<p>The Central Yunnan Water Diversion Project (CYWD Project) is a crucial water source initiative within Yunnan’s revitalization strategy. However, significant engineering challenges arise, such as tunnel mud and water inrush due to the presence of highly sandy dolomite. Therefore, understanding the mechanical properties of this dolomite is essential for ensuring safe construction in the tunnel engineering of the CYWD Project. This paper examines the highly sandy dolomite found in the Sinian strata of Zbdn and Zbd, located along the Yuxi section of the tunnel line, using both micro and macro testing methods. Microscopic analyses, including slice identification, CT scanning, and scanning electron microscopy, were conducted to determine the primary geological characteristics and classification standards of the sandy dolomite. Additionally, macro tests, such as in-situ needle penetration tests (NPT), uniaxial compressive strength tests (UCS), and shear tests, were performed. Using the least squares method and regression analysis, relationships between the needle penetration index (NPI), UCS, and shear strength were established. This study established reliable relationships between the needle penetration index, uniaxial compressive strength, and shear strength parameters of highly sandy dolomite encountered in the CYWD Project. The geological features were also characterized using macro- and micro-scale testing, providing a theoretical basis for the project’s design and safety. This conversion relationship offers a theoretical basis for the design, construction, and safety evaluation of the CYWD Project. The parameters developed are sufficiently reliable for evaluating engineering in areas with highly sandy dolomite.</p> Graphical abstract <p></p>