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采用真三轴仪和环境扫描电子显微镜(XL30 ESEM-FEG),从宏微观上初探了黏性土层中泥水盾构开挖面的稳定机理,研究了不同应力水平下泥浆作用对开挖面土体强度和变形特性的影响,并通过颗粒流数值模拟对实验结果进行了验证。结果表明:①对于黏土类渗透系数较低(K<10-8 m/s)的地层,由于泥浆几乎不流入地层而不能形成泥膜,无法依靠泥膜建立开挖面的稳定机制,但过滤解质间水流产生解质摩擦力及适当的泥浆支护压力对土体颗粒产生的挤压作用均有利于开挖面保持稳定。②过滤解质挤压作用的发挥存在有效泥浆支护压力上、下限值。当支护压力小于其压力下限值时,泥浆作用对土体强度和变形的影响均不大;当支护压力大于其压力上限值时,泥浆中水的渗透开始逐渐软化土体,导致了土体强度的降低、变形增大;而当支护压力处于上、下限之间时,挤压作用的发挥使得过滤解质的压缩,相互间的范德华力增大,透水性降低,外在表现为泥浆作用使得土体强度提高,变形量减小。③基于黏性土与水接触时的软化特性,盾构在长时间停止掘削时,不宜单纯采用泥浆压力来保持开挖面的稳定,而应充分利用盾构本体正面挡板来保持地层的稳定。
The mechanism of excavation surface of muddy water shield in cohesive soil was studied from the perspective of macro-micro with the use of true triaxial apparatus and environment scanning electron microscope (XL30 ESEM-FEG). The effects of mud action on the excavation surface Soil strength and deformation characteristics of the impact, and the particle flow numerical simulation of the experimental results were verified. The results show that: (1) For the formations with lower clay permeability coefficient (K <10-8 m / s), mud can not be established by mud film because the mud does not flow into the formation and mud can not be formed. However, Disintegration of water between the mass-produced friction and proper mud support pressure on the soil particles generated by extrusion are conducive to the excavation surface remained stable. ② filter the role of the role of extrusion squeeze effective mud support pressure on the lower limit. When the supporting pressure is less than the lower limit of pressure, the effect of mud on soil strength and deformation is not large. When the supporting pressure is greater than the upper limit of pressure, infiltration of water in mud gradually softens the soil, resulting in The strength of the soil decreases and the deformation increases. When the supporting pressure is between the upper and lower limits, the extrusion of the filter makes the compression of the filter-substance, the van der Waals forces between each other increased, the water permeability decreases, the external The performance of the mud makes soil strength increased, the amount of deformation decreases. ③ Based on the softening characteristics of clay when it is in contact with water, when the shield stops digging for a long time, it is not appropriate to use the mud pressure to keep the stability of the excavation surface. However, the front shield of the shield body should be fully used to keep the stratum stable .