type of foundation 62-09-18

FOUNDATION FOOTING

Foundation The foundation system of building, its substructure, is a critical link in transmission of building loads to the ground. Foundation is a structure built to transfer the dead loads and live loads or weight of building to the material below.

CLASSIFICATION  Foundation are generally classified as either deep or shallow. The depth bearing area of shallow foundation generally is no deeper than about the width of the bearing surface. Deep foundation provide support for a structure by transferring the loads to competent soil and rock at stone depth below the structure.

Foundation Shallow Deep Spread Basement Combine Caissons Strip Piles

Shallow foundation  Shallow foundation can be either footing or pad. They consist reinforced concrete slabs formed directly on a prepared soil base. Footing may be spread, combined, or continuous. Terzaghi and peck define that shallow foundation as the footing width equal to or greater than its depth.

Spread footing  Spread footing They typically 0.9 to 2.4 to 3m square. Their bearing surface is typically less than 2.5 times their width (<2.5B).

Combine footing  Combine footing are similar to spread footing but support two or more columns

Continuous or Strip  Continuous or Strip footing is an elongated shallow foundation that typically support as single row of column or a wall or other type of strip loading.

Shallow Footings By definition D/B < 4 D B

Rectangular and strip footings Wall loading Structural load Rectangular footing Strip footing

Applications Large Distributed Very Large Concentrated Weight Weight Low Weight Weak Weak Rock or Strong Rock Soil distributed over competent Soil

Load limitations Shallow foundations can Shallow foundations are cope with compression limited in tension capacity and inclined loads Dby the footing weight C

Limit States Serviceability Ultimate

Deep Foundation  It is opposite to shallow foundation. It has been developed to increase bearing capacity/stability and reduce settlement by build them deeper than shallow one due to building going larger and heavier. It can be divided into 3 types as details later on.

Basement Large Distributed Very Large Concentrated Weight Weight Low Weight Weak Weak Rock or Basement Soil distributed over Strong Rock competent Soil

Caissons Box Caisson (floating) Open Caissons Pneumatic Caissons

Axial Capacity of Single Piles

Methods Pile driving formulae Static load test Dynamic or Statnamic load test Static formulae

Pile driving formulae  e.g. Hiley formula Ru = e.W.h . (set + tc / 2)  Newton’s law - two rigid bodies  Efficiency? F s  Static resistance only D  Correlate tc  MORE details later

Pu Axial Capacity W Qs Pu = Qb + Qs - W Qb

Axial Capacity Fu Fu + W = Pbase + Pshaft Pshaft Shear failure at pile shaft W Pbase Bearing failure at the pile base

Tension Capacity Tu - W = Pshaft,t < Pshaft,c Pshaft,t Shear failure at pile shaft

Axial Capacity of Pile Groups

Applications Large Distributed Very Large Concentrated Weight Weight Low Weight Soft to Firm Clay Dense Sand Strong Rock

Group PCuag pacity Pile Cap • Overlapping stress fields Pug  n.Pup • Progressive densification Pug = e.n.Pup • Progressive loosening • Case-by-case basis