Method of forming a hole in a hard ground structure

Abstract

A method of forming a hole in a hard ground structure including the step of obtaining a drill-bit with a turning axis having: a central portion and first and second axially spaced ends; and a plurality of protruding blades. Each blade has first and second ends, a first end portion, a second end portion, a middle portion, and a circumferentially facing leading portion. The circumferentially facing leading portion of each blade has at least one discrete hard cutter thereat. The method further includes the step of turning the drill-bit around its axis in a first direction so that the blades are advanced, circumferentially facing leading portion first, while pulling the drill-bit axially, with the first drill-bit end in a leading direction, through the hard ground structure to thereby cause the discrete cutters to cut the hard ground structure.

1 . A method of forming a hole in a hard ground structure, the method comprising the steps of:
 a) obtaining a drill-bit comprising:
 a central portion having a longitudinal axis and first and second axially spaced ends; and 
 a plurality of blades protruding radially from the central portion, each blade having: 
 a first blade end, a second blade end, a first end portion, a second end portion, and a middle portion, 
 the first end portion extending from the first blade end to the middle portion, 
 the middle portion disposed between the first end portion and the second end portion, 
 the second end portion including the second blade end and extending from the middle portion towards the second end of the drill-bit; and 
 a circumferentially facing leading portion, 
 the circumferentially facing leading portion of each blade having at least one discrete hard cutter placed thereat; and 
   b) turning the drill-bit around the longitudinal axis in a first direction so that the blades each advances in a circumferential direction, circumferentially facing leading portion first, while pulling the drill-bit axially, with the first drill-bit end in a leading direction, through the hard ground structure to thereby cause the discrete cutters to cut the hard ground structure as the drill-bit is pulled to form the hole in the hard ground structure.   
     
     
         2 . The method of forming a hole in hard ground structure according to  claim 1  wherein the discrete hard cutters are polycrystalline diamond cutters. 
     
     
         3 . The method of forming a hole in hard ground structure according to  claim 1  wherein the at least one discrete hard cutter on each blade is on the first end portion of each blade. 
     
     
         4 . The method of forming a hole in hard ground structure according to  claim 3  wherein there are a plurality of the discrete hard cutters on the first end portion of each blade. 
     
     
         5 . The method of forming a hole in hard ground structure according to  claim 1  wherein the circumferentially facing leading portion of each blade has a curved shape between the first and second blade ends. 
     
     
         6 . The method of forming a hole in hard ground structure according to  claim 4  wherein the discrete hard cutters each has a cutting edge and the cutting edges on each blade are arranged to cooperatively extend in a curved shape. 
     
     
         7 . The method of forming a hole in hard ground structure according to  claim 1  wherein the middle portion of each blade comprises a radially outwardly facing surface that is substantially parallel to the longitudinal axis. 
     
     
         8 . The method of forming a hole in hard ground structure according to  claim 7  wherein a discrete hard element is fixed at the radially outwardly facing surface of each blade to provide wear resistance. 
     
     
         9 . The method of forming a hole in hard ground structure according to  claim 1  wherein the drill-bit comprises at least a one nozzle between adjacent blades and further comprising the step of directing a fluid under pressure through the at least one nozzle to clear foreign matter from between the adjacent blades. 
     
     
         10 . The method of forming a hole in hard ground structure according to  claim 1  wherein the step of turning the drill-bit while pulling the drill-bit comprises turning the drill-bit while pulling the drill-bit with a component that is threadably engaged with the drill-bit at one of the axially spaced ends of the drill-bit. 
     
     
         11 . The method of forming a hole in hard ground structure according to  claim 10  wherein the other of the axially spaced ends of the drill-bit is threaded to engage a component usable to advance the drill-bit axially. 
     
     
         12 . The method of forming a hole in hard ground structure according to  claim 3  wherein the at least one discrete hard cutter on each blade is on the second end portion of each blade. 
     
     
         13 . The method of forming a hole in hard ground structure according to  claim 1  wherein each blade defines an edge at the circumferentially facing leading portion and the at least one discrete hard cutter extends radially outwardly beyond the edge. 
     
     
         14 . The method of forming a hole in hard ground structure according to  claim 1  wherein the at least one discrete hard cutter has a rounded cutting corner. 
     
     
         15 . The method of forming a hole in hard ground structure according to  claim 1  wherein the at least one discrete hard cutter has a cylindrical shape. 
     
     
         16 . The method of forming a hole in hard ground structure according to  claim 1  wherein the drill-bit has a radial dimension and an axial dimension and the axial dimension is greater than the radial dimension. 
     
     
         17 . The method of forming a hole in hard ground structure according to  claim 16  wherein the axial dimension is not greater than 1.5 times the radial dimension. 
     
     
         18 . The method of forming a hole in hard ground structure according to  claim 16  wherein the axial dimension is on the order of 1.2 times the radial dimension.