## 3 Analysis of Ground Deformation Characteristics in Water-Rich Soft Stratum  
According to the investigations of [PERSON] et al. [8; 26], the surface settlement trough resulting from the single shield tunnel can be illustrated by the Gaussian curve:  
\[S(x)=\frac{AV_{L}}{Kz_{0}\sqrt{2\pi}}\exp\left(-\frac{x^{2}}{2\left(Kz_{0} \right)^{2}}\right) \tag{1}\]  
where \(S(x)\) is the surface settlement at \(x\) from the tunnel centerline; \(V_{L}\) is the ground loss ratio; \(K\) is the settlement trough width coefficient; \(z_{0}\) is the buried depth of the tunnel axis. The surface settlement produced by the first tunnel construction and the additional surface settlement generated by the second tunnel construction are fitted using the Peck formula, and the two fitting curves are superimposed to obtain the double-line tunnel's surface settlement curve. Table 1 shows the settlement fitting results of the measuring point settlement data for each monitoring section. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Monitoring** & \multirow{2}{*}{**Sectation**} & \multirow{2}{*}{**Stratum**} & \multirow{2}{*}{**\(z_{0}\)/m**} & \multirow{2}{*}{**\(d\)/m**} & \multirow{2}{*}{**\(S_{\text{max}}\)/mm**} & \multirow{2}{*}{**\(V_{\text{L1}}\)**} & \multirow{2}{*}{**\(V_{\text{L2}}\)**} & \multirow{2}{*}{**\(K_{\text{1}}\)**} & \multi  
Where \(d\) is the center distance of the double-line tunnel; \(S_{\max}\) is the maximum surface settlement; \(V_{L1}\) and \(V_{L2}\) are the ground loss ratio of the first tunnel construction and the additional ground loss ratio of the second tunnel construction, respectively; \(K_{1}\) and \(K_{2}\) are the settlement trough width coefficient of the first tunnel construction and the settlement trough width coefficient of the second tunnel construction, respectively; \(Adj.R_{1}^{2}\) and \(Adj.R_{2}^{2}\) are the adjustment coefficient of the first tunnel construction and the adjustment coefficient of the second tunnel construction, respectively (the closer the adjustment coefficient is to 1, the higher the fitting degree). (1)  Applicability analysis of Peck formula  
The surface settlement caused by the first tunnel construction was fitted to obtain \(Adj.R_{1}^{2}\) = 0.87-0.99 and an average of 0.97. The additional surface settlement caused by the second tunnel construction was fitted to obtain \(Adj.R_{2}^{2}\) = 0.71-0.99 and an average of 0.89. It may be inferred that the Peck formula is applicable for analysing and forecasting surface settling induced by double-line tunnel construction in water-rich soft stratum. (2)  Analysis of settlement trough width coefficient  
The settlement trough width coefficient is an empirical coefficient related to soil characteristics that should be analysed independently depending on the stratum combination. The width coefficient of the settlement trough \(K_{1}\) = 0.44-0.49 for the first tunnel construction, with an average of 0.46; the width coefficient of the additional settlement trough \(K_{1}\) = 0.48-0.53 for the second tunnel construction, with an average of 0.50 when the shield tunnel is constructed in the homogeneous soft stratum. The width coefficient of the settlement trough \(K_{1}\) = 0.30-0.41 or the first tunnel construction, with an average of 0.35; the width coefficient of the additional settlement trough \(K_{1}\) = 0.43-0.48 for the second tunnel construction, with an average of 0.46 when the shield tunnel is constructed in the upper-soft and lower-hard stratum. It may be deduced that the settlement trough width coefficient \(K\) under homogenous soft stratum is more than that under upper-soft and lower-hard stratum, and that the \(K\) of the second tunnel construction is bigger than that of the first tunnel construction. The increase in \(K\) is due to the disturbance of the stratum caused by the first tunnel construction. (3)  Analysis of ground loss ratio  
The ground loss ratio is significantly related to the stratum condition and the construction level, so the data are of high discreteness.