How to determine Bearing Capacity of soil from SPT Value

Bearing Capacity of soil from SPT Value 

Bearing Capacity of Soil: Bearing Capacity is the capacity of soil to support the loads applied to the ground. Here we will discuss how to determine bearing capacity of soil from SPT value.

Read:Types of Foundation

How to Determine Bearing Capacity of Soil From SPT Value: The Standard Penetration Test (SPT) is an in-situ test which is carried out in borehole to determine soil bearing capacity . This test measured the resistance of the soil strata to the penetration undergone. SPT value can determined by counting the number of blow required to penetrate the last 12in (300 mm approx.) of a 18 in.( 450 mm approx.) sampler. After getting this value we can easily determine the bearing capacity of soil by following formulas:

Meyerhof's Formula:

For footing width 4 feet or less:

Q_a= (N/4) / K

For footing width greater than 4 feet:

Q_a = ( N/6) [( B+1)/B]² / K

Bowle's Equation:

For footing width 4 feet or less: 

Q_a= (N /2.5) /K

For footing width greater than 4 feet: 

Q_a= (N/4) [( B+1)/ B]² / K. 

Where, 

Qa= Allowable bearing capacity of soil in, kip/sft   

N = SPT Number Below the Footing

B = Width of footing in foot 

D = Depth from ground level to the bottom of footing,  in foot

K=  1+ 0.33( D/B) which will be less than or equal to 1.33

Curing of Concrete slab

Curing: Curing of concrete is a process by which fresh wet concrete is allowed to complete its reaction to attained its desire strength. By this method concrete is protected against loss of moisture required for hydration and kept within the recommended temperature range. 

Necessity of Curing of Concrete slab:

1) To enhance hydration of concrete to achieve desire strength.

2) Well cured concrete has minimum thermal, plastic and drying shrinkage crack which make concrete more water, tight results durable concrete.

3) In-adequate curing results weak and dusty surface of concrete, results a poor abrasion resistance.