泥质石灰岩地层高速铁路隧道底鼓原因分析

Causes for Floor Heave of High-Speed Railway Tunnels in Argillaceous Limestone Strata

针对泥质石灰岩地层高速铁路隧道底鼓现象,为底鼓整治措施提供理论依据和数据支撑,依托西成高铁ZJY隧道,通过分析隧道监控量测、仰拱填充及轨道板结构变形、底部围岩变形和仰拱结构受力数据,研究隧道底部荷载分布特征及对结构的影响。采用分析隧道初始应力场和开挖应力场的方法,结合岩体物质成分及微观结构鉴定、膨胀性和蠕变试验,以应力场为纽带,提出隧道周边岩层的物理力学分区,建立隧道分层差异蠕变模型。研究结果表明:1)隧道底鼓是岩体蠕变造成的。2)隧道开挖后底部应力重分布影响区中靠近仰拱的15 m范围内微晶结构方解石发生大量持续蠕变造成底鼓变形。3)模型显示,隧道开挖前地层岩性差异形成不均匀的初始应力场,隧道开挖后在仰拱下方不同深度将形成多个承载区,深浅承载区内岩性差异的岩体同时发生蠕变变形。4)隧道开挖前地层中存在蠕变现象,同一岩性地层内水平差应力中位数较最大值降低超25%。5)隧道开挖后泥灰岩地层蠕变成分最高达80%左右,发生蠕变的差应力门槛,约5 MPa(下限)。6)蠕变试验显示,在隧道等效圆仰拱下方0.5 m左右,可能存在蠕变的差应力峰值,约15 MPa(上限),推测仰拱接触应力的峰值可能在1 MPa左右。

The phenomenon of floor heave is common in high-speed railway tunnels in the argillaceous limestone strata.Hence,a case study is conducted on the ZJY tunnel of the Xi'an-Chengdu high-speed railway to provide theoretical guidance and data support for floor heave treatment.Briefly,the distribution characteristics of the tunnel floor load and its impact on the tunnel structure are examined by analyzing the tunnel monitoring data,inverted arch filling,track plate structure deformation,floor's surrounding rock deformation,and inverted arch structure stress.Further,by analyzing the initial and excavation stress fields of the tunnel and based on the identification of the composition and microstructure of the rock mass material and expansion and creep experiments,the physical and mechanical zoning of the surrounding rock layers of the tunnel is proposed;additionally,a layered differential creep model of the tunnel is established using the stress field as a link.The research results of this study are as follows:(1)Tunnel floor heave is caused by rock creep.(2)After tunnel excavation,numerous continuous creeps of microcrystalline calcite occurred within 15 m near the inverted arch in the influence area of stress redistribution at the tunnel floor,resulting in the deformation of the floor heave.(3)The model shows that before tunnel excavation,there existed an uneven initial stress field due to differences in the lithology of strata.After tunnel excavation,multiple bearing zones were formed at different depths below the inverted arch and creep deformation was experienced by rock masses with different lithologies in the deep and shallow bearing zones.(4)The creep phenomenon occurred in the strata before tunnel excavation,and the median of the horizontal differential stress in the same lithological formation was reduced by more than 25% compared with its maximum value.(5)The creep composition of the argillaceous limestone strata after tunnel excavation is up to approximately 80%.The differential stress threshold for creep is approximately 5 MPa(lower limit).(6)The creep test shows that the creep differential stress peak value may be approximately 15 MPa(upper limit);the peak value position is approximately 0.5 m below the tunnel's inverted arch(equivalent to circle).The peak contact stress of the inverted arch is speculated to be approximately 1 MPa.