Loess exhibits poor engineering properties, such as low strength and poor water stability. Conventional materials used for improving loess, such as cement and lime, result in environmental pollution issues throughout their production and application processes. To assess the efficacy of bio-based materials, including calcium alginate (CA), xanthan gum (XA), cotton fibers (CO) and flax fibers (FA) in the treatment of loess, the improved soil's strength, disintegration, and water resistance were examined. Subsequently, an optimal amendment approach was determined, and dry -wet cycle tests and microscopic observation were performed. The results show that 1.0 % calcium alginate can effectively enhance the strength of loess, significantly improving its resistance to disintegration with almost no observable disintegration; permeability is significantly reduced, and water repellency is enhanced. 2.0 % xanthan can improve the strength and disintegration resistance of loess, but the improvement in strength is lower than that of calcium alginate. Additionally, the improved soil with XA experiences a flocculent disintegration in static water, which cannot maintain the soil structure. Cotton fibers and flax fibers can enhance both compressive and tensile strength of the soil. The content of 0.45 % flax fibers is considered the optimal choice as it has no effect on water stability. Combining the above results, the combination of 1.0 % CA and 0.45 % FA has been selected to improve the loess, which effectively improves the comprehensive mechanical properties and water stability of the composite improved soil. The decrease in strength and mass loss rate are significantly reduced after dry -wet cycle tests. Microscopic tests show that calcium alginate connects soil particles by Ca2+ ionic bridges, which allows the cementing materials to fill the loess pores and exert the role of agglomeration and coagulation to enhance the integrity of the loess. This study shows that the bio-based material with calcium alginate as the main body can effectively improve the mechanical strength and water stability of the loess.

The crumb tests, the pinhole tests, the double-hydrometer tests, the pore water soluble cation tests and the exchangeable sodium ion percentage tests are the common methods for identifying the dispersivity of the fine-grained soils,which are complex and time-consuming. Based on the dispersive mechanisms of the fine-grained soils, the soil samples with different clay contents and sodium carbonate mass fractions are prepared artificially to analyze the suitability of the conventional discrimination methods for dispersivity and to propose a rapid and accurate discrimination method. The results show that the dispersive soils can be divided into physical dispersive soils which can be called low cohesive soils, chemical dispersive soils and physical-chemical composite dispersive soils. It also can be found that 10% of the clay content is the upper limit of physical dispersivity of the fine-grained soils. The mud ball tests, the pore water soluble cation tests and the exchangeable sodium ion percentage tests can be applied to all fine-grained soils, and the pinhole tests and the double-hydrometer tests are suitable for the fine-grained soils with a clay content no lower than 10%. The results of the mud ball tests should be used as the discrimination criterion for dispersivity if the clay content is lower than 10%, otherwise the discrimination criterion for dispersivity should be the strongest dispersivity results of the mud ball tests and the pinhole tests.The double-hydrometer tests, the pore water soluble cation tests, the exchangeable sodium ion percentage tests, and the pH tests are used as the explanatory tests for the dispersive mechanisms of the fine-grained soils, which have no influences on the comprehensive discrimination.

分别以仿岩溶碳酸氢钙(CFPK)溶液和毛乌素沙地风积沙为固沙材料和加固对象,通过化学试验、力学试验、水理试验以及微观试验,探究二氧化碳压强和反应时间对CFPK溶液浓度的影响,分析CFPK溶液固化沙的工程性能,揭示其加固机理.结果表明:CFPK溶液浓度随着二氧化碳压强的增大而增大,随着反应时间的增加先增大而后保持稳定.呈散粒状的风积沙经过CFPK溶液处理后,其表面形成一层固结层,具有较高的表面强度、较好的抗风蚀性和耐水性.随着CFPK溶液用量的增加,固化沙的表面强度和抗风蚀性能逐渐提高.仿岩溶碳酸氢钙可在沙颗粒间分解形成具有胶结作用和填充作用的碳酸钙,能够有效加固风积沙.

The disposal of calcium carbide slag (CCS) is still a serious problem for areas that rely on the polyvinyl chloride industry, especially in the northern part of China. To assess the early effectiveness of CCS in treating dispersive soil, mechanical, chemical, and microscopic tests were conducted. The pH and conductivity EC were also measured to evaluate the effect of active ions. Validation test was also conducted on a natural dispersive soil from northern Shaanxi to prove the improving effectiveness of CCS on the dispersivity of soil. Results showed that adding 2% CCS significantly limits the dispersivity of the soil and improves its resistance to water erosion and mechanical properties. Increases of 11 times and 4.8 times were observed when CCS content increased from 0% to 5% and curing time increased from 0 to 28 days for compressive and tensile strength, respectively. The correlation between dispersivity and mechanical properties with pH and EC during curing was found to be significant. This relationship is closely linked to the dissolution and consumption behavior of the active ions that are abundant and contributed by the functional oxides in the CCS. Microscopic tests indicated that the porous particle structure of CCS improves the mechanical properties and limits the dispersivity of soil, due to physical strengthening and carbonization reaction in the early stage of CCS application. The subsequent release of Ca2+ and the formation of C-S-H/C-A-H cementitious hydrates played a vital role in controlling chemical dispersivity and further improving the mechanical properties of the dispersive soil. This was accomplished through ion replacement and pozzolanic reactions that were supported by the abundant active ions. Validation test show that CCS could efficiently improve the engineering properties of dispersive soil and the recommended mixture ratio is 2-5%.