## 1 Introduction
[20] conducted a series of large-scale in-situ direct shear tests on soil-rock mixtures with different moisture contents and particle size distributions and obtained the influence of the above factors on the shear strength of soil-rock mixtures, as well as the relationship between normal stress and shear strength of soil-rock mixtures. [PERSON] et al. [21] conducted large-scale direct shear tests on soil-rock mixtures in the middle reaches of the Jinsha River and obtained the influence of rock block size ratios on the deformation mechanism of soil-rock mixtures. [PERSON] et al. [22] conducted in-situ large-scale direct shear tests on the boundary between the stepped bedrock slope and the fill soil and obtained the stress evolution and failure process of the rock. Unlike traditional direct shear tests, in push shear tests there is no normal load applied to the specimen, so the shear plane can freely develop along the edge of the specimen. In addition, large-scale horizontal push shear tests simulate actual forces in situ, avoiding the drawbacks of indoor test sampling disturbance and size effects. In recent years, many scholars have verified the reliability of this test: [PERSON] et al. [23] conducted push shear tests on soil-rock mixtures in the Tiger Leaping Gorge area, obtained shear strength parameters such as cohesion and internal friction angle, and plotted an accurate three-dimensionalsliding surface. [PERSON] et al. [24] conducted in-situ horizontal push shear tests on soil-rock mixtures in Baidian County, Hunan Province, and obtained the mechanical strength and failure characteristics of soil-rock mixtures in the region. [PERSON] et al. [25] conducted in-situ push shear tests on mudstone in Santa Barbara, Italy, and obtained accurate ranges of local mudstone strength parameters, establishing a relationship model between internal friction angle and rock mass volume block content. [PERSON] et al. [26] conducted large-scale on-site shear tests on 10 specimens of red sandstone embankments on a certain highway in Hunan Province and obtained the mechanical evolution process and shear strength variation curve of red sandstone at different moisture contents, further standardizing the procedure of on-site shear tests for red sandstone. [PERSON] et al. [27] conducted large-scale in-situ horizontal push shear tests on soil-rock mixtures in natural and saturated states, obtaining complete sliding surfaces and the attenuation law of mechanical parameters after immersion in water. However, the research objects of the above studies mainly focus on soil-rock mixed fill foundations and soil-rock mixtures, and there is limited information and data available for on-site testing of carbonaceous mudstone. Therefore, it is urgent to carry out large-scale in-situ horizontal push shear tests on carbonaceous mudstone. This study conducted on-site large-scale horizontal push shear tests on carbonaceous mudstone. The aim is to obtain accurate shear strength and failure characteristics of the material, and to quantify the impact of this failure on the high cut slope of carbonaceous mudstone through finite element simulation. Finite element simulation has become an important tool in geotechnical engineering research due to its significant advantages in slope stability analysis. Currently, software such as MIDAS, ABAQUS, and COMSOL have been widely used for simulating slope stability before and after rainfall [28; 29]. These tools also enable researchers to evaluate the role of different protective measures in slope protection. [PERSON] et al. [30] used MIDAS GTSNX to assess the stability of geocells in slope protection. [PERSON] et al. [31] used COMSOL6.0 to simulate the variation law of the safety factor of slopes with weak joints under freeze-thaw cycles. [PERSON] et al. [32] analyzed the stability of sandy red clay slopes under different nitrogen values using finite element software ABAQUS CAE 2020.