## 4 Pavement Scale Model Test  
### Stiffness Degradation of Pavement Slab  
A laboratory scaled model test is carried out to investigate the effect of inhomogeneous horizontal subgrade support on the mechanical response of the pavement structure. According to the similarity principle, a reduced scale of 1:5 was selected. The plane size of the test panel is set as 1 m \(\times\) 1 m, and the thicknesses of the panel are 0.07 m and 0.08 m, respectively. Rubber plates and silica gel plates are used to simulate the inhomogeneous subgrade support of the pavement, see Figure 9. The reaction modulus is measured by a bearing plate method under four common conditions, including: four silica gel plates (10 cm thick); one rubber plate (5 cm thick) and three silica gel plates (5 cm thick); two rubber plates (5 cm thick) and two silica gel plates (5 cm thick); and three rubber plates (5 cm thick) and one silica gel plate (5 cm thick). The positions of the strain gauges are shown in Figure 10. The reaction moduli of the four conditions are 42.08 MPa, 50.29 MPa, 60.16 MPa and 70.13 MPa (more details in Table 6), respectively, and the measurement test of the reaction modulus of the pavement's foundation is shown in Figure 11. A loading platform is assigned to simulate the effect of aircraft load on the rigid pavement, which weigh 120 kg, see Figure 12.  
circumstance. The conclusion quantifies the influence of reaction modulus variation along the horizontal direction of the pavement panel, and the control standard of the reaction modulus under various pavement slab types is also proposed, drawn as follows:  
1. When inhomogeneous subgrade support is used instead of uniform subgrade support, the flexural tensile stress and vertical displacement of the pavement structure increase. For B737-800 aircraft, when the slab thickness is 0.38 m and the change rate of inhomogeneous subgrade support increases from 0% to 85.71%, the flexural tensile stress of the pavement slab increases by 1.60 MPa, and the flexural tensile stress can increase as much as 34%. 2. The flexural tensile stress of the pavement slab increases with inhomogeneous subgrade support. For A320 aircraft, when the thickness of the pavement is 0.36 m and the change rate of inhomogeneous subgrade support increases from 14.29% to 85.7%, the flexural tensile stress of the pavement increases from 4.51 MPa to 6.93 MPa, and the flexural tensile stress of the pavement is increased by 34.9%. 3. By increasing the thickness of the pavement slab, the range of the change rate of inhomogeneous subgrade support can be effectively improved. For A320 aircraft, as the thickness of the pavement slab increases from 0.36 m to 0.4 m, the inhomogeneous degree limit of the top support can be increased from 38% to 70%. 4. To ensure the safety of the pavement slab structure, when the thickness of the pavement slab under the action of the A320 aircraft is 0.36 m, 0.38 m, or 0.40 m, inhomogeneous subgrade support should not exceed 38%, 57.5%, or 70%, respectively. When the thickness of the pavement slab is 0.36 m under the action of the B737-800 aircraft, the flexural tensile stress of the pavement exceeds the ultimate flexural tensile stress of the material; when the thickness of the pavement is 0.38 m or 0.40 m, the inhomogeneous subgrade support should not exceed 33% or 62%, respectively. 5. The strain generated by the pavement slab increases when inhomogeneous subgrade support is considered by the model test. Increasing the thickness of the rigid pavement slab and reducing the inhomogeneous subgrade support can effectively reduce the strain generated by the stress of the rigid pavement. Conceptualization, X.H. and B.S. ; methodology, X.H. ; software, C.T. ; validation, X.H., B.S. and Z.L. ; formal analysis, X.H. and L.Q. ; investigation, B.S. and Z.L. ; resources, X.H. and B.S. ; data curation, X.H. and B.S. ; writing--original draft preparation, X.H. and B.S. ; writing--review and editing, X.H. and B.S. ; visualization, B.S. ; supervision, B.S. ; project administration, X.H.