In order to quantitatively reveal the hydro-mechanical（HM） coupling effect of the weak structural planes in the dam abutment after a high arch dam project put into operation

the dam abutment rock samples of main faults of Jinping I high arch dam were collected

and the specimens were prepared by using remolding method

then a series of triaxial compression tests were performed on the replica specimens under hydrostatic pressures of 0

1

2

3 and 4 MPa in the MTS Rock Mechanics Testing System. The results show that the strength parameters of Jinping I arch dam abutment faults material have significant hydraulic pressure weakening effect

the friction coefficient f changes a little when the water pressure increases

the average weakening rate is less than 7%

while the cohesion c significantly decreases when the water pressure increases and the maximum weakening rate is up to 100%. Considering the combined effect of strength parameters f and c

the average weakening rate of the anti-shear strength τ of the main faults is around 25% under engineering condition of 3MPa water pressure and10 MPa normal stress. A prediction model of structural plane strength parameters under different water osmotic pressures was established

and according to the effective stress principle

the weakening rule and mechanism of shear strength of structural plane were analyzed preliminarily. The test results have been applied in the dam abutment stability study of the Jinping I high arch dam

and the research methods can provide the reference for the research of the mechanical properties of weak structure plane under multi-field coupling condition.