## 4 Application Example
### Case for Impact Loading
#### 4.2.2 Numerical Result  
The damaged situations for the multi-layer slab under the first drop weight impact for the experiment and numerical model are presented in Figure 17. It is found from the numerical simulation that the AC layer is penetrated through, and the drop weight head is impeded by the HSC layer due to the high compressive strength. Such findings from the numerical model are consistent with the observation in the physical test. It is observed that no severe and moderate damage happened in the ECC layer. Additionally, the integrity of both HSC and ECC layers is kept after the first impact.  
The damage situations for the multi-layer pavement slab under the second drop weight impact and the numerical model are given in Figure 18. The simulation results indicate that the HSC layer stopped the impactor; however, severe damage happens at the top surface and in the middle at the side of the HSC layer. Severe damage occurs at the rear surface of the HSC layer, as well. For the ECC layer, it is shown that the cracking occurs and propagates from the centre at the top surface. However, the damage area is smaller than that of the HSC layer. The cracks are also found in the middle at the side of the ECC layer, and similar to the experiment, the crack does not propagate through the thickness of the layer. Figure 19 compares the numerical results with the experimental results about the rear surface of ECC layer after the second impact for the multi-layer slab. It is found that the damaged contour and cracking pattern were similar. Such results further indicate the reasonable close agreement between the numerical analysis and the experimental results using the K  
Figure 17: Damage of the multi-layer slab after the first impact: (**a**) damage pattern of slab in the laboratory test; (**b**) damage pattern of slab in the numerical simulation.  
Table 12 compares the numerical results with the experimental data for the multi-layer slab under two times of the drop weight impact. After the first impact, the settlement from the numerical results is close to that obtained from the experiment at P2. A big deviation is found in between the numerical results and experiment results on the settlement at P3. This might be attributed to the dislocation of the potentiometer at P3 upon impact, which could lead to a misreporting of the settlement at P3. In addition, the settlement at P1 is lower in the numerical results compared with the experimental results. This could be attributed to the erosion process in the numerical model or, more specifically, the energy released phenomena. At the second impact, since no erosion technology is employed for the HSC layer, the numerical results are more reasonable. In the impact simulation, the HSC layer suffered deformation instead of being penetrated, and hence, no erosion technique was adopted to trigger the energy released phenomena. Thus, the settlement profile of the pavement slab decreased with the increase of the radial distance from the centre, which indicated that the whole pavement slab bent during the impact. In general, the numerical models provide reasonable estimations on the settlements of the multi-layer slab under impacts, in particular under the second impact load, though discrepancies exist at certain regions.  
Figure 19: ECC bottom after the second impact: (**a**) damage pattern of the bottom of ECC layer in the laboratory test; (**b**) damage pattern of the bottom of ECC layer in the numerical simulation.  
Figure 18: Damage of multi-layer slab after the second impact: (**a**) damage pattern of slab in the laboratory test; (**b**) damage pattern of slab in the numerical simulation.