泥水盾构支护压力设定范围及其影响因素分析

与土压平衡盾构对掘进面的被动支护不同,泥水盾构是依靠液态介质实现对掘进面的主动支护。泥水支护的关键是选择合适的泥水和支护压力从而形成并维持泥膜的完整性。基于泥水劈裂(渗透破坏)和仓筒理论给出了泥水支护压力的上下限。结合静水压力、土体特性、盾构直径和覆土厚度等因素研究了支护压力区间特性(可设定范围)。研究表明:支护压力下限主要受静水压力和土体摩擦角的影响,其中静水压力起决定性作用。一般情况下,泥水压力设定可以取为静水压力+20 kPa;支护压力上限为泥水劈裂(渗透破坏)压力,主要受静水压力和覆土厚度的影响。增加覆土厚度可以提高地层的泥水劈裂(渗透破坏)抗力,从而改善地层的泥水支护特性,增大泥水支护压力区间长度。然而,增加静水压力只可以平移泥水支护压力区间,而不能使其增大。泥水支护压力区间长度还受土体摩擦角的影响,而其它因素影响较小。考虑泥水支护区间长度的影响,实施带压换刀的隧道覆径比不宜小于0.8～1.0。

Range of support pressures for slurry shield and analysis of its influence factors

The earth pressure balanced shield supplies a passive support for the tunnel face. However, the slurry shield offers an active support for the tunnel face with slurry (liquid medium). The key work for slurry support is to choose a suitable slurry and a support pressure to form a slurry cake and maintain its integrity. Based on the theory of soil fracturing and the wedge-prism model, the upper and lower bounds of slurry support pressures are supplied. Slurry support pressures are analyzed with consideration of hydrostatic pressures, soil properties, tunnel diameters and earth covers. It is suggested that the lower bound of the support pressure is mainly affected by hydrostatic pressure and soil friction, especially by the hydrostatic pressure. The slurry support pressure can be usually set as 20 kPa more than the hydrostatic pressure; the upper bound of support pressure is soil fracturing (seepage failure) pressure, mainly affected by hydrostatic pressure and earth cover. The soil fracturing (seepage failure) pressure can be increased by increasing the thickness of earth cover. And then the ranges of slurry support pressure can be also enlarged. However, the ranges of slurry support pressure can only be moved but not enlarged by increasing the hydrostatic pressure. The range length of slurry support pressure is also affected by the soil friction rather than other factors mentioned above. Considering the setting of slurry pressure in shield cutter replacement condition, the ratio of earth cover to tunnel diameter should be larger than 0.8~1.0