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Lempung

Lempung

Pasir

Introduction Oedometer test Primary & Secondary compression e – log σ’ plot Compression index (Cc) & coefficient of

volume compressibility (mv) Over consolidation ratio (OCR)

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Assumptions: A homogenuous, saturated soil Soil particle and water are incompressible Vertical flow of water The validity of Darcy’s law Small strains

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The increase of load above the soil surface will increase the porewater pressure

For sandy soil, the porewater will easily dissipated, becoming immediate settlement

For clay soil, the porewater will dissipated as a function of time.

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Sandy Soil Clayey SoilAfter

ConstructionAfter

ConstructionAfter

Consolidationσ = A A Aσ = B B Bσ' = A+B A A+Bu = 0 B 0

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The change in volume of the soil caused by the expulsion of water from the void and the transfer of load from the excess porewater pressure to the soil particles

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Also called as “Creep”

The change in volume of fine grained soil caused by adjustment of the soil fabric (internal structure) after primary consolidation completed

The rate of settlement from secondary compression is very slow compared to primary consolidation

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Normally Consolidated (NC), OCR =1:Present effective overburden pressure is the maximum pressure that the soil was subjected in the past

Over Consolidated (OC), OCR >1:Present effective overburden pressure is less than that the soil experienced in the past. The maximum effective past pressure is called preconsolidation pressure, σc

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Under Consolidated (UC), OCR < 1

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0''

σσ cOCR =

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1. Produce back the straight line part BC of the curve

2. Determine the point (D) of max curvature on the recompression part (AB)

3. Draw the tangent to the curve at D and bisect the angle between the tangent and the horizontal through D

4. The vertical through the point of intersection of the bisector and CB produced gives the approximate of preconsolidation pressure

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For Normally Consolidated (NC) Clay:

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Hitunglah penurunan konsolidasi yang terjadi biladiberi tekanan Cc diasumsikan = 0.009(LL-10)

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