Ground Improvement with a Single Injection of a High-Performance All-in-one MICP Solution

Abstract

All-in-one injection strategy has been developed recently as an efficient method in microbially induced carbonate precipitation (MICP). In this method, engineers try to delay the beginning of precipitation and consequently distribute reagents homogeneously on a soil mass. In this article, a series of experiments have been carried out to modify all-in-one solution strategy and promote its uniformity. Primarily, the concentration of all-in-one solutions was optimized and the result showed that all-in-one solution with a 2 M concentration of urea/calcium chloride was completely consumed. The short columns treated by one-time one-pore volume (PV) injection of 2 M all-in-one solution provided approximately 450 kPa in UCS test. In the second step, magnesium substitution for calcium was investigated to improve the strength and homogeneity of biocementation. This substitution raised the UCS by approximately 70%, and 800 kPa was acquired. XRD analysis confirmed that Mg2+ changes the mineralogy of precipitation from vaterite to aragonite. Hence, the higher strength of columns treated with the magnesium-substituted solutions is attributed to the higher hardness of aragonite crystals than that of vaterite. Finally, the bacterial transport of all-in-one solutions showed that magnesium substitution for 20% of calcium cations, enhances its potential to provide a homogeneous biocement on large-scale projects.