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<p>Dispersants are commonly used as conditioning agents to prevent clogging during earth pressure balance shield tunneling in clayey ground. However, its conditioning effect hinders pressurized dewatering, thereby complicating subsequent muck treatment, such as transportation and landfill. To address this issue, three types of flocculants, polydimethyldiallylammonium chloride (PDADMAC), cationic polyacrylamide (CPAM), and polymeric ferric sulfate (PFS), were investigated as alternative or combined conditioning agents to enhance post-tunneling muck dewatering. The time-dependent dewatering process of samples with single-flocculant and combined-flocculant conditioning was tested. Results show that dispersant (sodium hexametaphosphate) reduces drainage channels by fragmenting clay particles, while forming a dense and blocking mud cake during filtration, whereas all three flocculants improve the dewatering of the dispersant-conditioned samples. The dewatering efficiency of single flocculants is enhanced and then declines with dosage, with optimal values of 0.6% PDADMAC, 0.5% CPAM, and 0.8% PFS; among them, 0.6% PDADMAC achieves the best overall performance. Within the effective dosage range, higher plastic limits correspond to lower final water contents of the filter cake. Notably, the combined-conditioning method, at optimal dosages of 0.4% PDADMAC, 0.167% CPAM, and 0.267% PFS, significantly enhances charge neutralization, bridging, and agglomeration, converts clay into a coarse-grained, macro-porous structure, and reduces water content from 40 to 22.67% within 30&#xa0;min. This study presents an effective conditioning strategy that mitigates the drawbacks of dispersant treatment and enhances post-tunneling muck dewatering.</p>

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Effect of Flocculant on Dewatering of Dispersant-Conditioned Clay Soil in Earth Pressure Balance Tunneling

  • 期刊论文

  • 发表日期：

    2026年4月28日

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  • Shuying Wang,
  • Shaoxiang Guan,
  • Chao Li

摘要

Dispersants are commonly used as conditioning agents to prevent clogging during earth pressure balance shield tunneling in clayey ground. However, its conditioning effect hinders pressurized dewatering, thereby complicating subsequent muck treatment, such as transportation and landfill. To address this issue, three types of flocculants, polydimethyldiallylammonium chloride (PDADMAC), cationic polyacrylamide (CPAM), and polymeric ferric sulfate (PFS), were investigated as alternative or combined conditioning agents to enhance post-tunneling muck dewatering. The time-dependent dewatering process of samples with single-flocculant and combined-flocculant conditioning was tested. Results show that dispersant (sodium hexametaphosphate) reduces drainage channels by fragmenting clay particles, while forming a dense and blocking mud cake during filtration, whereas all three flocculants improve the dewatering of the dispersant-conditioned samples. The dewatering efficiency of single flocculants is enhanced and then declines with dosage, with optimal values of 0.6% PDADMAC, 0.5% CPAM, and 0.8% PFS; among them, 0.6% PDADMAC achieves the best overall performance. Within the effective dosage range, higher plastic limits correspond to lower final water contents of the filter cake. Notably, the combined-conditioning method, at optimal dosages of 0.4% PDADMAC, 0.167% CPAM, and 0.267% PFS, significantly enhances charge neutralization, bridging, and agglomeration, converts clay into a coarse-grained, macro-porous structure, and reduces water content from 40 to 22.67% within 30 min. This study presents an effective conditioning strategy that mitigates the drawbacks of dispersant treatment and enhances post-tunneling muck dewatering.