Iskanje po katalogu digitalne knjižnice

Opis: The paper presents a 3D analysis (3DA) to evaluate the particle shape and size of silica and calcareous sands. The particles of calcareous sand are found to be less spherical than those of silica and crushed calcareous sands. Furthermore, the results indicate that the average sphericity (SPH) holds an inverse relationship to the particle size. However, in each sample the larger particles have higher SPHs than the smaller particles. In addition, the 3DA yields smaller particles than the sieve analysis (SA). Owing to a variety of particle shapes, causing particle interlocking, especially for calcareous sand, the particles cannot pass through the sieves by their shortest dimension. This paper discusses the effects of particle characteristics on the shear strength properties. Although the calcareous sand shows higher peak and residual shear strength properties, it tends to reach a lower shear strength at a small shear strain and a lower dilation than the silica sand. Moreover, the findings prove that the residual shear strength increases with the mean particle size. The sample with smaller particles shows less dilation under low vertical stress, while high vertical stress yields less compression. The relationship between the particle shape and shear strength properties is discussed based on the 3DA results.
Ključne besede: shear strength, sphericity, particle shape, calcareous sand
Objavljeno: 18.06.2018; Ogledov: 61; Prenosov: 5
Celotno besedilo (875,50 KB)

Opis: Unsaturated soils are maintaining their importance for researchers and there is still much need to investigate the many engineering aspects of these soils. A new technique is proposed here to predict the variation of the bearing capacity of unsaturated soils with matric suction. The proposed method is an extension of conventional bearing-capacity theories and conceptually based on the logarithmic model of the shear strength of unsaturated soils, which only include one unknown, unsaturated parameter (the airentry value, AEV). The possibility of predicting the unsaturated bearing capacity of soils is shown by the saturated effective shear-strength parameters c' and Ø' and the AEV from the soil-water retention curve (SWRC). Considering the necessity of validating new methods with other researchers’ data, the proposed equation is tested using the published unsaturated experimental study by the author, in addition to some reported experimental studies on the shear strength for unsaturated soils and also a model footing loading on unsaturated sand under controlled suction conditions. The results of the study indicate that there is a good comparison between the “unsaturated bearing capacities” obtained via predicted and measured unsaturated strength parameters (ctotal , Ø) and also between the measured/ calculated bearing values of a model footing loading. Consequently, it is shown that, without needing complex unsaturated testing facilities, the proposed equation is capable of predicting the unsaturated bearing capacity for both fine-grained and sandy soils, requiring only one unsaturated parameter, which can be obtained from the SWRC or predicted using the basic soil-index properties.
Ključne besede: unsaturated soils, unsaturated bearing capacity, suction strength, foundation design
Objavljeno: 18.06.2018; Ogledov: 65; Prenosov: 3
Celotno besedilo (347,24 KB)

Opis: This paper presents the results of 120 determinations of the shear modulus (G) of a saturated granular soil (20–40 Ottawa sand) in different conditions of relative density (Dr), effective consolidation pressure (σ’ c) and level of torsional excitation (Te). The equipment used was a resonant-column apparatus manufactured by Wykeham Farrance and the tests were performed with relative density values of 20, 40, 60 and 80%, effective consolidation pressures of 50, 100, 150, 200, 250 and 300 kPa, and torsional excitations of 0.025, 0.05, 0.1, 0.2 and 0.4 volts (V), leading to shear strains (γ) between 0.002% and 0.023%. The results led to very simple empirical expressions for the shear modulus as a function of the angular strain for different effective consolidation pressures and void-ratio values.
Ključne besede: resonant column, resonant frequency, shear modulus, relative density, effective consolidation pressure, dynamic shear modulus
Objavljeno: 18.06.2018; Ogledov: 54; Prenosov: 5
Celotno besedilo (1,31 MB)

Opis: In this study, using an in-situ, air-flow test in Essen, the impacts of different factors on multiphase flow and land uplift during and after compressed-air injection were investigated using numerical simulations. A loosely coupled, two-phase flow and geo-mechanical modeling approach, linking two numerical codes (TOUGH2/EOS3 and FLAC3D) was employed to simulate the in-situ, air-flow test for comparing the simulated and measured results. As the compressed air is injected, it flows upwards and laterally, and the vertical effective stress near and above the injection zones decreases owing to the pore pressure increasing here, causing an expansion of the soil skeleton in the corresponding zones. The land uplift, induced mainly by support actions from lower deformed soils, is relevant to the distribution of the porosity increments in the soil interior, and it increases rapidly during air injection. After the compressed-air injection stops, the land uplift decreases gradually to zero due to the overpressure dissipation. With a combination of intensive rainfall, the land uplift is slightly greater near the borehole, but it is significantly greater at a distance from the borehole than the land uplift with no or low rainfall, but the air-injection rate remains almost unchanged due to the unchangeable pore pressure near the injection region. As the intrinsic permeability increases or the air entry pressure decreases in the injected strata, both the land uplift and the air injection rate increase, but the time required for the land uplift to become zero is slightly advanced with either a small permeability or a high air entry pressure.
Ključne besede: loosely coupled two-phase flow and geo-mechanical model, in-situ, air-flow test, compressed-air injection, multiphase flow, land uplift, air loss
Objavljeno: 18.06.2018; Ogledov: 61; Prenosov: 5
Celotno besedilo (1,75 MB)

Opis: This research is an effort to correlate the index properties of granular soils with the California Bearing Ratio (CBR) and the compaction characteristics. Soil classification, modified proctor and CBR tests conforming to the relevant ASTM methods were performed on natural as well as composite sand samples. The laboratory test results indicated that samples used in this research lie in SW, SP and SP-SM categories based on Unified Soil Classification System and in groups A-1-b and A-3 based on the AASHTO classification system. Multiple linear regression analysis was performed on experimental data and correlations were developed to predict the CBR, maximum dry density (MDD) and optimum moisture content (OMC) in terms of the index properties of the samples. Among the various parameters, the coefficient of uniformity (Cu), the grain size corresponding to 30% passing (D30) and the mean grain size (D50) were found to be the most effective predictors. The proposed prediction models were duly validated using an independent dataset of CBR tests on sandy soils. The comparative results showed that the variation between the experimental and predicted results for CBR falls within ±4% confidence interval and that of the maximum dry density and the optimum moisture content are within ±2%. Based on the correlations developed for CBR, MDD and OMC, predictive curves are proposed for a quick estimation based on Cu , D30 and D50. The proposed models and the predictive curves for the estimation of the CBR value and the compaction characteristics would be very useful in geotechnical & pavement engineering without performing the laboratory compaction and CBR tests.
Ključne besede: CBR, regression, model, prediction, compaction characteristics
Objavljeno: 18.06.2018; Ogledov: 23; Prenosov: 33
Celotno besedilo (830,76 KB)