Abstract:
A system and method for supporting a structural foundation supported by a subterranean earth strata. A plurality of support piling segments are disposed in a columnar array beneath the foundation. Each segment has a central channel for receiving a tension or reinforcing member. The distal end of the tension member is anchored beneath the first or lowermost segment in the array. The anchor is sized such that it may not be withdrawn or pulled up through the channels in the segments. After the desired depth of the column is reached, a tension adjustment mechanism is affixed to the proximal end of the tension or reinforcing member and tightened to provide additional compressive force and strength to the columnar array.

Description:
[0001]     This application claims priority to co-pending U.S. Provisional Application Ser. No. 60/489,403, filed Jun. 24, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention pertains to the field of lifting, repairing, leveling, and supporting structural foundations, more particularly the field of driving piling segments on top of each other into the earth beneath a structural foundation to form a columnar array or piling for supporting the foundation.  
       BACKGROUND OF THE INVENTION  
       [0003]     Currently available methods of constructing columns and pilings underneath existing structural foundations share many features. Most drive, one at a time, with a jack, precast concrete segments with centrally located longitudinal holes into soil beneath a foundation. In some embodiments all the segments are slid onto a cable or strand that is epoxied into the first segment and extended out the piling top as the segments are driven to the ultimate depth; in others, reinforcing rod is inserted through the segment holes after the piling is complete. In either case, jacking is stopped and the piling is completed when a desired combined vertical reactive and friction force equals a predetermined jacking force. The piling is generally completed by placing a cap on top of the topmost piling segment, jacking the foundation up from the cap to its desired position, placing spacers and shims between the cap and foundation, removing the jack, and backfilling the space between the piling, cap, spacers, and foundation.  
         [0004]     A weakness common to the state-of-the-art foundation support systems is a lack of lateral stiffness in the finished pilings. The requirement of providing support under an existing structure in most cases precludes the use of a continuous, one-piece piling. Construction of a piling with successive stacking of short segments makes possible the lifting and support of an existing foundation, but the resulting stack is likely to be unstable over time. Although the finished stacked piling is essentially embedded in a hole and surrounded by soil, the soil may not be stable. In many cases the foundation to be supported was in need of repair precisely because the underlying soil had shifted due to clay content, seasonal moisture variations, water table fluctuations, neighborhood blasting, or seismic events.  
         [0005]     The introduction of a reinforcing rod or cable into the central hollow portion of a segmented piling, even with subsequent filling of the hollow with epoxy or grout, while improving initial alignment of the piling segments, adds little to the lateral stiffness or columnar strength of the completed piling.  
       SUMMARY OF THE INVENTION  
       [0006]     Applicants&#39; invention is a support system and process for installing post-tensioned segmented support pilings under structural foundations. By applying tension to a reinforcing member that extends the full length of the piling, all the segments are put into compression, essentially converting the stack or column into a continuous entity. Such post-tensioning and compression provide significantly more resistance to shear stress than epoxy or grout injected into the central conduit of the segments. Applicants&#39; post-tensioned pilings resist shifting underground strata more successfully and for longer periods than currently available pilings. The unique anchor structure significantly reduces the likelihood that the tensioning member extending through the segments will be pulled through and out any of the segments in the column. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  illustrates a cylindrical or rectangular concrete piling segment, a reinforcing member and a threaded coupling inserted through the segment&#39;s central channel, and an anchor mechanism that prevents travel of the reinforcing member back through the segment hole.  
         [0008]      FIG. 2  shows the invention in place with a first piling segment being driven, a second segment awaiting placement and a reinforcing member extending through the segments.  
         [0009]      FIG. 3  shows a completed piling column with numerous segments, a reinforcing member tensioned with a tension adjustment at the top of the column and an anchor at bottom of the column, a piling cap, and two spacer blocks.  
         [0010]      FIG. 4  illustrates an alternative embodiment with a plurality of reinforcing members attached to a bridle.  
         [0011]      FIG. 4A  is a view taken along line  4 A- 4 A of  FIG. 4 .  
         [0012]      FIG. 5  illustrates yet another embodiment wherein reinforcing members extend along external slots in the segment as well as through the central conduit.  
         [0013]      FIG. 5A  is a view taken along line  5 A- 5 A of  FIG. 5 .  
         [0014]      FIG. 6  shows an embodiment with a large washer anchor and a bullet nose cover. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]      FIG. 1  illustrates the first end ( 10 ) of a reinforcing member ( 14 ) completely inserted through the substantially centrally located channel ( 18 ) in the body ( 17 ) of the segment ( 12   a ). The channel ( 18 ) is substantially parallel with the longitudinal axis L of the first piling segment ( 12   a ), the axis L being substantially vertical when the first piling segment is in its final installed position. The reinforcing member ( 14 ) has a second end ( 11 ) which will extend from the top of the last or uppermost segment when the column is completed. The member ( 14 ) has a length longer than the anticipated height of the final piling column. The reinforcing member may be cable, rod, bar, or any other suitable material for providing columnar strength to the support as will be described further.  
         [0016]     An anchor mechanism ( 20 ) is attached to the protruding first end ( 10 ) of the reinforcing member ( 14 ), the anchor is sized to prevent the withdrawal of the first end of the reinforcing member back through the piling segment channel.  
         [0017]      FIG. 2  shows a portion of excavated subterranean strata or earth ( 23 ) beneath the area of the structural foundation ( 22 ) to be supported at least sufficient to accommodate a jacking pump ( 24 ) and jack ( 25 ), a slotted guide block (if needed) (not shown), and the first piling segment ( 12   a ). The first piling segment ( 12   a ) is placed into excavated earth beneath the structural foundation ( 22 ) to be supported. As needed a slotted guide block (well known in the art) is slid onto the reinforcing member ( 14 ) and the guide block is placed on top of the first piling segment. The guide block serves to first guide the reinforcing member angularly away from the jack ( 25 ) and to secondly guide the reinforcing member ( 14 ) substantially horizontally away from the jacking area and out from under the structural foundation ( 22 ). The guide block can be built into or attached to the jack ( 25 ). Depending on the flexibility of the reinforcing member ( 14 ) and the geometry and configuration of the jacking means ( 24  and  25 ), the guide block may not be needed.  
         [0018]     The first piling segment ( 12   a ) is driven or jacked into excavated earth beneath the structural foundation ( 22 ) to be supported then a second piling ( 12   b ) segment, substantially identical to the first piling segment ( 12   a ), is slid between the guide block and the first piling segment ( 12   a ) onto the second end ( 11 ) of the reinforcing member ( 14 ) as far as the first piling segment will allow.  
         [0019]     The second piling segment ( 12   b ) is then driven or jacked into excavated earth, thus driving the first piling segment ( 12   a ) deeper below the structural foundation ( 22 ). Next, additional piling segments ( 12   c - 12   z ) are repetitively slid onto the reinforcing member ( 14 ) beneath the guide block and successively jacked each into excavated earth until a last, topmost piling segment ( 12   z ) causes the piling to reach a desired depth or the jacking means to reach a desired reactive force. The axis of each of the central conduits is axially aligned with an adjacent conduit.  
         [0020]     In  FIG. 3  it may be seen that the guide block is removed and a piling cap ( 30 ) has been placed on the reinforcing member ( 14 ). The piling cap ( 30 ) has a substantially centrally located channel ( 32 ) through which is inserted the second end ( 11 ) of the reinforcing member ( 14 ) until the piling cap ( 30 ) is resting on top of the last piling segment ( 12   z ). Again, it should be noted that he axis of the central conduits of each segment is aligned with the central conduit of the adjacent segment.  
         [0021]     The second end ( 11 ) of the reinforcing member is severed a desired distance above the top of the piling cap and a tensioning device ( 40 ) is mechanically attached (or cause to be threaded) to the second end ( 11 ) of the reinforcing member ( 14 ) substantially adjacent to the top of the piling cap. Then, with a desired torque, the tensioning device is tightened on the second end ( 11 ) of the reinforcing member ( 14 ), thereby introducing a tensile force into the reinforcing member ( 14 ) and a compressive force (or columnar strength) into the captured stack or column of piling segments. The tensioning device may be as simple as a threaded nut locking down onto a threaded coupling attached to the reinforcing member. The second end ( 11 ) of the reinforcing member ( 14 ) may be severed before the piling cap is attached, or after the post-tensioning is complete.  
         [0022]     Using the piling cap ( 30 ) as a base, the structural foundation ( 22 ) is jacked to its desired position above the piling cap ( 30 ), a spacer block or blocks ( 34 ) placed between the piling cap ( 30 ) and the structural foundation ( 22 ), the jacking means ( 24  and  25 ) removed, and the excavated area backfilled around the piling cap, spacer block, and structural foundation. Steel or metal shims may be inserted between the spacer block and the structural foundation if needed.  
         [0023]     As an example of other embodiments (see  FIGS. 4, 4A ,  5 , and  5 B), the present invention can be practiced with more than a single reinforcing member ( 15   a - 15   d ) in or on a segmented piling ( 12   a ). The first piling segment ( 12   a ) could be fitted with a metallic bridle ( 52 ,  FIG. 4 ) or basket-like device ( 53 ,  FIG. 5 ), or an embedded device (not shown), to which multiple reinforcing members may be attached. The reinforcing members may be contained in inside channels ( 18 ) in the individual segments ( FIGS. 4 and 4 A), or they may extend externally ( FIGS. 5 and 5 A) in slots on the segment ( 12   x ). Some or all of the reinforcing members may then be post-tensioned with means similar to that in the embodiment described above.  
         [0024]     Alternatively, the earth may or may not be excavated such that the first piling segment is driven into excavated earth but once the second piling segment is placed on top of the first segment and driven, the first piling segment is driven into unexcavated earth. Another embodiment has the first piling segment being driven into unexcavated earth.  
         [0025]     In another embodiment ( FIG. 6 ), a large washer ( 60 ) may be used as part of the anchor such that it has substantially the same diameter as the piling segment. This larger washer ( 60 ) provides a protective end surface to the first piling segment ( 12   a ) to reduce damage to the first piling segment as it is being driven into the earth. Where appropriate, a bullet shaped nose member ( 62 ) may be attached to the washer ( 60 ) and cover the anchor mechanism nut ( 20 ). This nose member ( 62 ) both protects the first piling segment ( 12   a ) and makes it easier to drive the first piling segment into the earth.  
         [0026]     While the reinforcing member ( 14 ) is shown (see  FIG. 1 ) being secured beneath the segment ( 12   a ) by the washer and nut arrangement to form the anchor mechanism ( 20 ), other means for rigidly securing the member in a manner so as to prevent removal of the first end of the reinforcing member through the first piling segment could be used. For example, the washer could be welded to the reinforcing member or a cotter pin could be inserted through the reinforcing member below the washer.  
         [0027]     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon the reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications that fall within the scope of the invention.