# Intelligent Compaction Measurement Value in Variability Control of Subgrade Compaction Quality
## 5 Conclusions  
This paper describes the results from a research study that was conducted to compare the vibration modulus \(E_{vib}\) and the newly proposed index \(E_{vc}\) with location-specific in situ test results. The main findings gained from the above work are summarized as follows. * Intelligent compaction was based on a theoretical concept and field experiment that the real-time vibration response to the subgrade was manifested in compaction indexes. Figure 8: A 3D distribution map of compaction effect: (**a**) variation in \(E_{vib}\) with the strength of underlying layer is 60 MPa, 80 MPa; (**b**) variation in \(E_{vc}\) when the strength of underlying layer is 60 MPa, 80 MPa; (**c**) variation in \(E_{vib}\) when the strength of underlying layer is 60 MPa, 80 MPa, 93 MPa; (**d**) variation in \(E_{vc}\) when the strength of underlying layer is 60 MPa, 80 MPa, 93 MPa. Application of these indexes was able to capture the difference of the subgrade stiffness and use it to estimate the compaction quality. * In this paper, a detailed method is given to utilize \(E_{vc}\) as a real-time index to control the variability of the compaction modulus in the condition which the strength of the underlying layer is large or uneven. The procedure of establishing the database and simulation results based on the elastic double-deck subgrade are also presented. * A field experiment was conducted on this test strip to analyze the influence law of different thicknesses of the filling layer and the strength of the underlying layer on the subgrade modulus \(E_{vib}\). It can be concluded that the correlation of thickness with the overall compaction quality is negative, and the correlation of strength with that is positive. Furthermore, the over-high strength underlying layer will affect the monitoring value of the traditional continuous compaction control index, so that the measured value is greater than the actual strength of the current roller layer. * Simulation results of the corresponding \(E_{vc}\) were acquired by specific targets of the database. It was concluded that the variability in \(E_{vib}\) of the subgrade decreases gradually with an increasing number of filling layers, and the variability in \(E_{vc}\) of the filling layer remains at a lower level. * The modulus variability in the cut to fill subgrade mainly comes from the strength difference in the underlying layer, not the thickness difference in the filling layer. It was suggested that the modulus variability in the filling layer may increase with supplementary roller compaction, only considering the variability in \(E_{vib}\) of the subgrade. * A critical aspect of this proposed index \(E_{vc}\) is that it is able to improve the quality control of the subgrade stiffness. It was demonstrated through filed tests that \(E_{vib}\) can be used to monitor the overall compaction quality in real time, and \(E_{vc}\) was extracted to identify the compaction quality of the filling layer. While the results presented herein are promising, it is necessary to point out that the tests so far have focused on the cut to fill subgrade. As the effects of strength and the filling thickness are considered separately, further tests can be designed to explore the effects of them superimposed on each other. Finally, it should be noted that IC does not provide a direct measurement of \(E_{vc}\), rather it provides an indirect \(E_{vc}\) value. Thus, further discussion and research are necessary to address this issue in future studies. The authors confirm contributions to the paper as follows: Conceptualization, Z.W. ; Data curation, Z.W. ; Formal analysis, Z.W. ; Writing--original draft, Z.W. ; Writing--review & editing, J.Q. & J.L. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.