Evaluation of a new microtunneling propulsion system
In June 1992, a full-scale field test was conducted at Louisiana Tech University to determine the capability of a new microtunneling propulsion system called "LLB" (Laying pipes of Low Bearing force) to install a polyvinyl chloride (PVC) pipe in a range of soil conditions. The technique and the necessary equipment for this system have been developed by Kidoh Construction Company of Osaka, Japan, after 40 years of experience in pipe jacking techniques. In this method, a newly developed air-inflatable internal gripper system for microtunnel boring machines enables PVC or other flexible pipes to be jacked long distances. The primary thrust force of the microtunneling machine is transmitted through a steel liner casing which runs inside the product pipe. The frictional resisting force is transmitted through the "gripper mechanism," which binds the internal surface of the plastic pipe sections to the liner casing. With this new method, the jacking pipe experiences less axial compressive forces than with conventional methods of microtunneling. This allows microtunneling methods to utilize a variety of pipe materials, thereby enhancing the cost effectiveness of microtunneling to open-trench construction. The results of this evaluation program show that the LLB microtunneling system is able to successfully install a low bearing capacity pipe (such as Lamson Vylon PVC sewer pipe) in several different soil conditions.