# Investigation on Vibration Influence Law of Double-Shield TBM Tunnel Construction
## 6 Conclusions  
Relying on the tunnel construction section of the double-shield TBM in Qingdao Metro Line 4, the construction vibration caused by the double-shield TBM has been monitored and analyzed. Subsequently, the transverse and longitudinal influence trend of peak acceleration has been studied. Finally, the vibration influence range of the double-shield TBM construction that affects human comfort is obtained. The conclusions are summarized as follows:  
1. The vibration caused by double-shield TBM construction mainly occurs in the excavation stage. The time-domain curves of the vibration acceleration can be divided into three stages: rising stage, stable stage, and falling stage; the peak acceleration mainly occurs in the stable stage. 2. The vibration frequencies in the X, Y, and Z-directions at the same depth are relatively close. The main vibration frequency of the plain fill is 20-30 Hz, and the medium and coarse sand is 40-50 Hz. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Building Type** & \begin{tabular}{c} **Influence Range in Front** \\ **of Cutter-Head (m)** \\ \end{tabular} & \
\begin{tabular}{c} **Influence Range behind** \\ **the Cutter-Head (m)** \\ \end{tabular} &
\begin{tabular}{c} **Influence Range on Both** \\ **Sides of Tunnel Axis (m)** \\ \end{tabular} \\ \hline Operating rooms & 38 & 10 & 17 \\ Residential houses, office buildings, classrooms, hotels, etc. & 29 & 8 & 10 \\ Shopping malls, cinemas, restaurants, etc. & No effect & No effect \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The vibration influence range of double-shield TBM construction. 3. In terms of transverse vibration trend, the maximum peak acceleration is located above the tunnel excavation section, and the farther the measuring point is from the tunnel axis, the smaller the peak acceleration. For longitudinal vibration trend, the peak acceleration is largest when the cutter-head reaches the monitoring section. Moreover, as the distance decreases, the peak acceleration gradually increases after the cutter-head reaches 35 m in front of the monitoring section. After passing through the monitoring section, the peak acceleration drops sharply. 4. For human comfort in an operating room, the vibration influence range by double-shield TBM construction is 38 m in front of the cutter-head, 10 m behind the cutter-head, and 17 m on both sides of the tunnel's axis. In terms of residential houses and office buildings, the vibration influence range is 29 m in front of the cutter-head, 8 m behind the cutter-head, and 10 m on both sides of the tunnel's axis. Moreover, it has no effect on human comfort in shopping malls, cinemas, restaurants, etc. Notably, the research results are limited to the current formation or a formation of the same type. Actually, the vibration monitoring results are affected by many formation factors, such as the compactness of the rock mass, degree of fissure development, groundwater, etc. These have a great influence on vibration acceleration. Moreover, the results of this paper do not consider the effect of tunnel burial depth; it is meaningful to study the relationship between the tunnel buried depth and the vibration influence range. The peak acceleration in the manuscript is the actual maximum value of on-site vibration monitoring. However, there will be differences between the actual vibration and the monitoring results. Further, we will use a probabilistic approach to estimate peaks [35; 36] and perform error analysis [37; 38]. The results can provide a reference for the vibration effect of double-shield TBM passing through houses, highways, and bridges. It also has strong practical significance for resolving disputes that double-shield TBM tunnel construction affects the lives of inhabitants. Conceptualization, X.W. and Y.J. ; methodology, Z.L. and L.F.; field test, Z.L. and G.Z. ; data curation, Z.L. and G.Z. ; data analysis, Z.L. and G.Z. ; writing--original draft preparation, Z.L. ; writing--review and editing, X.W. and L.F.; supervision, X.W. ; project administration, X.W.