Cast-in-situ pile construction involves deep excavation and complex construction techniques. You must consider the soil conditions, load-bearing capacity, and other factors.
Most importantly, it involves many highly skilled labourers as you have to do everything on-site. Hence, it will take longer than precast piles and helical piles. In this article, I will walk you through the right way to be installed cast in situ piles.
What are the Advantages of Cast-in Situ Piles?
Minimum Vibration
The cast in situ pile method produces minimum vibration. A steel casing is inserted into the ground, and concrete is mixed and poured through it. This method causes minimal or no forceful impact on the soil.
Maintenance Free
Cast in situ piles are made from strong, long-lasting concrete. They can withstand underground stresses or external elements without any adjustments or replacements.
Resistant to Environmental Impacts
The cast in situ pile uses a continuous concrete pouring method to avoid weak points between segments. It makes them resistant to earthquake and wind forces.
Cost-effective
You don’t need to import any materials and equipment for the installation of cased cast in situ piles. Local materials and machinery are enough to complete the project.
Easy Installation
Contractors use lightweight reinforcement cages that are easier to manoeuvre and install. It causes minimal strain to the crane to lower the cage into the drilled shaft.
No Chance of Breaking Piles
Contractors don’t use hammering equipment to drive the pile into the ground. You don’t need to worry about pile breakage during installation.
No Extra Transportation Cost
In driven and bored cast in situ piles, contractors mix the concrete materials and pour them on-site. You don’t need to transport any prefabricated piles. This minimizes the overall transportation costs.
Limitations and Challenges of Cast in Situ Piles Driven
Compromise in Quality Consistency
It is challenging to maintain high-quality concrete mix always as they are poured from an elevated height. Skilled labourers and active on-site workers must avoid wrong concrete mix proportions, inaccurate batching, and incomplete mixing.
Continuous Inspection
The site inspectors must be highly active and qualified to ensure daily operations comply with plans and regulations. It might be time-consuming to take concrete samples for testing.
Potential Defects
If appropriate methods are not strictly followed, it can lead to cracks, voids, or segregation in the concrete. You must abandon the pile and replace it with a new one. This can be costly and long-delayed.
Soil Sampling Accuracy
It is not 100% possible to consider all the unforeseen variations in soil. This may affect soil sampling tests, so you will have to adjust the pile design again.
Access and Space Constraints
Due to limited locations, bringing heavy equipment to urban areas can sometimes be challenging. Rural areas may have challenging terrains, making carrying heavy equipment for cast-in-situ pile projects hard.
How to Install Cast in Situ Piles in Step by Step?
Are you wondering how to driven cast in situ piles? Below are the steps to follow, step by step.
Step: 01—Plan About Cast in Situ Pile Project
The first step is investing in the site to test the soil properties and appropriate pile depth. You will also have to consider pile design on various pile specifications.
List all the essential materials and equipment needed for casting in situ piles. Also, determine what type of construction methodology you will use, such as drilling or driving technique, Tremie method, or direct mud circulation method.
Step: 02—Set Up A Bentonite Pumping System
Does your construction area have unstable or waterlogged soils? If so, you must use Bentonite pumping systems. It will form a temporary wall around the excavation.
Also, the borehole will be protected from unwanted groundwater. You won’t have to worry about placing the concrete mix appropriately.
If you have selected the bored cast in situ piling method, use a driller to reduce manual tasks and improve pile size accuracy. It will also ensure a stable borehole wall.
If you are working in a remote location, keep an electric generator for continuous electric supply. It will prevent unwanted delays, especially during essential tasks like concrete pouring.
Step 03—Create A Borehole into The Ground
Next, a drilling rig with an auger creates a borehole for the concrete pile. Based on the pile design, maintain the desired diameter and depth. Otherwise, it will compromise the actual load capacity.
There should be no soil collapse or borehole deviation. Keep the drilling rig and auger position at a right angle to the horizon.
Clear the soil between the adjacent soils to maintain the required distance between piles and ensure optimal pile performance.
Step: 04— Insert A Steel Casing
Does your preferred area have loose, sandy, weak, or saturated soils? If so, a steel casing can support the borehole wall and maintain borehole integrity during drilling.
You won’t have to worry about the unwanted entry of soil into the borehole during excavation. There will be no weak spots during concrete placement. Soil or groundwater won’t be able to contaminate the fresh concrete.
Step: 05— Use A Rotary Pile Drilling Machine
Next, use a rotary pile drilling machine to excavate a clean, cylindrical hole. Depending on the project requirement, maintain an accurate depth and diameter.
If you want to reach significant depths, use a hydraulic rotary pile drilling machine. This advanced equipment allows you to maintain more accurate hole diameters and drilling speed. You can effortlessly adapt to hard-to-reach areas or tight spaces.
Another plus point of hydraulic rotary pile drilling is its minimal environmental impact. Compared to traditional rotary pile drilling machines, it generates less noise and air pollution.
Step: 06— Pump Bentonite Fluid into The Borehole
It is necessary to pump bentonite fluid from a mixing tank and pumping machine for excavation into the borehole.
This special fluid also works as a protective layer to prevent groundwater from entering the borehole. Hence, you won’t have to worry about a proper concrete placement.
Depending on the soil conditions, water salinity, etc., you can use sodium-activated bentonite, modified bentonite clays, or organic bentonite.
For instance, sodium-activated Bentonite fluids are better for sand or gravel soil to avoid unwanted fluid loss.
Step: 07— Clean the Loose Soil and Debris
Clean the inner and surrounding area properly before inserting the reinforcement steel cage into the borehole and pouring the concrete mix. Remove all the loose soil and debris.
It will help the reinforcement cage to protect the borehole walls. Plus, the cage will firmly stay in place without unwanted movement.
In addition, the loose soil and debris should be appropriately cleaned to promote a proper bonding between the pile and surrounding ground after the concrete mix is poured.
You won’t have to worry about any pockets within the concrete. There won’t be any voids or uneven distribution of concrete placement.
Step: 08— Insert A Reinforcement Steel Cage Into The Borehole
Enter a prefabricated steel reinforcement cage into the borehole. Its specifications will vary depending on the project requirements.
Its unique grid pattern includes horizontal bars (ties) and vertical bars (longitudinal). Most are made of Steel rebar. They support the concrete pile sufficiently and prevent unwanted breaking or cracking issues.
Step: 09— Insert A Tremie Pipe
Next, a Tremie pipe is inserted into the reinforcement cage to ensure proper concrete is poured under water. The cement paste won’t wash away easily.
This will promote continuous concrete discharge at the bottom of the borehole. It will also maintain a stable interface between fresh and hardening concrete.
Step: 10— Take Out The Steel Casing
After pouring the concrete mix appropriately, wait until the concrete has gained enough strength and the surrounding soil remains stable.
The time frame can be anywhere between 24 hours to 48 hours. Then, withdraw the temporary casing using lifting hooks or vibrating hammers.
What are the Disadvantages of Cast in Situ Piles?
Hard to Maintain Quality
Contractors create cast-in-situ piles on site. However, consistent quality is often challenging to maintain due to variable soil conditions, potential defects, and human factors.
Intensive Labor
Cast-in-site piles involve excavation, reinforcement cage assembly, and concrete pouring. You can’t use factory equipment and robots. Hence, a good number of labourers are needed.
Higher Concrete Costs
Poor craftsmanship, such as improper borehole cleaning, poor concrete flow, inadequate compaction, etc., can increase the overall cost of concrete.
Slow Installation Time
Prefabricated piles can’t be used in the cast-in-situ piling method. You must give the piles enough time to cure and achieve your desired design. This method could be better for speedy construction.
Weather Dependent
Cast in situ piles are done on-site. Extreme weather or climates, like heavy rains, floods, etc., can delay the overall construction project.
Frequently Asked Questions (FAQ’s)
To ensure the quality of concrete in the cast in situ piles, use high-quality materials, design the mix carefully, test fresh concrete, ensure proper pouring and vibration, and conduct rigorous post-curing quality control tests.
The depth of cast in situ piles can vary significantly depending on the project requirements and ground conditions. Typically, these piles can range from 10 meters to over 60 meters deep. The depth is determined based on the soil profile, the load-bearing capacity needed, and the structural requirements of the building.
Yes, cast in situ piles are suitable for use in seismic zones. Their deep penetration into the ground provides enhanced stability and resistance to seismic forces.
The curing time for concrete in cast in situ piles typically ranges from 7 to 28 days, depending on the type of cement used, the concrete mix, environmental conditions, and the chemical additives included in the mix.
Environmental conditions significantly affect the installation of cast in situ piles. Factors such as groundwater level, soil type, temperature, and weather conditions can impact the drilling process, concrete setting, and curing times. For instance, high groundwater levels may require casing or drilling fluids to stabilize the hole. At the same time, low temperatures can slow concrete curing, necessitating using accelerators or heaters to maintain the process within the necessary time frame.
Yes, cast in situ piles are suitable for residential construction, especially in areas with unstable soil, near water bodies, or where the soil conditions cannot support traditional shallow foundations.
Conclusion
Cast in situ pile is a highly popular method for modern construction foundations due to its versatility, adaptability, and performance. There are so many cast in place concrete piles advantages, especially for high-rise buildings, bridges, and structures. We have already outlined the right way to be installed cast in situ piles. If you still have queries, feel free to reach out to us anytime.