In order to quantitatively describe the toughness and stability of a semi-infinite transversely isotropic medium including multiple rectangular cracks

the interaction between two coplanar or parallel rectangular cracks under a uniform distributed normal or tangential load is analyzed; and the corresponding stress intensity factor (SIF) is calculated. By employing dual boundary element method and based on the fundamental solutions for two joined transversely isotropic solids

the variation of the SIF with the distance between free surface and crack surface is investigated. And the influence of the side ratio of the rectangular crack

the free surface and the distance between two cracks on the interaction between two coplanar or parallel cracks is studied. Results show that the existence of the free surface causing the SIF of rectangular crack in semi-infinite extent is bigger than those in infinite medium. The side ratio and distance between two cracks exert an obvious influence on the interaction between two coplanar or parallel cracks

but the free surface has little influence on the interaction between two coplanar or parallel cracks.