ABSTRACT
The application of polymer flocculants plays a pivotal role in the slurry separation process of shields, and the dispersant used for treating cutter mud cakes can significantly impact the effectiveness of polymer flocculants, potentially leading to reduced efficiency in slurry separation. Experiments were conducted to select appropriate flocculants and investigate the influence of dispersants on flocculant effectiveness, aiming to assess the effect of flocculants and explore the relationships and mechanisms governing their influence. Changes in the patterns of slurry flocculation were revealed in terms of flocculation-driven precipitation and vacuum-filtration effects. The purpose of this article is to provide a reference for the field application of polymer flocculants in the shield field. The conclusions are as follows. Inorganic flocculants containing 0.5% polyaluminum chloride (PAC) exhibit the most effective flocculation, demonstrating strong charge neutralization action. Organic flocculants containing 0.1% cationic polyacrylamides (CPAM) exhibit the most effective flocculation, demonstrating strong bridging and net capture effects. The dispersant sodium hexametaphosphate (SHMP) can significantly weaken the charge-neutralizing action of flocculants and slightly enhance bridging and net capture effects. SHMP can impede the flocculation of slurry with PAC. For CPAM, SHMP can enhance the flocculation of slurry at a low mass fraction (0.1% and 0.3%), while SHMP can significantly hinder flocculation at a high mass fraction (0.5% and 1%). A low mass fraction of SHMP reduced slurry viscosity to 246.3 mPa.s and enhanced vacuum filtration, while a high mass fraction of SHMP increased slurry viscosity to 667.2 mPa.s and hindered vacuum filtration. In conclusion, while dispersants reduce the effectiveness of inorganic flocculants at any mass fraction, a small number of dispersants enhances the performance of organic flocculants; thus, the organic flocculant CPAM is recommended for slurry separation.
ABSTRACT
Field monitoring of foundation pits alone cannot predict the future deformation of retaining structures. Numerical simulations can predict the deformation of foundation pits and the working state of retaining structures to avoid the risk of foundation pit damage in advance. Accurate inversion of the soil parameters used for simulation and prediction is a key step. The associated multivariable problem is transformed into a single-variable problem by using the interval influence coefficient. Soil layer weightings and excavation step weightings are introduced and exploited to optimize the calculation process, and the soil parameters are calculated through inversion based on the least squares method. Based on actual engineering, the excavation sequence is regarded as a progressive sequence for back analysis, and the parameters of each soil layer are calculated through dynamic calculations with the excavation process in a cycle comprising inversion, prediction, reinversion and reprediction. The soil parameters after inversion are used to predict the maximum value and the depth of the deep horizontal displacement of the retaining structure, which verified the feasibility of the back-analysis method. Compared with the results before inversion, after the final inversion, t the overall error of section 2 is reduced by 67.24%, the overall error of section 3 is reduced by 40.5%, and the overall error of section 4 is reduced by 35%. The prediction curves are all close to the monitoring displacement curves, which plays a good guiding role and ensures the safe construction of the foundation pit. A new effective idea is proposed for the inverse analysis of the composite formation parameters of the deep foundation pit engineering.