Abstract
The peak and residual strengths of rock materials are important parameters for the stability evaluation of rock engineering, especially water diversion tunnels. A friction-strengthening model based on Hoek–Brown model is proposed to determine peak and residual strength of rock. The proposed model parameter, contact friction coefficient of rock, controls the nonlinearity of the peak strength and residual strength. With a great amount of data from publications examined, the relationship between the friction coefficient and the parameters in the Hoek–Brown model is studied. A new field method using drilling process monitoring was proposed to predict the peak strength and residual strength. The results show that the predicted strength for four types of rock is in good agreement with those of the standard tests in laboratory. Their errors are within the error range of 15% compared to the results from the tested results in laboratory. Although the proposed model is empirical, the parameters in the proposed model have clear physical meaning, and it can successfully predict the peak strength and residual strength of hard rock, medium rock, and weak rock using drilling process monitoring in the field. This practical method should have a great potential for field application in rock engineering.
Highlights
Data CollectionA great amount of the peak and residual strength data were collected from 28 various rock types
Where σ1 is the major principal stress, σ3 is the minor principal stress, UCS is the unconfined compressive strength of intact rock, and s, a, and m are material constants
A drilling process monitoring apparatus is used to measure the thrust force, torque force, penetration rate, rotation speed, and penetration depth per rotation of hard rock, medium rock, and weak rock such as granite, limestone, slate, and red sandstone. e rotation speeds of drilling are applied at 200–600 rpm for each rock type. e penetration rates of drilling are set as 0.1–1.2 mm/min. e relationships between the thrust force and torque force of each rock are obtained as presented in Figure 6. e triaxial compressive strength, triaxial residual strength, cohesion, and internal friction angle of each type of rock are obtained in the laboratory
Summary
A great amount of the peak and residual strength data were collected from 28 various rock types. Erefore, the data is collected at low confining pressures, which are lower than 60 MPa. In addition, the four rock types (limestone, slate, granite, and red sandstone) were obtained by a drilling process by monitoring apparatus (DPM) [23]. Where σ1 is the major principle stress, σ3 is minor principal stress, UCS is the unconfined compressive strength of intact rock, λ and b are the model parameters, and tanθ is the contact friction coefficient between the fracture faces of the rock, which can be determined by drilling process monitoring. In consideration of the frictional strength mobilization in the deformation stage of rock, the damage of macroscopic fracture significantly leads to a large loss of cohesion.
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