The present study aimed to assess the potential of a bio-inspired algorithm, multi-objective grey wolf optimization algorithm (MOGWO), to optimize the strength properties (California bearing ratio (CBR) and unconfined compressive strength (UCS)) of an expansive subgrade soil. This optimization process involves the use of two additives, namely a bio-polymer, pregelatinized corn starch (PGCS), and a nanoparticle agro waste, rice husk ash (RHA), blended with the soil in different mix ratios determined by a 32 factorial experimental design. The CBR samples were cured for 7 days, while the UCS samples were cured for 1, 7, and 28 days. To optimize the expansive subgrade soil strength, regression models were developed using PGCS and RHA as predictors for CBR and UCS, serving as fitness functions in the slightly modified MOGWO optimization technique. Next, the optimization analysis produced non-dominated solutions. The results obtained from the laboratory experiments and optimization analysis revealed that there was significant improvement in the UCS and CBR of the soil. These improvements can be attributed to the pozzolanic reaction between the soil-RHA matrix, the formation of intercalated and exfoliated nanocomposites, and the hydrophilic interaction of PGCS. By applying the slightly modified MOGWO technique, the study achieved optimal enhancements in UCS (710.3 kN/m2) and CBR (24.2%) when the expansive subgrade soil was mixed with 0.2637% PGCS and 12.2413% RHA. The results demonstrate the potential of the MOGWO technique in improving the properties of expansive subgrade soil.

Soft clay soil is a concern in geotechnical engineering due to its low strength and high compressibility. Soil improvement with stabilization techniques is an interesting topic in the field of geotechnical engineering and pavements. Nanomaterials and biogeotechnicalbased soil improvement are in high demand, as is the case with the objective of this research which is to determine the effect of the addition of nano lime, nano silica, and chitosan biopolymers to soft clay soil on its mechanical properties. The ratio of additives in this study was taken based on previous research, namely 2% nano lime, 4% nano silica, and 0.1% chitosan biopolymer from shrimp shell waste. Specimen variations consist of initial soil, soil mixed with biopolymers, soil mixed with nanomaterials, and soil mixed with biopolymers and nanomaterials. The mixing method in this study was carried out by mixing the additives according to the percentage of the initial soil dry weight, then water was added to the mixture. Compaction and unconfined compression strength (UCS) tests were conducted on each specimen. The results show that mixing soil with nanomaterials and chitosan provides advantages in mechanical properties. This can be seen from the increase in the UCS value which is up to 11 times that of the initial soil and the increase in the maximum dry density value. Soil stabilization using nanomaterials and chitosan biopolymers has a good impact on the environment. Reducing the ratio of lime in soil stabilization on a project scale can reduce CO2 emissions during production and the use of chitosan biopolymer additives can reduce marine biota waste, especially invertebrates.