Apparatus for on-grade boring

Abstract

A method for installation of an underground pipe includes an initial step of boring a pilot hole through the ground at a predetermined grade angle by extending a drill string having a steerable boring bit mounted thereon through the ground. Upon reaching an end location for the pilot hole, the bit is removed from the drill string, and an expander having a diameter greater than the pilot hole is attached to the drill string, which expander is backed by an impact device such as a pneumatic impactor including a striker that delivers repeated impacts to a rearwardly facing surface of the expander, and by a pipe drawn along behind the expander. The expander is pulled back through the pilot hole at the grade angle while the impactor is operated to aid progress of the expander through the ground and pull the pipe into place behind the expander. Typically in this method the replacement pipe is coupled to a rear end of the expander and the boring bit has a sonde housing containing a sonde attached thereto to indicate to an operator the orientation of a steering face on the boring bit.

1 . An apparatus for installation of an underground pipe, comprising: 
 a forwardly tapering cutting back reamer having front and rear connecting portions, wherein the front connecting portion is configured for attaching the cutting back reamer to a drill string for rotation therewith, and the rear connection portion includes a bearing joint;    an expander connected to the cutting back reamer by the bearing joint so that the expander does not substantially rotate as the drill string and cutting reamer rotate, which expander has a larger outer diameter than the cutting back reamer and is configured to form a hole by compaction of surrounding soil; and    an impact device including a striker that delivers repeated impacts to a rearwardly facing surface of the expander.    
   
   
       2 . The apparatus of  claim 1 , further comprising means for pulling a pipe along behind the expander and impact device.  
   
   
       3 . The apparatus of  claim 1 , further comprising a tubular body having substantially the same outer diameter as a maximum outer diameter of the expander, which tubular body extends rearwardly from the expander, wherein a ratio of effective length of the expander and body to the diameter of the body is at least 3.5 to 1.  
   
   
       4 . The apparatus of  claim 1 , wherein the cutting back reamer has a maximum outer diameter no more than 90% of the maximum outer diameter of the expander.  
   
   
       5 . An apparatus for installation of an underground pipe, comprising: 
 a forwardly tapering cutting back reamer having front and rear connecting portions, wherein the front connecting portion is configured for attaching the cutting back reamer to a drill string for rotation therewith, and the rear connection portion includes a bearing joint, wherein the cutting back reamer is configured to permit steering of the cutting reamer by rotation through less than 360 degrees and return to its starting position for one or more cycles;    means connected to the bearing joint for pulling a pipe along behind the cutting back reamer without substantial rotation of the pipe.    
   
   
       6 . The apparatus of  claim 5 , further comprising a sonde housing mounted in alignment with a steering portion of the cutting back reamer for rotation therewith to indicate to an operator the orientation of the steering portion of the back reamer.  
   
   
       7 . The apparatus of  claim 6 , wherein the cutting back reamer has a generally conical shape, and the steering portion comprises a cut away steering face on one side thereof.  
   
   
       8 . The apparatus of  claim 6 , wherein the cutting reamer has a forwardly tapering, generally conical shape and is mounted non-concentrically relative to the drill string, such that the steering portion comprises an eccentrically extending portion of the cutting reamer.