Consolidation Settlement of Spread Foundation

Engineeering Projects

What is Consolidation Settlement of Spread Foundation?

Consolidation settlement is caused due to the expulsion of pore water from the voids of a saturated soil mass under the prevailing excess hydrostatic pressure induced by load imposed on a foundation.

Settlement of Footing in Clay

The total settlement is given by:

s = s_i + s_c + s_s

Where s is the total settlement, si is the immediate settlement, sc is the consolidation settlement and ss is the secondary settlement,

The consolidation settlement is given by:

s_c = H\dfrac{\Delta c}{1 + e_0}

= m_v \times \Delta P \times H   ———- (1)

For normally consolidated clay, the consolidation settlement is given by:

s_c = \dfrac{C_c}{1 + e_0}log_{10}[\dfrac{P_0 + \Delta P}{P_0}]H            ………(2)

Where, H = Significant Depth

\Delta e = Change in void ratio

e0 = Initial void ratio

\Delta P = Change in pressure

MV = Coefficient of volume compressibility

Cc = Compression Index

P0 = Effective overburden pressure

The compression index is the straight portion of the e-log p curve and is given by:

C_c = \dfrac{\Delta e}{log_{10}}[\dfrac{P_0 + \Delta P}{P_0}]         ……..(3)

Indirectly the compression index for normally consolidated clay is given by:

Cc = 0.009(WL – 10)   ———- (4)

Where, WL is the liquid limit.

Correlation to consolidation settlement – The assumption that the pore pressure induced is equal to the imposed load on foundation is not correct and is less than load imposed. To account for this some correction is necessary. The following corrections are suggested.

S. No

Soil Consistency

Correction Factor, µ

1

Very sensitive clay

1.0 to 1.2

2

NC clay

0.7 to 1.00

3

OC clay

0.5 to 0.7

4

Heavily OC clay

0.2 to 0.7

The corrected settlement is given by, sc (corrected) = µsc (odeometer)   ———- (5)

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