Pilot Tube Microtunneling (PTMT), also referred to as guided auger boring, guided boring method and auger drilling.
This method can be applied for the installation of small diameter pipes which require high accuracy in line and grade. This technique is a combination of the existing trenchless technologies including auger boring, microtunneling and horizontal direction drilling. PTMT employs augers for excavation and soil removal and the jacking system for pushing the pipes similar to auger boring. It uses theodolite with camera as the guidance system. The target with LEDs is mounted in the steering head and is monitored through TV monitor, which is similar to the guidance system of microtunneling. The process of PTMT includes pilot boring and reaming, which is typical operation for horizontal directional drilling.
A camera-mounted theodolite is set up as the guidance system in the driving shaft. The camera will be connected to the video monitor installed at the driving shaft and is used for monitoring the line and grade of the target with LEDs mounted in the pilot head.
A bore hole is drilled with a steering head/pilot head connected to pilot rods whose size is smaller than the required pipe size. The process proceeds with rotation and thrust of pilot rods. Deviations are continuously adjusted through the video monitor surveillance of the illuminated target via the theodolite.
When the steering head reaches the receiving shaft, the cutting head/reamer and casing with auger inside area connected to the last segment of pilot tube. Then the cutting head/reamer and auger enlarges the pilot bore hole by rotating and thrusting the reamer and casing. The cutting head and pilot rods can be retrieved at the receiving shaft. This process is repeated until all pilot rods are removed.
After the reamer reaches the receiving shaft, an adapter is installed at the end of the last casing which connects the casing and product pipe. The product pipe is pushed by the jacking frame while the casings are retrieved at the receiving shaft. The augers remove the soil in the casings, and then retrieved at the driving shaft. This process is repeated until all casings and augers are removed.