## 3 Influence of NFTBT Structure's Size Parameters
### Influence of Distance between the Centers of Adjacent Grouting Holes  
After the greening and paving are completed, during the tram running stage, the NFTBT's structure is under the combined effect of the tram load, its self-weight, and the paving layer weight, as well as the stress on the track slab and the adjustment layer under the conditions of the different distance between the centers of the adjacent grouting holes. The change curve is shown in Figure 23. It is evident that:  
1. The stress difference of the NFTBT's structure under the different distance between the centers of the adjacent grouting holes conditions is small (<0.2 MPa); the stress value  
Figure 21: Influence of thickness on temperature stress of track slab (In legend identification, “+” means positive temperature gradient; “\(-\)” means negative temperature gradient).  
Figure 22: Influence of thickness on temperature stress of adjustment layer (In legend identification, “+” means positive temperature gradient; “\(-\)” means negative temperature gradient).  
of the NFTBT slab and the grouting hole is larger, and the stress change amplitude of other parts including the rail platform is small. It is evident that the distance between the grouting holes has little effect on the overall force of the track structure. 2. The stress amplitude of each measuring point at the adjustment layer is smaller than the track slab, and the overall change amplitude is much smaller than the strength value of the concrete. Among them, the stress amplitude at the bottom of the boss is larger, and there is a minimum value when the center distance of the adjacent grouting hole is 2400 mm. 3. The change in the center distance between the grouting holes has little effect on the stress of the track structure. However, a larger distance between the centers of the adjacent grouting holes can reduce the number of grouting holes in the track slab. For a comparative analysis, it is recommended to set the distance between the centers of the adjacent grouting holes to 2200 mm according to the length of the track slab.  
The change in the maximum internal force of the track structure with the distance between the centers of the adjacent grouting holes under the temperature load is shown in Figures 24 and 25.  
According to Figure 24, the stress in the track slab and at the grouting hole under the positive temperature gradient increases first and then decreases with the increase of the center distance of the grouting hole. The stress trend of the grouting hole under the negative temperature is the same, but the stress in the slab under the negative temperature  
Figure 23: Stress variation curve of track structure under different distance between the centers of adjacent grouting holes conditions: (**a**) Track slab; (**b**) Adjustment layer.  
Figure 24: Influence of the distance between the centers of adjacent grouting holes on temperature stress of track slab (In legend identification, “+” means positive temperature gradient; “\(-\)” means negative temperature gradient).  
shows the opposite trend. The stress state of the grouting hole of the track slab under the temperature gradient load is relatively unfavorable, and there is a maximum at 2400 mm.  
According to Figure 25, as the center distance of the grouting holes gradually increases, the stress change trend of the adjustment layer is basically consistent with that of the track slab. Under a positive temperature gradient, the stress of the adjustment layer increases first and then decreases, with a maximum value at 2400 mm. Under a negative temperature, the stress change trend at the bottom of the boss is consistent, but the stress in the slab is basically stable. According to the displacement and stress variation law of the track structure, the stress state of 2000 mm and 2800 mm in this stage is relatively excellent.