粉质黏土隧道超前支护作用效果研究

Research on effect of advanced support in silty clay tunnel

以哈尔滨地铁1号线三期为工程背景,采用现场试验与数值模拟相结合的手段,针对超前支护在粉质黏土隧道中的支护作用效果,分别对地表沉降、拱顶沉降、围岩压力、混凝土喷层应力、格栅钢架应力的变化特征和规律进行研究,结果表明,(1)浆液扩散范围过小且不均匀,当前注浆量对土体的改良作用较差,浆土体力学参数并未提高太多,其各项指标与普通土体无异;(2)粉质黏土地层对隧道开挖引起的变形具有一定的抵抗性,超前支护存在与否,变形都能在短时间内稳定;(3)围岩压力横向分布存在明显差异,格栅钢架应力随围岩压力同步激增,说明在粉质黏土隧道中超前支护不具有改善围岩压力不均匀分布、延缓围岩荷载释放的时空效应;(4)格栅钢架最大应力仅为其屈服强度30%左右,混凝土喷层最大应力仅为其轴心抗压设计强度的13.6%左右,强度储备足够保证隧道结构的安全;(5)塑性区范围约为1.5~3.0 m,小导管在径向上并未穿过塑性区,其支护作用实际上是对周围土体的挤密作用,增加其密实度,远远未达到调动围岩自身承载力的效果。

In order to find out the supporting effect of advanced support in silty clay tunnel, the ground settlement, crown settlement, surrounding rock pressure, concrete shotcrete stress and grid steel frame stress are studied by the methods of field test and numerical simulation with the third-phase project of Harbin Metro Line 1 as the engineering background. The conclusions of the study are as follows:(1) Grout diffusion range is too small and uneven, the improving effect of current grouting capacity for soil is poor; the mechanical parameters of the slurry soil have not been raised too much; and its indexes are no different from those of the ordinary soil mass.(2) Silty clay stratum has a certain resistance to the deformation caused by tunnel excavation; the tunnel deformation can reach stability in a short time whether or not the advanced support exists or not.(3) There are obvious differences in lateral stress distribution of surrounding rock; and the grid steel stress increases rapidly in accordance with the increase of the surrounding rock pressure, illustrating that the time and spatial effects of the advanced support which improve uneven surrounding rock load and delay the release of surrounding rock pressure in the silty clay tunnel is not existent.(4) As the range of plastic zone is 1.5-3.0 m roughly and the small pipe do not go beyond the plastic zone on the radial, the supporting effect of them is actually the compaction effect they have on the surrounding soil, which increases its density but cannot reach the effect of arousing the self-supporting capacity of surrounding rocks.(5) The maximum stress of the grid steel frame is only about 30% of its yield strength and the concrete shotcrete layer maximum stress is only about 13.6% of its axial compressive strength, which means it has a sufficient strength reserve to ensure a greater safety.