Effect of helix bending deflection on load settlement behaviour of screw pile

A screw pile has higher end bearing capacity than any other straight pipe piles due to its larger helix with respect to central shaft. However, larger helices are not frequently used as it will bend and may reduce the actual bearing capacity of the ground. In the present study, the effect of helix bending deflection on the load settlement behaviour and ultimate bearing capacity is investigated. To achieve the objectives, model scale pile load tests were conducted. The effect of helix bending on the load settlement behaviour at higher stress level was also investigated in this research. The helices with different helix-to-shaft-diameter ratios and thicknesses were used, so that clear difference of deformed and non-deformed screw piles in the load settlement behaviour can be observed. Dry Toyoura sand in dense state was used as a model ground. It is observed from test results that the helix bending deflection starts affecting the load settlement behaviour of the ground if it is more than the critical helix bending deflection. The ratio of critical helix bending deflection to outstand length decreases with increase in helix-to-shaft-diameter ratio, and its relationship is presented in this study. It is also observed that the Roark’s formula for flat circular plate having uniform load over a very small circular area with fixed outer edges showed good agreement with the measured helix bending deflection. In order to estimate the optimum helix thickness, the well-agreed equation is also modified with respect to critical helix bending deflection.

     

Development of Statistical Models to Predict the Mechanical Properties of Some Metamorphic Rocks from P-Wave Velocity and Certain Physical Properties

Geotechnical and Geological Engineering - Strength and elastic properties of rocks have vital importance for the design of structures in several rock engineering projects. Additionally, these...     

Turbulence measurements in stratified and well-mixed estuarine flows

From mean velocities measured in estuarine flows it has been found that the velocity distributions are log-linear in stratified flows and logarithmic in well-mixed flows. The results of salinity measurements reveal that the mean salinity profiles are geometrically similar and expressible as a power law. The buoyancy parameters, such as the Monin-Obukhov length scale, the gradient and the flux Richardson numbers, are independent of the flow state. The gradient and the flux Richardson numbers are almost equal, indicating the existence of a local equilibrium layer. The non-dimensional parameter describing dissipation rates of turbulent kinetic energy is a constant of 0·2 and 0·3 for stratified and well-mixed flows respectively. In well-mixed flow the drag coefficient varies with time approaching a constant of about 3·2 × 10^?3 when the flow is stratified. The shape of the turbulent energy spectra are generally flatter and broader in stratified as compared with those of well-mixed flows.     

焉耆盆地生态系统服务价值对土地利用/覆被变化的响应

运用土地利用/覆被类型动态度、土地利用/覆被程度模型和生态系统服务价值估算模型,分析了新疆焉耆盆地1990-2011年LUCC变化引起的生态系统服务价值的变化。结果表明：（1）在1990-2011年,焉耆盆地水域、湿地、沙地、耕地和建设用地均呈增加趋势,而盐碱地、草地和林地面积呈减少趋势,总体上研究区的土地利用程度为中下水平。（2）在1999-2011年,研究区的生态系统服务总价值总体上呈增加的趋势,其中水域和耕地对生态系统服务总价值贡献率较大,草地和林地对生态系统服务总价值有明显的负贡献。（3）在1990-2011年,研究区的各类生态系统的气候调节、水源涵养和废物处理功能的生态系统服务的总价值远远大于粮食生产和原材料供应功能的总价值。因而对区域的水土资源实行合理与有效的利用是实现焉耆盆地生态系统服务功能维持和可持续发展的关键。     

Hydrogeochemical evaluation and statistical analysis of groundwater of Sylhet,north-eastern Bangladesh

Acta Geochimica - To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and...     

Lunar concrete: Prospects and challenges

The possibility of using concrete as a construction material at the Moon surface is considered. Dissimilarities between the Earth and the Moon and their possible effects on concrete are also emphasized. Availability of constituent materials for concrete at lunar surface is addressed. An emphasis is given to two types of materials, namely, hydraulic concrete and sulfur concrete. Hydraulic concrete necessitates the use of water and sulfur concrete makes use of molten sulfur in lieu of cement and water.     

Analysis of radio astronomy bands using CALLISTO spectrometer at Malaysia-UKM station

The e-CALLISTO system is a worldwide network that aims to observe solar radio emission for astronomical science. CALLISTO instruments have been deployed worldwide in various locations that together can provide continuous observation of the solar radio spectrum for 24 h per day year-round. Malaysia-UKM is a strategic equatorial location and can observe the Sun 12 h per day. This paper gives an overview of the spectrum allocation for radio astronomy, which falls in the specified operating frequency band of the CALLISTO spectrometer. The radio astronomy bands are analyzed at the Malaysia-UKM station according to the International Telecommunication Union recommendations. Some observational results are also presented in this paper.     

Evaluation of aquifer environment under Hazaribagh leather processing zone of Dhaka city

Hazaribagh is a densely populated area of Dhaka city where about 185 leather processing industries have been operating and discharging solid and liquid wastes directly to the low-lying areas, river and natural canals without proper treatment. The area is covered by alluvial deposits of Holocene age and is underlain by Pleistocene Madhupur clay. The Dupi Tila Formation of Mio-Pliocene age underlain by this yellowish gray to brick red clay bed serves as the main water-bearing aquifer of Dhaka city. To assess the environmental degradation as well as the groundwater environment, major anions, cations and heavy metals of water samples, heavy metals and organic carbon content of sediment samples were analyzed in this study. Analyses of tannery effluent detect high concentration of Na⁺, Mg²⁺, Cl⁻ and SO ₄ ²⁻ followed by Ca²⁺, NH ₄ ⁺ and K⁺ with remarkable contents of some trace elements, mainly Cr, Fe, Mn, S, Ni and Pb. Higher accumulations of Cr, Al and Fe are observed in topsoil samples with significant amounts of Mn, Zn, Ni and Cu. Concentrations of ions and all the investigated trace elements of sampled groundwater were within the maximum allowable limit for drinking water of the Department of Environment, Bangladesh (DoE), and World Health Organization (WHO). However, excessive concentrations of Cr, Pb, etc., have already been reported in the shallow groundwater (10–20 m) of the area. Due to excessive withdrawal the vulnerability of groundwater contamination in deeper parts cannot be avoided for the future.     

The impact of intensive groundwater abstraction on recharge to a shallow regional aquifer system: evidence from Bangladesh

Quantitative evaluations of the impact of groundwater abstraction on recharge are rare. Over a period (1975??007) during which groundwater abstraction increased dramatically in the Bengal Basin, changes in net groundwater recharge in Bangladesh are assessed using the water-table fluctuation method. Mean annual groundwater recharge is shown to be higher (300??00?mm) in northwestern and southwestern areas of Bangladesh than in southeastern and northeastern regions (<100?mm) where rainfall and potential recharge are greater. Net recharge in many parts of Bangladesh has increased substantially (5??5?mm/year between 1985 and 2007) in response to increased groundwater abstraction for irrigation and urban water supplies. In contrast, net recharge has slightly decreased (??.5 to ???mm/year) in areas where groundwater-fed irrigation is low (<30% of total irrigation) and where abstraction has either decreased or remained unchanged over the period of 1985??007. The spatio-temporal dynamics of recharge in Bangladesh illustrate the fundamental flaw in definitions of “safe yield??based on recharge estimated under static (non-pumping) conditions and reveal the areas where (1) further groundwater abstraction may increase actual recharge to the shallow aquifer, and (2) current groundwater abstraction for irrigation and urban water supplies is unsustainable.     

End bearing capacity comparison of screw pile with straight pipe pile under similar ground conditions

In the present study, the end bearing capacity of screw and straight pipe pile under similar pile tip area and ground conditions were investigated. The effect of increasing overburden pressure was also considered in this research. Pile load tests on close-ended screw and straight pipe piles were conducted in the small scale. Dry Toyoura sand was used to develop the model ground. The sand was compacted at relative density of 70, 80 and 92 %. It was observed that in case of straight pipe pile, load settlement curve plunges downward without increase in load around settlement equals to 10 % of pile tip diameter, whereas in case of screw pile, the load settlement curve plunges around settlement equals to 15 % of pile tip diameter. Moreover, the screw piles having helix-to-shaft diameter ratio 2–4.1 showed 2–12 times higher end bearing capacity than straight pipe piles with similar pile shaft diameter. It was also observed from the test results that the end bearing capacity of single-helix screw pile was in average 16.25 % less than straight pipe pile with similar pile tip area and ground conditions irrespective of the effect of increasing overburden pressure.