BITUMINOUS STABILISATION AND TYPES

Bituminous Stabilisation

Bitumens are non-aqueous system of hydrocarbon that are soluble in carbon di-sulphide.Bitumen stabilisation is generally done with asphalt as binder.In any inorganic soil which can be mixed with asphalt is suitable for bituminous stabilisation. In cohesionless soils, asphalt binds the soil particles together and thus serves as a bonding or cementing agent.In cohesive soils, asphalt protects the soil by plugging its voids and water proofing it.It helps the cohesive soil to maintain low moisture content and to increase the bearing capacity.The amount of bitumen required generally varies between 4-7% by weight.The actual amount is determined by trail.

There are four types of soil bituminous stabilisation:

1. Soil Bitumen
2. Sand Bitumen
3. Oiled Earth
4. Water Proofed Clay Concrete

1. Soil Bitumen 

Soil bitumen is a water proof, cohesive soil system.The best results are obtained if the soil satisfies the following criteria:

• Plastic Limit Less than 18%
• Liquid Limit Less than 40%
• The maximum size of the particle should not be greater than one-third the compacted thickness of the soil-bitumen.

The quantity of bitumen varies from 4 - 7% of the dry weight.

2. Sand Bitumen

This bitumen stabilised cohesionless soil system.The sand should be free from vegetal matter or lumps of clay.The sand may require filler for its mechanical stability.However, it should not contain more than 25% minus No.200 sieve material for dune sand and not more than 12% in case in other types of sand.The amount of bitumen varies from 4 - 10%.

3. Oiled Earth

In this system, a soil surface consisting of silt-clay material is made water proof by spraying bitumen in two or three applications.The bitumen penetrates only a short depth into the soil.The amount of bitumen required is about 5 litres per square meter of the soil surface.

4. Water Proofed Clay Concrete

A soil possessing a good gradation is water proofed by a uniform distribution of 1 - 3% of bitumen in this system.Soils of three different gradations have been recommended.  

Factors Affecting Bituminous Stabilisation

1. Types Of Soil

Bituminous stabilisation is very effective in stabilising sandy soils having little or no fines.

2. Amount Of Asphalt

The quality of bitumen-stabilised soil improves with the amount of asphalt upto a certain limit.

3. Mixing

The quality of bitumen-stabilised soil improve if the soil is mixed thorough.

4. Compaction

The dry density of bitumen soil depends upon the amount and type of compaction.It also depend upon volatile content.

Chemical Soil Stabilisation

In chemical soil stabilisation, soils are stabilised by adding different chemicals.These chemicals react with the soil which in return cause its structure to be changed.The chemical seal the space between particles, leaving no room for water to penetrate through.Among the most common chemicals that are used for soil stabilization include sodium chloride, calcium chloride and sodium silicate.The main advantages of chemical stabilisation is that setting time and curing time can be controlled. Chemical stabilisation is however generally more expansive than other types of stabilisation. The following chemicals have been successfully used:

1. Calcium Chloride
2. Sodium Chloride
3. Sodium Silicate
4. Chrome Lignin
5. Polymers
6. Other Chemicals

1. Calcium Chloride

Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2.When calcium chloride is added to soil it causes colloidal reaction and amend the characteristics of soil water.When calcium chloride is dissolved it reduces the loss of moisture from the soil.It also reduces the chances of frost heave, as the freezing point of water is lowered.This method is very effective for stabilisation of silty and clayey soil which lose strength with an increase in water content.

2. Sodium Chloride

Sodium chloride is commonly known as salt with the chemical name NaCl.Sodium chloride is mixed with the soil either by the mix-in place method or by the plant-mix method.It should not be applied directly to the surface.When sodium chloride is added to the soil, crystallisation occurs in the pores of the soil and it forms a dense hard mat with the stabilised surface.

3. Sodium Silicate

Sodium silicate are colorless glassy or crystalline solids or white powders.Sodium silicates, as well as other alkali silicates have been successfully used for soil stabilisation.Sodium silicate gives strength to soil when it react with it and make the soil impervious.This method of stabilisation is relatively inexpensive but its long term stability is doubtful.

4. Chrome Lignin

Lignin is an organic substance binding the cells,fibers and vessels which constitute wood and the lignified elements of plants.Chrome lignin is formed from black liquor obtained during sulphite paper manufacture.Sodium bicarbonate or potassium bicarbonate is added to sulphite liquor to form chrome lignin.It slowly polymerises into brown gel.

5. Polymers

Polymers are long-chained molecules formed by polymerising of certain organic chemicals called monomers.Polymers may be natural or synthetic.When a polymer is added to a soil reaction takes place.Polymers mainly affect the aggregation and strength of soils through their interactions with fine clay particle.Coating of adsorbed polymers on clays can increase their steric stabilisation by preventing clay particles from approaching each other as closely.

6. Other Chemicals

Apart from the above mentioned chemicals some other chemical are also used for soil stabilisation which are as fallows:

 

A. Some water proofer such as alkyl chloro silanes, siliconates amines and quaternary ammonium salts have been used for water proofing of soils.

B. Dispersant such as sodium hexa-metaphosphate, are used to increase electrical repulsion and to cause dispersed structure.

C. Coagulating chemicals such as calcium chloride and ferric chloride have been used to increase the electrical attraction and to form flocculated structure in order to improve the permeability of the soil.

Advantages Of Chemical Soil Stabilisation

• It gives more strength to the soils.
• It improves the permeability of soil.
• It this method the setting time and curing time can be controlled.

Disadvantages Of Chemical Soil Stabilisation

• Require extra experienced labor.
• Chemicals should not be used directly to the surface.
• This method of stabilisation is more expensive relatively to other methods.

LIME STABILISATION - METHOD & BENEFITS

 Lime Stabilisation

Lime stabilisation is done by adding lime to the soil.It is very useful for stabilisation of clayey soils.When lime reacts with soil, there is exchange of cations in the adsorbed water layer and a decrease in plasticity of the soil occurs.The resulting material is more friable than the original clay and is therefore, more suitable as subgrade.Lime stabilisation improve the density and bearing capacity of the soil.Lime-soil stabilisation is useful to construct sub-base and base course for pavement.Lime treated soil is more suitable for warm regions where temperature is very high and for colder regions it is not suitable.

Quick lime is more effective as stabiliser than the hydrated lime, but the latter is more safe and convenient to handle.Generally the hydrated lime is used.It is known as slaked lime.Lime stabilisation is not effective for sandy soils because these soils can be stabilised in combination with clay, fly-ash or other pozzolanic materials.The ratio of fly ash to lime varies between 3 to 5.The fly ash is used about 10 - 20 % of the soil weight.

Method Of Mixing Lime Into Soil

The method of mixing lime into soils for stabilisation involves following steps:

• The soil which need stabilisation is scarified and pulverized by suitable equipment.

• Now add some amount of lime to the pulverized soil either the powder or slurry form and then mixed with suitable equipment.

• If lime powder is used then water is sprayed all over the soil.

• After spraying the water leave this mixture for 1 to 4 days. Lime-soil reaction is slow process and it required some time.

• Once the lime-soil reaction take place then spread the soil to required grade and compact it with rollers.

• When compaction is completed and the soil achieve the required dry density, the compacted lime-soil layer is allowed for curing for 1 week. 

• Finally after 1 week of curing the field tests are conducted to check water content and maximum dry density of compacted soil.

Factor Affecting Lime Soil Stabilisation

The following are the factors which affecting lime-soil stabilisation:

1. Soil Type
2. Lime Type
3. Lime Content
4. Compaction
5. Additives
6. Curing 

Benefits Of Lime Soil Stabilisation

• It is easy to mix with soil.
• It reduces the plastic properties of the soil when wetted.
• It sets slowly, the time interval between mixing and compacting is not critical.
• Cost of stabilisation is reasonably low.

WHAT IS SOIL SUCTION?

Soil Suction

Soil suction is considered as the summation of matric suction (ψ_{m) and osmotic suction (π).}

Soil suction is defined as the state of the soil when it is under reduced pressure.It is measured in terms of the height of the water column (h) suspended in the soil.

Soil Suction Formula

Soil suction can be represented as common logarithm of the height of the water column (h).The value of 'h' is substituted in centimeters.

 

Pf = log10 (h)

For example: The height of the water column is 100cm.Hence, the Pf value is given by:

 _{Pf = log10 (h)}

     _{= log10 (100)}

     _{= log10 (10^2)}

     _{= 2 x log10}

     _{= 2}

_{Similarly, for a height of column = 1 cm.}

Hence the Pf value is given by:

 Pf  = log10 (h)

 Pf   = log10 (1)

 Pf   = 0

Soil suction can also be represented in atm, kPa, kg/cm2 and bar. 

FACTOR AFFECTING SOIL SUCTION

The suction in soils depends mainly on the following factors:

1. Particle Size

In general the smaller the particle size, the greater is the soil suction.The soils with fine particles have a large number of small pores with small radii of menisci. It results in large capillary rise and hence greater suction.

2. Water Content

 Water content is also known natural moisture content, is the ratio of the weight of water to the weight of the solids in a given mass of soil.As the water content of a soil decreases, the soil suction increases and it attains the maximum value when the soil is dry.

3. Soil Structure 

Soil structure describes the arrangement of the solid parts of the soil and of the pore space located between them.The soil structure governs the size of interstices in the soils.As the soil suction depends upon the size of interstices, a charge in the soil structure affects the soil suction.

4. Denseness of Soil

As the denseness of a soil increases, generally soil suction increases.When the soil is loose, with a low density the pores are of large radius and the soil suction is low.

5. Temperature

A rise in temperature causes a reduction in surface tension (Ts) of the water.Consequently, the soil suction decreases as the temperature increases.

6. Dissolved Salts

The surface tension of water increases with an increase in impurities, such as salt.

7. Angle of Contact

The angle of contact between water and soil particles depends upon the mineralogical composition of soils.As the angle of contact (𝛉) increases, the soil suction decreases.The soil suction is maximum when the angle of contact is zero.

8. Wetting Cycle

As discussed in the preceding section, for the same water content, the soil suction is greater during the drying cycle than in the wetting cycle.

WHAT IS FROST ACTION IN SOIL?

Frost Action In Soil

Frost action in a soil is a phenomena that occurs in the winter and early spring climates.There are two type of frost action Frost heavy and Frost boil.Frost heavy is a phenomenon in which the water molecules present in the pores freeze during lower temperature which results in the expansion of the soil.Frost boil is the phenomenon of loosing of the soil when the  frozen soil starts to thaw.Frost boil occurs after the frost heavy process.

Frost Heavy In Soils

Frost heavy is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated into the soil. This results in an increase in the volume of soil because when water is converted into ice there is about 9% increase in its volume.If the porosity of soil is 45% and soil is saturated, the expansion of the soil would be (0.09 x 45) = 4.05%. In other words, there would be a heavy of about 4 cm in every one meter thickness of the soil deposit.Due to frost heavy, the soil at the ground surface is lifted.

The frost have observed in most of the soils is much more than a heavy of about 4 cm per meter.This is due to the fact that when the ice lenses are formed in the soil due to freezing of water, the water film from the adjacent soil particles is also removed.The weight of overlying soil restrains vertical growth of the ice and promote the formation of lens-shaped areas of ice within the soil.The soils which are prone to frost action are mainly silts and fine sands.These soils have large capillary rise due to relatively fine particles.

Civil Insta

Frost Boil In Soils

A frost boil, also known as mud boils or mud circles are small circular mounds of fresh soil material formed by frost action and cryoturbation. After the occurence of frost heavy, if the temperature rises the frozen soil thaws and free water is liberated.Thawing process starts from the upper layer and moves downwards.The liberated water is trapped in the upper layer while the lower layers are still frozen.The strength of soil in upper layer is reduced due to its softening caused by an increases in water content.The process of softening of soil due to liberation of water during thawing is known as Frost boil.

Frost boils are among the most common features of patterned ground the pervasive process shaping the topology of soils in periglacial regions.They generally from regular patterns of polygons.Frost boils are a type of nonsorted circle and are characterized from other circle by barren centres of mineral soil and intercircle region filled with vegetation and peat.It is named after skin boils due to similarities in their formation processes although subsequent research has shown other methods of formation.

Frost boil affects the structures resting on the ground surface.The effect is more pronounced on highway pavements.A hole is generally formed in the pavement due to extrusion of soil and water under the action of wheel loads.Coarse grained soils are not affected much by frost boil, as the quantity of liberated water is small and that too is drained away quickly.The soils most prone to the softening effects are silty soils.These soils have low plasticity index and become very soft with a small increase in water content.

Civil Insta

8 WAYS TO CONTROL SOIL EROSION AT CONSTRUCTION SITES

Soil Erosion At Construction Sites

Soil erosion is a major concern for construction sites, especially if the project is very large.Most of time it is neglected by the Site Engineers or Supervisors.At construction sites it occurs due to heavy runoff due to rain or any other construction activities result in the washing away of soil, which is a slow process but if not rectify initially can result in delay of project which increases the overall cost of project.

Soil erosion can be caused by a variety of factors.Depending on this factor and the severity of the issue, solutions vary.The control of soil erosion helps preserve and protect the construction site and the structure.

Measures To Control Soil Erosion At Construction Sites.

1. Divide the project into sections.
2. Minimize disturbed area on the construction site.
3. Runoff water control method
4. Slope protection
5. Soil stabilization
6. Dewatering
7. Sediment control traps
8. Construction entrances

1. Divide The Project Into Sections

This is a very effective method to control soil erosion at construction sites.In this method working lands at site are divided into different sections.

2. Minimize Disturbed Area On The Construction Sites

During the preparation of a site for construction, it is advised to disturb only those area which are required  for the project.The remaining area of the site should be left undisturbed to protect the topsoil.

3. Runoff Water Control Methods

Some off the methods used to control the runoff water within and around the construction sites are as fallows:

• Geotextile: It is a commonly used for erosion control and soil improvement in a variety of construction projects such as road, pipelines and embankments.Depending on the application, geotextiles may have an open mesh weave, a warp-knitted structure or a closed fabric or nonwoven surface.The specific type of geotextile used is based on several criteria, including separation, filtration, drainage, reinforcement, sealing and protection.

• Soil Nail: Soil nail provides a resisting force against slope failures and offers relatively quick installation.The procedure involves drilling into the soil and placing steel bars into it.

• Riprap: It is a commonly used technique to protect soil from erosion in areas where there is a high degree of concentrated runoff. Riprap is a layer of very large stones interlocked together to act as a barrier on slopes that are unstable because of seepage problems or areas that are receiving a large concentrated flow.Large stone aggregate is poured onto geotextile membranes to keep the ground from being carried away by water.

• Turbidity Barriers: Turbidity barriers are useful in multiple ways, it can prevent soil erosion as well as water contamination.They are typically made of a geotextile membrane that floats and is anchored to the bottom of the water body with weights and used for sediment control.

• Articulated Concrete Blocks: Articulated concrete blocks are available in a thickness of wide variety and shapes.They are used as sloping structure on waterway embankments or manmade drainage systems.

• French Drains: It is a underground piping system called drain tile.The drain tile may also be performed to allow water to seep into the soil below the tile, while excess water travels to the exit point.French drains are installed with a slope of about 1 inch of drop per 10 feet of horizontal run.

4. Slope Protection

The slope protection can be protected by several methods in order to control soil erosion.Some of the method are as fallows:

• Silt Fencing: The purpose of silt fencing is to retain the soil on disturbed land at construction site.It is a temporary sediment barrier made of porous fabric.

• Fiber Rolls: It is a temporary erosion control and sediment control device used on construction sites to protect water quality in nearby streams, rivers, lakes and seas from sediment erosion.It is made of straw, coconut fiber or similar material formed into a tubular roll.Each fiber roll is installed on a horizontal contour level in shallow trenches 2 to 4 inches deep and fastened to the ground with wooden stakes.

• Mats: Mats laid on the soil surface to protect against the washout of soil due to action of rain and surface water.It is also often to provide surface protection when used with slope stabilisation and soil retention system such soil nailing, soil panels and soilcell.

5. Soil Stabilization

Soil stabilization is a physical or chemical treatment which increase or maintain the stability of a soil or improve its engineering properties.It can be achieved either temporary or permanently depending on the requirement of the project.The use of wood binders, mulch and blankets can act as a temporary measure while the permanent methods include seeding, channel stabilization, green buffer and planting. 

6. Dewatering

Dewatering is a term used to describe the action of removing groundwater or surface water from a construction site.Normally the dewatering process is done by pumping or evaporation.

7. Sediment Control Traps

Runoff water on construction sites can be reduced by employing sediment control traps or basin.These units help the sediments to settle before the water is discharged.The sediment basins are constructed with a capacity to store at least two year of stormwater.

 

8. Construction Entrances

A stable construction entrances mainly made up of crushed stone helps to reduce the amount of sediment getting carried away.This entrance required regular maintenance  and it is made at a length of 50 feet.

WHAT IS SOIL LIQUEFACTION - CAUSES AND EFFECTS

Soil Liquefaction

Soil liquefaction is a phenomenon in which saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during earthquake.Soil liquefaction occurs in a fully saturated soil.

Causes Of Liquefaction

The soil is a mixture of soil particles that are connected together.These particles are naturally rest upon each other due to gravity.Soil liquefaction occurs due to sudden and rapid load on the soil particles.The sudden water pressure leads to soil losing its cohesive strength.Once the soil loses its cohesion, it gets softened, weak and loses its solid properties that are converted to liquid properties.

Effects Of Liquefaction

1. Sand Boiling
2. Surface Landslides
3. Damage To Offshore Structures
4. Failure Of Dams And Retaining Walls
5. Failure Of Structure Under Earthquake

1. Sand Boiling

When liquefaction occurs below the surface that is fully compacted, the water pressure below the surface makes the water to break out like a bubble.These come out as boiling water.This is called as sand boiling.

2. Surface Landslides

The term landslide describe a wide variety of processes that result in the downward and outward movement of slope-forming materials including rock, soil, artificial fill or a combination of these.The failure of water carrying bodies can result in surface landslides.

3. Damage To Offshore Structure

Liquefaction is common in soil that is submerged.These conditions cause huge damage for the bridge construction, structures supporting submerged soil deposit.

4. Failure Of Dam And Retaining Wall.

The soils supporting Dams and Retaining walls undergoes liquefaction which results in the collapse of these structures.

5. Failure Of Structure Under Earthquake

Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking.They can either split or lean bringing complete collapse of the structure.Past earthquake records have shown a huge failure of building structures due to liquefaction.When these types of hazards take place it can't provide enough time to evacuation, thus it result in a huge loss of life and property.

Method Of Reducing Soil Liquefaction Hazards

1. By Avoiding Liquefaction Susceptible Soils
2. Built Liquefaction Resistant Structures
3. Improve The Soil

1. By Avoiding Liquefaction Susceptible Soils

Avoid construction on liquefaction susceptible soils.There are various criteria to determine the liquefaction susceptibility of a soil.By characterizing the soil at a particular building site according to these criteria one can decide if the site is susceptible to liquefaction.

2. Built Liquefaction Resistant Structures

If it is necessary to construct on liquefaction susceptible soil because of space restrictions, favorable location, or other reasons, it may be possible to make the structure liquefaction resistant by designing the foundation elements to resist the effects of liquefaction.

3. Improve The Soil

Improving the soil involves mitigation of the liquefaction hazards by improving the strength, density and drainage characteristics of the soil.This can be done using a variety of soil improvement techniques.