Stress Wave Theory Research Articles

Frequency distribution of different joint slopes containing ceramic soil under seismic wave action

The dynamic response characteristics of high and steep slopes under the action of earthquakes and blasting was focused on, especially the frequency distribution and propagation laws, which are crucial for slope stability assessment. Using stress wave theory as the theoretical basis and advanced FLAC3D numerical simulation technology, we systematically analyze the frequency response of slope under different joint conditions under seismic waves. The nonlinear characteristics of reflected P-wave coefficient and the significant sensitivity of joint to incident wave frequency are revealed when the Angle of incident P-wave changes. The results show that with the increase of the incidence Angle of the incident P-wave, the reflection coefficient of the reflected P-wave decreases slowly at first and then increases sharply to 1.0. The reflection coefficient of the wave at the joint is more sensitive to the frequency of the incident wave. In a biplanar rock mass, multiple reflections of waves between structural planes produce transmitted waves with different time differences.

A novel experimental method for studying rock collision

This paper introduces a new experimental method for studying rock collision by making full use of the beauty of stress wave theory. In this method, a newly developed energy transmission component was placed between the gas gun and the transmitted bar of a split Hopkinson pressure bar (SHPB). The forementioned component consists of an incident bar which moves frictionlessly within a specified distance, a circular steel plate welded to the incident bar, and a support base which is bolted to the SHPB bed. A rock specimen is attached to the farther end of the incident bar. When the striker bar, propelled by the gas gun impacts the incident bar, a compressive stress wave is transmitted from the incident bar to the rock specimen. When the compressive wave arrives at the free end of the rock specimen, it is reflected into a tensile wave. Then when the pure stress becomes tensile and it is over the tensile strength of the glue at the interface between the rock specimen and the incident bar, the rock specimen is ejected, and then the ejected specimen will collide with the transmitted bar. During specimen flight, the velocity of the rock specimen can be measured by a laser instrument, while the remained energy transferred to the transmitted bar is measured by strain gauges attached to it. The process of rock specimen flight before collision and fragment flight after collision can be photographed using a high-speed camera. This experimental method can be used to not only study a collision between a moving rock and another object, but also imitate a drop weight test. By using this new method, seven rock collision tests were successfully conducted.

Research on a Honeycomb Structure for Pyroshock Isolation at the Spacecraft–Rocket Interface

Honeycomb is a splendid kind of structure for aerospace engineering with the advantages of light weight, good shock absorption, and good structural stability. This article aims to provide methods to isolate Pyroshocks based on a honeycomb structure and guarantee the safety of such equipment against a high-frequency shock response. According to stress wave theory, an equation for stress wave transmittance of the honeycomb structure is derived considering the effect of cell wall length and thickness, where desirable honeycomb parameters are obtained. The complexity of the transfer path of the honeycomb structure is exploited to build the spacecraft–rocket interface, which could increase the impedance of the stress wave dramatically. Both finite element analysis and experiments are carried out to validate the shock isolation strategies. The influence of parameters, such as cell wall length and the thickness of the stainless-steel honeycomb, on the isolation performance is analyzed. It is revealed that the honeycomb structure has a significant effect on Pyroshock isolation performance when the wall length of the honeycomb cell is 8 mm and the thickness of the cell is 0.1 mm.

High-impact dynamic loading method for calibration of triaxial acceleration sensors

Abstract In this study, a high-impact dynamic loading device was designed to generate a three-dimensional pulse excitation signal with high intensity shock acceleration and achieve triaxial synchronous calibration of a triaxial acceleration sensor. A light-gas gun interior ballistic model and a sensor mechanical response model were developed, and the relationships between the bullet impact velocity, barrel length, and initial chamber pressure were obtained. Additionally, the transformation relationship of the sensor’s triaxial acceleration in different coordinate systems was derived. Based on the stress wave theory and the finite element method, the influence of the bullet impact velocity on the variation pulse, and different slope and deflection angles on the triaxial acceleration were analyzed. By optimizing the parameter design, machining the prototype, and conducting high-impact dynamic loading tests, the results showed that the deviation between theoretical and measured values of the generated triaxial acceleration signal was small, and the maximum deviation was less than 4%. This indicated that the proposed high-impact dynamic loading device satisfied the calibration requirements for calibrating triaxial acceleration sensors, which can generate a three-dimensional acceleration with a peak value of not less than 700 000 m s−2.

Rock-like material under large diameter SHPB dynamic splitting tension: meso-damage mechanical behavior and stress wave propagation model

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.

Exploring Dynamic Spalling Behavior in Rock–Shotcrete Combinations: A Theoretical and Numerical Investigation

Spalling is a widespread dynamic disaster during blasting excavation in underground engineering. To clarify the coupled dynamic response and spalling behavior of an underground tunnel with a spray anchor, an investigation based on the rock–shotcrete combination was conducted using theoretical and numerical methods. The mathematical representation of stress wave propagation between rock and shotcrete was deduced based on the elastic stress wave theory. A novel method for predicting the location and time of initial spalling in a rock–shotcrete combination was proposed. A numerical simulation was conducted to verify the validity of the proposed theoretical method. In addition, the effect of the material’s tensile strength, the loading amplitude, and the thickness of shotcrete on the stress evolution and spalling characteristics was studied. The results demonstrate that the initial spalling locations are sensitive to the relationship between the normalized tensile strength of the rock, shotcrete, and interface. A high incident amplitude can cause the initial spalling in rock, and the shotcrete or rock–shotcrete interface can cause initial spalling due to a low incident amplitude. The stress evolution and spalling characteristics are sensitive to the thickness of shotcrete. The location of the initial spalling failure changes with the thickness of the shotcrete. An appropriate increment in thickness and normalized strength of the shotcrete is beneficial to the dynamic stability of underground engineering.

Experimental Study on Dynamic Tensile Mechanical Behavior and Fracture Mechanical Characteristics of Sandstone with a Single Prefabricated Fissure

The structural stability of engineering rock mass under dynamic disturbance is directly associated with the fracture mechanics properties in engineering practice. Fully understanding the rock’s fracture mechanical behavior and crack evolution caused by stress concentration at the crack tip in engineering rock mass under dynamic load can offer useful insight into the rock’s dynamic fracture mechanism. A dynamic test using split-Hopkinson pressure bar (SHPB) test system was performed on a single prefabricated fissure sandstone centrally cracked Brazilian disk (CCBD) specimens. Based on the theory of fracture mechanics and one-dimensional stress wave theory, the dynamic crack initiation criterion of CCBD specimen is proposed, and the regression model of sandstone’s dynamic fracture toughness under the coupling effect of fissure angle and strain rate is established by using response surface methodology (RSM). The influence of strain rate and fissure angle on stress wave characteristics, dynamic tensile mechanical behavior, and fracture mechanics characteristic was investigated in this study. The findings demonstrate that: (1) The fissure angle plays a pivotal role in determining the failure mode of sandstone. As the fissure angle increases, three distinct failure modes emerge in the sandstone specimens, while variations in strain rate have minimal impact on the fracture mode of these specimens. (2) Alterations in the fissure angle result in changes to the waveform of transmitted waves. When the fissure angle is below 30°, the transmitted wave exhibits “double peak” characteristics; when it exceeds 30°, a “single peak” waveform is observed. This phenomenon can be attributed to diffraction principles governing incident waves. (3) When the impact pressure is 0.2 MPa, the peak load initially exhibits an increase followed by a decrease, with the peak load reaching its maximum at a fracture angle of 60°; when the impact pressures are 0.3 and 0.5 MPa, there exists a negative correlation between the peak load and the fissure angle. (4) The influence of strain rate on sandstone’s fracture resistance is predominant, with alterations in fissure angle exerting an auxiliary effect on this property. The research results can provide a theoretical and experimental basis for dynamic disaster prevention in urban underground space.

Dynamic crushing behaviors and failure of cylindrical lithium-ion batteries subjected to impact loading

The mechanical property and failure prediction play a significant role in engineering applications of lithium-ion batteries (LIBs), but with great difficulties due to their complicated internal structures. This paper mainly focused on dynamic crushing behaviors and internal failure mechanisms of cylindrical LIBs subjected to different impact loadings for the safety assessment and protection design. A series of dynamic experiments were conducted on typical 18650 LIBs using the drop weight impact test system. The force-electric-thermal responses and impact failure modes of the cells with state of charge (SOC) dependence were experimentally explored under different impactor types. The finite element (FE) model was also established to reveal the failure mechanisms of the battery under high-velocity impact, and its accuracy was validated by the comparison between the experimental and corresponding FE results. Furthermore, the dynamic failure mechanisms of cylindrical cells using the stress wave theory were also explored in this work. It was shown that except from impact velocities, there were significant effects of the SOCs and impactor types on dynamic responses and internal failure modes of LIBs. The failure displacement of the cell will decrease with the increase of impact velocity, but it was insensitive under low-velocity crushing. Based on the FE results, the relationships between failure displacement and impact velocity and impactor diameter were established under flat-end cylinder head impacting. This work can provide some references for multi-functional dynamic integrity design and safety assessment of LIBs.

Performances of fissured red sandstone after thermal treatment with constant-amplitude and low-cycle impacts

In the engineering practices, it is increasingly common to encounter fractured rocks perturbed by temperatures and frequent dynamic loads. In this paper, the dynamic behaviors and fracture characteristics of red sandstone considering temperatures (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and fissure angles (0°, 30°, 60°, and 90°) were evaluated under constant-amplitude and low-cycle (CALC) impacts actuated by a modified split Hopkinson pressure bar (SHPB) system. Subsequently, fracture morphology and second-order statistics within the grey-level co-occurrence matrix (GLCM) were examined using scanning electron microscopy (SEM). Meanwhile, the deep analysis and discussion of the mechanical response were conducted through the synchronous thermal analyzer (STA) test, numerical simulations, one-dimensional stress wave theory, and material structure. The multiple regression models between response variables and interactive effects of independent variables were established using the response surface method (RSM). The results demonstrate the fatigue strength and life diminish as temperatures rise and increase with increasing fissure angles, while the strain rate exhibits an inverse behavior. Furthermore, the peak stress intensification and strain rate softening observed during CALC impact exhibit greater prominence at increased fissure angles. The failure is dominated by tensile damage with concise evolution paths and intergranular cracks as well as the compressor-crushed zone which may affect the failure mode after 400 °C. The second-order statistics of GLCM in SEM images exhibit a considerable dependence on the temperatures. Also, thermal damage dominated by thermal properties controls the material structure and wave impedance and eventually affects the incident wave intensity. The tensile wave reflected from the fissure surface is the inherent mechanism responsible for the angle effect exhibited by the fatigue strength and life. Ultimately, the peak stress intensification and strain rate softening during impact are determined by both the material structure and compaction governed by thermal damage and tensile wave.

Impact-resistance mechanism of gradient ceramic/high entropy alloy composite structure

The gradient ceramic/high-entropy alloy (HEA) composite combines the high hardness of ceramics and the high toughness of metal alloys with a gradient spacious distribution. It is designed to improve the penetration resistance as a promising protective material with high specific stiffness and strength. In this work, the equivalent model of gradient ceramic/HEA composite material is established by adopting layered structure design, and the material properties of gradient material with different ceramic volume content are calculated. Combined with stress wave theory and numerical simulation of the separated Hopkinson pressure bar, the stress wave propagation under impact is studied for the gradient ceramic/HEA composite and the ceramic/HEA double-layered material. The anti-penetration mechanism is scrutinized. The interlaminar wave impedance increase gradually in the gradient composite but smaller than in double-layered material. The coefficient of reflected stress wave in the gradient composite is much smaller than that of the double-layered material. With the increment of ceramic volume content, the reflected wave amplitude in the gradient composites gingerly decreases. Opposed to the distinct interlayer interfaces that discontinue stress waves in the double-layered material, the internal interface of the gradient composite is much more tranquil and modulate the stress wave smoothly and synchronically with the gradient of composite. The smoothened internal interface is the key and the mechanism the better impact resistance of the gradient material. Our results might be beneficial in material design of the protective materials for impact resistance.

Research on visualisation of plain concrete crack depth detection based on tracer and hand-held radar

ABSTRACT Detecting the concrete crack depth has always been a technical problem. The traditional detection methods，which are based on stress wave theory, have limitations such as low accuracy, complex operation, time-consuming and laborious procedures. This paper proposes a new method based on the combination of tracer and hand-held radar to better complete this task. Its main procedures include firstly spreading tracer diffusion to the bottom of the crack propagation, and then mapping the location of the air-tracer interface by radar waves, thus visualising the crack depth information. This paper elaborates the detection principle of this new method, carried out the feasibility numerical analysis and simulation verification. Also, the concrete standard crack specimens were made, together with relevant experimental researches. As to the feasibility of the method, it is verified by using common distilled water and saturated sodium chloride solution as tracers. The detection effects of these two tracers are compared and analysed by comparing the test data with the actual depth of the specimen. This research innovatively applies tracers to actively improve the electrical ability of concrete cracks, and then uses radar to detect the electrical distribution of cracks, realising the visual detection of crack depth.

The energy dissipation mechanism of bi-metal Kevlar\ itanium fiber metal laminate under high-velocity impact

Fiber Metal Laminate (FML) is an impact resistant material widely used in marine and aerospace engineering structures that need to withstand impact damage, especially deck and bulkhead structures. To investigate the effect of titanium skin on energy dissipation, a series of ballistic impact experiments were performed on a bi-metal FML in this study. The FML were made of Ti–6Al–4V (TC4) skins and orthogonally woven Kevlar-129 fabric impregnated with E54-epoxy resin. Thus, this FML can be also called as bi-metal Kevlar/titanium FML. In addition, a numerical model based on stress wave theory is proposed to study the energy dissipation mechanism of the bi-metal FML under high-velocity ballistic impact. The residual ballistic velocity of the numerical model is verified by the experimental data in this paper and previous experimental data, showing that the numerical model is a more efficient method to analyze the energy dissipation mechanism of bi-metal FML. According to the numerical results, as the dominant energy dissipation, the perfectly inelastic collision of titanium skins dissipated 43%–62% and 17%–27% of total energy at the high-velocity penetration and ballistic limit, respectively. However, regardless of whether the FML has been penetrated, the compression-shear of Kevlar interlayer dissipated 24%–27% of total energy. Furthermore, the numerical calculations also show that the ballistic limit increases approximately linearly with the relative titanium skin thickness when the front titanium skin of the FML is thicker. Finally, this paper proposes a simple specific energy absorption prediction formula that helps to evaluate the energy dissipation capacity of FML.

Effect of polyurea coating with different mechanical properties on blast resistance of aluminum alloy circular tube structures: Experiments vs numerical simulations

Polyurea has attracted extensive attention in the field of anti-blast protection over the past few years. Two types of polyurea were prepared and their quasi-static and dynamic mechanical properties were examined to investigate the effect of polyurea coating with different mechanical properties on the blast resistance of the metal circular tube structure. A set of automatic spray equipment was designed and manufactured to spray polyurea efficiently on the circular tube structure. On that basis, the anti-blast test was performed using the two types of polyurea coated on the surface of 6063-T5 aluminum alloy circular tubes with different thicknesses. The macro and micro damage characteristics of polyurea coated aluminum tubes were obtained using the field tests, the metallographic microscope and the scanning electron microscope (SEM) technology. Numerical simulation models were built to elucidate the dynamic response process. The results suggest that polyurea is capable of significantly enhancing the blast resistance performance of the aluminum alloy circular tube. In contrast, polyurea with better energy absorption effect under high dynamic load may not exhibit higher protective efficiency. Whether the polyurea and the aluminum tube can always maintain the adhesion relationship and deformation together under the action of blast has been confirmed as a vital factor. Lastly, the energy absorption mechanism and influence mechanism of different kinds of polyurea were revealed using the Fourier Transform Infra-Red (FTIR) technology in accordance with the stress wave theory.

Loading measurement for intermediate strain rate material test based on dynamic oscillation

Loading measurement is one of the critical components of mechanical tests. Different technologies are applied for loading measurement at different spans of time and space. In the past century, the quasi-static hypothesis has been widely applied for low-speed loading conditions (strain rate < 1/s), and the stress wave theory has been applied for high-speed loading conditions (strain rate > 1000/s). However, so far, the feasibility of the quasi-static and stress wave approaches for loading measurement is questionable under intermediate strain rate loading conditions (1 000/s > strain rate > 1/s).For quasi-static approach, the signal ringing (caused by dynamic oscillation) is the main problem that hinders the accuracy of the loading measurement with the increment of strain rate. In this present study, in order to tackle the ringing signal obtained from the intermediate strain rate material test, a signal recognition algorithm was introduced, named the semi-period perturbation algorithm (SPPA). As SPPA is based on the first-order spring-mass oscillatory model, the corresponding test method for intermediate strain rate test was called single-mode method (SMM). To satisfy the basic hypothesis of SPPA, the corresponding load cell and material specimen was designed. Through modal analysis and dynamic simulations, SPPA and the load cell-specimen assembly were proved effective in restoring the loading signal from the ringing signal. Based on the high-speed tests of 6061 aluminum alloy and Q235 steel, and compared with the preponderant material test approach based on SEP 1230/ISO 26,203–2 sample, the SMM was proved effective in the loading measurement of intermediate strain rate tests. What's more, based on the accessibility of the test design and the simplicity of the data processing procedure of SMM, this method exhibited great application potential for similar mechanical scenarios of impact tests.

Stress wave propagation characteristics and impact resistance of laminated composites under impact loading

SHPB simulation of TC4/2024AL/TC4, TC4/TA2/TC4, and TC4/Al3Ti/TC4 laminated composites under different impact velocities of strike bar was carried out by ANSYS/LS-DYNA. Then stress distribution of the laminated composites under impact loading was theoretically analyzed according to the one-dimensional stress wave theory. Influencing factors of stress distribution and energy attenuation were emphatically analyzed, including impact velocities of the strike bar, wave impedance of interlayer, and plastic deformation. The results show that, when the impact velocity is determined, impact resistance is negatively correlated with the impedance of the interlayer. Under certain conditions, impact resistance is negatively correlated with impedance of interlayer, and positively correlated with impact velocity. In addition, the accumulation of plastic deformation could make residual stress distribution along the position coordinate axis shows a trend of gradual increase from both sides to the middle position.

Stress wave propagation through a 180° bend junction in a square cross-sectional bar

• Longitudinal stress wave can flow through a 180° bend as if it were a straight rod. • Long duration waves can be recovered without distortion after navigating the bend. • 1-D wave propagation principles successfully describe the phenomena for long waves. • Flexural waves are generated at the junction due to asymmetric deformation. • The junction behaves as a low pass filter and can be used to shape the pulse. Longitudinal elastic stress wave propagation through a 180° bend junction connecting two square bars is analyzed using analytical and numerical approaches and validated against experiments. The aim is to identify conditions under which the one-dimensional stress propagation principles can be applied to this geometry despite complete reversal of the stress wave path and study the mechanism of wave propagation through this geometry. By assuming the junction to move as a rigid body parallel to the input wave direction, the influence of the bend is analyzed for different pulse shapes and durations. For long duration stress pulses, the bend allows the stress wave to “flow” through the junction without distortion, whereas for short duration stress pulses, the wave undergoes significant dispersion. The junction behavior was further analyzed using finite element analysis and the results compared well with those of the analytical model. The wave motion through the junction results in asymmetric deformation of the junction, which generates flexural waves of different amplitudes in both the input and output bars. In general, stress pulses with constant peak amplitude and a smooth transition to the peak value suffer minimal dispersion as they traverse the junction. It is concluded that one-dimensional stress wave theory can be used to successfully model the propagation of long-duration longitudinal stress pulses around a 180° bend junction.

Study on the Combined Effect of Inclined Natural Fracture and Water Jet Slot on the Blast-Induced Crack Propagation Law

For the purpose of uncovering the influence law on the explosion stress wave transmission and blast-induced crack propagation by inclined natural fracture and water jet slot, the influential mechanism for the transmission law of explosion stress wave due to inclined natural fracture was analyzed based on stress wave theory in this article. Next, the evolution law of explosion stress wave and blast-induced crack propagation affected by inclined natural fracture and water jet slot were simulated by ANSYS/LS-DYNA, and an experiment was conducted to understand the crack propagation law under explosion shock wave loading. The results indicate that the existence of inclined natural fracture will affect the “guiding effect” of water jet slot on blast-induced crack propagation by changing the propagation path and mechanical properties of the explosion stress wave. When the distance between inclined natural fracture and blast hole is too small, the water jet slot cannot play a guiding role in propagation process of blast-induced main crack. With the increase of the distance, the propagation direction of blast-induced crack is affected by both inclined natural fracture and water jet slot. When the distance increases further and exceeds a certain value, inclined natural fracture cannot affect the guiding effect of water jet slot in propagation process of blast-induced main crack.

Peridynamic investigation of dynamic damage behaviors of PBX confined in spherical steel shells

The bond-based peridynamics (PD) modeling is employed to investigate the dynamic damage response of polymer bonded explosive (PBX) confined in spherical steel shells under impact loading. The softening behavior of PBX is reasonably well captured by a bilinear constitutive model defined for PD bonds. The simulation results indicate that the damage behaviors of PBX depend on the impact speed. At the low impact speed, the damage of PBX is characterized by the absence of the longitudinal cracks. In contrast, the presence of longitudinal cracks leads to the serious damage of spherical shell of PBX at the high impact speed. The dynamics of stress wave such as reflection and transmittance at the solid boundary are analyzed based on the stress wave theory, providing a comprehensive understanding of how the external confinement affects dynamic damage response of PBX. The effects of Young's modulus of steel shells on the damage of PBX are also examined. The simulation results illustrate that the damage of PBX depends on the property of the external steel shell, but is almost independent on the property of the internal steel shell. These interesting phenomena can be well understood based on the dissipation of impact energy of the flyer. The presented computational results offer rigorous basis for the full understanding of the dynamic damage response of PBX in the more complicated confinement conditions.

Theoretical analysis of the deformation for steel gas pipes taking into account shear effects under surface explosion loads

Ground blast loads are of great importance to the safe operation of steel and gas pipelines, and the results obtained from traditional theoretical formulas for pipeline safety prediction are in error with the actual measured data. In this paper, full-size field tests and corresponding numerical simulations are carried out using Timoshenko beam theory and explosion stress wave theory, which consider shear effects. At the same time, combined with the theory of foundation stiffness and pipeline stiffness flexibility ratio, a modified theoretical model is obtained in line with the actual conditions of the site, which can accurately calculate the deformation and displacement of pipeline underground explosion load, and greatly reduce the error of theoretical prediction results. The innovation of the research results in this paper is that the theoretical stress in the Timoshenko beam can be replaced by the circumferential strain. On the other hand, the modified theoretical solution can obtain the critical weight of explosives to prevent pipeline damage at different buried depths. It provides a theoretical basis for the protection of pipelines’ underground blast loads and provides research ideas for the safe protection and design of pipelines.

Influence of blasting load directions on tunnel stability in fractured rock mass

Tunnels in fractured rock masses are typically damaged by dynamic disturbances from various directions. To investigate the influence of blasting load directions on the stability of a tunnel with a pre-crack nearby, blasting tests were conducted on the physical models of an external crack around a tunnel (ECT) in this study. Failure modes of the tunnels were analysed based on stress wave theory. The Riedel–Hiermaier–Thoma (RHT) material model was employed to perform the numerical simulations on ECT models. Stress distribution around the tunnels and final failure patterns of the tunnels were characterised. The results show that, under blasting loads, the pre-crack propagates and then new cracks initiates on the incident side of the tunnel. These cracks extend towards each other and eventually coalesce. Blasting load directions significantly influence the ultimate failure mode of the tunnel in the fractured rock masses. The new cracks on the shadow side of the tunnel appear at different positions when the blasting stress waves come from various directions. The results are meaningful to the analysis of tunnel stability and optimisation of the tunnel support scheme.