# Experimental Study on the Mechanical Properties of Xinyang Red Clay Improved by Lime and Fly Ash
## 1 Introduction
The second is to analyze the failure mechanism of soil after adding the improved material. [PERSON] et al. [23] mixed rubber waste into clay, studied the failure mode of improved soil through an unconfined strength test, and proposed an expression to estimate the strength of improved soil. [PERSON] et al. [24] incorporated a certain amount of cement-modified silt with debris waste particles, and derived the correlation formula between unconfined strength and the amount of added material based on the experimental data. [PERSON] et al. [25] used lime and bamboo ash to improve an expansive soil, and established a polynomial model relationship between the compression index and the added improved material. [PERSON] et al. [26] enhanced soil properties by adding fly ash, lime sludge, and polypropylene fiber to the soil. Through a series of laboratory experiments, the results were compared and a significant improvement in the strength of the soil was found, and these admixtures had a positive effect on the stability enhancement of the clay soil. The third is to explore the mechanism of improving engineering soil microscopically by means of scanning electron microscopy and X-ray diffraction [27]. [PERSON] et al. [28] used scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) to evaluate the microstructure of bagasse ash, glass powder, and silica fume poorly modified graded sand. [PERSON] et al. [29] used metakaolin to improve clay sand. XRD showed that the cement compound calcium silicate hydrate appeared in the improved soil, and SEM imaging showed that with the addition of metakaolin, the scattered structure of the soil changed to a flocculent structure, thus enhancing the strength of the soil. [PERSON] et al. [30] used cement and metakaolin admixture to improve the compacted soil, and used X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and mercury injection to analyze the microstructure, showing that the addition of metakaolin increased the number of hydration products and made the distribution of microscopic pores denser. [PERSON] et al. [31] synthesized polymer-modified black clay from industrial wastes. Through mineralogical identification, morphology, and element analysis, the microlevel changes of geopolymer-treated soil were defined. According to the microanalysis, this method was superior to lime. [PERSON] et al. [32] improved expansive soil with alkali-excited fly ash, and analyzed the microstructure of untreated and treated BCS samples by SEM, XRD, and FTIR spectra, showing that the combination of soil particles and the formation of dense microstructure produced higher strength and reduced expansion and shrinkage characteristics. However, there are few studies on the engineering mechanical properties and microstructure of red clay improved by mixed lime and fly ash. Particularly, more systematic studies on the mechanical properties and microstructure of the improved soils are needed. For this reason, a soil improvement study from the Xinyang region was conducted as a case study for analysis. In this paper, Xinyang red clay was improved by single and compound lime and fly ash, and the engineering mechanical properties of the soils were compared and analyzed under different improvement methods. Using scanning electron microscopy and X-ray diffraction, the mechanism of lime and fly ash improving red clay was analyzed microscopically, which can provide a reference for road engineering and slope engineering in areas with red clay.