**4. Engineering Case Analysis**

The project supported by this test is the Lushan Tunnel Project shown in Figure 14. The Lushan Tunnel is located in Fuyang, Hangzhou City, Zhejiang Province. It is a section of the newly-built Huhang Railway. The main surrounding rock grade is Grade V, and the area sections that need to collect point cloud data for flatness detection are mainly concentrated in the initial support section of the tunnel. A total of 30-m-long section areas are collected. The mileage section is DK109+870~DK109+900, whichever is selected The 2 m part is used as the analysis object of this experiment. The parameters of some regional sections of the Lushan Tunnel Project are shown in Table 3.

**Figure 14.** Field view of the tunnel.

The experiment uses a three-dimensional laser scanner to scan the surface of the initial support of the tunnel and collect the point cloud data of the surface of the initial support of the tunnel in a section of the area. After the point cloud data is preprocessed, the surface point cloud data of the initial support of the tunnel is curved and smoothed by the programming method to obtain the final flatness calculation datum. The normal vector distance is obtained according to the datum plane, to calculate and analyze the flatness of the initial support surface of the tunnel.


**Table 3.** List of regional parameters of Lushan Tunnel.
