How we can findout the strength of soil condition in site ?

 Just dig out the soil for3 ft and if the soild is not waterlogged and clayey or silty clay soil then it will have bearing capacity of about1 ton/sqft

you can perform plate load test on the natural soil to indecate the bearing capacity in addition to the moduls of elastisty of the soil.

however you could find all the soil properties from NSPT