Description For Individual Bearing And Cylindrical Bearing Method
Description For Individual Bearing And Cylindrical Bearing Method
Methodology Description For Individual Bearing Method And Cylindrical Bearing Method.
In the first section of this proposal, background information on screw piles is discussed and also the overview of the context of screw piles over stresses centered on the history and insinuations of screw piles in regard to their merits and demerits. The proposal objectives are also discussed followed by design essentials. Consequently, design methods are provided in this proposal which is grouped axial capacity agenda via numerous methods, for example, individual bearing method and cylindrical shear method. The project is concluded by comparing the two different methods mentioned above.
Helical piles also known as screw piles are a steel screw- in pilling and ground anchoring system which is applied in building foundations which are deep. The helical piles have been used extensively in Western Canada to support superstructures mostly with applications in power transmission towers, camps, and commercial buildings. The load structure is transmitted into the pile by the shaft and the most commonly used material in the fabrication of helical piles is steel and galvanized to repel corrosion. The invention of helical pile first took place by Irish Engineer known as Alexander Mitchell and it was first used in the foundation system for river moorings in 1830. Currently, the use of helical piles has adapted to the trends and engineers’ requirements (Phoon, 2008, p. 156). Description For Individual Bearing And Cylindrical Bearing Method
The screw pile foundation is still used broadly and they usage has prolonged from lighthouses to rail, roads, telecommunications and building work. The use of screw pile foundations is necessary since they lessen the effect on the environment and it is cost efficiency (Prakash, 2006). Transportation of soil from the site is not a must since during screwing foundation there is less soil displacement. This method reduces the cost of transportation and reducing the carbon footprint of the project.
The most important aspect of helical pile foundation include a reduction in carbon footprint, risk reduction in the workforce, cost reduction, the project is accomplished in a shorter period, accessibility and installation are very easy.
Summary Of Helical Piles And Anchors Advantages
- Can be installed in any weather
- Environmental friendly
- Quick and easy to install
- Immediate loading
- Torque-to capacity correlation.
The objective of this proposal is to deliver better precision for entirely the project approaches available on perpendicularly encumbered screw piles and to illustrate the contrasts and methodology description for Individual and cylindrical bearing method. Description For Individual Bearing And Cylindrical Bearing Method
Description And Scope
The screw pile according to Arup Geotechnics in the year 2005, were originally applied as anchors and hence, were centered nearby tensile loads for example buried pipelines and transmission towers. The applications of screw pile have increased and currently, they are used in structures subjected to lateral and compressive loading.
There are various conditions which are hindering the performance of the screw pile, for example, the rocky soils, boulders, and bedrocks as discussed by Schmidt and Nasr in the year 2004. The axial capacity of the piles is reduced when some piles are trimmed for installation assistance into gravel consisting of cobbles as discovered by the Sakr (2011). There are dissimilar methods of design namely cylindrical shear method and individual bearing method
The downward pressure known as crowd and torque is applied during installation screw pile but the crowd effect on the design process has not been found through the piles can arrive at their required depth as a result of an increase in the crowd as claimed by Vito and Cook (2011).
A strong ground condition is needed before installation of screw pile since in a condition like this the theoretical and actual base pressure is substantially less as asserted by Abramson and Yttrium (2003).
The helical plate elevates bearing capacity can be expressed using a formula as a non-dimensional function factors as mentioned by Maruipolshii & Trofimenkov (2005). In the case of multi-helix anchors, the most methods which are used in calculating the pullout capacity are the cylindrical shear method and individual bearing method (Musial, 2011, p. 34).
Theoretical Methods Of Calculating Pile Capacity
The soil strength, geometry of the pile, overburden pressure and embedment depth influence the axial capacity of the helical pile.The shallow and depth failure modes can be used in grouping the behavior of helical pile. The catastrophe is localized nearby the helices in case of deep behavior while the failure plane lengthens to the ground surface in case of shallow anchors (Musial, 2011, p. 54).
The critical embedment ratio can be used in determining the shallow and deep behavior of the helical plates using (H/D) cr where H is the embedment depth while helix diameter is represented by D. There are two possible failure mechanism in the case of helical piles and they both rely on helices vertical spacing such that when there is a large spacing between the helices then the capacity of the pile can be obtained using individual bearing capacity. (Mayne, 2008, p. 341).
Using this method known as individual bearing method, the capacity of the pile can be estimated from the cumulative value of the of the individual helix bearing capacities. Every helical plate is considered as an individual plate which bears on the soil above the helix when the pile is subjected to tensile loads and bears on the soil below the helix when the pile is subjected to compressive loads (Rao, 2007, p. 15). The capacity of a helical pile in consideration of individual helix bearing failure can be calculated as;
When the spacing ratio is small, then the catastrophe tends to take place laterally the cylindrical failure surface confined by the helices. To approximate the compressive capacity of helical piles then the cylindrical shear model is recommended. In this particular method, the occurrence of failure takes place along the surface of cylindrical shear with an equivalent diameter to the average diameters of the helix (White, 2010, p. 456).
The pile capacity would be equal to the sum of the mobilized shear strength along the surface of cylindrical shear, shaft resistance and soil bearing beneath the bottom helix for a pile in compression as well as the bearing capacity of the soil above the uppermost helix in the case of uplifting piles. From the cylindrical shear model, the calculation of axial capacity can be done by;
The torque correlation factor can be used in an approximation of helical piles where the estimation of the capacity is done centered on correlation and installation torque factor (Henry, 2009).
Equipment Used In Carrying Out The Experiment
The Model Anchors
Two sets of model anchors made with mild steel pipes welded using steel screw plates were investigated. The set 1 anchors were a bit smaller compared to Set 2 anchors. The screw plates had different diameters of 75mm and 33mm (Paulo, 2016, p. 6)
The Soil Used.
A marine clay soil from a coastal deposit was used in this experiment and this type of soil consisting of silt and sand approximately 90% and 30% respectively. The plastic and liquid limit for the soil were 32% and 82% respectively (Henry, 2009, p. 173).