Construction of a drilled shaft

In firm soils, the dry method (also known as the open hole method) can be used to build the shaft. The construction procedure is generally as follows  

During drilling of the shaft, certain construction control measures can be implemented such as checking for verticality, in situ soil sampling and final determination of the founding depth of each shaft. 

In the case of caving or squeezing soil, that is, where the hole will experience side collapse before or during placement of the concrete, two most common construction techniques for preventing these problems are the use of casing or the use of drilling fluid. 

The hole is drilled in conventional methods until encountering the caving strata. 

A steel pipe (casing) is inserted into the hole and advanced past the caving strata. Usually vibratory hammers are used for this purpose. The diameter of this casing is less than the diameter of the upper part of the shaft. 

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