浅埋大断面黄土隧道地表裂缝特征及形成机理浅析

Analysis of Characteristics and Formation Mechanism of Ground Surface Cracks of Shallow Buried Loess Tunnel with Large Section

地表裂缝是浅埋黄土隧道常见的工程灾害之一,通过现场调研和理论分析,对董志塬区长段落浅埋大断面黄土隧道地表裂缝的特征和形成机理进行初步总结,并提出针对性施工建议。结果表明:黄土隧道地表裂缝沿隧道中线向两侧呈对称分布,地面整体呈"锅底状"下凹形。地表裂缝宽度与隧道埋深呈负相关,裂缝间距与隧道埋深呈正相关。隧道埋深分别在20,50~60 m内时,地表裂缝间距分别为1.5~2.1倍、1.9~3.5倍洞径。地表裂缝发育主要经历"孕育期-急剧变形期-平稳期"三个阶段。降雨当天及降雨后1~3 d内,地表沉降变形量达到稳定变形量的50%以上,降雨量对地表变形及地表裂缝的发展具有一定的"预兆性"和"前瞻性"。黄土隧道地表裂缝主要是由于开挖扰动而形成的潜在滑动楔形体向隧道内部临空面滑动、黄土层内的洞穴裂隙等压缩沉降、洞顶上覆土体自重与支撑体系强度不平衡等因素综合导致的。

Ground surface crack is one of the common engineering disasters in shallow buried loess tunnels.The typical characteristics and formation mechanism of ground surface cracks of loess tunnels with large sections in Dongzhiyuan regions are preliminarily summarized based on field investigations and theoretical analysis,and pertinent construction suggestions are put forward.The results show that ground surface cracks of loess tunnels in Dongzhiyuan regions are symmetrically distributed along both sides of the middle line of the tunnel,and the whole surface is in the shape of"pot bottom"concave.The width of the ground surface cracks is negatively correlated with the depth of tunnel,and the crack spacing is positively correlated with the depth of tunnel.When the depth of tunnel is within 20 m and 50~60 m,the ground surface crack spacing is about 1.5~2.1 times and 1.9~3.5 times the diameter of tunnel respectively.The development of the ground surface cracks mainly experience three stages:gestation stage,rapid deformation stage and stationary stage.The amount of surface settlement deformation is more than 50%of that of stable deformation on the day of rainfall and within 1~3 days after rainfall,thus rainfall has certain"foreboding"and"foresightedness"to the development of ground surface deformation and ground surface cracks.Ground surface cracks of loess tunnels in Dongzhiyuan regions are mainly caused by the sliding of the potential sliding wedge to the free surface inside the tunnel due to the excavation disturbance,the equal compression settlement of the cave fissures in the loess layer,and the imbalance between the self-weight of the soil above the tunnel roof and the strength of the supporting system.