基于坍落度的砂卵石地层土压平衡盾构渣土改良配方研究

针对成都轨道交通17号线一期工程土压平衡盾构法施工在砂卵石地层中遇到的难题，如螺旋输送机喷涌导致开挖面压力失控、卵石堆积于压力舱底部滞排等，采用膨润土和泡沫剂等对现场砂卵石进行室内渣土改良试验。结果表明： 1)改良剂的优化配比膨润土掺入质量比为5%，泡沫掺入体积比为10%~30%，即可使渣土的坍落度、和易性、抗渗性均保持良好，达到塑性流动状态。2)以渣土的坍落度在150~200 mm且无离析为改良的前提条件，以最小膨润土使用量为优化目的，建立砂卵石渣土坍落度与改良剂膨润土和水掺入量之间的三维曲面图，根据离析与非离析区域边界确定膨润土泥浆最经济的膨水比为1∶6。将试验结果应用于该工程的砂卵石地层土压盾构工程实践，掘进效率以及盾构工作的安全性得到显著提高。

Soil Conditioning Scheme for Earth Pressure Balance Shield Tunneling inSandy Cobble Strata Based on Slump Test

When earth pressure balance (EPB) shield tunneling in the sandy cobble strata of Phase 1 project of the Chengdu rail transit line 17, it encounters difficulties, such as unstable pressure on the excavation face caused by water and mud gushing from screw conveyor and the cobbles accumulating at the bottom of the pressure chamber. As a result, the bentonite slurry and foaming agents are used in a laboratory test to condition the sandy cobble strata. The results are as follows: （1）The optimal modifier mixing proportions of bentonite is observed with a mass ratio of 5% and foam with a volume ratio of 10%~30%. On the basis of this, the soil′s fluidity, workability, and impermeability can be maintained in an optimal state. （2）With the objective of using the minimum quantity of bentonite using a 150~200 mm soil slump with no segregation, a three dimensional curved surface is established for the interaction between soil slump, bentonite amount, and water volume. Moreover, a mass ratio of bentonite to water of 1∶6 is determined to provide the most economic benefit based on the boundary between segregation and anti segregation areas. Furthermore, these results have been applied to the test results for the Phase 1 project of Chengdu rail transit line 17, resulting in a safe and highly efficient shield tunnel.