Biaxial compression behavior and stability analysis of wedge blocks in tunnel sidewalls: Experimental investigation and support effect evaluation

In complex jointed rock masses, wedge blocks are likely to form on the tunnel sidewalls after excavation, and the mechanical properties and stress environment of the surrounding rock have a significant impact on their stability. In this study, cubic rock specimens with prefabricated wedge blocks and arched tunnel features were tested under biaxial compression. Acoustic emission (AE) and digital image correlation technologies were used to monitor crack propagation and specimen failure in real-time. The results showed that supported specimens exhibited higher strength during both the peak and post-peak stages, with a slower strength decline after the peak. The support regulated AE hit rates and enhanced energy storage capacity. Different specimens displayed varying strain evolution, with supported specimens generally having higher lateral strain than shear strain. In unsupported specimens, tensile and shear stresses were concentrated at the wedge block apex, while supported specimens showed more complex stress variations, especially under the influence of wedge blocks. Stable specimens experienced shear sliding failure, while extremely stable specimens experienced both shear sliding and tensile fracture. As horizontal stress ( σ 3 ) increased, specimen strength and wedge block failure both increased. Triangular wedge blocks played a decisive role in tunnel stability, with extremely stable triangular blocks providing greater safety. In addition, a typical stability analysis method for wedge blocks was proposed. The findings provide a scientific basis for rock mass stability assessment and support measure selection in tunnel design.