MODELING AND ANALYSIS OF A SMALL-DIAMETER PNEUMATIC BORING TOOL

This paper-documents the development, solution, and application of a c omputational model for the dynamic response of a small diameter; pneum atic tool used for boring horizontal tunnels in the soil. The model co nsists of (i) the tool component kinematics and kinetics, (ii) mechani cs Of the tool and soil interactions, (iii) the compressible air dynam ics, and (iv) the pressure control valve switching logic. The resultin g model is represented by a set of coupled, sixth-order nonlinear diff erential equations. The boring tool design has several unique features , including dual pistonheads and a pilot-pressure actuated spool valve used to control the oscillatory piston. Implementations of these and other tool features in the computational model is discussed at length. The dynamic simulation and associated parametric studies establish th e feasibility of the design far small diameter (25.4 mm) horizontal bo ring reals. Results for this design predict tunneling rates of about 6 0 meters/hr in a medium clay soil.