A Bioinspired Technique for Improving the Interaction Between Cohesive Soil and Geotextile Reinforcements

Abstract

Reinforced soil structures often cannot perform properly when there is a weak interface which is not capable of mobilizing the required shear strength between fine-grained soils and the reinforcing elements. The calcium carbonate precipitation (CCP) technique adopted in this research has proved to be extremely useful in removing this deficiency. In this study, plant-derived urease-induced calcium carbonate precipitation (PDUICCP) was used as a novel method to improve the performance of the interface. Instead of using commercial-grade purified urease, the extract of soybean seeds was mixed with calcium chloride and urea to prepare a precipitating solution to reduce the costs. In addition, xanthan gum was used as a benchmark to examine the efficiency of the calcium carbonate precipitation process. Modified direct shear tests were performed on the kaolin clay specimens with two different relative compactions, three concentrations of the precipitating solution, and three different geotextiles to assess the performance of the proposed method. The results revealed that the application of the proposed method improved the interfacial shear strength considerably with the interface efficiency increasing from 12 to 270% depending on the geotextile texture and roughness, the relative soil compaction, and the concentration of the precipitation solutions. The highest increase in the interfacial shear strength for all the concentrations of the precipitating solutions was obtained when the polypropylene nonwoven geotextile was used. In all the cases, increasing the relative soil compaction enhanced the interfacial shear strength and interface efficiency. The optimal concentration of the constituents in the precipitating solution was obtained when 0.64 molar (M) calcium chloride and 1 M urea were used. The results of this study can mark the beginning of a new type of geosynthetics with multiphase strength parameters after the addition of environmentally friendly materials. Moreover, they pave the way for using fine-grained soils as the bulk backfill material in reinforced soil structures where coarse-grained soil is not readily available.