Optimization of defoaming-flocculation-dewatering indices of earth pressure balance (EPB) shield muck using response surface methodology and desirability approach

Abstract

In situ recycling is one of the most effective methods to dispose of earth pressure balance (EPB) shield waste muck with residual foaming agents with high moisture content. In this context, response surface methodology (RSM) was employed to quantify the effects of independent variables, including flocculant dosage, defoamer dosage, and muck drying mass (MDM) and their interactions on defoaming-flocculation-dewatering indices. The polymeric aluminum chloride (PACL) and hydroxy silicone oil-glycerol polypropylene ether (H-G) were selected as the flocculant and defoamer. The contents of surfactants and foam stabilizers in residual foaming agents were determined using the proposed empirical equation. The defoaming ratio, antifoaming ratio, turbidity, moisture content, filtration loss ratio, and fall cone penetration depth were considered as dependent variables. The accuracy of developed RSM models was verified by the analysis results of variance, residuals, and paired t-test. Combined with the desirability approach, an optimal mixing ratio of 0.078 wt% PACL, 0.016 wt% H-G, and 27.882 wt% MDM was recommended, leading to a defoaming ratio of 98.34 vol% for residual foams and a moisture content of 56.72 wt% for pressure-filtration cakes. Our findings were demonstrated to be able to provide useful guidance for prediction and optimization of the in situ recycling indicators of EPB shield waste muck in metro tunnel construction sites.