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There are several precautions that need to be considered while inspection and construction of bored pile foundation is preceded. These precautions will be discussed in the following sections.
Fig.1: Bored Pile Construction
Precautions for Bored Piles Construction and Inspection
If the pile is built in water bearing soil, then it is required to provide casing to seal off water bearing soil layers. It is required to remove materials and soils that attached to the inside surface of the casing both prior to casing installation and concrete placement. The casing should reach to impervious layer below soil water bearing soil. Lastly, if such measures cannot be carried out properly, then it is advised to use bentonite to stabilize water bearing soil layer.
Fig.2: Provision of casing that extended below water bearing soil layer
It is recommended to provide casing though loose soil to support pile shaft to prevent the failure of the shaft wall. This casing is possible to be pulled up after the placement of concrete is ended.
Fig.3: Utilization of casing in loose soil
It is advantageous and encouraged to make comparison between soil and rocks excavated from the bottom of the boreholes and results of site investigation to confirm the results of the exploration. If the size of the pile is too small for workers to carry out inspection at the bottom of the pile, then the pile bore hole can be inspected through lowering source of light into the borehole and any debris or soil crumbs need to be taken out before the placement of concrete. It should be known that, such process can be applied for shallow piles.
Fig.4: Inspection of boreholes of pile foundation
If the borehole of the pile is deep, then the above strategy cannot be employed for inspection. It is recommended to plumb the entire depth of the borehole of the pile prior to the placement of concrete. This can be done by inserting a cage to the bottom of the pile hole. This value is compared with the precisely measured depth of the hole that obtained during drilling. Consequently, the comparison between these two values would demonstrated whether any soil materials fallen into the pile hole bottom or not. To make sure and check the data employed for the design of the pile, shear tests should be done for undisturbed samples taken from the bottom of the pile borehole.
Fig.5: Undisturbed borehole sample
If it is required to manually place concrete into sizable diameter under reamed pile, then softened soil material and other fallen material need to be removed. Moreover, if underground water is accumulated at the bottom of the hole, then it is required to take out the water using suitable means such as pumps to dry out the base of the hole prior to concrete. If this issue cannot be solved and the water cannot be taken out completely, then it advised to use underwater concreting to tackle such problem.
Fig.6: Water accumulation at the bottom of borehole
Another precaution that need to be accounted for during pile construction is that the period between the completion of pile hole excavation and the placement of concrete should not be greater than 6 hours. So, it must be as short as possible.
Fig.7: Concreting pile foundation
When labors are required to work at the base of pile hole, then it is mandatory to create a safe environment for the workers. For example, casings can be used to prevent the falling of soil material from the side of the pile shaft. The casing should be adequately secured, and it needs to be extended above the ground level to avoid falling of rocks and tools into the pile hole. This is because falling off tools and rocks would create a serious threat on the life of labors. Moreover, labors should not be allowed to work at the base of the pile without the use of helmets to protect their head and harness to left then up in dangerous circumstances for instance when labors are injured or overcome by gas.
Fig.8: Use of helmets by workers
Furthermore, it is recommended to allocate one person at top of hole to prevent falling off stones or tools into the pile hole and ensure that equipments and materials are secured adequately to avoid any undesired event. When the working place is left at the end of the day, the top of the pile hole should be covered properly. It is encouraged to keep gas detecting tools and other required equipment at and arrange them is a suitable working sequence. It is required to conduct gas tests frequently especially when the pile pass through layer of peat or in organic clays or when an old gas main is encountered. Finally, all works and activities need to be carried out according to applicable code of the region or state.
