## 4 Conclusions  
This paper comprehensively presents an analysis of tunnel displacements and ground surface settlements during the construction of a large-section loess tunnel. Representative sections using pipe roofs and leading ductules as pre-supports are investigated, based on which the effects of the two pre-supports are compared. The main findings of this research are as follows:  
(1) Significant tunnel displacements occurred during the excavation of large-section loess tunnel. The monitoring results suggested the tunnel displacements were related to the construction process and space position, which were mainly concentrated in the excavation stage of the upper bench and middle bench. However, some differences in the proportion of the arch settlement and horizontal convergence were identified in the excavation stage of the upper bench and middle bench, suggesting a proportion of 20.4-56.7%, 8.2-65.9% and 6.2-77.1%, 2.8-79.4% respectively.  
(2) During the excavation process, tunnel deformation lasts for a long time, and the influence of excavation of the lower bench and the inverted arch on tunnel displacement should not be ignored. A high proportion of tunnel displacements, including the arch settlements and horizontal convergences, were identified in some monitoring sections, reaching up to around 20%. This explains the necessity of monitoring the tunnel displacement during the entire process.  
(3) The ground surface settlement trough in the concerned zone excavated by three-bench seven-step excavation method is no longer symmetric, with respect to the tunnel centerline. In the excavation of the middle bench and lower bench, the ground settlements caused by the early excavation  
Figure 15: Distribution of maximum arch settlement and horizontal convergence stage in all monitoring sections.  
side were larger than those caused by the later excavation side. Therefore, the ground settlement trough curves were deviated to the early excavation side, with no adjustment to the Gauss distribution.  
(4) A comprehensive comparison of the results of tunnel displacement and ground surface settlement in the pipe roof section and the leading ductile section suggests that the effect of pipe roof on the ground reinforcement was better, particularly in the control of arch settlement. The mean value of the arch settlements in the leading ductile section was reduced from 33.4 mm to 23.5 mm compared to the pipe roof section. The pipe roof had greater disturbance to the soil outside the reinforcement ring when reinforcing the ground in advance, which caused earlier ground response.  
Conceptualization, D.L. and D.Z.; Data curation, D.L. and Q.F.; Formal analysis, D.L. and L.C.; Investigation, D.L. and A.L.; Methodology, D.L. and Q.F.; Validation, D.L. and D.Z.; Writing--Original draft preparation, D.L.; Writing--Review & editing, D.L. and Z.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Key Research and Development Programs of China, grant number 2017 YFC0805401 and Chinese National Natural Science Foundation, grant number 51678035.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.