How to determine a Pile foundation is need or not?
Nature of soil and nature of land where you intend to construct house decides foundation of your house.
To decide the nature of foundation required the simplest way is to conduct a soil test at the plot.If the plot is small a single soil test at center of the plot will be sufficient,likewise if it is a large plot many soil samples might be required from different areas of your plot.Use a soil test rig which goes down to 40-45 feet take core samples of the soil .This sample can be then tested at a soil test laboratory .With the soil test results a structural engineer can guide you regarding the foundation requirements for your proposed house.