The stability of karsts tunnels is related to the distribution of karsts area.In order to the determine the most unfavorable distribution of parts of the cave for the stability of the tunnel,this paper quantitative analyzes the effects of the different parts of the cave distribution on the tunnel displacement field,stress field ,distribution of plastic zone and principal stress distribution.Background with Yiwan Railway tunnel in a karat.Four kinds of conditions ,no caves around the tunnel,cave located in the tun-nel side,cave located at the top of the tunnel and cave located at the bottom of the tunnel,are simulated by FLAC software.The cave location of the most unfavorable stability of the tunnel is the tunnel side.%岩溶隧道的稳定性与岩溶的分布部位有关。定量分析不同分布部位的溶洞对隧道位移场、应力场、塑性区分布规律及主应力分布规律的影响，来确定对隧道稳定性最不利的溶洞分布部位。以宜万铁路某岩溶隧道为背景，利用 FLAC 软件模拟分析隧道周边无溶洞、溶洞位于隧道侧部、溶洞位于隧道顶部和溶洞位于隧道底部4种工况下隧道的稳定性状况，得出对隧道稳定性最不利的溶洞位置是隧道侧部。
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