In the process of shield TBM construction, an annular gap will be formed between the surrounding rock and the segment, and pea gravel is the main material to fill the annular gap. It is of great significance to carry out quantitative research on the morphological characteristics of pea gravel for its material properties. The test is carried out with four kinds of pea gravel samples, including artificial gravel and natural pebble, combined with digital image analysis and particle size analysis. To analyze the test results, six quantitative indicators of particle morphology from three aspects of the contour shape, angular shape, and particle size were firstly obtained, and then the quantitative indexes were used to describe the morphological characteristics of the pea gravel samples. Finally, the image analysis results and the particle size analysis results were compared to verify the reliability of the image analysis results. The research results show that with the help of digital image analysis, the quantitative indexes of the morphological characteristics of pea gravel can be obtained quickly and effectively, which provides a basis for the screening and quality control of pea gravel in TBM constructed project.

Pea gravel filling is a very important process in TBM construction. The study of filling process has a certain engineering application value for analyzing the quality of filling layer and optimizing the filling process. Based on the advantages of PFC in the study of discrete bodies, this paper carries out multi-scheme simulations of the pea gravel filling process and analyzes the forced movement of the pea gravel particles to explore the distribution characteristics and its influencing factors. The results show that: fill the middle, upper, and top (Supplementary) of the segment ring in sequence, and the filling layer is distributed in four sections, among which particles with different particle sizes in the range of 0° ~ 45° and 75° ~ 135° are seriously distributed in layers, large particles are close to the side of the tube segment and the side of the surrounding rock respectively. In the range of 45° ~ 75°, there is a phenomenon of local particle stratification. In the range of 135° ~ 180°, there is a problem of insufficient filling. The layered distribution is affected by the particle size combination, surface friction coefficient and squeezing force of the filling pea gravel particles. By changing the position of filling holes and adding filling holes, the filling range of each hole is controlled, thereby reducing the squeezing force of the particles before the filling of the range is completed. And then the step-filling method was used, which can significantly reduce the layered distribution area and make the particle distribution more regular. The filling range of the filling holes should be controlled within 45°, but the top holes of the filling layer are prone to blockage, which is not suitable for filling a large number of particles. Therefore, the filling range of the filling holes in specific locations needs further study. This research result can provide a certain reference for the design of filling scheme.