## 4 Field Test Construction Results  
Figure 9 shows the relationship between the unit water content and dry unit weight for field-compacted hardfills, i.e., hardfills mixed on-site using the same type of aggregates with  
Figure 8: Relationship between unconfined compressive strength in elastic range and elastic modulus of hardfill.  
the maximum particle diameter of 80 mm as used in the indoor laboratory test by matching the PSD and mixing ratio to the laboratory test conditions (i.e., a unit cement content of 80 kg/m\({}^{3}\) and three unit water contents of 70, 85, and 100 kg/m\({}^{3}\)) and compacted on-site using a vibration roller. The change in the dry unit weight according to the unit water content shows that the dry unit weight increases in the case of the 50 cm lift compaction but decreases in the case of the 75 cm lift compaction. Thus, it shows a difference from the results from the indoor laboratory test, in which the values gradually increased in all mixing conditions. Regarding the range of changes in the unit water content, the average dry unit weight is in the range of 2232-2455 kg/m\({}^{3}\), i.e., generally similar to the indoor test results (2357-2468 kg/m\({}^{3}\)) but shows a slightly larger range. In particular, the difference in the dry unit weight according to the lift thickness is larger with the unit water content of 70 kg/m\({}^{3}\) than with other unit water contents.  
Prior to this study, a preliminary test was conducted for the same type of aggregate. In the preliminary test, the maximum dry unit weight was measured using a compaction test [3; 30] on a standard specimen with an aggregate with a maximum allowable particle size of 37.5 mm. Figure 10 shows the calculations of the relative compaction using the indoor test results and field compaction measurement results in this study. For the three unit water contents, both the 50 cm and 75 cm lift compactions show relative compactions in the range of 101.7-108.3%. Thus, both exceed 100%. These results are owing to the fact that the size and compaction energy of the hardfill aggregate in the field compaction conditions are larger than those in the standard specimen compaction conditions.  
Figure 11 shows the results from uniaxial compressive strength tests for 28-day cores collected after 28 d from field-compacted hardfills. For comparison, the test results for the large indoor specimens were plotted together. The uniaxial compressive strength of the field-compacted hardfill cores ranges from 5.3 to 8.2 MPa in the unit water content range of 70 to 100 kg/m\({}^{3}\) for the two lift thicknesses. The overall difference is more than doubles the range of 1.62-4.11 MPa in the indoor test results, and the largest strength value is observed at the unit water content of 85 kg/m\({}^{3}\). Thus, there is a rather large difference from the trend of the indoor test results. As can be seen from the error bars added in the data plot, there are larger variations in the indoor test results. The large variations in the indoor test results may be attributed to the fact that, for a large indoor specimen with  
Figure 9: Compaction results for field-constructed hardfill (dry unit weight).  
large aggregate particles in a mold, uniform compaction tends to be hardly achieved by vibrating tamper, compared with a roller-compacted field core. As a result, it seems that less uniformly compacted indoor specimens exhibit lower strength. Even acknowledging such differences, the relatively large difference between the laboratory (indoor) and field tests suggests that the strength measurements from laboratory specimens under similar mixing conditions can generally be evaluated conservatively.  
Figure 11: Uniaxial compressive strength of field-constructed hardfill (28 d of age).  
Figure 10: Relative compaction of field-constructed hardfill.