Recently

increasing attention has been given to hydraulic fracturing phenomena in core wall of rockfill or soil dams. However

most of the studies are carried out from the macro prospective

and the fracturing mechanism is still disputable. In this paper

the hydraulic fracturing problem is analyzed using the particle flow code (PFC) from the micro prospective. The occurrence and development of hydraulic fracturing is simulated. Results show that the fracturing pressure Pf increases with the increasing of the vertical stress in an approximately linear way

which agrees well with experimental results. Under the high hydraulic gradient condition

the maximum principal stress near crack tip is decreased because of the wedge effect of water. Hydraulic fracturing will probably occur when the maximum principal stress is less than or close to the water pressure of upstream of core wall. In addition

it is also illustrated that the main reason of hydraulic fracturing in core wall is that the tension stress exceeds the tensile strength of the soil.