Explanation of the Drill Systems AP1000 Becker Hammer Drill
The significant features of the Becker Hammer drilling method that set it apart from other drilling methods are:

  • The unique method of driving a casing with a percussion hammer without the necessity of rotation.
  • The casing is a double wall drive pipe with a large center opening which allows even large cobbles to be lifted without prior crushing.
  • Drilling and casing the hole are combined in one operation. No duplication of effort by first drilling, then casing, then cleaning out the casing.
  • Provides automatically, as part of the drilling process, a continuous and accurate geological sample of the penetrated formation (the drill in fact penetrates the formation by sampling it).
  • Due to the rapid rate of penetration, field engineering time is significantly reduced.
The Becker Hammer Drill is able to penetrate sand, gravel and boulder formations at speeds greater than conventional methods, and with immediate and accurate analysis of the formations encountered.

With the Becker Method, a double wall drive pipe is driven by a percussion hammer, while compressed air is forced down the annulus of the drive pipe. The compressed air continuously lifts the material penetrated by the drive bit to the surface through the center of the double wall pipe. At the top of the drive pipe the geological material is diverted and passes through a discharge hose to a cyclone which slows down the discharge velocity. The discharged material is accumulated in suitable containers as it emerges from the cyclone, and samples are taken at specified intervals for analysis of the formations drilled. As the center of the drive pipe is always clear and the bit always remains on the bottom of the hole, SPT, Calmod or Shelby samples can be taken at any time, of if required, PVC Pipe, overburden casing, piezometers, inclinometers or other instruments can be set before the drive pipe is withdrawn. Upon reaching bedrock, a hydraulic rotary attachment can be set into position and conventional drilling methods can proceed with the double wall pipe serving as the overburden casing. Chip sampling with tricone rock bits or diamond coring can be readily achieved as the difficulty of penetrating the overburden has been overcome. On completion of a hole, the double wall drive pipe is withdrawn by a puller system comprised of two hydraulic cylinders.
The Becker double wall drive pipe is a highly designed and thoroughly engineered product and its efficiency and reliability have been proven over many years of use. The drive pipe is fabricated from two heavy duty pipes, one inside the other, and handles as one unit. Several drive pipe sizes are available including:

  1. 5 ½ inch O.D. X 3 ¼ inch I.D.
  2. 6 5/8 inch O.D. X 4 ¼ inch I.D.
  3. 9 inch O.D. x 6 inch I.D.
The drive bit is made of tempered cast steel of a special alloy tough enough to withstand the continuous impact. Bits come in various designs to suit different formations encountered. The basic drive bit has an outside diameter equal to the drive pipe. With a bit the same diameter as the drive pipe, the possibility of sample contamination is remote.
 
 
4 tooth crowd in bit and 8 tooth crowd out bit
8 tooth crowd out open and 8 tooth crowd out closed bit
The continuous sampling that occurs ensures that no critical formations such as soft seams, water bearing zones, organic layers or clay layers are missed. With other drills that sample by the tube or coring method, soil formations can be missed and critical strata may be overlooked. Air is generally used as the drilling fluid. However, in certain cases such as heavy clays, water saturated silts and sand or to control dusty conditions, water may be injected with the air as the drilling medium. For this reason, most drills are equipped with a water pump. When drilling with compressed air, the sample material is lifted continuously at an air speed of approximately 5000 feet per minute. Penetration rates up to 50 feet per hour can be achieved in gravel , sand and cobble formations, accompanied by a continuous sample with optimum recovery. The drill is equipped with a detachable, hydraulic rotary drive. This unit conveniently attaches under the diesel hammer and in minutes converts the rig into a rotary drill. Large boulders can then be triconed, or bedrock can be cored using a regular core barrel. In addition to the regular constant–recovery sampling, the Becker Hammer drills are equipped with 140 lb. automatic drop hammers (300 lb. auto hammers on request) for Standard Penetration Testing (SPT) using a Split Spoon, use of Shelby tube testing for laboratory use, hydraulic piston sampling and the use of other special samplers.

In addition to the sampling techniques described above, the Becker Hammer drill is widely used for Becker Penetration testing, also know as Becker Density Testing. The Becker Penetration Test (BPT) consists of counting the number of blows required to drive the casing one foot into the ground while recording bounce chamber pressures. By counting blows for each foot of penetration, a continuous record of penetration resistance can be obtained for the entire soil profile. The Becker Penetration Test (BPT) has been found highly sensitive with a wider range than SPT in accurately determining denseness of any sand – gravel formation or of water bearing sand, and is used extensively in liquefaction investigations.
 
 
6 5/8" O.D. 8 tooth crowd out Becker bit and SPT drive shoe comparison
Bounce chamber pressure gauge
In 1986, Leslie F. Harder, Jr. and H. Bolton Seed, carried out research sponsored by the National Science Foundation at the University of California, Berkeley, CA on the use of the Becker Hammer Drill and the Becker Penetration Test in coarse grained soils. The resulting report “Determination of Penetration Resistance for Coarse-grained Soils Using the Becker Hammer Drill” (Report # UCB/EERC-86/06) created a set of standard procedures for performing the Becker Penetration Test. Using the recommended procedure, a new correlation between the Becker Penetration Test (BPT) and Standard Penetration Test (SPT) was developed and is widely used today.

Later research by A. Sy, and R.G. (Dick) Campanella in 1994 considered the energy output of the Becker Drill diesel hammer and the end bearing component of the driven Becker Hammer casing. Their research is summarized in “Becker and Standard Penetration Tests (BPT – SPT) Correlations with Consideration of Casing Friction” and “BPT-SPT Correlations for Evaluation of Liquefaction Resistance in Gravelly Soils.” The Sy and Campanella approach involves instrumenting the Becker Hammer drill with a Pile Driving Analyzer and selecting representative blows for CAPWAP analysis. Further information on Becker Hammer Drill Instrumentation can be found on GRL Engineers, Inc.’s website at the following link : http://www.pile.com/grl/services/becker/default.asp
 
Instrumented section of Becker Hammer drill pipe for PDA collection
 
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