Pipe Ramming in Chansha, China

Changsha , the capitol city of Hunan province is major tourist and a very important transportation hub in South East China. The North South Beijing - Guangzhou railway runs through this city and its feeder railway lines allow onward passengers and cargo to reach cities in southwest and northwest China .

A natural gas pipeline from the Northern gas producing fields serving the City required a new pipeline be installed across and under this key North South railway at several locations. The gas company applied to the railway company for permission to install the pipeline and various suitable trenchless methods were submitted for consideration and approval. After deliberate consideration, the railway company accepted the pipe ramming process. Pipe ramming was deemed the safest and most appropriate technique due to its simplicity, cost-efficiency and the process would not contribute to potential ground heave or ground settlements situations that would affect track performance. The new gas pipeline had to be installed before the end of July 2005. Natural gas delivery was scheduled to commence at the beginning of August. Delay in completion would cost the gas company $25,000 per day in lost revenue, plus a host of administration, management and, most importantly, customer problems.

His case study looks at the first of several ramming jobs required by the natural gas company to install 600-mm steel casing as carrier pipes for installing 350-mm high-pressure steel gas pipeline inside.

The ramming distance under the twin railway tracks was 42 m and 6 m below the tracks. Trains operate in opposing directions as close as 20 minutes apart and thus any form of open trenching or even employing technologies that would have the slightest inclination to affect track performance were not allowed. The ramming project was awarded to Wei Hua Trenchless Technology Company based, in Guanzhou. The steel casing to be installed is 600 mm in diameter with a 15-mm wall thickness. All together there will be six similar rams in this project. The first ram described in this article was the most challenging. The twin tracks were on a raised ridge 6 meters above existing rice paddy fields. To create the ramming pit, the creek supplying irrigation waters to the fields had to be dammed and water diverted to continue its downstream flow. The dam was created with sandbags and two 300-mm PVC pipes were positioned to divert the slow flowing water.

Scheduled train service
continued during the
pipe installation.

Here, is the ramming pit. Note
the sandbag dam and the two
PVC pipes on the left, diverting
irrigation water downstream.

The spoils swallowed by the
casing pipe during the ramming
were purged by compressed
air.

Another challenge was the casing pipe to be installed. This casing serves as the conduit for the high-pressure natural gas pipeline. The railway company insisted that this casing pipe must have the same corrosion-protection treatment as the gas pipeline itself, both outside and inside. Engineers from both gas company and railway maintenance division had concerns that the ramming process could damage the applied surface treatment.

For this project, Wei Hua Trenchless selected a HammerHead Mole® pipe ramming tool for the job. The tool has more than adequate power to deliver a successful ram and its size and weight facilitates ease of mobilization in and out of the paddy fields, which was served only by a narrow unpaved road. The contractor also realized the available air reverse feature of this tool will enable it to disengage from the ramming collets without outside assistance, saving the need to bring in additional mechanical equipment.

Prior to commencement, Jack Dong from Balama Prima-Prima, HammerHead's China Dealer and Wing Chan of HammerHead® (ETC) attended a pre-construction meeting to address concerns from the railway, as well as the natural gas company. Dong and Chan also assisted the contractor in detailing the casing front-end soil shoe design, pit layouts, pit-based preparation, guide rails setup and on-grade casing installation and most importantly to assure minimum or no damage to the casing corrosion protection treatment during the ramming process. Once these issues were addressed and engineers from both the client and contractor side were satisfied, the ramming pit began to take shape and the casing pipe and tooling started showing onsite.

At the ramming pit, a sandbag dam and the two PVC pipes diverted irrigation water downstream. The ground was relatively soft and concrete was poured to establish a stable platform for the placement of guide rails to ensure accurate launching of the casing pipe. Once the setup was complete, the first casing pipe was placed on the guide rails and the 400-mm tool and collets were assembled at the casing end. A final round of inspection was made to ensure the entire setup was completed, the 1,000 cfm air compressor was fired up and the 400-mm tool activated. The initial 6 m of pipe was rammed in slowly and full impact force from the HammerHead® tool was applied only when the entire project team was satisfied that the casing was being delivered along the intended path.

Scheduled train services continued to operate throughout the casing pipe installation process. Engineers monitoring the track were relieved that the track experienced no measurable vertical or lateral deviations from the impact energy released by the ramming tool.

The ram was only temporarily halted to weld on another section of casing pipe before continuing. A specialist from the gas company was onsite to apply the corrosion protection the exposed welding joint area, perform tests and approve the treatment before authorizing the recommencement of the ramming process.

The ram was almost perfect and there was great relief when the casing pipe emerged on target into the receiving pit a day later. Inspection to the casing corrosion protection treatment was carried out immediately and engineers were surprised to find that there were minimal or no surface scratches that would affect he integrity of the corrosion protection layer. Next the spoils swallowed by the casing pipe during the ramming process were purged by compressed air and the interior surfaces inspected.

Employing the pipe ramming method, Wei Jua Trenchless delivered a solution to the gas company allowing it to install the high-pressure gas delivery pipeline under the railway tracks and connecting it to distribution lines servicing its customers. The railway company was more than pleased that this trenchless methodology performed better than anticipated and will evaluate the process further with the possibility of adopting pipe ramming processes as an approved process for future applications.

With the success of this and other recent major pipe ramming projects in China , the construction industry there will soon recognize the process is relatively simple and safe to execute, as well as being cost-effective when compared with other tunneling methods when applied in the right environments. The future of pipe ramming in China can only get brighter from here on.


Appeared in Trenchless Technology International Magazine, September 2005