Skip to main content

About Safe Bearing Capacity


About Safe bearing capacity

 Excavate a pit of required depth. (preferably equal to the depth of foundation)
Take a solid ball or square cube of known weight and dimension.
Drop the ball or square cube several times, from a known height on to the bottom surface of excavated pit.
Calculate the average depth of impression made several times on the bottom surface of the excavated pit. Let “d” is the average depth of impression.

CALCULATION

Calculate the ultimate resistance of soil ( R ) using the formula given below.

R = (w * h) / d

Where,

R = Ultimate resistance of soil (in kg)

d = Average depth of impression (in cm)

w = Weight of the solid ball or square cube (in kg)

h = Height of fall of solid ball or cube (in cm)

If “A” is the cross-sectional area of the solid steel ball or cube, then resistance of soil per unit area is calculated using following formula.

Resistance of soil per unit area (in kg/cm2) = R / A

Safe bearing capacity (in kg/cm2) = R / (A * F.O.S)

Where,

F.O.S = Factor of safety

NOTES TO REMEMBER

F.O.S varies from 2 to 3 depending upon the type of structure and site condition.
In order to get reliable test result, perform this test on different types of soil and then use your judgment to reach at any conclusion.
Instead of using solid steel ball or square cube, we can also use CBR test plunger, or Cone (used for cone penetration test)
PRESUMPTIVE BEARING CAPACITY

The table given below shows the presumptive bearing capacity values for different types of soils. This table will guide you to reach at any conclusion after conducting the test.

 Allowable safe bearing capacity for different types of soil :     

  • Rock 32.40
  • Soft rock 4.40
  • Coarse sand 4.40
  • Medium sand 2.45
  • Fine sand 4.40
  • Soft shell / Stiff clay 1.00
  • Soft clay 1.00
  • Very soft clay 0.50                                       
NOTES TO REMEMBER

 For non-cohesive soils the values should be reduced by 50% if the water table is above or near base of footing.
These values should be used only for preliminary design. The actual bearing capacity of soil should be calculated as per the standard codes.
Labels:

Comments

Post a Comment

Popular posts from this blog

Hardy slab and where it use

  HARDY SLAB :- These kind of slabs are generally seen in Dubai and China. This  slab is constructed by hardy Bricks. Hardy bricks are hollow bricks and made up of concrete Hollow blocks are used to fill portions of the slab thickness it saves the  amount of concrete and hence the own weight of the slab is reduced. This kind of slab has a more thickness when compared with the conventional one. The thickness of hardy slab is 0.27m. The method of installing Hardy slab is different from normal  and it is clearly explained below: This is a one of the types of concrete slabs. The dimensions of Hardy brick is 40cm x 20cm x 20cm The process of execution is as follows: Step 1   : Formwork is arranged and then shutters are fixed on the formwork. Step 2  : Hardy blocks are placed on the shutter with one brick gap on the entire shutter. Step 3  : The gaps between the bricks are called as rib. Reinforcement is provided in a form of beam within the ...
4 comments
Read more

Waffle slab and where to use

  WAFFLE SLAB :- Waffle slab is a reinforced concrete roof or floor containing square grids with deep sides. This kind of slab is majorly used at entrance of hotels, Malls, Restaurants for good pictorial view and to install artificial lighting. This a  type of slab where we find hollow hole in the slab when the formwork is removed.  Firstly PVC trays (pods) are placed on shuttering then reinforcement is provided between the pods and steel mesh is provided at top of the pods and then concrete is filled. After concrete sets the formwork is removed and PVC pods are not removed. This forms hollow hole in it in which hole is closed at one end. The concrete waffle slab is often used for industrial and commercial buildings while wood and metal waffle slabs are used in many other construction sites. This is a one of the types of concrete slabs. Where to use? A waffle slab is a type of slab with holes underneath, giving an appearance of waffles. It is usually used where lar...
3 comments
Read more

Mix design calculation for M50 grade Concert

CONCRETE MIX DESIGN EXAMPLE – M50 GRADE CONCRETE Grade Designation = M-50 Type of cement = O.P.C-43 grade Brand of cement = Standard best quality cement Admixture = Sika [Sikament 170 ( H ) ] Fine Aggregate = Zone-II Sp. Gravity Cement = 3.15 Fine Aggregate = 2.61 Coarse Aggregate (20mm) = 2.65 Coarse Aggregate (10mm) = 2.66 Minimum Cement (As per contract) =400 kg / m3 Maximum water cement ratio (As per contract) = 0.45 Concrete Mix Design Calculation: – 1. Target Mean Strength = 50 + ( 5 X 1.65 ) = 58.25 Mpa 2. Selection of water cement ratio: Assume water cement ratio = 0.35 3. Calculation of water content: Approximate water content for 20mm max. Size of aggregate = 180 kg /m3 (As per Table No. 5 , IS : 10262 ). As plasticizer is proposed we can reduce water content by 20%. Now water content = 180 X 0.8 = 144 kg /m3 4. Calculation of cement content: Water cement ratio = 0.35 Water content per m3 of concrete = 144 kg Cement content = 144/0.35 = 411.4 k...
1 comment
Read more