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Characterization of jointed rock masses and evaluation of their mechanical properties are challenging tasks in rock engineering. This paper presents an experimental investigation of the response characteristics of drilling energy to the discontinuity of rock mass using a drilling method. The linear relationship between the drilling energy and discontinuity frequency is revealed, which only depends on the rock type, and is independent of calculation units. A new empirical method for determining the rock quality designation (RQD) versus the variation of drilling energy is proposed based on the discontinuity frequency. Comparison between the prediction and in situ investigation results demonstrates that the RQD can be estimated from this empirical method. The E m / E r (modulus ratio) and σ cm / σ c (strength ratio) versus RQD relations are modified for the determination of rock mass strength and deformation modulus in order to consider the continuous variation of E m / E r and σ cm / σ c with the model parameter η , which is related to the drilling energy and modulus of elasticity of intact rock and the variation of drilling energy for rock mass. The results show that the modified E m / E r (σ cm / σ c) versus RQD relations can give proper values compared with the field test results as well as compared with the various proposed relations from RMR, Q and GSI. The modified relations can provide a practical, fast and easy-to-use method for the estimated rock mass strength and deformation modulus, but they are only a first approximation. [ABSTRACT FROM AUTHOR]

Abstract Damage evolution salt rock under fatigue loading at different stress amplitudes, loading frequencies, and loading rates was investigated in the laboratory. Under conditions of fatigue loading, damage of salt rock can be divided into three stages: initial damage, constant-velocity damage, and accelerated damage. The results of the fatigue tests indicate that higher stress amplitudes, higher loading frequency, and higher loading rate lead to decreased fatigue lifetime. Based on the experiments, a model for the prediction of fatigue life versus stresses, frequency, and loading rate was proposed. Comparison between the model and the experimental results shows that fatigue lifetime can be estimated and predicted from this model. Based on the three-stage damage trend, the cumulative fatigue damage is numerically predicted by considering a double term power damage model. The proposed model captures the characteristics of damage evolution in salt rock under fatigue loading, with the parameters of the model obtained from experimental data. [ABSTRACT FROM AUTHOR]

Accurate, fast, and reliable estimation of field rock strength is significant for the assessment of rock mass strength. This paper presents a novel method to continuously estimate the field strength parameters of rock by incorporating a deep convolutional neural network (DCNN) technique into the drilling process. A DCNN model is established based on the stochastic pooling method and softmax loss. The proposed CNN model framework includes : (1) collecting drilling performance parameters of intact rock, (2) establishing a strength parameter database via standard laboratory tests , (3) training the proposed CNN model using images created from the dataset of drilling performance parameters and rock strength parameters (unconfined compressive strength (UCS), cohesion, and internal friction angle), and (4) performing a new estimation to evaluate the reliability of the trained CNN model. The experimental results show that the predicted rock strength parameters are within the accepted error range of 10% compared to the results from the conventional standard test. The proposed CNN shows superior performance for UCS estimation of various rock types and achieves higher accuracy than the Mohr–Coulomb criterion. In particular, the proposed method can overcome major limitations of analytical models based on the force limit and energy equilibrium method. This method enables continuous and reliable field measurements of rock strength parameters at a speed several orders of magnitude faster than the standard test. This continuous and practical technique has been applied in an engineering problem in the Hanjiang-to-Weihe River Project of China and shows potential for field applications in rock engineering. [ABSTRACT FROM AUTHOR]