Field tests on mechanical behaviors during assembly of segmental linings of Qianjiang tunnel

Qianjiang tunnel is one of the soft soil shield tunnels with the largest diameter by now. In order to obtain the detailed mechanical behaviors from construction to service stage, field tests on the whole ring at the typical formation are carried out. The internal forces of linings are measured step by step during the whole process of assembling stage. The results show that the internal forces of linings are influenced by the variation of relative positions and contacts between segments, and fluctuate and are slightly adjusted and finally reach a new equilibrium state. Most of the measured internal forces during assembly of segments are usually 30% less than of the theoretical values in service, while higher, even more than 10 times, than the theoretical values during assembly. The measured values gradually approach to the theoretical ones during assembly after different levels of fluctuations or jumps. It is important to note that the variation curves of monitoring data have some individual mutations, and some even more than 3 times the theoretical values at service stage. By adjusting the relative contacts and positions between segments, the mutations return to be normal quickly. However, this process, causing local high stress possibly, has an influence on the durability and long-term bearing capacity of segments. The above characteristics should be considered carefully during the design and construction of similar projects in the future.