This article discusses pile foundation problems and solutions for them. Pile foundations are a broad field that needs to be studied in detail to identify the deficiencies of the structure.
However, when constructing piles, there is an important aspect that must be considered and taken into account to avoid major problems in construction.
We cannot observe with the naked eye the state of the pile or what is happening underground. What we can do is follow proper construction procedures to ensure quality control and assurance.
Even though Pile Foundations are designed by an expert, the pile can fail if constructed incorrectly.
Let's discuss each of the design questions in detail.
Stack Tray
One of the most important works that must be carried out at the beginning of the construction of a pile.
If it goes wrong, everything we do will be subject to the original error.
It is true that we cannot always maintain the accuracy of the implantation as precisely indicated in the drawings. However, we must at least ensure that the tolerance limit is respected.
Most guidelines specify the pile construction tolerance as 75 mm. However, different guidelines specify different ranges depending on the type of construction.
The following table lists the tolerances allowed in the project.
| code | Allowed tolerance |
| ACI-336 | 4% of the diameter or 75 mm, whichever is smaller |
| EN 1536 standard | 100mm; for pile diameter (D) ≤ 1000 mm
0.1D to 1000 150mm D>1500 Design for a tilt angle of less than 1 in 15, limited to 20 mm/m Version with inclination between 1 in 4 and 1 in 15, limited to 40 mm/m |
| KP4 – The big goal | 75mm |
| BS 8004 | No more than 1 in 75 vertically or 75 mm
For bored piles with an inclination angle of up to 1 in 4, a deviation of up to 1 in 25 is allowed. |
If the pile tolerance is within limits, the pile design is accepted. The building designer must consider the acceptable tolerance in his design.
For example, if the allowable tolerances for pile deviation are 75 mm, the superstructure must be designed accordingly. We cannot change the column position by moving the post.
So we need to design the floor beam to support the column loads when there are two piles or just one pile. If there are three or more piles, this can be taken into account for the piles and an increase in the pile load due to movement towards the support must be taken into account when assessing the pile capacity.
If the deviation is greater than the limit allowed for the arrangement of piles in the block, it must be checked after construction and the necessary adjustments made. The designer should design the floor joists for eccentricity as much as possible, check the increase in pile capacity by moving the piles, check the block plates for new eccentricity, etc.
Digging piles and anchors
When excavating or drilling piles, we must take several aspects into consideration.
Let's discuss each of them.
- Steel case deviation
Steel casing is used when the soil is very weak and collapse cannot be absorbed by the bentonite fill. The depth of the enclosure can reach the end of soft soil such as peat.
The center of the box may vary when placed as it collapses during placement. Even if the center of the box is checked after placement, it may be crooked.
Furthermore, during excavations, the lining may deviate from its original position because the soil does not have sufficient transverse rigidity.
This could be avoided by inserting the lining into the hard soil layer to a suitable depth and checking the position of the lining before and after concreting.
Tolerances can be checked against the relevant standard or as indicated in the table above.
- Excavation collapse
When building pile foundations, soil collapse is inevitable. However, it can be minimized by controlling the density of the bentonite suspension.
Regular checks must be carried out to ensure that the density is within acceptable limits.
- Lots of water in the pile
As excavation continues beyond the water table, water will seep into the excavation pit.
The bentonite level must be checked regularly to prevent water from entering the post. Since the density of bentonite is higher, there is less chance of water movement.
Additionally, the density of the bentonite should be checked regularly and necessary adjustments made as necessary to maintain the required density of the bentonite.
- Lateral movement and lifting of adjacent piles
In general, the distance between piles is approximately 2.5 to 3 times the diameter of the pile.
When driving into pile casings, there is a possibility that the surrounding piles will move.
This must be done very carefully and lateral movements can be minimized or avoided.
- settlements
Driving the piles causes excessive vibrations in the ground.
Even though this keeps vibrations within acceptable limits, the effects of vibrations can lead to settlement of adjacent structures.
Particularly for structures built on shallow foundations, settlement can occur during pile foundations. Furthermore, excessive vibration can cause serious problems.
As the structure settles, cracks can occur and even the old structure or improperly constructed structures can collapse.
For this reason, vibrations due to the design must be minimized as much as possible. The use of new tools, electric drills, etc. can reduce vibration.
- With sufficient base and termination
The embedment depth is indicated in the pile design drawings. However, determining the starting and ending points of the embedding depth is a challenging task.
The embedment depth of a pile is determined based on several factors. Some of these are information from the well log, rate of penetration into the rock, observation of rock samples, etc.
Additionally, on-site tests such as Point Load Testing could be carried out to determine the strength of the rock. It may be related to the bearing capacity of the rock. This way we can determine the condition of the rock and decide on termination accordingly.
- Poor cleaning of the pile tip
It is essential to clean the battery properly. Cleaning the pile is called rinsing.
This can be done based on parameters determined through the bentonite test. The top of the bet is not visible. Therefore, we decide whether to clean the pole.
The bentonite is removed from the excavation pit and mechanically cleaned, removing the washed sand and mud. It is pumped from the top of the excavation pit. The bentonite is removed from the base of the post for cleaning.
This process continues until it is ensured that there is no more mud/sand in the bentonite.
During the washing process, among other things, the balance of the sludge, the balance of the reservoir and the sand content are checked.
| Properties for bentonite suspensions | |||||
| Property | Unit | stages | Test Equipment | ||
| Fresh | Ready to reuse | Before concreting | |||
| density | g/ml | <1.10 | <1.25 | <1.15 | Mud balance |
| Marsh Viscosity (946 ml) | second | 32-50 | 32-60 | 32-50 | Swamp funnel |
| Sand content | % | N/A | N/A | <4 | Sand content |
| pH | 7 to 11 | 7 to 12 | n/a | PH meter | |
The ranges specified in the table above can be respected before concreting. Values may vary from specification to specification. The date can be found in the project specification.
Concreting problems
Problems commonly observed during construction are highlighted below.
- If the concrete is strong enough
Generally, piles are cast in grade 30 concrete. This value may vary from country to country.
Insufficient compressive strength of the concrete in the pile leads to serious design problems.
As the pile is an underground structure, correction is very difficult. If the actual load exceeds the bearing capacity of the pile, additional piles may be erected.
- Voids in concrete
Since the self-compacting concrete is poured into the pile, no vibration is required. Furthermore, due to the depth of the pile, it is very difficult to vibrate the concrete to achieve better agitation.
Due to design problems, voids may appear in the pile. This may be due to poor concrete quality and inconsistent workability of concrete.
Regular inspection and monitoring of concrete quality could prevent these problems.
- Mix concrete with bentonite
The concrete is poured so that it does not mix with the bentonite.
First, the contractor is placed in the slot of the bored pile. Then the concrete is poured at the contractor. The contractor is then slowly lifted so the concrete can flow.
The contractor is then filled with concrete again. The contractor is then slightly elevated so that the concrete can gradually flow. This process continues with the concreting of the pile.
The contractor's end is always in the fresh concrete and we never elevate the contractor to the top level of the concrete pile when pouring the concrete.
We are trying to get to the end of this Embed the contractor at least 1-1.5 m into the fresh concrete avoid mixing fresh concrete with bentonite.
- Bulges and constrictions
During the construction phase, concrete can swell or contract.
Cold tapering the pile exposes the reinforcing cage and reduces the cross-sectional area of the pile.
A reduction in the cross section of the pile leads to a reduction in the bearing capacity of the pile.
- Temperature increase in concrete
The temperature rise of the pile must be checked at least at the beginning of the pile construction.
The first pile could be checked using the strain gauges and temperature fluctuations could be monitored.
Based on the results of the data analysis, specific adjustments can be made.
Reinforcement cage movement
- Raising the reinforcement cage
At high concreting speeds, the reinforcing cage may lift. The concreting process must therefore be carried out in a controlled manner.
Once the container has been raised, we can no longer lower it. Raising the cage beyond the embedment length causes serious problems in pile construction.
This may result in the stack being abandoned.
- Lack of reinforcement cover
Lateral movement of the reinforcement cage may result in its lateral exposure. This may be due to the ground collapsing on one side of the pile excavation.
