采用FLAC3D软件分析了圆形断面、矩形断面、直墙式断面和曲墙式断面形状隧道开挖在III级围岩中的位移和应力集中分布规律。圆形断面隧洞围岩位移最小，应力集中系数最小，塑性区厚度最小，应力集中系数最大点距洞面的距离最大，即支护结构受到的围岩压力最小;与圆形断面隧洞相比，曲墙式隧洞围岩位移、应力集中程度和塑性区仅次于圆形隧洞，曲墙式断面是合理的隧洞断面形式；矩形隧洞围岩位移、应力集中程度和塑性区最大；直墙式隧洞围岩位移、应力集中程度和塑性区仅比矩形隧道略小，与矩形一样，直墙式断面是不利的隧洞断面形式。

The distribution rules of stress and displacement of grade III surrounding rock during excavation of tunnels with circular crosssection, rectangular crosssection, straight wall and arch crosssection and curved wall crosssection are analyzed by FLAC3D software respectively. The tunnel with circular crosssection has the smallest displacement, stress concentration coefficient and plastic zone, while the tunnel with rectangular crosssection has the largest displacement, stress concentration coefficient and plastic zone. The point with maximal stress concentration coefficient has the farthest distance from working face of tunnel with circular crosssection, which means the support structure bears the minimal surrounding rock pressure. The numerical value of displacement, stress concentration coefficient and plastic zone for the tunnel with curved wall crosssection and straight wall and arch crosssection ranges between that of tunnel with circular crosssection and rectangular crosssection. So the circular crosssection and curved wall crosssection are practicable tunnel crosssection shapes, rectangular crosssection and straight wall arch crosssection are not.