Thermal damage and energy evolution characteristics in process of impact failure of sandstone after high temperature treatment were studied by split Hopkinson pressure bar (SHPB) system. The ultrasonic P‐wave velocity, density, porosity, peak stress, E_T/E₀, thermal damage, fracture, and energy evolution characteristics of sandstone with temperature during the experimental process were explored. Results show that, with the increase of temperature, the ultrasonic P‐wave velocity and density decrease, while the porosity increases. It is found that the peak stress and E_T/E₀ decrease with the increase of temperature, and the decreasing trend is fitted with the simple cubic equation. Above 600°C, dynamic peak stress and E_T/E₀ decrease rapidly. The thermal damage of rock increases with the increase of temperature, which is in accordance with the logistic curve model. The thresholds of damage strain energy release rate are 200°C and 800°C in this research. Its total input strain energy decreases with the increase of processing temperature and decreases sharply when the temperature is over 600°C. The variation of total input strain energy has small change at the range from 400°C to 600°C.

Metakaolin (MK), which has a fine particle size and higher activity in high alkaline environments, has been widely used in the fields of soil treatment engineering to stabilize soils. MK is used to replace part of ordinary Portland cement (OPC) with 0 : 15, 2 :13, 4 : 11 and 6 : 9 mass ratios of MK to OPC in this study. The mechanical property (e.g. stress‐strain relationship, strength, and deformation performance) and microstructure characteristics of MK‐based geopolymer cemented silty clay are investigated using unconfined compressive strength (UCS), nuclear magnetic resonance (NMR), and scanning electronic microscopy (SEM) tests. In addition, strength increase coefficient (ζ_s) and elasticity modulus increase coefficient (ζ_e) are defined to evaluate the effects of curing time on the mechanical property of MK‐based geopolymer cemented silty clay. Moreover, the relationships among porosity, UCS, and E₅₀ of MK‐cemented silty clay are studied. By incorporating 2% MK, the UCS and E₅₀ of MK‐cemented silty clay at 28 d are 1.32 and 1.30 times compared with MK0 group, respectively. The increase rate of UCS and E₅₀ from 1 d to 7 d is faster compared with that from 7 d to 28 d. Furthermore, the microstructure of the sample modified by 2% MK is most homogeneous and dense. Finally, the optimistic mass ratio between MK and cement is 2 : 13 for silty clay in this test condition.

The dynamic stress‐strain relationship of artificial frozen silty clay under one‐dimensional coupled static and dynamic loads is obtained using modified split Hopkinson pressure bar (SHPB) equipment. The variation in dynamic compressive strength, dynamic deformation modulus, energy dissipation, and failure mode of artificial frozen silty clay with axial precompressive stress ratio are studied in this research. Experimental results indicate that the dynamic stress‐strain curves under uniaxial state and one‐dimensional coupled static and dynamic loads can be divided into four stages, i.e., compaction stage, elastic stage, plastic stage, and failure stage. The dynamic compressive strength, first‐stage deformation modulus, second‐stage deformation modulus, and absorbed energy density of artificial frozen silty clay present a trend of first increase and then decrease with the increase of axial compressive stress ratio, and the axial compressive stress ratio corresponding to the peak value is 0.7 in this test. In addition, there is a very similar effect of axial precompressive stress ratio on dynamic compressive strength and second‐stage deformation modulus of artificial frozen silty clay. At 0.4 axial compressive stress ratio, spall phenomenon appears at circumferential direction and center position of the frozen soil specimen has no obvious failure. Shear failure appears at 0.7 to 0.9 axial compressive stress ratio, and the larger the axial compressive stress ratio applies, the more obvious the shearing surface appears; moreover, comminution failure mode appears at 1.0 axial compressive stress ratio.

Split‐Hopkinson pressure bar (SHPB) tests were conducted for sandstone after recurrent heat‐cool (H‐C) cycles. Physical and mechanical properties, damage, and fracture characteristics of sandstone after the H‐C cycle were explored. Additionally, the damage variable and release rate of damage strain were defined to describe the damage degree of the sandstone specimen after recurrent H‐C cycles. Finally, the relationship between mass fractal dimension of fragmentation and cycling number was discussed. Results show that the P‐wave velocity and density decrease with the increase of cycling number, while the porosity increases. It was found that the dynamic compressive strength and relative elastic modulus decrease with the increase of cycling number. 20 cycles is the critical point for the low temperature (L‐T) group and moderate temperature (M‐T) group, while it is 4 cycles for the high temperature (H‐T) group. With the increase of cycling number, both the damage variable and release rate of damage strain of rock increase, while the destruction degree of sandstone becomes greater, and the corresponding fragments show more evenly.

To investigate the coupling damage characteristics of rock after high-temperature treatment under impact load, dynamic uniaxial compression tests for deep sandstone specimen under laboratory conditions varying with high temperature (i.e., 25C, 100C, 300C, 500C, 700C, and 900C) and strain rate (i.e., 170s^-1, 205s^-1, and 240s^-1) were performed using splitting Hopkinson pressure bar (SHPB) system. Coupling damage variable of deep sandstone was deduced based on the Lemaitre equivalent strain theory. Moreover, the damage parameters of deep sandstone were systematically determined according to the test data, and the effects of high temperature and strain rate on damage growth curves were investigated. Finally, a dynamic compound damage constitutive model, which could consider the coupling damage, was established and verified to describe the dynamic mechanical characteristic of deep sandstone. Theoretical and experimental results indicated that the simulated stress-strain curves matched the test data well and the proposed coupling damage constitutive model could reflect the high temperature-induced weakening and strain rate strengthening effect.