Soil bearing capacity (2024)

FAQs

What is my soil bearing capacity? ›

Estimating Soil Capacity

Soil capacity is measured in pounds per square foot (psf). The load-bearing capacity of soils range from 4,000 psf for sedimentary rock to as little as 1,500 psf for clay and silt. Soils that are a predominantly sand or gravel typically fall in the middle, from 2,000-3,000 psf.

IS 6403: Code of practice for determination of bearing capacity of shallow foundations.

You can get a pretty good idea of the soil bearing capacity in the trench bottom using a hand penetrometer. This pocket-sized device is a spring-loaded probe that estimates the pressure the soil can resist and is calibrated to give readings in tons per square foot.

Estimating soil bearing capacity can be done through field tests that measure the soil's reaction to applied loads. Standard penetration test (SPT) involves driving a steel rod into the soil at a constant rate and recording the number of blows required to penetrate a certain depth.

The maximum load per unit area which the soil can withstand without any displacement or settlement or shear failure is called the “Safe bearing capacity of the soil.”

The bearing capacity of soil is calculated using the formula: qf = c'Nc + γDNγ + 0.5γBNγ.

Field tests like Plate bearing test, Standard penetration test, Pressuremeter test and Field vane shear test are generally used to determine bearing capacity of soil. Because of high range of bearing capacity of soil the load for field tests is so high, similarly the reaction load is much more.

Which soils have highest bearing capacity? ›

For the stability of your structure, you would like to have soil that has good bearing capacity. Gravel and sand are the soils with higher bearing capacity while silts and clays typically have lower capacities.

The allowable bearing pressure is the maximum pressure that can be applied to the soil without causing failure. The ultimate bearing capacity, on the other hand, is the maximum pressure that can be applied to the soil before it fails.

Concept: IS: 6403 – 1981 code of practice is used for the determination of bearing capacity of the shallow foundation. In this code a modification was done on ultimate bearing capacity formula which was first given by Brinch Hansen and known as Brinch Hansen's method.

The split-spoon sampler that is attached to the drill rod is placed at the testing point. A hammer of 63.5 kg (140 lbs) is dropped repeatedly from a height of 76 cm (30 inches) driving the sampler into the ground until reaching a depth of 15 cm (6 inches). The number of the required blows is recorded.

The CBR test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area. The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. The harder the surface, the higher the CBR value.

The general formula for the bearing capacity of soil is qᵤ = c'Nc + γDNγ + 0.5γBNγ. Where qᵤ is the ultimate bearing capacity, c' is the cohesion of soil, Nc, Nq, and Nγ are bearing capacity factors, D is the footing depth, B is the width of the strip footing, and γ is the unit weight of soil.

Engineers use mathematical models, computer simulations, and empirical data to assess the load-bearing capacity of a structure accurately. This process involves calculating the internal forces and stresses acting on different parts of the structure and comparing them to the capacity of the materials being used.

The allowable bearing pressure is the maximum pressure that can be applied to the soil without causing failure. The ultimate bearing capacity, on the other hand, is the maximum pressure that can be applied to the soil before it fails.