Pipe ramming is a well-known method of installing or replacing underground pipes in which an impact tool is used to push a pipe through the earth. A pneumatic impact tool is attached to a first pipe section and used to drive the pipe section into and through the earth. The impact tool engages the pipe section by means of an adapter such as a cone or a set of collets. See Bouplon U.S. Pat. No. 4,329,077, May 11, 1982. After the first pipe section has been driven into the earth, the impact tool is disconnected from the pipe section and a second pipe section is welded or otherwise attached to the trailing end of the first pipe section. The impact tool is then connected to the second pipe section to continue the ramming operation. Additional pipe sections are added and rammed into the earth until the leading end of the pipe reaches the desired endpoint.
In the case of small pipes, i.e., less than 6 inches, the leading end of the rammed pipe is typically closed, with a conical fitting or cap. Larger diameter pipes are rammed with the leading end of the pipe open. Spoil trapped inside the pipe is removed periodically as the pipe advances or, for shorter runs, after the entire length of pipe has been installed. The spoil may be removed from the rammed pipe with an auger, pressurized air or high pressure water. Pipe ramming is particularly suited for installing or replacing pipe under and through structures such as roadbeds for rail road tracks and highways where other methods, such as horizontal drilling, could cause settlement and/or collapse of overlying structures. Hydraulic systems have also been used for pipe pushing; see for example Lenahan U.S. Pat. No. 6,206,345, Mar. 27, 2001.
Referring to FIG. 1, when ramming an open-ended pipe 101, a cylindrical soil shoe 102 may be installed on the inside surface of the leading end of the pipe. The purpose of soil shoe 102 is to compact the spoil entering pipe 101 and create a small clearance between the spoil and the inside surface of the pipe as the pipe is rammed through the earth. The small clearance created between pipe 101 and the spoil reduces friction between the inside surface of the pipe and the spoil, facilitating the ramming process. An external soil shoe 103 may be placed on the outside surface of pipe 101 for essentially the same purpose. Water is introduced into the pipe in order to soften the debris inside, turning it to mud. A water line 104 extends along the outside of the lead pipe section to a radial hole 106 through both the pipe wall behind soil shoe 102. Hole 106 is spaced from the rear edge of soil shoe 102. Water line 104 is made from a series of 0.5″ steel pipes joined by a series of 0.5″ steel couplers, the forwardmost coupler 107 is a T-fitting having a side hole therein that communicates with hole 106 and its front end closed by a threaded plug. This arrangement has been used in pipe ramming generally but not, as far as the present inventor is aware, in connection with culvert swallowing operations wherein the pipe is pushed in around an existing pipeline or culvert of smaller diameter.
In another known method, during ramming of a large diameter pipe, resistance is encountered and it become difficult or impossible to complete the run. In some cases, a smaller pipe has been rammed through the inside of the larger one and used to continue the pipe ramming operation, creating telescoping pipe sections. Such a method involves placing a smaller pipe inside of a larger one, but the large pipe is not replacing the smaller one.
While the prior art soil shoe of FIG. 1 may, to some degree, reduce friction between pipe 101 and spoil captured in the pipe during the ramming operation, further reduction of such friction is desirable, as are improved techniques for removing spoil from inside a pipe after it has been rammed into the earth. This is especially the case where an existing pipe or culvert is to be replaced by ramming a larger diameter pipe into the earth around the existing pipe. When an existing pipe is “swallowed” by a larger diameter replacement pipe rammed into place around it, spoil compacted between the replacement and existing pipe hinders removal of the existing pipe. Removal of the trapped spoil using conventional techniques such as auguring or water blasting may also be blocked or hindered by the existing pipe. The present invention provides an improved method of pipe ramming that addresses these difficulties.