Semi-automatic apparatus of the permeability coefficient for cutoff walls in expansive soil areas

The permeability coefficient of most cutoff walls with plastic materials is less than 10⁻⁶ cm/s, it exceeds the measurement range of the existed devices. For the permeability coefficient testing for cutoff walls with low permeability, there are complex in the automatic system of pressure control, difficult in the keeping stability of hydraulic pressure, high in the measurement precision, leaky in the contact surface between the fixing apparatus and the measured specimen. Firstly, based on the characteristic analysis of cutoff walls, the hydraulic pressure was accurately controlled when the valve of atmospheric pressure control with high precision worked in with the electromagnetic valve, the hydraulic pressure was controlled. Secondly, the shape of inner space for the fixing apparatus of the specimen is developed, the leakage of the contact surface between the fixing apparatus and the specimen was greatly decreased. The test showed that the semi-automatic apparatus could realize automatic control of the hydraulic pressure accurately with the combined action of an electromagnetic valve and a pressure reducing valve, the leakage of the contact surface could be basically avoided. The testing apparatus can be used in penetrability tests and detection of project quality for cutoff walls with low permeability.