Loess is widely distributed around the world, encompassing regions in East Asia, Central Asia, Central Europe, the United States, northern Russia, interior Alaska, and various parts of South America [1]. In China, approximately 6.6% of the land area is blanketed by loess [2]. Loess is characterized by its loose structure, high porosity, and sensitivity to moisture [3–5]. Therefore, in conditions of sustained rainfall the structural strength of the soil undergoes a notable reduction which leads to a rapid decrease in both mechanical strength and deformation modulus [6–11]. Consequently, soil collapse will result in uneven settlement within loess roadbeds. To ensure the safe construction and operation of projects in these areas, it is imperative to implement measures aimed at enhancing the engineering geological properties of loess [12–15]. According to existing research, the treatment of loess-based foundations or roadbeds encompasses various measures, including compaction, replacement, and composite foundation techniques [16]. In the field of engineering, methods for enhancing highway foundation soils can be categorized into three primary approaches: physical, chemical, and comprehensive improvement strategies [17]. The physical improvement primarily involves the addition of geotextile fabrics [18] and polymer fibers [19] to the soil or modifying particle grading by incorporating materials such as slag, sand, and gravel to bolster the soil's physical and strength properties [20]. Chemical enhancement techniques usually include introducing materials into the soil, such as cement [21], lime [22], or chemical solutions [23]. Chemical reactions between these additives and soil particles create new substances with enhanced strength properties, thereby improving the overall strength and stability of the soil. Comprehensive amendment techniques are the combination of both physical and chemical amendments. [24].
Currently, loess improvement mainly involves the use of lime, fly ash, lignin fiber alone or a combination of both. Osula et al. [25] conducted an investigation into the impact of curing time on loess improvement using lime and cement. Boadman et al. [26] observed that in lime-improved soils, ion exchange and agglomeration of clay particles significantly increase early strength, while volcanic ash reactions primarily enhance later strength. Helenn [27] conducted indoor experiments to investigate the engineering properties of lime-amended soils. Liu and Zhao et al. [28–29] delved into the key factors influencing the compaction, compression, and strength properties of lime-amended loess within the context of the Zhengzhou West High-Speed Railway. Furthermore, Liu [30] and Zhang et al. [31] carried out a series of investigations on lignin-amended loess, revealing that lignin effectively enhances the strength of loess. At the microscopic level, lignin acts to cement soil particles and fill pores. Results from Liu et al. [32] indicated that lignin incorporation effectively boosts the strength of loess while improving its water-holding capacity and water stability. Moreover, Hou et al. [33] delved into a multidimensional analysis of lignin-amended loess, pinpointing calcium lignosulfonate as a novel curing material capable of enhancing particle cementation and structural compaction. Gao [34]and Zhong et al. [35] conducted research on lignin fiber-amended loess using sampling methods, which revealed significant impacts on the strength of ameliorated loess.
Existing studies have mainly focused on the improvement of loess properties by lime or lignin as a single inorganic or organic modifier. The combination of inorganic and organic materials to improve loess is less studied. In addition, lime is a widely distributed, inexpensive and easy to obtain geotechnical engineering materials, will be a certain amount of lime and loess mixed to improve the engineering properties of loess and the formation of lime stabilized loess has been a common method of improving loess and its improved mixing ratios and technology has been relatively mature, but the lime-improved soil is easy to be softened in contact with water, and a large amount of dust will be generated during the construction process. As a kind of organic material with large storage capacity and environmental protection, the application of lignin in loess improvement can greatly improve the engineering performance of loess such as water loss disintegration, softening, etc., and the biological curing agent has the advantages of less pollution and less dust. Therefore, this time, lime and lignin are used to improve loess roadbed together.
Currently, numerical simulation methods for performing roadbed settlement calculations are divided into three main categories: finite element method, finite difference method, boundary element method, finite difference method and boundary element method.The finite element method is widely used in geotechnical engineering calculations because of its simple concept, easy to grasp, accurate results and other advantages.Li Junhong [36] used ABAQUS to simulate the effect of the depth of influence of drainage strips on the consolidation of soft foundations; Alielahi et al. [37] used Settle 3D software to simulate the effect of drainage strips with stacking pre-compression technology to improve the performance of foundations; Kazem et al. [38] pointed out that if the parameters of the soil in the software of Settle 3D were chosen appropriately, it was possible to reasonably estimate the time of settling and consolidation.Luo [39] Simulation of vertical displacement of composite-amended loess roadbed along depth direction using MIDAS/GTS software.Auersch et al [40] established a numerical model of railroad track-roadbed and investigated the distribution law of the dynamic response inside the model of railroad track-roadbed. The distribution of dynamic response inside the track-roadbed model was investigated.
This time, MIDAS/GTS is adopted, which is a finite element analysis and design software developed for geotechnical and tunneling engineering, and it is a special software for geotechnical engineering, applicable to geotechnical, underground structures, tunnels, subways and other fields, and it is able to carry out the analysis of the construction stage, the analysis of the load bearing capacity and deformation, and the analysis of the stability of slopes, and so on. High-speed railroad operation often involves vibration loads, the vibration load research of railroad roadbed is less and vibration load is the focus of railroad roadbed research, MIDAS/GTS provides the corresponding time course analysis method, which can better respond to the settlement of the roadbed in the process of high-speed railway rapid operation.
This paper investigates the impact of lime and lignin dosages on the behavior of loess through a comprehensive series of tests including compaction tests, unconfined compression tests, and triaxial shear tests. Additionally, numerical simulations were employed to analyze the effects of lime and lignin at varying dosages on the enhancement of loess for roadbed applications, resulting in the optimal dosage for enhancing loess, as obtained from this study. The findings of this research provide new insights and experimental references for enhancing roadbeds in loess regions.