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Stabilizing the surrounding rock provides an important environmental safeguard for tunnel blasting. To investigate the damage characteristics and rupture mechanism of the surrounding rock in long-distance tunnels under cyclic explosive loading, it takes the in-situ surrounding rock and rock samples of diversion tunnel underneath the highway as the study object. The impact splitting test was carried out with the SHPB test system. It revealed the mechanical behaviors and energy evolution characteristics of the rock body. It is also introduced the 4D ultra-high-definition imaging technology of the mine roadway to further analyze the in-situ fissure expansion mechanism of the tunnel peripheral rock under the cyclic explosive loading. The results show that: ① The splitting stress-strain curves of granite and tuff under impact splitting are different from the “stress yield” characteristic of impact compression. But they have the “residual stress” characteristics. The peak stress and dynamic growth factor DIF show a positive linear growth trend; The strain time curve does not exhibit the characteristic of “later reduction” deformation during impact compression. It exhibits the characteristic of “later stability” deformation as an elastic brittle material. ② The rock mass impacting energy - time curve undergoes an evolutionary stage of “initial slow growth - fast linear growth - later stable”. The energy conversion ratio of the rock mass under the same impact energy level satisfies the following conditions: reflected energy ratio > dissipated energy ratio > transmitted energy ratio; The overall damage and failure of the rock mass exhibits a state characteristic of “central splitting + loading end crushing → central splitting + loading end crushing + semi circular fracture → overall crushing”. ③ A peephole imaging test combining “less domains and more tests” and “more domains and less tests” is proposed. The crack propagation characteristics of the in-situ surrounding rock hole wall are mainly manifested in following evolutionary stage: “microcrack development → crack propagation → slow propagation → stop extension”. There is no significant phenomenon of fragmentation detachment and further inward extension. ④ The observation results of the D1 hole of the top pipe tunnel at the foot of the mountain and the D2 hole of the Shancha maintenance tunnel have verified the good boundary control blasting effect; The impact splitting results of rock samples taken from the original site of the tunnel provide an effective theoretical basis and reference for the design of pre blasting drilling and blasting schemes.

An in-depth understanding of the mechanical properties and damage and fracture mechanism of selected rocks in a diversion tunnel plays an important role in promoting the efficient construction and safety of rock blasting excavation in a diversion tunnel. To study the mechanical properties and damage evolution characteristics of selected rocks in diversion tunnels under uniaxial loading, the uniaxial compression and uniaxial splitting tests of granite and tuff were carried out. In terms of mechanical properties, the evolution characteristics of complete stress-strain curves, instantaneous modulus-strain curves, and input energy density-strain curves were analyzed. In the aspect of damage characteristics, the macroscopic and mesoscopic failure modes were analyzed and the damage fracture mechanism was revealed. Compression-shear failure mainly occurred in granite and tuff under uniaxial compression, showing the characteristics of elastic-brittle fracture failure. Both granite and tuff showed a failure mode of coexistence of “compression-shear failure zone at the loading ends” and “tension-shear failure zone in the middle” under uniaxial splitting. The compression-shear fracture of granite was relatively smooth, and the matrix and mineral particles produced fine particles due to friction in the process of shear slip. The compression-shear fracture of tuff was relatively rough and the characteristics of shear slip were not prominent enough. The fracture failure of granite and tuff was mainly caused by the common fracture of rock matrix and mineral particles. Based on the Lemaitre equivalent strain principle, the pre-peak-post-peak two-stage damage constitutive model established by Weibull statistical distribution theory can accurately describe the static stress-strain relationships of granite and tuff under uniaxial compression.

The mechanical behavior of splitting tensile damage and the law of stress wave propagation of rock-like materials (RLM) are of great significance to further reveal the dynamic disaster mechanism of the deep rock mass. The meso-damage mechanical behavior and stress wave propagation characteristics of RLM disks under impact splitting were studied by using a large diameter split Hopkinson pressure bar (SHPB). In terms of dynamic damage, the splitting tensile stress-compression strain curves of RLM disks obviously showed three stages of mechanical behavior evolution: initial elastic-plastic deformation, pre-peak plastic damage, and post-peak brittle fracture failure. The macro-damage of RLM disks increased with the increase of strain rate. The meso-tensile fracture was the result of both the initial meso-damage and the impact splitting meso-damage. The dynamic splitting damage variable defined based on the damage fracture energy can accurately describe the damage evolution characteristics of impact splitting on RLM disks. In the aspect of stress wave propagation, the peak value of transmission stress showed an advanced effect with the increase of incident stress wave. In the early stage (0–50 μs), the transmission stress wave ratio (σT/σI) increased with the increase of strain rate, while in the later stage (82–200 μs), the transmission stress wave ratio (σT/σI) decreased with the increase of strain rate. The stress wave propagation law in the process of impact splitting on RLM disks was clearly revealed based on the stress wave propagation model established by the one-dimensional elastic stress wave theory. Finally, the dynamic mechanical mechanism of splitting damage and fracture of RLM disks under different strain rates was discussed deeply.

To explore the dynamic compression behavior and damage evolution characteristics of “rigid-flexible coupling” surrounding rock supporting structure. Split Hopkinson pressure bar (SHPB) was used to carry out constant amplitude cyclic bi-directional impact compression tests on the combination specimens of “rigid-rigid: rock (sandstone)-like material (RLM) - normal cement mortar (NCM)'', “rigid-flexible: RLM - rubber cement mortar (RCM)'' and “flexible-rigid: RCM - high-performance supporting concrete (HPSC)''. The characteristics of stress-strain curve evolution, stress attenuation, strain growth, energy transformation, damage evolution characteristics, and damage state were compared and analyzed. The results show that compared with RLM-NCM, RLM-RCM and RCM-HPSC had remarkable dynamic yield ductility and excellent impact resistance. RCM and HPSC can work together to hinder the dynamic damage development of “rigid-flexible coupling” supporting structure and surrounding rock. Based on the one-dimensional stress wave propagation theory, the stress wave propagation models of rigid-flexible combination specimens under SHPB cyclic bi-directional impact were established, and the corresponding stress wave propagation equations were derived, which profoundly revealed the propagation law and attenuation mechanism of stress waves in SHPB impact rigid-flexible combination tests. Finally, based on the energy drive theory and residual energy theory, the impact instability energy criteria of surrounding rock under the rigid component combined support system and “rigid-flexible coupling” component combined support system were analyzed and discussed.

To promote the application of rubber-cement composites as the main bearing structure and key components in practical engineering under frequent dynamic disturbances, in this work, the split Hopkinson pressure bar (SHPB) cyclic impact tests of rubber-cement composite specimens with four different confine modes were carried out in which the impact load increased sequentially. The relationship between average strain rate, ultimate strain and impact times and the relationship between peak stress, damage energy, ultimate strain and incident energy were analyzed. The results showed that the appropriate confine reinforcement treatment can make rubber-cement composite give full play to its deformation ability when it was completely damaged. Carbon fiber-reinforced polymer (CFRP) sheet and steel cylinder can work together with the rubber-cement composite matrix to resist impact load, which effectively improves the structural strength, damage fracture energy, and cyclic impact resistance of the rubber-cement composite. Finally, based on the effect difference of confine modes, the simplified plane force models of rubber-cement composite specimens with four different confine modes were established, which clearly revealed the completely different impact resistance mechanism of the rubber-cement composites with different constraints under cyclic impact loading.

Improper disposal of waste tires will not only bring environmental impact and safety risks but also cause a serious waste of resources. In the field of civil engineering materials, waste tire particles are used as a substitute for non-renewable aggregates to produce flexible rubber-cement composites (RCC). To explore the high-speed slicing stability of RCC, this test took normal cement mortar (NCM) and rubber cement mortar (RCM) as research objects. The SHPB tests with the same impact energy level and the high-speed slicing tests with a slice thickness range of about 1.4 mm ~ 4.4 mm were carried out. The results showed that NCM and RCM showed different stability differences in the process of high-speed slicing. In the case of ensuring the integrity of the slice, the minimum thickness of the slice can be better decreased with the increase of the rubber content. Finally, from the perspectives of split Hopkinson pressure bar (SHPB) test results and mesoscopic structure states, the essential reason for ensuring the stability of high-speed slicing lied in the improvement of rubber particles (dominant role) and pores on material deformation and flexible energy dissipation.

The recycling of waste tire rubber resources and its application in the field of civil engineering materials have the importance of the economy, environmental protection, and promoting the development of civil engineering materials. In this work, rubber cement mortar short-column was used as the research object, and the cyclic loading-unloading tests with finite cycles were carried out under three different loading modes (I, II, and III). A series of basic characteristics of rubber cement mortar under three different cyclic loading-unloading modes were further discussed and analysed, such as energy, deformation, damping ratio, failure mode mechanism, and crack development mechanism. The results showed that when the rubber content was 30%, the energy damage was reduced by 13.7 ~ 45.7%, and the cumulative damping ratio was increased by 57.0%. The evolution characteristics of the hysteresis loops in the loading-unloading curves in the form of ''non-closed crescent'' were explained. The development mechanism of cracks based on the principle of minimum energy was revealed, and the evolution characteristics of cracks were confirmed. The crack resistance effect of rubber cement mortar was explained by the property of damping energy dissipation of rubber particles. The purpose is to better apply rubber-cement composites to seismic structures, underground structures, and road engineering.

In order to obtain the relationship between fractal dimension and energy dissipation of rock-like materials under initial stress state, a variable cross-section split Hopkinson pressure bar (SHPB) test system with active confining pressure loading device was used to carry out impact compression and splitting tests on cemented sand specimens. The impact test results show that (1) the prediction value on the fragmentation degree of cemented sand specimens by using the fractal model is basically consistent with the screening results of actual test, which verifies the applicability of the fractal calculation model given in this study; (2) the more the fracture energy dissipated in the crushing process of cemented sand specimens, the more serious the fragmentation degree is, and accordingly the larger the fractal dimension is, that is, the fracture energy is positively correlated with the fractal dimension; (3) there is an exponential relationship between the fractal dimension and energy dissipation of cemented sand specimens under initial stress, which is so different from that under no initial stress. The experimental results in this study can be used to modify the fractal damage model for rock blasting considering the initial stress.

The damage degree and fracture mechanism of the rock are important to the bearing performance of the rock mass and the stability of the overlying structure. Most of the existing damage models for characterizing rock damage exclude the range of postpeak stress or do not consider the compaction and closure stage of the fracture, and the description of the quantitative damage of sandstone is not accurate enough. In addition, the description of the rock fracture mechanism under load is not exact enough. Aiming at the problem of quantitative damage and fracture mechanism of the loaded rock, this paper adopts acoustic emission (AE) to monitor the loading process of sandstone under uniaxial loading. In accordance with the characteristics of the AE signal, the loading stage of sandstone under uniaxial load is divided into three stages: initial hit stage, hit stability stage, and hit instability stage. By modifying the traditional damage model and combining the AE signals of the sandstone under the load, a modified damage mechanics model is obtained, which can fully express the entire loading stage. Furthermore, through the analysis of AE signals, the fracture mechanism of sandstone under uniaxial load is studied. The results show that the modified damage model can quantitatively describe the damage at different loading stages which include two areas including the fracture compaction closure stage and the postpeak stress stage. The failure and instability of sandstone under uniaxial load is mainly shear failure. The research results can provide a reference for the nondestructive testing of sandstone and engineering reliability in geotechnical engineering.

An in-depth understanding of the pre-peak mechanical damage and energy-evolution characteristics of typical hard-rock in a diversion tunnel under cyclic load is of great significance to promote the safe and efficient construction of the diversion tunnel and the stability of surrounding rock. To study the pre-peak mechanical characteristics and the competition mechanism between energy storage and energy dissipation of typical hard-rock in a diversion tunnel under cyclic loading-unloading, combined with the internal drilling and blasting excavation of the actual engineering rock mass and the external vehicle cyclic load environment of the diversion tunnel, the cyclic loadingunloading tests of typical granite and tuff in diversion tunnel were carried out. Based on the analysis principle of mechanics and energy, the strain variables, modulus variables, energy variables and damage variables of granite and tuff under cyclic loading-unloading test were defined. The cyclic mechanical properties and energyevolution characteristics of granite and tuff under pre-peak load were analyzed. The competition mechanism between pre-peak energy storage and pre-peak energy dissipation of granite and tuff and the evolution law of strain damage variable and energy damage variable were revealed. The selection principle of rock sample size and the limitation of the test scheme were further discussed. The study of the damage evolution of rocks close to failure (pre-peak stage) under cyclic load is helpful to better understand the damage and failure mechanism of rocks in practical engineering problems. [ABSTRACT FROM AUTHOR]