Piling Build Sequence
Health and Safety - Check if all required documentation is in place, refer to Piling Health, Safety and Environmental Post for more information.
Piling Platform - a check needs to be done to ensure the piling platform has been installed to the drawing
A professional survey should be conducted to answer the following questions:
Pile Probing - Process of checking proposed pile locations for obstructions or voids before piling equiptment arrives on site.
This is done to avoid delays which could cause expensive standing time charges.
An excavator (pictured below) is used to drive a steel tube into the ground at a pile location.
It is a good idea to pile probe a percentage of or all piles around site.
Pile probing in progress
Logistics - A competent manager can assess the following questions visually, refer to Piling Logistics Post for more information:
Drawings –
Piling Operations:
The below sequence is for CFA piling however, many of the points are applicable to other methods too:
1. Mobilisation - this is when everything required for the piling operation is delivered to site, offloaded and set up for use.
2. Setting out - a surveying engineer will be required in most cases to mark out physical pile locations off the drawings.
They use specialist surveying equipment mostly total stations for this and can use spray paint or pins hammered into the ground for marking out.
An Engineer setting out on a construction site
3. Positioning the Rig: the CFA piling rig is positioned over the first pile location. The rig consists of a vertical mast, a hydraulic motor, and the hollow continuous flight auger.
4. Drilling: The CFA piling rig's hydraulic motor rotates the continuous flight auger, which drills into the ground.
As the auger drills, soil is displaced upwards, creating a borehole. The rig operator has data within the rig showing him if the pile is vertically straight, this is also checked regularly by operatives with use of a spirit level.
5. Installing Concrete: at the same time as the drilling process, concrete or grout is continuously pumped through the hollow stem of the auger.
The concrete rises to the top of the borehole as the auger penetrates deeper into the ground.
6. Removing the Auger: Once the required depth is reached, it is gradually withdrawn from the ground whist maintaining the concrete level in the borehole to avoid collapse.
Piling rig auger drilling into the ground
7. Reinforcement: reinforcement steel cages are lifted into position with the crane and lowered into the wet concrete usually using an excavator one the auger is withdrawn.
Note: not all piles require reinforcement.
Pile reinforcement cages
8. Curing and Setting: The concrete is left to cure and set, creating a solid cylindrical pile.
After Piling is complete:
Once some or all the piles are installed there are several testing options which are subject to the project specification. These include:
Pile Integrity Test (PIT): a non-destructive test used to assess the integrity of a pile.
It involves sending stress waves through the pile using a handheld device or a permanent sensor.
Any irregularities or defects in the pile can be detected based on the reflection of the stress waves and results are presented as a graph.
It must be done once piles have been cut down to the right level, and is often undertaken for all piles on the job.
Pile Integrity testing
Crosshole Sonic Logging (CSL): is another non-destructive test used for integrity evaluation.
It involves sending ultrasonic pulses through a tube in the concrete of an in-situ pile.
The waves are recorded by receivers placed in nearby access tubes, and the data is analysed to identify potential defects or variations in the pile.
A report is produced showing graphical results, this should explain how to interpret the graphs contained.
CSL Diagram
Static Load Test: In a static load test, a predetermined load is applied to the pile using a large counterweight and hydraulics.
It's deformation and settlement under the load are measured.
This test helps determine how much load in pile can take, ultimate load capacity, and how behaviour of the pile.
If done early in the piling process this may allow further piles to be shallower based on structural calculations.
Static Load Test
Dynamic Load Test: involves striking the pile with a falling weight, often using a hammer or a specialized impact device.
The resulting response of the pile is measured and the pile's load capacity is estimated based on dynamic formulas.
Statnamic Load Test: The statnamic load test is a combination of a static and dynamic test.
It uses a high-pressure hydraulic system to apply a controlled static load to the pile.
After reaching a predetermined load level, the static load is quickly released, generating a dynamic response.
The test provides both static and dynamic data, allowing for a more comprehensive analysis.
Thermal Integrity Profiling (TIP): a non-destructive testing method that can be used for drilled piles. Uses temperature sensors to measure temperature changes within a concrete pile over time.
Variations in the temperature profile of the pile can indicate potential defects, such as voids, honeycombing, or segregation.
Pile Driving Monitoring: Pile driving monitoring involves measuring and analysing the dynamic behaviour of the pile during installation.
Sensors on the rig are used to capture data on hammer impact, pile penetration, and soil resistance, providing valuable information about pile capacity and soil conditions.
What happens next?
Once piling is complete the next main works activities that follow are usually excavating for Pile caps and Pile cropping. This will be covered in posts to follow.
Definitions
Ground obstructions - any material found in the ground which could impact works. e.g. concrete foundations, bricks, watercourse and tree roots
Standing time - the time a worker or equipment is at work but nto actively enganged in productive tasks. If the reason for this is a Main Contractor risk then there will likely be commercial implications
Concrete curing - process of allowing freshly poured concrete to gain its intended strength - generally lasts several days
Pile integrity - whether or not there are any defects in the material of the pile
Pile settlement - how much a pile sinks into the ground once loaded
Posts to Follow
We plan to go into more details about piling and add sections on:
· Health, Safety & Environment
· Quality
· Programme
· Commercial
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