Estimation of volumetric block proportions from 1D boring of bim-materials considering different block forms

Abstract

Understanding the mechanical behavior of block-in-matrix geomaterials (bim-materials) is crucial for estimating the stability and designing reinforcements for natural slopes. This behavior is primarily influenced by the volumetric block proportion (VBP). Typically, the VBP is estimated using in-situ 1D boring data, which can differ from the actual 3D VBP. To address this discrepancy, uncertainty factors were introduced by Medley (1997) and subsequently refined by Napoli et al. (2022a) to estimate the actual 3D VBP from the linear block proportion (LBP) obtained via 1D boring. In this study, the coefficient of variation (COV) is further refined by incorporating the effects of block morphology. Actual 3D block geometries were reconstructed using CT scanning, focusing on four typical block geometries: spheroidal, prolate, oblate, and blade shapes. A novel method for generating virtual 3D block assembly models was developed, achieving an 86 % reduction in the time required to generate a 3D block assembly model for a 42 % VBP configuration by minimizing the number of blocks to be assessed and optimizing vertex checks. In total, 88 block assembly models were established with varying VBPs, block forms, and engineering dimensions (L_c), to examine their effects on COV values. The updated COV values were then applied to estimate VBP in bim-materials in the Scott Dam and Shuping landslide case studies. The reliability of these COV values was confirmed by comparison with previous studies by Medley and Napoli et al. under similar conditions. The analysis revealed that COV values decrease with increasing sampling length (N) and VBP, reflecting the lower heterogeneity of block distributions. Spheroidal blocks exhibit the highest COV values, while blade and oblate blocks show the lowest. Notably, VBP and block form were found to have a significant impact on COV values, particularly within the 13 % to 32 % VBP range, whereas the influence of engineering dimensions L_c is minimal. The updated COV values provide a more means of estimating actual VBP from in-situ borehole LBP measurements. This improvement is critical for enhancing the accuracy of stability assessments in engineering projects involving bim-materials.