Such unfavorable structural planes as weak interlayers play a decisive role to the stability of rocks surrounding underground openings in some cases and the safety of supporting structures. Using a FEM program FINAL of Austria that adopts a COJO element a perfect element to simulate the characters of weak interlayers

this paper has conducted systematic numerical tests to study the stability of a tunnel surrounded by rocks containing weak interlayers and the safety of supporting structures. In studying

the emphases are put on three situations where the interlayers are distributed at intervals of 0.2 spans

0.5 spans and 1.0 spans respectively. Some quantificational results about the influence of weak interlayers with those three different spacing intervals are summarized

especially the influence on the deformation

stress of surrounding rocks as well as the inner force of shotcrete supporting structure. These results have referential and guiding significance to the site selection and layout

the majorization of supporting system and the construction of underground openings of the same kind.