# Experimental Study on a Granular Material-Filled Lining in a High Ground-Stress Soft-Rock Tunnel
## 3 Granular Filling Materials and Test Methods  
### Granular Filling Materials  
Based on the granular material-filled lining support principle, a unit body was selected for a confined compression test. The support reaction force, maximum settlement, deformation settlement law, and supporting effect of compressible granular filling materials (sand, soil, and ceramicsite) in a tunnel with surrounding rock deformation were studied.  
Based on the above principles, the filling materials were required to 1 provide a certain amount of deformation space for the surrounding rock; 2 homogenize the lining forces during the surrounding rock creep; 3 significantly decrease the expansion of the plastic zone during the creep process of the surrounding rock so that the final creep variable of the surrounding rock is significantly reduced; 4 reduce overall construction cost and other requirements; and 5 combine previous research on granular filling materials conducted by the team members. Therefore, the materials selected in this paper were as follows:Sand with excellent fluidity and low compression crushing properties. First, the purchased river sand was dried, and impurities and gravel particles were manually removed. Screening produced coarse sand with an average particle size of 1-0.5 mm and fine sand with an average particle size of 0.25-0.125 mm.  
Soils with low fluidity and high compression crushing properties. Following the drying of the soil, impurities and gravel particles were removed manually. The more uniform 8 mm and 4 mm single soil particles were obtained via screening.  
8 mm ceramsite with superior fluidity and excellent compression breakage. The ceramsite is made of clay after high-temperature roasting and expansion. Its interior is a honeycomb structure, which has the characteristics of low strength, high porosity, and low cost. Ceramsites were purchased in Yichang City, Hubei Province. Before use, the low-strength lightweight ceramsites were dried in the sun, and the broken and incomplete particles were manually removed, and then more uniform 8 mm single-grain ceramsites were obtained after screening.  
The selected granular filling materials are shown in Figure 3, and their physical parameters are listed in Table 1. The particle size distribution curve of the granular material is shown in Figure 4.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Material** & **Natural** & **Natural Moisture Content** & **Density** & **Bulk Density** & **Permeability** \\
**Categories** & **Void Ratio** & **(\%)** & **(g/cm\({}^{3}\))** & **(g/cm\({}^{3}\))** & **Coefficient (m/d)** \\ \hline Fine sand & 0.071 & 10 & 2.60 & 1.65 & 1.20 \\ Coarse sand & 0.143 & 15 & 2.55 & 1.60 & 25.50 \\
4 mm soil & 0.518 & 18 & 2.55 & 1.70 & 0.30 \\
8 mm soil & 0.908 & 22 & 2.50 & 1.68 & 0.45 \\ Ceramsite & 0.475 & 10 & 1.40 & 0.60 & 6.60 \\ \hline \end{tabular}
\end{table}
Table 1: Physical parameters of the filling materials.  
Figure 3: Granular filling materials. (**a**) Fine sand with particle size < 0.25 mm. (**b**) Coarse sand with particle size > 0.5 mm. (**c**) Soil with a 4 mm particle size. (**d**) Soil with an 8 mm particle size. (**e**) Ceramsite with an 8 mm particle size.