Foundation Engineering - Slide Share PPT.ppt
- 2. Definition The process of determining the layers of natural soil deposits that will underlie a proposed structure and their physical properties is generally referred to as site investigation. 2
- 3. The purpose of a soil investigation 1. Selection of the type and the depth of foundation suitable for a given structure. 2. Evaluation of the load-bearing capacity of the foundation. 3. Estimation of the probable settlement of a structure. 4. Determination of potential foundation problems (for example, expansive soil, collapsible soil, sanitary landfill, and so on). 5. Establishment of ground water table. 6. Prediction of lateral earth pressure for structures like retaining walls, sheet pile bulkheads, and braced cuts. 7. Establishment of construction methods for changing subsoil conditions.
- 4. SOIL BORING
- 5. Boring tools
- 6. Boring tools
- 7. Boring tools
- 8. Boring tools
- 9. Preparation of Boring Logs 1. Name and address of the drilling company 2. Driller’s name 3. Job description and number 4. Number, type, and location of boring 5. Date of boring 6. Subsurface stratification, which can he obtained by visual observation of the soil brought out by auger, split-spoon sampler, and thin-walled Shelby tube sampler 7. Elevation of water table and date observed, use of casing and mud losses, and so on 8. Standard penetration resistance and the depth of SPT 9. Number, type, and depth of soil sample collected 10. In case of rock coring, type of core barrel used and, for each run, the actual length of coring, length of core recovery, and ROD
- 10. Disturbed vs Undisturbed (%) 100 . . . . . . 2 2 2 D I D I D O AR Good quality samples necessary. AR<10% sampling tube soil area ratio Thicker the wall, greater the disturbance.
- 12. Rock coring
- 13. Rock Core Drilling Done with either tungsten carbide or diamond core bits Use a double or triple tube core barrel when sampling weathered or fractured rock Used to determine Rock Quality Designation core barrel
- 14. FIELD STRENGTH TESTS The following are the major field tests for determining the soil strength: 1. Vane shear test (VST). 2. Standard Penetration Test (SPT). 3. Cone Penetration Test (CPT).
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- 20. Footings
- 21. Footing Footing Definition Footings are structural members used to support columns and walls and to transmit and distribute their loads to the soil in such a way that the load bearing capacity of the soil is not exceeded, excessive settlement, differential settlement, or rotation are prevented and adequate safety against overturning or sliding is maintained.
- 22. Types of Footing Types of Footing Wall footings are used to support structural walls that carry loads for other floors or to support nonstructural walls.
- 23. Types of Footing Types of Footing Isolated or single footings are used to support single columns. This is one of the most economical types of footings and is used when columns are spaced at relatively long distances.
- 24. Types of Footing Types of Footing Combined footings usually support two columns, or three columns not in a row. Combined footings are used when tow columns are so close that single footings cannot be used or when one column is located at or near a property line.
- 25. Types of Footing Types of Footing Cantilever or strap footings consist of two single footings connected with a beam or a strap and support two single columns. This type replaces a combined footing and is more economical.
- 26. Types of Footing Types of Footing Continuous footings support a row of three or more columns. They have limited width and continue under all columns.
- 27. Types of Footing Types of Footing Rafted or mat foundation consists of one footing usually placed under the entire building area. They are used, when soil bearing capacity is low, column loads are heavy single footings cannot be used, piles are not used and differential settlement must be reduced.
- 28. Distribution of Soil Pressure Distribution of Soil Pressure When the column load P is applied on the centroid of the footing, a uniform pressure is assumed to develop on the soil surface below the footing area. However the actual distribution of the soil is not uniform, but depends on may factors especially the composition of the soil and degree of flexibility of the footing.
- 29. Distribution of Soil Pressure Distribution of Soil Pressure Soil pressure distribution in cohesionless soil. Soil pressure distribution in cohesive soil.
- 30. Design Considerations Design Considerations Footings must be designed to carry the column loads and transmit them to the soil safely while satisfying code limitations. The area of the footing based on the allowable bearing soil capacity Two-way shear or punching shear. One-way bearing Bending moment and steel reinforcement required * * * *
- 31. Design Considerations Design Considerations Footings must be designed to carry the column loads and transmit them to the soil safely while satisfying code limitations. Bearing capacity of columns at their base Dowel requirements Development length of bars Differential settlement * * * *
- 32. Size of Footing Size of Footing The area of footing can be determined from the actual external loads such that the allowable soil pressure is not exceeded. pressure soil allowable weight - self including load Total footing of Area footing of area u u P q Strength design requirements
- 33. Differential Settlement Footing usually support the following loads Dead loads from the substructure and superstructure Live load resulting from material or occupancy Weight of material used in backfilling Wind loads
- 34. Pile Foundation
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