 4 and 5  whereby protruding portions of the leading edges  46  form respective teeth  50 . The leading edges  46  can be angle-cut to form acute angles defining the teeth  50 . The protrusions defined by the teeth  50  trap a stem-protecting soil layer  52 , which is packed tightly against the outside surface of the stem shell  40  and protects same from wear associated with displaced spoilage  54  moving counter to the auger rotating direction ( FIG. 5 ). 
   The auger bit  20  also includes flighting  56  including a lower, right-hand flighting section  58  and an upper, left-hand flighting section  60  associated with the stem lower and upper sections  24 ,  26  respectively. The flighting sections  58 ,  60  converge at the transition  32  to form a V-shaped flighting point  62 . At the transition  32  the stem  22  diameter substantially equals the flighting  56  diameter whereby substantially all of the displaced soil material is displaced laterally and compacted into the sides of the borehole  13 , i.e. “full” displacement. Conversely, the maximum exposure of the flighting  56  occurs in proximity to the stem lower and upper ends  28 ,  30 . 
   The flighting  56  is equipped with anti-wear protrusions comprising blocks  66  mounted on the upper face of the lower flighting section  58  and generally extending radially outwardly from the stem outer shell  40  to a flighting edge  64 . A suitable number of blocks  66  are located at appropriate intervals along the lower flighting section  58  and form protective packed-soil flighting shields  68 , which reduce abrasive contact between displaced spoilage  54  and the upper surfaces of the flighting lower section  58 , as shown in  FIG. 6 . The auger bit  20  includes yet another anti-wear protrusion consisting of an extra flighting layer  69  mounted (e.g. welded) to the underside of the lowermost portion of the lower flighting section  58 . The extra flighting layer  69  can significantly prolong the useful service life of the auger bit  20 , which might otherwise require earlier replacement due to the severe wear conditions that this lowermost portion of the flighting  56  are often subjected to during drilling operations. 
   The auger bit  20  can include a removable and replaceable tip  70  adjacent to and including the stem lower end  28 . The tip  70  terminates at a cutting tool  72 , which can be configured for the particular soil conditions encountered at a job site. Exemplary cutting tool configurations which are known in the prior art are shown in  FIGS. 7–9 .  FIG. 7  shows the cutting tool  72 , which is particularly configured for medium to hard clay, weathered shale and similar soil conditions.  FIG. 8  shows a cutting tool  74 , which is particularly configured for loam and similar soils.  FIG. 9  shows a cutting tool  76 , which is particularly configured for rock, concrete and similar soil conditions. Various other tips and cutting tools can be utilized with the auger bit  20  of the present invention. 
   IV. Foundation Pile Forming Method 
   In the practice of the method of the present invention, the transport vehicle  6  is transported to a job site and the mast  8  is raised. The rotary drive  10  can be fully raised to commence a drilling procedure. Kelly bar extensions (not shown) are known in the prior art and provide additional boring depth capability by extending the auger  19  above the top of the mast  8 . The rig  4  can be manually and/or automatically adjusted for relatively precise positioning of the borehole and for plumbing the mast  8 . The rotary drive  10  rotates the auger  19  clockwise for the bit flighting configuration shown, i.e. right-hand through the flighting lower section  58 . The weight of the auger  19  can be augmented by the weight of the rig  4  exerted through the crowd winch  16 , which the operator can control in order to maintain a relatively constant downward pressure on the auger  19 . The cutting tool  72 ,  74  or  76  breaks through the subsurface soil, rock, etc. and the right-hand lower section flighting  58  advances the auger  19 , while conveying spoilage upwardly in a helical path defined by the lower section flighting  58 . The upwardly-expanding diameter of the stem lower section  24 , which is associated with its tapered configuration, tends to force the displaced spoilage outwardly, compacting same with the borehole  13  periphery. 
   The left-hand upper flighting section  60  pushes displaced material downwardly for lateral displacement and compaction adjacent to the full-displacement, auger bit transition  32 . Such displacement and compaction provides several benefits. Little or no spoilage is extracted onto the ground surface  11 , thus eliminating or reducing expenses and problems associated with spoilage disposal. Moreover, the periphery of the borehole  13  is compacted and stabilized, thus facilitating the pile formation by effectively retaining the wet grout. Without such stabilization, considerable volumes of grout could flow laterally into the adjacent soil, particularly in loose and sandy soil conditions and in over-excavated boreholes. 
   After reaching the desired depth, the auger  19  is extracted using the cable network  15 . Rotation in the same direction is maintained through the downward insertion stroke and through the upward extraction stroke, whereby soil displacement can occur throughout both strokes. Simultaneously with extracting the auger  19 , cementous material, such as grout  36 , is discharged through the discharge opening  38 . The weight of the column of grout  36  in the auger  19  tends to force the grout  36  into the borehole  13  under considerable pressure, which tends to minimize voids and air pockets. 
   After the borehole  13  is substantially filled with grout  36 , the cable network  15  can be used to hoist a suitable reinforcing cage  78  on the mast  8 . The reinforcing cage  78  can then be lowered into the wet grout  36 . Suitable guides (not shown) can be provided for properly spacing the reinforcing cage  78  inwardly from the borehole  13  periphery whereby the reinforcing cage  78  is substantially centered therein. The reinforcing cage  78  can be suspended in the wet grout  36  by a suitable suspension device attached to the upper end of the reinforcing cage  78 . 
   It is to be understood that the invention can be embodied in various forms, and is not to be limited to the examples discussed above. Other components and configurations can be utilized in the practice of the present invention.