Introduction: Improving the mechanical properties of soil is an essential prerequisite for construction on unstable soils. In this regard, selecting environmentally compatible materials for soil improvement is an essential method for sustainable development, especially in natural resource development projects.
Materials and Methods: In this study, Following field classification of the soils along the proposed forest road alignments of the second series of Dr. Bahramnia Forestry Plan, three 160-kg samples of highly plastic clay soil (CH), one of the most problematic soil types for construction were collected randomly at regular intervals of 250 meters from a depth of 10-50 cm below the roadbed surface. Then, three types of bio-polymers including xanthan gum, guar gum and beta-glucan were then added to the CH soils at concentrations of 0, 0.1, 0.2, 0.4, and 0.6% by weight. The samples were mixed with the biopolymers using an industrial mixer. The effect of these biopolymers were evaluated immediately after mixing (day 0) and after a 28-day curing period. The measured properties included the Atterberg limits (plastic limit and liquid limit), Proctor compaction characteristics, particularly maximum dry density (MDD), and California Bearing Ratio (CBR). The liquid limit test was performed using a Casagrande apparatus, the plastic limit test using a kneadability test and the CBR test using a uniaxial device in the soil mechanics laboratory. Statistical analyses were performed in a factorial design with three main factors including the type of biopolymer, the amount of biopolymer and the curing time as dependent variables in SPSS software.
Results: The results showed that with increasing treatment concentration, the amount of pulp index decreased significantly. for xanthan, the greatest decrease was observed after 28 days of treatment (22% decrease) and with the addition of 0.4% xanthan to CH soil. for beta-glucan, the greatest decrease in pulp index was observed after adding 0.6% beta-glucan and after 28 days (21.3% decrease). Guar also exhibited a decreasing trend in the plasticity index as its concentration increased. . Analysis of variance revealed that biopolymer type, concentration, and curing time had significant effects on the maximum dry density of the soil. The greatest increases in MDD (28.4%) and CBR (112%) were observed after 28 days of curing with the addition of 0.4% xanthan to the CH soil.. Thus, it can be seen that 0.4% xanthan is the most suitable treatment for strengthening CH soil as a base for development projects in forest ecosystems.
Conclusion: Xanthan is an effective biopolymers for improving the engineering properties of CH soil as a base for construction projects in forest ecosystems. This biopolymer fills the voids in the soil and also binds with fine clay particles, thereby increasing the dry density of the soil. Thus, this biopolymer can be used in an optimal amount and with economic considerations for patch stabilization of unstable forest road subgrades.