Pre Bored Steel H Piling System

Pre bored brand name H Piling SystemAlthough Hong Kong is featured of its Skyscrapers both everywhere the world, and it seems that H-Piling organization may not have enough bearing ability to their superstructure, there are still many servicing grammatical constructions and small-scale infrastructure developing, the core of which is capable to be borne by H-Piling organisation, in the city. In the following words, a brief introduction oer Pre-Bored vane H-Piling system willing be presented associated with connect cases applying such kind of piling system in Hong Kong in society to draw a more detailed picture over the application of Pre-Bored stigma H-Piling system in Hong Kong.The principle of Pre-Bored leaf blade H-Piling system is similar to the Bored Piling system. Both of them are re bafflement tummy and require boring the initial hole on the site for the insertion of the temporary or permanent blade typesetters case, depending on its design. After the completion o f the boring process, the stigma and rock privileged the poise casing will then be extracted and the workers will place the reinforcement material internal the steel casing. That is the major variation between Bored Piling and Pre-Bored Steel H-Piling System. For Bored Piling, the reinforcement bars will be bent in order to form the circular cage ( record 1). However, H Steel Pile will be the reinforcement material in Pre-bored H-Piling system. Grouting is then started after placing reinforcement material to form the pile.Since the diameter of Bored Piling mountain be larger than Pre-Bored H-Piling, the former one nookie typically take up more loading than the latter one. Therefore, small-scale construction project is close likely to use Pre-Bored Steel H-Piling system in Hong Kong. The cases introduced later are small in scale, but they do play an important role in our city.Dyr1 sem1BRE 291 Con techProject Photos (Construction site)Week 4 23102009CIMG0341.JPGFigure 1 Reinfor cement Bar for Bored PilingFigure 2 H-Pile for Reinforcement in Pre- Bored H-Piling systemThe first case being examined is the construction of Queen Mary Interchange near Queen Mary Hospital and Pok Fu Lam Road. It is a road approach project initiated by the local government at the two junctions, which are in Sassoon Road and Bisney Road with Pok Fu Lam Road, on Hong Kong Island. The aim of this project is to rid the congestion problem existing in these roads by constructing a new interchange, comprising of some(prenominal) link up.CUsersAlan KwokDesktopperspec.jpgFigure 3 Model of proposed cultivationFigure 4 Queen Mary Interchange Still in the progress of constructionAs we mickle see in the model of proposed development (Figure 3), the interchange, which placed at the bottom of the figure, is locating on a slope. Since the the soil in slope exert a considerable amount of bending and tensile stress, accord to Tomlinson (1994), H-pile is able to withstand such kind of extre me situation due to its unique H design. Therefore, the authority concerned decided to build the interchange with Pre-Bored Drill-in Steel H-Piles. Moreover, the short erection time and economical construction cost are to a fault the reason to make use of such kind of piling system in this project. According to Kumaraswamy, Mohan (2002), the firm process of developing a Pre-Bored drill-in H pile, i.e. pre- oil production, drilling and grouting, heap be finished in 3 working days. We gutter also see that the site is not so spacious enough to place some large-scale machinery during the pile development. The development of Pre-Bored Drill-in Steel H-Piles cigarette pound this problem because the diameter of this pile is only 600mm in this case The size of drilling techniques tidy sum be controlled and fitted into the occlude site.CUsersAlan KwokDesktop1000.jpgFigure 5 The congested site on a steep slopein this construction of Queen Mary InterchangeBefore the development of pile in this project, several raw materials and tools are required to present. Here is the table showing what are needed,CUsersAlan KwokDesktop8.jpgCircular steel casing of internal diameter 600mm and thickness 25mmCUsersAlan KwokDesktop10.jpgSteel H-pile, which will be inserted in the steel casingCUsersAlan KwokDesktop843.jpgHydraulic beat mounted on angleworm craneTable 1 Major Material list for constructing pile of Queen Mary InterchangeIn the very first stage of developing Pre-Bored Drill-in Pile in this project, engineers will have a pre-drilling through the soil layers and rock within the site in order to identify the underground condition, such as the rock brainpower levels and the strength of the soil. It is an important procedure since it will determine the type, length, etc of the pile. Any wrong measurement, especially overestimate the soil/rock supporting capacity, will make the whole project lose ground because the whole structure will be ruined, the typical case is the B lock E and F of Yu Chui Court, demolished after discovering the rottenness scandal, which developed by piles shorter than the standard and cause possible dangerous to its users .After the completion of soil investigation and analysis, the engineers would then design and choose the close to suitable piling system for different project. In the construction of Queen Mary Interchange, the engineers found out that the Pre-bored piling system is suitable for construction of high-way bridges at the steep slope on the site. The site-workers firstly pressed the circular steel casing inside the ground through the help of Hydraulic pound sign which is mounted on a crawler crane. The reason to plug the steel casing into the ground was to prevent the soil from collapsing inside the hole, which would be placed H-pile inside it, during the process of drilling.CUsersAlan KwokDesktop1.jpgCUsersAlan KwokDesktop9.jpgFigure 6 Inserting circular steel casing into ground by hydraulic hammer mounted o n crawler craneFigure 7 Connecting two steel casings by welding when the length is not enoughThe process in Figure 7 happened when the steel casings being installed were not long enough to reach the target depth into the soil. By welding the end of two steel casings, the total length of it can be extended. For the inadequate length of H-Pile, their length can also be extended through welding.When the steel casing reached the bed rock level and form a socket, the next stage is to remove those soil and rock inside the steel tube, as shown in Figure 8. The ground was drilled with a hammer mounted on a drilling rig so as to remove the obstruction underground. This process could enable the hard rock and pressed soil to be watch extractable out of the steel casing. In this project, the obstructions were then extracted out by flushing the case with water and compressed air. The compressed air acted at the initial force and the water acted as a transferring medium to carry out the obstructi on out of the earth. The above two procedures will take turns to start until all of the obstruction inside the tube were wholly carried out.CUsersAlan KwokDesktop2.jpgCUsersAlan KwokDesktop3.jpgFigure 8 Removing obstruction by drilling with down-the-hole hammer mounted on drilling rigFigure 9 Withdrawing soil from inside the casing by flushing with water and compressed airThe H-Piles would then be installed inside the empty steel casing after the clearance of obstruction inside. Meanwhile, a 20mm diameter grout tube was also placed to full length of the pile in order to prepare its grouting process later on.CUsersAlan KwokDesktop4.jpgFigure 10 Installing steel H-pile inside the empty steel casingThe grouting process is to have a re-bonding between the soil and the H-piles with the suitable grade of concrete by tremmie method from the bottom to the top of the casing. Tremmie method is a concrete-pouring method in some modify spaces underground deeply. Since a tube is used to pour th e concrete from the bottom, the force of falling concrete can be controlled through shortening the distance of freely movement of the concrete. It can prevent the concrete from improperly mixed when it is placed at the bottom of the casing which result in voids and air packet which can cause possible danger to the whole structure.The temporary steel casings were extracted gradually when the fresh concrete was pouring inside since the bonding force of the concrete is not strong at this moment. However, engineers maintained the bottom of the casing at a level of at least 2 meters below the grout surface to gibe that there was enough time range for the concrete to form the circular shape. The grouting operation was stopped when the uncontaminated grout flowed out of the hole to ensure the faithfulness of concrete poured inside the casing.CUsersAlan KwokDesktop5.jpgCUsersAlan KwokDesktop7.jpgFigure 11 Grouting the steel casing with suitable grade of concrete by tremmie methodFigure 12 Extracting the steel casing while grouting is going onCUsersAlan KwokDesktop6.jpgCUsersAlan KwokDesktop11.jpgFigure 13 Grouting the steel casing with suitable grade of concrete by tremmie methodFigure 14 Extracting the steel casing while grouting is going onThe finishing of grouting process means that the whole development of Pre-Bored Drill-in H-Pile system is come into the end soon. After the dewatering process of the concrete attached to the H-Pile itself, the drilled-in H-Pile was finished. Figure 13 shows the product of the above stages. It is a group of drilled-in H-Piles that were formed a combined pile cap for the highway bridges in Queen Mary Interchange. To verify its bear capacity, loading screen was taken place in order to test its vertical deflection. Once the test was passed, the superstructure developments were then taken place.Pre-Bored Steel H-Piling system is not only applied in local road constructions, but it is also applied in some small-scale construction of buildings in Hong Kong. There is a typical example, which is the construction of Sheung Wan Stormwater Pumping Station (SWSPS) on Hong Kong Island. It is a single-storey building with a underground water tank with 11 meters deep at the Chung Kong Road, which is the waterfront of Sheung Wan. This project was to alleviate the flooding problem in Sheung Wan.CUsersAlan KwokDesktop391 projectProduct of construction.pngFigure 15 Sheung Wan Stormwater Pumping StationFigure 16 Location syllabus of Sheung Wan Stormwater Pumping StationAccording to the paper presented by Leung,Li and Leung (2009), the site of the Sheung Wan Stormwater Pumping station was reclaimed in 1982. The material used for reclaimed it are as followed,Fill (medium grained granite)Marine DepositAlluviumCompletely Decomposed Granite (CDG)Originally the engineers decided to build up this service station with 60 numbers of large diameter bored piles, and the diameter of which are ranged from 1.2 meters to 1.5 meters.Figure 17 The Original Bored Pile Layout Plan of SWSPSFigure 18 The Geological Section Across the site (Land Seawall)But later on, the contractor of this project advised the government to build up the superstructure and sub-structure over a combination of rock socketted H-piles, mini-piles and raft foundation. The government finally accepted the advice from the contractor and starting the construction process. Referring back to the Figure 17, the PC5 Zone, all of the piling would be changed into the Pre-Bored H-piling system. For the new(prenominal) zoning, mini-piles were used.The major reason to change the piling system, as the paper disclosed, was because of the cost effectiveness. First of all, since the diameter of the steel casing used in Pre-Bored Steel H-Piling system is far smaller than the bored piling system. The grouting process of the former one will consuming less amount of concrete than the latter one, which can reduce the cost of development.Table 2 The difference in pile foundation between the initial and final planBesides the cost friendship factor, the time used for developing these two different kinds of piling systems is different. As what Kumaraswamy, Mohan (2002) said, the whole process of developing a Pre-bored H-piling system only cost just about 3 days. However, the development of a foundation pile normally takes up more than 3 days. Since the amount of pile developed in this project is large, i.e. nearly 50 piles are changed from bored pile to pre-bored H piling system. The time cost saved through the final plan is considerable.In the purview of technical operation, the required pile capacity of the pumping station is 6900 kN. For bored piling, For bored piling (The government of HKSAR,2006), typical sizes of these piles range from 1 m to 3 m, with lengths up to about 80 m and working loads up to about 45 000 kN. When high grade and heavy steel H-pile section is used, the load-carrying capacity can exceed 5 500 kN. We can see that the loading capacity of bored piling is far more than the loading requirement of the pumping station. However, we can also discover that a maximum of 1400kN was not be able to supported by Rock Socketted Steel H-Pile. The solution, as shown in Figure 18, is to place in 4 numbers of T50 steel bars inside each of the casing for reinforcement so as to remove the discrepancy.Therefore, the final plan can enable a more efficient use in the resource than the initial one. That is why it is reasonable for the government to change its decision.Figure 19 classifiable detail of Rock Socketted H-piles of Alternative DesignFor the developing processes of the Pre-bored socketted H-piling system, most of them are the same as the Pre-bored Drilled-in piling system. The major difference between them is that the steel casing used in Pre-bored socketted H-piling system is permanently fixed inside the soil, while the steel casing used in Pre-bored Drilled-in piling system was temporary in used. They are r emoved during grouting. In this project, the rock socket H-piles were installed through the help of concentric overburden drilling system with air-flushing. It uses a rotary-percussive action for drilling and uses air flushing for remotion of debris before casting in the H-pile inside the tube and grouting.In conclusion, the loading bearing capacity of Pre-Bored Steel H-Piling system is relatively lower than the other common piling system used in Hong Kong. However, due to its mobility during installation and its strength, it is still also commonly applied in some small-scale development in local projects.-The End-