Development Of A High-Capacity Tensiometer And Its Application

Tensiometer is a sensor used for directly measuring matric suction in soil. The measurement range of conventional tensiometer has generally been confined to less than 100 kPa due to the cavitation of water in the tensiometer. At present, the application of high-capacity tensiometer in geotechnical engineering is restricted because of its complicated saturation procedures and some problems caused by insufficient saturation such as slow response, short duration and poor stability. Furthermore, the use-cost of high-capacity tensiometer is commonly higher, especially in mainland of China. Therefore, it is highly desirable to develop a high-capacity tensiometer to extend the application of tensiometer to cover matric suction values normally encountered in geotechnical engineering.A low cost(material cost below 2000 yuan) tensiometer was developed to directly measure matric suction greater than 100 kPa in this study. The tensiometer mainly consists of a general-purpose pressure transducer made in China and a ceramic disk with air entry value of 5 Bar. The development of the tensiometer can greatly reduce the use-cost of high-capacity suction probes in mainland of China and can offset the situation of deficiency of domestic high-capacity tensiometers. The manufacture of the tensiometer and certain saturation procedures assure that the tensiometer can measure matric suction in soil above 100 kPa. The developed tensiometer illustrated fast response and good measurement stability in evaporation tests and in compacted soil sample suction measurement tests and reached the performance level of tensiometers abroad. In addition, it's worth noting that the high suction measurement ability of the tensiometer can be restored using an immersion method after measured matric suction is higher than the air entry value of the ceramic disk. This feature is especially useful in the field when a high pressure facility for pre-pressurization is not readily available and the suction measurement ability of the tensiometer needs to be restored for subsequent use.The developed tensiometer after testing its performance was applied to soil-water characteristics curve measurement test, a slope model test and insitu matric measurement. Soil-water characteristics curves measured by tensiometer and pressure plate are nearly consistent. In the field, the developed tensiometer showed corresponding change of measured suction with environment changes such as rainfall and high temperature, and had a measurement duration of about 25 days. These applications above can further extend the application of high-capacity tensiometer and accumulate more experiences to use.