富水圆砾地层盾构渣土改良技术研究

为解决土压平衡盾构在富水圆砾地层中渣土不易改良及易喷涌问题,采用昆明地铁4 号线圆砾土作为试验材料,以膨润土泥 浆、羧甲基纤维素(CMC)与聚丙烯酰胺溶液(PAM)作为主要改良材料,泡沫作为辅助改良材料开展室内改良渣土坍落度和常水头渗透性试验。试验结果表明: 1)在塑流性方面,仅用泥浆或泥浆与CMC 混合改良时,圆砾土流动性过大; PAM 加入到泥浆改良渣土中时,能够提高渣土的塑流性; 泡沫的掺入对泥浆和PAM 共同改良渣土的塑流性无影响。2)在渗透性方面,CMC、膨润土泥浆和PAM 均可有效改善渣土渗透性,且渗透系数随着注入比的增加而增大; 泡沫的掺入对泥浆和PAM 共同改良渣土的渗透性无影响。根据试验结果可知: 当地下水头约为25 m 时,可将膨润土泥浆配比1 ∶ 4(1%CMC)、膨润土泥浆注入比(BIR)= 25%、PAM 注入比(PIR)= 12. 5%、泡沫注入比(FIR)= 20%或膨润土泥浆配比1 ∶ 3、BIR= 25%、PIR= 7. 5%、FIR= 20%作为此圆砾地层的渣土改良参数。

Experimental Study on Ground Conditioning Technology for EPB Shield Boring in Water-rich Gravel Stratum

During earth pressure balance (EPB) shield tunneling in water-rich gravel stratum, the ground is difficult to condition and the water is easy to spew out from the screw conveyor. Hence, the bentonite slurry, carboxymethyl cellulose (CMC) and polyacrylamide solution (PAM) are used as main conditioning materials, and the foam is used as auxiliary conditioning material for the laboratory slump test and constant head permeability test on gravel of Kunming Metro Line No. 4. The test results show that: (1) When the bentonite slurry or the mixture of bentonite slurry and CMC is used, the flow plasticity of conditioned gravel is overlarge; while the flow plasticity of the gravel conditioned by bentonite slurry and PAM can be improved, and the foam has no effect on flow plasticity of gravel conditioned by bentonite slurry and PAM. (2) The CMC, bentonite slurry and PAM can improve the ground permeability, and the permeability coefficient of the gravel increases with the increase of conditioning materials; while the foam has no effect on the permeability of gravel conditioned by bentonite slurry and PAM. According to the test results, the bentonite slurry ratio, the bentonite injection ratio (BIR), the PAM injection ratio (PIR) and the foam injection ratio (FIR) are determined as 1 ∶ 4 (with 1% CMC), 25%, 12. 5% and 20% or 1 ∶ 3, 25%, 7. 5% and 20%, respectively to condition the gravel in Kunming Metro Line No. 4when the water head height is about 25 m.