# Analysis of the Working Performance of a Back-to-Back Geosynthetic-Reinforced Soil Wall
## 2 Experimental Study and Numerical Modeling  
### Description of the Wall  
Located in the eastern part of Shandong Province, Qing-Yan-Wei-Rong Intercity Railway is a passenger-dedicated railway line that was the first high-speed railway built in that region with a design speed of 250 km/h. The starting point is Qingdao, and it passes through Yantai and Weihai; the destination is Rongcheng. It was completed in August 2014 and was officially put into service on 28 December 2014. This study is based on remote observation tests of the GRSW near Rongcheng Station (shown in Figure 1).  
The subgrade is formed by an 8.8 m tall BBGRSW with a 1.7 m thickness of filling soil at the top. This was the first application of this type of structure on a Chinese high-speed railway and represents a bold attempt in the history of Chinese high-speed railway. The back-to-back GRSW is an attempt to study whether this type of structure meets the requirements of a high-speed railway; therefore, the frequency of the live loads applied to  
Figure 1: BBGRSWs near Rongcheng Station. (**a**) Left side of the BBGRSW; (**b**) right side of the BBGRSW.  
it is approximately four to five trains per month, and the dead load of the track is applied to the subgrade.  
The left side of the subgrade is a paneled module block. The dimensions of the concrete modular blocks on the left panel are 0.5 m \(\times\) 0.3 m \(\times\) 0.3 m with the reinforcement buried among the blocks. The right side face of the subgrade is wrapped with a cast-in-situ concrete panel outside. The concrete is C35, 0.3 m thick, and has the same reinforcement layer arrangement as the left side. The reinforcements are TGDG EG130R HDPE uniaxial plastic geogrids with lengths of 8.0 or 10.5 m and 0.3 or 0.6 m, respectively, as the vertical spacing with the machine direction perpendicular to the wall. As the height of the subgrade is 10.5 m, the minimum length of reinforcement should be 7.35 m; therefore, a reinforcement of 8.0 m was selected. As the maximum width of the subgrade is 16.0 m, several geogrid layers were overlapped and not connected. The foundation below the subgrade is a cement-fly ash-gravel (CFG) pile composite foundation, the column diameter is 0.4 m, square arranged, and the column length is 4.0 m. A 0.5 m thick gravel layer is located upon the composite foundation and on that is the back-to-back GRSW.  
On the basis of the Standard for Acceptance of Earthworks in High-speed Railways (TB 10751-2018), the coefficient of compaction \(K\) (the ratio of dry density on-site to the maximum dry density of the soil) should be no less than 0.92, which indicates that the filling soil has not been compacted to 100%.  
The field tests of the retaining wall during the service period include the base pressure, lateral earth pressure, vertical pressure, lateral displacement, settlement, and geogrid strain. The observation elements include the earth pressure cells, displacement meter, single point settlement meter, and strain gauges. The elements were buried in the wall during the construction progress, and the retaining wall has been continuously monitored using wireless remote monitoring equipment. The details of the instruments are shown in Table 1 and the layout scheme is shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Range** & **Precision** \\ \hline \hline VW earth pressure cell & 0–1 MPa & \(\pm\)0.1\% FS \\ Strain gauge & 0–30 mm & \(\pm\)0.5\% FS \\ Single point settlement meter & 0–200 mm & \(\pm\)0.5\% FS \\ Displacement meter & 0–50 mm & \(\pm\)0.05\% FS \\ \hline \hline \end{tabular}
\end{table}
Table 1: Details of the instruments.  
Figure 2: Arrangement of the monitoring instruments (unit: cm).