Civil Engineering Projects

Drainage and Dewatering | Building Construction

2012-02-08T18:50:36Z

Introduction to Drainage and Dewatering

In this article, we will discuss and classify drainage and dewatering in brief.

What is drainage?

As the name itself suggests, drainage is the process in which the free water is removed with the help of gravity in order to maintain stable soil conditions.

Drainage can be classified into two categories:

Surface drainage
Sub-surface drainage

What is Surface drainage?

The water that runs on the surface of the ground is collected and or diverted into a water body.

Sub-surface drainage

It is the collection and disposal of ground water. It is also called as dewatering.

What is dewatering?

The process in which the water is removed from a foundation pit;

when it is situated below the ground water table or
when it is surrounded by a coffer dam.

Why is dewatering done?

Only understanding the definition of dewatering is not enough. It is essential to know the reason as to why it is done.

Some times in some areas, the water table is high. This causes trouble and discomfort during construction. The water is pumped out so as to keep the excavation dry. Excavation has to be kept dry so that concreting can be done.

Sometimes temporary dewatering may suffice. Temporary dewatering is draining out the water at the time of construction and it is then followed by restoration to its original water level as soon as the construction is complete.

What is permanent dewatering and why it is done?

Permanent dewatering is removing the subsurface gravitational water throughout the life of the structure. This is done to protect the structure from moisture and dampness.

Check out: Causes of Foundation Damage | Moisture

Advantages of Subsurface drainage

It helps in improving the properties of the soil

Helps in the stabilization of soils

Let us consider the case of “Fine grained soil”

The water removed from fine grained soil is not much but the improvement in the properties of the soil is significant.

Helps in reducing hydrostatic pressure acting at the base of the structure

Methodology to be adopted for Sub-surface drainage:

The methodology adopted at a site would depend on various factors. They are as follows:

Characteristics of the soil
Position of the water table
Time period

Also check out:

Inceptor Ditches

Conduits | Building Construction

2012-02-05T13:50:04Z

Construction of Conduits | Civil Engineering

In the previous article, we discussed “Types of Underground Conduits”. Now we will proceed with our discussion on “Construction of Conduits”.

Underground conduits can also be termed as buried conduits. They are constructed in variety of shapes with different materials used for construction.

Load on the conduit

The characters of the conduit determine the load withstanding capacity of the conduit. They are as follows:

Material of the conduit
Shape
Type of the support

For example:

If we take the example of a concrete conduit (rigid material), the load that the concrete conduit can withstand would depend on the following:

Strength of the concrete pipe
Quality of the foundation bedding

How to determine the strength of the conduit?

A three edge bearing test has to be conducted in order to determine the strength of the conduit.

Three edge bearing test

This test simulates a very severe loading condition which would rarely occur in the actual conduits. This helps us determine the maximum load the conduit can take. It has been seen that the conduits can take greater load than that obtained in the test.

Manufacturers supply the customers with charts of conduit design. The load factors for different shapes of conduits are totally based on three things:

Type of bedding
Conduit projection
Settlement ratio

Conduits (with and without Bedding)

Flexible Conduits

The factors affecting the load carrying capacity cannot be well defined. These conduits sometimes undergo failure due to excessive deflection.

Reason for failure of rigid conduit

Rigid conduits fail due to rupture of the pipe wall.

Types of Underground Conduits | Civil Engineering

2012-02-05T13:49:31Z

Underground Conduits

What are conduits?

Conduits have different meanings in different subjects.

For example:

Geographically, conduits could refer to a channel carrying water, underground tunnel or waterway (river or canal).

In terms of electrical systems, it may refer to an electrical conduit, HVAC (duct) etc.

Electrical Conduits

We are referring to the conduits which is laid underground and used for variety of purposes.

For example:

Sewers
Drains
Culverts
Water mains
Gas lines
Electrical cables
Telephone lines

Load on Underground Conduits

Conduits are subjected to immense load and pressure since they are underground. In this, forces acting on conduits due to external loads are considered.

Underground conduits should be capable of withstanding the external load. When the conduits are under pressure, they should be able to withstand the internal pressure under extreme conditions.

The external forced acting on the conduit depend upon a number of factors. They are as follows:

The buried depth

Rigidity of the conduit

Method of installation

Preparation of conduit bedding

Live loads

Dead loads

Conduits are classified into various categories for ease in analysis. They are as follows:

Ditch Conduits
Negative Projecting Conduits
Tunnelled Conduits
Positive projecting conduits
Imperfect Ditch Conduits

With this we come to the end on the discussion on “Various types of Underground Conduits”.

We will study “Construction of Conduits” in a stepwise manner in our succeeding articles.

Construction of Earth Tunnels | Building Construction

2012-02-01T08:29:05Z

How to construct Earth Tunnels?

In this article, we will discuss the procedure of the construction of the Earth Tunnels in a stepwise manner. It will be useful to you all in understanding and remembering the procedure.

We would be studying the construction method of tunnel in two types of soils:

Firm soil
Soft soil

Step1:

Excavation of the ground from below. It is similar to the process used in mining.

Step2:

Check the type and bearing capacity of soil. The method of construction would depend upon the ability of soil to support itself temporarily during construction.

It also depends on the ability of the soil to withstand the magnitude of pressure imposed on it during construction.

Construction of Earth Tunnel

Step3:

It is important to understand the factors that affect these parameters. They are as follows:

Depth of the tunnel
Diameter of the tunnel
Properties of the soil
Ground water table

Support to the Tunnel

Most of the time, the tunnel requires temporary support during construction and a permanent support after construction.

Step 4:

Soil type assessed: Firm soil

Construction Method:

The excavation is started at the roof level of the tunnel and progresses downwards.

Step5:

For the initial support of the incremental excavation, the liner plate is used.

What are Liner Plates?

Liner plates are flanged steel plates. When multiple liner plates are bolted together, they form a continuous wall.

An alternative to Liner plates

Sometimes, laggings are used in place of liner plates. Laggings are wooden or steel horizontal planks braced by steel frames.

Step6:

After placing the liner plates and bolting them together, the excavation is carried on to a further step and the procedure of placing is repeated until the complete section of the tunnel has been excavated.

In short;

First, we excavate

Second, place the liner plates for support and carry on further excavation

Step7:

Type of soil: Soft soil

Type of support used for constructing a tunnel: Cyclindrical support

It is jacked through the soil. It is also called shield.

The face of the tunnel is supported by a bulkhead fitted with doors through which excavation of a limited portion of the face can be done.

Step 8:

A permanent lining (for permanent support of the tunnel) is constructed inside the shield after some excavation has been done.

The procedure is then repeated; that is,

First, shield is jacked through the soil

Second, permanent lining is constructed inside the shield after some amount of excavation

Third, shield is jacked further down,

Excavation is done

Permanent lining is done until the complete section is obtained.

Interview with Architect Javed Kachchhi | Construction Site Inspection

2012-01-25T18:18:47Z

What to do on a”Site Inspection/Site Visit”?

Students are always curious and nervous about site visits since this is never taught in any of the colleges in the world. Students have absolutely no idea as to what is to be done when an engineer or Architect is expected to inspect the site. By site, I mean construction site….

I took some time out and tried getting in touch with Architect Javed Kachchhi, the Founder and Chief Architect of the firm “Archeng Designers” based in Hyderabad, India. He is a well known Indian Architect who specializes in Modern sustainable construction.

Check out his biography: Architect Javed Kachchhi | Modern Indian Architect

He is an Architect, Structural Engineer and an Interior Designer. That is the reason why I was so hung up on trying to get in touch with him and write about his experiences about site inspection.

Here we go….

My first question was…

Me: Sir, could you tell us, What exactly is “Site Inspection” or “Site Visit”?

Ar. Javed Kachchhi: Well, let me be very specific. I am sure your readers would like that.

On a site inspection, an Architect/Engineer has to take a complete survey of the site. He has to inspect each and every element that is constructed on site and make sure that the construction is being carried on as per the drawings given by the Architect.

Me: Who monitors the site?

Ar. Javed Kachchhi: Monitoring the site is the work of Site Engineers. Site Engineers have to have a degree in Civil Engineering in order to qualify for the job.

Me: Who appoints the site engineers?

Ar. Javed Kachchhi: It is the Architect who suggests or appoints the site engineer in case of a small scale project. In case of large scale project, Project Management consultant is hired to do the job.

Me: What does Project Management Consultants team comprise of? What is their job on site?

Ar. Javed Kachchhi: Project Management Consultants (PMC) comprises of a number of site engineers, project managers, assistants etc. They all have the knowledge of building construction so that they could supervise the work efficiently.

Me: What does an Architect do?

Ar. Javed Kachchhi: Let’s me give you an example of a Small project. Say a Villa…

When I design a villa which is a project with a single structure, it is easier for me to supervise the work since the contractor is always in touch with me.

Now I will tell you what is my job on site?

Identifying the mistakes in construction made by the workers. Clarification of any or all doubts that the workers or the Contractors might have.

Sometimes, the workers end up making terrible mistakes. To correct the mistakes in construction, we generally ask the workers to demolish that particular part and reconstruct it again.

But sometimes, it so happens that it becomes very difficult to demolish the incorrectly constructed part because demolishing it could make the venture end in loss. Such cases have to be scrunitized by Architects and Engineers. A solution for the problem is to be looked for.

Me: What are the types of mistakes committed by the workers on the construction site?

Ar. Javed Kachchhi: Let’s begin with foundation…

When the design for isolated foundation is given with a sloping pedestal. Workers generally make a mistake while making the pedestal of the footing which is to be strictly avoided.

This is where the role of a site engineer comes in. He keeps a watch on all the activities of the workers on site and of course the quality of construction.

Quality control engineers are also hired for large scale projects. Say for a housing project where 2000 villas are to be constructed.

Mistakes while casting the beams:

Sometimes the beams casted on site may not be in a proper line. It could be disoriented. Thickness, depth and its concrete quality has to be checked and corrected on time.

Mistakes made while connecting columns and beams:

The joint where columns and beams meet have to be taken care of. Poor joints could result in structural instability.

Mistakes made in the elevation of the building:

Elevation is the toughest part to deal with. You really need highly skilled labour if you want to get your elevation right without any wastage of material as a result of reconstruction.

What is the scenario of Construction sites in towns? How is it different from cities?

Well, when we are visiting a construction site in a town, it is a very different experience. Since, a town is a very small place, everyone out there knows you.

The contractors and workers are directly in touch with you. In a way, this is good because lot of mistakes could be avoided in construction.

But, the trouble starts when the client starts cribbing about the petty issues…

I will give you an example:

Sir, please do something. The plumber hasn’t come.

Or the electrician has not turned up.

Or the carpenter is not working faster… Or he is wasting a lot of material.

All the above mentioned trouble is not really common in cities. The contractor takes care of it and the client knows for a fact that he is not supposed to trouble the Architect for such petty matters.

Me: Who appoints a contractor?

Ar. Javed Kachchhi: One must always be careful while suggesting or appointing a contractor for a project. This becomes a problem for many architects. Once you suggest someone, it becomes your responsibility that the contractor is not corrupt and works efficiently.

The client will keep complaining or might even refuse to pay your fees in case the contractor or the workers you suggested are not efficient enough.

With this, we come to the end of the discussion on “Site Inspection during Building Construction”.

Check out some of the Mega Projects by Architect Javed Kachchhi:

CSK Green Villas

Prestige County

Other Projects

Understanding Load Calculations | Structural Design

2012-01-18T15:59:40Z

Load Calculations | Design of Buildings

In our earlier article, we discussed “Different types of loads” and their importance in Structural design.

Now we will move on with our further discussion on the following points:

Design principle assumption and notation assumed
Design Constant
Assumptions regarding Design
Loads on Beams
Loads on slabs

Design principle assumption and notation assumed:

The notations adopted throughout are same as given in IS:456:2000

Density of material used in accordance with reference to IS:857-1987s

Sr.no	Material	Density
1	Plain concrete	24 KN/m3
2	Reinforced cement concrete	25 KN/m3
3	Flooring material (cement mortar)	1.00 KN/m3
4	Brick masonry	19 KN/m3

Design constant

Using M20 and Fe415 grade of concrete and steel respectively for columns and footings

Therefore:

Fck – i. e. Characteristic strength for M15 – 15 N/mm2

Fck – i. e. Characteristic strength for M20 – 20 N/mm2

Fy – i. e. Characteristic strength for steel – 415 N/mm2

Assumption regarding Design

Slab is assumed to be continuous over interior support and partial fixed on the edge, due to monolithic construction of walls over it.
Beams are assumed to be continuous over interior support and they frame in to the column at the ends.

Load on Beams

Description of load of slab on beam

The load of slab is dispersed on to the supporting beams in accordance with clause 23.5 of IS:456-1978, which states that the load on beams supporting solid spans, spacing in two directions at right angles and supporting uniformly distributed loads.

Self weight of beams

This load acts on the beams as a UDL, this is calculated after assuming the suitable cross section (by stiffness/deflection consideration) of the beam.

Load due to brick masonry wall

In a framed structure, brick masonry are used to construct curtain walls. They do not carry or transfer any load. Hence, the masonry walls do not have to thick.

Point load from intersecting beam

If there is any beam meeting the beam then the load of that beam is considered as point load.

Loads on slabs

Three types of loads are to be considered for the design of slabs:

Dead load of the slab
Live load of the slab
Floor finish load

Dead load of the slab

Self weight of slab acts:

This load acts as UDL, this is calculated after assuming the 1m wide square strip and suitable thickness consideration.

Floor finish load

This load also acts as UDL and this is calculated after assuming suitable intensity over 1m wide strip.

Live load on the slab

This is the temporary load on its intensity depends on type and occupancy of building.

The intensity can vary with the type of building.

Introduction to the calculation of the loads | Building Construction

2012-01-18T15:59:29Z

Load Calculations | Types of Loads

Students find it difficult to understand the concept of loads although it is a very simple concept. We are going to write a series of articles on “Load Calculations” and help you all in understanding different types of loads that are to be considered for structural designing and also how to calculate them.

In this article, we will discuss different types of loads with examples.

In our next article, we will cover the following points:

An object is subject to mainly two types of forces:

Live loads
Dead loads

Basically, an object subject to any type of force which could be gravitational force (weight), pressure or anything affects the object is called a load.

This concept is used in Mechanical and structural engineering. Let’s take in terms of Structural Engineering. Whenever a structure is designed, these concepts are taken into consideration because real world objects are analyzed in order to design the structure. This is very important in terms of structural stability.

What are “Dead loads”?

As the name itself suggests, dead loads could be termed as self weight of the non-living objects. It could be the weight of the materials, equipments or any other components in the structure that will remain permanent throughout the life of the structure.

Dead load has to be considered in order to make the structural design accordingly. Dead loads vary from structure to structure. Every building is unique and has different considerations.

An additional load is considered in case additional forces build up in a structure in case of settlement or due to secondary effects of pre-stress construction or due to shrinkage of concrete.

For the calculations of dead loads, we could also consider,

Columns
Beams
Footings
Lintels
Furniture
Machinery and other equipment
Walls
Floors
Roofs
Ceilings
Stairways
Built-in partitions
Finishes (POP – Plaster of Paris)
Cladding (Use of various materials which increase the self weight of the structure) etc.

Basically, all the permanent loads are to be considered.

What are “Live loads”?

Unlike dead loads, live loads are variable. We could term them as probabilistic loads. Live load varies from time to time.

As the name suggests, live load is the load of human beings living in the building. Their movement is not fixed. The number of people at a time in a structure can also vary.

For example:

A person lives in a 4BHK apartment with his wife and two kids. If he happens to throw a party for 50 persons, the live load on the structure increases considerably for that period of time.

As soon as the guests leave, the number of persons reduces from 50 to 4.

So, here’s what I mean by variable force.

Let’s take another example:

Live load to be considered while designing a staircase:

Pressure of the feet
Wind load on the stair in case the staircase is located outside the house

Live load to be considered while designing the roof:

Movement of workers on the roof during construction, maintenance along with their materials and equipments

Also, if the owner of the house plans to make a terrace garden on the roof, that adds additional load to it.

For dwelling houses to a 10KN/m2. In any building project, slabs are assumed to be 100m thick from stiffness/deflection consideration.

Beams are taken separately and the self-weight is calculated and added separately on the frame. The net weight of the above load is multiplied by a load of 1.5 for concrete.

Also, check out:

Bending moment and Fixed moment calculations

Fly ash Bricks | Building Materials and Construction

2012-01-07T14:31:44Z

Fly ash Bricks | An alternative Building Material

Fly ash bricks are masonry units that are used in the construction of buildings. They are considered to be a part of good and affordable building materials. They contain Class C fly ash and water.

Fly ash bricks are made by compressing Class C fly ash and water at 4000psi and then curing is carried on for 24 hours at a temperature of 66 degrees Celsius steam bath. Air entrainment agent is used to toughen the bricks.

Fly ash Bricks

Since the concentration of calcium oxide is very high in class C fly ash, the brick is described as self cementing.

It is considered to be a good alternative to traditional mud bricks since the method of manufacture of fly ash is energy efficient that is it helps save energy, brings about reduction of mercury pollution and plus it is cost effective.

Raw materials used for the manufacture of Fly ash Bricks:

Fly ash – which is the primary ingredient

Sand or Stone dust – as fine aggregate

Lime – source of calcium carbonate which results in the bricks being called “Self-cementing bricks”.

Gypsum – to enhance the fineness of the shape of the bricks

Cement – to increase bonding and strength

General Characteristics of Fly ash Bricks

The standard size of the brick is 230x110x70

The bricks are manufactured and tested as per IS 12894-2002

Fly ash bricks are sound, compact and uniform in shape, size and colour. Smooth rectangular faces of the bricks are accompanied with sharp and square corners.

Fly ash Bricks | Available in various colours and shapes. The above picture shows the bricks in dark peach colour with three holes on it. These holes are used for grouting. The mortar is poured into these holes for proper bonding in between the bricks.

They are free from visible cracks, warpage, flaws and organic matter.

Compressive strength: 7.5N/mm2 on an average

Water absorption: <8%

Advantages of Fly ash Bricks

They have high strength which is their primary benefit to be used for construction.

Due to uniform size and thickness of joints, plaster consumption is minimized compared to clay bricks, thereby saving cement to the extent of 25% to 30%.

Due to lesser water absorption, there is no dampness in walls.

Gypsum plaster, Plaster of Paris can be applied directly without the basecoat of plaster.

Wastage is very less as compared to clay brick.

The bonding between the bricks is excellent since there is high concentration of calcium oxide in it.

Uses of Fly ash Bricks

Fly ash bricks are used for the construction of various types of buildings such as:

Factories
Warehouses
Power plants
Homes
High rise structures

Basically, they are used in every kind of construction that can be possibly executed with the help of traditional bricks.

Types of Bonds in Brickwork | Stretcher and Header Bond

2011-12-31T11:20:33Z

Bonds in Brickwork | Building Construction

In our previous articles, we discussed “what is a bond?” and “Rules for good Bonding”. Let us start our further discussion on types of bonds.

Different types of bonds are:

Stretcher bond
Header bond
Facing bond
English bond
Flemish bond
Dutch bond
English cross bond
Brick on edge bond
Raking bond
Zigzag bond
Garden wall bond

Now we will proceed with our in depth discussion on “Stretcher bond” and “Header bond”.

What is a Stretcher Bond?

As the name itself suggests, stretcher bond is formed by laying bricks horizontally as stretchers on the faces of walls. The length of the bricks is along the horizontal direction of the wall.

Stretcher bond | Exposed Brickwork of a Restaurant

Stretcher bond is used when walls of half brick thickness are to be constructed. The average size of the brick is 9cmx9cmx18cm. If the wall of thickness 9cm is to be constructed, then stretcher bond can be used.

Various types of wall constructions are done using this type of bond.

Sleeper walls
Partition walls
Division walls (internal dividers)
Chimney stacks

Isometric View of the Stretcher Bond

It should however be remembered that this bond is only possible in case of walls with less thickness and the bond will fail if the thickness of the walls is more than half of the length of the brick.

Now let us move on with our brief discussion on “Header Bond”.

The square face of the brick which measures (9cm x 9cm x 9cm) is called as “header”.

When all the bricks are placed as headers on the faces of the walls, the bond formed is called “Header Bond”.

Header Bond in Elevation

Stretcher bond is used for the construction of walls of half brick thickness whereas header bond is used for the construction of walls with full brick thickness which measures 18cm.

Header bond is also known as heading bond. The overlap is kept equal to half width of the brick. To achieve this, three quarter brick bats are used in alternate courses as quoins.

Isometric View of Header Bond. The bricks that are highlighted in dark brown colour are called "Three quarter Brick bats".

Since header bonds lacks strength in pressure transmission along the length of the wall, it is not preferable to use this kind of bond for load bearing walls.

Header bond is useful when the design demands curved surfaces to be constructed. In such cases, stretcher bond cannot be used. Apart from using it for curved surface, it can also be used for the brickwork in foundations.

So here we come to the end of the discussion on Header Bond and Stretcher bond. In our next article, we will discuss “English Bond” in detail.

Bonds in Brickwork | Building Construction

2011-12-31T11:20:37Z

Various types of bonds in Brick work

What is a bond?

When bricks are laid adjacent to each other forming a groove in between the bricks which is filled by cement mortar is called a bond. Bonding helps in even distribution of loads over a large area.

There are various types of bonds. Bricks are arranged in courses in such a way that they are tied together and also care is taken of the vertical joints that are formed when bricks are arranged in courses. The bricks used for the purpose of masonry construction are uniform in size.

Bilbee herring bond

The rule is, “Vertical joints of the successive courses of bricks should not coincide, that is, a continuous vertical joint across the wall should be avoided since it will gradually result into cracks development.” The strength and stability of the wall is less as compared to the properly bonded brickwork. Improperly arranged bricks forming continuous vertical joints are also called “unbounded walls”.

Like I mentioned earlier, there are various types of bonds; these bonds are distinguished by their appearance which basically means their bonding style (fashion in which bricks interlock to tie themselves together).

Rules for good bonding:

Good bond is possible if:

Uniform size bricks are used

Length of the brick is twice its width plus one joint inorder to obtain a uniform lap.

Minimum of 1/4th of the brick is placed along the length of the wall and ½ of the brick should be placed across the thickness of the wall.

Use of brick bats is avoided

The centre line of header and stretcher in the alternate courses is made to coincide with each other in order to obtain a stable wall.

Stretchers are used in the facing.

Headers are used in the hearting.

To increase the stability and bonding, every sixth course should be provided as a header course on both sides of the wall.

This was all about “bonding”. Now we will list out various types of bonds and discuss them in detail in our succeeding articles.

Stretcher bond
Header bond
Facing bond
English bond
Flemish bond
Dutch bond
English cross bond
Brick on edge bond
Raking bond
Zigzag bond
Garden wall bond