Porosity Fractal Dimension Research Articles

Strength properties and reinforcement mechanism of bio-enzyme stabilized marine soils

Bio-enzyme was used to stabilize the marine soils of Ningbo. Strength tests, XRD tests and SEM tests were used to analyze the strength and microstructure properties of bio-enzyme and cement stabilized soil. The results of strength tests show that the bio-enzyme not only has obvious reinforcing effect when added alone, but also can promote the solidification of cement. The results of XRD tests show that there is no new substance formation during the solidification process when only bio-enzyme added, which indicates that the process is a physical effect. The results of SEM tests show that the bio-enzyme can improve the pore arrangement, pore morphology and pore size of the soil, and reduce the directional fractal dimension, probability entropy, porosity fractal dimension and pore shape fractal dimension, which makes the orientation of the pores better, the order of the particles higher, the pore size more uniform, and the degree of particle agglomeration higher, therefore increasing the strength. In all the microstructure parameters, the fractal dimension of pore morphology has the greatest influence on the strength of stabilized soil, that is, promoting the aggregation of soil particles is the main role of bio-enzyme in improving the strength of stabilized soil.

Effects of curing time and ice-to-water ratio on performance of cemented paste backfill containing ice slag

With the continuous development of mining-with-backfill technology, more requirements are proposed for the utilized backfill materials, such as cold-loading, heat-saving, energy-storing, and seepage-proofing. In this paper, a new type of backfill material was proposed by introducing ice into cemented paste backfill (CPB), which is referred as the iced CPB (ICED_CPB) technology. Such an ICED_CPB technology can be used to meet the challenges in hot workplaces that are being frequently encountered as the mining depth increases. The performance of ICED_CPB under the coupled effect of curing time and ice/water ratio (IWR) was investigated experimentally. Some factors affecting the performance of CPB, such as the number of pores (N), porosity fractal dimension (Dc), roundness (RD), permeability (K), unconfined compressive strength (UCS), electrical resistivity (ER) and longitudinal wave velocity (VL) were investigated and their relationships were discussed. The results indicate that the optimum IWR was determined to be 1.2 for the ICED_CPB system in this study. The influence of IWR on N, Dc, K followed a decrease-then-increase pattern while followed an increase-then-decrease pattern on RD, UCS, ER and longitudinal wave velocity. N, Dc, and K increased while RD, UCS, ER and longitudinal wave velocity decreased with increasing curing time.

RESEARCH ON PORE MICROSCOPIC CHARACTERISTICS OF LIGNINMODIFIED LOESS

In order to further research the microscopic mechanism of the lignin-modified loess, the pore microscopic characteristics of the lignin-modified loesswithdifferent lignin contents is analyzed based on SEM.Moreover, the variation of microscopic parameters of the lignin-modified loess with different lignin contents is studied based on PCAS.Combined with the unconfined compressive strength test to evaluate the effect of lignin-modified loess. The results show that lignin can effectively fill the pores of loess and enhance the cementation between particles. The content of lignin has a great influence on the microscopic characteristics. Under the curing age of 28 days, the facial porosity, average pore area, pore porosity fractal dimension and average form factor first rapidly decrease and then slowly increase with the increase of lignin content, while the fractal dimension is completely opposite, and the probability entropy of modified loess with the lignin content of 2% and 4% is low. The modified loess with the lignin content of 2%has the highest compressive strength, while too much lignin content will reduce the compressive strength.

Porosity controls and fractal disposition of organic-rich Permian shales using low-pressure adsorption techniques

The pore structure characteristics of the Lower and Upper Permian shales belonging to the Barren Measures and Raniganj Formations, respectively, were investigated using the low-pressure N2 adsorption-desorption experiments. It was found that the kaolinite content of the Barren Measures shales strongly influenced the Brunauer-Emmett-Teller specific surface area (BET SSA). However, it was the Rock-Eval temperature maxima (Tmax) for the Raniganj Formation shales that influenced the BET SSA values. These shales are dominantly mesoporous and display a negative correlation between BET SSA and average pore radius. Nitrogen adsorption-desorption isotherms are of type IIB and type IV, displaying H2, H3, and hybrid H3-H4 hysteresis patterns. A strong positive correlation exists between average pore radius and the difference in volumes of gas adsorbed at the last-two-highest relative pressures measured. Samples with steeper isotherm slopes at the higher relative pressure range were those with the highest average pore radii. Porosity fractal dimension, D2 displayed a positive correlation with BET SSA and Tmax, and a negative correlation with average pore radius. It is thus concluded that shales with the lowest average pore sizes and highest thermal maturities are marked by larger SSA and more complex pore structures. One of the tested samples (CG 1019) with the highest D2 value is associated with the lowest D1 fractal dimension value. That counter intuitive relationship may reflect analytical constraints of the nitrogen adsorption method at lower relative pressures.

Experimental Study on the Micro-mechanism for Strength Anisotropy of Intact Loess

To investigate the micro-mechanism for the anisotropy in the strength of intact loess in Xining, China, a series of consolidated-undrained shear tests were carried out, with a triaxial apparatus, on intact loess at different shear angles and depths. In this study, a scanning electron microscope (SEM) was used to examine sheared samples and generate their scanned images, which were used to analyze the morphology and the connection mode of soil particles qualitatively. Also, a particles and cracks analysis system (PCAS) was used to estimate the porosity, the probability entropy, and the porosity fractal dimension quantitatively. Test results reveal that the morphology of soil particles was mainly circular or oval at the direction parallel to the natural sedimentary surface. Soil particles were mainly in direct contact. The porosity of the soil was relatively lower when the pores were arranged in a regular pattern. With an increase of the shear angle, the morphology of soil particles gradually became schistose and the connection between soil particles turned into indirect point contacts. The porosity of the soil was gradually enlarged when the pores were not arranged in a regular pattern. The normalized pore size firstly decreased and then increased with the increase of the shear angle. Based on the analysis of the micro-mechanism for the anisotropy in the strength, the relationship between the macro-mechanism and the micro-mechanism for the anisotropy in the strength of intact loess was established and proved.

The Text Analysis on the Relationship between Slide-Zone Loess Porosity Microstructure and Dynamic Parameters

Through analyzing slide-zone loess porosity microstructure and quantitative analysis, the article can obtain the relation between variational characteristics of slide-zone loess porosity micro-structure and dynamic stress. Experimental results show that slide-zone loess microstructural parameters with load increasing appears a certain laws, and we can use simple linear equation to stand for the relation between porosity quantity or porosity area or porosity morphology ratio and dynamic stress. There is a negative correlation between porosity quantity and dynamic stress, but to other microstructural parameters and dynamic stress, it is a positive correlation. All of these laws are closely related to porosity transformation that forming under axial dynamic stress. It is worth mentioning that porosity fractal dimension with increasing dynamic stress increases, appearing linear correlation. When the confidence coefficient is 0.05, their correlation is well. Synthesizing above study, there is some guiding significance for establishing loess microstructure mechanical model and soil mass microstructural mechanics.

Pore Structure Analysis on Hardened Paste of CaO-Al<sub>2</sub>O<sub>3</sub>-P<sub>2</sub>O<sub>5</sub> Cement

CaO-Al2O3-P2O5cementitious material (PAC) is a type of new developed hydraulic cement, which has excellent cementitious performance and mechanical property. In cement based materials, the pore structure of hardened cement paste has a significant effect on their performance, such like strength, permeability and durability. In the current paper, pore structure parameters of hardened PAC paste samples in five different curing stages were measured respectively by MIP (Mercury Intrusion Porosimetry). The pore fractal features (pore volume, pore area, porosity) were investigated with fractal theory. Results showed that the porosity of hardened PAC paste does not exactly decline with elongation of curing age and increase of compression strength. The PAC pastes pore structures have typical fractal nature which changes with curing age and pore diameter distribution. The fractal feather of hardened PAC paste can be effectively understood by using porosity fractal dimension.

Structure of surface cracks in soil and muds

Image analysis of photographs of surface cracks in cultivated soils for a variety of types (Vertisol, Andosol, Mollisol), and surface cracks in mud deposits shows various similar geometric characteristics. Analysis of the skeletal structure of these crack networks indicates that the relations of intersections and numbers of crack segments show a tendency to lie between those of square and hexagonal networks while the relations between particles and the number of bounding crack segments which define particle contours indicates the presence of more segments than found in a hexagonal network. Crack length distribution appears to be symmetric on log length–linear frequency co-ordinates. Area distributions of pore size or crack width indicate that the cultivated soils have a regular, symmetric distribution on log width–linear area percent occupied co-ordinates while muds have skewed distributions. Particle size abundance (defined by crack boundaries) indicates a non-linear cumulative frequency distribution on a log frequency–log size analysis that suggests non-fractal relations. Measurement of the fractal dimension of crack patterns using box counting indicates that as the porosity increases the regularity of the distribution of the cracks increases. Cultivated soils show the greatest irregularity for a given porosity. Each type of crack structure (soils, muds) has a linear relation on a porosity–fractal dimension plot. The surface area spatial characteristics of the crack network and the particles defined by them appear to be different.

Structure and self-similarity in silty and sandy soils: the fractal approach : J Soil Sci V42, N2, June 1991, P167–185

SUMMARY Soil structure was studied using the concept of fractals and related to soil texture and aggregate properties such as surface charges and aggregate stability. The mass and porosity fractal dimensions (Dm and Dp) of silty and sandy soils were determined on in situ soils using a variety of soil sections (thin, very-thin and ultra-thin), by image analysis on a continuous scale from m to 10−9 to 10−1m. Surface fractal dimensions (Ds) of these soils were determined on < 2 mm air-dried samples using mercury porosimetry and the fractal cube generator model. The results suggest that soils are not pore fractals but mass and surface fractals with Dm= 1.1 Ds when the dimension of the embedding Euclidean space d is 3. The soil structures could possibly be described by fractal diffusion-limited aggregation with complex interconnected aggregates or by fractal cluster–cluster aggregation models. As a preliminary conclusion, the fractal approach appears to be a potentially useful tool for understanding the underlying mechanisms in the creation or destruction of soil structure.

Structure and self‐similarity in silty and sandy soils: the fractal approach

SUMMARYSoil structure was studied using the concept of fractals and related to soil texture and aggregate properties such as surface charges and aggregate stability. The mass and porosity fractal dimensions (Dm and Dp) of silty and sandy soils were determined on in situ soils using a variety of soil sections (thin, very‐thin and ultra‐thin), by image analysis on a continuous scale from m to 10−9 to 10−1m. Surface fractal dimensions (Ds) of these soils were determined on &lt; 2 mm air‐dried samples using mercury porosimetry and the fractal cube generator model. The results suggest that soils are not pore fractals but mass and surface fractals with Dm= 1.1 Ds when the dimension of the embedding Euclidean space d is 3. The soil structures could possibly be described by fractal diffusion‐limited aggregation with complex interconnected aggregates or by fractal cluster–cluster aggregation models. As a preliminary conclusion, the fractal approach appears to be a potentially useful tool for understanding the underlying mechanisms in the creation or destruction of soil structure.