Highly susceptible to moisture changes, expansive soils are widely recognized as problematic soils. Swelling-induced damages to overlying engineering structures result in financial loss and billions of dollars in repair costs annually worldwide. Therefore, to mitigate swelling potential, various soil amendment approaches have been investigated to date. Sustainable soil treatment techniques such as microbially induced carbonate precipitation, although enjoying a low CO2 footprint, suffer from challenges pertinent to the use of living microorganisms at field scale treatments. Hence, the current study aims to explore the feasibility and efficiency of using enzyme-induced calcium carbonate precipitation (EICP) as an alternative eco-friendly method, yet to be examined for improving swelling characteristics of clayey soil. For this purpose, a series of laboratory experiments from macro- to microstructural scales involving free swell tests, swell pressure, pH measurement, X-ray powder diffraction, Bernard calcimeter, confocal Raman spectroscopy, and scanning electron microscopy have been conducted on the EICP-treated expansive samples. The experimental program focuses on the influence of constituent concentrations used in the EICP treatment on the swelling potential to obtain the optimal EICP solution. The study reveals that EICP can result in more than 60% reduction in the free swell index compared to untreated soil conditions. The results indicate that the EICP technique can double calcium carbonate content within expansive soil, increasing it by as much as 220%. Finally, it is demonstrated that there is a strong correlation between the amount of precipitated calcite and enhancement in the free swell index.

In modern construction projects, a significant challenge arises from the consequential impacts of developing adjacent structures. The interplay of stresses within neighboring foundations can lead to a range of issues, such as deformation, leaning, cracking, instability, and various other damages. Among the numerous factors affecting foundation interaction, this research uniquely focuses on the impact of soil type, utilizing precise physical modeling through a 1 g testing apparatus. To enhance measurement accuracy, image processing techniques are employed in conjunction with LVDT and displacement gauges. The study systematically investigated the roles of five distinct deposit types -soft clay, loose sand, silty sand, loess, and low-compacted Tehran clay -in the manifestation of settlement and tilt arising from foundation adjacency. Subsequent to this evaluation, a comprehensive examination of strategic measures aimed at preventing and mitigating damages resulting from foundation interaction is undertaken. For silty sand, a detailed comparison of five remediation techniques is conducted, while in other soil types, only densification method is applied to address settlement and tilt. The comparison is based on the reduction in settlement and tilt, after the implementation of remediation methods under new foundation. Results highlight the crucial role of soil properties in determining damages from foundation adjacency. Notably, Tehran soil with low density exhibits maximum settlement in its loose state, while loess soil shows the highest settlement in the dense state. The exploration of soil improvement methods reveals that diaphragm walls and pile groups are influential in minimizing tilt and settlement of existing foundations, while pile groups proved to be the best remediation method in controlling displacements of new foundation.

The subject of this paper is to evaluate the emerging sustainable soil improvement techniques by using agricultural plant-based additives for problematic soils and their effectiveness in improving the mechanical and physical properties of the soil. This research focused on expansive black cotton soil, mostly problematic soil that causes damage to civil engineering infrastructures when it encounters moisture changes. Therefore, it is an engineering requirement to stabilize/change unsuitable soils by using local materials by blending one another or modifying the property to improve its state of weakness. In this study, the problematic expansive black cotton soil was artificially replicated from the combination/mixture of low expansive and highly expansive clay soils. The agricultural wastes/biomass such as rice husk powder, bamboo powder, wheat straw, sugarcane bagasse, and shredded paper (celldoron) were used to investigate the improvement in the treated soil. These plant-based additives were selected based on local availability, Affordability, and efficiency. The replicated soil specimen was tested for the basic geotechnical engineering properties such as atterberg limit test (LL, PL) and free swell ratio (FSR). In additon, the agricultural waste additives were evaluated for water holding capacity and cellulosic composition.