• Geomechanics and Engineering
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• 제19권2호
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• pp.141-151
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• 2019

A novel theoretical solution is presented for created (zero initial radius) cavity expansion problem based on CamClay model and considers the effect of initial anisotropic in-situ stress and drained conditions. Here the strain of this theoretical solution is small deformation in elastic region and large deformation in plastic region. The works for cylindrical and spherical cavities expanding in drained condition from zero initial radius are investigated. Most of the conventional solutions were based on the isotropic and undrained condition, however, the initial stress state of natural soil mass is anisotropy by soil deposition history, and drained cavity expansion calculation is closer to actual engineering in permeable soil mass. Finally, the parametric study is presented in order to the engineering significance of this work.

• Geomechanics and Engineering
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• 제18권3호
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• pp.225-234
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• 2019

A numerical stepwise approach for cavity expansion problem in strain-softening rock or soil mass is investigated, which is compatible with Mohr-Coulomb and generalized Hoek-Brown failure criteria. Based on finite difference method, plastic region is divided into a finite number of concentric rings whose thicknesses are determined internally to satisfy the equilibrium and compatibility equations, the material parameters of the rock or soil mass are assumed to be the same in each ring. For the strain-softening behavior, the strength parameters are assumed to be a linear function of deviatoric plastic strain (${\gamma}p^*$) for each ring. Increments of stress and strain for each ring are calculated with the finite difference method. Assumptions of large-strain for soil mass and small-strain for rock mass are adopted, respectively. A new numerical stepwise approach for limited pressure and plastic radius are obtained. Comparisons are conducted to validate the correctness of the proposed approach with Vesic's solution (1972). The results show that the perfectly elasto-plastic model may underestimate the displacement and stresses in cavity expansion than strain-softening coefficient considered. The results of limit expansion pressure based on the generalised H-B failure criterion are less than those obtained based on the M-C failure criterion.

• 한국자동차공학회논문집
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• 제12권2호
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• pp.32-38
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• 2004

This study was performed to investigate the behavior of liquid and vapor phase of fuel mixtures with different piston cavity diameters in a optically accessible engine. The conventional engine was modified as Central Injected DI gasoline engine with swirl motion. Two dimensional spray fluorescence images of liquid and vapor phase were acquired to analyze spray behavior and fuel distribution inside of cylinder using exciplex fluorescence method. Piston cavity geometries were set by Type S, M and L. The results obtained are as follows. In the spray formation after SOI, the cone angle and width of the spray were decreased at late injection timing. With a fuel injection timing of BTDC $180^{\circ}C$, fuel was not greatly affected in a piston cavity but generally distributed as homogeneous mixture in the cylinder. With a fuel injection timings of BTDC $90{\circ}C$ and $60^{\circ}C$, fuel mixture was widely distributed in near the cavity center. As a injection timing was late in the compression stroke, residual width of fuel mixture was narrow in proportion to piston cavity.

• Geomechanics and Engineering
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• 제13권6호
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• pp.907-928
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• 2017

The effects of seepage force and out-of-plane stress on cavity contracting and tunnel opening was investigated in this study. The generalized Hoek-Brown (H-B) failure criterion and non-associated flow rule were adopted. Because of the complex solution of pore pressure in an arbitrary direction, only the pore pressure through the radial direction was assumed in this paper. In order to investigate the effect of out-of-plane stress and seepage force on the cavity contraction and circular tunnel opening, three cases of the out-of-plane stress being the minor, intermediate, or major principal stress are assumed separately. A method of plane strain problem is adopted to obtain the stress and strain for cavity contracting and circular tunnel opening for three cases, respectively, that incorporated the effects of seepage force. The proposed solutions were validated by the published results and the correction is verified. Several cases were analyzed, and parameter studies were conducted to highlight the effects of seepage force, H-B constants, and out-of-plane stress on stress, displacement, and plastic radius with the numerical method. The proposed method may be used to address the complex problems of cavity contraction and tunnel opening in rock mass.

• Restorative Dentistry and Endodontics
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• 제45권2호
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• pp.11.1-11.9
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• 2020

Objectives: This study compared the flow and filling of several retrograde filling materials using new different test models. Materials and Methods: Glass plates were manufactured with a central cavity and 4 grooves in the horizontal and vertical directions. Grooves with the dimensions used in the previous study (1 × 1 × 2 mm; length, width, and height respectively) were compared with grooves measuring 1 × 1 × 1 and 1 × 2 × 1 mm. Biodentine, intermediate restorative material (IRM), and mineral trioxide aggregate (MTA) were evaluated. Each material was placed in the central cavity, and then another glass plate and a metal weight were placed over the cement. The glass plate/material set was scanned using micro-computed tomography. Flow was calculated by linear measurements in the grooves. Central filling was calculated in the central cavity (㎣) and lateral filling was measured up to 2 mm from the central cavity. Results: Biodentine presented the least flow and better filling than IRM when evaluated in the 1 × 1 × 2 model. In a comparison of the test models, MTA had the most flow in the 1 × 1 × 2 model. All materials had lower lateral filling when the 1 × 1 × 2 model was used. Conclusions: Flow and filling were affected by the size of the test models. Higher grooves and materials with greater flow resulted in lower filling capacity. The test model measuring 1 × 1 × 2 mm showed a better ability to differentiate among the materials.

• Imaging Science in Dentistry
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• 제36권3호
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• pp.145-149
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• 2006

Purpose : To assess the width of the labial alveolar bone of the incisive canal and the width of the incisive canal on spiral computed tomographic images of the anterior portion of the maxilla. Materials and Methods : Study materials included 38 CT scans taken for preoperative planning of implant placement. Axial cross-sectioned image entirely showing the incisive canal was selected and scanned with 600 DPI resolution. The width of the labial alveolar bone of the incisive canal at an orifice to the oral cavity, middle portion, and an orifice to the nasal cavity and the diameter of the incisive canal at the middle portion were determined by two specialist using Digora for Windows 2.1 The statistical analyses were carried out using SPSS 12.0.1. Results : When the maxillary central incisors remained, the mean labial alveolar bone width were $6.81{\pm}1.41mm,\;6.46{\pm}1.33mm$, and $7.91{\pm}1.33mm$. When the maxillary central incisors were missed the mean width were $5.42{\pm}2.20mm,\;6.23{\pm}2.29mm$, and $7.89{\pm}2.13mm$. Conclusions : The labial alveolar bone width at middle portion and an orifice to the nasal cavity were of no statistical significant difference according to presence of the maxillary central incisors (P>0.05). The width between oral cavity and nasal cavity, middle portion and to nasal cavity revealed statistically significant difference (P<0.05).

• 한국해양공학회지
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• 제10권3호
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• pp.105-116
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• 1996

In this paper, we report the experimental results for the flow pattern and the material transport around a cavity subject to a sinusoidal external flow at the far region to ward the open side of the cavity. A tilting mechanism is used to generate a oscillatory flow inside a shallow rectangular container having a cavity at one side. The surface flow visualization is performed to obtain the unsteady behavior of vortices generated at two edges situated at the entrance of the cavity. It was found that at the period 4.5 sec., the behavior of the vortices is asymmetric, and there exists a steady residual flow in the cavity. The bottom flow patterns are also visualized. There are two regions outside of the cavity where the bottom fluid particles concentrate. The material transport in this flow model is very peculiar; fluid particles in the cavity flows outward through the passage along the walls starting from the edges, and particles in the outer region approach the cavity from the central region.

• Geomechanics and Engineering
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• 제19권3호
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• pp.217-227
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• 2019

This study focuses on an improved prediction model to determine the limiting grouting pressure of compaction grouting considering the ground surface upheaval, which is caused by the three-dimensional conical shearing failure. The 2D-dimensional failure curve in Zou and Xia (2016) was improved to a three-dimensional conical shearing failure for compaction grouting through coordinate rotation. The process of compaction grouting was considered as the cavity expansion in infinite Mohr-Coulomb (M-C) soil mass. The prediction model of limiting grouting pressure of compaction grouting was proposed with limit equilibrium principle, which was validated by comparing the results in El-Kelesh et al. (2001) and numerical method. Furthermore, using the proposed prediction model, the vertical and horizontal grouting tube techniques were adopted to deal with the subgrade settlement in Shao-huai highway at Hunan Provence of China. The engineering applicability and effectiveness of the proposed model were verified by the field test. The research on the prediction model for the limiting grouting pressure of compaction grouting provides practical example to the rapid treatment technology of subgrade settlement.

• Geomechanics and Engineering
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• 제20권5호
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• pp.399-410
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• 2020

Cavities often develop behind the vault during the construction of double-arch tunnels, generally in the form of various defects. The study evaluates the impact of cavities behind the vault on the mechanical and failure behaviors of double-arch tunnels. Cavities of the same sizes are introduced at the vault and the shoulder close to the central wall of double-arch tunnels. Physical model tests are performed to investigate the liner stress variation, the earth pressure distribution and the process of progressive failure. Results reveal that the presence of cavities behind the liner causes the re-distribution of the earth pressure and induces stress concentration near the boundaries of cavities, which results in the bending moments in the liner inside the cavity to reverse sign from compression to tension. The liner near the invert becomes the weak region and stress concentration points are created in the outer fiber of the liner at the bottom of the sidewall and central wall. It is suggested that grouting into the foundation soils and backfilling injection should be carried out to ensure the tunnel safety. Changes in the location of cavities significantly impact the failure pattern of the liner close to the vault, e.g., cracks appear in the outer fiber of the liner inside the cavity when a cavity is located at the shoulder close to the central wall, which is different from the case that the cavity locates at the vault, whereas changes in the location of cavities have a little influence on the liner at the bottom of the double-arch tunnels.

• Geomechanics and Engineering
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• 제6권5호
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• pp.503-515
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• 2014

On the basis of Hoek-Brown failure criterion, a numerical solution for the shape of collapsing block in the rectangular cavity subjected to seepage forces is obtained by upper bound theorem of limit analysis. The seepage forces obtained from the gradient of excess pore pressure distribution are taken as external loadings in the limit analysis, and the pore pressure is easily calculated with pore pressure coefficient. Thus the seepage force is incorporated into the upper bound analysis as a work rate of external force. The upper solution of the shape of collapsing block is derived by virtue of variational calculation. In order to verify the validity of the method proposed in the paper, the result when the pore pressure coefficient equals zero, and only hydrostatic pressure is taken into consideration, is compared with that of previous work. The results show good effectiveness in calculating the collapsing block shape subjected to seepage forces. The influence of parameters on the failure mechanisms is investigated.