护盾式TBM隧道管片壁后豆砾石分布规律

Distribution Characteristics of Pea Gravel Behind Segment in Shield Tunnel Boring Machine Tunnels

作为管片与围岩间的连接层,TBM隧道中的豆砾石对管片受力具有重要意义。受施工技术、地质条件等影响,豆砾石填充不密实、分布不均匀的现象时常发生,导致管片出现错台、开裂、渗漏水等灾害,故探明豆砾石分布特征是分析管片受力的基础。对此,依托青岛地铁TBM隧道项目,采用地质雷达对管片壁后豆砾石分布特征进行现场测试,并进行单环管片豆砾石吹填数值模拟,分析了隧道直行段、转弯段豆砾石在管片壁后的迁移过程,讨论了地质条件、吹填压力、塌方等因素对吹填质量的影响规律。结果表明:在TBM隧道施工中,拱顶、隧底及转弯段外侧下部为豆砾石空洞多发部位,拱顶与隧底空洞长度大于1m,主要表现为层间脱空,转弯段外侧下部豆砾石空洞规模较小且不密实;地质条件越差,豆砾石出现空洞的概率及规模越大,强风化地层表现最为明显;塌方通过阻碍豆砾石迁移路径、增加碰撞耗能影响豆砾石吹填质量,但影响范围仅在塌方处;提升豆砾石吹填压力可以改善拱顶和隧底豆砾石填充状态,地质条件越好,改善程度越明显,强风化地层豆砾石吹填质量改善不明显;管片壁后豆砾石空洞按照形成原因分为3类:碰撞耗能、塌方掉块和转弯段间隙变小,并给出了3类空洞的多发部位、特征及施工控制建议。

Pea gravel plays a crucial role in segment stability as the connecting layer between the segment and the surrounding rock in TBM tunnels.Due to the influence of construction technology and geological conditions,the phenomena of dense filling and uneven distribution of pea gravel often occur,leading to various disasters such as dislocation,cracking,and water leakage.The distribution characteristics of pea gravel behind the segment ring form the basis for analyzing segment stress.Within the context of the Qingdao metro TBM tunnel project,geological radar is employed to examine the distribution characteristics of pea gravel behind the segment wall.Subsequently,a numerical simulation of single-ring pea gravel filling is conducted.This study analyzes the migration process of pea gravel behind the segment wall in both straight and curved sections of the tunnel and discusses the impact of geological conditions,filling pressure,collapses,and other factors on the quality of the filling.The results indicated that during TBM tunnel construction,the arch crown,tunnel bottom,and lower part of the outer side of the line’s turning section are the areas most prone to pea gravel empty tunnels.Moreover,the pea gravel empty of the arch crown and tunnel bottom exceeds 1 m,while those at the lower part of the outer side of the turning section are smaller and less dense.Poorer geological conditions increase the probability and scale of voids in the pea gravel behind the segment,with strongly weathered strata showing the most significant effects.Collapses impact pea gravel reclamation by obstructing migration paths and increasing energy demands,although their impact is limited to the collapse site.Enhancing the hydraulic fill pressure of the pea gravel can improve the fill quality at the vault and tunnel bottom;the improvement is more pronounced under better geological conditions,though it does not significantly enhance the filling quality in strongly weathered strata.Based on the causes of formation,the pea gravel cavities behind the segment ring are categorized into three types:collision energy dissipation,collapse block,and smaller clearance in the turning section.Additionally,the study presents the frequent parts,characteristics,and construction recommendations related to these activities.