High-accuracy GPS Monitoring of Riverbed Deformation Due to Shield Tunneling

In general, the deformation of riverbed is difficult to be measured by conventional deformation measuring techniques, such as level gauges and total stations. The application of high-accuracy global positioning system (GPS) in the long-term monitoring of riverbed deformation was introduced by taking the shield tunneling under the Hutuo River in Shijiazhuang as an example in this paper. The method has the flexibility of estimating the average deformation (relative displacements) during different time spans. The 24-hour deformation measurements can achieve sub-millimeter accuracy, and the 1-hour deformation measurements can achieve a few millimeter accuracy. According to the GPS observation, the 24-hour deformation measurements can achieve sub-millimeter accuracy. Settlement started at about 3 to 4D(outer diameter of tunnel) before the shield workface was reached. The settlement rate reached its maximum during the departure of shield tail. The influence of the later excavated tunnel on the lateral horizontal displacement of the riverbed was greater than that of the previous constructed tunnel. The GPS monitoring method described in this paper can be used for long-term monitoring of ground deformation caused by underground engineering construction and operation.