Methods of Soil Exploration - Soil mechanics - Civil Engineering

Methods of Soil Exploration

The methods available for soil exploration may be classified as follows:

• 1. Direct methods: Test pits, trial pits or trenches.
• 2. Semi-direct methods: Borings
• 3. Indirect methods: Soundings or penetration tests and geophysical methods

Test Pits

• This test is suitable only for small depths up to 3 m.
• For excavation of pervious soils at great depths, lateral supports or bracings are required.
• Useful for conducting field tests, such as plate bearing test.
• Test pits are usually made only for supplementing other
• methods or for minor structures.

Boring

• Boring is a method of making or drilling bore holes into the ground for obtaining soil or rock samples from known or specified depths.
• Depending upon the type of soil and the purpose of boring, the following methods are used for drilling the holes.

Types of Boring

1. Auger boring:

• This method is effective for subsurface investigations of highways, railways and airfields, where the depth of exploration is small.
• This method is, generally, used in soils which can stay open without casing or drilling mud, such as clays, silts, etc.

The main disadvantage of auger boring is that the soil samples are highly disturbed.

2. Wash boring:

• Used for exploration below ground water table for which the Auger method is not suitable.
• This method cannot be efficiently applied in hard soils, rocks and soils containing boulders.
• The hole is advanced by a combination of chop-ping action and jetting action.

3. Rotary drilling:

• It is used in clay sands and rocks. This method is not suitable if material contains large percentage of particles of gravel
• The hole is advanced by rotating a hollow drill rod which has a cutting bit at its lower end.

4. Percussion drilling:

• This method is suitable for making holes in rocks, boulders and other hard strata.
• It is useful for drilling holes in glacial tills containing boulders.
• In this method, a heavy chisel is alternately lifted and dropped in a vertical hole.

5. Core drilling:

• • This method is used for drilling holes and obtaining rock cores.
• • Diamond-cutting edge is used.

Spacing of Borings

• The spacing of borings or the number of borings depends on the type, size and weight of the proposed structure, variation in soil conditions.
• For an area of about 0.4 hectare, one bore hole or trial pit in each corner and one is the centre should be adequate.
• For smaller and less important buildings, one bore hole at the cente is sufficient.

Depth of Borings

Normally, the depth of boring should be one and half times the width of the footing below the foundation level.

Soil Sampling

• It is the process of obtaining soil samples from the desired depth at the desired location in a natural soil deposit to assess the engineering properties of soil.
• The devices used for the purpose of sampling are known as soil samplers.

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Limiting Moment of Resistance of a RCC Beam

The limiting Moment of Resistance of a RCC Beam is given as:

M_u,lim = 0.362Bf_ck X_u,lim (d-0.42 X_u,Lim)

Where symbols have their usual meaning

Further, the X_u,lim/d ratio depends on grade of steel being used, which is referred from the below table:

Grade of Steel	Xu,lim/d
Fe 250	0.53
Fe 400	0.48
Fe 500	0.46

Development Length of Steel bar in RCC

Development length:

(i) The calculated tension or compression in any bar at any section shall be developed on each side of the section by an appropriate development length or end anchorage or a combination thereof.

ϕ = Diameter of bar

τbd = Design bond stress = Permissible value of average bond stress

The value of bond stress is increased by 60% for a deformed bar in tension and a further increase of 25% is made for bars in compression.

In case of bundled bars in contact the development length is increased than that for individual bar by

1. 10% for two bars in contact
2. 20% for three bars in contact
3. 33% for four bars in content

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Moisture Contents of Soil

Field Capacity:

• It is the amount of water that remains in the soil after all the excess water at saturation has been drained out.
• when sandy soils are allowed to drain for approximately 24 hours after saturation, field capacity is reached.

Saturation Capacity:

• It is the soil water content where all soil pores are filled with water and water readily percolates or drains out from the root zone by gravitational force.
• The metric suction at this condition is almost zero and it is equal to the free water surface.

Permanent Wilting Point:

• Permanent wilting point is considered as the lower limit of available soil moisture.
• At this stage, water is held tightly by the soil particles that the plant roots can no longer obtain enough water to satisfy the transpiration requirements; and remain wilted unless the moisture is replenished.

Readily available moisture: 

• Readily available moisture is that portion of available moisture that can be most readily extracted by plants.

• In general, readily available moisture is approx 75 % of the available moisture.

Available moisture:

• The difference in water content of soil between field capacity and the permanent wilting point is called available moisture.

SC = Saturation capacity, FC = Field capacity, OMC = Optimum moisture content, PWP = Permanent welting point and UWP = Ultimate welting

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Types of Flow in Open Channels - Critical flow - Civil Engineering

Types of Flow in Open Channels

Depending upon the change in depth of the fl ow with respect to space and time, open channel flows can be classified as follows.

1. Steady and unsteady flow

• When the discharge rate is constant, the flow is a steady flow. The sectional areas at diff erent sections may be different. So mean velocity of fl ow at diff erent sections may also be diff erent

2. Uniform and non-uniform or varied flow

• When depth of flow is same at all sections, the flow is a uniform flow. This means that velocity is same at all sections. Water surface is parallel to bed in this case. In a non-uniform flow, depth of section and mean velocity is different at different sections. Water surface is not parallel to bed in non-uniform flows.
• A non-uniform or varied flow can be:
• 1. Rapidly varied flow (RVF)
• 2. Gradually varied flow (GVF)

3. Laminar flow and turbulent flow

• The laminar motion of fluid is characterised by the motion in layers (i.e., laminar), parallel to the boundary surface.
• The conditions favourable for laminar flow are:
• 1. High viscocity (m)
• 2. Low mass density (r)
• 3. Low mean velocity (V)
• 4. Small flow passage (L)

4. Subcritical flow, critical flow and super critical flow

Critical flow

• It is defined as the flow at which specific energy is minimum or the flow corresponding to critical depth is defined as critical flow.
• Relation of critical velocity with critical depth is: `v = (gh)^(1/2)
• Froude number is 1 for critical flow.

Tranquil flow or streaming flow or sub-critical flow

• When the depth of a flow in a channel is greater than critical depth (hc), the flow is said to be sub-critical flow.
• Froude number is less than 1 for sub-critical flow.

Torrential flow or shooting flow or super-critical flow

• When the depth of a flow in a channel is less than critical depth (hc), the flow is said to be sub-critical flow.
• Froude number is greater than 1 for sub-critical flow.

 

Also It can be categorized into various types based on different parameters such as flow velocity, depth, roughness of the channel bed, and characteristics of the fluid. Some of the common types of flow in open channels include:

1. Uniform Flow:

   In uniform flow, the flow velocity, depth, and other flow properties remain constant along the channel reach. This type of flow occurs when the slope of the channel, the roughness of the bed and banks, and the discharge remain constant. Uniform flow is often observed in long, straight channels with constant cross-sectional shape.

2. Non-Uniform Flow:

   Non-uniform flow occurs when the flow properties vary along the channel, typically due to changes in channel slope, cross-sectional shape, or hydraulic characteristics. This type of flow is common in natural channels where there are variations in bed roughness, channel geometry, or where there are hydraulic structures such as bends, constrictions, or expansions.

3. Steady Flow:

   Steady flow refers to a condition where the flow properties at any point in the channel remain constant over time. The flow rate, velocity, depth, and other parameters do not change with time. Steady flow can occur in both uniform and non-uniform flow conditions.

4. Unsteady Flow:

   Unsteady flow occurs when the flow properties change with time at a particular point in the channel. This can happen due to sudden changes in discharge, channel geometry, or other hydraulic conditions. Unsteady flow is often observed during flood events, rapid changes in upstream flow rates, or when hydraulic structures are operated.

5. Critical Flow:

   Critical flow occurs when the flow velocity equals the wave celerity, resulting in specific flow conditions known as critical depth. At critical flow conditions, small disturbances in flow depth or velocity can propagate upstream or downstream without any change in their amplitude. Critical flow is important in the design and analysis of hydraulic structures such as spillways and culverts.

6. Subcritical Flow:

   Subcritical flow occurs when the flow velocity is less than the wave celerity, leading to gradually varying flow profiles downstream. In subcritical flow, disturbances propagate upstream, and flow properties change gradually along the channel. Most natural river flows are subcritical.

7. Supercritical Flow:

   Supercritical flow occurs when the flow velocity exceeds the wave celerity, resulting in rapidly varying flow profiles downstream. In supercritical flow, disturbances propagate downstream, and flow properties change rapidly along the channel. Supercritical flow is often observed in steep channels, hydraulic jumps, and in high-velocity flow situations.

These are some of the fundamental types of flow in open channels related to soil and fluid mechanics. Understanding these flow types is essential for various engineering applications, including the design of drainage systems, irrigation canals, river management, and flood control structures.

Each type of flow with some examples to illustrate their characteristics:

1. Uniform Flow:

   Imagine a straight canal with a constant slope, width, and depth. If the flow rate (discharge) remains constant and there are no changes in the channel's cross-sectional shape or roughness, the flow properties (velocity, depth) will also remain constant along the length of the canal. This is an example of uniform flow. It's like water flowing steadily through a long, straight pipe at a constant rate.

2. Non-Uniform Flow:

   Consider a river that encounters a meander or a bend. As the river flows through the bend, the velocity and depth of the flow change. Near the outer bank of the bend, the flow is faster and deeper, while near the inner bank, the flow is slower and shallower. This variation in flow properties along the channel represents non-uniform flow. Another example could be a sudden constriction or widening of the channel, causing changes in flow properties.

3. Steady Flow:

   Think of a canal with water flowing steadily through it. The flow rate, velocity, and depth at any given point in the canal remain constant over time. As long as there are no sudden changes in the channel or upstream conditions, the flow properties do not fluctuate. This represents steady flow. It's like a faucet with a constant stream of water flowing out.

4. Unsteady Flow:

   Imagine a dam releasing water into a river at a variable rate over time. As the flow rate from the dam changes, the flow properties downstream of the dam also change. This fluctuation in flow properties with time represents unsteady flow. Another example could be a sudden flood event causing rapid changes in flow rates and depths in a river.

5. Critical Flow:

   Consider water flowing through a narrow channel at a certain velocity. If the flow velocity reaches a critical value, known as critical velocity, the flow becomes critical. At this critical velocity, the depth of flow reaches a specific value known as critical depth, and the flow properties exhibit unique characteristics. An example of critical flow is when water flows through a hydraulic jump, such as at the base of a spillway.

6. Subcritical Flow:

   Imagine water flowing gradually downstream in a river with a velocity slower than the wave celerity. In subcritical flow, small disturbances in flow propagate upstream, and the flow properties change gradually along the channel. This is typical of most natural river flows.

7. Supercritical Flow:

   Consider water flowing rapidly downstream in a steep channel with a velocity greater than the wave celerity. In supercritical flow, disturbances propagate downstream, and the flow properties change rapidly along the channel. An example of supercritical flow is the flow downstream of a hydraulic jump, where the flow abruptly changes from subcritical to supercritical.

These examples should help you grasp the concept of different types of flow in open channels and how they relate to soil and fluid mechanics

Open channel

An open channel is a conduit through which fluid flows with a free surface exposed to the atmosphere. Unlike a closed conduit, such as a pipe, which contains the fluid within its boundaries, an open channel allows the fluid to flow freely along an open path. Here's a more detailed description:

1. Fluid Flow: 

   An open channel typically carries liquids such as water, although it can also carry other fluids like oil or sewage. The flow can be driven by gravity, pressure differences, or other forces.

2. Free Surface: 

   One distinguishing feature of an open channel is that the surface of the fluid is open to the atmosphere. This means that the top surface of the flowing liquid is exposed to air, allowing interactions such as evaporation and gas exchange to occur.

3. Channel Geometry: 

   Open channels can have various shapes and sizes, including natural formations such as rivers and streams, as well as man-made structures like canals and flumes. The geometry of the channel, including its width, depth, and cross-sectional shape, influences the behavior of the flowing fluid.

4. Boundary Conditions: 

   Unlike closed conduits where the fluid is confined within solid boundaries, open channels have boundary conditions determined by the interaction of the fluid with the channel bed and banks. Factors such as bed roughness, bank slope, and vegetation can affect the flow characteristics.

5. Hydraulic Considerations: 

   The study of open-channel flow involves analyzing the behavior of fluids in these open conduits. Engineers and scientists use principles from fluid mechanics, hydraulics, and sediment transport to understand and predict the behavior of open-channel flows.

Examples of open channels include:

• Rivers and streams: Natural watercourses that flow along the Earth's surface.
• Canals: Artificial waterways constructed for irrigation, navigation, drainage, or flood control purposes.
• Ditches: Small channels dug to drain water from fields or convey runoff.
• Flumes: Structures designed to measure the flow rate of water in open channels.
• Culverts: Structures that allow water to flow beneath roads, railways, or embankments.

Understanding open-channel flow is essential in various engineering and environmental applications, including water resource management, flood forecasting, hydraulic structure design, and environmental protection.

 

 

Importance of flow in Engineering study

Different types of flow in open channels have varying levels of importance and utility in engineering applications, depending on the specific requirements and objectives of the project. Here's a breakdown of how each type of flow is commonly used in engineering:

1. Uniform Flow:

   • Usefulness: Uniform flow is often desirable in engineering applications where a steady, predictable flow rate is required, such as in irrigation canals, water supply systems, and open-channel drainage networks.
   • Example Application: Designing irrigation systems for agricultural fields often requires maintaining a constant flow rate to ensure uniform water distribution.

2. Non-Uniform Flow:

   • Usefulness: Non-uniform flow is prevalent in natural watercourses and can also be engineered to achieve specific objectives, such as mitigating erosion or controlling sediment transport.
   • Example Application: Designing riverbank protection measures to prevent erosion may involve considering non-uniform flow patterns near bends or constrictions.

3. Steady Flow:

   • Usefulness: Steady flow conditions are essential for many engineering analyses and designs, providing a basis for hydraulic calculations and stability assessments.
   • Example Application: Designing hydraulic structures like weirs or culverts often relies on steady flow assumptions to predict water levels, velocities, and pressure distributions.

4. Unsteady Flow:

   • Usefulness: Unsteady flow analysis is crucial for predicting and managing flood events, analyzing transient phenomena, and designing hydraulic structures subjected to variable flow conditions.
   • Example Application: Flood forecasting and emergency management systems use unsteady flow modeling to predict river behavior during storm events and develop evacuation plans.

5. Critical Flow:

   • Usefulness: Critical flow conditions are important in hydraulic engineering for understanding hydraulic jumps, designing spillways, and analyzing flow transitions.
   • Example Application: Designing spillways for dams involves ensuring that flow rates can be safely discharged without causing damage or erosion, which often requires consideration of critical flow conditions.

6. Subcritical Flow:

   • Usefulness: Subcritical flow is commonly encountered in natural watercourses and is relevant for various engineering applications, such as river habitat restoration, sediment transport modeling, and ecosystem management.
   • Example Application: Designing fish passages or habitat enhancements in rivers requires understanding how subcritical flow conditions affect water velocities and habitat suitability.

7. Supercritical Flow:

   • Usefulness: Supercritical flow conditions are essential for analyzing hydraulic jumps, designing high-speed channels, and optimizing energy dissipation in hydraulic structures.
   • Example Application: Designing energy dissipators for high-velocity flows in spillways or diversion channels involves optimizing flow conditions to prevent erosion and minimize turbulence.

In summary, each type of flow in open channels serves specific engineering purposes and is selected based on the project's objectives, constraints, and hydraulic considerations. Understanding the characteristics and applications of different flow types is essential for designing efficient and resilient hydraulic systems and structures.

Importance of Critical Flow study in Spillway design:

Critical flow conditions play a crucial role in the design and operation of spillways for dams. Spillways are hydraulic structures built to safely discharge excess water from a reservoir during periods of high inflow or flood events. Ensuring that flow rates can be safely discharged without causing damage or erosion is a primary concern in spillway design, and critical flow conditions are fundamental to achieving this objective. Here's a more detailed explanation of how critical flow considerations are relevant in spillway design:

1. Hydraulic Jump Formation: One of the key aspects of spillway design is managing the energy dissipation of the discharged flow to prevent erosion and downstream scour. When high-velocity flow discharges from a spillway into a lower-energy environment, such as a downstream channel or riverbed, a hydraulic jump typically forms. A hydraulic jump is a phenomenon where the flow transitions from supercritical to subcritical, resulting in rapid energy dissipation and turbulence. Critical flow conditions are crucial in determining the characteristics and stability of the hydraulic jump.

2. Energy Dissipation: Critical flow conditions are associated with the formation and stability of hydraulic jumps, which play a critical role in dissipating the excess energy of the discharged flow. By promoting the formation of hydraulic jumps, spillway designers can effectively dissipate the kinetic energy of the flowing water, reducing its erosive potential and minimizing downstream impacts such as scour and erosion.

3. Chute and Stilling Basin Design: Spillway structures often include features such as chutes and stilling basins, which are designed to facilitate the formation and stabilization of hydraulic jumps. Chutes are sloped sections that accelerate the flow, while stilling basins are typically flat or gradually sloping areas where the hydraulic jump occurs and energy dissipation takes place. Critical flow considerations inform the design of these structures to ensure that hydraulic jumps form reliably and safely under a range of flow conditions.

4. Flow Capacity and Discharge Efficiency: Critical flow conditions also influence the capacity and efficiency of spillways in discharging flow from the reservoir. By optimizing the design to promote critical flow and hydraulic jump formation, engineers can maximize the flow capacity of the spillway while minimizing the risk of erosion and damage downstream. This allows for the safe and effective management of flood events and reservoir operations.

In summary, critical flow considerations are essential in spillway design for dams to ensure the safe and efficient discharge of excess water while minimizing erosion and downstream impacts. By understanding and leveraging critical flow conditions, engineers can design spillways that effectively dissipate energy, prevent damage, and protect downstream communities and infrastructure during flood events.

Froude number and Critical Flow

The Froude number` (\(Fr\))` indeed plays a crucial role in determining critical flow conditions in open-channel flow. When the Froude number is unity `(\(Fr = 1\))` at a certain depth of flow, it indicates critical flow conditions. This critical flow condition is characterized by the flow velocity being equal to the wave celerity, resulting in a balanced relationship between gravitational and inertial forces. At this point, the flow is said to be at critical velocity, and the depth at which this occurs is referred to as the critical depth `(\(y_c\))`.

The Froude number is defined as the ratio of flow velocity to the square root of the product of gravity and flow depth:

`\[ Fr = \frac{V}{\sqrt{g \cdot y}} \]`

Where:
- `\( V \)` = Flow velocity
- `\( g \)` = Acceleration due to gravity
- `\( y \)` = Flow depth

When` \( Fr = 1 \)`, it signifies that the flow velocity is critical, meaning that the flow velocity is just sufficient to overcome the gravitational forces acting on the flow, resulting in critical flow conditions.

In summary, the Froude number being unity at a specific depth indicates critical flow conditions, where the flow velocity equals the wave celerity, and this depth is known as the critical depth. Thank you for pointing out the connection between Froude number, critical velocity, and critical depth in open-channel flow.

 

 

The concepts of subcritical, critical, and supercritical flow in open-channel hydraulics, along with explanations of celerity and energy:

1. Subcritical Flow:
- Definition: 

•  Subcritical flow occurs when the flow velocity `(\(V\))` is less than the wave celerity `(\(C\))`, resulting in a Froude number `(\(Fr\))` less than 1 `(\(Fr < 1\))`.

- Characteristics: 

• In subcritical flow, the flow depth `(\(y\))` is relatively deep compared to the wavelength, and gravitational forces dominate inertial forces. Waves propagate upstream in subcritical flow, and disturbances in flow properties gradually attenuate.

- Froude Number Relationship: 

• `\(Fr < 1\)`

- Example: 

• Steady flow in a natural river channel with moderate velocity, where the flow depth is greater than the critical depth.

2. Critical Flow:
- Definition: 

• Critical flow occurs when the flow velocity (\(V\)) equals the wave celerity (\(C\)), resulting in a Froude number (\(Fr\)) equal to 1 (\(Fr = 1\)).

- Characteristics: 

• At critical flow conditions, gravitational and inertial forces are in balance, and waves neither advance nor retreat. Critical flow often occurs at critical depth (\(y_c\)).

- Froude Number Relationship: 

• `\(Fr = 1\)`

- Example: 

• Hydraulic jump in a spillway, where the flow velocity transitions from supercritical to subcritical.

3. Supercritical Flow:
- Definition: 

• Supercritical flow occurs when the flow velocity `(\(V\))` exceeds the wave celerity `(\(C\))`, resulting in a Froude number `(\(Fr\))` greater than 1 `(\(Fr > 1\))`.

- Characteristics: 

• In supercritical flow, the flow depth `(\(y\))` is relatively shallow compared to the wavelength, and inertial forces dominate gravitational forces. Waves propagate downstream in supercritical flow, and disturbances in flow properties rapidly amplify.

- Froude Number Relationship: 

 `\(Fr > 1\)`
- Example: 

• Rapid flow over a hydraulic jump, where the flow velocity is high, and the flow depth is shallow.

Celerity:

• Celerity `(\(C\))` refers to the speed at which waves or disturbances propagate through a fluid medium. In the context of open-channel flow, wave celerity is the speed at which small disturbances in flow properties (such as depth or velocity) travel along the flow direction. It is calculated as the square root of the product of gravity `(\(g\))` and the flow depth `(\(y\))` for steady, uniform flow:

`\[ C = \sqrt{g \cdot y} \]`

Energy in Open-Channel Flow:
The energy associated with open-channel flow consists of two components:
- Kinetic Energy: 

• This is the energy associated with the flow velocity `(\(V\))`. It represents the energy per unit weight of fluid due to the motion of the fluid particles.

- Potential Energy: 

• This is the energy associated with the elevation of the flow. It represents the energy per unit weight of fluid due to the gravitational force acting on the fluid.

The total energy per unit weight of fluid, also known as specific energy `(\(E\))`, is the sum of kinetic and potential energies:

`\[ E = \frac{V^2}{2} + g \cdot y \]`

Where:
- `\( E \)` = Specific energy
- `\( V \)` = Flow velocity
- `\( g \)` = Acceleration due to gravity
- `\( y \)` = Flow depth

In critical flow conditions, the specific energy is minimized, leading to the formation of a hydraulic jump where excess kinetic energy is dissipated as turbulence and potential energy increases.

Understanding the relationships between flow velocity, celerity, Froude number, and energy is crucial for analyzing and designing open-channel flow systems and hydraulic structures. These concepts are fundamental to hydraulic engineering and play a significant role in various applications, including flood management, river engineering, and water resource development.

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Types of Shear Failure in foundation

Types of Shear Failure

1. General shear failure:

• It occurs in dense sand or stiff clay.
• A heave on the sides is always observed in general shear failure.
• The failure surfaces extend up to the ground level.
• 
  

2. Local Shear Failure 

•  It occurs in medium-dense sand or on in clay of medium consistency.
• Failure surface extend to the ground surface after considerable vertical movement.
• A heave is observed only when there is a substantial vertical settlement

Some characteristics of local shear failure are:

• 1. Failure is not sudden and there is no tilting of footing.
• 2. Failure surface does not reach the ground surface and slight bulging of soil around the footing is observed
• 3. Failure surface is not well defined
• 4. Failure is progressive
• 5. In the load-settlement curve, there is no well-defined peak
• 6. Failure is characterized by considerable settlement directly beneath the foundation
• 7. Significant compression of soil below the footing and partial development of plastic equilibrium is observed.
• 8. Well-defined wedge and slip surface only beneath the foundation.

Local shear Failure

Important Points

• In General Shear Failure  A well – defined failure pattern is observed.

3. Punching shear failure:

• It occurs in loose sand or soft clay.
• No heave is observed and failure surface does not extend upto the ground level.
• Only vertical movement of footing.

Criteria for General Shear Failure and Local Shear Failure

• 1. For a cohesionless soil, if  Φ is >36°, a general shear failure is likely to occur and, if  fΦ< 29°, local shear failure occurs.

• 2. If failure strain is less than 5%, general shear failure will occur and local shear failure occurs at a failure strain of 10–20%.

• 3. It relative density is greater than 70%, general shear failure would occur and if it is less than 35% local shear occurs.

• 4. If N > 30, GSF occurs and if N < 5, LSF occurs.

• 5. If e < 0.55, GSF occurs. If e > 0.75, LSF occurs.

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Ten Fun and Exciting Facts About Engineering - VK Study

Ten 'Fun and Exciting' Facts About Engineering

The snowboard was invented by an engineer?  

• With some engineering twists and turns along the way, the snowboard has become a marvel of geometry, chemistry, and biomechanics. Since the snowboard allows deft turns, ski manufacturers have quickly adopted some of the snowboard innovations, enabling skiers to turn with less effort.
• 
  
  
  
  

Engineers design running shoes for protection, performance, and comfort?  

• Engineers understand how much force travels from the ground through the shoe to the foot. Through the work of engineering, weight is distributed throughout the whole foot -- heel to toe.
• 
  
  
  
  

A civil engineer created the slippery part of the water slide?  

• A civil engineer designed a pumping system to circulate just the right amount of water to the flume. Without the right flow of water, there is no ride. Additionally, civil engineers have designed the slide to withstand the weight of people, the water, and even the force of the wind blowing on it.
• 
  
  
  
  

The launch and return of spacecraft, from the Apollo to the Shuttle, is a monumental engineering triumph?  

• The space program has greatly expanded the world's knowledge base. The technological advancement by engineers in energy, communications, materials, structures, and computers, have made space travel possible.

The Ferris Wheel is considered one of the greatest engineering wonders in the world?  

• The first Ferris Wheel was created by Pittsburgh, Pennsylvania engineer, George W. Ferris, in 1893. The wheel is supported by two 140-foot steel towers and connected by a 45-foot axle -- the largest single piece of forged steel ever made at that time.

Engineers make interactive television possible?  

• Engineers are involved in all aspects of interactive TV technology, from designing new cables, to creating new film emulsions, to engineering better sound quality. This technology allows viewers to select any program, film, or game from more than 500 channels.

Engineers play an instrumental role in the theme park industry? 

• Theme park engineers are involved in designing, building, lighting, and even controlling the crowd flow in theme parks around the world.

Companies and universities are using engineers to form the Virtual Reality and Simulation Initiative?

•  This technology applies computer simulation and visualization to 3-D modeling projects, such as virtual offices.

Bioengineers are creating a new and exciting medical technology?  

• This technology will utilize virtual reality to help surgeons reconstruct facial birth defects.
• Computer engineers, in conjunction with animators, have created special effects in movies such as "Jurassic Park," "Forrest Gump," and "Interview with the Vampire"?  Through "morphing" technology, images are digitally mastered to appear realistic.

Sources:
Baine, Celeste. The Fantastical Engineer. Farmerville, LA: Bonamy Publishing, 2000.

http://www.discoverengineering.org/
http://www.greatachievements.org/
http://www.inventors.about.com/

https://www.nspe.org/resources/press-room/resources/ten-fun-and-exciting-facts-about-engineering

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Euler's formula for long column- Strength of Material

Euler’s theory:

• This theory is valid only for long columns only.
• This theory is valid only when slenderness ratio is greater or equal to critical slenderness ratio.
• For any slenderness ratio above critical slenderness ratio, column fails by buckling and for any value of slenderness ratio less than this value, the column fails in crushing not in buckling.

Euler’s critical load formula is,

`e = (pi^2*EI)/l^2`

• Euler’s formula is applicable when, Crushing stress ≥ Buckling stress

For mild steel,

E = 2 × 105 N/mm2

σcr = 330 N/mm2

 λ ≥ 80 N/mm2

• When slenderness ratio for mild steel column is less than 80, the Euler’s theory is not applicable.

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Theories of failure - Strength of Material

Theories of Failure and shapes - Strength Of Material

Maximum Principal Stress theory or Rankine theory

Maximum Principal stress theory or rankine theory

Maximum principal strain theory st. venant's theory

st. venant theory or max principal strain theory

maximum shear stress theory

maximum strain energy theory

maximum strain energy theory 

maximum shear strain energy theory 

In short 

For brittle material

Theories of failure	Shape
Maximum Principal Stress theory  (RANKINE’S THEORY)	Square
Maximum Principal Strain theory  (St. VENANT’S THEORY)	Rhombus
Total Strain Energy theory  (HAIGH’S THEORY)	Ellipse

For Ductile material

Theories of failure	Shape
Maximum Shear Stress Theory  (GUEST AND TRESCA’S THEORY)	Hexagon
Maximum Distortion Energy Theory  (VON MISES AND HENCKY’S THEORY)	Ellipse

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Contra flexure, Shear Center and Max Shear Stress - Strength of Material

Contra flexure Point occur at Bending Beam - SOM

• Where Bending Moment changes sign on Bending Moment Diagram.
• In a bending beam, a point is known as a point of contra flexure if it's a location at which no bending occurs.
• In a bending moment diagram, it is the point at which the bending moment curve intersects with the zero lines.
• In other words where the bending moment changes its sign from negative to positive or vice versa.
• A point of contra flexure occurs in the overhanging beam.

Important Point

Section	τmax/τavg	τNeutral axis / τavg
Rectangular/square	3/2	3/2
Solid circular	4/3	4/3
Triangle	3/2	4/3
Diamond	9/8	1

Shear centre: 

• The shear centre is the point through which if the resultant shear force acts then member is subjected to simple bending without twisting.

Location of shear centre:

• (i) Shear centre generally does not coincide with the centroid of section except in special cases when the area is symmetrical bout both axis.
• (ii) Shear centre always lies on the axis of symmetry if exists.
• (iii) If there are two or more than two axis of symmetry exist, then shear center will coincide with point of intersection of axis of symmetry. In this case shear centre of area will be same as centroid of area.
• (iv) If a section is made of two narrow rectangles then shear centre lies on the junction of both rectangles.

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Permissible Limit of Solids in water for Concrete - IS 456:2000 - Vk Study Civil

Permissible Limit of Solids in Concrete - IS 456:200 - Vk Study Civil

According to Indian Standard Code of Practice 456:2000 Fourth Revision

Permissible limits for solids is shown in table below - Potable water is considered satisfactory for mixing Concrete 

Table 1. Clause5.4 

Permissible Limit for Solids in Water for Concrete

Solids	Tested as per	Permissible limit,Max
Organic	IS 3025 part 18	200 mg/l
Inorganic	IS 3025 part 18	3000 mg/l
Sulphates as SO2	IS 3025 part 24	400 mg/l
Chlorides	IS 3025 part 32	2000 mg/l for Plain Concrete
Chlorides	IS 3025 part 32	500 mg/l for Reinforced concrete
Suspended  Matter	IS 3025 part 17	2000 mg/l

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OPTIMUM COMPACTION WET & DRY - civil engineering vk

Optimum Compaction Wet and dry 

Dry of Optimum Compaction and Wet of Optimum compaction

Comparing between and dry and wet of optimum compaction

Properties changes with compaction	Dry optimum	Wet of Optimum
Structure after compaction	Flocculated (Random)	Dispersed (Oriented)
Water deficiency	More	Less
Permeability	More,  Isotropic	Less,  Isotropic
Compressibility
at low stress	Low	Higher
at high stress	High	Lower
Swelleability	High	Low
Shrinkage	Low	High
Stress strain Behavior	Brittle,high peak, Higher elastic modulus	Ductile, No peak, Lower elastic modulus.
Strength (undrained) as mould after saturation	High	Much lower
Construction Pore Water  Pressure	Low	High

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Sensitivity of the Soil related to shear strength in Laboratory test - Civil Engineering Study VK

SENSITIVITY OF SOIL - Soil Mechanics

Sensitivity elated to shear strength of soil in Laboratory test

•     It is defined as the ratio of undisturbed strength to that of the remoulded strength

•     Sensitivity = Undisturbed Strength / Remoulded Strength

Sensitivity of Soil

Sensitivity	Nature of Soil
1	Insensitive
1 to 4	Normal
4 to 8	Sensitive
8 to 16	Extra -Sensitive
>16	Quick

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TYPES OF TEST ON BRICKS - IS code 3495 - civil engineering study

TYPES OF TEST ON BRICKS - civil engineering study

Types of Tests On Bricks IS code 3495 

Following tests are conducted on bricks to determine its suitability for construction work.

• Absorption test
• Crushing strength test
• Hardness test
• Shape and size
• Color test
• Soundness test
• Structure of brick
• Presence of soluble salts (Efflorescence Test)

 

 WATER Absorption Test on Bricks - 3495 PART 2

• Absorption test is conducted on brick to find out the amount of moisture content absorbed by brick under extreme conditions. 

Apparatus:

• Oven, 
• Weight balance, 
• Tray

PROCEDURE

• Take any five random bricks from a lot of brick as a specimen.
• Dry the specimen in a ventilated oven at a temperature of 105°C to 115°C till it achieves considerably constant mass.
• Cool the specimen to room temperature and take its weight (M1).

Testing:

• When the specimen is completely dry, then immerse it in the clean water at the room temperature (27 ±2°C) for 24 hours.
• Remove the specimen from the water after 24 hours and wipe out water with a damp cloth and weigh the specimen.
• Take the weight (M2) of the specimen after 3 minutes of removing from the water.
• Points to be Taken Care:

• When you take M1, If the Specimen is warm while touching, it shall not be used for the test. Test it when you feel it cool.

Result:

• Note down the M1 and M2.
• Percentage of Water absorption of brick by its mass, after 24-hour immersion in cold water is calculated by the following formula
• (M2-M1)/M1*100

• For a good quality brick the amount of water absorption should not exceed 20% of weight of dry brick.

TYPE                         WATER ABSORBTION

FIRST CLASS         < 20%     OR 15% AVERAGE

SECOND CLASS     < 22.5%  OR 20% AVERAGE

THIRD CLASS         < 25%      OR 25% AVERAGE

 

Crushing Strength or Compressive Strength Test on Bricks - IS 3495 PART 1

• Place the specimen with flat face s horizontal and mortar filled face facing upwards between plates of the testing machine.
• Apply load axially at a uniform rate of 14 N/mm2 (140 kg/cm2) per minute till failure occurs and note maximum load at failure.
• The load at failure is maximum load at which the specimen fails to produce any further increase in the indicator reading on the testing machine.

•  Compressive Strength of Bricks = Maximum Load at Failure (N)/Average area of bed face (mm2)
• The average of result shall be reported.

• Crushing strength of bricks is determined by placing brick in compression testing machine. 
• After placing the brick in compression testing machine, apply load on it until brick breaks. 
• Note down the value of failure load and find out the crushing strength value of brick. 

compressive strength in N/mm2

>10.5     first class

7.5  second class

5.5  third class

 

compressive strength of common bricks should not be used if it is  less than 3.5N/mm2

 

 

Bricks Class Designation	Average compressive strength of Bricks
	Not less than (N/mm2)	Less than (N/mm2)
350	35	40
300	30	35
250	25	30
200	20	25
175	17.5	20
150	15	17.5
125	12.5	15
100	10	12.5
75	7.5	10
50	5	7.5
35	3.5	5

 

Efflorescence Test on Bricks - IS 3495 PART - 3

• A good quality brick should not contain any soluble salts in it. 
• If soluble salts are there, then it will cause efflorescence on brick surfaces.

Type	area affected
Nill Effloresence	Very Low
Slight	0-10%
Moderate	10-50%
Heavy	>50%
Serious	>50% + deposit are  present in powder forms Heavy Flakes

 

WARPAGE TEST - IS 3495 PART 4

• check the bricks for warpage of brick like concave and convex warpage with the help of glass or stell surface

 

Hardness Test on Bricks

• A good brick should resist scratches against sharp things. 
• So, for this test a sharp tool or finger nail is used to make scratch on brick.
•  If there is no scratch impression on brick then it is said to be hard brick.

for any doubt finger nail means

 

Shape and Size Test on Bricks (dimension test) - IS 1077

• Shape and size of bricks are very important consideration. All bricks used for construction should be of same size. The shape of bricks should be purely rectangular with sharp edges.
• Standard brick size consists length x breadth x height as 19cm x 9cm x 9cm.
• To perform this test, select 20 bricks randomly from brick group and stack them along its length , breadth and height and compare. 
• So, if all bricks similar size then they are qualified for construction work.

 

Dimension Test

Dimension should not greater than below value Length -19×20= 380 ± 12 cm Breadth - 9×20 = 180 ± 6 cm Height - 9×20 = 180 ± 6 cm here 20 indicate 20 no of bricks used in sample

 

Color Test of Bricks

• A good brick should possess bright and uniform RED color throughout its body.

 

Soundness Test of Bricks

• Soundness test of bricks shows the nature of bricks against sudden impact.
• In this test, 2 bricks are chosen randomly and struck with one another. 
• Then sound produced should be clear bell ringing sound and brick should not break. 
• Then it is said to be good brick.Soundness Test of Bricks

 

Structure of Bricks

• To know the structure of brick, pick one brick randomly from the group and break it. 
• Observe the inner portion of brick clearly. It should be free from lumps and homogeneous.Structure of Bricks

 

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What are the properties of high density concrete in dry state?

High density Concrete

• 1. High density concrete is those concrete which have best packaging with the presence of finest to coarse particles of substance of concrete which gives best denseness of concrete.

• 2. It is achieved by using the knowledge of concrete with skills.

• 3. It is achieved by using of some admixtures or additionally use of special ingredients of concrete

• 4. For making high density concrete first step is choosing the right materials for it.

• 5. It requires heavier aggregates with specific gravity of 3.5 to 4.which give

• 6. Some Natural aggregates used in High dense concrete is Limonite, Haematite, Magnetite,Barite etc.

• 7. like finest grade of cement.small to higher proportion of fine to coarse aggregate which gives better packaging of concrete and most important part is using of water reducing agent which removes extra part of water some plasticize,skilled labor who knows how to mix it.

• 8.for mixing or preparation first coarsest aggregate is spread on floor then finer particles are spread over it in order of their degree and after that mix thoroughly till homogenous mix obtain after that water and plasticizer are used.

• 9. now we ready for making high density concrete 

• 10. for next steps we want some form-work and compaction instruments which imparts the density of concrete. during these process some precautions are taken like taking the precaution for not having segregation, bleeding, too much water, honey combing, too much time taken for preparing and using of green concrete etc.

How to know what is high density concrete

• For knowing what is high density concrete and where is it use and how it works we must know all about the Properties of high dense Concrete.

Properties of high density Concrete

1. It is highly durable.

2. It Have highest toughness. 

3. It is impermeable.

4.Sulfate resisting properties, 

5. It is heavier than other concrete work

6. It have very high mechanical properties as strength and durability.

• Strength of concrete at 28 days - greater than 40MPa
• coefficient of thermal expansion is almost twice than normal concrete
• shrinkage is about 1/4 to 1/3rd of normal concrete

7. High Shielding properties from all radiations and other mechanical forces.

8. It reduces the intensity of neutrons, gama and other rays by absorbing its particles and gives shield against radiation on nuclear projects. and shield are electronic instruments from high temperature and radiations.

9. Ease of Constructions due to its process of manufacturing.

10. weight of High density concrete is very high in the range of 3360 to 3900 kg/m3

11. It is Highly Dense - 

• Higher the density of concrete higher the absorption of radiation

12. Absense of air voids

For more you should read on following link page

Types and Properties

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CIVIL ENGINEERING SUBJECTS

LIST OF ALL SUBJECTS RELATED TO CIVIL ENGINEERING STUDY

We provide list of all the civil engineering subjects which is essentials and without it no one never be a civil engineering.... Students who study or will study in college still reads these following subject.

• Engineering Mechanics

• Environmental Engineering

• Soil Mechanics

• Concrete Technology

• Reinforced concrete construction (RCC)

• Strength of Material (SOM)

• Structural Steel Engineering

• Structure Analysis

• Solid Waste Management

• Structural Engineering Design

• Fluid Mechanics

• Irrigation Engineering

• Surveying or Survey Engineering

• Engineering Mathematics 

• Geo-technical Engineering

• Applied Physics

• Engineering Chemistry

• Elements of Electrical Engineering

• Engineering Drawing and Planing

• Building Materials

• Building Construction

• Foundation Engineering

• Construction Management

• Waste Water Management

all the above subjects and its syllabus which is most important related to civil engineering exams and practices are discussed later with another posts

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Irrigation and Its Methods in Civil Engineering Study

Irrigation and Its Methods for Engineering Purpose

Irrigation

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CHAPTER HIGHLIGHTS

☞ Introduction
☞ Types of irrigation
☞ Methods of irrigation
☞ Water requirements of crops
☞ Irrigation efficiencies
☞ Irrigation requirements of crops
☞ Crop seasons
☞ Water logging and drainage

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GENERAL UNDERSTANDING

The following are the main concerns on irrigation:-

1 How to apply

• i.e. what should be the method of irrigation: Border Flooding method, furrow irrigation method,sprinkler irrigation method, drip irrigation method etc.

2.How much apply

• i.e. how much moisture the soil can hold in its pores or Moisture holding capacity of Soil.

3.When to apply

• i.e. when has the soil moisture level depleted to 50 to 60% of moisture holding capacity and when is the time to irrigate. In other words, what should be the frequency of irrigation.

DEFINITION OF IRRIGATION

Irrigation may be defined as the science of artificial application of water to the land, in accordance with the crop requirements throughout the crop period for full-fledged nourishment of the crops.

CROP YIELD AND PRODUCTION IN IRRIGATION

The crop yield from irrigation is expressed as quintal/ha or tonnes/ha. The productivity of the crop is expressed as crop yield per mm of water applied.

Increase of yield or Productivity can be achieved by following methods in IRRIGATION

• Land shaping or land leveling
• Suitable crop rotation and crop planing
• Using high yielding varieties of seeds
• Using chemicals and Fertilizers
• Suitable methods of Irrigation adopted.
• Lining of canal and other bodies.
• Drainage of Irrigated land by surface and subsurface drainage.

ADVANTAGES AND DISADVANTAGES OF IRRIGATION

Advantages of Irrigation

Direct advantages of IRRIGATION

• Increase in food Production
• Protection against drought
• Revenue generation
• Mixed Cropping

Indirect advantages of IRRIGATION

• Power generation
• Transportation
• Ground water table
• Employment

Disadvantage of Irrigation

• Water logging due to excess irrigation
• Ground water pollution due to seepage of nitrates resent in soil as fertilizer etc.

Overall Benefits of Irrigation

• 1. Increase in food production
• 2. Protection from famine
• 3. Cultivation of cash crops
• 4. Eliminating mixed cropping
• 5. Addition to the wealth of the country
• 6. Generation of hydroelectric power
• 7. Domestic and industrial water supply
• 8. Inland navigation
• 9. Canal planting
• 10. Improvement of ground water storage

Effects of Irrigation

• 1. Breeding places of mosquitoes
• 2. Water logging
• 3. Damp climate

TYPES OF IRRIGATION PROJECTS

Irrigation projects	Irrigation Potential (CCA)	Cost of Project
Major	>10000 ha	>5 crores
Medium	2000 - 10000 ha	>.5 to 5 crores
Small	less than 2000 ha	>.25 to .5 crores

TYPES OF IRRIGATION

Types of Irrigation
Flow Irrigation					Lift Irrigation
Perennial Irriagation	Direct Irrigation	Inundation Irrigation	Storage Irrigation	Combined Storage and Diversion scheme	(well irrigation)
(The water required is supplied to the crop through out the year)	(diversion scheme) (or) (River canal irrigation) (Water is directly diverted to canal without storing)	(The irrigation is carried out by deep flooding)	(storage scheme) (or) (Tank irrigation) (Water is stored in dam (or) reservoir)	(Water is stored in dam (or) reservoir and then diverted to canal)	(Subsoil water is lifted to the Surface and conveyed to agricultural fields.)

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• 1. Surface irrigation.
• 2. Subsurface irrigation.

Surface irrigation

Surface irrigation can be further classified into 

a. Flow irrigation.- i.e. flow under the action of gravity
b. Lift irrigation.- i.e. water is lifted by pumps etc for supplying water.

Flow irrigation can be further sub-divide into

x. Perennial irrigation - water is supplied on whole base period or continuous required water supply.

y. Flood irrigation - uncontrolled irrigation or soil is kept submerged and thoroughly flooded with water.

Sub-surface irrigation

Sub-surface irrigation may be divided into two types.

a. Natural sub-irrigation - water leakage from channels etc.

b. Artificial sub-irrigation - by artificial mechanism.

METHODS OF IRRIGATION

• Free flooding method
• Border flooding method
• Check flooding method
• Basin flooding method
• Furrow irrigation method
• Sprinkler irrigation method
• Drip irrigation method

Free flooding or Ordinary flooding

• Also called wild flooding as the movement of water is not restricted.
• Initial cost of land preparation is low but labour requirement are usually high.
• Water application efficiency is also low
• Suitable for close growing crops, pastures, etc. particularly where land is steep.
• It may be used on rolling land or topography irregular where borders, checks, basins,furrows are not feasible.

Border flooding

• Land is divided into no of strips, separated by low levees called borders.
• Each strip is of 10 to 20 metres in width and 100 to 400 m in length.
• Water flows slowly toward the lower end and it infiltrates into the soil as it advances.
• When water reaches the lower end of the strip the supply is turned off.
• Size of supply ditch depends upon the infiltration rate of the soil and width of border strip.
• This method is most popular.

Check Flooding

• Similar to ordinary flooding except water is controlled by surrounding checked area with levees.
• Close growing crops such as jowar or paddy are preferred.
• Deep homogeneous loam or clay soils with medium infiltration rates are preferred
• Suitable for both more permeable and less permeable soils 
• less time required for highly permeable soil and vice-versa.

Basin flooding

• Special type of check flooding and adopted specially for orchard trees.
• One or more trees are generally placed in the basin and surface is flooded.
• Shape of basin can be square, rectangular, circular or it may be irregular.
• Flatter the land surface, easier it is to construct the basin
• Coarse sands are not suitable for basin irrigation Because of high percolation losses.
• Size and shape of basins are mainly determined by the land slope. the soil type, the available stream, the required depth of irrigation water to the applied.

Furrow Irrigation or Furrow method

• Water is applied to the land to be irrigated by series of furrows
• Furrows are small, parallel channels, made to carry water for irrigating the crops.
• Infiltrated water spreads laterally between furrows.
• The crops are usually grown on the ridges between the furrow.
• One half to one fifth area of land is wetted.
• Suitable for wide range of soil types, crops and land slopes.
• Preferred on uniformly flat or gentle slopes which should not exceed .5%.
• furrows can also be similar to long narrow basin.
• labor requirement and land preparation is reduced as compare to flooding.

Sprinkler irrigation method

• In the form of spray over crop through pipe system.
• Known as overhead irrigation.
• Used for all types of crops except rice and jute.
• Used for all types of soils except very heavy soils with low infiltration rates.
• Beset suited for very light soils as deep percolation losses are avoided.
• This suit undulating topography and hence land leveling is not necessary.
• This methods is used mainly by cultivation of tea coffee and vegetables in out country.

Notes :- 

• for rice and jute standing water is required
• light soils are sandy and silty with very little clay. generally easy to work, warm up quickly, dry out rapidly.

Drip irrigation method

• Latest method.
• Popular in areas with acute scarcity of irrigation water and salt problems.
• Water and fertilizer is slowly and directly applied to the root zone of the plants in order to reduce losses due to evaporation and percolation.
• Also known as Trickle irrigation
• Help of specially designed emitter and drippers.
• Centrifugal pump is best suited for this method.
• Best suited for row crops such as tomatoes, grapes,corn,citrus,melons,fruits,cauliflower,cabbage etc.

Water Requirements of Crops

• The water holding capacity of soil is the main characteristics which has to be taken into account for ideal irrigation. Thus the following topics deal with the water holding characteristics of soil and the parameters which help to measure it.

Classes of Soil Water

1. Saturation capacity:

• The amount of water required to fill the pore spaces between soil particles by replacing all air held in pore spaces. It is also called maximum moisture holding capacity or total capacity.

2. Field capacity:

• It is the moisture content of soil after free drainage has removed most of gravity water. It is the upper limit of water content available to plant roots.

3. Permanent wilting point:

• Plants can no longer extract sufficient water from the soil for its growth.This is also known as wilting coefficient. If the plant does not get sufficient water to meet its needs,it will wilt permanently. For most of the soils wilting coefficient is about 150% of hygroscopic water.

4. Temporary wilting:

• This will take place on a hot windy day but plant will recover in cooler day.

5. Ultimate wilting:

• At ultimate wilting point the plant will not regain its turgidity even after addition of sufficient water to the soil and the plant will die. It is similar to hygroscopic coefficient.
• Hygroscopic coefficient = 2/3(permanent wilting point)

6. Available moisture:

• Moisture content of soil between field capacity and permanent wilting point.

7. Readily available moisture:

• 75% of available moisture is known as readily available moisture. Readily available moisture depth, d w = S × d (Field capacity – Optimum moisture) = Sd (FC – OM)

8. Moisture equivalent

• = Field capacity = (1.8 to 2) × (Permanent wilting point) = 2.7 (Hygroscopic coefficient)

9. Available moisture depth

• = (d w ) = Sg × d × [F C – w C]
• Where
  S g = Apparent specific gravity of soil
  F c = Field capacity
  w c = Wilting coefficient.

10. Frequency of irrigation

• f= dw/Cu
• Where dw = Readily available moisture depth
• cu = Evapo-transpiration loss

11. Base period:

• Total time between first watering done for preparation of land for sowing of crop and last watering done before its harvesting is called base period.

12. Crop period:

• Total time elapsed between sowing of crop and its harvesting is called crop period.

13. Duty (D):

• It is the area of land in hectares which can be irrigated for growing any crop if one cumec of water is supplied continuously to the land for entire base period of crop.

14. Delta (∆):

• Total depth of water over the irrigated land required by a crop grown on it during the entire base period of the crop.
• Crop Average = Delta (cm)
• Rice = 120
• Wheat = 37.5
• Cotton = 45
• Tobacco = 60
• Sugarcane = 90

`Duty  = 8.64 × Base period / Delta`

B = Base period in days

∆ = delta in metres.

15. Consumptive use or evapotranspiration:

• It is thetotal loss of water due to plants transpiration and evaporation from the land.
• Lysimeter is used to measure Cu .One cumec day = 8.64 hectare metres, it is a volumetric unit.
• It is total volume of water supplied@ 1 cumec in a day.

Irrigation Efficiencies

1. Water conveyance efficiency ( η c ):

• It is the ratio of quantity of water delivered to the field to the quantity of water diverted into the canal system from reservoir.

2. Water application efficiency ( η a ):

• It is the ratio of quantity of water stored in the root zone of plants to the quantity of water delivered to the fields.

3. Water use efficiency ( η u ):

• It is the ratio of quantity of water used beneficially including the water required for leaching to the quantity of water delivered.

4. Water storage efficiency [ η s ]:

• Ratio of quantity of water stored in the root zone during irrigation to the quantity of water needed to bring water content of the soil to field capacity.

Irrigation Requirements of Crops

1. Consumptive irrigation requirements (CIR):

It is the amount of water required to meet the evapotranspiration needs of a crop CIR = Cu − Re

Re = Effective rainfall

2. Net irrigation requirement (NIR):

Amount of irrigation water required to be delivered at the field to meet evapotranspiration and other needs such as leaching NIR = Cu – Re + Le

Where, L e = leaching

3. Field irrigation requirement

`(FIR) = NIR/ ηa`

4. Gross irrigation requirement

`(GIR) = FIR / ηc`

5. Paleo irrigation:

• It is the watering done prior to sowing of crop.

6. Kor watering:

• The first watering after the plants have grown few cm high is known as kor watering

7. Outlet factor:

• Duty of water at canal outlet is known as outlet factor.

8. Gross command area (GCA):

• Total area which can be irrigated by canal system if unlimited quantity of water is available is known as gross command area.

9. Culturable command area (CCA):

• The portion of the GCA which is culturable or cultivable.
• CCA = GCA – Uncultivable area

10. Culturable cultivated area:

• That portion of CCA which is actually cultivated during a crop season.

11. Capacity factor:

• Ratio of mean discharge of canal for a certain duration to its maximum discharge capacity.

12. Time factor:

• Ratio of number of days the canal has actually run during a watering period to the total number of days of the watering period.

Crop Seasons

1. Kharif crops:

• These are the crops which are sown in the month of April and harvested in the month of September. Examples: Rice, maize.

2. Rabi crops:

• These are the crops which are sown in October and harvested in March. (Also called winter crops) Examples: Wheat, tobacco.

3. Perennial crops:

• These are the crops for which the water is supplied throughout the year. Example: Sugarcane

4. Hot weather crops:

• These are the crops which are grown between Kharif and Rabi season, i.e., from February to June.

5. Summer crops:

• The hot weather crops and Kharif crops are combinedly called as summer crops.

6. Dry crops:

• Crops grown without irrigation and depend only on rainfall for survival.

7. Wet crops:

• The crops which require irrigation are known as wet crops.

Water Logging and Drainage

 

Water Logging

• It is the condition in which there is excessive moisture in the soil making the land less productive.
• The depth of water table at which it tends to make the land, water logged, depends on the
• 1. height of capillary fringe and
• 2. type of crop.

 

Causes of Water Logging

• 1. Excessive rainfall in the area
• 2. Flat ground profile
• 3. Improper drainage of surface run-off
• 4. Excessive irrigation

 

Effects of Water Logging

• 1. Causes anaerobic conditions near roots of plants.
• 2. Causes salinity of soil.
• 3. Causes growth of wild aquatic plants.
• 4. Lowers the soil temperature which effects the activities of bacteria.
• 5. It makes cultivation difficult as the water logged areas cannot be easily cultivated.

 

Water Logging Control

• 1. By providing efficient under drainage
• 2. By preventing seepage from reservoirs
• 3. By introducing crop rotation
• 4. By improving natural drainage of area
• 5. By introducing lift irrigation

 

Drainage

• It is the means of preventing land from getting water logged as well as to receive the land already water logged.

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