New Pipeline Construction Product Allows for Simple Installation of Standard PVC Pipe in Houston HDD Project

By Dennis Shumard, P.E., MASCE, and Pat Moravits, BRH-Garver Construction | March 2014, Vol. 69 No. 3

BRH-Garver submitted conventional AWWA C900 PVC for the trenchless application. The design engineer cautioned that pushing the pipe through a reamed hole for a 200 to 250-feet could cause over-insertion of the pipe joint. It is rather straight forward to understand why over-insertion of the joints of a conventional pipeline in a pushed HDD installation would be difficult to prevent without a physical limitation of some sort. The installation of a gasketed pipe joint requires a certain amount of force to cause the gasket to deflect and affect a seal. That amount of force for eight and 12-inch pipe can be between 1,000 and 2,000 pounds force (lbf).

Once the gasket is deflected and the joint is sealed, a relatively small amount of force is required to continue inserting the spigot into the bell until the joint is assembled per instructions. The amount of force required to push the pipe through the HDD bore easily exceeds this lower force. As a result, the additional force required to push the pipe through the bore will also cause over-insertion and stress build-up in the assembled joints. This excessive stress can result in joint leaks or pipe bell failure.

Because all PVC pipe manufacturers provide cautions about over-insertion of the joints, a physical means of prevention was required. The contractor provided additional submittal information to the engineer on the use of the Mega-Stop product as that means of protection against over-insertion. BRH-Garver also included information about the maximum push capacity of the equipment anticipated to be used in the installation and pushing of the pipe. The Mega-Stop does not have, nor does it need, a pressure rating. Therefore, its use has no effect on the pressure rating of the pipe. As a result, component pressure ratings and system test pressures were not affected. The use of the standard C900 PVC pipe and the Mega-Stop was approved for this application and project.

Mega-Stop

There are many different materials used in waterworks piping. Each material has its own particular strengths and weaknesses; however, no material is perfect for every application. For over 35 years PVC pipe has proven to be a very reliable and durable piping material accounting for two-thirds by weight of plastic pipe and almost half of all installed pipe by length in 2004. The simple installation of PVC pipe has exposed one of its few and infrequent weaknesses – bell splits caused by over-insertion. There have been several industry papers presented that address this subject.