不同阳离子对泥水盾构泥浆稳定性影响试验研究

Experimental study on effects of different cations on stability of slurry within slurry shield

针对泥水盾构在滨海地区或海底掘进时含盐地层侵入会导致泥浆稳定性下降的问题,通过向泥浆中掺入盐溶液,测试泥浆泌水率、■电位、特征粒径、滤失量等参数变化,利用胶体絮凝机理分析泥浆在不同盐溶液掺入下的稳定性。试验表明:①相较于掺入淡水,向膨水比为1∶15的泥浆中掺入浓度为1%的盐溶液时,泥浆■电位下降、特征粒径增大、滤失量增加;②盐溶液通过降低■电位和稀释作用影响泥浆稳定性。当掺入比超过5%后,继续掺入时,若盐溶液为NaCl则泥浆特征粒径d10继续增大而d50,d85基本不变,泥浆颗粒絮集、不泌水;若盐浓液为CaCl2、MgCl2,则特征粒径d10,d50,d85均基本不变,泥浆出现絮降、泌水;③Ca^2+、Mg^2+比Na^+对泥浆稳定性影响更大,故在不同海域采用泥水盾构掘进时,应根据地下水盐分含量及种类有针对性地考虑其对泥浆稳定性的影响。

In view of the problem that the high-salinity stratum intrusion during construction of submarine tunnels by the slurry shield will lead to the decrease of the stability of slurry,this study aims to investigate the effects of different salt solutions on the stability of slurry via colloidal flocculation mechanism by adding salt solutions into slurry and testing change of the parameters such as bleeding rate,zeta potential,characteristic particle sizes and seepage discharge of the slurry.The results show that compared with that by adding fresh water,the slurry by adding 1%salt solution in which the quality of water is 15 times that of bentonite,the zeta potential of slurry decreases,and its characteristic particle sizes and seepage discharge increase.The salt solution affects the stability of slurry mainly by decreasing its zeta potential,which promotes slurry particles to flocculate and to dilute the slurry.When the mixing ratio is more than 5%and keeps to increase,if the salt solution is NaCl,the zeta potential changes a little and then keeps steady,and the characteristic particle size d10 of the slurry continues to increase,while d50 and d85 remain basically the same.The particles of slurry coagulate,and the slurry remains stable and does not bleed.If the salt solution is CaCl2 or MgCl2,the zeta potential decreases continuously,the characteristic particle sizes d10,d50 and d85 remain basically unchanged,resulting in flocculation and bleeding.Ca^2+and Mg^2+have a greater influence on the stability of slurry than Na^+.Therefore,when using the slurry shield to excavate the subsea tunnels in different sea areas,the effects of groundwater on the stability of slurry should be considered in accordance with the chemical type of groundwater.