The problem of hydraulic fracturing in core of earth-rockfill dam is an important and unsolved geotechnical problem. In this paper

the mechanism to induce and propagate hydraulic fracturing is investigated based on analyzing loading and deformation in the core. It is indicated that the incipient impounding period is the most dangerous one during which the hydraulic fracturing may occur easily in the core; and that the hydraulic fracturing does not take place in a core with perfect homogeneous soil. The cracks or local serious weaknesses in the core and the incipient impounding period are two important conditions to induce the hydraulic fracturing; and the essential cause to induce the hydraulic fracturing is the existence of local high hydraulic gradient. Finally

a simple test is performed to validate the above mechanism. The suggestion to further study on the criteria

numerical simulation to the hydraulic fracturing are presented.