## 5 Conclusions  
Based on the highway construction project from Jinan to Gaoqing, the standard penetration of large-diameter tubular piles was monitored at a construction site based on monocular visual digital photography. Moreover, an indoor test model was developed per practical engineering conditions to study the construction effect of large-diameter tubular piles. Some major conclusions could be drawn. 1. When large-diameter tubular piles penetrate from the loose stratum to aleurite and then to silt, the relationship between the penetration and time function (blow counts) evolves as a piecewise function. This, which is a logarithmic function in the early stage, a gently sloping linear function in the middle stage, and a sharply sloping linear function in the late stage. The penetration rates vary significantly under different strata conditions. 2. According to the measurement data regarding pile deviation, the squeezing effect increases and then weakens during adjacent pile construction and pile-jumping construction. The maximum squeezing effect is observed as the adjacent pile is penetrated by about 20 m or the jumping pile is penetrated by about 10 m. The monitored pile is  
Figure 18: Affect region of a pile penetrating the strata. influenced greatly by the construction of adjacent piles, similar to the results of the pile-jumping construction method. 3. The plugging effect can be divided into three stages: the formation of a soil plug, increases in the frictional force between the soil plug and pile wall, and closure. In the first stage, it is manifested as a convex arch. In the second stage, the soil plug gradually changes from a convex arch to a concave arch. In the third stage, the soil plug is closed completely. Such engineering characteristics are similar to those of closed-ended piles. 4. The horizontal and longitudinal spheres of influence of surrounding soil masses expand gradually with increases in the penetration depth of tubular piles. More specifically, vertical influences are significantly greater than horizontal influences. The contour lines the of vertical and horizontal spheres of influence form a rectangular distribution. 5. When the plugging effect of a tube is closed, a horizontal squeezing effect of the surrounding piles of soil mass is developed. The horizontal sphere of influence expands, including the shear failure zone, radial compression zone, and hemispherical expansion zone. Among them, the radial compression zone is expanded to the point where it is nine times the pile diameter away from the pile axis, and the hemispherical expansion zone extends to the depth where it is 1.5 times the pile length. In conclusion, digital photography technology is innovatively applied to the field monitoring process of large diameter pipe piles, which provides a cost-effective technical means to obtain the dynamic penetration value of large diameter pipe piles, and these data are of great significance to the field construction and optimization design of large diameter pipe piles. At the same time, digital photography technology can realize high-precision dynamic monitoring of the penetration value of large-diameter pipe piles in laboratory tests, which provides technical support for studying the dynamic evolution law of large-diameter pipe pile construction effect and optimizing construction parameters. Writing--review and editing, G.Z. and S.Z. ; formal analysis, Z.L. ; writing--original draft, W.X. and S.L. ; investigation, Z.W. and Y.W. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation Item (grant no. 52204097), the Natural Science Foundation of Shandong Province (grant no. ZR2020 QD049) and the Shandong Transportation Science and Technology Project (grant no. 2017B59). Not applicable. The data used to support the findings of this study are available from the corresponding author upon request ([EMAIL_ADDRESS]).