# Experimental Investigation into the Number of Phases in Debris Flows
## 5 Results
### Response of the Water in Experimental Shurries to Mechanical Forcing
#### 5.3.2 The Moment When Load Is Applied (90 min)  
When the external load was imposed at \(t=90\) min, a sharp fall in \(h\) occurred in the loading tube, with decreases up to 1.2 cm depending on \(h_{\rm s0}\). In contrast, the two observation tubes showed a comparatively small increase in \(h\) (only up to 0.4 cm), which tended to decrease with increasing \(h_{\rm s0}\).  
Interestingly, analogous response behaviors occurred in the \(h_{\rm p}\) of the piezometer tubes themselves, with the loading piezometer lowered by 0.1-1.3 cm, and the observation tubes slightly elevated by 0.3 cm.  
As expected, the response of \(h_{\rm m}\) to the loading was similar to the changes observed in \(h\) and \(h_{\rm p}\). The \(h_{\rm m}\) values around the loading tubes dramatically decreased by 1.2-2.6 cm, and those around the observation tubes increased slightly, with heights of 0.1-0.4 cm.  
Accordingly, the \(R\) values of the loading tubes abruptly increased from 0.69-1.03 at \(t=89\) min to 0.92-1.52, whereas those of the observation tubes decreased slightly, and the amplitudes of the changes were only 0.01-0.04.  
Equally important, loading caused little variation in the rate of increase in \(PCD\).  
3.3 The Stage in Which the h of the Loading Tube Is Lower than That of the Observational Piezometers  
In the subsequent period of 10-220 min (average of 90 min), the previously lowered \(h\) for the loading tube increased slowly to a level comparable to that of the observational piezometers. For the loading tubes with \(h_{\rm s0}\) of 6 cm, within the appreciably affected range of loading, the recovery of the head required 10-210 min (average 105 min). Quite surprisingly, the \(h\) of the observational piezometers continued to rise slowly, following their original trend before loading, or even at lower rates than before loading, almost as though the loading event did not occur.  
During this stage, the \(h_{\rm p}\) and \(h_{\rm m}\) values of all three piezometers decreased at extremely low rates (average 0.9 mm/50 min and 0.8 mm/50 min, respectively). Consequently, the differences in the \(R\) values between the loading and observational tubes widened further to the order of 0.21-0.88, and were anti-correlated with \(h_{\rm s0}\).  
It is noteworthy that no obvious change in the rate of increase in \(PCD\) was observed at this stage relative to that during the 30-89 min stage.  
3.4 The Stage in Which the h for the Loading Tube Is Higher than That for the Observational Piezometers  
Compared to the end of the previous stage, the \(h\) of the loading tube increased up to 1.7 cm above that of the observational tubes, which lasted 290-500 min until the end of the experimental runs, except for DYG-2-0.57 with a \(h_{\rm s0}\) of 12 cm, JJG-2-0.53 with a \(h_{\rm s0}\) of 12 cm, and JJG-2-0.54 with a \(h_{\rm s0}\) of 12 cm. In this stage, the rate at which the \(h\) values of all of the piezometers changed was very slow, with maximum rising and falling rates of 0.9 and 0.4 cm/h, respectively, so that their time trends were dome-shaped (mainly DYG slurries) or even semi-dome-shaped (mainly JIG slurries).  
The slowly descending trends of \(h_{\rm p}\) and \(h_{\rm m}\) were still as discernible as in the previous stage, with subsidence rates of approximately 0.2-1.5 and 0.2-1.4 mm/h, respectively.  
At the end of the experiment at \(t=600\) min, the \(R\) values for the loading and observational tubes remained in the order of 1.28-2.15 and 0.79-1.17, respectively, and the differences in \(R\) between them were maintained at 0.28-1.18.  
As expected from the change in \(h_{\rm m}\) of the piezometers, the final \(PCD\) of the 36 runs was only 1.9-11.0%.  
Taken together, loading caused significant and persistent changes in \(h\), \(h_{\rm p}\), \(h_{\rm m}\), and \(R\) values for the loading tube, but little or no response of \(h\), \(h_{\rm p}\), \(h_{\rm m}\), and \(R\) in the observation tubes, and a rate of increase in \(PCD\) occurred.