Triaxial Stress State Research Articles

Grouting seepage characteristics in microfracture under triaxial stress conditions: Device design and experimental study

Water plugging by grouting in rock microfracture is a technical challenge in deep underground engineering. In this paper, a novel grouting test system was developed, which can simulate microfracture grouting tests under triaxial stress conditions. A specimen preparation method that can monitor the seepage and diffusion of microfine cement slurry in microfracture was also proposed. Microfracture grouting model tests were conducted on sandstone-like specimens to investigate the effects of confining pressure, roughness, and microfracture aperture on the seepage and diffusion characteristics of sandstone-like specimens. The test results show that microfine cement slurry can effectively seal the microfracture. However, when the microfracture aperture is small or the roughness is large, the slurry is easy to gather and deposit at the inlet, resulting in the phenomenon of "seepage filtration", which makes it difficult for the slurry to be injected into the microfracture. The pressure at the measuring point gradually decreases along the seepage and diffusion direction of the slurry, and the decreasing trend increases with the increase of microfracture roughness. The nonlinear relationship between the slurry volume flow rate and the hydraulic gradient can be described by Forchheimer's law. Moreover, both coefficients a and b in Forchheimer's equation show a gradual increase with increasing microfracture roughness. This study can provide a meaningful reference for the development of rock microfracture grouting technology in deep engineering.

Influence of steam curing on cyclic triaxial characteristics of recycled aggregate concrete: Experimental analysis and DEM simulation

The engineering application of steam-cured recycled aggregate concrete (often in a cyclic triaxial stress state) can not only improve the recycling efficiency of resources, but also accelerate the construction progress. In this paper, we adopt a combination of laboratory experiments, theoretical analysis and numerical simulation to study the cyclic triaxial characteristics of recycled aggregate concrete (RAC) under different curing regimes (20℃, 40℃, 60℃ and 80℃). The results indicate that as the steam curing temperature increases, the internal damage caused by high temperature continues to intensify, and the cyclic triaxial failure mode of RAC transitions from shear failure to compression failure, and its peak strength, dynamic elastic modulus, and dilatancy angle all show a downward trend. A linear prediction model is established based on the strong correlation between peak strength and steam curing temperature. As the loading cycles increase, the dynamic elastic modulus and dilatancy angle of RAC show exponential and linear downward trends respectively, and the decline rate increases with the increase of steam curing temperature, and the prediction models for dynamic elastic modulus and dilatancy angle are established based on quantitative relationships between variables. On the basis of experimental analysis results, a cyclic triaxial DEM model considering real recycled aggregates is established by introducing steam-cured damage indexes into the mesoscopic parameters, and its applicability in predicting cyclic triaxial mechanical properties of RAC under different curing regimes is verified. The research outcomes can save a lot of test cost and time consumption for developing steam-cured concrete with better performance, and have important theoretical guidance and practical significance for the wide application of steam-cured concrete.

Effect of temperature on permeability of mudstone subjected to triaxial stresses and its application

In order to prevent leakage of pyrolysed oil and gas and the release of contaminants from the top and bottom strata, it is essential to carry out a comprehensive study of the seepage behaviour of these strata under high temperature triaxial stress conditions. The findings of this study will contribute to the development of effective strategies for the containment and integrity monitoring of subsurface reservoirs and storage environments. Mudstone, serving as both the upper and lower strata, offers an effective barrier due to its inherently low permeability. In order to explore the change rule of mudstone sealing performance under high temperature triaxial stress, an air-heated low permeability rock mass air permeability measurement system is used to measure the ground stress buried 500 m deep and the temperature variation characteristics of mudstone permeability on the roof and floor of Jimsar oil shale in Xinjiang under 100 °C. It was found that the permeability of stressed mudstone decreased with the temperature rising up to 100 °C. The primary factor influencing the outcome was the thermal expansion of the mudstone. The magnitude of the drop value was contingent upon the triaxial stresses that could potentially be induced by the application of significant tensile forces, resulting in a relatively minor drop value. The average hydraulic radius of pore in the mudstone was also calculated, which also exhibited continuous reduction as heating up to 100 °C and the degree of reduction could reach 68%. The capacity, that prevent oil & gas and contaminant from moving cross strata as a barrier, would be strengthened when the mudstone strata from roof and floor experienced the temperature low than 100 °C. The barrier performance of mudstone as a pollutant migration barrier layer to gas pollutant migration during in-situ heat injection mining of oil shale was further evaluated.

Size and microstructural factors affecting the micro-hole expansion ratio and fracture toughness of dual phase steel sheets

The microscopic hole expansion ratio (μHER) of a ferritic-martensitic (∼10 %) dual phase steel was measured using a novel in-situ scanning electron microscope based miniature hole expansion setup. The effect of extrinsic parameters such as specimen thickness and machining conditions, and intrinsic parameters such as hardness differential (ΔH =Hα'-Hα) between the soft ferrite matrix and hard martensite islands on μHER values was studied. The miniature HER setup allowed site-specific measurement of microscopic strain localizations in the DP microstructure through high resolution digital image correlation under the triaxial state of stress. The results from these experiments were juxtaposed against another triaxial state of stress ahead of a crack tip, in a fracture toughness (JIc) test using the single edge notched tensile (SENT) geometry for the same thickness and microstructural conditions of DP steel. It was found that the tempered DP specimen with lower ΔH resulted in a ∼45 % higher μHER as compared to the as-received DP600, although both specimens exhibited similar JIc values. This apparent discrepancy between the trends in μHER and JIc values was explained in terms of the differences in failure modes, triaxiality and plastic zone evolution in the two conditions.

Fractional Derivative-based Burger Creep Model for Soft Rocks and its Verification Using Tunnel Monitoring Results and Experimental Data

AbstractConsidering the creep behavior of soft and weak rocks is critical for analyzing the long-term stability of underground constructions. This paper introduces a novel creep constitutive model to characterize the creep behavior of rocks under uniaxial and triaxial stress states. The fractional derivative Abel dashpot was used to improve the Burger model, and a viscoplastic component was added in series with the modified Burgers model to replicate the tertiary phase of rock creep. The effectiveness of the model was verified using creep test data from various soft rocks and monitoring measurements from a tunnel excavated in heavily jointed weak rock masses. Furthermore, a sensitivity analysis was carried out to assess the impact of the model parameters on creep deformation, and a comparative study was performed to evaluate the efficacy of the suggested model in modeling the accelerated stage of rock creep compared with some existing models. The strong agreement observed between the calculated results and both the creep test data and tunnel monitoring measurements underscores the accuracy and validity of the proposed model. The comparative analysis further revealed that the proposed model offers the highest fitting efficiency for describing the tertiary stage of rock creep. These findings suggest that the model effectively captures the creep behavior of rocks and precisely represents the entire creep process.

Impact of triaxial stress state at various pavement depths on the dynamic modulus of asphalt mixture

The mechanical characteristics of asphalt mixture are closely related with its stress state, temperature, and loading rate, therefore, the loading condition of the asphalt mixture's dynamic modulus test should be consistent with the actual temperature, loading frequency, and stress state that are applied to the mixture in actual pavement, thus can the test produce an objective result that can accurately reflect the actual stress-strain relationship for the asphalt mixture. However, due to limitations in the loading capacity of current dynamic modulus test equipment, the present modulus tester cannot yet set such a loading condition whose stress state is consistent with that of asphalt mixture in actual pavement. As a result, the modulus testing results of the current test may not accurately reflect the actual stress-strain characteristics of an asphalt mixture under real traffic loads. Therefore, this paper aims to figure out the impact of stress state on asphalt mixture’s dynamic modulus, and firstly conducts a numerical analysis to ascertain asphalt pavement’s triaxial stress state at different depth, then, utilizing the nonlinear elasticity theory of Soil Plasticity, proposes a theoretical model that can reflect triaxial stress state’s effect on asphalt mixture’s dynamic modulus, and then, arranges a series of triaxial dynamic modulus tests for asphalt mixture in different stress state to verify the model’s effectiveness, and meantime analyzes stress state’s influencing rule to asphalt mixture’s dynamic modulus. Their results indicate, the asphalt mixture of the actual pavement is in an obvious triaxial stress state, and that the higher the triaxial stress state, the larger the dynamic modulus, particularly for the mixture near the surface, whose high stress state will lead to their dynamic modulus to be significantly larger than that of the underlying course, while the model proposed in this paper can to a large extent reflect this impact.

Mechanism of Subsurface Deformation Transmission and Geomechanical Response Inversion in Carbon Capture and Storage Project: Integrating Small Baseline Subset-Interferometric Synthetic Aperture Radar, Mechanical Experiments, and Numerical Simulation

Summary In the context of carbon capture and storage (CCS) engineering, ensuring the stability of the caprock is paramount to mitigating CO2 leakage, thus constituting a pivotal engineering challenge in CO2 geological sequestration. With the injection of CO2, pore pressure accumulates within the reservoir, bringing forth risks including diminished effective stress within the formation, surface deformation, occurrence of microseismic events, and potential caprock failure. Therefore, it is necessary to explore the geomechanical issues in CCS projects. This study focuses on the Daqingzijing in the Jilin Oilfield as the study area, utilizing the small baseline subset (SBAS)-interferometric synthetic aperture radar (InSAR) method to conduct a deformation time-series analysis in the well group area under injection and production conditions. The results reveal variations in deformation sensitivity among the sites, with surface displacements correlated to fluid injection and production, demonstrating temporal delays. At the H79 North block, the time effect is relatively minimal, with rapid propagation of formation deformation. Surface displacement in the H46 block appeared 4 months later than behind cumulative fluid volume changes. By conducting triaxial creep tests on shallow mudstone samples from the Songliao Basin under various triaxial stress states, a constitutive creep equation for caprock rocks was obtained. The numerical models of elastic and creep constitutive equations were established. The results show that the creep model exhibits superior accuracy by comparing with InSAR monitoring data (the root mean square error values of elastic and creep constitutive geomechanical models were 6.7 mm and 1.7 mm, respectively). Additionally, based on the experimental and simulation results, this study explores the transfer mechanisms of formation deformation and the inverse relationship between deformation and pore pressure. This study provides theoretical support for the geomechanical safety analysis in corresponding CCS projects.

A comparative study of three types of strength criteria for rocks

Currently, the unified strength criterion (USC), the three-dimensional Hoek-Brown (3D H-B) criterion and the generalized unified strength theory (GUST) are the three types of typical rock strength criteria. In this paper, a comparative study of the three types of strength criteria is performed for rocks. Based on the nonlinear characteristics of rock strength on meridian and deviatoric planes, the USC can predict rock strength under triaxial stress state. The USC is composed of two failure functions on meridian and deviatoric planes. The failure surface of the USC in principal stress space satisfies smoothness and convexity. The predicted strength for five types of rock under the true triaxial tests were compared among the USC, the GUST, and the 3D H-B criterion. The results indicate that the USC can effectively reflect the influence of the intermediate principal stress on rock strength and accurately predict rock strength under both triaxial tension (σ1=σ2>σ3) and triaxial compression (σ1>σ2=σ3). Additionally, the conventional triaxial tests were conducted on other eight types of rock to measure the strength on meridian plane. The predicted strengths for the eight types of rock on meridian plane were compared between the USC and the original H-B, which suggests that the USC is suitable for various types of rock and provides higher accuracy.

Creep behavior of BFRP-confined coal gangue concrete under sulfate and high stress conditions

To recycle the coal gangue more economically and effectively, the basalt fiber reinforced polymer (BFRP) and coal gangue concrete (CGC) are combined to form a novel supporting structure in the underground mines, BFRP-confined CGC (FCGC). However, the underground mine environment is rich in sulfate corrosive ions, and meanwhile, the structure is subjected to a high sustained load. Thus, this paper presents an experimental and theoretical investigation on the long-term deformation properties of FCGC under sulfate and high stress conditions. The effects of inner concrete, FRP layer, stress-to-strength ratio, sulfate concentration and load duration time on the shrinkage and creep behavior were clarified in detail. The findings indicate that the shrinkage of FCGC is relatively lower as the BFRP confinement weakens the moisture exchange between inner CGC and external environment. In addition, under sulfate and high stress conditions, the creep strain and specific creep increase continuously in the early stage, while the growth rate gradually slows down in the later stage, where the high stress-to-strength ratio is the key factor. Moreover, when compared with a single high stress condition, the creep strain of FCGC is relatively larger under sulfate and high stress coupling conditions, attributed to the sulfate corrosion on the BFRP wraps. Theoretically, the ACI 209 was modified to predict the nonlinear creep of CGC, by introducing the coal gangue influence coefficient and the increasing coefficient of nonlinear creep. Furthermore, based on the creep model of CGC and BFRP, the nonlinear calculation model of FCGC was developed considering the creep of CGC under a triaxial-stress state and the interaction between inner CGC and BFRP confinement. Validations against the experimental results show that the nonlinear creep model of FCGC works well.

Experimental study on pore structures and mechanical properties of ferroaluminate cement under sulfate attack

Ferroaluminate cement (FAC) emerges as a special cement with outstanding durability, offering promising applications. However, the resistance to sulfate attack of FAC remains inadequately understood. In this paper, the impact of sulfate attack on the pore structure of FAC concrete is explored through nuclear magnetic resonance (NMR) tests from a microscopic perspective. Meanwhile, the macroscopic mechanical characteristics of concrete attacked by sulfate are investigated under different loading conditions, including splitting tensile and conventional triaxial compression. NMR test analysis shows that as the degree of erosion increases, the number of mesopores and macropores in FAC concrete decreases while the number of micropores increases. The changes in pore structure distribution alter the mechanical response of specimens. The discussion of strength characteristics, deformation behavior, and energy parameters in conventional triaxial tests reveals that FAC concrete attacked by sulfate exhibits superior mechanical properties under confining pressure. Uniaxial strength results indicate that sulfate attack has less impact on specimens under tensile stress state than under compression. Based on the experimental findings, this paper introduces a sulfate attack impact factor to capture the uniaxial strength changes. Further, a multiaxial strength criterion is developed to describe the strength properties of sulfate-attacked concrete under triaxial stress conditions.

Experimental study on the deformation and failure characteristics of cement stone under true triaxial stress state

The cement stone is widely utilized to fill the gap between the formation and the casing in wells. A clear understanding of the deformation and failure mode of cement stone under true triaxial stress state is necessary to ensure the safety and stability of wells. To analyze the three-dimensional deformation and failure characteristics of cement stone, the loading paths with constant Lode angle were employed in conducting true triaxial tests on cement stone. The stress-strain curve and failure mode of cement stone are first analyzed. Then, the three-dimensional deformation characteristics are discussed in meridian and deviatoric planes. Both peak strength and deformability increase with minimum principal stress, but show a tendency to increase and then decrease with intermediate principal stress coefficient. With the increase of minimum principal stress and intermediate principal stress coefficient, the failure mode of cement stone transforms from brittle to ductile behavior. Under elastic stage, the strain path in the meridian plane is a straight line, and is under constant Lode angle within the deviatoric plane. Due to the existence of plastic strain, the strain path in the meridian plane displays a downward convex shape. The strain path in the deviatoric plane deviates from the reference of constant Lode angle for stress, directly reflecting the Lode angle dependence of deformation. Both deformation and failure characteristics of cement stone are dominated by the three-dimensional stress state. Besides, deformation of cement stone is closely related to the failure characteristics of cement stone.

Criterion for residual strength and brittle-ductile transition of brittle rock under triaxial stress conditions

The critical condition with respect to the brittle-ductile transition (BDT) is of great significance in understanding the distinction between brittle and ductile behavior for rocks. In this paper, we develop the two criteria for the residual strength and BDT point of brittle rock based on linear elastic fracture mechanics. The effect of the microcrack friction and slip friction of brittle rock on the residual strength and BDT point is analysed. Two models are derived to predict the critical confining stress and critical compressive stress at the BDT point for brittle rock, and a new brittleness index is proposed. The reliability of models is validated by using a great number of test data from previous publications. The results show that the stress of the BDT point increases with increasing microscopic friction on the microcrack, and decreases with increasing macroscopic sliding friction. The critical confining stress and critical compressive stress at the BDT point are predicted, which is qualitatively consistent with laboratory tests. The results also show that the two criterion have the capability to predict the residual strength and BDT point, which has provided useful insights into the mechanics of brittle-ductile transition in brittle rocks.

A new improved 3D Hoek-Brown criterion

The Hoek-Brown strength criterion has been widely used to estimate the strength of intact rocks and rock masses, and has been continuously developed. However, in the latest version of the standard, the criterion still ignores the influence of the intermediate principal stress. To study the different effects of intermediate principal stress on rock failure under triaxial or multiaxial stress states, this paper proposes a modified three-dimensional H-B strength criterion, which can be reduced to the H-B criterion, three-dimensional Priest criterion, Jiang’s (2012) criterion, and the Cai criterion. Multiaxial test data of six intact rocks were used for validation and applicability analysis. The results show that the proposed criterion can well describe the trend of multi-axial test data of six kinds of rocks, and the average mismatch of the six types of rocks is controlled within 10 MPa, which is much smaller than the fitting error of the original H-B criterion, Mogi criterion and Jiang’s criterion, indicating that the criterion has a good prediction effect on rock strength. The proposed criteria can provide a basic theory for the future construction of in-situ rock mass strength.

An improved dual shear unified strength model (IDSUSM) considering strain softening effect

This study proposes an improved dual shear unified strength model by introducing the plastic internal variable which reflects the collective effects of strain softening, intermediate principal stress and unequal strength under tension and compression. The improved model is then simplified into simple forms for typical stress states, including uniaxial tension and compression, plane stress pure shear and tri-axial stress states. The smooth method and conjugate gradient method are utilized to facilitate its numerical implementation, avoiding numerical singularity and non-convergence in the solution process. The physical meanings of the parameters are further clarified and their values for self-compacting concrete are determined from the results of triaxial compression tests through a combination of direct determination, equation solution and back propagation (BP) neural network optimization. Validated against the test results, the improved model gives a more accurate prediction than the traditional dual shear unified strength model and Mohr-Coulomb model, in terms of both the overall trend and representative values. Validation results show that the improved model is applicable to materials for which the compressive strength is greater than the tensile strength and the tensile strength is greater than the shear strength.

Mesoscale mechanism of damage in fracture process zone of CFRP laminates simulated with triaxial stress state-dependent constitutive equation of matrix resin

The three-dimensional failure process experimentally observed by synchrotron radiation X-ray computed tomography (SR X-CT) regarding the influence of the interfiber distance is discussed on the basis of the results of numerical experiments. Triaxial stress states in the fracture process zone of carbon fiber reinforced polymers were analyzed on the mesoscale under mode I and mixed-mode (mode I + II) loading. Yield and damage models depending on stress triaxiality were used to accurately simulate three-dimensional stress states in the damage zone around the crack tip. Owing to the heterogeneity of composites, deviatoric stress is prominent in the thin resin region where the interfiber distance is small under mode I loading. On the other hand, matrix resin is triaxially stressed in the middle point between carbon fibers in the thick resin region where the interfiber distance is large. Under mode II loading, the shapes of fiber/matrix debonding depended on the interfiber distance. Areas with stress concentration were found owing to a large debonding area in the thick resin region resulting in a matrix cracking-prone stress state. These findings explain the damage and failure processes well observed by SR X-CT and provide a fundamental understanding of the damage mechanism at a mesoscale.

Creep deformation characteristics and control technology in deep mine soft rock roadway

In order to control the strong ageing creep and large deformation of deep soft rock roadway effectively, with the 61–71 track on the uphill of the mining area in Suzhou, Anhui as the research background, the triaxial creep test of mudstone was conducted using the TYJ-1500 M rock mechanics testing system. The creep deformation and failure characteristics of mudstone were analyzed. Additionally, the creep deformation characteristics of deep soft rock roadways were obtained through FLAC3D numerical simulation experiment, and the control techniques for deep soft rock roadway was proposed. The results showed that the axial strain and lateral strain of the specimen were mainly instantaneous strain and creep strain under triaxial stress conditions, and the both confining pressure and the axial pressure have a significant impact on the deformation and creep failure strength of the specimen. Under the condition of high ground stress and complex geological structure, the high stress concentration of roadway roof and floor and two bottom angles is the main cause of creep failure of soft rock roadway, and the large degree of surrounding rock fragmentation and unreasonable support mode reduce the bearing capacity of surrounding rock and aggravate the creep failure of roadway. The 'anchor net cable shotcrete + floor and two corners in floor bolt-grouting + deep and shallow hole grouting + secondary reinforcement support' combined support method was proposed and industrially tested, with average deformation of the roof, floor, and two sidewalls being 111.9 and 62.5 mm, respectively, representing 13.2 and 10.3% of the deformation under the original support scheme.

Mechanical properties and constitutive model of artificial frozen sandy soils under true triaxial stress state conditions

Triaxial compression tests were conducted on frozen sandy soils under a constant minimum principal stress (σ3 = 1.6 MPa) and various intermediate principal stresses (σ2 = 1.6, 3.4, 5.2, 7.0, 8.8, 9.8 MPa). The purpose of the research was to investigate the influence of intermediate principal stress on mechanical properties of frozen soil, and to establish a constitutive model to predict the stress-strain relationship of frozen soil under complex stress state. The test results obtained demonstrated that the crack damage stress and failure stress initially increase and then decrease with an increase in the intermediate principal stress. However, the crack initiation stress exhibits an initial increase up to a specific value, after which it stabilizes. From the perspective of crack propagation, the influence mechanism of intermediate principal stress on the strength was discussed. With the variation of stress state, the difference between intermediate principal strain and minimum principal strain gradually increases. The deformation difference was revealed using the stress superposition principle and Poisson's effect. Finally, the constitutive model based on the Weibull distribution and Drucker-Prager strength criterion can accurately represent the stress-strain relationships of frozen sandy soils under true triaxial stress states.

Cold Recycling Technology for Airfield Pavement Rehabilitation Practices

Cold recycling technology has recently achieved significant success in highway maintenance and construction applications. In this study, the potential of incorporating emulsion-based cold recycled layers into airfield pavement design is explored. The permanent deformation resistance of cold recycled (CR) mixtures was characterized under various stress states and loading conditions to provide a realistic representation of the loads induced by aircraft tires on typical airfield pavement structures. Finite element modeling simulations of several airfield structures incorporating a CR layer were leveraged to derive the triaxial stress states induced by the moving load of various aircraft tires on the CR layer. A mix design was developed using a common approach. The simulated stress states were then projected and applied to the developed mix design in triaxial compression repeated load permanent deformation experiments. The influence of time and temperature dependence of the material on permanent deformation was also studied. The experiment highlighted the sensitivity of the mixture to tire pressure, surface layer thickness, vehicle speed, and temperature. The results indicate that the selection of cold recycling applications for airfield pavement should account for the unique site-specific conditions and the structural composition of the pavement where the CR layer will be incorporated. The evident viscoplastic characteristics in CR mixtures in the triaxial repeated load experiments highlighted the importance of considering them in the structural design of the CR layer.

Experimental and numerical analysis of injection-induced permeability changes in pre-existing fractures

This paper presents a combined laboratory and numerical investigation on the injection-induced permeability changes in pre-existing fractures. The analyses conducted were primarily based on the results of an innovative laboratory experiment designed to replicate the key mechanisms that occur during hydraulic stimulation of naturally fractured rocks and/or faulted zones. The experiment involved pressure-controlled fluid injection into a laboratory-scale pre-existing fracture within a granite block, which was subjected to true triaxial stress conditions. Rough and smooth fractures are investigated, and the results are discussed. Based on the experimental results, two contributing mechanisms were considered to describe the pressure-driven permeability changes in pre-existing fractures: (1) elastic opening/closure leading to a reversible permeability change, and (2) fracture sliding in shear mode, causing dilation and hence an irreversible permeability increase. With these assumptions, an aperture-dependent permeability function was adopted to couple the hydraulic flow with the mechanical deformations along the fracture. Subsequently, a 3D coupled hydro-mechanical model was developed to replicate fluid-injection tests conducted at various conditions, including different stress conditions and fracture surface roughness. The employed modeling framework effectively captured the experimental observations. Our results indicate that the maximum permeability increases twofold.

Mechanisms of void nucleation on neat and Glass Syntactic PolyPropylene using in situ synchrotron radiation tomography

The mechanisms of void nucleation of a hollow glass syntactic foam during tensile loading were studied in depth. Flat-notched geometries, cut-out from neat and Glass Syntactic PolyPropylene (GSPP), were investigated by in situ microtomography. Notched specimens with two notch root radii, 4 mm and 0.15 mm named respectively N4 and N0.15, to set initial triaxial stress state in the minimum cross section, were observed. Tomographic data sets, with a resolution of 1.3μm, from stepwise tensile loading, at the SOLEIL synchrotron radiation facilities, were retrieved from the notched zone. In addition, they allowed gathering both the width and thickness evolution in the minimum cross section, and the notch opening displacement during the tests.In line with literature, neat PolyPropylene (PP) showed crazes concentration at the specimen core in N4 specimen, whereas, in N0.15 specimen, they were located at the notch root. In isolated Hollow Glass Microspheres (HGM), mechanisms of crazing and debonding were correspondingly highlighted in the PP matrix and at the poles of HGM. Finally, in GSPP, decohesion follows the same trend as in neat PP, i.e. at the specimen core and near the notch, respectively in N4 and in N0.15 geometry. Scenarios of void nucleation and propagation were outlined. The initiation of the brittle crack in the GSPP is mainly due to the matrix-HGM decohesion followed by the coalescence of near neighbouring caps.