When drilling with a slurry TBM (Tunneling Boring Machine) below the sea bottom, the fresh bentonite slurry will be mixed with the seawater and transformed into a salty bentonite slurry. This paper describes a theoretical study into the seawater circulation in the TBM excavation chamber and proposes a model to predict the amounts of seawater that may be mixed during tunneling and presents experimental investigations to determine the permeability of bentonite in the salty water. Modeling calculations reveal that the percentage of seawater in the slurry can be 0 ∼ 80 % of the total amount of water present in the recycled slurry, depending on the soil conditions, TBM operations, and slurry recycling and treatment procedures. Experimental results show that if augmenting the seawater content from 10 % to 80 %, the permeability of sand for bentonite slurry () increased from 2.82 × 10 m/s to 3.57 × 10 m/s due to a decrease in viscosity while the permeability of the filter cake () displayed an increase ranging from 3.23 × 10 m/s to 2.91 × 10 m/s. Excavating with a TBM is still possible, however, a potential threat is the sedimentation of the bentonite particles in salty slurries with high seawater contents, resulting in a concentration gradient of the bentonite in the excavation chamber during standstill. For secure undersea tunneling, it is better to decrease the seawater content in the slurry. Following the theoretical model described in this paper, this can be done by decreasing the advance rate of the TBM, increasing the inlet slurry volume flow, or increasing the percentage of supplemented fresh bentonite slurry.

中文翻译：

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泥水TBM开挖室内海水循环及其对膨润土渗透性的影响

当在海底以下使用泥浆TBM（隧道掘进机）进行钻探时，新鲜的膨润土泥浆会与海水混合并转化为咸味膨润土泥浆。本文介绍了 TBM 开挖室中海水循环的理论研究，提出了预测隧道施工期间可能混合的海水量的模型，并进行了确定膨润土在咸水中的渗透性的实验研究。模型计算表明，根据土壤条件、TBM 作业以及泥浆回收和处理程序，泥浆中海水的百分比可能为回收泥浆中总水量的 0 ∼ 80%。实验结果表明，当海水含量从10%增加到80%时，由于粘度降低，膨润土浆料砂的渗透率从2.82×10m/s增加到3.57×10m/s，而渗透率滤饼（）的增加范围为 3.23 × 10 m/s 至 2.91 × 10 m/s。使用TBM挖掘仍然是可能的，然而，潜在的威胁是膨润土颗粒在海水含量高的咸泥浆中沉积，导致在停工期间挖掘室中膨润土的浓度梯度。为了安全地进行海底隧道施工，最好减少泥浆中的海水含量。根据本文描述的理论模型，这可以通过降低 TBM 的推进速度、增加入口泥浆体积流量或增加新鲜膨润土泥浆的补充百分比来实现。