How To Verify The Given Bearing Capacity of Any Soil

We can use the “slowly applying load” method to verify the given bearing capacity of the soil.

⇒ Let’s assume the given safe bearing capacity of the soil is 16 t/m².   

⇒ To verify the bearing capacity of this soil, add an initial test load on the platform. The initial test load should be twice the safe bearing capacity, i.e. 32 t/m², and write down the settlement.

⇒ When settlement stops, the load on the platform is increased by 50 per cent of the initial load, i.e. 16 t/m² and settlement is again noted.   

⇒ Now, for both cases of loading, if the settlement does not exceed 17 mm and 25 mm respectively, So, we can say that the given safe bearing capacity of the soil is correct.

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3 Types of Soil Samples

The following are the 3 types of samples which can be obtained with different sampling devices:

1. Undisturbed Soil Samples

The soil sample, in which the particle size distribution as well as the soil structure and the properties of the in situ stratum, remain preserved, is termed as undisturbed soil samples. Such soil samples are required for shear strength and consolidation tests. 

This soil samples can be collected by stopping the boring process at a certain level and then inserting the appropriate sampler below the bottom of the bore. 

2. Representative or Disturbed Soil Sample

The soil sample which contains the same particle size distribution as in the in situ stratum, but the natural structure of sample gets partly or entirely disturbed and modified, is called a representative or disturbed soil sample.

Such disturbed soil samples can be used for

1. Identification of soil types
2. Determining Atterberg limits, specific gravity, organic and carbonate content.
3. Compaction tests etc.

3. Non-representative Soil Sample

These are mixtures of soil from different soil strata. These samples are obtained by auger boring or sedimentation of wash boring. Such samples may help in determining the depth at which major changes in soil profile occur. 

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Unified Soil Classification

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Vane Shear Test On Soil

Vane shear test is a simple and quick test, used either laboratory or in the field.

Aim of Vane shear test 

To determine the undrained shear strength of cohesive soil.

Testing Equipment For vane shear Test

⇰ A vane shear testing equipment consists of four thin plates, called vanes, welded orthogonally to a steel rod.

⇰ A torque measuring arrangement, such as a calibrated torsion spring is attached to the rod. The steel rod is rotated by worm gear and worm wheel arrangement.

The procedure of Vane Shear Test

⇰ A pit is first of all made into the ground up to a depth at which the shear strength is to be tested.  

⇰ The vane tester is then pushed or driven carefully into the soil below the bottom of the pit, to a depth somewhat greater than the length of the vane. 

⇰ The torque rod is now rotated (usually 1° per minute). The rotation is continued till the soil falls, which will be indicated by the sudden decrease of torque without any back movement of torque wheel.  

⇰ The maximum torque (T) given till failure is measured and recorded. The shear strength (𝛕f) is calculated by using the following equation; 

𝛕f = 2T / πd²[ H + d/3] 

Where, H = Height of the vane And, d = Diameter of the vane.

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Consolidation Settlement Analysis of Soil