## 4 Measurement Results Analysis and Discussion
### Structure Stress  
The attenuance of the structure stress (AOS) is introduced to characterize the attenuation characteristics of the structure stress. AOS is defined as the ratio of the attenuation of the structure stress to the initially measured stress. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **AOP after Rapid Attenuation (AOPr)** & **AOP of Stabilization Stage (AOPs)** & **AOPr/AOPs** \\ \hline E11 & 0.15 & 0.23 & 0.65 \\ E13 & 0.25 & 0.32 & 0.78 \\ E31 & 0.20 & 0.39 & 0.51 \\ E33 & 0.14 & 0.29 & 0.48 \\ E51 & 0.15 & 0.45 & 0.33 \\ E53 & 0.08 & 0.14 & 0.57 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The ratio of the attenuance of the lateral earth pressure (AOP) after rapid attenuation to the AOP of the stabilization stage. Figure 8: Measured stable earth pressure and calculated Rankine earth pressure versus depth. \[\text{AOS}=\frac{\sigma_{att}}{\sigma_{ini}} \tag{2}\]  
Here, \(\sigma_{att}\) is the attenuation amount of the structure stress and \(\sigma_{ini}\) is the initial measured stress. Figure 9 shows the variation in AOS with time. The greater the change in AOS (in units of time), the faster the structure stress attenuates. During this period, the structure stress was measured 16 times. The variation of the structure stress with time was obtained. The structure stress was the greatest when the initial installation was completed. In Figure 9, the change in the structure stress at each depth can also be divided into four stages, similar to the change in the earth pressure. However, the change in AOS shows a slow increase stage within ten days after the completion of shaft excavation, which is different from the change in AOP. Combined with the practical situation on site, this phenomenon can be explained as follows: (i) The structure internal stress rapidly increases, due to the applied prestress; (ii) then, the stress  
Figure 9: Time series of the structure stress attenuance at two monitoring points: (**a**) Below the surface at 1 m; (**b**) below the surface at 3 m; and (**c**) below the surface at 5 m.  
attenuates as the soil is gradually compressed; (iii) and finally, the soil behind the structure is gradually consolidated, which gives rise to an increase in AOS. It is concluded that the stress attenuation of the prefabricated supporting structure is different from the phenomenon of the prestressed anchor cable [25]. In Figure 9, the AOS is not consistent at the two monitoring points at the same depth. In addition, there are differences in AOS at different depths. The highest stable AOSs were 0.21, 0.26 and 0.09 at depths of 1 m, 3 m and 5 m, respectively. AOS is less than AOP, because AOS has a slow increase stage after the completion of shaft excavation. Table 2 shows the ratio of the AOS after rapid attenuation to the AOS of the stabilization stage. When the rapid attenuation stage is completed, the attenuation of the structure stress has been completed by 50% or more. The AOS of the stabilization stage at S51 is negative, which shows that the stress in the stabilization stage increases rather than attenuates when compared to the initial stress. This is considered to be due to the insufficient initial prestress at the S51 monitoring point. The prestress is applied by six prestressed components (see Figure 3), which may result in a small prestress at the S51 monitoring point, due to the uneven prestress. Since the stress at the S51 monitoring point is smaller than that of other positions, the stress at the S51 monitoring point gradually increases with the stress redistribution after the completion of construction; thus, the AOS of the stabilization stage at the S51 measuring point is negative. Figure 10 shows the variation in the measured stable structure stress with depth. Si1 and Si3 represent the measured stable structure stress. In Figure 10, the structure stress values of both Si1 and Si3 increase with depth, and they are 22.4 MPa and 28.6 MPa at a depth of 5 m, respectively.