考虑围岩应力释放的饱和Q2黄土大断面隧道预留变形量研究

Study on the Reserved Deformation of Large Cross-section Tunnel Saturated Q2 Loess Considering the Release of Surrounding Rock Stress

由于饱和黄土具有含水率高、强度低、稳定性差的特点,饱和黄土隧道施工过程中常遇到初期支护沉降变形过大、预留变形量难以确定等问题。考虑到饱和Q2黄土承载力小,无法计算位移释放率和体积释放率,应力释放率成为研究大断面饱和黄土隧道预留变形量的有效手段。鉴于此,本文提出了饱和黄土隧道围岩应力释放率计算思路,研究了围岩变形特性及预留变形量。结果表明,饱和软黄土隧道施工过程中,围岩最终变形量受施工时间影响较大,大多数断面在监测时间范围内仍有较大变形速率,围岩应力释放不充分;现场围岩应力释放率在25%~30%之间,当应力释放率超过30%,拱顶沉降量迅速增大,围岩易产生失稳;建议饱和Q2黄土隧道施工预留变形量为35 cm,变形控制值在25 cm。

Due to the characteristics of high moisture content,low strength,and poor stability of saturated loess,problems such as excessive initial support settlement deformation and difficulty in determining reserved deformation are often encountered during the construction of saturated loess tunnels.Considering the small bearing capacity of saturated Q2 loess,it is hard to calculate the displacement release rate and volume release rate,and the stress release rate has become an effective means to study the reserved deformation of large cross-section saturated loess tunnels.This article proposes a calculation method for the stress release rate of saturated loess tunnel surrounding rock,and conducts a detailed study on the deformation characteristics and reserved deformation amount of the surrounding rock.The results show that the final deformation of the surrounding rock during the construction process of saturated soft loess tunnels is greatly affected by the construction time,and most sections still have a large deformation rate within the monitoring time range,resulting in insufficient stress release of the surrounding rock.The stress release rate of the on-site surrounding rock is between 25%and 30%.When the stress release rate exceeds 30%,the settlement of the arch crown rapidly increases,and the surrounding rock is prone to instability.It is recommended to reserve a deformation of 35 cm for the construction of saturated Q2 loess tunnel,with a deformation control value of 25 cm.