## 4 Compaction Quality Evaluation System and Its Indices
### Evaluation System for Compaction Quality
#### 4.2.2 Real-Time Compaction Measurement Indices  
The real-time collection of compaction parameters and roller acceleration spectrum is based on the RTCM system. Referring to Figure 1, the collection process is performed in the following three steps.  
(1) The position and vibration state data of rollers can be collected by the GPS orientation and vibration state monitoring modules installed on the roller. Combined with real-time kinematic global positioning system [34], the horizontal positioning accuracy can reach 1 to 2 cm and the vertical accuracy can reach 2 to 3 cm. The roller acceleration signal can be obtained by the acceleration monitoring module (including the accelerometers and encoders) that is installed on the center of the roller's drum. The rotation of eccentric masses produces eccentric force and causes the drum to vibrate at a certain frequency. It has been confirmed that with the continuous compaction of dam materials, the material stiffness and modulus will constantly improve and the corresponding amplitude of roller signal acceleration will constantly change [7; 14; 15].  
2. The above data will be sent to the application server through data terminal unit of global system for mobile communications. Via the calculation of application server, we can obtain the real-time compaction parameters (i.e., \(N_{s}\), \(N_{p}\), \(N_{v}\) and \(N_{l}\)). The 3D compaction monitoring client will read above masses and visualize them as shown in Figure 3. The material parameters (i.e., \(M_{S}\) and \(M_{m}\)) can be collected by the PDA collection system as illustrated in Reference [13]. Meanwhile, the acceleration amplitude spectrum can be obtained from the roller acceleration signal by Fast Fourier Transform [16], based on which the indices \(CMV\) and \(CCV\) can be acquired [28]. \[\left\{\begin{array}{l}CMV=\mathrm{C}_{0}\cdot\frac{A_{2\Omega}}{A_{ \Omega}}\\ CCV=\left(\frac{A_{0.5\Omega}+A_{1.5\Omega}+A_{2.5\Omega}+A_{3\Omega}}{A_{2.5 \Omega}+A_{3\Omega}}\right)\times 100\end{array}\right.,\] (4) where \(A_{\Omega}\) and \(A_{2\Omega}\) are the drum acceleration amplitudes at the fundamental frequency \(\Omega\) and the first harmonic component of the real-time acceleration response signal. \(C_{0}\) is the site calibration constant. \(A_{0.5\Omega}\) represents the first subharmonic, and \(A_{1.5\Omega}\), \(A_{2.5\Omega}\) and \(A_{3\Omega}\) denote the other higher-order harmonics.
3. Based on correlation analysis, the real-time physical indices across the working face can be predicted by compaction and material parameters [13]. Additionally, for the lack of a strict theoretical basis for, and physical significance of, \(CMV\) and \(CCV\), the character parameters of the original acceleration amplitude spectrum (i.e., \(A_{0.5\Omega}\), \(A_{\Omega}\), \(A_{1.5\Omega}\), \(A_{2\Omega}\), \(A_{2.5\Omega}\), \(A_{3\Omega}\)) are chosen as the original prediction inputs for the prediction of mechanical indices. SVR with CFA is employed to establish the real-time prediction model and the system client will access the data continuously and perform a visual display for the real-time feedback control.