Why black cotton soil is not suitable for foundation?
Black cotton soil is not suitable for foundation because it swells excessively when wet and it shrinks excessively when dry. So it is not suitable because of its property to undergo a volumetric change due to variation of moisture content.
Which foundation is suitable for black cotton soil?
The under-reamed pile foundation is the best for black cotton soil. It has bulbs at its lower end. If this bulb is given below the critical depth of moisture movement in black cotton soil, the foundation will be secured to the ground, and it would not move with movement (shrinkage and swelling) of soil.
Is black cotton soil good for foundation bed?
Under Reamed Piles in Black Cotton Soil It is the safest and economical option to construct the foundation in black cotton soil. In this type of foundations, the building or a house is anchored to the ground at the depth where the ground movement due to changes in moisture content is negligible.
What precautions should be taken for foundation in black cotton soil?
Precautions to be Taken
- The maximum load on black cotton soil should be limited to 5 tonnes/m2.
- Foundation should be placed at a depth where the cracks cease to extend.
- The main wall of the building must be provided with all round reinforced concrete ties or bands.
What is black cotton soil?
Black cotton soils are inorganic clays of medium to high compressibility and form a major soil group in India. They are characterized by high shrinkage and swelling properties. The Black cotton soils is very hard when dry, but loses its strength completely when in wet condition.
What are the causes of foundation failure?
Causes of foundation failure
- Sub-soil moisture movement.
- Unequal settlement of sub-soil.
- Unequal settlement of masonry.
- Lateral movement of sub-soil.
- Lateral pressure on the wall.
- Atmospheric action.
- Weathering of sub-soil due to tree and shrubs.
How can you tell black cotton soil?
The degree of expansion being more in the case of the former. Soil suction is another quality that can be used to characterise a soil’s affinity for water on its volume change behaviour. ADVERTISEMENTS: Black cotton soil is heavy clay soil, varying from clay to loam; it is generally light to dark grey in colour.
What are the characteristics of black cotton soil?
Table 3.1 Geotechnical properties of soil used
Properties Black Cotton Soil Maximum Dry Density (kN/m3) 15.16 Optimum Moisture Content 21.96 (%) Unconfined Compressive Strength(KN/m2) 84.92
What is the minimum depth of foundation in black cotton soil?
Minimum depth of foundation in black cotton soil:– The minimum depth of foundation in black cotton soil should be at least 1.5m, Foundation of footing trench is made wider than required and the extra width is filled with granular materials of loam & sandy soil to prevent intimate contact of black cotton soil with the …
How do you treat black cotton soil?
Black cotton soil is mixed with lime in varying proportions of 2%, 4%, and 6%. The lime-mixed soil is then cured for a duration of 3 days. The mixture is then oven-dried for 24 hours. The results of various tests carried out on black cotton soil mixed with varying percentages of lime are tabulated in Table 3.
What are the disadvantages of black soil?
Kharif in dependable rainfall areas (750mm-1250mm/yr) means considerable loss of water through runoff, considerable loss of nutrients, considerable soil erosion and loss of one crop. Black soil have low fertility and are poor in organic matter, nitrogen, available phosphorous and zinc.
What is an example of foundation failure?
One example of a famous foundation failure right here in Texas is South Padre Island’s Ocean Tower. However, construction of the tower couldn’t be completed because of foundation problems discovered in early 2008. The expansive soil beneath the tower began to compact, causing the building to sink and lean.
What happens when a foundation fails?
Spreading structural damage. When a foundation is weakened it causes a domino effect, putting excessive stress and strain on the structure it was designed to support.
What is black cotton soil good for?
It is mainly known as black cotton soil because this soil is most suitable for the cotton crop. Along with cotton, the soil is suitable for the cultivation of crops like groundnut, wheat, tobacco, chillies, and jowar.
What can grow on black cotton soil?
Cotton grows best in soil with a pH between 5.8 to 8.0. Yield decreases are usually not severe until the soil pH drops below 5.5 to 5.2 on sandy loam and silt loam soils respectively, or above 8.5 for western irrigated soils in the USA. When the soil pH falls beyond this range, soil amendments are recommended.
What are the three characteristics of black soil?
What are the characteristics of black soil?
- Clayey texture and are highly fertile.
- Rich in calcium carbonate, magnesium, potash, and lime but poor in nitrogen and phosphorous.
- Highly retentive of moisture, extremely compact and tenacious when wet.
- Contractible and develops deep wide cracks on drying.
What are the properties of black cotton soil?
The Black Cotton soils are highly compressible and have extremely low bearing capacity. The soils have great shrinkage and swelling characteristics. The shear strength of the soils is incredibly low. Black Cotton soil is also known as Expansive soils.
Why do we use black cotton soil?
The black cotton soil blocks crack on drying. Lime was used as a stabliser because of its abundance in block cotton soil areas and its low cost. It has a reactive aspect which alters the soil properties to meet the specific engineering qualities viz., volume, stability, wet strength etc.
What is the benefit of black soil?
Black soils get very high fertility credits. These are suitable for leguminous crops such as cotton, turning, and citrus fruits. Certain crops include maize, Jowar, millets, linseed, tobacco, safflower, sugar cane, vegetables, and so on. Black soils are rich in calcium, potassium, and magnesium, but low in nitrogen.
What points should be kept in mind while designing and constructing foundations in black cotton soil?
The maximum load on black cotton soil should be limited to 5 tonnes/m2. If there is a chance for water to come in contact with foundation, then the load should be limited to 4.9 tonnes/m2. Foundation should be placed at a depth where the cracks cease to extend. The minimum depth of foundation should be at least 1.5 m.
Which of the below is a major problem associated with black cotton soil?
Black cotton soil is one of the major issues in India. When exposed to variation in moisture content they undergo high swelling and shrinkage making it more complicated for engineering point of view. Lime is added to black cotton soil and stabilization takes place by virtue of pozzolanic reaction.
Is black cotton soil good for foundation?
So, Building a foundation in black cotton soil is so risky . The swelling and shrinkage of expansive soil cause the settlement of building. When dry, it is very hard, but it loses strength completely when wet. It results in the development of the cracks in house.
Is black soil good for construction?
The advantage of black soil is that it has high moisture content & also full of organic matter making it suitable to grow plantation crops as cotton, tobbaco ,sugarcane. The disadvantage is that it becomes sticky when wet, it becomes difficult for ploughing so it should be ploughed before raining.
What are characteristics of black cotton soil?
How to avoid foundation failure in black cotton soil?
The cracks thus formed are sometimes 15 to 20 cm wide and 2.5 to 4.5 m deep. Therefore necessary precautions need to be taken during construction to avoid any damage to building foundation. Following precaution should be employed during construction on black cotton soil. The maximum load on black cotton soil should be limited to 5 tonnes/m2.
What causes cracks to form in black cotton soil?
Black cotton soil has a tendency to shrink and swell excessively. When these type of soil come in contact with water, they swell and when becomes dry, it shrinks. This alternate process of swelling and shrinking results in the differential settlement of foundation which in turn causes cracks in building.
What should the depth of black cotton soil be?
In case the depth of black cotton soil is only 1 m to 1.5 m, then completely remove the entire black cotton soil and place the foundation below that depth. Try to avoid direct contact of black cotton soil with foundation material.