Civil Site Knowledge

What Is A Septic Tank? | Causes Of Failure | Advantages | Disadvantages

A septic tank is a chamber built of concrete, fiberglass, or polythene and is placed beneath the ground or underground.

What Is A Shear Wall? | Where it is needed the most?

A shear wall is a vertical structural member constructed to resist lateral forces of wind and seismic (earthquake) activity.

Chaining/Taping On Level Ground And Sloping Ground

The process of measuring the distance between any two points by using a chain is called chaining. If used tape instead of a chain then the process is called taping. Generally, we use tape nowadays due to its accuracy and portability. Chains help us to measure the distance between any two points, which ultimately means it supports us to measure the area of any ground, as the surface of grounds can be divided into many points.

Level grounds are also called uneven ground which is the contradiction of plane surface. It is a very cozy job to measure distance on a plane surface. But it gets complexed when the surface is uneven or on a certain level.

Instruments required for taping on level grounds are:

· Tape

· Ranging Rod (minimum 3)

· Peg

· Arrows (minimum 10)

If we want to measure the distance between two points AB. Let us consider the distance between A and B is L. And let L be the distance greater than the total length of the tape. If we are using tape of 30m then L is greater than 30m. So to measure L, we divide L into different segments. One segment could be in the range of 10-20m.

Even though we have 30m tape, we do not utilize the whole tape and only use a maximum of 20m. It is because if we use the whole 30m of the tape then there is a sagging effect. This means the tape does not get stretched to its required potential as its own weight causes it to sag. So we use a maximum of 20m of our tape to measure distance in each segment.

Then the procedure to measure distance on level grounds are:

Step 1: Install peg in the two endpoints. Here, we install one peg at

mark A and another peg at mark B.

Step 2: Fix two ranging rod at the end stations (points) i.e. one rod at

station A and another at station B.

Step 3: 1^st person stands about 2m behind the ranging rod at the station

A. 2^nd person stands at point B with the ranging rod. 3^rd person carries a ranging rod and moves forward from point A. 3^rd person starts to move the ranging rod to and fro under the command of 1^st person until the ranging rod lies on line AB and mark that point as C. Then the third person installs an arrowhead at point C.

The ranging rod will lie on the line AB when this ranging rod will coincide or blocks the ranging rod at B when viewed by 1^st person at station A.

Step 4: This process is repeated several times and required

intermediate points are determined. Let us divide AB into 3 segments pointed as points A, C, D, and B.

Step 5: Now, we use the tape or chain. For this, we have preferred

tape. We measure the distance between those three segments using tape each segment at one time, starting from point A.

Important Tip: While measuring any segment, say AC we measure or use tape from the nearest ground level as possible. It is done to avoid the sag effect or the inaccurate measurement of distance due to the inclined installation of the ranging rod. Also, while measuring, we should make sure that we measure the perpendicular distance between any two points.

Let the recorded measurements of AC, CD, and DB be L1, L2, and L3 respectively. And consider them as forward length.

Step 6: Now, again we start to measure different segments. But this

time we start to measure from point B. For this, again we divide the length AB into several segments. But this time we start from point B. Now, the 1^st person starts at point B and starts ranging. Let the intermediate points be D’, and C’.

We cannot use the previous intermediate points C and D while measuring from B, because we have to provide an independent check. If we had used points C and D, then it would provide us a dependent check and it would not make sense as we just measured the same distance segments two times.

Let the recorded lengths of BD', D'C', and C'A be L1' L2' AND L3' respectively. Consider those lengths as backward lengths.

Hence, total forward length(L)= L1+L2+L3

Total backward length(L’) =L1’+L2’+L3’

Average length= (L+L’)/2

Discrepancy= │ L – L’ │

The average length is the required measurement of length L, only if the precision is greater than or equal to (≥) 1 in 2000. If precision does not lie within this range, then the whole process is carried out again, unless a precision is obtained. Then only the required length is obtained.

Precision=1/average length/discrepancy

What do you mean by precision is 1 in 2000 (1/2000)?

The precision is 1 in 2000. This means while measuring the distance of 2000m, the discrepancy should only be 1m. Or, while measuring the distance of 2000m, the fluctuating value (or change in value) between forward and backward length should only be a maximum of 1m.

Chaining/Taping on sloping ground

By the direct method,

The whole process is the same as above i.e. taping on level ground. For measuring the sloping ground, the precision should be 1 in 1000.

Here the distance between point A and B is L1+L2+L3 while starting from point A. Again we determine the different length segments initiating from point B. Finally, we check the precision using discrepancy and average length and obtain the required measurement.

Important Tip:

Q. How do we know the measurement reading we have taken is perpendicular value or exactly straight or accurate measurement?

Ans: suppose from the above figure, we have starting end of the tape is at A and we have to take perpendicular measurement with ranging rod at C. For this we fix, starting end of tape at A and lengthen tape towards the ranging rod at C. To obtain an exactly perpendicular measurement, we move the tape's end to and fro (or up and down) at in ranging rod at C until the shortest distance is measured at the tape in point C. This shortest distance in the tape is the exactly perpendicular measurement.

Q. What is the least count of engineering tape?

Ams: The least count of engineering tape is 2mm or 0.002m. Hence, while taking reading from tape in the field the third digit after the dot should always be a even number. For eg: 5.314m, 7.798m, etc

Here our reading is 5.314 means our length is 5.3m, 1cm and 4mm.

What Is Curing Of Concrete | Importance | Purpose | Methods

Curing of Concrete is the phenomenon of maintaining the presence of moisture in freshly placed concrete to complete the hydration process for getting the required potential strength of the concrete.

Why Is Curing of Concrete Important?

Concrete is the mixture of cement, sand, aggregate, and water in specific proportions. Concrete is the most prominent material required to build any structure, and within the concrete, cement is the most significant material. Cement acts as a binding material. Without cement, the concrete won't even settle initially.

In concrete, the water-cement reaction is exothermic. When concrete is placed in the desired place, the heat produced in the concrete due to the water-cement reaction evaporates the water in the concrete and causes moisture loss. So, to avoid the lack of water in the reaction of concrete, water is sprayed on the surface of the concrete.

If water is not sprayed then there will be a lack of moisture, due to which cement-water reaction does not occur anymore, causing a lack of formation of the required strength of concrete.

So, the purpose of curing concrete is listed below:

To maintain moisture in the slab so that concrete continues to gain strength.

To enhance strength, durability, permeability, etc. in the concrete.

Curing helps in avoiding shrinkage, cracks in the concrete.

How long does it take to completely cure the concrete?

The complete curing process might take almost a month depending upon the surrounding weather and temperature, ratios used in the concrete mix, placement, and finishing techniques.

After 24 to 48 hrs, the concrete settles initially and the formworks can be removed. A person can even walk on the surface of the concrete after initial settlement.

After 7 days, the formation of desired strength of concrete is partially completed. People can walk and ride vehicles at this stage above the concrete.

After 28 days, the concrete attains a strength of 90 to 95% of its true potential. The remaining 5% might take a year to complete depending upon the materials used.

Different methods of Curing the Concrete

Wet coverings: With the help of wet jute bags or hessian cloth placing at the top of the concrete provides continuous moisture in the concrete. Especially while curing concrete of staircase, we use this method.
Waterproof paper or plastic fil seal: By covering the structure with the help of a plastic sheet, the passing of air is avoided which further prevents the evaporation process in the concrete, and moisture presence is maintained.

Spraying: This is one of the easiest methods of curing concrete. We simply spray the water through the pipe in the concrete placement area in this method.
Ponding: Mainly in the structures like slabs, after the concrete is laid. It initially takes 24 to 48 hrs for initial settlement. After initially settled, water is maintained at the surface of the concrete of very low depth. This continuously provides moisture in the concrete.

Why Cantilever Beams Are Made Trapezoidal?

A cantilever beam is a horizontal, rigid structural component that is supported at one fixed end and free at the other. They bear load in the form of bending. When a horizontal force is applied to the free end in the cantilever, it transfers those forces to the column through the fixed end and then to the foundation and ultimately to beneath the ground, where those forces are re-distributed among the soil.

We often observe cantilever beam below our balcony, bridges, etc.

Cantilever beams are made trapezoidal because of the bending moment acting on them. We should provide more depth to the structure where there is more bending moment acting upon. Otherwise, the structure will collapse due to more bending or turning effect of the structure.

1. 1. When a point force is acted upon a Cantilever beam

Let us consider a weight (W) is acted upon a free end of the cantilever beam of length (l).

For equilibrium, vertical forces are zero

∑Fy =0

+w-Ry=0

Ry=W

W at free end tends to bend the beam downward. So, there is production of maximum bending moment in the fixed or support end. Hence to counter the maximum bending moment produced in the fixed end, more depth is provided in fixed end than in free end. Otherwise, the beam will collapse or shear off.

From bending moment diagram as well, maximum bending moment (Wl) is acted upon the fixed end of the cantilever beam and zero bending moment is acted on the free end of the cantilever beam even though weight is applied to the free end of the beam.

Since the bending moment is maximum at the fixed end, more depth should be provided in the fixed end to avoid collapse of the structure due to the turning effect and minimum depth should be provided at the free end of the cantilever beam.

2. When a uniformly distributed load is acted upon the beam

For uniformly distributed load as well, the maximum bending moment(WL^2/2) will be acted upon on the fixed end of the beam. So, the depth should be maximum on the fixed end of the cantilever beam.

We often see beams of rectangle shape as well. If we prefer on putting rectangle beams, then we must construct a beam of relatively more depth. Otherwise, due to the dead load on the free end, there is a high chance of collapse. Also, trapezoidal beams are more economical than rectangular beams. Rectangle beams only increases the cost of project. It does not have any significance.

Centering And Shuttering

Centering and shuttering are two of the ways to prepare formwork in the construction area. Formwork refers to all the arrangements done to support the fresh concrete mix until the strength is sufficient to support its own weight. Formwork is also known as temporary work. Formwork significantly helps us to determine the geometry, size, and shape of the masonry area.

Centering

Centering is usually the formwork, made generally from plywood, which is used to support the masonry on an arch or barrel vault before the masonry is placed and before it gains enough strength so that it can support its own weight. Centering will firmly support the masonry and form the curvature or shape and size of the arch or the vault. Centering can be reused to build multiple arches, depending upon the structure.

Centering supports the horizontal surfaces like slab, beam, chajja.

Centering can also be done using mild steel centering plates but we generally use plywood.

Equipment used for centering:

• Wall form and accessories

• Adjustable prop

• Telescope span

• Steel couplers

• Tie rod

• Wedge clip

• Single clap

• Step centering

• Centering plates

• Cup lock system

• Column farma

• Bracing and tying-in

• Tabular scaffolding

• Scaffolding propex

• Joint pin

• Scaffolding plank

• Fixed base plate

• Sikanja clamp

• Plane vibrator

• Needle vibrator

• Table vibrator

• Screen board vibrator

• Adjustable stirrup head

How is centering done?

For minor works, mud masonry is constructed for centering to match with the inner soffit of the arch or barrel vault, then plastered. Later, this masonry is dismantled when the arch is constructed and curved.

We generally use timber wood or steel for centering since, it is simplest, cheapest, easy to dismantle, and can be used several times. A plank with the horizontal bottom is selected whose width is normally 10cm, then it is supported on vertical timber posts called props, with wooden edges to tighten or loosen the centering. Nails and anchors are used to support the ply with each other or to get attached to the beam.

Shuttering

Shuttering is also a part of a formwork that is used to support the wet concrete mix until it gains strength for self-support.

Shuttering supports vertical structures like the wall, column, beam side, slab side, chajja side, etc.

Equipment used for shuttering

• Telescope span

• Wall form

• Single clamp

• Cup lock system

• Corner angle

• Adjustable stirrup head

• Shuttering couplers

• Wedge clip

• Column mould

• Ms planks

• Tie rod

• C channels

How is shuttering done?

Using plywood or steel, two sides or four sides of the column are secured in position by the use of clamps. For deep beams or RCC walls, it is mandatory to secure the shuttering at the central zone else the sides should get deformed on the outer side due to the pressure of concrete. This work is done by putting a tie bar through the beam. The tie beam consists of a mild steel rod with threading on both sides. The tie beam always remains in the RCC beam. The tie rod is inserted in a PVC pipe sleeve before putting in the beam if the bar is to be taken out. The tie rod remains in the concrete which can easily be taken out from the sleeve.

Differences between centering and shuttering

Centering	Shuttering
They are used to support the horizontal surface.	They are used to support the vertical surface.
They are generally done using plywood.	Then are done using steel or plywood.
They should be handled more carefully as vertical rods are throughout the structure to support large horizontal ply.	They are less risky as ply or steel is supported by rods or wood taking less space in the structure.
They are done while constructing surfaces like slab, chajja, beam, etc.	They are done for construction structures like column, wall, beam side, etc.

Controversial Heights Of Mount Everest

Controversial Heights of Mount Everest When it comes to surveying and height measurement, everyone is amazed with the height of Mt. Everest. It might sound amusing but the height of Mt. Everest has never been same. Its height has been fluctuating with time throughout the history. Some say Mt. Everest lengthens by some inch every year and some say equipment used for the height measurement was inaccurate. According to recent research, in 20th December 2020, new height of Mt. Everest has been published as 29,031.69 feet (8,848.86m).

At first, the British-East Indian measured the height of Mt. Everest, which they thought was accurate until in 1970 A.D. Chinese survey declared the height as 29,029.24 feet (8,848.11m). This measurement only gratified the Chinese. So with the help of more reliable technology in 1987 A.D. Italian survey used satellite surveying technique and marked the height as 29,108 feet (8,872m). A lot of people again questioned this measurement. So, again another Italian survey obtained the height as 29,023 (8,846m), using the GPS and laser measurement technology. In 1999 A.D. an American survey again measured the height of Mt. Everest and their yielding was 29,035 feet (8,850m), plus or minus 6.5 feet (2m). This reading or mainly 8,848 m was accepted by various specialist and this value was widely used until 2020, where it was re-evaluated as 8,848.86m. In conclusion, the height of Mt. Everest has always been around 8,848 despite the controversy. But due to certain factors like: snowing, lack of well-equipped height measuring technology, natural causes (like: earthquake) there has been minor deflection in the height of Mt. Everest.

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