Coarse-grained soil (CGS) is a vital geotechnical material extensively used in engineering projects. Scale effects pose challenges to accurately assessing its shear strength, and the influences of scaling methods and moisture content remain underexplored. This study investigates the effects of maximum particle size ($d_{\max }$), scaling techniques, and moisture content on the shear strength of CGS through large-scale direct shear tests and in situ direct shear tests. CGS samples from the Jilangtan platform in Qinghai Province, originally with a $d_{\max }$ of 60 mm, were scaled to 30 mm using the Equivalent Substitution Method (ESM) and Similar Gradation Method (SGM). Tests were conducted at moisture contents of 0.91% (air-dried), 2.45% (natural), and 7.66% (saturated). Results show that ESM consistently yields higher shear strength than SGM across all moisture levels. Scale effects are minimal under air-dried conditions but become pronounced at higher moisture contents. While all large-scale laboratory test results deviate somewhat from in situ findings, shear strength parameters derived from SGM align more closely with field observations.

The rock mass deformation modulus is one of the most important design parameters in a range of rock engineering applications. Its value is usually obtained directly through in situ testing or estimated indirectly on the basis of a rock mass quality classification system. Because in situ testing is generally costly, time-consuming, and presents operational difficulties, it cannot be carried out extensively, and many researchers have concentrated on developing indirect procedures to obtain information on the modulus of deformation, such as the RMR method, Q method, and GSI method. The purpose of this paper is to present a new system for estimating the rock mass deformation modulus called the BQ method, which is based on the BQ (basic quality) system. In this paper, the BQ system is first briefly reviewed, and then more than 60 in situ measurements from three large hydropower stations in China are used to develop a new relationship between BQ and the deformation modulus, based on a power function relationship. The paper also derives correlations based on the existing estimation formula and the relationship between BQ and other classification schemes, resulting in several recommended formulas for estimating the deformation modulus of a rock mass using the BQ method.