Abstract
In civil engineering, to improve weak foundations, many sand pillars are struck into the grounds using a casing pipe. If the sinking velocity of the sand level in the pipe is measured on-line accurately, a smooth construction can be then achieved. The measurement is reduced to that of a length of the air pillar in the pipe. The authors thus proposed a highly accurate pipe length measurement system, which applied a bank of Kalman filters to a linear dynamic model of the stationary wave generating in the pipe. Although the method realized an accurate on-line measurement of the error rate 0.01_??_0.08%, it was applied only on a stand-still steel pipe.
This paper thus tries to apply the system to the measurement of the actual sand level in a casing pipe. This application encounters, however, two new problems. One is that an electric signal caused by the vibration of the casing pipe superposes to that of the stationary wave in the pipe. The other is that the lengths of the air pillar measured with low and high order modes models are different because of the complicated structure of the pipe.
The paper presents a practical measurement system which overcomes the two problems and realizes an accurate on-line sand level measurement in the pipe.
