土压平衡盾构刀盘挤土效应及刀盘开口率对盾构正面接触压力影响

Effect of cutterhead compressing the front soil and influence of head aperture ratio on contact pressure of EPB shield to the front soil

土压平衡盾构推进时,由于刀盘挤土作用,盾构必然挤压前方土体,并产生附加接触压力。该附加接触压力是土压平衡盾构在周围土体中产生附加应力的主要来源之一。建立刀盘挤土模型,推导盾构附加接触压力计算公式,该公式综合考虑刀盘开口率、刀盘转速、推进速度及土层性质等因素。现场监测刀盘开口率40%的土压平衡盾构及刀盘开口率85%的双圆土压平衡盾构推进时在前方土体中产生的附加应力,得到开挖面处的附加接触压力。监测结果证明推导公式的科学性,可以在施工中推算不同参数时盾构施工产生的附加应力,对盾构推进时的环境保护有重要意义。计算公式及监测结果说明,刀盘面板有明显的挤土作用,即使达到出土率的平衡状态,盾构前方依然存在附加应力场,刀盘开口率越小,刀盘转速越慢,推进速度越快,附加压力越大。

During EPB shield tunneling, the front soil is compressed by the cutterhead, and additional stress occurs, causing unbalance of pressure between the chamber and the cutting face. In order to reduce the potential risk, a model was introduced for calculating the additional stress, combining various parameters such as head aperture ratio, cutterhead rotation speed, advance rate and soil characteristics. The additional stresses on site for different types of tunnel machines, including traditional metro tunnel EPB and DOT shield, were monitored. The relationships between different parameters in the model were verified through analyses of these data, and it reveals that controlling these stresses may have significant effects on environment protection in the construction process. It is also concluded that the wheels of the cutterhead would compress the front soil, even after the balance of the excluded earth volume, and that smaller head aperture ratio, slower cutterhead rotation speed and faster advance rate will result in larger additional stress.