Design method and application of filter material for tube well dewatering in highly permeable strata

As an effective approach to avoid environmental problems caused by dewatering, the design of filter material for tube well dewatering in water-rich and highly permeable strata is critical to dewatering engineering in complex urban environment. Although theory of seepage has been well developed, a rational method for determining the particle size of filter materials has not yet been established. Based on soil filtration and pressure-reduction mechanisms of filter layers, this study proposed a design criterion of tube well dewatering filter material with effective interlayer coefficient E_c=2\sim 3 and non-uniformity coefficient C_u\leqslant 2 as control indexes. Through discrete element numerical simulation, the particle loss characteristics and porosity variation of the formation-filter material system in the seepage process were analyzed. The microscopic mechanism of the filter material to achieve a self-stable state by intercepting fine particles was revealed. The results show that when the effective interlayer coefficient E_c\leqslant 3 , the fine particle loss is less than the critical value of 3%, and the porosity stabilizes accordingly. The proposed design criterion was further validated through field pumping tests. This study provides a theoretical basis for the design of tube well dewatering filter material, which can improve the safety of foundation pit dewatering projects in water-rich and highly permeable strata.