1.CLASSIFICATION OF SOILS

SOIL

SOFT SOILSPREADING

SOILHARD SOIL

SOFT SOIL:

1. These are compressible soils.

2. They deform under loading.

3. These are clayey soil.

4. These soil is suitable for ordinary constructions.

SPREADING SOIL

These are non cohesive soil.

They try to spread under loading conditions.

Sand, gravel and murrum are examples.

If spreading can be prevented then load can be applied.

HARD SOIL

These are incompressible soil.

These are suitable for heavy loading without yielding.

Solid rocks, stony soils are the examples.

Multistory buildings, water tanks can be built with out

any soil alteration.

2.FIELD IDENTIFICATION OF SOIL

SOIL

COARSE GRAINED SOIL

FINE GRAINED SOIL

COARSE-GRAINED SOIL

These soils consists of mineral fragments and easily it

can be identified.

Gravel and sand are the best examples.

It can be further classified into fine, medium ,or coarse.

Grains may be rounded, sub-rounded or sub-angular.

Other minerals like shale or clay may be present but it

can be identified by using magnifying glass.

FINE GRAINED SOIL

In fine grained soils, mineral identification is not

possible with the aid of equipments.

Silt and clay are the best examples.

It can be classified further as organic and inorganic soil

based on presence and absence of organic material

respectively.

Grain size, plasticity are some of the physical properties.

3.INDIAN STANDARD CLASSIFICATION

SYSTEM (ISCS-IS:1498-1970)

SOIL

COARSE FINEHIGHLY

ORGANIC

1. COARSE GRAINED:

In the total mass of soil, half of the soil mass having particle size larger than 75micron IS sieve size.

2. FINE GRAINED:

In the total mass of soil, half of the soil mass having particle size smaller than 75micron IS sieve size.

3. HIGHLY ORGANIC SOIL:

These soil contain large percentage of fibrous organic matter like peat and decomposed vegetation.

4.BEARING CAPACITY OF SOIL

➢ As the load of any structure is finally transmitted

to the soil laying below the foundation of the

structure. Hence it is important to know the

strength and behavior of the soil.

CONTINUED……

➢ Bearing capacity of soil is defined as load

carrying capacity of the soil over it per unit area

without causing excessive settlement and

displacement.

➢ Bearing capacity of soil depends on properties of

soil like cohesiveness, particle size and

compactness etc.

➢ Bearing capacity also depends on moisture

content present in the soil.

4.1 ULTIMATE BEARING CAPACITY

➢ It is defined as maximum load that can be

applied on the soil with out any failure.

4.2 SAFE BEARING CAPACITY

➢It is defined as permissible load applied on unit

area with out causing failure of the soil.

5. CLASSIFICATION OF SOIL BASED ON

PARTICLE SIZE

6. DETERMINATION OF SAFE BEARING

CAPACITY OF SOIL

6.1 PLATE LOAD TEST METHOD:

1. This is the field test for determining the ultimate

bearing capacity of soil.

2. Bearing capacity of soil can be determined by placing

steel plate at the foundation level.

3. Record the settlement corresponding to each load

increment.

4. The load is increased gradually till the plate sinks at

rapid rate.

5. The total value of load above the plate is noted and

divided by the area of the steel plate. It gives the

ultimate bearing capacity of soil.

CROSS SECTION OF PLATE LOAD TEST

CONTINUED ….

6.2 PROCEDURE

➢ Earth is excavated at the site where foundation is to be

laid.

➢ Width of pit should be at least greater than 5 times the

width of test plate.

➢ At the centre a small depression is made which is equal

to bearing plate.

➢ The dimensions of test plate is not greater than 25mm

(thickness) and size 300 to 750mm.

➢ Load is applied to the test plate through column centrally

placed and load applied with the help of hydraulic jack.

➢ The load applied by using gravity loading of reaction

truss method.

CONTINUED…..

➢ The settlement of plate is noted by means of dial gauges

mounted on independent datum bar.

➢ A graph is plotted against settlement and load intensity

(ton per meter square).

CONTINUED…..

7. METHODS OF IMPROVING THE SAFE

BEARING CAPACITY OF SOIL (SBC)

1. Compacting the soil:

It can be done in two ways

1.1 By hand Compaction by spreading broken stones or

gravel or sand and ramming well in the bed of trenches.

1.2 By driving piles either of wood or concrete or driving

and removed, sand is filled in the then and rammed.

CONTINUED…..

2. Increasing depth of the foundation: This method is

uneconomical as the depth increases SBC of soil

increases.

Increase in depth of

foundation

3. Increasing the width of foundation: To decrease the

intensity of pressure which helps in increase in load

carrying capacity.

Increasing width

of foundation

4. By providing drainage of soil: Open joints may be laid

just below the foundation. It is the best method at water

logged areas.

Drainage provided below foundation

5. By laying sheet piles over the ground of shallow

foundation.

Sheet piling

CONTINUED…..

6. Grouting the concrete into holes made on the ground.

Grouting of concrete into holes.

CONTINUED…..

7.Replacing the poor soil by imported soil to a depth of

1.5m filled in the layer by layer by ramming.

8. By adding Chemicals to solidify the soil. Chemicals like

calcium chloride.

Spraying of chemicals

9. By laying geo textile material over weak soils.

Geo-textile material

8.SAFE BEARING CAPACITY OF DIFFERENT SOIL

Types of soil Catagory SBC in kN/m2

Depth in

meter

Types of

foundation

Rocks Hard Rock 3240 1.20 Spread

Footing

Soft Rock 440 1.20 -do-

Non cohesive Gravel, Sand 440 1.20 -do-

Fine sand, Silt 150 1.20 Combined

Footing

Fine sand 100 1.80 -do-

Cohesive soil Medium Clay 440 1.80 Strap footing

Soft clay 100 3.0 Deep/pile

foundation

Black cotton

soil

130-160 5.0 Pile

foundation

Prepared by,

Naveen Kumar B.S.

Lecturer,

Department of Civil Engineering,

Government Polytechnic, Raichur