5. Extraction of temporary steel casing.
Concrete will be placed at the level slightly higher than the temporary steel casing. The steel casing will then be extracted. During detaching of steel caging, concrete shall be maintained inside the steel cage at least 3 meters in order to prevent collapse of drilling hole. This event also prevents the leakage of medium-soft soil through the borehole before the temporary steel casing is loosened. Concrete shall be placed higher than the required level of approximately 50-75cm. The excess concrete will be utilized if the pile-head level is below the ground level. All preventions must be made to ensure that concrete at the required pile level will not be contaminated following the extraction of steel casing.