## 4 Application Example
### Case for Blast Loading
#### 4.1.2 Numerical Result
Based on the damage pattern in the field blast test, the crater on the top face of the HSC is shown to be shallow and with a thickness of less than 10 mm. However, after cracking occurred at the bottom of the HSC layer, the numerical model shows that the bottom of the HSC layer has experienced severe cracking. This might be due to the combination of the bending of the HSC layer under the blast load and the reflection of the stress wave at the bottom interface. In the numerical model, the interface between HSC and ECC is assumed to be fully bonded. However, ECC is more flexible than HSC, and thus, it would cause tensile stress at the bottom of the HSC layer when deformed together. The compression stress wave from the top face would also travel within the HSC layer and reflect as a tension stress at the interface, which could cause spalling. Based on the damage pattern in the numerical model, the HSC layer might be considered having failed, while the field observation suggests that HSC may have partially failed. In the field blast test, the four accelerometers were installed at the mid-side of pavement slab (as shown in Figure 9). These accelerometers were used to measure the vertical and horizontal acceleration of the pavement slab subjected to blast loading. For the horizontal acceleration, due to the centre of the charge being closer to one side of the pavement slab; there were two different horizontal acceleration readings; while in the numerical model, it was assumed that the explosive occurred in the centre of the pavement slab. Thus, in this section, only the vertical acceleration from the field  
Figure 12: Damage contour for the AC and HSC layer in the multi-layers pavement: (**a**) damage contour of the AC layer in the numerical simulation; (**b**) damage contour of the HSC layer in the numerical simulation. blast test was compared with that of the numerical model. In the numerical model, the raw nodal acceleration contained considerable numerical noise. The ELEMENT_SEATBELT_ACCELEROMETER could be used to eliminate numerical noise and obtain more accurate node acceleration. The vertical acceleration from the blast testing is compared with that of the numerical model as shown in Table 7. The results from both the blast testing and the numerical simulation are comparable. The maximum difference of vertical acceleration between the blast testing and the numerical model is about 10%, and the numerical model predicted slightly higher in the vertical acceleration than that of the blast test. The pressure values in the corresponding points in the numerical model are compared with pressures obtained from the blast test, as summarized in Table 8. The layout of the total pressure cell in the blast could be referred to Figure 9. The pressure values from the numerical simulation are shown to be close to that from the blast test for TPC2; while for TPC3, it has a 20% discrepancy with the numerical simulation considering the inherent variation in the blast test. TPC1 was damaged during the blast test, and hence, no pressure reading was recorded from it. The numerical model predicts that the pressure might be as high as 13 MPa at that point, which is far beyond the maximum measurement capacity of the pressure cell installed. That can explain why TPC1 was destroyed due to the overwhelming blast loading.