## 3 Influence of NFTBT Structure's Size Parameters
### Influence of Width of Track Slab  
After the greening and paving are completed, in the tram running stage, the NFTBT's structure has the combined effect of the tram's load, its self-weight, and the paving layer weight; the displacement of the track slab under different widths is shown in Figure 16, and the displacement measurement points are shown in Figure 6.  
Figure 14: Influence of length on temperature stress of track slab (In legend identification, “+” means positive temperature gradient; “ –” means negative temperature gradient). Figure 15: Influence of length on temperature stress of adjustment layer (In legend identification, “+” means positive temperature gradient; “ –” means negative temperature gradient). According to Figure 16, under the condition of imposing an uneven settlement and the combined action of the tram load and the uneven settlement, as the width increases, the displacement of each point of the track slab gradually decreases, and the track slab displacement change law is basically the same under different working conditions. The displacement at the main settlement position of the roadbed is the largest, and a certain amount of warping occurs in the width of the track slab, but the displacement of each working condition fluctuates slightly with the change in the track slab's width, and thus the track is at the starting point of uneven settlement (near measurement point 5). The maximum difference of slab displacement is 0.5 mm. Combined with the data of measuring points 4-6, the difference in the deformation degree of each track slab is small. It is evident that the width has little effect on the displacement. At this time, in order to control the project cost, it is not necessary to use a large width design. To compare and analyze the structural stress of the NFTBT under different track slab widths, according to the key monitoring positions of the track structure determined in Section 2.3, the unfavorable stress at the key positions has been analyzed. The main stress change curve in the track slab and the adjustment layer is shown in Figure 17, and it can be concluded that:  
1. In the case of the width of the track slab, the stress changes at each measuring point are not large. Since the grouting hole and the stress in the track slab are the largest, the stress and displacement of the grouting hole and the center of the track are the control factors for the optimal design of the NFTBT at this stage. 2. As the width of the track slab increases, the stress in the track slab varies the most, showing a trend of first decreasing and then increasing, while the stress at the grouting hole first increases and then decreases very steadily. However, the stress variation of the whole NFTBT's structure is not large (<0.097 MPa)
3. The stress difference in key positions of the NFTBT's structure under different width conditions is small, and the width of the track slab also affects the overall area and weight of the structure and the occupied land. Considering the stress and deformation of the track structure, uneven settlement, and the conditions under the combined effect of the tram load, in order to facilitate construction and maintenance, the width of the NFTBT should not be too long, so 2400 mm and 2500 mm are recommended as the width for site laying. Figure 16: Track slab displacement under different width conditions. The change in the maximum internal force of the track structure with the width under the temperature load is shown in Figures 18 and 19. According to Figure 18, the stress fluctuation amplitude of the track slab is smaller than those of the adjustment layer, which are 0.244 MPa and 0.318 MPa. The stress value  
Figure 19: Influence of width on temperature stress of adjustment layer (In legend identification, “+” means positive temperature gradient; “\(-\)” means negative temperature gradient). Figure 17: Maximum stress change curve of track structure under different width conditions: (**a**) Track slab; (**b**) Adjustment layer.