SIMULATION OF ROCK CRACK AND PERMEABILITY IN DAM FOUNDATION DURING HYDRAULIC FRACTURING

Hydraulic fracturing is one type of thedam internal erosion leading to concentrated leaks and dam failure. During reservoir impounding,cracks in rock or soil can be initiated and expanded by water pressure. The crack expansionincreasesthe permeability of the soil or rock foundations.A numerical model of crack deformationwas established based on the finite elements methodto study crack characteristics due to hydraulic fracturing pressure.The crack of 1 mm wide and 600 mm long is modeled on 1x1 m of rock mass with the overburden pressure and pore pressure in the crack. The permeability of crack rock with orientations was examined using the equivalent permeability based on crack width due to hydraulic fracturing.The results revealed that crack closure variedwith the elastic modulus of the fillerand the orientation along the crack surface. During reservoir impounding, the crack openingswere related to hydraulic pressure and crack orientation. The model of crack opening indicated that the vertical crack orientation was likely to widen more than the horizontal crack orientation,with crack openings in the range0.003-0.37 mm. The range inrock crack permeability with such crack openings was 5x10-6-1.65 m/s thatagreedwell with the range of field permeability based on the Lugeon test of 1.27x10-4 to 4.96x10-3 m/s. Crack openings due to hydraulic fracturing can be used to predict the rock crack permeability within the hydraulic fracturing area in the dam or its foundation.