Soil support remains sorely neglected for many underground pipe installations, which can lead to poor performance or even failure of one of society’s most important forms of infrastructure.
Underground pipes are often overlooked by the general public due to their concealment beneath the surface of the earth. However, these pipes are critical to infrastructure as they perform a range of functions essential to modern society.
They provide channels of delivery and discharge for water and sewage, which has always been critical to the collective health of urban communities. In the modern era, pipes have also played an essential role in the transportation of fossil fuels that are the very lifeblood of industrialised economies.
In more recent decades, underground pipes have assumed a critical role as utilities corridors for electrical communication links such as copper telephone wires or fibre optic cables, which underpin advanced economies in the Internet era.
Amster Howard and Jesse Beaver, the facilitators of the American Society of Civil Engineers (ASCE) Design and Installation of Buried Pipes course run in partnership with Engineering Education Australia, believe certain aspects of underground pipe installation continue to remain neglected during the construction process, which can lead to the impeded performance or even outright failure of buried pipes
“While most buried pipe projects consider the soil-structure interaction requirements, implementation is often lacking due to poor, or even no, inspection during construction,” said Howard, a Colorado-based pipeline installation expert with over 30 years of experience conducting research on buried pipes and troubleshooting of pipe installation projects for the US Bureau of Reclamation.
“There are many case histories of pipe failure due to lack of inspection. For example, a boulder the size of a washing machine was dumped on top of a pipe that led to its collapse several years later. In another case a contractor beat a pipe down to grade using an excavator bucket, breaking the pipe yet still leaving it in place,” said Beaver, a US national consultant on the structural performance of buried pipes and other buried structures.
Beaver and Howard note that poor soil support for underground pipes leads to a range of defects that pose a serious threat to human safety within the immediate vicinity of installations.
“Inadequate pipe support can lead to differential settlement, opening joints and excessive deflection. These occurrences can create a void over the pipe, causing a sinkhole on the surface and subsequent harm to people,” said Howard.
New methods have emerged for enhancing the safety of underground pipes by improving soil support as well as pipe design and installation design. Greater effort is needed to disseminate these techniques amongst engineers, however, as many members of the profession remain unaware.
“There are updated design methods, soil testing standards and embedment materials that many design engineers and specification writers are not familiar with. However, maintaining awareness of the latest concepts can be cost effective for both pipe and installation design,” said Beaver.
Beaver and Howard note that the most effective methods for improving pipe support are implemented during the installation phase.
“Good support in the haunch area of the pipe is essential. A good installation method would be to use clean gravel and compaction using jetting and vibration,” said Howard. “An even better method is to use flowable fill, and the best method is to use native flowable fill because of reduced cost and environment friendliness.”