Bearing Capacity of soils and for engineers.pptx

Its involves bearing Capacity of soils and measures to take to increase bearing Capacity of soil to build your infrastructure.

1. BEARING CAPACITY Centre for Geographical Information System (GIS) University of the Punjab, Lahore

2. Bearing capacity The Bearing Capacity is perhaps from one of the most important topics in engineering geology In engineering geology , Bearing Capacity is the capacity of soil or rock to support the loads applied. The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce failure in the soil. In simple words, the load-carrying capacity of foundation soil or rock which enables it to bear and transmit loads from a structure. Soils behave in a complex manner when loaded so, it is important to know the bearing capacity of soils. By dividing the ultimate bearing power of soil by a factor of safely, the bearing capacity of a soil is obtained.

3. Why we need bearing capacity?? The stability of foundation depends on: The load carrying capacity of the soil beneath the foundation. The settlement of the soil beneath the ` foundation. Settlement? It is defined as the vertical movement of the ground, generally caused by the changes in stresses within the earth.

4. Important terminologies Ultimate Bearing Capacity: Maximum pressure which a foundation can withstand without the occurrence of shear failure of the foundation. Gross Bearing Capacity: The bearing capacity inclusive of the pressure exerted by the weight of the soil standing on the foundation, or the ‘surcharge’ pressure, as it is sometimes called. Net Bearing Capacity: Gross bearing capacity minus the original overburden pressure or surcharge pressure at the foundation level; obviously, this will be the same as the gross capacity when the depth of foundation is zero, i.e., the structure is founded at ground level

5. Safe bearing capacity: Ultimate bearing capacity divided by the factor of safety. The factor of safety in foundation may range from 2 to 5, depending upon the importance of the structure, and the soil profile at the site. Methods to determine bearing capacity The following methods are available for the determination of bearing capacity of a foundation: Bearing capacity tables in various building codes

6. Analytical methods Plate bearing tests Penetration tests Laboratory tests Plate bearing tests are load tests conducted in the field on a plate. These involve effort and expense. Penetration tests are conducted with devices known as ‘Penetrometers’, which measure the resistance of soil to penetration. Laboratory tests which are simple, may be useful in arriving at bearing capacity, especially of pure clays.

7. BEARING CAPACITY FROM BUILDING CODES illustrated by the building codes all codes give lists of soil types and the respective safe or allowable bearing capacity it is presumed that the soil can support the indicated pressure with safety against shear failure and without undue settlement

8. ANALYTICAL METHODS OF DETERMINING BEARING CAPACITY The theory of elasticity—Schleicher’s method. The classical earth pressure theory—Rankine’s method, Pauker’s method and Bell’s method. The theory of plasticity— Fellenius ’ method, Prandtl’s method, Terzaghi’s method, Meyerhof’s method, Skempton’s method, Hansen’s method and Balla’s method.

9. How to increase the bearing capacity? Increasing Depth of Foundation: In granular soil the bearing capacity increases with the depth due to the confining weight of overlying materials. Chemical Treatment: In this treatment certain chemicals are grouted in the place of cement grout. The chemical used is such that it can solidify and gain early strength. Grouting : Bore holes in sufficient numbers are driven in the ground and cement grout is forced through these under pressure Due to which the bearing capacity of soil is increased.

10. Compaction of soil: Due to the compaction of soil the bearing capacity of the soil increases resulting in reduction in resting settlements Drainage of soil: Due to the presence of water in the soil the bearing capacity of the soil is decreased hence by draining out water the void ratio is improved resulting in higher bearing capacity

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