Evolution of Meso-Structure of Intact Loess during Wetting

2012 ◽  
Vol 204-208 ◽  
pp. 188-191
Author(s):  
Xiang Wei Fang ◽  
Chun Ni Shen ◽  
Pei Jiang Cheng ◽  
Long Wang
Keyword(s):  
Volumetric Strain ◽  
Ct Images ◽  
Deviatoric Stress ◽  
Cell Stress ◽  
Degree Of Saturation ◽  
Triaxial Apparatus ◽  
Evolution Of Structure ◽  
Ct Data ◽  
Intact Loess

To study the evolution of meso-structure of unsaturated intact loess during wetting, a series of CT-triaxial-collapse tests were conducted using CT-multi-function triaxial apparatus. The distinct CT images and detailed CT data were attained nondestructively during wetting. A parameter and an evolution variable which characterized evolution of meso-structure were defined based CT data. An equation describing the evolution of structure during wetting was proposed. The equation reflected the influences of net cell stress, deviatoric stress and suction on the evolution of meso-structure. In the equation, volumetric strain, deviatoric strain and incremental degree of saturation are included.

Evolution of Meso-Structure of Intact Loess during Loading

2011 ◽  
Vol 243-249 ◽  
pp. 2460-2463
Author(s):  
Chun Ni Shen ◽  
Xiang Wei Fang ◽  
He Wen Wang ◽  
Yun Xie ◽  
Gang Li
Keyword(s):  
Ct Images ◽  
Structure Parameter ◽  
Shear Tests ◽  
Triaxial Apparatus ◽  
Ct Data ◽  
Intact Loess

A series of triaxial shear tests on unsaturated intact loess were conducted using CT-multi-function triaxial apparatus. The distinct CT images and relevant CT data were obtained nondestructively during triaxial shear. CT data was used to define a structure parameter and an evolution variable which characterized the evolution of meso-structure. An equation is proposed to describe the evolution of meso-structure of unsaturated intact loess during loading, which reflects the influences of net cell pressure and suction on the evolution of meso-structure.

scholarly journals AUTOMATIC LUNG NODULE DETECTION BASED ON STATISTICAL REGION MERGING AND SUPPORT VECTOR MACHINES

2017 ◽  
Vol 36 (2) ◽  
pp. 65 ◽  
Author(s):  
Elaheh Aghabalaei Khordehchi ◽  
Ahmad Ayatollahi ◽  
Mohammad Reza Daliri
Keyword(s):  
Lung Nodule ◽  
Three Dimensional ◽  
Pulmonary Nodules ◽  
Ct Images ◽  
Support Vector ◽  
Svm Classifier ◽  
Region Merging ◽  
Three Dimensional Objects ◽  
Ct Data ◽  
Statistical Region Merging

Lung cancer is one of the most common diseases in the world that can be treated if the lung nodules are detected in their early stages of growth. This study develops a new framework for computer-aided detection of pulmonary nodules thorough a fully-automatic analysis of Computed Tomography (CT) images. In the present work, the multi-layer CT data is fed into a pre-processing step that exploits an adaptive diffusion-based smoothing algorithm in which the parameters are automatically tuned using an adaptation technique. After multiple levels of morphological filtering, the Regions of Interest (ROIs) are extracted from the smoothed images. The Statistical Region Merging (SRM) algorithm is applied to the ROIs in order to segment each layer of the CT data. Extracted segments in consecutive layers are then analyzed in such a way that if they intersect at more than a predefined number of pixels, they are labeled with a similar index. The boundaries of the segments in adjacent layers which have the same indices are then connected together to form three-dimensional objects as the nodule candidates. After extracting four spectral, one morphological, and one textural feature from all candidates, they are finally classified into nodules and non-nodules using the Support Vector Machine (SVM) classifier. The proposed framework has been applied to two sets of lung CT images and its performance has been compared to that of nine other competing state-of-the-art methods. The considerable efficiency of the proposed approach has been proved quantitatively and validated by clinical experts as well.

scholarly journals Compression and shear strength characteristics of compacted loess at high suctions

2017 ◽  
Vol 54 (5) ◽  
pp. 690-699 ◽  
Author(s):  
Charles Wang Wai Ng ◽  
Hamed Sadeghi ◽  
Fardin Jafarzadeh
Keyword(s):  
Volumetric Strain ◽  
Degree Of Saturation ◽  
Continuous Increase ◽  
Direct Shear Tests ◽  
Vapor Transfer ◽  
Zero Degree ◽  
Reduced Rate ◽  
Shear Box ◽  
Compacted Loess ◽  
High Range

Compression and shear behavior of a loosely compacted loess is investigated via two series of saturated and unsaturated direct shear tests. The vapor transfer mechanism is used to modify a shear box device for control of suction at high range. In spite of significant volumetric strain upon wetting (up to 14%), suction-induced volumetric shrinkage is less than 2% for all suction levels considered because of the as-compacted moisture content at the dry side of the optimum value. During shearing, all unsaturated tests dried to high suctions indicate a strain-softening mode of failure associated with noticeable dilation. There is a continuous increase in peak strength with suction but at a reduced rate, which cannot be captured by the improved Bishop’s effective stress model, as it underestimates the contribution of high suctions by approaching zero degree of saturation. Unsaturated tests at high suctions also show an increased rate of dilation with suction for both values of net stress, which cannot be predicted well by the classical stress–dilatancy models. It is shown that for suction values beyond 8 MPa, dilation angle increases by 2° and 6° per 100 MPa increase of suction under net stress of 50 and 200 kPa, respectively.

A new simple system for measuring volume changes in unsaturated soils

2002 ◽  
Vol 39 (3) ◽  
pp. 757-764 ◽  
Author(s):  
C W.W Ng ◽  
L T Zhan ◽  
Y J Cui
Keyword(s):  
Volume Change ◽  
Unsaturated Soils ◽  
Volumetric Strain ◽  
Apparent Volume ◽  
Differential Pressure ◽  
Simple System ◽  
Measuring System ◽  
Volume Changes ◽  
Ambient Temperatures ◽  
Triaxial Apparatus

A new simple system for accurately measuring overall total volume changes in unsaturated soil specimens with a triaxial apparatus is introduced in this paper. The basic principle of the measuring system is to record changes in the differential pressure due to changes in the water level inside an open-ended, bottle-shaped inner cell caused by volume change in the specimen and inside a reference tube using an accurate differential pressure transducer. Several important steps were taken to improve the accuracy and sensitivity of the measuring system. Detailed calibrations were carried out to account for apparent volume changes as a result of changes in cell pressure, fluctuation in the ambient temperatures, creep in the inner cell wall, and relative movement between the loading ram and the inner cell. The calibration results demonstrate that the measuring system is reasonably linear, reversible, and repeatable. The estimated accuracy of the measuring system is in the order of 32 mm3 (or 0.04% volumetric strain for a triaxial specimen 38 mm in diameter and 76 mm in height) once the system is properly calibrated.Key words: unsaturated soils, volume-change measurement, open-ended, bottle-shaped, inner cell, differential pressure, calibration.

Architecture Concrete Mesostructure Analysis Based on CT Image Fracture Process

2011 ◽  
Vol 368-373 ◽  
pp. 2638-2641
Author(s):  
Liang Zhao ◽  
Chang Hua Li ◽  
Fa Ning Dang ◽  
Deng Feng Chen
Keyword(s):  
Spatial Distribution ◽  
Volume Expansion ◽  
Fracture Process ◽  
Ct Images ◽  
Spatial Distributions ◽  
Ct Image ◽  
Destruction Process ◽  
Ct Data ◽  
The Relationship ◽  
Variation Process

Scanning observation on meso evolution of fracture in concrete is carried out by means of computerized tomography (CT) on uniaxial compressive condition. The cracks in the mortar expansion, in particular, the bond of mortar and aggregate which is key regions of concrete damaged, are drawn out through CT image and CT data, and the destruction process of the concrete can be divided into four stakes, compression, enlargement, the expansion of the CT crack,and destruction. According to the character of CT image，MMD is used to analyze the CT images of the concrete specimens in 4 stages of deformation. The components of the CT images are classified and the spatial distributions of crack or cavity, mortar and aggregate are obtained. The variation process of the relationship between distributions of crack or cavity magnitude and stress are obtained from classification maps. The specimens experienced the process of condensed, volume expansion, crack propagation, coalescence and failure. The method can not only reflect the spatial distribution of the materials but also simplify the following analyses that follow.

scholarly journals MRI-based Treatment Planning with Electron Density Information Mapped from CT Images: A Preliminary Study

2008 ◽  
Vol 7 (5) ◽  
pp. 341-347 ◽  
Author(s):  
C. Wang ◽  
M. Chao ◽  
L. Lee ◽  
L. Xing
Keyword(s):  
Electron Density ◽  
Radiation Treatment ◽  
Dose Calculation ◽  
Ct Images ◽  
Planar Imaging ◽  
Mr Images ◽  
Dosimetric Accuracy ◽  
Tissue Contrast ◽  
Preliminary Study ◽  
Ct Data

Nowadays magnetic resonance imaging (MRI) has been profoundly used in radiotherapy (RT) planning to aid the contouring of targets and critical organs in brain and intracranial cases, which is attributable to its excellent soft tissue contrast and multi-planar imaging capability. However, the lack of electron density information in MRI, together with the image distortion issues, precludes its use as the sole image set for RT planning and dose calculation. The purpose of this preliminary study is to probe the feasibility and evaluate an MRI-based radiation dose calculation process by providing MR images the necessary electron density (ED) information from a patient's readily available diagnostic/staging computed tomography (CT) images using an image registration model. To evaluate the dosimetric accuracy of the proposed approach, three brain and three intracranial cases were selected retrospectively for this study. For each patient, the MR images were registered to the CT images, and the ED information was then mapped onto the MR images by in-house developed software generating a modified set of MR images. Another set of MR images with voxel values assigned with the density of water was also generated. The original intensity modulated radiation treatment (IMRT) plan was then applied to the two sets of MR images and the doses were calculated. The dose distributions from the MRI-based calculations were compared to that of the original CT-based calculation. In all cases, the MRI-based calculations with mapped ED yielded dose values very close (within 2%) to that of the CT-based calculations. The MRI-based calculations with voxel values assigned with water density indicated a dosimetric error of 3–5%, depending on the treatment site. The present approach offers a means of utilizing MR images for accurate dose calculation and affords a potential to eliminate the redundant simulation CT by planning a patient's treatment with only simulation MRI and any available diagnostic/staging CT data.

Residual Deformation Behavior of Reinforced Rock-Fill Materials

2010 ◽  
Vol 150-151 ◽  
pp. 1495-1499
Author(s):  
Yong Liang Lin ◽  
Meng Xi Zhang ◽  
Xin Xing Li
Keyword(s):  
Cyclic Loading ◽  
Deformation Behavior ◽  
Residual Deformation ◽  
Volumetric Strain ◽  
Test Results ◽  
Rock Fill ◽  
Triaxial Apparatus ◽  
Deformation Behaviors ◽  
Confining Pressures ◽  
Fill Materials

Reinforcement technology is widely used in rock-fill dams in high seismic hazard zones. The evaluation of reinforcement on deformation and safety is concerned and it is one of the major study objectives in rock-fill engineering. The residual deformation behaviors of reinforced rock-fill materials were experimentally studies by use of a triaxial apparatus. The effects were analyzed of intervals of reinforcement layers, confining pressures and the conditions of cyclic loading on residual deformation. Results show that reinforcement improves the residual deformation behaviors of rock-fill materials. Both the residual shear strain and the residual volumetric strain are deduced. Based on the test results, the mechanism of the influence of reinforcement on residual deformation is proposed tentatively.

Triaxial Shrinkages Tests of Unsaturated Compacted Clay

2011 ◽  
Vol 194-196 ◽  
pp. 1041-1044
Author(s):  
Dong Lin Wang
Keyword(s):  
Soil Water ◽  
Characteristic Curve ◽  
Experimental Tests ◽  
Degree Of Saturation ◽  
Mean Stress ◽  
Compacted Clay ◽  
Soil Water Characteristic Curve ◽  
Triaxial Apparatus ◽  
Soil Triaxial Apparatus ◽  
Shrinkage Coefficient

In this paper, The GDS unsaturated soil triaxial apparatus are employed for experimental tests to obtain the main characteristics of the drying paths for compacted clay. In order to study the soil water characteristic curve and shrinkage coefficient under deferent net mean stress. The results show that shrinkage index and the soil-water characteristic curve are dependent on net mean stress. At a given matric suction, with the increase of net mean stress, the void ratio and water content of soil sample is decrease, but the degree of saturation is increased.

scholarly journals Triaxial Wetting Test on Rockfill Materials under Stress Combination Conditions of Spherical Stress p and Deviatoric Stress q

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Yan-yi Zhang ◽  
Ze-ping Xu ◽  
Gang Deng ◽  
Yan-feng Wen ◽  
Shu Yu ◽  
...  
Keyword(s):  
Shear Strain ◽  
Power Function ◽  
Volumetric Strain ◽  
Deviatoric Stress ◽  
Dry Density ◽  
Initial Water Content ◽  
Test Results ◽  
Rockfill Materials ◽  
Function Relationship ◽  
Wetting Deformation

A GCTS medium-sized triaxial apparatus is used to conduct a single-line method wetting test on three kinds of rockfill materials of different mother rocks such as mixture of sandstone and slate, and dolomite and granite, and the test stress conditions is the combination of spherical stress p and deviatoric stress q. The test results show that (1) for wetting shear strain, the effects of spherical stress p and deviatoric stress q are equivalent, and wetting shear strain and deviatoric stress q show the power function relationship preferably. (2) For wetting volumetric strain, the effect of deviatoric stress q can be neglected because it is extremely insignificant, and spherical stress p is the main influencing factor and shows the power function relationship preferably. (3) The wetting strains decrease significantly with the increase in initial water content and sample density generally, but the excessively high dry density will increase the wetting deformation. Also, the wetting strains will decrease with the increase in the saturated uniaxial compressive strength and average softening coefficient of the mother rock. Based on the test results, a wetting strain model is proposed for rockfill materials. The verification results indicate that the model satisfactorily reflects the development law of wetting deformation.

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