Rock Bridge Research Articles

The Impact of Fracture Persistence and Intact Rock Bridge Failure on the In Situ Block Area Distribution

The in situ block size distribution is an essential characteristic of fractured rock masses and impacts the assessment of rockfall hazards and other fields of rock mechanics. The block size distribution can be estimated rather easily for fully persistent fractures, but it is a challenge to determine this parameter when non-persistent fractures in a rock mass should be considered. In many approaches, the block size distribution is estimated by assuming that the fractures are fully persistent, resulting in an underestimation of the block sizes for many fracture geometries. In addition, the block size distribution is influenced by intact rock bridge failure, especially in rock masses with non-persistent fractures, either in a short-term perspective during a slope failure event when the rock mass increasingly disintegrates or in a long-term view when the rock mass progressively weakens. The quantification of intact rock bridge failure in a rock mass is highly complex, comprising fracture coalescence and crack growth driven by time-dependent changes of the in situ stresses due to thermal, freezing-thawing, and pore water pressure fluctuations. This contribution presents stochastic analyses of the two-dimensional in situ block area distribution and the mean block area of non-persistent fracture networks. The applied 2D discrete fracture network approach takes into account the potential failure of intact rock bridges based on a pre-defined threshold length and relies on input parameters that can be easily measured in the field by classical discontinuity mapping methods (e.g., scanline mapping). In addition, on the basis of these discrete fracture network analyses, an empirical relationship was determined between (i) the mean block area for persistent fractures, (ii) the mean block area for non-persistent fractures, and (iii) the mean interconnectivity factor. The further adaptation of this 2D approach to 3D block geometries is discussed on the basis of general considerations. The calculations carried out in this contribution highlight the large impact of non-persistent fractures and intact rock bridge failure for rock mass characterization, e.g., rockfall assessment.

Cascade effect of rock bridge failure in planar rock slides: numerical test with a distinct element code

Abstract. Plane failure along inclined joints is a classical mechanism involved in rock slope movements. It is known that the number, size and position of rock bridges along the potential failure plane are of prime importance when assessing slope stability. However, the rock bridge failure phenomenology itself has not been comprehensively understood up to now. In this study, the propagation cascade effect of rock bridge failure leading to catastrophic block sliding is studied and the influence of rock bridge position in regard to the rockfall failure mode (shear or tension) is highlighted. Numerical modelling using the distinct element method (UDEC, Itasca) is undertaken in order to assess the stability of a 10 m3 rock block lying on an inclined joint with a dip angle of 40 or 80∘. The progressive failure of rock bridges is simulated assuming a Mohr–Coulomb failure criterion and considering stress transfers from a failed bridge to the surrounding ones. Two phases of the failure process are described: (1) a stable propagation of the rock bridge failures along the joint and (2) an unstable propagation (cascade effect) of rock bridge failures until the block slides down. Additionally, the most critical position of rock bridges has been identified. It corresponds to the top of the rock block for a dip angle of 40∘ and to its bottom for an angle of 80∘.

Study on Dynamic Evolution of Roof Crack and Support Timing of Secondary Tunneling for Large Section Open-Off Cut in Deep Mines

The stability of large section open-off cut in deep mines (LODM) is the key factor affecting the normal equipment installation and safe mining in fully mechanized top-coal caving face. The mechanical model shows that the deflection of the roof of the LODM is proportional to the cubic of span. In this paper, UDEC Trigon model is established, and the parameters of different coal measures strata are modified in detail. The evolution law, failure mode, and damage degree of roof cracks in secondary tunneling are studied, and the roof support effect is analyzed. The numerical simulation results show that the process of roof crack evolution after the primary excavation section and the second excavation section can be divided into three stages according to microseismic activities, and the reasonable supporting time can control the propagation of roof microcracks and reduce the development height of macrocracks. The rock bridge existing in the roof rock stratum after the combined support of long and short anchor cables can effectively limit the formation of macrocracks and their interaction; especially the key support in the interface area can reduce the development height of roof cracks in secondary tunneling and weaken the damage degree of roof rock stratum in the LODM. The field test shows that the moved volume of rib-to-rib and roof-to-floor of the LODM is stable at about 350 mm and 550 mm, respectively. The numerical simulation in this paper is helpful to understand the failure mode of roof in LODM with large mining height and provides a method for the design of its control technologies.

Compression‐induced crack initiation and growth in flawed rocks: A review

AbstractThe purpose of this review is to discuss the development and the contribution of the experiments and numerical simulations in compression‐induced failure characteristics of flawed rock specimens. Investigation is essential to understand the fundamental failures occurring in a rock bridge, for assessing anticipated and actual performances of the structures built on or in rock masses. The review begins by representing and discussing compression‐induced crack initiation and growth in flawed rocks and explaining the significance of studying these issues in Section 1. The crack initiation and growth behaviors in flawed rocks under uniaxial, biaxial, and triaxial compressions are described in depth in Section 2 where it is expected to distinguish 2‐D crack growth from 3‐D crack growth. After that, the failure characteristics of flawed rock specimens due to temperature treatments and hydraulic pressure are systematically reviewed. Numerical studies of the compression‐induced failure characteristics of flawed rock specimens based on different numerical theories and numerical models are comprehensively evaluated in Section 3. In Section 4, the new findings obtained recently from experimental and numerical studies are drawn. Finally, some aspects of prospective research and a brief summary are presented in Sections 5 and 6.

Applicability of Critical State Concept in Determination of Triaxial Strength of Non-Persistent Jointed Rock

Rocks encountered in civil and mining engineering structures are generally intersected by discontinuities. The triaxial strength behaviour of a jointed rock intersected by a discontinuity has been a topic of keen interest for the engineering fraternity. It is well established that the strength behaviour of such rocks is highly non-linear. In the past, Barton’s critical state concept has been used to correctly define the curvature of the non-linear failure envelopes of intact and jointed rocks. The aim of the present study has been to evaluate the applicability of the critical state concept for the rock, which is intersected by non-persistent discontinuity having weak foreign material. Triaxial strength tests were conducted on specimens of rock like model material. The specimens were intersected by a non-persistent discontinuity with various combinations of orientation, degree of persistence and number of joint segments. The range of confining pressure was varied from zero (uniaxial loading condition) to reasonably high (critical state) values. The study indicates that the rock intersected by discontinuity comprising of joint segments (having weak foreign material) and intact rock bridges, do follow the critical state concept. However, the triaxial strength behaviour is substantially affected by the presence of non-persistent joints. It is shown that the critical state concept based Modified Mohr–Coulomb (MMC) criterion can be used with confidence to model the triaxial strength of rocks. Correlations have been suggested to assess the criterion parameters based on attributes of the discontinuity and intact rock.

Analysis and determination of the behavioral mechanism of rock bridges using experimental and numerical modeling of non-persistent rock joints

Presence of rock bridges (RB) in natural non-persistent discontinuity sets is an effective factor on the stability of rock structures. Investigations show that the bearing capacity of jointed rocks is changed with variation of different joint parameters. Therefore, in order to investigate the effect of parameters such as contact area and number of rock bridges, normal load, angle, length, and number of joints on shear strength of non-persistent rock joints and also to recognize the interaction of these parameters on the mechanical behavior of joints, experimental design methods of Taguchi and central composite design (CCD) were used for the sample generation, testing and numerical modeling. The effective parameters on the shear strength of jointed samples were obtained based on the previous studies. Using the Taguchi method, 16 samples were tested at CNL condition and the effect of parameters such as normal stress, number, and area of rock bridges was investigated. To evaluate other joints parameters, 30 experiments were designed using CCD method and examined using numerical modeling. Using the analysis of variance (ANOVA), it was found that the obtained models are statistically significant. According to the results of ANOVA, the area of rock bridges and the angle of joints showed the highest and the lowest effect on shear strength of coplanar and non-coplanar jointed samples, respectively. The results displayed that the dominant failure for planar non-persistent joints is pure shear and a combination of tensile and shear cracks is created from the both tips of adjacent joints. Moreover, it was found that the dominant failure of non-coplanar joints is the combination of shear and tension. Bonded particle model (BPM) and smooth joint model (SJM) were also applied for numerical modeling. A new method was considered for applying SJ to the models, which solved the interlocking problem during the test.

Effect of the number of coplanar rock bridges on the shear strength and stability of slopes with the same discontinuity persistence

Analyzing the shear resistance of a potential sliding surface based on discontinuity persistence usually does not consider the number of coplanar rock bridges. To examine the effect of the dispersion/number of rock bridges on the shear strength and rock slope stability, direct shear tests and large-scale rockslide simulations were conducted employing the 2D particle flow code (PFC2D). The shear strength of rock bridges under different configurations and the same discontinuity persistence was analyzed based on both the shear behavior controlled by the stress response and crack propagation. The results at both the laboratory and slope scales indicate that the shear resistance decreases with increasing dispersion/number of rock bridges due to multiple rock bridges breaking separately, the mechanism of which is that the rock bridge system more easily experiences initial failure with increasing dispersion/number of rock bridges. On this basis, a function of the strength reduction coefficient with the number of rock bridges was established considering the laboratory-scale numerical simulation results. A feasible stability analysis method, i.e., the improved limit equilibrium method based on the strength reduction coefficient, was proposed to consider the effect of the dispersion/number of rock bridges on the slope stability, which is a useful innovation to ensure that the stability analysis method of potential rockslides, including coplanar rock bridges, is more realistic and accurate.

Hybrid finite‑discrete element simulator based on GPGPU‑parallelized computation for modelling crack initiation and coalescence in sandy mudstone with prefabricated cross-flaws under uniaxial compression

Discrete element method or extended finite element method is often adopted to simulate crack initiation, propagation, and coalescence. However, the transition of rock from continuous medium to the discontinuous medium cannot be simulated. Moreover, previous studies on propagation and coalescence of prefabricated flaws often focus on single or multiple parallel prefabricated flaws. In reality, the fractures in rock mass usually exist in the form of cross flaws. To solve the inconsistency, the uniaxial compression of rock samples with prefabricated cross-flaws is modelled in this study through the GPGPU-parallelized Y-HFDEM IDE, and the modelling results are compared with those from laboratory experiments. The effects of four geometric parameters of the prefabricated cross-flaws on the crack initiation, propagation, and coalescence process are explored: (1) the joint continuity parameter k, (2) the angle α between the axial load direction and the dip direction of the primary flaw, (3) the angle β between the direction of the rock bridge and the dip direction of the primary flaw, and (4) the angle γ between primary and secondary flaws. It is found that numerical simulation results are in good agreement with those of laboratory experiments in terms of not only the qualitative crack initiation, propagation, and coalescence processes but also the quantitative crack initiation locations and stress, crack propagation mechanism, and coalescence locations. It is concluded that the presence of the prefabricated cross flaws promotes the rock samples fracture more seriously during uniaxial loading. Moreover, two new crack coalescence mechanisms that have not been reported in previous studies are observed through numerical simulations and laboratory experiments. Thus, compared with laboratory experiments, the GPGPU-parallelized Y-HFDEM IDE provides another cheaper but more flexible and robust tool for the study on the crack initiation, propagation, and coalescence process in rocks with prefabricated flaws.

Influence of acid rain on slope instability mechanism—a case study in Sichuan provincial highway, China

Acid rain has important influences on the physical and mechanical properties of rock as a result of mineral conversion and dissolution of cement. There are clear spatial correlations between the occurrence of slope failure and rainfall pH value in acid-rain areas. Although some fatal landslides have been ascribed to acid rain, those landslides all consisted of sedimentary rocks that generally contained carbonate minerals, which are particularly susceptible to dissolution in acidic conditions. This paper describes the mechanical deterioration of the structural plane based on acid-rain simulation experiments on a slope cut in hard rock along Sichuan provincial highway S211, China. In the experiments, the cohesion and internal friction angle of the structural plane fell to 35.4% and 6.8% of their original values, respectively, and the strength deterioration exhibited a power-law relationship with the exposed area of the rock bridges. Mineralogical and hydrochemical analyses including polarising microscopy, X-ray diffraction, scanning electron microscopy, and inductively coupled plasma optical emission spectrometry were employed to describe the micromechanisms of weakening. Mechanical weakening of the structural plane is attributed to deterioration of both the composition and the structure. Transformation from hard essential minerals to clay minerals through pyroxene chloritisation, plagioclase illitisation, illite smectitisation, and chlorite dissolution reduced the strength properties of rock bridges. In addition, abundant secondary micro-cracks were formed by propagation of worm-like dissolution pits, thus disintegrating rock bridges and further reducing the strength of the structural plane. This paper provides a better understanding of slope failure mechanisms in areas affected by acid rain.

Study on the fracture behavior of prefabricated fissures granite based on DIC and laser scanning techniques

AbstractThe initiation, propagation, and coalescence of cracks in the rock bridge are the root causes of rock failure. However, the identification of cracks propagation paths is a problem in rock mechanics. This paper studies the evolutionary law of the strain field in the rock bridge region of granite with pre‐fissures using 3D‐DIC after equivalence and simplification. Based on the real crack initiation mechanism of “relative slip between regions” proposed in this paper, combined with the priority order of crack propagation at the edge of the rock bridge, the pattern of cracks propagation and coalescence was obtained. We analyze the fracture characteristics in roughness and morphology to verify the validity of the proposed mechanism. The tensile and shear failure areas around the rock bridge were identified quantitatively, and the roughness, fractal dimension, and energy consumption of the sections formed by tensile failure and shear failure are different.

A process-based coal swelling model: Bridging the gaps between localized swelling and bulk swelling

Injection of CO2 and coal seam gas production induce coal swelling/shrinkage. Laboratory tests indicate that coal swelling may go through several stages from localized swelling at fracture surfaces to bulk rock swelling. The coal Langmuir swelling strain constant normally ranges from 0 to 0.04. This study provides a process-based coal swelling model that covers the whole swelling procedure. We account for three swelling strains, videlicet, the matrix swelling strain, fracture swelling strain, and bulk rock swelling strain. Dynamic partial separation coefficients are employed to quantify the contributions of the matrix swelling strain to bulk swelling and the fracture (cleat) aperture reduction, bridge the gaps between localized swelling and bulk swelling, and link the three types of strains. This model is inserted into a permeability model and verified against permeability measurement and rock swelling data. The three samples used for verification are bituminous coals from the Illinois Basin (depth of ~ 200 m) in the US and Henan Province in China (depth of ~ 310 m). In essence, the swelling model is also applicable to other coal types with a linear relationship between the matrix swelling strain and adsorbed gas content. By matching with long-term permeability measurement data, multiple permeability evolution stages are observed due to the swelling transition. Sensitivity analyses show that the matrix block size, matrix swelling properties, and diffusivity control the duration, occurrence, and magnitude of matrix swelling’s contribution to local and bulk swelling during swelling transition, while rock bridge swelling properties have a marginal influence on coal swelling.

Experiment and numerical simulation on cracking behavior of marble containing double elliptic holes under uniaxial compression

When a rock mass has undergone a long period of geological structural change, various defects such as pores and cracks. Here, the effects of defects on the mechanical properties of a rock mass were investigated. In this research, the strength, deformation and crack evolution behavior of marble containing double elliptic holes under uniaxial compression were evaluated by experiment and numerical simulation. The experimental results show that the dip angle α affects the strength, ultimate failure mode, crack initiation and propagation of marble specimens. As the dip angle increase, crack initiation loci transfer from the elliptic hole surface to the tip. For the ultimate failure mode, the cracks are mainly tensile when α is low, the cracks are mainly shear cracks when α approaches 75°, at 90°, the marble specimen is subject to tensile failure. ANSYS/LS-DYNA was used to simulate the marble specimens containing double elliptic holes, the numerical simulation results show good agreement with the experimental results. Analysis of tensile stress contours in a marble specimen and the different stress states at measuring points. Showed that tensile cracks initiate in the middle of the elliptic hole surface when the dip angle is small, and then the initial position of the tension crack shifts to the tip with increasing dip angle. This is consistent with the experimental findings in which there is no joint crack between the two elliptical holes in the marble specimens when the dip angle is small. A rock bridge fracture appears between the elliptical holes when α is close to 90°.

Experimental Study on Shear Mechanism of Rock-Like Material Containing a Single Non-Persistent Rough Joint

The geometrical and mechanical properties of non-persistent joints as well as the mechanical behavior of intact rock (rock bridges) are significantly effective in the shear strength of weakness planes containing non-persistent joints. Therefore, comprehensive knowledge of the shear mechanism of both joints and rock bridges is required to assess the shear strength of the planes. In this study, the shear behavior of specimens containing a single non-persistent rough joint is investigated. A novel procedure was used to prepare cast specimens embedding a non-persistent (disc-shaped) rough joint using 3D printing and casting technology, and the shear strength of the specimens was examined through an extensive direct shear testing program under constant normal load (CNL) condition. Three levels for three different variables of the joint roughness, rock bridge ratio, and normal stress were considered, and the effects of these factors on the shear behavior of prepared samples were tested. The experimental results show a clear influence of the three variables on the shear strength of the specimens. The results show that the normal stress applied to the jointed zone of weakness planes is considerable, and thus joint friction contribution should be taken into account during shear strength evaluation. Furthermore, the dilation mechanism of the specimens before and after failure was investigated through a digital image correlation analysis. Finally, a camcorder was used to analyze the location and sequence of the initiated cracks.

Influence of weak inclusions on the fracturing and fractal behavior of a jointed rock mass containing an opening: Experimental and numerical studies

To gain a better understanding of the interaction between weak inclusions and jointed rock masses, a conceptual model containing a joint set and an opening is prepared, and cases involving unfilled and filled openings are considered. The influence of weak inclusions on the fracturing and fractal behavior of these models is investigated by using laboratory experiments, the rock failure process analysis (RFPA) code and the fractal geometry. An overhanging beam model is proposed to explain the initiation mechanism of tensile cracks around the unfilled and filled openings. The RFPA simulations provide deep and quantitative insight into the fracturing behavior. The coalescence patterns of the surrounding rock mass obtained from physical and numerical tests are in reasonable agreement, and can be classified into two categories: shearing along the joint set and cutting through the rock bridges. The inclusion with a low strength exerts little influence on the failure pattern but has an appreciable reduction in the stress values and an appreciable increment in the mechanical properties. The crack coalescence exhibits fractal properties, and there are good correlations between the fractal dimension and mechanical properties of these jointed rock specimens containing unfilled and filled openings.

Experimental study of crack evolution in prefabricated double-fissure red sandstone based on acoustic emission location

The development of micro-cracks during damage to rocks affects the propagation of macroscopic cracks on the surface. To explore the crack evolution among pre-existing flaws in rocks, based on the acoustic emission (AE) source location results, the paper analysed the influences of micro-crack development on failure mode. By analyzing AE characteristic parameters, the main controlling factors affecting the development of micro-fractures are determined. The results show that: (1) the development of micro-cracks in rock samples presents a trend of having a high-energy fracture point, the low-energy and small fracture region, the extensive fracture region, and a macroscopic fracture zone. (2) The difference in rock failure mode arises from the influence of rock bridge on the number, location, and extension direction of high-energy fractures, which results in the difference in the formation of main damage zone in rock samples. (3) The total number of micro-cracks, the proportion of shear cracks, and mixed-mode cracks gradually increase with the increase of the rock bridge inclination angle, leading to the gradual evolution of rock samples from simple tensile failure mode to complex crack penetration mode. The variation of the rock bridge inclination angle affects the stress direction of the rock particles at a microscopic level, while it affects the direction of macroscopic crack propagation at a macroscopic level.

Shear Behavior of Marlstone Containing Parallel Fissure under Normal Unloading

Shear tests under normal unloading were carried out to further study the shear mechanical behavior of marlstone containing parallel fissures. The results reveal that the failure on the rock bridge is tensile failure except for the limited extrusion failure at the tip of the prefabricated fissure. The failure on both sides is generally tensile-shear mixed failure, in which the tensile failure is mainly concentrated in the middle of both sides. In general, it can be summarized as a tensile-shear failure mode of STS-T-STS (S means shear failure, T means tension failure). The failure normal stress of the specimens gradually increases and then decreases with the increase of the fissure inclination, increases with an increase in the initial normal/shear stress, and decreases with the increase of the unloading rate. Strong dilation occurred in the shear process of the specimens, which shows obvious arch effect. The variation law of dilatancy deformation and horizontal deformation in the stage of normal stress unloading is just opposite to that of the failure normal stress. The increasing effect of high shear stress on shear deformation is greater than that of dilatancy deformation, while the inhibiting effect of high normal stress on dilatancy deformation is greater than that of the shear deformation.

Shear Mechanism of Non-Persistent Notches Using Punch Shear Test

Experimental and discrete element methods were used to investigate the effect of non-persistent notch angle on the shear behavior of joint’s bridge area. A punch-through shear test was used to model the gypsum cracks under shear loading. Gypsum samples with dimension of 150 × 150 × 50 mm were prepared in the laboratory. Within the specimen model and near the one edge, two notches were provided. Six different configuration systems were prepared for notches. In these configurations, the length of notches was taken as 2 cm. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 × 100 mm. Similar to those for joints configuration systems in the experimental tests, i.e. six models with different rock bridge lengths and rock bridge joint angle were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the notch angle. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. The failure pattern and failure strength are similar in both methods, i.e. the experimental testing and the numerical simulation methods.

Failure Characteristics of Complicated Random Jointed Rock Mass Under Compressive-Shear Loading

Most natural rock masses contain a large number of random joints and fissures, and most of the rock masses at the rock engineering are commonly in both compression and shear stress environment. However, the research on the failure characteristics of complex random jointed rock mass under compressive-shear loading is still limited. To address this gap, this paper uses the particle flow code 2D to establish a discrete fractured rock mass model and carry out a series of numerical tests with different compressive-shear angles (α) and different joint geometric parameters. The effects of compressive-shear angle and joint geometric parameters on the strength and failure characteristics of fractured rock masses are studied. The results indicate that with the increase of α, the peak strength of the specimen decreases gradually, and the failure mode changes from the composite shear failure mode (Mode-I) to a plane shear failure mode (Mode-II) and then to intact shear failure mode (Mode-III). Specifically, the three failure modes occur in the specimens with α = 15°, 30° or 45°, 60°, respectively. The existence of joints affects stress distribution on rock mass during the loading process. Furthermore, the stress at the joint tip is relatively concentrated, while on both sides of the joint is smaller. Three kinds of crack coalescence patterns are observed: tensile, shear, and tensile-shear mixed coalescence. The inclination angle of the rock bridge between adjacent joints affects the specific type of coalescence.

Crack coalescence in rock-like specimens with two dissimilar layers and pre-existing double parallel joints under uniaxial compression

Layered rock masses with joints are widely found in nature. Their mechanical behavior plays a key role in rock engineering applications. However, previous studies have concentrated on the single lithologic layer, and few studies have reported the crack coalescence mechanism in layered rock masses with joints. In this study, uniaxial compression tests were performed on jointed rock-like specimens with two dissimilar layers. The acoustic emission (AE) and the digital image correlation (DIC) techniques are employed to investigate the crack coalescence process of specimens with two dissimilar layers. The influence of the joint angle and rock bridge angle on the mechanical behavior and failure processes in layered rock masses is investigated. The results show that the peak strength is associated with the joint angle and the rock bridge angle. Seven types of crack coalescence have been identified in the specimens, which are not only related to the joint angle and the rock bridge angle but also influenced by the rock layers. Cracks easily coalesce when the joint angle and the rock bridge angle are small. However, when the joint angle and the rock bridge angle are larger, it is difficult for cracks to initiate and propagate in the layer with higher strength. The failure mechanism of the specimens is primarily caused by crack propagation in the layer with lower strength.

Time-dependent behavior of rock-like specimen containing multiple discontinuous joints under uniaxial step-loading compression

Rock with multiple discontinuous joints widely exists in rock engineering, and its mechanical properties are complex, which greatly increases the difficulty of engineering design and construction. Time-dependent deformation characteristics and long-term strength evaluation of jointed rock masses remain poorly understood. In this work, the creep experiments of rock-like specimens with multiple discontinuous joints under uniaxial step-loading compression are carried out to explore the influence of joint geometry (rock bridge length, joint length, joint angle, and joint spacing) on creep strain, long-term strength, and failure pattern of specimens with multiple discontinuous joints. The following conclusions are drawn from the test results: 1) The deformation of jointed rock specimens has evident time-dependent effect, and the cumulative creep deformation increases as creep load increases; 2) The strength of jointed rock specimens under loading changes with time, and the ratio of long-term strength and creep peak strength ( σ∞/ σc) of the tested specimens ranges from 41% to 96%; 3) The distribution of initial joints affects the creep fracture modes of rock-like specimens. The rupture of rock-like specimens with different joints distribution is mainly caused by the growth of wing cracks and quasi-coplanar secondary cracks. Three different failure modes are observed from these specimens: i) tensile failure with cracks across the joint plane; ii) shear failure with cracks along the joint plane; and iii) tensile failure with cracks along the joint plane. Based on the principles of damage mechanics and fracture mechanics, a theoretical mechanistic model considering both the closure stage of pre-existing open joints and time-dependent propagation stage of new cracks is established. Considering the influence of joint length, joint angle and joint density, the evolution of creep strain of rock-like specimen with multiple discontinuous joints is analyzed. The theoretical model results agree well with the experimental results, which indicates that the established model can replicate the creep failure process of jointed rock mass. These theoretical and test results help us better understand the effect of multiple joints on the long-term behavior of rock mass.