285 efficiency of dual-insert combinations with different geometries under in-situ stress conditions, and the effects of penetration velocity and depth. 2.5 Analysis Methods In response to the differences brought by spherical and conical insert shapes during the rock-breaking process, this paper employs the rock brittleness index to evaluate the difficulty of insert penetration, the load stability index to assess the fluctuation during penetration, and the rock-breaking efficiency index (along with indicators such as cuttings particle size distribution) to evaluate the work efficiency during insert penetration into rock. The specific analysis methods are as follows. (1) Rock Brittleness Evaluation Index. The rock brittleness index is an important indicator for judging the difficulty of rock failure under the action of an indenter. In engineering, the uniaxial compressive strength and Brazilian splitting strength of rock are commonly used for this purpose. Equation (1) presents three different strength ratios widely used in previous studies to indirectly quantify brittleness based on strength(Yagiz, 2009). 1 2 3 2 c c t c t t c t B B B σ σ σ σ σ σ σ σ − ⋅ = = = + ， ， (1) In the equation, σc represents the uniaxial compressive strength of the rock specimen, in MPa; and σt represents the Brazilian splitting tensile strength of the rock specimen, in MPa. This paper adopts the Rock Brittleness Index (BIm) proposed by Saffet Yagiz(Yagiz, 2009), which is based on rock sample tests from 48 tunnels worldwide. This index is defined as the ratio of the maximum indentation load (kN) on the specimen to the corresponding penetration depth (mm), as shown in Equation (2). max m F BI d = (2) In the equation, Fmax represents the maximum indentation load, in kN; d represents the indentation depth/displacement, in mm. (2) Rock-Breaking Efficiency Evaluation Index. Specific Energy (SE) is a key metric for studying the efficiency of cutter rock-breaking. Equation (3) defines the concept of specific energy as the energy consumed to break a unit volume of rock. Based on specific energy theory, numerous researchers have adopted it as a unified comparative metric when evaluating cutter rock-breaking efficiency under different working conditions. 0 = d i c c Fdx W SE V V = ∫ (3) In the equation, W represents the work done by the cutter in breaking rock, in J; Vc represents the volume of broken rock, in m³; and Fi represents the load at a specific position, in N. Based on the sieve analysis results from standard sieves, the mass distribution proportion of rock fragments under different particle sizes can be obtained. Equation (4) can be used to more clearly describe the distribution pattern of the average fragmentation block size (dm).
RkJQdWJsaXNoZXIy MTM0Mzk2