July 2016
A pipejacking first for Shenzhen in Guangdong Province, China
The Futian sewage treatment plant project in Shenzhen is an important emission reduction sewage cleaning project for Guangdong Provence, China. As part of the construction works a pipe jacked sewer pipeline some 713 metres long with an internal diameter of 3 metres was required to protect the National Mangrove Nature Reserve. The underground pipeline will transport 600,000 cubic metres of sewage water per day, and provide effective protection for the wetland ecosystem in Shenzhen.
Whilst the concept of the plan is simple in reality the situation is somewhat different. The pipe jacked tunnel runs alongside one main Avenue of Shenzhen, as close as 5 metres in places. Ground conditions along the route also varied considerably from silty conglomerate and medium weathered granite, through totally weathered granite and slightly weathered granite to plain fill and rock fill and conditions in between. The tunnelling machine also passed close to a gulch, which only added to a very complex geological environment. So accuracy at the cutterhead was vital.
As well as the complex geology the tunnel itself was design as two straight sections with one curve 388 meters in length with a radius of 888.88 meters.
Given that this was the first project in the region to attempt such a complex pipeline installation it was vitally important that the right guidance system for the tunnelling machine was selected. Having investigated the options an SLS-Microtunnelling LT system from VMT was selected based on its very successful history on complex pipe jacking projects.
VMT’s SLS-Microtunnelling LT system is designed for the guidance of long distance and curved pipe jacking applications for pipe diameters above 1 m using servo motorised laser total station which is mounted inside the tunnel which moves together with the pipeline. The actual position of the laser total station is continuously calculated with help of the known as-built position of the previously installed pipes. The SLS-Microtunnelling LT system also recognises TBM drift and with the system installed in the front part of the tunnel (inside the first 90 m) laser refraction does not influence the measurements.
Engineers from VMT SH (the local VMT subsidiary) were on site throughout the project to initially set up the system and monitor progress throughout the work. The local team was also trained to use the system effectively as the project took place. Despite access difficulties at the start of the drive in February 2016 which were overcome with team work and experience in such set-ups, the project holed successfully on target on 24 April 2016.
