Three-dimensional Discrete Element Simulation of Interaction between Aqueduct and Tunnel

In this investigation the effect of interaction between aqueduct and tunnel on the ground settlement has been examined using PFC3D. At first, the calibration of PFC3D was conducted based on UCS test results rendered from three different ground layer. Then intact model with dimension of 70 m × 20 m × 34.5 m (x × y × z) was built. These models are consisted of 8 layers with different mechanical and geometrical properties. Four different configurations for aqueduct were created in four models. Diameter of aqueduct was 2 m and its depth was different in four models. After aqueduct generation, tunnel with diameter of 9 m and length of 20 m was drilled in depth of 22 m. After tunnel drilling, the settlement data of ground surface were picked up. After tunnel simulation, the effect of support lining was investigated on the ground settlement. For this purpose, after each step of tunnel drilling, lining support with diameter of 35 cm was performed. The results show that the maximum value of settlement occurred when aqueduct reach to head of tunnel. Also the safety has maximum value when the distance between aqueduct and tunnel wall was 4.5 m. the ground settlement before and after support lining shows that ground settlement reach to zero by support application

Fracture Mechanism of Brazilian Discs with Multiple Parallel Notches Using PFC2D

This study presents crack initiation, propagation and coalescenceat or near pre-existing open cracks in a numericalmodel under Brazilian test. Firstly, Particle Flow Code intwo dimensions (PFC2d) was calibrated with respect to thedata obtained from experimental laboratory tests to ensurethe conformity of the simulated numerical models response.Brazilian discs contain one, two, three, four, and five parallelcentred cracks (45° to the horizontal) under compressiveline loading. Models containing two and three cracks havedifferent joint spacing and joint configuration. In model consistingone flaws, tensile cracks initiated from notch tip andpropagates in direction of compressive loading till coalescewith model edge. By increasing the number of notch, first typeof tensile crack initiated at the tips of outer flaws and coalescedwith model edge. Also second type of tensile cracksinitiates from middle of inner flaws and coalesce with tip ofthe neighbouring flaws. The results show that joint spacingand joint configuration has important effect on the failure patternin model consisting two and three notch. Experimentaland numerical results rendered by other researchers showed agood agreement with the numerical results in the coalescencecharacteristics in cracked model. In addition, crack initiationand coalescence stresses in models were analyzed and comparedwith those in the single-flawed model

Crack growth mechanism in granite specimens with non-persistent joints under punch shear through test

Experimental and numerical methods (Particle Flow Code) were used to investigate the effect of echelon notches on the shear behavior of the joint’s bridge area in granite. A punch-through shear test was used to model the granite cracks under shear loading. Granite samples with dimension of 20 mm×150 mm×40 mm were prepared in the laboratory. Within the specimen model and near the edges, four edge notches were provided. Nine different configuration systems were prepared for notches. In these configurations, the length of each notch was taken as 3 cm, 4cm and 5 cm. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 mm×100 mm using the particle flow code in two dimensions (PFC2D). Similar to those joints’ configuration systems in the experimental tests, i.e. 9 models with different rock bridge lengths and different rock bridge joint angles 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 rock bridge length and the rock bridge angle.  Shear strengths of the specimens were related to fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behavior of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the rock bridge angle.  The strength of samples decreases with increasing the joint length. The failure pattern and failure strength are similar in both methods, i.e. the experimental testing and the numerical simulation

Comparative evaluation of the effects of three hydraulic calcium silicate cements on odontoblastic differentiation of human dental pulp stem cells: an in vitro study

Objective: The study aimed to compare the response of human dental pulp stem cells (hDPSCs) towards three hydraulic calcium silicate cements (HCSCs) by measuring cytotoxicity and expression of dentinogenic genes. Methodology: Dental pulps of five impacted mandibular third molars were extirpated as a source for hDPSCs. Next to culturing, hDPSCs were subjected to fluorescence-activated cell sorting after the third passage to validate stemness of the cells. Human DPSCs were exposed to diluted supernatants of OrthoMTA (OMTA), Biodentine (BD) and Calcium-Enriched Mixture (CEM) at concentrations 10, 25, 50 and 100% at the first, third and fifth day of culture. Then, cells were exposed to 10% concentrations supernatant of HCSCs to determine DSPP and DMP1 gene expression, using a quantitative polymerase-chain reaction. Data were analyzed using one-way and three-way ANOVA, followed by Tukey post hoc statistical tests. Results: Optimal cell proliferation was observed in all groups, regardless of concentration and time-point. HCSC supernatants were non-cytotoxic to hDPSCs at all three time-points, except for 100% Biodentine on day five. On day seven, OMTA group significantly upregulated the expression of DSPP and DMP1 genes. On day 14, expression of DMP1 and DSPP genes were significantly higher in BD and OMTA groups, respectively. Conclusion: Biodentine significantly upregulated DMP1 gene expression over 14 days, whereas CEM was associated with only minimal expression of DSPP and DMP1 . &nbsp

Comparative evaluation of the effects of three hydraulic calcium silicate cements on odontoblastic differentiation of human dental pulp stem cells: an in vitro study

Objective The study aimed to compare the response of human dental pulp stem cells (hDPSCs) towards three hydraulic calcium silicate cements (HCSCs) by measuring cytotoxicity and expression of dentinogenic genes. Methodology Dental pulps of five impacted mandibular third molars were extirpated as a source for hDPSCs. Next to culturing, hDPSCs were subjected to fluorescence-activated cell sorting after the third passage to validate stemness of the cells. Human DPSCs were exposed to diluted supernatants of OrthoMTA (OMTA), Biodentine (BD) and Calcium-Enriched Mixture (CEM) at concentrations 10, 25, 50 and 100% at the first, third and fifth day of culture. Then, cells were exposed to 10% concentrations supernatant of HCSCs to determine DSPP and DMP1 gene expression, using a quantitative polymerase-chain reaction. Data were analyzed using one-way and three-way ANOVA, followed by Tukey post hoc statistical tests. Results Optimal cell proliferation was observed in all groups, regardless of concentration and time-point. HCSC supernatants were non-cytotoxic to hDPSCs at all three time-points, except for 100% Biodentine on day five. On day seven, OMTA group significantly upregulated the expression of DSPP and DMP1 genes. On day 14, expression of DMP1 and DSPP genes were significantly higher in BD and OMTA groups, respectively. Conclusion Biodentine significantly upregulated DMP1 gene expression over 14 days, whereas CEM was associated with only minimal expression of DSPP and DMP1