The issue of problematic disposal of excavated material, commonly referred to as muck, generated during tunnel boring machine (TBM) excavation has emerged as an environmental challenge amidst the escalating demand for sustainable engineering solutions. TBM excavation operations necessitate the use of a slurry to bolster the excavation process and aid in muck conveyance. Typically composed of bentonite, this TBM slurry is conventionally discarded along with the excavated spoils, posing risks to human safety and raising environmental contamination apprehensions. This study aims to explore a novel slurry material as a means to mitigate the toxicity associated with muck disposal. Given the notable adsorption capabilities of bentonite, alternative options such as kaolinite clay and xanthan gum biopolymer are under consideration. Through experimental analysis, various combinations of bentonite clay, kaolinite clay, and xanthan gum are examined to assess their effectiveness in enhancing tunneling performance and optimizing transport properties. The evaluated parameters encompass rheological characteristics, swelling behavior, permeability, suspended viscosity and stickiness. Employing statistical analysis integrated with random weighting factors and the measured properties of each slurry candidate, competitiveness of each slurry candidate is analyzed. The findings of this investigation, accounting for 47.31% priority across all probabilistic scenarios, indicate that a specific blend consisting of bentonite and xanthan gum (2.5% bentonite, 0.75% xanthan gum) demonstrates considerable promise as a substitute for conventional bentonite-based slurries (7.5% bentonite) in TBM excavation applications.

This paper discusses efforts made by past researchers to steady the expansive (problematic) soils using mechanical and chemical techniques - specifically with EPS beads, lime and fly ash. Administering swelling of problematic soils is critical for civil engineers to prevent structural distress. This paper summarizes studies on reduction of swelling potential using EPS, lime and fly ash individually. Chemical stabilization with lime and fly ash are conventional methods for expansive soil stabilization, with known merits and demerits. This paper explores the suitability of different materials under various conditions and stabilization mechanisms, including cation exchange, flocculation, and pozzolanic reactions. The degree of stabilization is influenced by various factors such as the type and amount of additives, soil mineralogy, curing temperature, moisture content during molding, and the presence of nano-silica, organic matter, and sulfates. Additionally, expanded polystyrene (EPS) improves structural integrity by compressing when surrounded clay swells, reducing overall swelling. Thus, EPS addresses limitations of chemicals by mechanical means. Combining EPS, lime and fly ash creates a customized system promoting efficient, long-lasting, cost-effective and eco-friendly soil stabilization. Chemicals address EPS limitations like poor stabilization. This paper benefits civil engineers seeking to control expansive soil swelling and prevent structural distress. It indicates potential of an EPS-lime-fly ash system and concludes by identifying research gaps for further work on such combinatorial stabilizer systems.