Abstract: Developed during the Chinese national 7th and 8th Five-Year key science and technology research project, geomembrane strain gauge was firstly used in-situ to monitor the strain of waterproof geomembrane in the 2nd-stage upstream cofferdam of the Three Georges Project and their good capability for measuring large strain were verified. All the 18 strain gauges placed in the cofferdam at different elevation had made good performance in measuring the strain of the cofferdam during construction. In section 0+500, all of the 10 gauges had measured large strain up to 11 %-19 %; most of them worked well till the measured value reaching their measuring limits. They only destroyed within 3 months after installated due to quick loading at the construction time. The others worked continually till Oct. 22, 2001 (just before the removal of the cofferdam). Their life-spans were longer than 3 years. Some of the gauges in sections 0+500 and 0+930 reached rapidly to 16 %-20 % during the flood season in the summers of 2000 and 2001; it seems that large strains, even cracks, probably occurred in the soil mass of cofferdam.

Key words: geomembrane strain gauge, monitoring, waterproof geomembrane, 2nd-stage upstream cofferdam of Three Georges Project