Civil Engineering Resource

Site Investigation

An investigation of project site is essential for judging its suitability for proposed engineering works, and for preparing adequate and economic designs.

Site investigation is also necessary for analysing the safety or causes of failures of existing structures, for selecting construction materials, and for deciding upon the construction methods to be applied.

In general, the purpose of site investigation is to obtain necessary information about the soil and hydrological conditions, and to know the engineering properties of the soil which will be affected.

The methods of investigation depends largely on the engineering project and the site.

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Construction of 60 MVA Transformer Plinth in a 132 /33 kV Substation

After the soil test is carried out to know the bearing capacity of the foundation soil, the transformer Plinth is designed.

Below is the procedure for constructing the transformer Plinth in a Substation.

1. From the Substation layout drawing, the Surveyor uses the total station to set out the points. The plinth center line is very important. There are usually three plinths having the same base.

2. After setting out of the plinth, the excavation begins. Before the excavation is done, the finished grade level value is noted and the Top of concrete (TOC) value is noted and used as reference for excavation height. The level instrument is used to determine the heights.

The excavation is usually done with the excavator unless the soil needs Pile foundation.

3. After excavation, the pit is cut to appropriate size: length, width, and height.

4. With the aid of the center lines: x and y, and the conical and bubble plum, the center lines of the plinths are fixed in the pit

5. The blinding of the base follows with the casting of the PCC - plain cenent concrete.

6. The PCC is cured, the concrete casting of the base follows.The positions of the reinforcements are marked on the PCC in the pit for the three pillars and the reinforcements are placed with proper bracing.

7. The base of the plinth is cast with dense graded concrete and well vibrated. Then, properly cured.

8. The fixing of the formwork follows. The height of the plinth is usually from 2 m and above. The formwork must be strong and properly braced The anchor steel plates must be properly fixed in position.

9. Concrete casting of the plinth - there are three pillars. It is advisable to cast the center pillar one half first , then cast the side pillars one half each, then return to complete the center and the side pillars. This will avoid the swaying of the pillars and the shape will be maintained. After concrete casting the, it is cured.

10. The concrete casting of the oil catchment area