Abstract
In this paper, the strain rate effect on mechanical properties, failure modes, acoustic emission (AE) characteristics, and energy mechanism of the karst limestone was analyzed based on uniaxial compression tests with different strain rates (5 × 10−6–5 × 10−4/s). The results showed that the peak strength increased linearly and peak strain increased quadratically with the logarithm value of the strain rate. Moreover, the strain rate effect on elastic modulus was not significant. Under low strain rates, the rock was damaged seriously, AE signals appeared continuously, and the cumulative number of AE signals was high. Under high strain rates, the total quantity of the macroscopic cracks decreased, but the crack length extended with better coalescence. The AE peak significantly increased under high strain rates, while the cumulative AE activity significantly reduced. The energy evolution of the karst limestone failure process had significant stage characteristics, and the strain energy ratio presented an S-shape. The maximum value of the elastic strain energy at peak stress showed a linear relationship with the logarithm value of the strain rate.
Highlights
The strain rate effect on mechanical properties, failure modes, acoustic emission (AE) characteristics, and energy mechanism of the karst limestone was analyzed based on uniaxial compression tests with different strain rates (5 × 10− 6–5 × 10− 4/ s). e results showed that the peak strength increased linearly and peak strain increased quadratically with the logarithm value of the strain rate
The total quantity of the macroscopic cracks decreased, but the crack length extended with better coalescence. e AE peak significantly increased under high strain rates, while the cumulative AE activity significantly reduced. e energy evolution of the karst limestone failure process had significant stage characteristics, and the strain energy ratio presented an S-shape. e maximum value of the elastic strain energy at peak stress showed a linear relationship with the logarithm value of the strain rate
Zhang et al [38] used the bonded particle model to investigate the AE characteristics of rocks under different compressive loading rates, and the results showed that total cracks, tensile cracks, shear cracks, and AE event numbers all increased with the loading rate
Summary
Karst limestone was obtained at mileage GK2730-2485 in Qiyueshan Highway Tunnel, Hubei Province. e rock density was 2.69 g/cm, and the P-wave velocity was approximately 4900 m/s. E rock density was 2.69 g/cm, and the P-wave velocity was approximately 4900 m/s. The samples were prepared as Φ 50 mm × 100 mm cylindrical samples according to the International Society for Rock Mechanics. The RMT-150B rock mechanics test system with a control range of strain rates of 10− 2–10− 6 s− 1 was used. E displacement control mode was adopted in the test. E strain rates were set from 5 × 10− 6 to 5 × 10− 4 s− 1. Four strain rates were selected, and each test was repeated 2 times to reduce test errors. The DS5-8B AE detection system was used for the real-time monitoring of AE signals. The AE monitoring remained synchronized with stress loading, and all the tests were conducted at room temperature
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