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Numerical study of the dynamic active lateral earth pressure coefficient of cohesive soils
Mehrab Jesmani, Hossein Alirezanejad, Hamed Faghihi Kashani, Mehrad Kamalzare, 2017, izvirni znanstveni članek

Opis: Retaining walls are proposed in many projects, such as bridges, coastal structures, road constructions and wherever lateral support is required for the vertical surface of an excavation. The active lateral pressure coefficient of soil, Ka , is an important parameter for studying the static and dynamic behaviors of these retaining walls. Many studies have evaluated this coefficient in static situations, but in most previous dynamic studies, researchers have worked on the behavior of cohesionless backfill soil or made simplifying assumptions (e.g., pseudo-static status) for cohesive soils as backfill soil. In this study, the size of the active lateral earth pressure coefficient (Ka) was studied in a full dynamic situation (Kae). A retaining wall with cohesive backfill soil is evaluated using the finite-difference method (FDM) and the effects of important soil and loading properties are assessed. The model is based on Mohr-Coulomb failure criteria under seismic loading. The results show that the value of Kae at the top of the wall, where it is highly sensitive to any variation in the soil and loading properties, is greater than one due to the high pressure value induced by the horizontal dynamic acceleration and the presence of tension cracks.
Ključne besede: dynamic active lateral earth pressure coefficient (Kae), cohesive backfill soil, finite difference method (FDM), tension cracks, retaining wall, seismic loading
Objavljeno: 18.06.2018; Ogledov: 71; Prenosov: 6
.pdf Celotno besedilo (3,26 MB)

Prediction of California Bearing Ratio (CBR) and Compaction Characteristics of granular soil
Attique ul Rehman, Khalid Farooq, Hassan Mujtaba, 2017, izvirni znanstveni članek

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: 29; Prenosov: 47
.pdf Celotno besedilo (830,76 KB)

Stress-dilatancy behavior of sand incorporating particle breakage
Fangwei Yu, 2017, izvirni znanstveni članek

Opis: This paper presents the stress-dilatancy behavior of sand incorporating particle breakage. A series of the drained triaxial tests were conducted on the Silica sand No.5 and the pre-crushed sands that were produced by several drained triaxial tests on Silica sand No.5 under 3MPa confining pressure in simulating the high-pressure shear process to result in particle breakage, to investigate the stress-dilatancy behavior of sand incorporating particle breakage. For a given initial void ratio, particle breakage was found to result in deterioration of the stress-dilatancy behavior in the impairment of the dilatancy of sand to become more contractive with a reduction in the maximum dilatancy angle and the excess friction angle (the difference between the peak-state friction angle and the critical-state friction angle). By introducing the concept of the skeleton void ratio in considering particle breakage, a linear stress-dilatancy relationship between the maximum dilatancy angle-over-the excess friction angle and peak-state skeleton void ratio was proposed in semi-logarithmic plane and popularized to the mobilized stress-stain state as a stress-dilatancy equation pertaining to particle breakage, which would be useful in assessing the evolution of the stress-dilatancy behavior of sand during particle breakage.
Ključne besede: dilatancy angle, friction angle, particle breakage, sand, triaxial tests
Objavljeno: 18.06.2018; Ogledov: 34; Prenosov: 3
.pdf Celotno besedilo (1,43 MB)

3D response of an excavation adjacent to buildings supported by inclined struts
Zahra Sabzi, Ali Fakher, 2017, izvirni znanstveni članek

Opis: The presented study focuses on field observations and a 3D numerical analysis of open-cut excavations adjacent to a building supported by inclined struts. The performance of the struts in carrying the building loads and decreasing the deflections is investigated. Struts reduce the amount of deformations and also create a corner effect similar to the diaphragm walls corner. The influence of the distance between the struts is studied and the optimum struts interval is proposed. The most effective configuration of struts installation in reducing the deflections and building damage is proposed. A displacement-based design guideline is also presented based on the results of numerical studies.
Ključne besede: measurement, 3D finite-element analysis, displacement-based design
Objavljeno: 18.06.2018; Ogledov: 40; Prenosov: 5
.pdf Celotno besedilo (2,85 MB)

Determining the grain size distribution of granular soils using image analysis
Nihat Dipova, 2017, izvirni znanstveni članek

Opis: Image-processing technology includes storing the images of objects in a computer and processing them with the computer for a specified purpose. Image analysis is the numerical expression of the images of objects by means of mimicking the functioning of the human visual system and the generation of numerical data for calculations that will be made later. Digital image analysis provides the capability for rapid measurement, which can be made in near-real time, for numerous engineering parameters of materials. Recently, image analysis has been used in geotechnical engineering practices. Grain size distribution and grain shape are the most fundamental properties used to interpret the origin and behaviour of soils. Mechanical sieving has some limitations, e.g., it does not measure the axial dimension of a particle, particle shape is not taken into consideration, and especially for elongated and flat particles a sieve analysis will not yield a reliable measure. In this study the grain size distribution of sands has been determined following image-analysis techniques, using simple apparatus, non-professional cameras and open-code software. The sample is put on a transparent plate that is illuminated with a white backlight. The digital images were acquired with a CCD DSLR camera. The segmentation of the particles is achieved by image thresholding, binary coding and particle labeling. The geometrical measurements of each particle are obtained using an automated pixel-counting technique. Local contacts or limited overlaps were overcome using a watershed split. The same sample was tested by traditional sieve analysis. An image-analysis-based grain size distribution has been compared with a sieve-analysis distribution. The results show that the grain size distribution of the image-based analysis and the sieve analysis are in good agreement.
Ključne besede: image analysis, image processing, grain size, sand
Objavljeno: 18.06.2018; Ogledov: 42; Prenosov: 6
.pdf Celotno besedilo (1,27 MB)

Assessments of the hydraulic conductivity for predicting the swelling characteristics of compacted expansive soils
Hakan Güneyli, 2017, izvirni znanstveni članek

Opis: The swelling behaviour of expansive soils is significant in geotechnical engineering since it causes severe damage to civil structures. The swelling characteristics need to be well known for satisfactorily safe and economic engineering designs. A direct determination of the swelling characteristics requires considerable time and money, involving serious experimental effort. Alternatively, several indirect estimation techniques developed using empirical regression models available in literature are widely used in practice. These empirical estimation techniques have generally been assessed as a function of the soil properties, i.e., consistency limits, density, moisture content, clay fraction and type, and cation-exchange capacity. This paper describes the dependence of the percentage swell (S%) and the swell pressure (σsp) obtained from a free-swell (FS) test and a constant-volume swell (CVS) test, and the primary swell time (PST), in which almost 90% of the swelling occurs as strain, which is considered as a new swelling characteristic in this study, on the hydraulic conductivity (k) controlled by a change in the gradation of compacted expansive soils. In addition, the rate of primary swelling (Cps), which is the primary swelling phase’s slope of the curve of percentage swell vs. log time, and the ratio of (Cps/k) were used to analyse their relationships with the swelling characteristics. This study provides the empirical methods that can be utilized to obtain indirect estimations of the percentage swell (S%), swell pressure (σsp) and primary swell time (PST) depending on k, Cps and Cps/k, in addition to, or with, the conventional parameters. The correlation coefficients of the regression analysis, having high performance, and indicating strong relationships between the swelling characteristics and the indices proposed in this study, state that these empirical prediction equations can be used safely in engineering practice.
Ključne besede: swelling characteristics, gradation, hydraulic conductivity, rate of primary swelling
Objavljeno: 18.06.2018; Ogledov: 26; Prenosov: 4
.pdf Celotno besedilo (2,21 MB)

Quality control for the construction of a tailings dam
Wojciech Tschuschke, Magdalena Wróżyńska, Jędrzej Wierzbicki, 2017, izvirni znanstveni članek

Opis: Every day the mining industry produces large amounts of mine tailings. In the case of copper ores exploited in Poland, the post-flotation tailings constitute 95% of the excavated rock and all the tailings are deposited in dumps, which are supported by outer dams. The durability and stability of these earth structures determine the safe operation of the entire object. The selection of adequate-quality soils for the construction of the dams is a crucial factor limiting the risk of its potential failure. Very large depositories require sufficiently large amounts of soil for the construction of the dams. An alternative to this classic approach is the use of the deposited tailings. In this solution the amount of mine wastes stored in the depository is reduced, there is no need to exploit the deposits of natural soils and the potential capacity of the depository increases. This paper presents the principles of the construction technology for hydraulically filled dams; the criteria for the selection of proper soil gradation and the physical properties of the sediments to be used in the construction of the dams; the principles of quality control for earth works; and the methodology of the geotechnical control tests. The effects of the applied technology on the condition of the natural environment are also discussed.
Ključne besede: post-flotation sediments, tailings dams, geotechnical control tests
Objavljeno: 18.06.2018; Ogledov: 29; Prenosov: 4
.pdf Celotno besedilo (674,70 KB)

Effects of the particle shape and size of sands on the hydraulic conductivity
Ali Firat Cabalar, Nurullah Akbulut, 2016, izvirni znanstveni članek

Opis: This study aims to investigate the effects of some physical properties of sands (e.g., size and shape) on the hydraulic conductivity (k). The paper presents the results of an extensive series of experimental investigations performed using sands with different sizes and particle shapes. Three different particle size ranges (0.60- 1.18 mm, 1.18- 2.00 mm, and 0.075- 2.00 mm) of sands (i. Crushed Stone Sand, CSS; ii. Trakya Sand, TS; iii. Narli Sand, NS; iv. Fly Ash Pellets, FAP; v. Leighton Buzzard Sand, LBS) having distinct shapes, including roundness, R, and sphericity, S (Ri=0.15, Si=0.55; Rii=0.43, Sii=0.67; Riii=0.72, Siii=0.79; Riv=0.65, Siv=0.89; Rv=0.78 Sv=0.65) were tested in a constant-head permeability testing apparatus at a relative density (Dr) of about 35% and constant room temperature (20°C). The experimental results showed that the sands having different shapes (R, S) with the same size and gradation characteristics (cc , cu , D10 , D30 , D50 , D60) result in different k values. The scanning electron microscope (SEM) images indicate the physical differences/similarities among the sands used during this investigation. A comparative study of the tests results and the estimated hydraulic conductivity values using empirical equations previously developed for the hydraulic conductivity prediction of soils by certain researchers are presented.
Ključne besede: sand, shape, size, hydraulic conductivity
Objavljeno: 18.06.2018; Ogledov: 35; Prenosov: 4
.pdf Celotno besedilo (587,55 KB)

Evaluation of dynamic soil pressures acting on rigid culverts
Deniz Ulgen, Mehmet Yener Özkan, 2016, izvirni znanstveni članek

Opis: The seismic safety of underground structures (culvert, subway, natural-gas and water-sewage systems) plays a major role in sustainable public safety and urban development. Very few experimental data are currently available and there is no generally accepted procedure to estimate the dynamic pressures acting on these underground structures. This study aims to enhance the state of the prevalent information necessary to understand the dynamic behaviour of box culverts and the stresses acting under dynamic excitations through experimental analyses. For this purpose, a series of shaking-table tests were conducted on box-type culverts buried in dry sand. To simulate the free-field boundary conditions, a laminar box was designed and manufactured for use with a 1-g shake table. Two culvert models having different rigidities were tested under various harmonic motions in order to examine the effect of the flexibility ratio on dynamic lateral soil pressures. Based on the test results, a simplified dynamic pressure distribution acting on the sidewalls of the culvert model was suggested. Then, a dynamic lateral coefficient was defined for the proposed peak pressure value in the distribution. The values of this coefficient were obtained as a function of the shear strain by considering the relative stiffness between the soil and the underground structure.
Ključne besede: box culvert, dynamic earth pressure, shaking table, dynamic soil-structure interaction, laminar box, dynamic lateral coefficient
Objavljeno: 18.06.2018; Ogledov: 26; Prenosov: 2
.pdf Celotno besedilo (584,65 KB)

Rheological properties of marine sediments from the port of Koper
Jasna Smolar, Matej Maček, Ana Petkovšek, 2016, izvirni znanstveni članek

Opis: Subaqueous, fine-grained, cohesive sediments are continuously fluidized by waves and other disturbances that cause their movement, which can be described with numerical models incorporating rheological parameters. The rheological behaviour depends on the soil (solid) type, the volume concentration, the salinity and the testing methods. In this study, rheological investigations of marine sediments from the Port of Koper were carried out by using two coaxial cylinder rheometers (DV3T HB, Brookfield and ConTec Viscometer 5). The influence of the specimen volume, the size of the gap and the type of measuring spindles were analysed and compared. The measured data were evaluated using the Bingham model. For each data set, the boundary between the sheared (“fluid”) and the un-sheared (“solid”) material was calculated and then the calculated boundary was used instead of the outer radius of the cylinder for the evaluation of the rheological parameters, where necessary. A good comparison of the results was found when using this approach. The results are also in agreement with the literature data. The ConTec Viscometer 5, primarily designed for mortars and concrete, was shown to be also suitable for the investigation of sediments.
Ključne besede: marine sediments, Bingham model, yield stress, plastic viscosity, coaxial cylinder rheometer, plug flow, Bay of Koper
Objavljeno: 18.06.2018; Ogledov: 38; Prenosov: 2
.pdf Celotno besedilo (709,57 KB)

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