Evaluation of the Effectiveness of a Soil Treatment Using Calcium Carbonate Precipitation from Cultivated and Lyophilized Bacteria in Soil’s Compaction Water

Microbial-induced carbonate precipitation (MICP) is a bio-inspired solution where bacteria metabolize urea to precipitate. This carbonate acts as a bio-cement that bonds soil particles. The existing framework has focused mainly on applying MICP through infiltration of liquid bacterial solutions in existing soil deposits. However, this technique is inefficient in soils with high fines content and low hydraulic conductivity, and thus few studies have focused on the use of MICP in fine soils. The main objective of this study was to evaluate the effect of MICP applied to compaction water in soils containing expansive clays and sandy silts. This approach searches for a better distribution of bacteria, nutrients, and calcium sources and is easy to apply if associated with a compaction process. In soils with expansive minerals, the effect of MICP in swelling potential was explored at laboratory and field scales. In sandy silts, the evolution of the stiffness and strength were studied at the laboratory scale. The treatment at the laboratory scale reduced the swelling potential; nevertheless, no significant effect of MICP was found in the field test. In sandy silts, the strength and stiffness increased under unsaturated conditions; however, subsequent saturation dissolved the cementation and the improvement vanished.

Settlement Analysis of Dredged Material and Its Stabilization Using Surkhi/Brick Dust

Soil stabilization is the phenomenon by virtue of which the soils are altered to enhance their physical Properties. The process aims to increase the shear Strength of soil thus improving its load bearing capacity to support pavements and foundations. Diverse range of soil materials varying from Expansive clays to granular materials can be treated by a diverse set of Additives like silica, lime, fly-ash, cement and so on. In J&K, the most common types of soils are the alluvial soils which get deposited in river beds as a result of sedimentation. River Jhelum in J&K is one of the major hotspots for accumulated sediments with an estimate of about 36 lakh cubic meters of sediments in its river bed, leaving very little space in it to take excess water. Subsequently, it is severely threatened by the Phenomena of still higher levels of sedimentation and hence consequent Floods. Dredging practices are a challenge for the maintenance of rivers and their Spillways. In Geotechnical Engineering, the valorisation of dredging Sediments and their Use in public works is increasingly prospected by Researchers in recent Years. Moreover, Floods in Kashmir valley in September 2014 compelled the Govt. Of Jammu and Kashmir to take Necessary steps in order to avoid similar situation in near future. This project therefore intends to study the stabilization of dredged material procured from Sindh Nallah having a higher content of alluvial Soil using Surkhi/Brick dust as an additive. Soil stabilization by this means can be utilized on airport pavements, highway pavements, earthen dams and many other situations where sub-soils are not suitable for construction. Keywords: Sindh Nallah, Dredged material, Surkhi, OMC, MDD, CBR, Direct Shear test.

Improvement of Strength and Volume-Change Properties of Expansive Clays with Geopolymer Treatment

Expansive soils are conventionally treated with chemical stabilizers manufactured by energy-intensive processes that significantly contribute to carbon dioxide emissions globally. Geopolymers, which are synthesized from industrial byproducts rich in aluminosilicates, are a viable alternative to conventional treatments, as they are eco-friendly and sustainable. In this study, a metakaolin-based geopolymer was synthesized, and its effects on the strength and volume-change behavior of two native expansive soils from Texas, with a plasticity index over 20 were investigated. This paper elaborates on the geopolymerization process, synthesis of the metakaolin-based geopolymer, specimen preparation, and geopolymer treatment of soils. Comprehensive material testing revealed two clays with a plasticity index over 20. They were each treated with three dosages of the metakaolin-based geopolymer and cured in 100% relative humidity for three different curing periods. The efficiency of geopolymer treatment was determined by testing the control and geopolymer-treated soils for unconfined compressive strength (UCS), one-dimensional swell, and linear shrinkage. Field emission scanning electron microscope (FESEM) imaging was performed on the synthesized geopolymer, as well as on the control and geopolymer-treated soils, to detect microstructural changes caused by geopolymerization. A significant increase in UCS and reduction in swelling and shrinkage were observed for both geopolymer-treated soils, within a curing period of only 7 days. The FESEM imaging provided new insights on the structure of geopolymers and evidence of geopolymer formation in treated soils. In conclusion, the metakaolin-based geopolymer has strong potential as a lower-carbon-footprint alternative to conventional stabilizers for expansive soils.