This paper studies three-dimensional diffraction of obliquely incident plane SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space using indirect boundary element method.The approach is validated by comparison with the literature,and the effects of cavity interval,incident frequency,and boundary drainage condition on the diffraction are studied through numerical examples.It is shown that,the interaction between two cavities is significant and surface displacement peaks become large when two cavities are close,and the surface displacement may be significantly amplified by twin cavities,and the influence range with large amplification can be as wide as 40 times of the cavity radius.Surface displacements in dry poroelastic case and saturated poroelastic cases with drained and undrained boundaries are evidently different under certain circumstances,and the differences may be much larger than those in the free-field response. This paper studies three-dimensional diffraction of obliquely incident plane SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space using indirect boundary element method. Approach is validated by comparison with the literature, and the effects of cavity interval, incident frequency , and boundary drainage condition on the diffraction are studied through numerical examples. It is shown that the interaction between two cavities is significant and surface displacement peaks become large when two cavities are close, and the surface displacement may be significantly amplified by twin cavities, and the influence range with large amplification can be as wide as 40 times of the cavity radius. SURF displacements in dry poroelastic case and saturated poroelastic cases with drained and undrained boundaries are evidently different under certain circumstances, and the differences may be much larger than those in the free-field response.