There are several issues that may be encountered during pile foundation construction. These problems will cause deficiency in the capacity of the pile unless they tackled properly.
These pile construction problems and with their causes and required measure to prevent them are discussed in the following sections.
- Major Issues During Pile Foundation Construction
- 1. Pile Formation Problems
- 2. Concrete Faults
- 3. Reinforcement Installation Issues
- 4. Working Load Faults
Major Issues During Pile Foundation ConstructionProbable Piling problems are classified as follows:
- Pile formation problems
- Concrete faults
- Reinforcement installation issues
- Working load faults
1. Pile Formation Problems
1.1 Concrete or Permanent Steel Casing DeteriorationConcrete or permanent steel casing may be damaged due to driving piles forcefully over obstruction or driven mandrel is out of plumb. Another problem that concrete or permanent steel casing may suffer from is their initial defection. This problem can be prevented by supervising casing installation and inspect the work before concrete placement. Finally, if this problem occurs, the pile should be withdrawn and reinstall it properly.
Driven of Shell and Mandrel
1.2 Collapse of Pile SidesIf casing is not provided, pile sides would collapse in soft and loose soil. This problem can be observed and solved supervisor. The solution is to install casing.
1.3 Excessive Water in PileGroundwater flow into the construction site is the cause of excessive water in pile. Utilization of steel casing or bentonite would eliminate this problem.
1.4 Lateral Movement and Uplift of Adjacent Pile While Pile Casings are DrivenIt is caused by displacement and heave around pile installation location. Such movements can be observed through checking plan position and level of neighboring piles. Engineer shall decide on the technique used to solve lateral movement and uplift of adjacent piles.
1.5 Settlement of Adjacent Structures or Adjacent GroundAdjacent settlement is caused by vibrations in sandy soil during driving piles. Sinking holes of bored piles in soft clay of water bearing sand is another cause of adjacent settlement of buildings. Such problem can be noticed by checking level of buildings or ground before and during pile construction. Lastly adjacent ground or structural settlement may be declined or minimized by keeping head of water in the casing during boring piles. Added to that, site engineer may select suitable solution for the problem.
2. Concrete FaultsPile construction problems due to concrete faults involve:
2.1 Inadequate Concrete StrengthInsufficient strength is due to poor mix design or concreting operation. Commonly, cylinder or cubic concrete samples are taken from each mix and tested to find out concrete strength. This issue is solved through proper mix design with appropriate workability and practice good quality control during concreting.
2.2 Voids in Concrete PileVoids may be formed due to improper compaction of concrete in piles with no casing or with casings that is not pulled up after construction is completed. In this case, the construction shall be monitored properly to ensure sufficient compaction of concrete using suitable techniques. Moreover, if casings are withdrawn, then the withdrawal of casing may lead to create voids in concrete. Voids can be prevented in this case by cleaning casings and guarantee that sufficient concrete volume is poured.
3. Reinforcement Installation IssuesSteel bars are likely to move laterally or being dragged down during compaction. There are number of reasons that led to reinforcement disposition for example improper placement of spacers, careless techniques, and defective anchorage of steels in some pile types. It is required to check steel cage during fabrication in accordance with specifications and monitor installation process to prevent such issue. Lastly, pile steel cages shall be supported firmly at the bottom and spacers need to be provided in accordance with applicable codes.
4. Working Load FaultsPiles may suffer damages due to testing loads or permanent working loads. In the following sections, working load faults will be classified based on the type of construction methods used.
- Driven pile working load faults
- Working load faults in bored piles
- Working load faults in mechanically augured piles
4.1 Driven Pile Working Load FaultsThere are number of factors that make the driven pile to suffer deterioration and damages under working loads. For example, improper concrete placement method that used for concrete in the core of driven shaft, lifting of pile due to ground heave, inadequate concrete in bulb for bulb ended; bored; and driven pile, wrong space employed, and insufficient driven resistance. These detrimental factors may be eliminated by checking volume of concrete placed, hammer drop and blows per miter, designated spacer type, and clear method of construction.
4.2 Working Load Faults in Bored PilesFactors that lead to bored pile damages under working load include weakening of ground around the pile due to wrong pile boring technique, insufficient concrete cover due to steel cage displacement, poor execution of concrete placement, and inadequate depth with respect to the soil or rock properties encountered. To ensure that sufficient depth is provided, it is required to check the consistency of spoil. Additionally, it is required to practice great cautions during boring and concrete placement to prevent undesired consequences of these operations.
4.3 Working Load Faults in Mechanically Augured PilesFactors that may lead to mechanically augured pile failure under working load include:
- Inadequate diameter to under reamed base. This could be prevented through continuous noticing of major drilling and under reamed machines are working as checked above the ground.
- In adequate depth with regard to encountered soil properties. it is recommended to monitor spoil during boring.
- Using improper technique for concrete placement
- Insufficient concrete cover
- Ground around shaft or beneath base weakened due to improper boring technique.