Precautions Required for Construction and Inspection of Bored Pile Foundation

Several precautions need to be considered while the inspection and construction of a bored pile foundation are 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 a casing to seal off water-bearing soil layers. It is required to remove materials and soils that are attached to the inside surface of the casing both before casing installation and concrete placement. The casing should reach the 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 the water-bearing soil layer.

Fig.2: Provision of casing that extended below water-bearing soil layer

It is recommended to provide casing through loose soil to support the 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 a comparison between soil and rocks excavated from the bottom of the boreholes and the results of the 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 borehole can be inspected by lowering the 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 a process can be applied to 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 into 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 be demonstrated whether any soil materials fell 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 a sizable diameter under the 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 is advised to use underwater concreting to tackle such a problem.

Fig.6: Water accumulation at the bottom of the borehole

Another precaution that needs 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 labourers are required to work at the base of a 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 rocks and tools into the pile hole. This is because falling off tools and rocks would create a serious threat to the life of labourers. Moreover, labourers should not be allowed to work at the base of the pile without the use of helmets to protect their heads and harness to leave them up in dangerous circumstances for instance when labourers are injured or overcome by gas.

Fig.8: Use of helmets by workers

Furthermore, it is recommended to allocate one person at the top of the hole to prevent falling stones or tools into the pile hole and ensure that types of equipment 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 in a suitable working sequence. It is required to conduct gas tests frequently especially when the pile pass through a 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 the applicable code of the region or state.

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