Eco-friendly materials have gained significant attention for soil stabilization and reinforcement in road construction and geo-environmental infrastructure, as traditional additives pose notable environmental concerns. In this study, three concentrations of Chitosan Biopolymer (CBP) (1.5 %, 3 %, and 4.5 %) as a bio-stabilizer, three proportions of Rice Husk Biochar (RHB) (0.5 %, 1 %, and 1.5 %) as a waste-derived filler, and three dosages of Hemp Fiber (HF) (0.2 %, 0.4 %, and 0.6 %) as reinforcement were used to treat sand-kaolinite mixtures (SKM). The samples were cured for 1, 7, 14, 21, and 28 days and subjected to varying numbers of freeze-thaw (F-T) cycles. A diverse range macro-scale laboratory tests, encompassing compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), F-T durability, ultrasonic pulse velocity (UPV), and thermal conductivity (TC), were performed on the treated samples. In addition, microstructural analyses using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) were conducted to correlate mechanical behavior with micro- scale properties. The optimal dosages of CBP and RHB were first determined through UCS tests, with 3 % CBP and 1 % RHB proving the most effective. These dosages were then used to analyze their impact on other mechanical properties. Results showed that the compressive and tensile strengths of the bio-stabilized soil at the optimum contents of additives increased by 2410.7 kPa and 201.2 %, respectively, compared to the control samples. Incorporating HF into the SKM-CBP-RHB mixtures significantly enhanced their F-T durability after 10 consecutive cycles, reducing strength deterioration and performance degradation compared to the untreated soil. The optimum composition (3 % CBP, 1 % RHB, and 0.4 % HF) led to a 6.1-fold increase in ITS and a minor 2 % reduction in performance after 10 F-T cycles. Moreover, HF incorporation improved the failure strain and reduced the brittleness of the stabilized soil. UPV and TC tests revealed that incorporating HF at levels up to 0.4 %, combined with the optimum CBP-RHB mixture, enhanced soil stiffness by 963.7 MPa and reduced thermal conductivity by 0.76 W & sdot;m-1 & sdot;K-1. The microstructural analysis confirmed these findings, showing enhanced interlocking between SKM and fibers via hydrogel formation. Overall, the study demonstrates that the CBP-RHB-HF composite markedly enhances soil strength and durability, making these additives highly suitable for applications like landfills, embankments, and slopes.

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.