A method for installing a helical pier using a polyurethane resin grout that results in a support structure capable of bearing heavy loads and exhibiting high lateral strength which is also nontoxic and non-hazardous to the environment

BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a method for the installation of a helical pier, or screw pile, and injecting a grout into the pile. 
         [0003]    2. Description of Related Art 
         [0004]    Screw piles have long been commonly used in connection with foundation underpinning, pipeline tie-downs and in other applications. They are generally used as support structures for heavy loads. 
         [0005]    In one known embodiment, a screw pile consists of an open-ended tubular shaft having one or more helixes externally mounted thereon adjacent to its pointed lower end. The shaft typically comprises a bottom anchor section carrying the helixes and one or more extension sections. The shaft has means, such as pin holes, at its upper end, for insertion of locking pins to connect the shaft with a drive head assembly which functions to rotate the pile into the ground. 
         [0006]    A screw pile will be characterized by load-carrying capacities once implanted in the ground. The load-carrying capacity of a screw pile can be increased by increasing its length and/or diameter or increasing the number of helixes. In addition, the nature of the ground into which the pile is implanted will also affect the load-carrying capacity of the pile. 
         [0007]    A problem inherent with screw piles is, due to their vertical shape and the fact that helixes loosen and disturb the soil as they wind therein, the screw piles do not offer lateral stability that is comparable to other foundations such as concrete footers. For this reason, it is known to inject grout, such as cement, into the borehole created by the screw pile to strengthen and harden the soil adjacent to the screw pile and improve its lateral stability. 
         [0008]    The problems inherent with known methods of injecting grout into a screw pile borehole include a lack of strength necessary to support certain heavy loads an the environmental issues created when using a toxic or hazardous grouts. There is accordingly a need for a method for installing a screw pile using a grout that is strong enough to allow the pile to support heavy loads, provide sufficient lateral stability, and also be nontoxic. 
       SUMMARY 
       [0009]    The present invention is a method for installing screw piles into a target subsurface formation and then stabilizing them with a polyurethane resin grout. In one embodiment, a screw pile is installed into a target subsurface formation using known a means, e.g., by rotationally driving the screw pile into the ground to penetrate the subsurface formation until the desired depth is achieved. Once the screw pile is set in place, injection tubes are then driven into the subsoil so that tube openings are positioned within the borehole and near the bottom anchor. Liquid polyurethane resin is then injected through the tube. As the borehole fills with resin, the tubes are withdrawn from the subsoil. The resin then hardens and stabilizes the screw pile in place. 
         [0010]    In an alternative embodiment of the present invention, a borehole may be predrilled using a drilling rig, with the screw pile then rotationally driven into the base of the borehole. Liquid polyurethane resin is then pored or sprayed (e.g., via spray-foam equipment) into the borehole and allowed to cure. The result is a pile that can bear heavy loads and exhibits high lateral strength using a method and materials that are nontoxic and non-hazardous to the environment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a side view of screw pile installed in a pre-drilled borehole using a method consistent with the present invention. 
           [0012]      FIG. 2  is a side view of a screw pile installed using a method consistent with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIG. 1 , in certain embodiments of the present invention, a borehole  1  is predrilled using any known means capable of creating a borehole such as the use of a drilling rig. A standard screw pile  2  is then installed in the predrilled borehole  1  using any known means for installing screw piles, such as rotationally driving the screw pile into the ground to penetrate the target subsurface formation  3  until the desired depth of the screw pile  2  is achieved. The screw pile  2  is preferably constructed of steel, although any solid material may be used for purposes of the present invention. Once the screw pile  2  has been installed, liquid polyurethane resin  4  is pored into the predrilled borehole  1 . The preferred liquid polyurethane resin  4  is two-part, high-density, geo-tech polyurethane resin, such as the pour foam systems manufactured by Urethane Technology Corporation, Inc., Newburgh, N.Y., but any liquid polyurethane resin  4  can be used. The liquid polyurethane resin  4  is then allowed to cure. The result is a screw pile  2  that can bear a large amount of vertical load that also significantly dampens any lateral oscillations of the load due to the high lateral strength provided to the system by the liquid polyurethane resin  4 . 
         [0014]      FIG. 2  illustrates an alternative embodiment of the present invention. As shown therein, the screw pile  5  is installed in a target subsurface formation  6  using any known means of installation, e.g., rotational drive of the screw pile  5  down through the subsoil. Once the screw pile  5  is installed to the desired depth, an injection tube  7  is injected into the target subsurface formation at an angle, as shown in  FIG. 2 . The outlet  8  of the injection tube  7  is positioned near the helixes  9  of the screw pile  5 . Once positioned, liquid polyurethane resin  11  is blown into the inlet  10  of the injection tube  7  and is ejected through the outlet  8 . The liquid polyurethane resin  11  mixes with the subsoil loosened during the installation of the screw pile  5  and begins to cure. As more liquid polyurethane resin  11  is injected into the subsoil, the injection tube  7  is slowly pulled up and out of the subsoil. As shown in  FIG. 2 , one or more injection tubes  7  may be injected at multiple locations around the screw pile  5  to better distribute the liquid polyurethane resin around the screw pile  5 .