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.
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.
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
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).
The element bends when a moment is applied to it. Every structural element has bending moment. Concept of bending moment is very important in the field of engineering especially Civil engineering and Mechanical Engineering.
Unit of measurement: Newton-metres (N-m) or pound-foot or foot-pound (ft.lb)
Bending moment is directly proportional to tensile and compressive stresses. Increase in tensile and compressive stresses results in the increase in the bending moment. These stresses also depend on the second moment of area of the cross section of the element.
What is Shear stress?
Shear stress is defined as the measure of force per unit area. Shear stress occurs in shear plane. There are many planes possible at any point in a structure which can be defined to measure stress.
Stress = Force/Unit area
Example: Bending Moment and Shear Force Calculations
Frame diagrams | Bending moment and shear force calculations
Construction of buildings can be divided into three main categories:
Load bearing construction
Composite construction
Framed construction
But among the three types, framed construction is widely used for all kinds of constructions.
An engineering structure is an assembly of number of elements transferring the loads and providing a form space to serve the desired function.
Building Construction and Design
The structural design is a science and art of designing, with economy and elegance, a durable structure is that which can safely carry the forces and can serve the desired function satisfactorily during its expected service life span.
The entire process of structural planning and designing requires not only imagination and conceptual thinking but of practical aspects, such as relevant design codes and byelaws, backed up by aple experience, institution and judgement.
The process of design commences with planning of a structure, primarily to meet the functional equipment of the user or client. The functional requirements and the aspects of the aesthetics looked into normally by an architect while the aspect of safety, serviceability, durability and economy of the structure for its intended use over the life span.
What is a building?
A building can be defined as a structure consisting of walls, floors, education, business, manufacturing, storage, hospitalization, entertainment, worship etc.
Normally all building are constructed according to drawings and specifications prepared by architects. Each city has prescribed building bye-laws to which building must confirm. The building bye-laws lay down norms like minimum front, side and rear backs, minimum height and area of habitable rooms, kitchen, bath, minimum area of windows, width of staircase etc, apart from respecting the bye-laws the building design should ensure optimum utilization of built-up space, thermal comfort, proper ventilation, desirable illumination and acoustical characteristics and it should satisfy the functional requirements of people who live and work in the building.
Now we will move on with the discussion in detail on the types of foundation damage occurring due to Settlement in the ground.
Lowering in the Groundwater level
When the buildings are built on compressible soils, the resulting stress on the soil causes the soil to compress. Raft foundations are used in these kind of soils.
Since the soil undergoes compression the upper portion of wooden piles rot when groundwater level sinks.
There are various conditions which can cause the changes in the groundwater level or pore water pressure. They are as follows:
Ice Static Rebound
Dewatering (seen in cities)
Ditches and pipes below the groundwater level
Deep Foundations and Basements (causing further drainage of the ground
Tunnelling
By the removal of foundation sills
Construction of non-permeable surfaces such as roads, pathways causing the least amount of natural precipitation
Use of deciduous trees should be avoided in areas with low groundwater. They require a lot of water for their growth. They pull all the water that is available around them causing the lowering of groundwater.
Have you ever realized how much carbon is emitted because of using concrete in the construction of buildings, highways, dams, bridges etc?
Well, here’s an answer to that. It is found that out of the 100% carbon dioxide emissions, 5% of the emissions are caused by human activities. Majority of the carbon emission is caused by usage of concrete in the constructions. How? Cement is an indispensible ingredient used for making concrete. Cement is made by baking limestone and clay powders under intense temperatures (high temperature). The intense heat which is required for the production of cement is achieved by burning of fossil fuels which in turn release large amount of carbon dioxide into the atmosphere.
Building Construction | We can just imagine to what extent the carbon dioxide would be released into the atmosphere.
Carbon dioxide is also released when the conversion of limestone takes place in the kilns. This conversion is called “Calcination”. It has been observed that the amount of carbon dioxide emitted during calcination is much higher than that which is released due to burning of fossil fuels.
Recently, a British company called “Novacem” came up with this concept of manufacturing ‘carbon-negative’ cement that absorbs more carbon-dioxide than it emits over its entire life cycle.
