Causes of Different Settlement Movement of Soil Movement

Movement of Soil • • • Shrinking and swelling of clay soil Consolidation of

Shrinking and Swelling of Clay Soil • Clay can hold a large amount of

Shrinking and Swelling of Soil Expansion and Shrinkage of soil results in the following:

Consolidation of Sandy Soil • Increase in external pressure leads to increase in load

Settlement caused by Consolidation of Soil

Organic matter in made-up ground • Presence of organic matter contribute to variations in

Loss of ground in Sandy Soils • Water can wash out the finer particles

Washing out of fine sand particles by underground water

‘Swallow Holes’ in limestone • Cavities formed by streams that dissolves the rock away

Movement due to Overloading • By faulty design • By design alterations • By

Vibration • By traffic • By machinery • By explosions. Example, buildings at Lower

Chemical Attack • Expansion reactions by chemicals existing in soils • Heaving caused by

Effect of Vegetation • Tree roots will cause clay soil to shrink • Foundations

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Causes of Different Settlement • • • Movement of Soil Movement due to Loading Vibration Chemical Attack Effect of Vegetation

Movement of Soil • • • Shrinking and swelling of clay soil Consolidation of sandy soil Organic matter in made-up ground Loss of ground in sandy soils ‘Swallow Holes’ in limestone

Shrinking and Swelling of Clay Soil • Clay can hold a large amount of water • When water is removed from clay, it shrinks • Conversely, when clay absorbs water, it expands and loses strength

Shrinking and Swelling of Soil Expansion and Shrinkage of soil results in the following: - • Lateral Movement of Soil • Vertical Movement of Soil ØLong Term Dome Effect ØLong Term Saucer Effect

Long Term Brick Wall Effect

Long Term Weakest Zone Effect

Long Term Big Crack Formed! Effect

Result of Dome Effect

Long Term Brick Wall Effect

Long Term Weakest Zone Effect

Long Term Effect Big Crack Formed!

Result of Saucer Effect

Consolidation of Sandy Soil • Increase in external pressure leads to increase in load on soil and water pressures • Water is being squeezed out and driven to other areas • As sandy soil consolidates, foundation settles very quickly

Settlement caused by Consolidation of Soil

Organic matter in made-up ground • Presence of organic matter contribute to variations in volume greatly • These soils are highly compressible • Foundations should never be built on made-up ground with refuse unless piling is used

Loss of ground in Sandy Soils • Water can wash out the finer particles • Happens when fine sand is washed out by water flowing underground • Bearing capacity is lost

Washing out of fine sand particles by underground water

‘Swallow Holes’ in limestone • Cavities formed by streams that dissolves the rock away • ‘Swallow holes’ are formed

Formation of Swallow Hole in Limestone

Swallow Hole in Limestone

Movement due to Overloading • By faulty design • By design alterations • By buildings used for a different purpose • Extent of movement caused by nature of soil and imposed load

Vibration • By traffic • By machinery • By explosions. Example, buildings at Lower Manhattan (Case Study : Eunos MRT Station)

Vibration by traffic

Chemical Attack • Expansion reactions by chemicals existing in soils • Heaving caused by sulphate-rich filling materials • Sulphate can also attack piles

Effect of Vegetation • Tree roots will cause clay soil to shrink • Foundations will unsettle if tree roots are found below them • Opposite is known as ground heave

Effects of Vegetation in Foundation