## 6 Conclusions  
In this study, the strength characteristics of a hardfill material and the stability of hardfill dams during earthquakes were investigated by conducting uniaxial compressive strength tests on both large indoor hard fill specimens and field-compacted cores and by performing a finite element analysis, respectively:  
1. From the results of the uniaxial compressive strength test on the large indoor specimens, the compressive strength tended to increase very gently with the unit water content in general for both types of aggregate PSDs, i.e., the upper limit (fine) and lower limit (coarse), mixed with a unit cement content of 80 kg/m\({}^{3}\) and three unit  
Figure 14: Results of FE analysis (required hardfill strength).  
water contents of 70, 85, and 100 kg/m\({}^{3}\), respectively. The strength range for the entire set of samples was 1.62-4.11 MPa, i.e., 3.15-4.11 MPa for the aggregate mix with the lower-limit PSD and 1.62-2.10 MPa for the aggregate mix with the upper-limit PSD. The uniaxial compressive strength of the aggregate mix with the lower limit PSD exceeded that of the aggregate mix with the upper limit PSD for the entire unit water content range. From the stress-strain relationship obtained from the uniaxial compressive strength test, the hardfill's elastic modulus was found to be in the range of approximately 220 to 609 times the uniaxial compressive strength.
2. Field compaction was performed with a vibration roller on the same type of aggregates as used in the indoor laboratory test by matching the PSD and mixing ratio to the laboratory test conditions. The results of the uniaxial compressive strength test on the cores collected from the field compacted hardfill after 28 d showed that the strength range for the entire core was 5.30-8.20 MPa, i.e., more than twice as large as the indoor test results, suggesting that the strength measurement of a hardfill through a laboratory test can conservatively evaluate the strength of a field compacted hardfill.
3. The results of the finite element analysis on the hardfill dams modeled using the parameters determined based on the laboratory test results showed that the largest value of the maximum tensile stress of 0.1 MPa occurs in the hardfill dam body with a slope of 1:0.6 when the artificial wave is applied. The maximum tensile stress tended to decrease overall as the slope of the dam body was relaxed. Furthermore, it was shown that the overall strength range obtained for the indoor laboratory specimens and field compaction cores exceeded the required strength of the hardfill, thereby securing seismic stability (except for the hardfill dam with a 1:0.6 slope to which artificial wave was applied).  
Formal analysis, W.C. and J.S.; Data curation, Y.K.; Writing--original draft, S.K.; Writing--review & editing, B.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Korea Water Resources Corporation.  
Not applicable.  
The authors wish to express their appreciation to the Korea Water Resources Corporation and the Expert Group for Earth and Environment Corporation for funding and supporting this work.  
The authors declare no conflict of interest.