## 6 Summary and Conclusions  
Extensive long-term triaxial creep tests on core specimens from Quxue Dam and Laojiaoxi Dam were performed at different radially confining stress levels in the range of  
Figure 16: Cohesion intercept and friction angle versus temperature.  
0.5-1.5 MPa and at different temperatures in the range of 5-30 \({}^{\circ}\)C. Based on the test results and the application of the generalized Kelvin model in the linear form of creep compliance, the author proposed a material stress-strain-time-temperature creep model (SSTTC model) for the analysis of asphalt cores in embankment dams.  
The following conclusions and findings were obtained:  
* The magnitude of radially confining stress levels has insignificant effects on the stress-strain relationship of HAC in the creep-stable state that has been compacted with a vibratory roller in the field.
* The long-term triaxial creep test results showed that the curves of creep strains with time could be fit well toward a strain-stable state by applying the generalized Kelvin model in the linear form of creep compliance with two Kelvin elements in the temperature range of 5-30 \({}^{\circ}\)C.
* The relationships of the viscoelasticity and temperature parameters were established based on the test results, and a material stress-strain-time-temperature creep model (SSTTC model) was proposed. The creep curves obtained using the SSTTC model showed good agreement with the test curves of the asphalt specimens with reasonable variations.
* The volumetric strain was compressive strain during the long-term triaxial creep tests. The asphalt concrete specimens failed at high strain levels, as the bitumen (binder) was torn off the aggregates.
* An equivalent Poisson ratio up to the creep-stable state was, based on the recorded axial and volumetric strains, estimated to be 0.37.
* The creep-stable modulus \(\mathrm{E_{cs}}\) of an asphalt core during construction is about 10 times lower than that in the adjacent transition zones. The asphalt core must resist the applied stresses from the transition zones by deforming.
* The relationships between the viscoelastic parameters and temperature for the SSTTC model must be determined for the asphalt mix used in the core, and the construction process and temperature changes in the asphalt core during construction and reservoir impounding must be specified. The strains in the asphalt core, calculated by using the SSTTC model in a numerical analysis, can be compared with the allowable strains of an asphalt concrete mix to evaluate the safety of an asphalt core in an embankment dam. If core cracking is likely to occur and could lead to unacceptable leakage or even dam rupture, the design of the ACED must be modified or mitigation measures must be introduced to prevent any serious and unacceptable consequences of the cracking.  
The research in this study was supported by the National Natural Science Foundation of China (no. 52039008).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the author.  
The author appreciates the assistance of [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] during the experimental work.  
The author declares no conflicts of interest.