土压平衡盾构平衡控制理论及试验研究

Theoretical and test studies on balance control of EPB shields

土压平衡盾构在掘进时有两种平衡状态,一种是盾构与前方土体接触压力和土水压力的平衡,另一种是出土的平衡。两种平衡状态只有在刀盘开口率非常大时才等价。由于面板的挤压作用,开口率较小的盾构两种平衡状态将有较大偏离。出土率是控制土压平衡的重要指标,当其接近100%时,盾构处于出土的平衡掘进状态。盾构掘进时很难直接控制出土率,可通过施工参数间接控制。推导出土率与螺旋机转速、推进速度的定量关系,通过模型试验验证三者关系;推导平衡状态时上述三个参数的关系,该关系可作为通过施工参数控制平衡状态的标准;提出通过模型试验确定平衡状态时参数匹配的方法。当出土率小于或大于100%时及采用开口率较小的面板式刀盘时,盾构将产生不平衡掘进。大部分土压平衡盾构不平衡掘进产生挤土作用,造成正的地层损失及附加的应力场。试验结果表明,不平衡推进时挤土量一部分产生体积应变,一部分形成正的地层损失,使盾构前方地表产生了隆起;现场试验测试了刀盘前方附加应力场的大小和范围。研究成果可以指导土压平衡盾构推进时的参数控制,对控制推进时地表变形有指导意义。

EPB shields may be in two types of state of balance during tunneling, one being the balance between the contact pressure of shield and the front pressure of earth and water, and the other being the balance in the mucking earth. These two balance states are equivalent only when the head aperture ratio is sufficiently large. Because of cutter head compression, large deviation occurs when shield cutter head has small head aperture ratio. Mucking earth rate is an important index to the control of earth pressure balance. When the mucking earth rate is 100%, the balance state of mucking earth is reached. It is difficult to directly control mucking earth rate during tunneling, but it may be indirectly controlled through adjusting shield construction parameters. The relationship between mucking earth rate, rotation speed of screw conveyor and advance rate is derived, and later verified by using model test data. Based on model tests, a method for determining the above relationship of balance state is presented. When mucking earth rate is not equal to 100%, or for shields using skin-plate cutter head, shield advance is under unbalanced state. Unbalanced tunneling of most EPB shields would generate positive loss of soil and secondary stress. The test results indicate that squeezing of shield caused some volumetric strain and positive ground loss. In addition, the magnitude and range of secondary stress in front of cutter head were tested.