What is cast in situ concrete pile?
This article focuses on the construction of bored cast in situ piles and the various aspects related to it, including the application conditions. The process involves digging a hole in the ground through percussive or rotary methods, using temporary or permanent casing or drilling mud. Once the hole is formed, it is filled with reinforced concrete to complete the construction.
Bored cast in situ piles are constructed by drilling a hole in the ground and are commonly used in foundation work. The construction process involves the use of appropriate techniques such as rotary or percussive methods, along with temporary or permanent casing or drilling mud. The final step involves filling the hole with reinforced concrete. This type of pile construction is preferred in situations where the foundation load is significant, and the soil conditions are variable.
The construction of bored cast in situ piles requires skilled workers and specialized equipment to ensure that the process is completed efficiently and safely. The pile’s quality is critical, and factors such as the diameter of the hole, depth, and reinforcement must be carefully considered to ensure the pile’s stability and longevity. Additionally, the application conditions must also be taken into account, including factors such as the soil type, ground water level, and load-bearing capacity of the foundation.
In summary, bored cast in situ pile construction involves drilling a hole in the ground and filling it with reinforced concrete. The process requires specialized equipment, skilled workers, and careful consideration of various factors such as soil conditions, load-bearing capacity, and application requirements.
Procedure for Construction of bored cast in situ pile
In this section, procedure used for the bored cast in situ pile construction is presented:
Prior to the commence of pile construction operation
Construction Program with Main Project Milestones:
The construction program outlines the key milestones and timelines for a construction project. It provides a roadmap for the project team and stakeholders to understand what tasks need to be completed and when, ensuring the project stays on track and within budget.
The program typically includes the following main project milestones:
- Project Initiation: This milestone involves setting up the project team, defining project goals and objectives, and identifying the key stakeholders.
- Design Development: At this stage, the project team works on developing the detailed design, including architectural, structural, and MEP drawings.
- Procurement: This milestone involves the procurement of construction materials, equipment, and services required for the project.
- Construction: This is the main phase of the project, where the actual construction work takes place, including site preparation, foundation work, structural work, MEP work, and finishes.
- Commissioning and Testing: This milestone involves testing and commissioning all systems and equipment to ensure they are functioning as per design specifications.
- Handover and Closeout: This is the final stage of the project, where the completed project is handed over to the client, and all necessary documentation and certifications are provided.
Templates and Quality Check Formats:
In order to ensure consistency and quality in the construction program, it is essential to have templates and quality check formats in place. These templates should be used to record important information about each milestone, such as project scope, timelines, budget, and risks.
The quality check formats should be used to verify that the work completed at each milestone meets the required quality standards. This can include inspections, testing, and reviews of documentation.
By using templates and quality check formats, the project team can ensure that all necessary information is recorded and that work is completed to the required standards, reducing the risk of errors and delays. These templates and checklists should be maintained throughout the project and updated as necessary to reflect changes in the project scope or timeline.
Setting out pile points.
To accurately set out pile points based on the design drawings, it is essential to adhere to the guidelines outlined in IS 2911. These guidelines specify the maximum allowable tolerance for pile diameter, which is crucial for ensuring the stability and safety of the overall structure. For piles with a diameter of 60cm or more, the largest allowable tolerance is either 75mm or D/2, while for piles with a diameter of up to 600mm, the tolerance limit is 50mm.
To ensure that the set out points are clear and fixed, it is important to use precision instruments such as total stations or theodolites. These instruments can help accurately mark out the pile positions and ensure that the points are not affected by other activities around the area. It is also important to establish temporary reference points (TR) to recheck the pile points before starting the piling activity. This will help ensure that the pile points are accurately set out and meet the required tolerance limits. By following these guidelines, we can ensure that the pile points are set out accurately and meet the necessary safety standards.
Fig.1:Set out pile location
Plan preparation for rig movement
A layout needs to be prepared that showcases the anticipated path for the movement of rigs. This layout should be based on the work program and the planned allocation of resources. The main objective of this layout is to ensure that all rigs can move smoothly without causing any disturbance or issues to other rig operations.
It is imperative that the layout is designed in such a way that it allows for easy movement of all rigs. This will provide the team with a clear understanding of how to plan their work for the next day. It is important to keep in mind that the layout should not hinder the progress of other rig operations and must be executed without causing any disruptions.
By following the guidelines mentioned above, the team will be able to create a well-designed layout that serves its purpose effectively. The layout will help to streamline the movement of rigs and provide a clear picture of how resources should be deployed. Overall, the creation of a well-planned layout will ensure that all rig operations run smoothly and efficiently.
Boring process
To position the rig over the pile point, it is important to ensure that the point has been accurately established. This can be done by comparing it with other reference points. By doing so, any discrepancies or errors in the established point can be identified and corrected before the rig is positioned over it.
Once the point has been established and verified, the rig can be moved into position. This is a critical step in the pile driving process, as the accuracy of the rig’s positioning will directly impact the success of the pile installation. Careful attention must be paid to ensure that the rig is positioned correctly and that all safety measures are taken to protect personnel and equipment during the installation process.
By following these steps and taking the necessary precautions, the pile driving process can be carried out safely and effectively, ensuring that the resulting structure is strong, stable, and able to withstand the forces it will be subjected to over time.
Fig.2:Positioning rig on pile spot
To ensure that the pile diameter is accurate, the diameter of the cutting tool used for the drilling should not be less than the required pile diameter by more than 75mm.
After positioning the drilling rig, the steel casing should be driven into the ground. The steel casing should be driven to a minimum depth of 1 meter below the ground level to provide support against lateral loads and movements at the site. Additionally, the use of steel casing can help combat difficulties that may arise from groundwater during the piling process.
In the case of loose soils, it is advisable to provide permanent steel casing or liners as per the consultant’s advice.
During the boring process, it is important to stabilize the borehole using bentonite or other suitable means. Regular estimation of the specific gravity of bentonite should be carried out to ensure that the consistency of the drilling mud is maintained throughout the boring and concreting operations. This measure is used to stabilize the borehole and prevent concrete from getting mixed up with the thicker suspension of the mud.
To ensure that the piles are driven straight, great care should be taken during the piling process.
Fig.3:Drilling pile borehole
Paragraph 1: To estimate the ‘N’ value of the founding strata, it is recommended to carry out penetration tests. It is also advisable to take and maintain soil or rock samples from the founding strata for future reference.
Paragraph 2: In addition to the founding strata, it is advisable to take soil samples from each intermediate soil strata at the specified depths mentioned in the soil test report.
Paragraph 3: The boring process should be concluded once the designated boring depth has been reached. To ensure accuracy, the borehole depth should be checked by measuring the bailer pipe length after it has been removed from the borehole, and a sounding technique should be used to recheck the borehole depth.
Reinforcement placement
A task has been assigned to lower a reinforcement cage into a borehole in a way that avoids any disturbance to the sides of the hole. This task requires a high level of precision and care to ensure that the reinforcement cage is positioned correctly without causing any damage to the borehole. It is important to maintain the integrity of the hole to ensure that it can function as intended and support any structures that may be built upon it. The process of lowering the reinforcement cage must be carried out in a vertical manner to ensure that it is properly aligned and can provide the necessary support once it is in place. This task requires specialized knowledge and expertise to carry out effectively, and it is crucial to follow proper procedures to ensure that the job is done correctly.
Fig.4:Prefabricated reinforcement cage for pile construction
Fig.5:Lowering pile reinforcement cage into borehole
To ensure there is enough cover, it is necessary to provide cover blocks all around the cage. These blocks should be placed in such a way that they cover the entire perimeter of the cage, leaving no gaps or spaces uncovered. Adequate cover is crucial for the well-being of the animal, as it provides a sense of security and privacy. Therefore, it is important to make sure that the cover blocks are of sufficient size and number to fully meet the needs of the animal. By taking these measures, the animal can live in a comfortable and secure environment.
Fig.6:Reinforcement cage cover block
To prevent sideways sway in the reinforcement cage, it is essential to equip it with sufficient stiffener bars. These bars should be installed in such a way as to provide adequate reinforcement and prevent any unnecessary movement. Additionally, stirrups, stiffeners, and laps should be welded together to ensure that there is no breakage. This is an important step in ensuring the overall strength and stability of the cage. By taking these precautions, the reinforcement cage can withstand various stresses and strains and remain secure in its position.
Fig.7:Reinforcement cage rebars
Bored cast in situ pile Concreting
IS 2911 provides guidelines for the use of concrete in pile construction. One important aspect is the range of slump that should be employed, which is from 150mm to 80mm. This is important to ensure the proper consistency of the concrete during the construction process.
To prevent any interruptions during the concreting process, it is essential to maintain a continuous flow from the start until the end of the work. This requires careful planning and execution of the construction process to avoid any delays or interruptions that could compromise the quality of the finished product.
The concreting process begins with the lowering of tremie pipes into the borehole. These pipes are commonly around 200mm in diameter, and they play a crucial role in ensuring a continuous flow of concrete during the construction process. It is essential to ensure that these pipes are properly placed and secured to prevent any blockages or interruptions in the flow of concrete.
Overall, following the guidelines set forth in IS 2911, and ensuring a smooth and uninterrupted concreting process is crucial to ensuring the quality and integrity of the finished pile.
Fig.8:Tremie pipe lowered into borehole of a pile
To ensure that the borehole bottom is properly cleaned before pouring concrete, it is recommended to follow certain steps. First, a hopper should be connected to the top of the tremie pipe. This hopper will serve as the initial container for the concrete. It is important to note that the joint between the hopper and the tremie pipe should be closed tightly with a steel plug prior to the first charge of concrete.
After the joint is secured, the hopper should be filled with concrete up to its full capacity. This ensures that there is enough concrete to fill the borehole. Once the hopper is filled, the steel plug can be removed to allow the concrete to flow down into the tremie pipe. It is crucial to ensure that the bentonite slurry present in the pipe is replaced before pouring the concrete.
By following these steps, the borehole bottom will be adequately cleaned before the concrete is poured, ensuring a proper and stable foundation.
Fig.9:Pile concreting using tremie method
To prevent the mixing of concrete with water or bentonite, it is important to keep the bottom end of the tremie pipe embedded within the laid concrete at least 2 meters deep. This ensures that when replacing bentonite from the bottom upwards, each subsequent charge is deposited within the already laid concrete. The tremie pipe should remain hollow after the first charge for this to be effective.
When extending pile concreting, it is recommended to reach at least 60cm to 90cm above the cutoff level. This will ensure that there is enough good quality concrete for proper embedment into the pile cap. In the event that the cutoff level is at ground level, it is permissible for the concrete to spill over until good quality concrete is visible. This ensures that the embedment into the pile cap is adequate and that the structure is strong and durable.
Fig.10:pile concreting tremie method
Applications of bored cast in situ concrete pile
Bored cast in situ pile can be a great choice for construction projects under certain conditions. One of these conditions is when it’s necessary to prevent noise from the construction site from affecting nearby buildings. In such cases, bored cast in situ pile is an appropriate option as it helps to minimize noise pollution.
Additionally, bored cast in situ pile is a suitable option when an end-bearing pile is needed and it must be socketed into rock. This is because this type of pile is capable of providing the necessary support and stability in such conditions.
Furthermore, bored cast in situ pile is an excellent choice when a high capacity pile is required. According to IS 2911 part 01- Section 02- 2010, this type of pile is preferred for weights ranging from 150 tonnes to 300 tonnes. With such high weight capacities, bored cast in situ pile can provide the necessary strength and stability for a variety of construction projects.