Investigating the impact of straw-to-tailings sand ratios on combined vertical drain performance

Given the shortcomings of inadequate vacuum transfer effectiveness, susceptibility to clogging, and environmental impact, i.e., white pollution, associated with standard plastic drainage boards, this paper introduces an innovative solution termed combined vertical drain (CVD). This CVD is composed of biodegradable straw materials and tailings sand. Through controlled indoor model experiments, the drainage and consolidation performance of the CVD is investigated across varying proportions of straw content. The findings indicate that increasing the concentration of straw within the mixture of straw particles and tailings sand (referred to as MST) within the drain distinctly mitigates the diminishment of the vacuum condition during the vertical drainage transfer. Optimal elevation of the straw component in MST can notably reduce the duration required for vacuum preloading and enhance displacement up to a certain value. Nonetheless, an excessive increase in the straw composition not only fails to enhance drainage effectiveness but also raises the organic matter level within the soil. Furthermore, compared with the average water content difference of soil in different model box test units after vacuum preloading, the average divergence in vane shear strength of test soil exhibits a more pronounced variation.