Abstract: It is a way to measure the internal force of pile foundation by sliding micrometer, and the anti-seepage measures during the installation of sliding micrometer tube are the key to achieve high quality test, while quantitative research on anti-seepage effect of measures is rare. A set of device for testing the anti-seepage ability of sliding micrometer tube was developed. The seepage flow of three common anti-seepage measures under different pressure differences was tested, and a formula for calculating the seepage flow was developed. The matters needing attention in the installation of the sliding micrometer tube were analyzed according to the site conditions. Test results show that when the internal pressure is higher than the external pressure, the seepage flow rate is much larger than that when the external pressure is larger than the internal pressure. Glue coating is a very effective anti-seepage measure, and generally no particles with a diameter over 0.005 mm will enter the sliding micrometer tube after adopting this measure. Increasing the water head in the sliding micrometer tube is beneficial to reduce impurities entering it, but the water head in the sliding micrometer tube can not be too much higher than the liquid levels in the borehole of the pile. After pouring concrete, if water overflow in the sliding micrometer tube happens, the orifice of the sliding micrometer tube should be closed to limit water overflow, and if the water level in the sliding micrometer tube falls, the orifice of the sliding micrometer tube should be opened to allow gas to enter it.

Key words: sliding micrometer, pile, stress test, anti-seepage measure