泥水盾构中劈裂压力影响因素研究

Influence factors of fracturing pressure during slurry shield tunnelling

泥水盾构在软弱含水地层中掘进时,泥水支护压力过大容易导致掌子面发生水力劈裂,从而引起掌子面坍塌。研究掌子面劈裂压力的影响因素对防止水力劈裂的发生有重要意义。由于现场试验实施困难、风险高,故设计制作了一种水力劈裂装置,并采用盲孔试样模拟隧道劈裂的发生。通过正交试验配制不同强度的人造黏土用于研究劈裂压力与强度的关系,并采用不同黏度的泥浆进行盲孔试样劈裂试验,分析泥浆黏度对劈裂压力的影响。研究结果表明:在两种加载条件下,劈裂压力随着无侧限抗压强度的增大线性增大。当泥浆黏度小于27s时,劈裂压力随泥浆黏度增大而增大,但随时间增长,增大速度变缓;当泥浆黏度大于27s时,随着黏度的增大,劈裂压力稳定在一定值基本不再增大;盲孔试样破坏后具有明显的劈裂面,且不同泥浆黏度时试样的劈裂面基本一致,均自盲孔底端斜向上延伸。

When slurry support pressure is large excessively during slurry shield tunneling at soft aquifer,hydraulic fracturing may occur causing collapse of excavation face.It is significant to investigate related influence factors of fracturing pressure to prevent occurrence of hydraulic fracturing in slurry shield.Considering the high challenge and safety risk in field test,a laboratory hydraulic fracturing apparatus was designed and blind hole samples were adopted to simulate fracturing during slurry shield tunnelling.Artificial clay with different strength was prepared by orthogonal test and it was used to study the relationship between fracturing pressure and soil unconfined compressive strength.Besides,slurry with different viscosity was adopted to conduct fracturing tests on blind hole sample,in which the effect of slurry viscosity on fracturing pressure was investigated.Test results show that fracturing pressure increases linearly with increase in unconfined compressive strength.When unconfined compressive strength is the same,the greater confining pressure is,the greater fracturing pressure will be,and the increment of fracturing pressure at each strength is basically equal to the increment of confining pressure.When slurry viscosity is less than 27 s,fracturing pressure increases with increas in slurry viscosity at a decreasing rate.When slurry viscosity is greater than 27 s,fracturing pressure almost stabilizes and hardly grows any more.There is obvious fracturing surface when the sample is fractured.Under different slurry viscosity,fracturing surfaces are basically the same,extending obliquely from the bottom of center hole,indicating that the failure mode of blind hole sample is not affected by slurry viscosity.