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Fissures and holes widely exist in rock mechanics engineering, and, at present, their failure mechanisms under complex compress and shear stress states have not been well recognized. In our work, a fracture mark, ξ, is introduced, and the kernel function of the smoothed-particle hydrodynamics (SPH) is then re-written, thus realizing the fracture modelling of the rock media. Then, the numerical models containing the fissures and holes are established, and their progressive failure processes under the compress and shear stress states are simulated, with the results showing that: (1) the improved SPH method can reflect the dynamic crack propagation processes of the rock masses, and the numerical results are in good agreement with the previous experimental results. Meanwhile, the improved SPH method can get rid of the traditional mesh re-division problems, which can be well-applied to rock failure modeling; (2) the hole shapes, fissure angles, fissure lengths, fissure numbers, and confining pressure all have great impacts on the final failure modes and peak strengths of the model; and (3) in practical engineering, the rock masses are in the 3D stress state, therefore, developing a high performance 3D SPH program and applying it to engineering in practice will be of great significance.

In order to systematically evaluate the damage degree in Jinping deep tunnels during excavation, an improved SPH algorithm with good Lagrangian characteristics is introduced. By modifying the derivative of the traditional SPH kernel functions, the brittle failure processes of particles are realized. The ‘Fissure Searching Generating Method’ (FSGM) has also been used to determine the establishment of joints and the tunnel excavation parts. Based on the Jinping tunnel engineering practices, numerical models are set up, and the damage degrees of the tunnel excavation under different buried depths, joint distances, positions and inclination angles are numerically simulated, and compared with the engineering site pictures to verify the rationality. (1) Typical “V” shaped shear failure zones are observed when no joints exist in the model, and the damage degree increases with the increasing tunnel buried depth. (2) The increase of joint-tunnel distance causes the damage degree to decrease, and the failure modes between the tunnel and the joint transform from tensile to shear failure. (3) The stability of the tunnel is less affected when the joint appears in the vault, north and south arch shoulder, but the tunnel is prone to becoming unstable when the joint appears in the north and south walls. (4) Steep and gentle dips of the joints greatly influence the excavation stability of the tunnel, while the excavation damage range becomes the smallest when the joint inclination angle is 45°. (5) The improved method can be well applied to predict and evaluate surrounding rock damage in Jinping tunnels.

Great achievements have been made regarding the stress field in the two-dimensional state, however the study of three-dimensional stress field visualization has still not been comprehensively examined. The model with internal cracks was prepared by the laser-medium interaction (3D-ILC), and with the aid of the photoelastic test technology, it visually showed the distribution characteristics of the stress field inside the rock with defects under the three-point bending test method. Primarily, based on the two-dimensional and three-dimensional stress optics law, the isometric fringes were converted into phase differences or optical path differences to visualize the stress field. Moreover, transparent glass, which had better transparency and brittleness closer to real rock was selected as the specimen material. Internal cracks changed the stress fringe distribution of the specimen, and the combination of 3D-ILC technology and photoelasticity provided a new way to visualize the three-dimensional stress field of brittle materials with internal cracks. Through the secondary development and utilization of ABAQUS finite element analysis software, the internal stress fields of brittle solid materials with horizontal internal cracks were visualized. Accurate characterization of the three-dimensional stress field of brittle solid materials has been a long-term goal pursued by researchers in the field of fracture, and it is also the basis and key to solving many practical engineering problems such as design, safety analysis and evaluation.

In this study, the smoothed particle hydrodynamics method was modified to the two-phase-improved kernel of smoothed particle hydrodynamics (2P-IKSPH). By mapping the water pressure of the water base particles to the solid base particles, the hydraulic fracturing processes of rock masses were realised in a set of unified equations, which could reduce the amount of calculation and improve calculation efficiency. The kernel function in the traditional SPH method was improved to realise the brittle fracture characteristics of solids. A solid–water coupling algorithm was also proposed to automatically transform the damaged solid base particles to water base particles; therefore, eliminating the need to search and regenerate the water base particles. The particle domain searching method was used to realise arbitrary generations of the initial fissure base particles, initial tunnel base particles, and initial water base particles. Three numerical examples are presented to illustrate the effectiveness of 2P-IKSPH, and the correctness of the proposed method was verified by comparison with previous experiments and numerical results. Finally, an engineering example of the progressive failure of a horseshoe-shaped tunnel during stress balance, tunnel excavation, and water filling was numerically simulated, indicating that 2P-IKSPH can be effectively applied to rock engineering.

The present work aims to propose a meshless method to establish the tooth meso-structures and model the tooth fracturing processes as well as investigate the influencing factors that affect the dental mechanical properties. To this end, the traditional kernel function in the SPH method has been improved by introducing a fracture mark ξ to realize the progressive failure processes of teeth; The "Particle Searching Method" has been proposed, which can realize the establishments of microstructures of teeth such as enamel, dentine, pulp, PDL and alvedar bones. The Weibull function is introduced to represent the heterogeneity of teeth, which can realize the random distribution characteristics of dental mechanical parameters. The simulation results of homogeneous and heterogeneous teeth show that the failure mode changes from tensile splitting (homogeneous) to shear failure (heterogeneous). Meanwhile, the fracture networks become more complex, and the failure stress decreases sharply. The cuspal angles also have a great impact on the teeth fracture characteristics. The failure modes changes from tensile splitting of the enamel tip to the cracking from the contact points between the enamel and the rigid ball; Different fssural morphologies have little influences on the teeth failure characteristics. The research results can provide some references for the applications of SPH method into biomechanical simulations such as teeth failure. Meanwhile, it can also provide some guidance for the understandings of the internal mechanisms of teeth fracture processes, the diagnosis and treatments of clinical diseased teeth as well as the design of bionic teeth materials.

The numerical simulation of rock fracture mechanics has been a major research hotspot and challenging area in the field of rock mechanics. Based on this background, a smooth particle dynamics numerical simulation method (RGIMP) is proposed to consider the failed material point. The RGIMP algorithm is simple in form, does not need to use multiple velocity fields, takes advantage of the efficient computational efficiency and stability of the GIMP itself, and simulates the brittle fracture process of the rock by the failure process of the material point, and the resulting cracks are display cracks. The accuracy of the RGIMP algorithm proposed in this paper was verified by uniaxial compressive numerical simulations of single-cleft standard cube specimen, double-cleft standard cube specimen, and double-cleft Brazilian disc specimen. The research results provide a certain reference for the application of smooth particle dynamics methods in rock mechanics engineering and understanding of rock fracture mechanisms.

The presence of random fissures has a great impact on rock slope stability. To investigate the failure modes and stability of rock slopes containing different types of pre-existing fissures, the fracture mark ξ was introduced to improve the kernel function in the traditional smoothed particle dynamics (SPH) method, and a novel numerical method, the improved kernel of smoothed particle hydrodynamics (IKSPH), was proposed to realise the microscopic damage characteristics of particles. The ‘random fissure generating method’ has been proposed for random fissure generation, and the gravity increase method has been embedded into the IKSPH program, thereby realising the stability analysis of rock slopes considering crack propagation processes. A typical steep rock slope is taken as a numerical simulation example considering the random distributions of preexisting fissures, and its failure modes as well as the stability under different conditions were simulated. The results show that the failure processes of the rock slope contain propagations of microcracks and then macrocrack penetrations. When the fissure length is short, shallow collapse failure modes can be observed; when the fissure length is long, the deep layer slide occurs, and the slope stability decreases with an increase in fissure length. The micro and macrocrack surfaces are basically consistent with pre-existing fissure angles, and the safety factor is the least at a fissure angle of 30°. The greater the fissure density, the greater the number of macrocracks, and the stability decreases with an increase in the number of pre-existing fissures. The research results can provide some references for disaster protection and understanding the failure laws of rock slopes. Meanwhile, combining the geological survey results with the numerical simulations and developing a high-performance IKSPH program will be a future research direction.

Defects widely exist in rock masses, which have great impacts on the rock mechanical properties. The pre-existing fissures and holes are two common rock defects. In order to study the influence of hole shapes and fissure geometries on the failure modes and mechanical properties of rock masses, the derivatives of kernel functions in the traditional SPH method have been improved by introducing a fracture mark ξ, and a novel numerical method named improved kernel of smoothed particle hydrodynamics (IKSPH) has been developed to realize the simulations of rock fracture processes. The Monte Carlo method has also been introduced into the proposed method to realize the formations of random fissures. The small-scale numerical rock specimens with different hole shapes as well as random fissures are established. The crack propagation processes, the failure modes and the mechanical properties under uniaxial compression are simulated, results show that: ‘Wing cracks’ initiate from the random fissures, whose locations and interaction modes differ according to the geometries of random fissures. For rectangle hole, the crack initiations mainly occur at the upper and lower edges as well as the corners; for circular hole, tensile cracks appear at the 6 and 12 o’clock directions, meanwhile, shear cracks initiate at the 5 and 7 o’clock direction after the tensile crack propagates to a certain extent; for trapezoid and triangle hole, crack initiations mostly appear at the corners of the hole; the length and quantity of pre-existing fissures have greater influences on the mechanical properties of rock masses than the hole shapes and fissure dip angles. The research results can provide guidance for the correct understandings of fractured rock mechanisms. Meanwhile, the proposed method can also provide references for the applications of SPH method into simulations of rock fracture mechanics. At the same time, future research focus should be put on the applications of IKSPH method into engineering practices and developing high-performance IKSPH programming.

The simulation of crack propagation processes in rock engineering has been not only a research hot spot among scholars but also a challenge. Based on this background, a new numerical method named improved kernel of smoothed particle hydrodynamics (IKSPH) has been put forward. By improving the kernel function in the traditional smoothed particle hydrodynamics (SPH) method, the brittle fracture characteristics of the base particles are realized. The particle domain searching method (PDSM) has also been put forward to generate the arbitrary complex fissure networks. Three numerical examples are analyzed to validate the efficiency of IKSPH and PDSM, which can correctly reveal the morphology of wing crack and the laws of crack coalescence compared with previous experimental and numerical studies. Finally, a rock slope model with complex joints is numerically simulated and the progressive failure processes are exhibited, which indicates that the IKSPH method can be well applied to rock mechanics engineering. The research results showed that IKSPH method reduces the programming difficulties and avoids the traditional grid distortion, which can provide some references for the application of IKSPH to rock mechanics engineering and the understanding of rock fracture mechanisms.

Deformation rate analysis utilizes deformation memory effect (DME) that is one of the fundamental properties of rock, to estimate in situ stress underground. It could be influenced by the stress history which has been subjected to in the past. To understand the influence under the cyclic loading path, in the experimental study, different stress levels were applied on sandstone samples and two types of granite samples. In the theoretical investigation, the sliding friction model consisting of multiple microstructure surfaces is considered in this paper. Both experiments and the theoretical model show that when the number of cyclic loading times keeps increasing, (1) the stress read at the DRA inflection is getting closer to the previously cyclic stress; (2) the angle at the DRA inflection becomes sharper, which gives clearer inflection point; and (3) the strain differential amplitude in the DRA curve gradually decreases and then toward a stable value. An upper limit exists for influence, indicating that the best cyclic loading times occur when the pulse amplitude of the strain differential stops changing. It is confirmed that the multiple cyclic loading method provides a better outcome for experiment using artificial preload when DME is utilized for stress reconstruction. Without other factors disturbing, the memory information of the in situ stress would hardly lose under the history of cyclic loading.

A stress analysis of a circular hole is one of the classical problems in mechanics. Internal cracks are inherent properties of materials, and they are mostly three-dimensional in form. However, studies on hole problems with three-dimensional internal cracks are still lacking. In this paper, internal cracks were generated in brittle materials containing circular holes based on 3D internal laser-engraved crack technology. Then, uniaxial compression tests were performed. The experimental results were compared with the existing literature, and theoretical and numerical simulation studies were carried out. The results show that: (1) The main crack shapes are the primary cracks and remote cracks. (2) The dynamic fracture characteristics existed in the formation of primary cracks and the surface of remote cracks. The tips of primary cracks were arc-shaped, and the surfaces of the remote cracks were curved. Remote cracks were tangential to the orifice where type III spear-like characteristics appeared. (3) The stress birefringence technology can be combined with 3D internal laser-engraved crack technology for internal crack stress information monitoring, the moire around the orifice was “flamboyant”, and the moire at the tip of the prefabricated crack was “petallike”. (4) The existence of internal cracks reduced the cracking and breaking load of the specimen, and compared with the intact orifice specimen, the upper primary crack, the lower primary crack, the remote crack and the failure load were reduced by 41.2%, 31.7%, 15.9%, and 32.3%, respectively. (5) The results of qualitative stress analysis of the orifice specimen were consistent with the initiation law of primary cracks and remote cracks. The K distribution based on M integral and the numerical simulation of crack propagation process based on the maximum tensile stress criterion were consistent with the law of primary crack growth. Compared with the current mainstream method of transparent rock research, 3D internal laser-engraved crack technology has certain advantages in terms of brittleness, crack authenticity, stress field visualization, and fracture characteristics, and the result will provide experimental and theoretical references for research on three-dimensional problems and internal cracks in fracture mechanics.

Prediction of tunnel surrounding rock deformation is important for tunnel construction safety evaluation. In this paper, machine learning algorithms are used to carry out a comparative study of the surrounding rock deformation prediction. The applications of Gaussian process regression (GPR), support vector machine (SVM), and long short-term memory network (LSTM) in the prediction of surrounding rock deformation sequences are compared and analyzed. The actual data of a diversion tunnel in a southwest region are used as an example to evaluate and compare the single-step prediction model and multistep prediction model established by the above algorithm. The results show that the machine learning algorithm has good operation effect on the prediction of surrounding rock deformation. Overall, the SVM model has the best prediction effect and outperforms the other two algorithms in terms of tracking the trend of data changes and the degree of data fit.

To investigate whether tumor texture features derived from pretreatment with 18F-fluorodeoxyglucose positron emission tomography (FDG PET) can predict histological response or event-free survival (EFS) in patients with localized osteosarcoma of the extremities treated by neoadjuvant chemotherapy (NAC). We retrospectively reviewed 35 patients with American Joint Committee on Cancer stage II extremity osteosarcoma treated with NAC and surgery. Primary tumor traditional parameters and texture features were measured for all 18F-FDG PET images prior to treatment. After surgery, histological responses to NAC were evaluated on the postsurgical specimens. A receiver operating characteristic curve (ROC) was constructed to evaluate the optimal predictive performance among the various indices. EFS was calculated using the Kaplan-Meier method and prognostic significance was assessed by Cox proportional hazards analysis. Pathologic examination revealed 16 (45.71%) good responders and 19 (54.29%) poor responders. Although both the texture features (least axis, dependence nonuniformity, run length nonuniformity, and size zone nonuniformity) and metabolic tumor volume (MTV) can predict tumor response of osteosarcoma to NAC, the traditional indicator MTV has the best performance according to ROC curve analysis (area under the curve = 0.918, p

The cohesion c and internal friction angle φ play different roles in the progressive failure process of the slope, which indicates that the reduction factors kc and kφ should be different in the calculation. Based on this, the program of double strength reduction factor method was compiled with FISH language, in order to study its application in the rock slopes under different distributions of weak interlayer, and the following conclusions were drawn: (1) the plastic zone calculated by double strength reduction factor method is generally distributed in the weak interlayer, which is basically consistent with the calculation result of the traditional method; (2) the degree to which c and φ play a role is related to the inclination angle of the bottom sliding surface of the unstable block θ. If θ kφ” can be adopted when θ

The predictions of failure zone during the foundation excavations will provide important guidance for the safety constructions of engineering structures. Based on this background, the smoothing kernel function in the traditional SPH method has been improved. The failure mark η is introduced into the program to realize the failure characteristics of particles at meso–scale. The “Killing Particle Method” has also been proposed, which can realize the simulations of complex excavation processes. The whole progressive failure processes of the excavation of a foundation pit are numerically simulated and the results show that (1) the failure zone of the excavated foundation pit without retaining walls appears at the corner and then gradually develops into the deep. However, the failure zone of the excavated foundation pit with retaining walls only develops longitudes along the retaining wall. (2) The stiffness of retaining wall has a great impact on the failure zone of foundation pit excavation. The greater the stiffness of retaining wall, the greater the damage degree. (3) The rationality of the proposed method is verified by the comparisons of the simulation results of the proposed method with the ABAQUS numerical examples and the engineering practices. Future research directions should focus on developing the 3D parallel IKSPH programs. The research results can provide some references for the applications of SPH method into predicting the failure zone of foundation pit excavations and ensuring the safety of engineering constructions.

In order to investigate the fracture mechanisms of the pressure tunnel lining under water-stress coupling, based on the traditional smoothed particle hydrodynamics (SPH) method, the solid-water particle interaction method, and the particle damage conversion algorithm are proposed to realize the hydraulic fracturing process, which is called the 2P-IKSPH method. The “particle domain searching method,” the “birth-and-death particle method,” and the “group discrimination searching method” have also been proposed to realize the simulations of complex processes of excavation, lining, and operation of the hydraulic tunnel. Taking the Guzeng hydraulic tunnel as an engineering example, the hydraulic fracturing of tunnel lining under different conditions is numerically simulated. Results show the following: (1) the 2P-IKSPH method can dynamically reflect the stress wave propagation processes of surrounding rock and the damage process of tunnel lining. (2) The lining damage mainly occurs on the vault and the arch foot. (3) The critical internal water pressure increases with the increase of the tunnel buried depth and the thickness of lining, but increases first and then decreases with the increase of the surrounding rock mass grade. The research results can provide some references for the optimization designs of tunnel lining and reinforcement of similar projects. Meanwhile, developing 3D parallelization program based on 2P-IKSPH will be the future research directions.

Formation and growth of hydraulic fractures can be strongly affected by pre-existing fractures in the rock mass. Until now the main attention was directed towards the investigation of the interaction between the hydraulic fracture and the pre-existing fractures intersecting its path, as they could significantly hamper its formation and growth, alter the geometry and produce additional leak-off. Less attention was paid to the interaction of the hydraulic fracture with parallel and coplanar pre-existing fractures, yet their interaction and coalescence can lead to unwelcome increase in the hydraulic fracture dimensions, change the direction of growth and in some cases result in undesirable effects such as environmental damage. In order to investigate the hydraulic fracture interaction with parallel pre-existing fractures we conducted a series of tests on transparent rectangular samples with two artificial cracks. One of the crack was loaded with pressurised fluid. The types of interaction were classified and the conditions of fracture coalescence formulated. The results will contribute to the understanding of hydraulic fracture propagation in fractured rock masses and mitigating environmental damage. Acknowledgements. Wang acknowledge support from the Natural Scinece Foundation of Jiangsu (BK20171130). The AVD and EP acknowledge support from the Australian Research Council through project DP190103260. AVD acknowledges the support from the School of Civil and Transportation, Faculty of Engineering, Beijing University of Civil Engineering and Architecture. Wang acknowledge support from the National Natural Science Fund (51409170,U1765204)

A method for three-dimensional crack propagation by the numerical manifold method (NMM) is analyzed. With the help of mathematical cover and physical cover, no Heaviside function is required to describe a crack in the NMM, and so the three-dimensional crack propagation with NMM can be analyzed being similar to that of two-dimensional cases. Mohr-Coulomb criterion with a tensile cut-off is used to analyze failure state of each crack tip line. A simplified method for determining the final propagating direction is described. According to the final propagating direction, a non-local crack tracking method is used to determine the updated crack tip line. Quadrilateral or triangle tracking method is selected according to the situation during propagation. For boundary faces, in order to make the deformed surface remain plane, new generated faces are needed to be triangulated. Three numerical examples are analyzed to validate the proposed 3D crack propagation method. The numerical results are all in good agreement with those results in the existing studies. Furthermore, a concrete gravity dam under water pressure with an overload factor is simulated and the progressive failure process of the concrete gravity dam is obtained, which demonstrates the applicability of the proposed method in practical engineering.

Brain magnetic resonance (MR) segmentation for hydrocephalus patients is considered as a challenging work. Encoding the variation of the brain anatomical structures from different individuals cannot be easily achieved. The task becomes even more difficult especially when the image data from hydrocephalus patients are considered, which often have large deformations and differ significantly from the normal subjects. Here, we propose a novel strategy with hard and soft attention modules to solve the segmentation problems for hydrocephalus MR images. Our main contributions are three-fold: 1) the hard-attention module generates coarse segmentation map using multi-atlas-based method and the VoxelMorph tool, which guides subsequent segmentation process and improves its robustness; 2) the soft-attention module incorporates position attention to capture precise context information, which further improves the segmentation accuracy; 3) we validate our method by segmenting insula, thalamus and many other regions-of-interests (ROIs) that are critical to quantify brain MR images of hydrocephalus patients in real clinical scenario. The proposed method achieves much improved robustness and accuracy when segmenting all 17 consciousness-related ROIs with high variations for different subjects. To the best of our knowledge, this is the first work to employ deep learning for solving the brain segmentation problems of hydrocephalus patients., ISBI 2020

Evaluation of slope stability under rainfall is an important topic of Geotechnical Engineering. In order to study the influence of anisotropy ratio (kr = kx/ky) and anisotropy direction (&alpha, ) on the seepage and stability of a slope, the SEEP/W and SLOPE/W modules in Geo-studio were utilized to carry out the numerical analysis of a homogeneous slope in Luogang District, Guangzhou City, China, which is based on the theory of unsaturated seepage and stability. Two kinds of soils (clay and sand) were included. Results show that: For sandy soil slope, the increase of kr promotes the rainfall infiltration, and the decrease of &alpha, prevents the rainfall infiltration. The maximum water content of the surface (MWCS) reaches maximum with the increase of kr and &alpha, The rising height of groundwater (RHG) is &minus, 3&ndash, 4 m and the safety factor (SF) is 1.3&ndash, 1.7. For clayey soil slope, variations of kr and &alpha, have little impact on the seepage characteristics and slope stability. The MWCS remains almost the same. The rainfall infiltration depth (RID) is 0.5&ndash, 1 m and the SF is about 1.7. Therefore, for sandy soil slope, it is not only necessary to consider the influence of kr, but also the influence of &alpha, For clayey soil slope, it can be treated as isotropic material to simplify calculation.

3D internal cracks are commonly distributed in rock masses, and their initiation and subsequent growth are believed to be responsible for the brittle fracture of materials under external loading conditions. This paper presents an experimental and numerical research on the fracture behaviours of brittle solid materials containing 3D internal cracks under a three-point bending test. We tested a series of cuboid glass samples including intact samples (group A) and samples with a pre-existing 3D internal crack at different depths (group B). The 3D internal laser-engraved crack (3D-ILC) method was applied to the fabrication of the 3D internal crack in the glass without any damage to the surface of the sample. We used the visualisation method of the stress field on the transparent samples during the test and performed a qualitative analysis. The experimental results indicate that the existence of a 3D internal crack drastically degrades the mechanical properties of glass and the characteristic loads, for example, crack initiation and failure loads, are positively correlated with the depth of the internal crack. The internal crack located in the central cross-section of the sample generally grows in the plane and finally reaches the sample end, causing splitting, a mainly mode I fracture. Wallner lines and dynamic fracture features are observed on the fracture surface of samples with a pre-existing crack under a three-point bending test, which have rarely been observed in compression tests. The 3D-ILC method was proven efficient in the experimental investigation of brittle fracture of materials containing a prefabricated 3D internal crack. The numerical simulation obtained the KI distribution at the crack tip and the crack growth path, which were consistent with those of the experimental results showing the fracture mechanical mechanism.