Advantages of Helical Piles
Discuss About The Geotechnical Geoenvironmental Engineering.
The installation of helical piles is carried out by applying torque to the pile head. This application has spread greatly in the recent years. This is due to their intrinsic advantages of installation that occurs rapidly over a short period of time with reduced vibration and noise, and it develops a very powerful hydraulic driving heads. The helical piles have the ability to be installed in areas with restricted hence they are the most preferred in foundation underpinning works. They also have high efficiency due to their ability to resist pullout and compression forces and they can be installed rapidly and loaded immediately (Livneh & Naggar, 2008). Studies and research done on the conduct of helical piles mounted in soil with fine texture show that the effects of installation do not affect the strength of the remolded cohesive soils. The research has however been done on only on the model of helical piles that are installed in the remolded materials and not the deposits of natural soil. Authors and researchers Bagheri and Naggar carried out studies on the impacts of disturbance of installation on the conduct of multi-helix piles in structured clays and they pointed out that driving piles into the cohesive soil yields a large amount of pore pressure inside the pile vicinity. At the point when the installation is done, the pressures of the pore begin to progressively dissipate. This allows for the soil that is around the pile to consolidate. At the period when the pile is consolidating, the soil, the strength of the soil shear as well as the pile bearing capacity tends to increase gradually (Byrne & Houlsby, 2015). They further reported that the results for the load tests of a pile that is driven into soft clay resulted to an increase in the bearing capacity of the pile.
Recent research work carried out by Samuel, Jonathan and Charles have identified that Helical screw piles have become a commonly used solution for the relatively low capacity, recyclable foundations that support rail and road signage and any other similar structures. They also pointed out that past studies on the behavior of helical piles in clay soils have mostly specified on the behavior of multi-helix screw piles that are loaded axial compression or the tension that has got a varying length of embedment (Cerato & Victor, 2009). When investigating the effect of the number of helical plates on the ultimate capacity in clay when using helical screw models that have a diameter of 75mm in a bed of clay, it was realized that the number of helical plates over a preset length of helical screw pile did greatly have an influence on the stiffness and capacity of the feedback from the piles. From this investigation, they were able to make a realization and hence a deduction that the highest capacity was attained when the spacing ratio was rated from 1.0 to 1.5. from a samples of data from field tests carried out on the capacity of uplift for the helical screw piles in clay when comparing them to the estimated capacities when using cylindrical failure as well as the individual capacities of plate bearing mechanisms, the study showed that in case of a failure mechanism that is assumed in design, it should at all point rely on the spacing ratio (El Naggar & Abdelghany, 2013). The researchers carried out their investigation by employing particle image velocimetry and transparent synthetic soil in order to make an observation of the failure of helical screws that have a spacing ratio of from 1.5 to 3.0 on the helical plate and also with an active length that is triple its diameter.
Recent Research on the Behavior of Helical Piles in Different Soil Types
The most currently used screw piles are mostly made of steel of high strength and they do consist of helices that are normally fixed to the shaft at some specific spacing and they also have a pointy toe in order to allow for better and easier installation to the ground. The use of helical piles has in the recent days been developed to structures that are subjected to lateral and compressive loading (El Naggar et al, 2012). Helical screw piles offer some structural resistance to tensile, lateral and compressive forces that come along with overturning moments. Researchers Abbas Mohajerani, Dusan Bosnjak, and Damon Bromwich determined that the context that surrounds the use of piles as the foundation of structures has been reliant on various trends. The advantages and disadvantages that result from the use of helical screws are vital when deciding on the conditions that are the most appropriate as well as beneficial when compared to other traditional methods of piling. This is because they are generally easy to install and also require reduced equipment. They are also well suitable for those areas that have restricted access. Most helical piles are reusable and also removable and hence need little dewatering. Most of these piles do offer increased acceptable and tensile compressive capacities, are able to work on slopes, and are mostly able to produce little noise as well as vibration during their installation. More overall is that they are cost-effective (Elkasabgy & El Naggar, 2013). The authors move ahead to describe the progress that has been made in relation to enhancing the axial capacities as well as the process of installation of the piles. They tend to purport that these improvements have been made are meant towards utilizing the helical piles as the main anchors and the foundations of making structures.
The improved use of helical piles in constructions has mainly been empowered by the several signs of progress in the hydraulic heads. A study aimed at authenticating the instability of the helical piles with relatively large diameters as well as evaluation of the axial capacities of the helical piles that are high performing and that are installed in cohesive soils will help determine the performance and installation characteristics of these helical piles (Fleming et al, 2014). This was also useful in determining the methodology of design for these high performing helical piles. The study carried out by Mohammed Sakr will, therefore, table the outcomes of an extensive axial tension and compression testing program that is executed on a large capacity helical piles that are mounted on cohesive soils. The outcome shows that helical piles are able to support generally higher axial compressive weights that go up to 275 tons or 2450 Kn. It was also realized that helical piles are also able to avail a viable option for the design of the foundations that provide support to loads that are relatively heavy. This is because the tensile capacities of the helical piles were recorded at an impressive high of 85% of the compressive capacity (Hu et al, 2014).
Installation Process of Helical Piles
The interest towards the use of helical piles has been on an upward trend and the global applications of this foundation have also been improving. One effective method of examining such foundations may be through carrying out the technique of centrifuge modeling in order to investigate the several aspects of helical foundations. Such was the motivation that drove Cristina De Hollanda Cavalcanti Tsuha into carrying out studies with a bid to solve this deficiency (Kurian & Shah, 2009). When describing the compilation of helical piles, Cristina says that they consist of either one or more helical bearing plates that are welded to the central shaft and often come in different sizes. The foundation is commonly placed in soil through the application of torque to the shaft. Helical foundations have commonly been utilized in applications such as energy transmissions, telecommunication towers, solar panels, retaining walls, distribution lines, for foundation repair as well for commercial and residential buildings. From her studies, it is also realized that the use of helical foundations has been deemed to succeed in the innovation and achieving a valuable solution for the foundations of wind turbines that are located on the offshores (Merifield, 2010). Her studies were also focused on the behavior of helical foundations that is applied to the uplift or pull-out forces, also known as helical anchors. Some of the main factors that determine the control the design of helical anchors include; type of anchor, type of soil, diameter and spacing of the helical units, shaft diameter, number of helical units, the angle of installation etc.
The use of helical piles has been commonly used to give support to several loads and to a variety of applications. This, therefore, makes it very important to quantify as well as qualify the performance characteristics as well as the axial capabilities of the helical piles. A geotechnical service manager, Mohammed Sakr carried out studies to determine the full scale axial as well as the uplift/tension program for testing that is carried out on huge volume helical piles that are installed in the soils that have no cohesion (Mittal et al, 2010). From the study, he came to a conclusion that the helical piles have in most cases established noteworthy resistance towards axial compressive and tensile loads. The study found out that the resistance towards axial compressive loads weighs up to 2920 kN which is approximately 656 kips while the resistance towards tensile loads weighs up to 2900 kN translated to 652 kips. The axial capacities of helical piles could be projected analytically either by using the cylindrical shear method or by using the individual bearing methods. When using the individual bearing method, it will assume that the bearing failure happens at each helix. The cylindrical shear method meanwhile tends to assume that a cylindrical shear failure surface that connects the lowermost and the uppermost helices will be formed and the axial capacity will be the resultant sum of the shear resistance that is along the cylindrical surface (Prasad & Rao, 2016). It should bear the resistance that is above the uppermost helix, the resistance of bearing that is below the bottommost helix and also the adhesion that is along the higher steel portion shaft that is above the helix level.
Design Methodology for Helical Piles
The use of anchors in the field of ocean engineering is meant for different purposes. They may mostly be used for the purpose of maintaining the position of the floating bodies that may include ships, submersible rigs, navigational buoys etc. they could also be used to bring stability to structures that are bottom fixed (Sakr, 2009). Several attempts in order to develop very dependable rational concepts for the design and development of these anchors have carried out with noticeable outcomes. Narasimha carried out studies on the importance of understanding the behaviors of the screw anchors as well as the importance of adopting them the foundations of towers. It was realized that marine environments could also employ the use of screw anchors in a bid to provide an enhancement to the vertical holding capacity of dead weight anchors. The behavior of the screw anchors as well as the under-reamed pile anchors are related and as a result, the screw plates that are availed in the screw anchors are meant to provide increased capacities. This is because they do the under-reams in the under-reamed piles. The study laid out the approaches of design for the under-reamed pile anchors in accordance to the suggestions brought forward by Mohan and Jain. They suggested that in the under-reamed pile anchors, a surface that is cylindrical and is between the under-reams was to be for the piles that have closely spaced under-reams (Stanier, 2013). Screw anchors are generally shafts made of steel and to which there are either one or more screw plates that are attached to it. The plates are usually placed at regular intervals. Their installation is a bit easy since they do not need any form of grouting in order to keep them in position.
Mohammed carried out studies to determine the performance of helical piles that are located on the sand. The outcomes of the detailed pile load-test program, as well as the observations that were made from the field while monitoring the helical piles, were used to determine their performances (Tsuha et al, 2010). The type of helical pile used were either those with one helix or those with two helixes mounted in oil sand. These results were important when designing and developing a theoretical model of design that could be used to set up helical piles in oil sand. From the research and the results, it was realized that it is possible for circular shaft helical piles to resist substantial lateral loads. A decisi0on on whether to use a one helix or multiple helixes greatly depends on the conditions of the soil as well as the capacities of the pile that are needed. It is normally assumed that the bearing failure always takes place at each helix. The overall axial pile pressure in tension or compression should result in the total of the capacities of each helix and also the shaft resistance. The study was able to identify the suitable criteria for failure for the helical piles that are mounted in oil sands, find out how helical piles perform under lateral loads and how installation torque and piles capacity relate (Tsuha et al, 2012).
Byrne, B.W. and Houlsby, G.T., 2015. Helical piles: an innovative foundation design option for offshore wind turbines. Phil. Trans. R. Soc. A, 373(2035), p.20140081.
Cerato, A.B. and Victor, R., 2009. Effects of long-term dynamic loading and fluctuating water table on helical anchor performance for small wind tower foundations. Journal of Performance of Constructed Facilities, 23(4), pp.251-261.
El Naggar, M.H. and Abdelghany, Y., 2013, June. Helical screw piles (HSP) capacity for axial cyclic loadings in cohesive soils. In Proceedings of the 4th International Conference on Earthquake Geotechnical Engineering, Thessaloniki-Greece in (pp. 25-28).
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