Research on Point Load Correction Factor Based on Electro-hydraulic Servo Point Load Meter.

A novel electro-hydraulic servo point load meter has been developed to address the limitations of existing point load meters, which cannot provide continuous and uniform loading. This new meter enables continuous and uniform loading with variable rates, thereby reducing the dispersion of test data and offering a technical solution for revising the current point load strength calculation formula. Experimental investigations were conducted to analyze the influence of loading rates (0.1 kN/s, 0.5 kN/s, 1.0 kN/s) on the existing point load strength correction method. Four types of rock samples, namely, fine-crystalline granite, coarse-crystalline granite, siltstone and marble, were utilized in the study. Each rock sample was tested at four different sizes: 203 mm3, 303 mm3, 403 mm3, 503 mm3. The objective was to examine how the loading rate affects the accuracy and effectiveness of the point load strength correction method. Initially, the correction index "m" from various domestic and foreign regulations was employed to calculate and analyze the test data, determining the appropriate correction index m, loading rate, and range of rock sample sizes. Subsequently, the relationship between the standard point load strength and uniaxial compressive strength was analyzed based on these findings. The research results indicate the following: (1) the larger the strength of the rock sample, the smaller the point load correction index m and all four rock samples demonstrated an increase in standard point load strength when solved using the four correction indices (m1, m2, m3, m4) with increasing loading rate. (2) With increasing sample size, the standard point load strength solved using correction indices m2, m3, m4 still exhibited a significant size effect, while the dimensional effect of the standard point load strength solved using m1 was not evident. (3) The conversion factors obtained through zero-intercept linear regression analysis for fine-crystalline granite, coarse-crystalline granite, siltstone, and marble were 16.45, 15.38, 15.17 and 14.83, respectively. These results indicate that the conversion factors for rocks with lower strength are smaller compared to those with higher strength. Highlights: The impact of four different rock samples with varying sizes on the existing point load strength correction method is analyzed under three loading rates. An investigation is conducted to determine the appropriate point load strength correction index for the four rock samples. The study identifies the optimal loading rate and size range for rock samples based on the modified correction index. The relationship between standard point load strength and uniaxial compressive strength is examined. [ABSTRACT FROM AUTHOR]