Foundation Engineering Civil

Prepared By MOHD HABEEB ULLAH SHAREEF STUDENT OF DCET, Hyd

www.engineeringcivil.com

FOUNDATIONDefinition : The low artificially built part of a structure which transmits the load of the structure to the ground is called foundation. OR A foundation (also called a ground sill) is a structure that transfers loads to the earth.


Major Building Parts

Superstructure

Substructure Foundationwww.engineeringcivil.com

Foundations are made in various materials. They could be reinforced cement concrete foundations or brick foundations or stone rubble masonry foundations etc. The choice of material to be used in the construction of foundations also depends on the weight of the structure on the ground. The bearing capacity of soil plays a major role in deciding the type of foundation. The safe bearing capacity of soil should be 180N/mm2 to 200N/mm2.


Foundation

Shallow Foundation

Deep Foundation

Spread Footing

Raft Foundation

Compensated Foundation

Pile Foundation

Caissons Foundation


Shallow FoundationsA shallow foundation is a type of foundation which transfers building loads to the earth very near the surface Shallow foundations are commonly used in smaller structures such as residences and small buildings whose floor height is limited to 10m Advantages a. Cost (affordable) b. Construction Procedure (simple) c. Material (mostly concrete) d. Labour (doesnt need expertise)www.engineeringcivil.com

Spread footingSpread footings may be built in different shapes & sizes to accommodate individual needs such as the following: a) Square Spread Footings / Square Footings b) Rectangular Spread Footings c) Circular Spread Footings d) Continuous Spread Footings e) Combined Footings f) Ring Spread Footings


MAT/RAFT FOUNDATIONMat foundation is use: a. when spread footings would cover more than 50% of the building footprint area a mat foundation will be more economical. b. When structural loads are so high or the soil condition so poor


Deep Foundations- Purpose: To transfer building loads deep into the earth. If the depth of the foundation is greater than its width the foundation is classified as a deep foundation. Types a. Pile foundation b. Caisson foundation


PILESIt is installed in the ground to transfer the structural loads to soils at some significant depth below the base of the structure.


CAISSON FOUNDATIONIts a prefabricated hollow box or cylinder. It is sunk into the ground to some desired depth and then filled with concrete thus forming a foundation.


PRECAUTIONS TO BE TAKEN- Seismic base isolation in seismic areas - Underpinning required to carry out repairs to the existing building or to add some changes in the foundations - Retaining walls to hold the soil back from caving in: Types of failure such as overturning, sliding and undermining should be avoided, non-reinforced or/and reinforced cantilevered retaining walls, drainage behind the wall to eliminate piping of water in soil - Water proofing and drainage of foundations - Basement insulation Frost protection through protective coatings and plastic foam insulation - Back-filling with properly draining soilswww.engineeringcivil.com

DESIGN STEPS: Step-1: Given Data Factored load on column Pu in KN Size of column, l x b in mm SBC of Soil in KN/sq.m Self weight of footing = 10% of Pu Step-2: Area of footing = Total Load/S.B.C Provide a suitable size of footing L x B Step-3: Net upward pressure intensity, Pu/area of footing. Step-4: Design for flexure Critical section occurs at the face of column l = (L l)/2 www.engineeringcivil.com Mutr =wl2/2

Step-5: Depth of footing d = (Mu/(2.76x1000)) Step-6: Calculation of area of steel, Mu = 0.87fyAst(d-0.42xu) Step-7: Check for One-way shear Critical shear force occurs at a distance ofd from face of the column Nominal shear stress, Tu = v/bd for 0.15% of steel from IS456:2000, Table-19 Permissible shear stress If :. Tc>Tv footing is safe in www.engineeringcivil.com shear.

a d

Check for Two-way shear or Punching ShearCritical shear occur at a distance of d/2 from face of the column. Nominal shear stress = v/2[(a+d)+(b+d)]d Permissible shear stress if Tv kTc .. Safe

d/2 a d/2


L/2

Retaining wallsA retaining wall is a structure designed and constructed to resist the lateral pressure of soil Retaining walls are built in order to hold back earth which would otherwise move downwards. Types: 1. Cantilever type 2. Counter fort type


Types of wall failure Wall fracture Overturning Sliding Undermining


Design Elements to Prevent Failure Relieve H2O pressure (for all 3 types of failure) Crushed stone Weeps Overturning Cantilevered Footing Reinforcing Sliding Keywww.engineeringcivil.com

Foundation Engineering Civil

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