## 1 Introduction
[22] adopted photogrammetry to conduct undrained tests on soft clay to reduce the influence of end constraints on conventional triaxial tests. The results indicated that photogrammetry was more accurate in measuring the soil sample's local peak stress than conventional triaxial tests. [PERSON] et al. [23] introduced the GeoPIV-RG technology into triaxial tests on the basis of [PERSON] and [PERSON] et al. The volume and global fine deformation of the soil sample were measured using steel column tests and silt tests. The steel column test verification method could accurately measure the volume (with an error of 0.36%), and the silt test demonstrated that GeoPIV-RG combined with speckles could measure the global deformation, providing an efficient, comprehensive, and fine method for studying the deformation characteristics of soil in triaxial tests. [PERSON] et al. [24] used a rigid cylinder to simulate triaxial soft clay under different confining pressures and in different media to conduct a series of triaxial accuracy verification tests and found that the average axial error obtained by the triaxial photogrammetry method was 0.056% and the average radial relative error was 0.17%. [PERSON] et al. [25] used the modified triaxial photogrammetry method to measure saturated sand. The results showed that the correction coefficient could reduce the refraction effect and enhance the measurement accuracy. [PERSON] et al. [26] utilized the triaxial photogrammetry method to measure mixed soil. The results indicated that light had a more significant effect on the radial direction, while the axial measurement could be negligible. The triaxial photogrammetry method met the measurement accuracy requirements. [PERSON] et al. [27] analyzed the shear banding pattern of Guilin red clay through photogrammetry technology, revealing the evolution process of soil strain localization. The results demonstrated that photogrammetry technology could effectively avoid the measurement errors of conventional triaxial tests. As shown in Table 1, the triaxial photogrammetry method is currently mainly used for unsaturated soils, and a few studies have been conducted on special rocks and soil, especially original soil samples. Most of the existing theoretical systems of soil mechanics are developed based on the experimental research of reshaped soil, without considering the influence of soil structure [28; 29]. The main difference between undisturbed and remolded soils is their structure and strength [30]. Undisturbed soil is the soil sample that retains its natural water content and structure, while remolded soil is the test soil that is made of undisturbed soil after drying and grinding according to the density and water content of undisturbed soil. In comparison to undisturbed soil, the strength of disturbed soil has diminished due to alterations in its structure. Since the mechanical properties of the undisturbed soil are different from those of remolded soil, in order to verify the effectiveness and reliability of photogrammetry for undisturbed soft soil, this paper uses finite elements to perform three-dimensional numerical simulation based on photogrammetry, which once again proves that photogrammetry