# Hypoplastic Modeling of Soil-Structure Contact Surface Considering Initial Anisotropy and Roughness
## 3 Model Validation
### Experiment on Contact Surfaces of Uniform Density Sand and Concrete  
This section evaluates the effectiveness of hypoplastic model in capturing the deformation behavior of sand-structure contact surfaces under a staged stress path. The  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Parameters** & \(\mathbf{\varphi_{c}}l^{\circ}\) & \(\mathbf{h_{n}}\)/\(\mathbf{\mathrm{MPa}}\) & \(\mathbf{n}\) & \(\mathbf{e_{i0}}\) & \(\mathbf{e_{i0}}\) & \(\mathbf{e_{i0}}\) & \(\mathbf{\kappa}\) & \(\mathbf{\beta}\) & \(\mathbf{R}\) \\ \hline Composite gravel & 42 & 3800 & 0.2 & 0.61 & 0.9 & 1.08 & 0.2 & 1.5 & 1 mm/10 mm \\ Uniform gravel & 40 & 3200 & 0.2 & 0.61 & 0.9 & 1.08 & 0.2 & 1.0 & 1 mm/10 mm \\ \hline \hline \end{tabular}
\end{table}
Table 4: Model parameters experiment of Changping composite gravel–artificial rough steel plate contact surface.  
Figure 8: Experimental results and simulation results for Changping uniform gravel–artificial rough steel plate contact surface under different roughness conditions.  
Figure 7: Experimental results and simulation results for Changping composite gravel–artificial rough steel plate contact surface under different roughness conditions.  
experiments referenced, conducted by [PERSON] [42], were designed to emulate the real-world behavior of a ship's hull, with a particular emphasis on the interaction between uniform density sand and concrete surfaces. In the experiments, the normal stress was incrementally ramped up from 102 kPa to 274 kPa under meticulously controlled displacement shear conditions, beginning with an initial void ratio of 0.68. The friction parameter was set to 0.85 based on the existing literature, with the specific model parameters outlined in Table 5.  
Figure 9 juxtaposes the experimental outcomes for uniform density sand interfacing with concrete under a progressive stress path against the predicted model curves. The transition point in Figure 9 denotes the juncture at which the normal stress undergoes a change. Initially, a normal stress of 102 kPa was imposed, and upon the shear displacement reaching 0.25 mm, this stress was escalated to 274 kPa. Notably, prior to the transition point, the predicted shear stress-displacement curve closely aligns with the empirical data. Post-transition, although the model's prediction is marginally lower than the experimental results in the lead-up to peak stress, there is a congruence in both the peak stress values and the timing of their manifestation. This concordance suggests that the model adeptly captures the shear behavior of soil-structure interfaces under a staged stress regimen.  
It should be noted that, although the predicted results are in good agreement with the experimental results, minor discrepancies are still observed, which can be attributed to several factors, including inherent model simplifications, assumptions made during model transformation, experimental uncertainties, and differences in boundary and loading conditions. However, the results are within the acceptable error margin for this type of study and that these minor discrepancies do not undermine the validity of the overall findings.