大厚度湿陷性黄土隧道现场浸水试验研究

对于穿越大厚度湿陷性黄土地层的隧道,其围岩湿陷变形会威胁隧道结构的稳定性。为了分析黄土围岩湿陷变形对隧道衬砌结构的影响机制,选取典型大厚度湿陷性黄土隧道场地,通过开展隧道场地地面浸水试坑试验及隧道仰拱浸水试验,测试了地面入渗和隧道基底入渗过程中不同埋深地层的湿陷沉降变形及地基的沉降变形、入渗过程中围岩的体积含水率变化分布、试坑周边地层的侧向位移、衬砌结构接触压力和轴力,研究了既有隧道黄土地层的湿陷变形特性及水分运移规律、隧道结构力学响应。结果表明,隧道开挖、衬砌作用扰动黄土结构,增大了围岩及深层黄土的渗透性;与天然黄土场地试坑浸水入渗比较,增大了竖向浸水范围,减小了水平向浸水范围。隧道围岩湿陷变形改变了围岩与衬砌结构的相互作用性状。围岩湿陷和地基软化作用增大了二次衬砌结构侧墙竖向荷载和侧墙围岩的挤压作用,引起拱脚地基承载力减小和沉降变形发展,拱顶、拱肩接触面呈受拉状态;仰拱中部地基土的抗力作用抑制其沉降变形,从而使得拱脚和仰拱中部出现显著的沉降差,导致仰拱混凝土开裂,形成纵向裂缝。此外,浸水范围内黄土的湿陷变形不仅引起竖向沉降变形,还会引起周围土体产生侧向水平位移;洞口边坡场地黄土的湿陷性和地层湿陷变形差异较大,反映了黄土山岭黄土场地地层条件复杂多变的特征。

Field immersion tests on tunnel in large-thickness collapsible loess

The stability of tunnel structure in large-thickness collapsible loess strata will be threatened by the potential collapse deformation of loess. In order to explore the mechanism of tunnel lining structure influenced by collapse deformation of the surrounding rock, field immersion tests are conducted on tunnel construction site of collapsible loess with large thickness. A series of parameters such as the volumetric water content of soil at different depths, collapse deformation of strata, settlement of tunnel foundation, lateral displacement of soil layer and stress condition of tunnel structure are measured in the infiltration process. The collapse deformation characteristics, infiltration laws of the loess site and mechanical change rules of tunnel lining structure are emphatically investigated. The results show that the depth of water infiltration at this site is much deeper than that at the natural loess site due to the greater permeability of the surrounding rock caused by tunnel excavation disturbance. The interaction between tunnel structure and surrounding rock is changed by the collapse of surrounding rock during water infiltration, such as the significant increase of the extrusion force at tunnel side wall and the vertical pressure at two flanks of tunnel inverted arch. Meanwhile, the subgrade reaction in the middle of tunnel inverted arch restrains the sedimentation of this area. A longitudinal crack formed in the middle of tunnel inverted arch is under the impact of differential settlement. In addition, with the increase of water infiltration depth, the collapse deformation of loess stratum is released layer after layer, and it includes the vertical and horizontal deformations. The collapsible loess site with large thickness in mountainous area has the complex characteristics of stratum soils, which is reflected by the tremendous difference of collapsible deformation in the immersion scope.