###### Abstract  
In this study, for triaxial compression testing in geotechnical engineering, large-scale triaxial shear tests of coarse-grained soil were performed under end-restraint and end-free (microfriction) conditions utilizing a large-scale triaxial shear apparatus and a self-developed microfriction load-transfer plate. Under end-restraint and end-free (microfriction) circumstances, the strength and deformation characteristics of the coarse-grained soil were investigated. Further, the effect of the end restraint on the stress-strain characteristics of the coarse-grained soil was analyzed. The findings showed that the coarse-grained soil's stress-strain curves under the end-restraint and end-free (microfriction) conditions displayed both softening under low confining pressures and hardening under high confining pressures. However, the stress-strain curves' tendency to soften under low confining pressures was more pronounced under the end-free (microfriction) condition. Due to the influence of the end constraint, the peak strength of the coarse-grained soil increased under the same confining pressure, although the increase was less than 10% when the specimen had the typical height-to-diameter ratio of 2 in the drained triaxial test. Meanwhile, the coarse-grained soil first displayed volumetric contraction under the low confining pressures, followed by volumetric dilation, and it displayed volumetric dilation under the high confining pressures. The volumetric contraction tendency of the coarse-grained soil was more pronounced in the first stages of shearing when the low confining pressures were present. As the shear increased, it became more obvious that the coarse-grained soil had a tendency to dilate under the end-free (microfriction) conditions. Throughout the shearing operation, the coarse-grained soil exhibited a high propensity toward shear contraction. The coarse-grained soil's strength values were not greatly impacted by the end limitation, but the deformation parameters were. Under the end-restraint  
stress-induced deformation. The frictional shear stress between the cap (base) and the sample limits the radial deformation at the end of a specimen. When the specimen is close to failure, it is either pressed into a \"drum shape\" or squeezed into a \"neck shape\". This phenomenon is called the end-restraint problem in triaxial testing [3] ([PERSON], 2007). The end restraint causes strain and stress inhomogeneity within a triaxial sample, which affects the stress-strain characteristics, pore water pressure or volume change, shear band distribution, and strength characteristics of the specimen [4] ([PERSON] et al., 1968). The end-restraint effect prevents the triaxial test results from reflecting the true mechanical properties of coarse-grained soil. Therefore, reasonably analyzing the mechanical properties of soil under the influence of end restraints has become a popular research topic. Since the beginning of the 20 th century, scholars around the world have conducted thorough and systematic studies on the effect of the end restraints of soils, obtaining abundant research results in laboratory tests and numerical simulations. Numerous experimental studies have investigated the effect of end restraints on stress-strain behavior during the triaxial testing of soils. [PERSON] (1983) [5] reported that as early as 1900, [PERSON] coated a solid sample end with paraffin in a compression test to reduce the influence of the end effect. The failure mode and stress distribution pattern were obtained for specimens with different height-to-diameter ratios. [PERSON] (1941) [6] used specimens with a larger height-to-diameter ratio to study the effect of end restraints. Results have shown that when the height-to-diameter ratio is greater than or equal to 2, the effect of end restraints on the strength can be ignored. In 1964, [PERSON] et al. [7] used an unrestrained sample cap (base) in triaxial tests for the first time along with a pressure plate, lubricant, and rubber film, which was called a lubricated sample cap.