The paper deals with influence of flat shell particles content in sand mixture material on its anisotropy of shear strength in dry state. This type of material is often found in coastal areas and is used to fill in spaces behind the retaining walls of the docks by dredging method. 18 direct shear experiments were performed for three different non-coherent sand-shell mixtures - sand without shell (6 exp.), a mixture of sand and shell in a volume ratio of 50% to 50% (6 exp.) and shells without sand (6 exp.). For each composite mixture, the bedding orientation angle of flat particles to the shear plane was beta = 0 degrees and 90 degrees. The results showed that the magnitude of the internal friction angle anisotropy depends on the volume content of the shells in the mixture. The difference in the friction angles at the filling angle beta = 0 degrees and 90 degrees increases with an increase in the proportion of shell in the composite. It is rapidly growing from 9.45% for sand without shell, to 17.33% at a ratio of sand and shell 1:1. With a further increase in the proportion of shells, the difference significantly reduces growth, in the case of a clean shell, the difference is only 18.30%.
Tailings dams are raised with time depending upon rate of generation of waste. A tailings dam can contain different particle sized materials within its dam body. The newly raised embankment in a ta ...
Soil improvement by dynamic compaction has been extensively used all around the world in large civil engineering projects. Limited number of laboratory tests has been conducted to study the behavio ...
At Aalborg University and other research institutions, model tests are performed on small-scale foundations. These foundations are often installed in sand which has to be prepared in a reproductive way. At Aalborg University the preparation is done by using poker vibrators. This paper investigates if this preparation technique affect the soil in regards to grain size distribution, homogeneity and stratification. The paper concludes that the preparation technique does not lead to any change of the soil.
With the urban population increasing, conurbation is getting more and more crowed, traffic jam happens everywhere. In this case, utilization of the underground space has become an effective way to undertake this set of problems. Tunnel construction is one of the important infrastructure projects, which is vital for enhancing the transportation networks, especially in congested cities. Tunnel projects are characterized by high risk, complexities, uncertainties, repetitive construction tasks, large budgets and long durations. Several tunneling method like earth pressure balance machine, slurry and variable density tunnel boring machine have been developed in the tunnel construction industry to improve the constructability of tunnels and decrease the impact on surrounding structures. This review paper presents a framework for selecting the appropriate tunneling method with respect to the induced ground surface settlements. Parameters which have significant influence on the ground surface settlement will also be discussed in this paper. This paper will help the contractors, engineers and designer in selecting appropriate method and estimating the required cost and time for construction of a tunnel.
Five Seismic Cone Penetration Tests (SCPT) were conducted at a test site in northern Denmark where the subsoil consists primarily of sandy silt with clay bands. A portion of the test data were collected every 0.5 m to compare the efficacy of closely-spaced down-hole data collection on the computation of shear wave velocity. A minimum of eight seismic tests were completed at each depth in order to examine the reliability of shear wave velocity data, as well as to assess the impact of the time interval between CPT termination and seismic test initiation on SCPT results. The shear wave velocity was computed using three different methods: cross-over, cross-correlation and cross-correlation "trimmed with window". In the "trimmed with window" technique the latter part of the signal is clipped off by setting the amplitude to zero. The result showed that more closely-spaced test intervals actually increased the variability of the shear wave velocity and that time interval between seismic tests is insignificant. Correlation between shear wave velocity and cone resistance for silty soils were also determined and assessed relative to other published data on multiple soil types.
A method of defining strength parameters from slope failures is presented in this study, based on combining finite element and optimization analyses. The strength reduction technique is used to determine the shear strain field. The slip surface is then obtained from shear strain contours by extracting the maximal strains in several vertical lines. This surface is used for the optimization process when comparing to the observed failure surface. The optimization algorithm computes the sensitivity matrix with fix increments to avoid stationary values of the objective function. Two illustrative examples are presented, one considering a simple homogenous slope and the second compose of a two-layered model. The results of the analysis show that the proposed technique is efficient to determining soil parameters from slope failures by retaining the advantages of finite element slope stability analysis.
El objetivo de este articulo es investigar el metodo de equilibrio limite mejorado, que combina el analisis de elementos finitos y de equilibrio limite en estudios de estabilidad de taludes, y describir su uso en aplicaciones geotecnicas practicas. El estudio cubre una revision critica del uso del campo de esfuerzos de elementos finitos dentro de un analisis de equilibrio limite para evaluar la estabilidad de taludes. Se hace especial hincapie en el supuesto comun de constancia del factor de seguridad a lo largo de la superficie de deslizamiento critica y la incorporacion del angulo de dilatacion, la resistencia a la traccion y la relacion de Poisson. Este estudio ha demostrado que el factor de seguridad a lo largo de la superficie de deslizamiento no es el mismo, por lo tanto, la suposicion del factor de seguridad constante del metodo de equilibrio limite debe usarse con precaucion. Se encuentra que la dilatacion y la resistencia a la traccion tienen efectos insignificantes en la determinacion del factor de seguridad. Sin embargo, pueden influir en alguna extension la ubicacion de la superficie de deslizamiento critica, particularmente en la cresta de la pendiente. La relacion de Poisson afecta ligeramente los esfuerzos cortantes sin una influencia significativa en el calculo del factor de seguridad. La representacion de los factores de seguridad locales se muestra mejor con el metodo mejorado; esta caracteristica es importante porque la ubicacion de las zonas mas criticas se puede evaluar y utilizar para guiar la implementacion de medidas correctivas.
Floor heave of soft rock roadway has been a significant geotechnical problem in deep mining for a long time. Based on physical simulation, mechanical model and regression analysis, the mechanical model of the floor failure depth was obtained, the calculation formula for the maximum was deduced, the patterns of deformation and instability were revealed, and the specific support design, enclosed bearing structure was put forward. Key findings of this study show that floor heave of soft rock roadway in deep coal mine is characterized by squeeze flow and sustains deformation of unsupported floor, which can do harm to the roadway stability, especially the supported ribs and roof. It approaches a negative linear correlation between the support strength of the whole roadway and the floor failure depth which is proved that the roadway support strength increases with the decrease of floor failure depth. Floor failure depth is about the same as the width of roadway. For a particular cases, the roadway support technology of enclosed bearing structure was proposed and applied to implementation, providing theoretical and practical basis for similar mining conditions in other coal mines.
Road is one of the main infrastructures that play a crucial role in economy development of countries. Pavement engineering is a key factor to design and construct optimum roads. Flexible pavement is one of the most applicable method in road construction that is made in a series of layers. The construction of this type of pavement is very fast and easy to repair and have a greater resistance in a wide range of temperature and additional layer always could be added at any time. There is a various modelling software to analyse flexible pavement structure. Kenlayer is one of the most effective application in analysing flexible pavement engineering. In this paper, the wellknown FEM package of kenlayer was used to evaluate flexible pavement deflection and stress distribution. In this research, the effect of different parameters such as layer moduli and poisson's ratio were changed and the stress and deflection were compared.
This paper presents a case study where numerical modeling, with the finite element method, has been utilized to assess future stability of a tailings dam in Northern Sweden. The finite element software PLAXIS was utilized to simulate future dike raisings for the years 2024 to 2034. The simulations were conducted by computing each dike raising, the subsequent consolidation of the soil and the stability of the dam during the process. The factors of safety directly after each dike raising resulted in values continuously below a recommended value of 1.5. To increase the dam stability, rockfill berms were stepwise added on the downstream slope of the dam. An optimization technique was applied to place as small volumes of rockfill as possible in the berms at the most suitable locations on the downstream slope. By adding various volumes of rockfill in the berms each year, sufficient stability of the dam was obtained in the simulations. The excess pore water pressures increased annually in the simulations. It was shown that the excess pore water pressures did not totally dissipate before the following dike was constructed. The highest excess pore water pressures were located deep in the impoundment and did not have large effects on the dam stability.
Thickening technology is one of the key points of tailings cemented filling mining. Taking the tailings slurry of Anshan Iron and Steel Group Corporation as the object of study, this paper carries out experimental study on the regulation of tailings intermittent sedimentation, according to whose result the particle sedimentation can be divided into four stages: acceleration, quasi uniform velocity, deceleration, and quasi quiescent, which reveals the relationship between sedimentation velocity and influence factor. According to the test, this paper gives a concept of homotactic sedimentation velocity, that is, taking the velocity from beginning to the sediment height reaching 80% of the total to get the average velocity as the sedimentation velocity, and then carrying out orthogonal experiment and range analysis to discuss the relationship between homotactic sedimentation velocity and slurry quality concentration, and flocculant unit consumption, and flocculant solution concentration. The result shows that the impact on the sedimentation velocity according to significance can be arranged as slurry quality concentration >flocculant unit consumption >flocculant solution concentration; finally, a BP neural network model is formed to analyze the effect on sedimentation velocity of flocculant unit consumption under different concentrations. The results show that there is an optimum dosage of flocculant corresponding to different concentrations of tailings mortar. When the concentration is too low or too high, the flocculation effect is not significant. For Anshan Iron and Steel Group Corporation's tailings mortar flocculation, the best slurry quality concentration is 20%, and the most suitable dosage of flocculant is 42 similar to 46g/t, while the sedimentation velocity can exceed 20cm/min.
Stability analyses of underground rock excavations are often performed using traditional deterministic methods. In deterministic methods the mean or characteristics values of the input parameters a ...
Mine backfilling is a process where the underground voids resulted from mining are filled with waste materials. The potential of co-depositing iron sand produced from smelting process with tailings sand was investigated in the present study. Different amounts of iron sand were mixed with the tailings sand to prepare cemented paste backfill (CPB) samples. Two types of binders were used. Uniaxial compression tests were performed for the CPB samples after 28 days of curing. The porosities of the samplers after curing were calculated to correlate the porosity with the uniaxial compression strength, UCS. Results from uniaxial compression tests showed that the amount of iron sand and the type of the binder influences the UCS, as well as content values of fines and porosity. These results demonstrated the possibility for a part of Fe-sand to be deposited together with the tailings sand to increase UCS values for the CPB samples, which will be beneficial for both mining operation and environmental protection.
The vane shear test method is used extensively in a variety of geotechnical exploration to determine the undrained shear strength fine grained clays and silts. A small scale physical model was developed to study the failure mechanism during the vane shear test. The soil was simulated using a mixture of amorphous silica and mineral oil, which becomes transparent when the refractive indices the oil and the silica are well matched. A special fabricated row cell equipped with vane shear device was developed to determine the strength of the transparent soil. One dimensional consolidation test was carried out to obtain the consolidation properties of the transparent soil. The laboratory vane shear test used is similar to the field vane shear test but is on smaller scale. The vane was mounted vertically at the centre of the rowe cell based which the vertical section aligned with the vane centerline was illuminated with laser light and sequence of digital image was recorded using a digital camera. Particle image velocimetry (PIV) was used to analyze the failure mechanism during vane shear test. The result obtained and the observation made in this study suggested that the failure zone was close to the conventional assumption of a uniform shear stress distribution at the vertical sides of the failure surface.
This study investigates the effect of soil cement column diameter and spacing on overall settlement beneath a road embankment situated on normally consolidated estuarine deposits in the South East Queensland region. The effect of Area Replacement Ratio (as) on settlement with consideration to column diameter and spacing variation is also compared to actual site settlement gauge data. The modelling was undertaken using Plaxis 2D and the results are discussed with respect to the variation in parameters as described. The sub surface profile was established during the investigation for the embankment and a series of oedometer tests were undertaken on samples obtained from the boreholes. The Plaxis inputs were calculated from the results of the oedometer tests and by several recognised methods as discussed in the paper. The aim of the research is to establish a graph suitable for initial settlement estimations on cement improved compressible soil.
