泥水劈裂试验伸展现象的力学分析

MECHANICAL ANALYSIS OF SLURRY FRACTURING PROPAGATION PHENOMENON

泥水盾构掘进时,在江中冲槽段等复杂条件下,泥水压力很难设定,稍有不慎就会发生泥水劈裂,甚至导致泥水喷发危及工程安全。为观察并研究劈裂伸展现象及其力学机制,在研制现场泥水劈裂仪并进行现场试验的基础上,建立泥水劈裂伸展模型,给出防止泥水劈裂的泥水压力上限设定的计算方法。研究表明:泥水劈裂伸展的力学特性不仅与地层性能有关,而且与所选用的泥浆特性有关。实际工程中,在地层性能不易改变的条件下,增加泥水重度、提高泥水黏性有利于阻止劈裂进一步伸展。劈裂发生后出现的泥水压力降低现象将有利于阻止泥水劈裂进一步伸展。在劈裂发生后,不能因为泥水压力下降而急忙增加泥水压力,这样不但泥水压力不能增加,反而会导致泥水劈裂的迅速伸展,加快泥水喷发的发生。绝大多数情况下,在泥水劈裂伸展的过程中泥水和地层的组合抗劈裂能力会逐渐变小。因此,预防泥水盾构开挖过程中的泥水喷发问题,要从预防泥水劈裂入手,对泥水压力的上限进行控制。

When slurry shield tunneling, slurry pressure can＇t be set easily under complex conditions, such as channel erosion of the riverbed. If it wasn＇t dealt with carefully, slurry fracturing or even slurry eruption would happen, which had negative effect on project security or led to project accident. In order to observe slurry fracturing propagation phenomenon and analyze its mechanism, in-situ slurry fracturing apparatus was made for the first time and in-situ tests were carried out. Based on these, a slurry fracturing propagation model was established~ and a calculation method for upper limitation value of slurry pressure set to prevent slurry fracturing was given. The results suggest that mechanical properties of slurry fracturing propagation are not only related to stratum properties, but also related to the chosen slurry properties. When properties of stratum can＇t be changed easily, increasing slurry bulk density and viscosity is beneficial to prevent slurry fracturing propagation during tunnel excavation. The phenomenon of slurry pressure reduction after slurry fracturing is beneficial to prevent slurry fracturing propagation. The slurry pressure should not be increased hurriedly after it becomes lower becauseof slurry fracturing; otherwise, not only the slurry pressure couldn＇t be added, but also it leads to slurry fracture stretch more quickly, which speed up slurry eruption. Anti-fracturing ability of slurry and stratum would mostly become smaller and smaller during slurry fracturing propagation. Therefore, the first step to prevent slurry eruption is to prevent slurry fracturing; and the upper value of slurry pressure should be limited.