## 4 Conclusions  
Laboratory tests and theoretical calculations on the mechanical properties of the tail brush and its pressure acting upon the shield tunnel segment during the shield posture adjustment were conducted in this study. The distribution of the brush-induced pressure was analyzed, and the model of the pressure distribution along the tunnel height due to vertical adjustment of the shield posture was proposed; the main conclusions are drawn as follows:  
1. The load-compression curve obtained from the laboratory tests showed that the tail brush has a two-stage compressive nature, i.e., the linear stage and the nonlinear stage. A line together with a polynomial function could fit the curve well, facilitating the subsequent calculation of the tail brush pressure around the segment circumference. 2. Through geometric analysis of the shield shell, tail brush and segment, a formula for the tail brush compression deformation and the corresponding pressure distribution along the segment circumference under arbitrary shield posture adjustment was obtained. The pressure induced by the tail brush under vertical posture adjustment was analyzed as an example. The result shows that, along the tunnel height, the compression deformation of the tail brush varies approximately linearly; with the increase in the posture adjustment, the distribution of the pressure becomes more uneven along the circumference and the maximum pressure increases significantly. 3. For ease of application, the distribution of the tail brush pressure upon the segment under vertical posture adjustment was studied: the distribution of this pressure along the tunnel height presents a three-fold linear form; according to this characteristic, a simplified formula was proposed and based on this formula, the distribution of the pressure could be calculated. Today, with the rapid development in underground transportation, the shield tunnel is widely used and faced with increasingly complex challenges, and calls for higher quality and safety requirements. As numerous studies have found, the tail brush extrusion could cause significant harm to the segment; it is necessary to consider the shield tail brush pressure in the calculations about the segment. In this case, Equations (9) and (10) or (10) and (20) based on the experiment are significant and convenient to be used in relevant calculations. However, the research in this article also has certain limitations, such as the fact that this paper focuses on the mechanical properties of the shield tail brush, and the regularity and calculation method of the pressure distribution acting upon the segment, but has not applied it in the calculations about the segment yet. In the future, the conclusions found by this paper can be used to investigate the effect of tail brush extrusion on the segment via calculations with a reasonable and experiment-based tail brush pressure value, to improve the segment design, and to determine the allowed distance of the shield posture adjustment during tunneling. Furthermore, the sealing performance is the key performance of the shield tail brush, and individual studies have paid attention to the relationship between the compression load of the tail brush and its sealing performance. Future studies could further explore this topic. Conceptualization, W.D. and Y.Q. ([PERSON]); methodology, X.C. ; software, X.C. ; validation, W.D., Y.Q. ([PERSON]) and X.C. ; formal analysis, X.C. and Y.Q. ([PERSON]); investigation, X.C. ; resources, W.D., Y.Q. ([PERSON]) and X.C. ; data curation, X.C. and Y.Q. ([PERSON]); writing--original draft preparation, Y.Q. ([PERSON]); writing--review and editing, X.C., Y.Q. ([PERSON]) and W.D. ; visualization, X.C. and Y.Q. ([PERSON]); supervision, W.D. and Y.Q. ([PERSON]); project administration, W.D. ; funding acquisition, W.D. and Y.Q. ([PERSON]). All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China, grant number 51978515 and 52090083.