Compressive Damage Research Articles

Multiple-stage dynamic responses and failure behaviors of surrounding rocks subjected to development blasting: Exponential and triangular paths

During the development blasting of circular tunnels, the detonation of multiple blastholes arranged on concentric circles induces a complex dynamic response in the surrounding rocks. This process involves multiple blast loadings, static stress unloadings, and stress redistributions. In this study, the dynamic stresses of the surrounding rocks during development blasting, considering multiple blasting-unloading stages with exponential paths and triangular paths (linear simplified paths of exponential paths), are solved based on the dynamic theory and the Fourier transform method. Then, a corresponding discrete element model is established using particle flow code (PFC). The multiple-stage dynamic stress and fracture distribution under different in situ stress levels and lateral coefficients are investigated. Theoretical results indicate that the peak compressive stresses in the surrounding rocks induced by both triangular and exponential paths are equal, while the triangular path generates greater additional dynamic tensile stresses, particularly in the circumferential direction, compared to the exponential path. Numerical results show that the exponential path causes less dynamic circumferential tensile damage and forms fewer radial fractures than the triangular path in the first few blast stages; conversely, it exacerbates the damage and instability in the final blast unloading stage and forms more circumferential fractures. Furthermore, the in situ stress determines which of the two opposite effects is dominant. Therefore, when using overly simplified triangular paths to evaluate the stability of surrounding rocks, potential overestimation or underestimation caused by different failure mechanisms should be considered. Specifically, under high horizontal and vertical stresses, the static stress redistribution with layer-by-layer blasting suppresses dynamic circumferential tensile and radial compressive damage. The damage evolution of surrounding rocks in multi-stage blasting under different in situ stresses is summarized and classified according to the damage mechanism and characteristics, which can guide blasting and support design.

Enhancing the Durability of Pre-Cracked Concrete: The Crucial Role of Metakaolin and Ground Granulated Blast Furnace Slag

This study conducted a rigorous experiment to assess the strength and durability of pre-cracked concrete modifiedwith metakaolin (MK) and ground granulated blast furnace slag (GBFS). Three categories of hardened concrete werecompared to conventional concrete, focusing on key parameters such as compressive strength, mass loss, openporosity, water penetration, capillary water absorption, and drying shrinkage. The assessments were performed undertwo levels of compression damage and exposure to sulfuric acid (5% concentration). The results demonstrated asignificant long-term improvement in compressive strength by incorporating MK and GBFS, despite a reduction of upto 80% in the presence of sulfuric acid. The F10 formulation exhibited the best performance, highlighting the positiveimpact of additives on concrete durability. Replacing cement with MK and GBFS at a 10% level was identified as theoptimal design for sewer structures due to minimal shrinkage compared to other formulations.

Assessment of the properties of interface-modified bamboo aggregates for sustainable concrete construction

To alleviate the serious loss of gravel resources, reduce carbon emissions and improve the sustainability of concrete materials, this study presents an innovative approach to develop a novel eco-friendly bamboo aggregate concrete. The proposed method involves utilizing the abundant and renewable Phyllostachys edulis (Moso) bamboo to create a new type of bamboo aggregate, as a substitute for conventional gravel aggregates. This study modified the bamboo surface using a composite effect of epoxy mortar and polyurethane adhesive to realize the direct application of bamboo aggregates. Compared to unmodified and polyurethane-modified bamboo, epoxy mortar-modified bamboo showed significantly improved physical and mechanical properties. Anti-corrosion properties tests revealed that the modified bamboo, especially epoxy mortar-modified bamboo, was less affected by acidic and alkaline corrosion than the unmodified bamboo and the mass loss rate was almost zero. In the early stages of alkaline corrosion, the strength of the bamboo increased, and then began to decrease after 28 d. The removal of the outer green bamboo significantly improved the adhesion of the adhesive to the bamboo surface, as confirmed by pull-out tests. A sufficient bonding area between the epoxy mortar-modified bamboo and the cement matrix remained after compression damage, whereas obvious debonding behavior between the cement matrix and unmodified and polyurethane-modified bamboo was observed. In summary, epoxy mortar modification significantly improved the comprehensive performance of bamboo aggregates. This study is expected to help improve the utilization rate of bamboo, promote bamboo concrete, and develop sustainable materials.

An elastoplastic damage ice material model based on modified Tsai-Wu yield criterion: Experiment, theory and numerical application

Ice, as a novel green and sustainable building material, has attracted more and more attention in building engineering. Appropriate ice material models are crucial for the performance analysis of the increasing ice structures. There is still challenging in modelling ice responses due to the complexity of ice. This study aims to present a nonlinear elastoplastic damage model for ice material. First, a triaxial compression test of artificial ice is conducted. Based on the test results, the modified Tsai-Wu failure criterion with better performance in the tensile zone and physical meaning for hydraulic strength is established. Then, combining plasticity theory with damage mechanics, an elastoplastic damage constitutive law considering the difference between tensile and compressive properties is proposed. The piecewise damage model and the Weibull exponential damage model are employed for compression and tension damage, respectively. Moreover, the numerical iterative algorithm is developed and a user-defined material subroutine (UMAT) is embedded in the finite element software ABAQUS to simulate the mechanical properties of ice. Furthermore, the constitutive model is verified by comparing the FEM results with the results of uniaxial compression, triaxial compression, and three-point bending tests. The results show that the constitutive model can well describe the stress-strain nonlinear behavior and capture the basic failure mode of ice materials. Finally, considering temperature affecting on the failure surface, a temperature dependent ice material model is developed. The current study would help in the design, operation and maintenance of ice structures.

Research on dynamic mechanical properties and damage model of ceramic materials under multi‐axial stress

AbstractDue to their exceptional impact resistance, ceramics are extensively used in various fields. However, unavoidable pores, microcracks, and inherent defects can degrade the performance of ceramic materials. A damage model of SiC ceramics under passive confining pressure was constructed based on the Lemaitre strain equivalence principle and the Weibull distribution function. This paper presented a dynamic damage model for SiC ceramics subjected to passive confinement pressure based on the principles of damage mechanics. Additionally, the split Hopkinson pressure bar device was employed to investigate the compressive strength and damage evolution of SiC ceramics at various shock pressures and confinement degrees. The experimental results indicate that constraints can reduce the damage to ceramics. The metal sleeve increased stiffness when compressing the ceramic material, allowing the specimen to convert from brittle–plastic–brittle. When sufficient constraints can be provided, the peak strain decreases gradually with the increase of the impact air pressure. Experimental data showing good agreement with the proposed model validated and analyzed the established model. Thinner boundary constraints cannot maintain the stability of ceramic structures, thicker boundaries do not significantly improve performance, and thicker boundaries can cause more weak areas. This paper provides guidance for the design of encapsulated ceramic composite armor by quantitatively studying the constraint thickness.

Performance Analysis of Shear Wall Joint Connection in Highrise Building Using Finite Element

Multi-story buildings have a risk of structural failure, especially at joint connections, including raft elements and shear walls, due to the interaction behavior of the shear joints. The problem raised in this research is how to analyze the performance of raft foundation shear wall structural connections in high-rise buildings. The researchers started by simulating the initial model using the element method to find out the detailed capabilities of the raft foundation and shear walls and obtain values that could measure the capabilities of the substructure used. The results of this research explain the results of the evaluation of connection performance, namely, the pile raft phase with fc' 35 MPa and the shear wall phase with fc' 50 MPa. From the analysis in this research, visualization from the ABAQUS program of the force conditions acting on the connection structure was obtained, namely compression damage of 0.0021 at an ultimate compressive stress of 43 MPa and 0.0006 at an ultimate compressive stress of 57.97 MPa. We also perform analytical calculations to determine the tensile and compressive strain values. In the future, it is hoped that it will be possible to make part of the reference the use of connections with similar models and sizes at project work stages with the same characteristics as a contribution to developing building structural safety requirements.

A multiaxial multiscale compressive thermo-mechanical damage model for Fiber Reinforced Cementitious Composites (FRCC)

In the current study, a multiaxial multiscale compressive stress-strain model for Fiber Reinforced Cementitious Composites (FRCC) was innovatively developed. The proposed model was on the basis of the theory of thermodynamics, multiscale theory and internal variable theory. The free energy function and dissipation function were established to characterize the elastic and plastic deformation of FRCC, respectively. The multiscale behaviors of FRCC in meso-scale and macro-scale was taken into account. In meso-scale, the energy dissipation functions of fiber in tension and bond-slip deformation in the interface transition zone (ITZ) were established. The resistance to cracking of cementitious matrix through the fiber bond stress were taken into account. In macro-scale, the thermo-mechanical coupling contributions of plastic damage, thermal damage, yield surface and hardening evolution were creatively considered in the potential function within thermodynamics framework. The influence of types and volume fractions of fibers on the reinforcement mechanism was discussed. When the temperature is higher than the melting point of fiber, the fiber influence coefficients was employed. The sensitivity of yield surface was discussed. The numerical predictions of this developed model were carried out for validation. The nonlinear stress-strain responses of concrete were accurately captured at temperatures ranges from 20 °C to 800 °C compared with the experimental data, which indicates the accuracy and applicability of the proposed model.

IMG-03. PRE-TREATMENT EVIDENCE OF ABNORMAL SUPRATENTORIAL WHITE MATTER IN CHILDREN WITH POSTERIOR FOSSA TUMOURS USING DIFFUSION MRI

Abstract BACKGROUND Over half of childhood brain tumours originate in the posterior fossa, which includes low-grade (e.g. pilocytic astrocytoma) and high-grade (e.g. medulloblastoma) tumours. Even though overall survival rates of paediatric brain tumours have substantially increased, survivors face neuropsychological impairments impacting behaviour, cognition, language and motor skills. Post-treatment outcomes are associated with structural changes within the brain, but it is unclear if observed microstructural damage is caused exclusively by radiotherapy or if there is earlier damage from the tumour and related effects. Diffusion MRI is a non-invasive technique that can be used to better understand white matter microstructure by quantifying water diffusion in the brain. Diffusion tensor imaging (DTI) can be used to assess white matter damage. METHODS In this work, we used DTI to understand white matter microstructure in 8 posterior fossa tumour patients prior to surgery. We compared individual patients to age- and sex-matched healthy controls in a one-against-many approach. RESULTS We demonstrate the presence of supratentorial white matter abnormalities prior to treatment in 3 patients. Before treatment, all patients are found to have significantly enlarged lateral ventricles relative to total brain volume (p<0.05). Patients with ventricle volumes >4% relative to brain volume correspond to significant changes in DTI parameters found in pre-treatment images, suggesting that hydrocephalus impacts white matter microstructure before surgery. Observed white matter changes are complex and patient-dependent, patients demonstrate compression (increased fractional anisotropy; FA) or diffuse oedema and damage (decreased FA). These white matter abnormalities persist over time, which could lead to cumulative damage, for example when adjuvant treatment involves radiotherapy. CONCLUSIONS To improve patient outcomes, pre-treatment imaging could be considered during individual treatment planning and risk evaluation to avoid further injury to white matter. Pre-treatment white matter abnormalities may have a bearing on neurocognitive patient outcomes, which will be the focus of future work.

The Scratch-Collapse Test: Are Electrodiagnostic Changes Measurable?

Carpal tunnel syndrome is commonly managed by hand and upper extremity surgeons. Though electrodiagnostics are considered the gold standard diagnosis, the scratch collapse test (SCT) was introduced to address uncertainty, despite remains controversial. To address this, we sought to identify if the SCT can correlate with EDS studies if the SCT can identify actual changes in measures of nerves. We reviewed patients who underwent electrodiagnostic studies (EDX) and SCT for carpal tunnel syndrome (CTS). Demographic data as well as sensorimotor amplitudes, latencies, and velocities on nerve conduction and electromyography were collected. Analogous values based on SCT findings were analyzed for statistical significance. Three hundred fifty patients with CTS were included. Sensory and motor velocities and amplitudes were significantly lower in patients with a positive SCT. Motor values were independent of age, though younger patients had larger measured changes. Obese patients did not show any motor EDX changes with the scratch collapse test, though thinner patients did. All changes were seen in nerve conduction only. Carpal tunnel can be a difficult problem to diagnose as one study does not singularly determine the condition. The SCT was introduced to facilitate easier diagnosis. We demonstrate that the SCT correlates with changes on nerve conduction studies, especially in relation to decreased amplitudes and velocities, suggesting that it does identify changes in nerve with compression, specifically axonal, and myelin damage. These findings support the use of the SCT maneuver to evaluate and diagnose in appropriate patients.

Investigation on uniaxial compression and fracture damage mode of prefabricated parallel double-jointed red sandstone.

As a special type of joint fracture, the fracture evolution characteristics of parallel double joints have important engineering significance for the stability analysis of fractured rock mass. In this work, a new method for calculating stress intensity factor of parallel double-jointed fractures was importantly proposed. Physical uniaxial compression tests were carried out on parallel double jointed red sandstone filled with cement mortar under different geometric parameters, and the macroscopic mechanical properties and failure characteristics of red sandstone are deeply analyzed. The results show that the larger the connectivity rate is, the smaller the peak stress and strain are. The increase of connectivity rate will affect the change rate of transverse strain in the center of rock bridge. The closer the dip angle of the joint is, the lower the peak stress is and the shorter the failure time is. The damage mode of joint tip encroachment affects the lateral displacement of the rock bridge center, and the displacement is always close to the first damage section. The closer the joint tip is to the load, the easier the end-face penetrating cracks occur. The research content can provide basic support for guaranteeing the stability of underground engineering rock mass.

An interface constitutive model of plastic tensile–compressive damage under impact loading based on continuous–discontinuous framework

Bullet penetration test is a classic impact loading test, which involves complex dynamic elastic–plastic response. Conventionally, this process was often described using a single high-strain-rate constitutive model, which could only capture a specific type of failure during the impact damage process. Furthermore, these constitutive models were mostly defined on element and posed the risk of computational divergence(element distortion). In this work, a novel constitutive model for combined tensile–compressive damage in interface element was developed within a Continuous–Discontinuous Element Method(CDEM) framework. This model successfully captures the processes of pit formation and target collapse during projectile penetration. The tension and compression damage parts of the developed interface constitutive model were validated through Brazilian splitting test and interface direct shear test. Subsequently, bullet penetration test is simulated and the post-penetration velocity is compared with published results from other studies, with computational errors found to be within 2.56%, thus validating the accuracy of the developed interface constitutive model.

Numerical Investigation of the Effect of Deltoid Radius on Tensile Load in T-joints

In this study, T-shaped joints were designed from composites with different deltoid radius. For this purpose, carbon fiber woven fabrics were preferred as reinforcement elements. Then, tensile analyzes were performed on these composite T-joints. The effect of the deltoid radius on the maximum tensile load and damage behavior of the structure was examined. As a result of the analyses, fiber tensile-compression damage images occurring in the structure for each deltoid radius were obtained along with the load-displacement graph. The Hashin damage criterion was preferred for damage onset. Material Property Degradation (MPDG) method was used for damage progression in progressive damage analysis. By increasing the deltoid radius from 6 mm to 12 mm, the maximum contact load increased by approximately 10%, and by increasing it to 18 mm, the maximum contact load increased by approximately 20.11%. Fiber compression damage, spread over a wide area on the lower surface of the flange where it does not come into contact with the web, was determined to be the dominant damage type, and it was determined that this damage decreased with the increase of the deltoid radius. it was observed that as the deltoid radius increases, the T-jointed composite structure exhibits more rigid material behavior.

Development in the Study of Mechanical Prop-erties and Damage Constitutive Models of Rub-ber-Reclaimed Concrete

Advances in rubber-reinforced concrete technology and its applications in engineering are cru-cial for the thorough recycling and safe disposal of waste tire rubber and construction debris. Rubber-reinforced concrete (RAC) is a concrete material produced by substituting some fine and coarse aggregates with waste rubber particles and recycled aggregates. The incorporation of waste rubber particles endows RAC with distinctive mechanical properties and a distinct damage constitutive model. The mechanical properties of rubber recycled concrete mainly in-clude compressive strength, tensile strength, flexural strength, and elastic modulus. Compared to traditional concrete, RAC exhibits slightly lower compressive and flexural strengths but sig-nificantly enhanced tensile strength. This is due to the changes in mechanical properties caused by the softness and elastic properties of rubber particles. In addition, the addition of rubber particles can also improve the energy absorption capacity and impact resistance of concrete. On the other hand, in order to describe the damage behavior of rubber recycled con-crete, some constitutive models were studied. Common models include linear elastic model, plastic model, and damage model. The linear elastic model is suitable for describing the be-havior of rubber recycled concrete during the elastic stage; The plastic model is suitable for describing its deformation behavior during the plastic stage; The damage model can better describe the fracture and failure behavior of rubber recycled concrete, including shear damage, tensile damage, and compression damage. Tailored to the unique characteristics of RAC, these models consider the stiffness of rubber particles and the deformation characteristics of the binding materials, enabling accurate predictions of the stress-strain behavior of RAC. In conclusion, rubber-reinforced concrete possesses excellent mechanical and durability proper-ties, which can be accurately described and predicted using appropriate constitutive models. These findings are crucial for advancing the application and development of rubber-reinforced concrete.

Study on triaxial compression performance and damage characteristics of fiber-reinforced ecological matrix cementing gangue gypsum fill material.

Polypropylene fiber was equally mixed into alkali-activated slag fly ash geopolymer in order to ensure the filling effect of mine goaf and improve the stability of cemented gangue paste filling material with ecological matrix. Triaxial compression tests were then conducted under various conditions. The mechanical properties and damage characteristics of composite paste filling materials are studied, and the damage evolution model of paste filling materials under triaxial compression is established, based on the deviatoric stress-strain curve generated by the progressive failure behavior of samples. Internal physical and chemical mechanisms of the evolution of structure and characteristics are elucidated and comprehended via the use of SEM-EDS and XRD micro-techniques. The results show that the fiber can effectively improve the ultimate strength and the corresponding effective stress strength index of the sample within the scope of the experimental study. The best strengthening effect is achieved when the amount of NaOH is 3% of the mass of the solid material, the amount of fiber is 5‰ of the mass of the solid material, and the length of the fiber is about 12 mm. The action mode of the fiber in the sample is mainly divided into single-grip anchoring and three-dimensional mesh traction. As the crack initiates and develops, connection occurs in the matrix, where the fiber has an obvious interference and retardation effect on the crack propagation, thereby transforming the brittle failure into a ductile failure and consequently improving the fracture properties of the ecological cementitious coal gangue matrix. The theoretical damage evolution model of a segmented filling body is constructed by taking the initial compaction stage end point as the critical point, and the curve of the damage evolution model of the specimen under different conditions is obtained. The theoretical model is verified by the results from the triaxial compression test. We concluded that the experimental curve is in good agreement with the theoretical curve. Therefore, the established theoretical model has a certain reference value for the analysis and evaluation of the mechanical properties of paste filling materials. The research results can improve the utilization rate of solid waste resources.

Study on the Meso-Failure Mechanism of Granite under Real-Time High Temperature by Numerical Simulation

In the development of geothermal resources in hot dry rocks, deep underground rock masses are typically subjected to real-time high-temperature environments. High temperatures alter the physical and mechanical properties of the rocks, directly affecting the safe and efficient utilization of hot dry rock resources. Therefore, a grain-based model (GBM) of particle flow code (PFC) was constructed based on uniaxial compression tests, and the model was verified according to macroscopic mechanical parameters and damage modes, in order to carry out the simulation study of the uniaxial compression of granite and explore the meso-failure mechanism of granite under real-time high temperature. The relationships between stress–strain curves and crack derivation, the evolution of microcracks, and the characteristics of acoustic emission activity and energy changes at different temperatures were investigated in conjunction with the results of laboratory tests. The results show that crack development, acoustic emission activity, and energy evolution during uniaxial compression include four main stages: initial compression, elasticity, plastic strengthening, and post-peak damage. The failure of granite is primarily controlled by mica and feldspar. During loading, intergranular tensile cracks first emerge within the granite, followed by intragranular tensile cracks, with shear cracks appearing last. As the temperature increases, the total number of microcracks continuously rises, the frequency of acoustic emission events increases, and both dissipated energy and boundary energy gradually decrease, showing an upward trend in the energy dissipation ratio, indicating an increase in thermal damage due to high temperatures. At 400 °C, the rate of microcrack formation increases significantly, with intergranular and intragranular cracks starting to coalesce into macroscopic cracks that extend outward. In the post-peak stage, the phenomenon of multiple peaks in acoustic emission events begins to appear. At 600 °C, the rate of microcrack formation reaches its maximum, with cracks extending throughout the sample to form a network of fractures, resulting in the granite exhibiting ductile failure characteristics.

Optimizing the Utilization of Steel Slag in Cement-Stabilized Base Layers: Insights from Freeze-Thaw and Fatigue Testing.

This paper presents a study on the mechanical properties of cement-stabilized steel-slag-based materials under freeze-thaw cycles for a highway project in Xinjiang. Using 3D scanning technology the specimen model conforming to the real steel slag shape was established. The objectives of the study are as follows: to explore the sensitivity between the macro- and micro-parameters of the specimen and to establish a non-linear regression equation; and to study the changes in mechanical properties of materials under freeze-thaw cycles, fatigue loading, and coupled freeze-thaw cycle-fatigue loading. The results show that there are three stages of compression damage of the specimen, namely, linear elasticity, peak plasticity, and post-peak decline. Maximum contact forces between cracks and particles occur mainly in the shear zone region within the specimen. The compression damage of the specimen is a mixed tensile-shear damage dominated by shear damage. When freeze-thaw cycles or fatigue loads are applied alone, the flexural strength and fatigue life of the specimens show a linear relationship of decline. The decrease in flexural modulus at low stress is divided into the following: a period of rapid decline, a relatively smooth period, and a period of fracture, with a tendency to change towards linear decay with increasing stress. In the case of freeze-thaw-fatigue coupling, the flexural modulus of the specimen decreases drastically by about 50% in the first 2 years, and then enters a period of steady decrease in flexural modulus in the 3rd-5th years.

Study on the Seismic Response of a Water-Conveyance Tunnel Considering Non-Uniform Longitudinal Subsurface Geometry and Obliquely Incident SV-Waves

The longitudinal seismic response characteristics of a shallow-buried water-conveyance tunnel under non-uniform longitudinal subsurface geometry and obliquely incident SV-waves was studied using the numerical method, where the effect of the non-uniform longitudinal subsurface geometry due to the existence of a local one-sided rock mountain on the seismic response of the tunnel was focused on. Correspondingly, a large-scale three-dimensional (3D) finite-element model was established, where different incidence angles and incidence directions of the SV-wave were taken into consideration. Also, the non-linearity of soil and rock and the damage plastic of the concrete lining were incorporated. In addition, the wave field of the site and the acceleration response as well as damage of the tunnel were observed. The results revealed the following: (i) a local inclined subsurface geometry may focus an obliquely incident wave due to refraction or total reflection; (ii) a tunnel in a site adjacent to a rock mountain may exhibit a higher acceleration response than a tunnel in a homogeneous plain site; and (iii) damage in the tunnel in the site adjacent to a rock mountain may appear in multiple positions, and the effect of the incidence angle on the mode of compressive deformation and damage of the lining is of significance.

Experimental and numerical studies on influences of wedge reinforcement on seismic performance of loose penetrated mortise-tenon joints

Wooden wedges significantly affect the rotational stiffness and load-bearing capacity of penetrated mortise-tenon joints (PMTJ). To clarify the role of wedges on the seismic performance of loose penetrated mortise-tenon joints, three types of full-scale PMTJs, including reference, loose, and wedge-reinforced joints, were tested under quasi-static loading. The deformation characteristics, hysteresis curves, rotational stiffness degradation behavior, and energy dissipation of PMTJs with wedge were analyzed. Three-dimensional nonlinear finite element models were established to simulate the wedge effects, and the stress states of joint were analyzed. The results indicated that the ultimate bending moment capacity of reference and loose joints was reached when the splitting failure of tenon occurred, while the wedge-reinforced joint reached such capacity when the transverse compression failure occurred at the wedges. The maximum bending moment of PMTJ with a 10 mm gap and a 25 mm gap were 18.3 % and 55.3 % lower than that of reference joint, while maximum bending moments of wedge-reinforced joint with a 10 mm gap and a 25 mm gap were 12.6 % and 17.03 % larger than that of reference joint, respectively. Numerical simulation showed that wooden wedge reduced stress concentration in the tenon and alleviated compression damage of the tenon. Higher load-bearing capacity and rotational stiffness were observed in joints when hardwood wedges were used, compared with that of soft wood. Wedge reinforcement could effectively improve the load-bearing capacity of loose PMTJ. These results yielded valuable data for the performance evaluation and retrofitting of penetrated mortise-tenon joints with wedges in traditional timber structures.

Damage and Fragmentation of Rock Under Multi-Long-Hole Blasting with Large Empty Holes

The technique of multi-long-hole blasting with large empty holes has been used in practice to break rock mass. However, the damage mechanism of rock mass surrounded by empty holes and boreholes under this type of blasting has not yet been well-understood and identified, which may lead to inappropriate design of the configurations of empty holes for multi-long-hole blasting. The present study investigates the damage modes and mechanism of rock mass under multi-long-hole blasting with large empty holes by conducting a field test and numerical simulations. The results show that multi-long-hole blasting with empty holes mainly causes compressive damage of rock mass around boreholes, reflected tensile damage near empty holes and ground surface, bending-induced tensile damage between empty holes and boreholes, shear damage along the side tangents and bottom of empty holes and boreholes, and tensile damage along the connection of boreholes caused by the superposition of stress waves. In addition, parametric studies are conducted to examine the effects of depths and diameters of empty holes and the spacing between boreholes and empty holes on the damage and fragmentation of rock mass under blast loads. It is found that the flexural stiffness and confined levels of rock mass can be greatly influenced by the variation of configurations of empty holes, which thus induces different damage and fragmentation under multi-long-hole blasting. Analytical formulas for the evaluation of shear and bending-induced damage of rock mass under multi-long-hole blasting are finally proposed to provide references for the design of empty holes in multi-long-hole blasting.

Experimental Study on the Strength and Damage Characteristics of Cement–Fly Ash–Slag–Gangue Cemented Backfill

In order to achieve the goal of effectively utilizing solid waste resources and improving mining stability, it is necessary to incorporate various types of solid wastes in the production of cemented backfill. For investigating the compressive strength and damage characteristics of Cement–Fly Ash–Slag–Gangue (CFSG) cemented backfill under loading, real-time X-ray Computed Tomography (CT) scanning was employed to capture two-dimensional (2D) grayscale slices and three-dimensional (3D) fracture models during uniaxial compression testing. The study quantitatively assessed the evolution of cracks and microstructural damage in CFSG cemented backfill. The results indicate that the specimens underwent four stages of transformation, including compaction, linear elasticity, yielding, and residual deformation, during the uniaxial compression process. The specimens exhibited a measured compressive strength of 3.44 MPa and a failure strain of 0.95%. As the axial strain increased, there was an increase in 2D porosity observed in the CT images and a greater dispersion of crack distribution. A 3D model constructed from CT slices illustrated the feature of cracking expansion, with the fracture volume gradually increasing during the elastic deformation phase and experiencing rapid growth during the yielding and residual deformation phases. The damage variable, obtained from the volume of 3D cracks, exhibited a slow-growth pattern, characterized by a rapid increase followed by a more gradual rise with the increase in axial strain. This study serves as a significant reference for comprehending the micro-mechanisms involved in the damage process and cracking characteristics of cemented backfill mixed with solid wastes under external loading conditions.