**6. Outlook**

The flatness detection method in this study is mainly for curved surfaces similar to the tunnel surface. For the traditional flatness detection methods, flatness detection can only be performed on relatively flat road surfaces or building walls. Through the research of the flatness detection method in this experiment, the purpose of flatness detection on a complex curved surface is realized. However, there are still some shortcomings in the research process:

(1) Obtaining the flatness calculation datum plane in the tunnel flatness detection calculation is a key step in calculating the flatness of the initial support of the tunnel, but how to determine that the flatness calculation datum obtained by processing is the most suitable and optimal solution flatness calculation datum plane, its treatment method is still worthy of further study.

(2) At this stage, there is no system for systematic evaluation of the flatness detection of the initial branches of the tunnel using 3DLS technology, so the construction of a more complete 3DLS tunnel flatness detection and evaluation system is the next research direction.

**Author Contributions:** Conceptualization and methodology, Y.D., L.X. and Z.W.; data curation, Y.D.; investigation, Y.D.; writing—original draft preparation, Y.D. and L.X.; writing—review and editing, Y.D., Z.W. and H.Z.; supervision, Z.W., H.Z. and Z.L.; Validation, Z.W. and Z.L.; Project administration, Z.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research was funded by the key project of Zhejiang Provincial Department of Transportation, and the gran<sup>t</sup> number is 2019015.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data used to support the findings of this study are included in the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
