A comprehensive review of biodegradable biopolymers' challenges and performance in improving soil mechanical characteristics

In recent years, there has been a significant focus on improving poor soil with the aim to modifying its geotechnical properties and addressing its environmental issues. The environmental problems associated with utilizing traditional materials to enhance poor soil have drawn particular attention to the application of novel, biodegradable materials like biopolymers. Based on their production source, we categorize biopolymers into three main types: plant-based, animal-based, and microorganism-based. The purpose of this research is to investigate, evaluate, and analyze soil improvement and stabilization studies using biopolymers in both quantitative and qualitative methods. The study provides charts and tables for the optimal sampling mode for biopolymers in soil tests in each study, considering effective parameters like biopolymer type, biopolymer content, curing time, and curing temperature. The article covers numerous tests, such as compressive strength, shear strength, Atterberg limits, permeability, California Bearing Ratio (CBR), compaction, one-dimensional consolidation, and penetration tests. This investigation also encompassed challenging issues related to the erosion resistance and durability of soils treated with biopolymers. The results of the wet-dry durability tests showed a gradual decrease in strength in the biopolymer-treated soils. Additionally, the microbial group's xanthan gum and gellan gum, the plant group's guar gum and agar, and the animal group's chitosan and casein demonstrated superior performance within their respective groups, leading to their selection as effective biopolymers for enhancing mechanical properties, availability, and cost. Microbial biopolymers outperform plant biopolymers in terms of enhancing the mechanical properties of soils because of their negative charge, which strengthens bonding, particularly in clay. Employed in soil pollution removal and heavy metal absorption, chitosan biopolymer effectively improves mechanical characteristics in the short term. Although animal biopolymers have weaker performance in improving hydromechanical properties due to less hydrophilicity than the other two groups, the mentioned feature makes this group perform well against water erosion.