A grading method for analyzing internal erosion processes of nano-silica improved sand

Abstract

Internal erosion (IE) often occurs in poor graded sand, one of the traditional treatments is reducing the permeability by grouting. Today, nano-silica becomes a choice of grouting materials as its low viscosity and good penetration capacity. According to present literature, the effect of decreasing loss mass during IE  after the improvement of nano-silica was rarely studied. One of the important reasons is that, mass loss during IE was previously focused and was weighed after filtering the effluent by electronic balance, more accurate weighing method should be studied after adding nano-silica which cannot be precisely weighed by electronic balance. In this paper, a new grading method is conducted to monitoring the particle size distribution in the effluent and illustrate the process of IE. Erosion time and permeability are also recorded and analyzed as comparison. The experimental results show that the grading method can monitor precisely the mass loss and the composition of the effluent, grading range of 1-1000 can be adopted to monitor the coagulation of silica gel particles (1-50 , average diameter 11±5 ) and fine sand particles (50-100 , average diameter 65±7 ), grading range of 1-1000 can be adopted to monitor the smaller coagulation of silica gel particles (concentrated in the range of 1-250 nm). Through grading method, the IE of nano-silica improved sand can be divided into three stages: Removal and release of unbonded nano-silica particles and unbonded fine particles; Movement and discharge of bonded particles; Expansion of pores and instability of the whole sample skeleton.