Underground Singapore 2011 8 DRILLING ASSISTANT CCFA Many factors contribute to the efficient drilling and subsequent concreting of CCFA piles. To assist and allow the operator to monitor all the various parameters the drill and extraction assistant programs have been developed. During the drilling phase the optimal performance is affected by the applied torque and crowd forces and rotation speed. These will need to be varied for each particular soil conditions encountered. In addition to these rig related factors the geometry of the casing and augers need also have an influence. All these factors are used in the drill assistant program to achieve the desired optimal performance, which is measured as the penetration per revolution. Control of this measure is widely accepted as a major factor in avoiding problem in CFA and CCFA piling. In particular there are the following benefits:
avoids over-flighting avoids corkscrew of auger optimizes the filling grade of the auger assists of operator
The exact details of the used drilling tools must be entered into the system:
Figure 7. input data sheet
D1 2
D during drilling. The peneDifferent ground conditions require consideration of the filling of the auger tration rate per revolution is calculated using the following parameters: d
d = D1 = D2 = Ψ = s = t =
diameter of the mandrel outside diameter of casing outside diameter of auger filling grade of auger auger pitch penetration depth
s
t
Figure 8. geometrical consideration of the penetration rate
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