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Comparison of Construction Techniques for Groundworks and Substructures

Paper Type: Free Essay Subject: Construction
Wordcount: 4799 words Published: 8th Feb 2020

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Task 1. Compare the different construction techniques, processes, materials and plant used in a project involving groundworks, foundations, and substructures to assess their suitability. This is expected to include advantages and disadvantages, and also a consideration of health, safety, and welfare issues. Learners should use sketches or referenced annotated diagrams from texts to illustrate descriptions.

 

Substructure can be defined as the structure under the ground level. It is where the main support of a building came from. The Health, Safety and Welfare Regulations 12 and 13 are established to protect people working on the area and require some adequate support to excavations to prevent accidents and injuries from happening. Excavation should be supervised my professionals and inspected by competent person with enough knowledge on the job. Reports should be filed for every detailing for the approval of safe conditions. The contractors and subcontractors are responsible for the health, safety, and welfare of their own employees. Everyone must cooperate in regulating the implemented rules to achieve success in the job and have a zero-rate accident. There are different ways and techniques on working with substructure. But what are their purpose and significant differences?

  • Groundwater Control – groundwater is what we call the water in the soil located above the level of the water table. Water can affect the integrity of soil depends on its class and type. Some soil has very fine particles that absorbs water very well, some has very large particles that gives hindrance to the water to pass through. In construction, the soil where the project will rise is carefully studied to evaluate the processes that they can apply in order to give stability to the foundation. The processes may be classified into couple of groups:
  • Permanent exclusion of water
  • Sheet piling – this process is used

to create a barrier or cut-off wall to

prevent flow of water to enter the

restricted area. The sheet piling

acts as a retaining wall to provide

enclosure to the excavation works.

Sheet piling requires high cost

materials and maintenance which

became one of the disadvantages

of using it. Also, the construction

of sheet piling brings vibration

and too much noise to the area

which made construction companies

neglect the idea.

  • Diaphragm wall – this process

is applicable to all types of soil
which made many companies
consider its flexibility. Low noise

and vibration is also a well-known

characteristic of this process. It can be

constructed in restricted spaces which

is a total advantage for areas with

small and limited spaces. But a downfall

of this process is that it is uneconomic.

It costs more especially it is formed

as a permanent structure.

  •                   Freezing – this method is suitable for every

soil types with moisture content in excess

of 8% of voids. The main principle of

freezing method is to insert freezing tubes

into the soil and produce a freezing solution

around to form ice in the voids, thus filling

the voids and soon create a wall of ice

that acts as impermeable barrier wall.

This method is said to provide soils

with extra mechanical strength with

 is great to increase the stability of

foundations. But the downside of

this method is the time of producing

the ice walls. It will take 10-17 days

to finish a 1 meter thick of ice wall

depending on the type of subsoil.

For works that requires quick freezing,

there is an available nitrogen that will

help fasten the circulation of ice in the

voids which costs more expensive.

A typical freezing system is shown in

the picture provided.

  •                   Chemical grouting – this process is mainly

used in medium-to-coarse sands and gravel

 to provide stability to the soil and can also

be used for working under the water-table level.

Injection pipes are being used in injection of

chemicals into the ground at 600mm centers.

 To increase the strength of the soil, chemicals

form a permanent gel or sol in the earth that

can also reduce the permeability of the soil.

“One-shot method” is what they call when a liquid

base is mixed with water that controls the

get-setting time before being injected into the

ground.

“Two-shot method” is an alternative to the

previous method. This method includes injecting

first the sodium silicate and then later the calcium

chloride to form a silica gel. The advantage of the

two-shot method is that the mixture immediately r

eacts and works, whereas in the one-shot method

the reaction of chemicals is delayed due to the full

penetration of subsoil. This method’s main disadvantage

is the thickness of its natural covering which requires

at least 2 meters.

  • Temporary exclusion of groundwater by lowering the water table
  • Wellpoint systems – this method is popular in

companies for it can reach 5 to 6 meters deep

of soil. It lowers the water level in non-cohesive soils.

It requires a multi-stage installation to exclude

water in the area shown in the figure. The main

principle of this method is vacuum water from

smaller diameter pumps attached to a header pipe.

The header pipe should be connected to two different

pumps – first one is to operate the excavation while

the second one is to standby for an emergency

failure of the first pump. It is essential to keep the

operation continuous and should not be stopped.

Failure cannot exist in this situation.

 

  •                Sump pumping – When working in open shallow

excavations, this method should be the best suitable

for it is good for subsoils particularly with gravel and

coarse sands. To reduce soil movement due to

settlement, the sump should be excavated below

the formation of the excavation. Sump pumping

can only have 7.50 meters of depth due to the

limitations produced by the suction lift of most pumps.

The advantage of this method is that it digs deeper

that other up to 7.50 m and at the same time

prevent movement of soil which is necessary for

the stability of foundation.

 

 

  •                Electro-osmosis – This process is uncommon in

the construction industry due to its costly price.

But this method is best for dewatering cohesive

soils such as silts and clays whereas other

pumping processes cannot perform. It is said that

soil particles carry negative charges which attracts

the positive charge of the water molecules which

therefore creates a balanced state; if the balance

is interrupted the water will flow. This process is

carried out by inserting two electrodes into the

ground and passing electric charges between them.

Sheet piling acts as positive electrode which will

also act as anode, and a wellpoint acts as negative

electrode. Electric current passes between them

which causes positively charged water particles to

flow to the wellpoint where it is collected to a

discharge. This method requires 1 Kw/m3 up to

 12 Kw/m3 which made it uneconomic on running

it alone.

  • Deep Trench Excavation – an excavation with over 3 meters deep can be considered as deep trench. Deep trenches should not be left open for too long, backfilling should be done as soon as the completion of a project. Precautions like that lessen the injuries and accidents that might happen with an open trench. The safety of the people working and living around the area is at topmost priority. Excavations in a rock stratum should also be observed for the stability it serves. Splits in the rock layers may lead to crumbling and falling of rock layers particularly when it is exposed on the atmosphere for long enough. However, there are methods that might help support the sides of deep excavations:
  •   Perimeter trench – when there are weak subsoils present, this method is suitable. It is made by excavating a perimeter trench on the deep trench. The size of the deep trench must be sufficient enough to gratify retaining walls and working space. The bottom of the deep trench should have a cover of 50 to 75 mm weak concrete to protect the base from drying when exposed to the atmosphere for a long period. This method is intended to use for weak subsoils, but can also be used for firm subsoils, whereas they should excavate the area first before placing the timbering in position. The figure shows the materials will be using in building a perimeter trench.

 

  • Cofferdams – is a system having a watertight perimeter enclosure. There should be no seepage in a cofferdam, but if there is any, it should be handled by small pumps. The soil is excavated from the enclosed and braced cofferdam. It is consists of interlocking steel sheet piles which keeps the cofferdams enclosed. A detailed illustration of cofferdam is presented below to fully understand the components of it.

 

  • Tunneling – is usually identified as a man-made passage underground. It is used as a mean of communication and transportation for years now. When working with tunnels having 6 meters deep, there are factors that should be consider. The nature of subsoils is important to know for it will determine the amount of timbering that is needed in construction of tunnel. The type of tunnel should also be considered for there are different types depending on the depth of excavation. Tunnels are also a great way to avoid traffic on busy roads. But like any other structures, The Construction Regulations 1996 established rules that needed to be followed in order to keep safety and health of the employees and community. The sketch below shows a plan of tunnel timbering with a more detailed view.

 

In order for the foundation to carry loadings exerted from the top of the building, it should be composed of durable materials with the right strength. The safety of the occupants relies on the materials and how it was used in the construction process. Concrete is sad to be the most suitable in constructing the foundations. Concrete is composed of proportioned cement, aggregates, and especially water.

  • Cement – binder of the concrete mix. It is manufactured from chalk and clay.
  • Aggregates – there are two types of aggregates. Coarse aggregate is a material retained on a 4mm sieve, while fine aggregates are generally the materials that pass through tha 4mm sieve. It can be natural disintegrated rocks or crushed stones.
  • Water – is available everywhere and can be easily use to paste the mixtures.

The mixes are expressed usually with the ratio 1 part cement, 3 parts of fine aggregates, 6 parts of coarse aggregates, and 0.4 to 0.5 water cement ratio. Be careful with the proportions for it will determine the strength of your concrete. Too much water may result to weak concrete, whereas too little amount of water may get concrete less workability.

Plants that are used in construction industry gives a lot of benefits to the engineers, contractors, and subcontractors. They are used for the following reasons:

  • It saves time and increase productivity
  • Reduced time means reduction in constructions costs.
  • Big plants carry jobs that manual workers cannot do
  • Less work for employees thus giving them more time to spend for other things in the field
  • High standard work because they are made to do specific job

Different types of plants that greatly benefit the substructure construction:

  • Excavating machines – used to excavate and load most soils. They are categorized into three purposes:
  • Universal excavators – this covers all types of excavations. This includes the power unit which is a tracked based machine with a capacity of 360 ° and altering some of its arrangement to have different excavating functions. This machine produces high output and is rope controlled.
  • Purposed designed excavators – these machines are designed to carry out one made excavation and has smaller bucket capacities that other types of excavators. These machines are hydraulic controlled with short cycle time.
  • Multi-purpose excavators – These machines have both front and rear attachments and can perform several excavating functions. They carry small excavation operations with low output fast and efficiently.
  • Skimmers – It is used for surface stripping and shallow excavation having 300 mm deep. But this type of machine is not common nowadays because of their limitations and other alternatives for excavation are available widely in the market.
  • Backaters – this machine is used in trench, foundation, and basement excavations. It is available for both universal power machine or a purpose designed hydraulic unit. This requires low-loader transport for travelling locations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Task 2. Compare fundamental techniques, processes, materials and plant used in the superstructure and external works for a given project. The suitability of medium- or high-rise buildings must be assessed. This is expected to include advantages and disadvantages, and also a consideration of health, safety, and welfare issues. Learners should use sketches or referenced annotated diagrams from texts to illustrate descriptions.

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Superstructure is the construction above the foundation or substructure. It is supported by the infrastructure which is also supported by substructure. Just like in substructure, safety is also the priority in superstructure. We should always put the safety, health, and welfare of the engineers, contractors, employees, and the future occupants of the building. There are different processes in the construction of superstructure and some of them are listed below.

  • Slabs – is a flat often rectangular concrete used in construction serves as the flooring system. We can use different types of slab depending on its purpose.
    • Simply Supported Slabs – this slab is not fixed to the support and are free to lift. They just rest on a bearing.
    • Concrete Slabs – concrete as a material is known to be strong in compression but weak in tension. If the member is heavily loaded, its tensile resistance may reach to its limit and cause a structural failure.

  • Reinforcement – usually are composed of steel bars which provides the member with more tensile strength. It is an essential to design this part thoroughly to ensure the additional strength of the member. Reinforcement are placed near the outside of the member with enough concrete cover that will protect the steel from corrosion and exposure from the atmosphere.


 

  • Beams – are always in horizontal form which is also a load bearing member. It is characterized by two different function. First is the “main beams” which transfers load coming from floors and other beams going to the columns. Another one is the “secondary beams” which transfers floor loads into the main beams. Beams also need reinforcement for it is also composed of concrete which has weak tensile strength. There are different types of reinforcement in beams. There is an ordinary tension and diagonal tension.

 

  •   Columns – a vertical load bearing part of the structure which transfer the loads coming from beams into the foundations. Columns usually differ on size, shape, and purpose. It is best to learn what type of column is suitable for you building that might give you economic benefit. Reinforcement is also necessary in columns. It should be built stronger because it holds the vertical part of the structural frame. When an earthquake exist, column plays a big role in resisting the movement of the building.

 

  • Materials – Most commonly used material in superstructure construction is mild steel or high yield steel. The two contain about 99% iron, 1% of proportioned manganese, carbon, sulphur, and phosphorus. Mid steel has 0.25% carbon, high yield steel has 0.40% carbon. Standard bar diameters are: 6, 8, 10, 12, 16, 20, 25, 32, and 40 mm. Grade notation: Mild steel – grade 250 or 250 N/mm2 characteristic tensile strength (0„25% carbon, 0„06% sulphur and 0„06% phosphorus). High yield steel – grade 460/425 (0„40% carbon, 0„05% Sulphur and 0„05% phosphorus). 460 N/mm2 characteristic tensile strength: 6, 8, 10, 12 and 16 mm diameter. 425 N/mm2 characteristic tensile strength: 20, 25, 32 and 40 mm diameter.
  •  Plants – the plants used in substructure are also being used in superstructure. They also serves purpose to the construction of structural frame. Using plants does not ensure economic savings since renting or buying plants are expensive. But it is surely give benefit and inconvenience to the employees. Just be wise in using plants to its full capacity and use it when it is really needed and should not be left standing on the side when not needed. Companies should make sure the time they are paying for plants are worth every coin. Examples of plants that are helpful in construction industry are the following:
  • Graders – this machine has similar concept with bulldozer but they have longer, sender, adjustable mould blade. Its main purpose is to finish the upper surface of a large area usually happens after the scraping or bulldozing. They can produce accurate finishes but it does not possess the power that a bulldozer has.
  • Bulldozers – Big machine that has a mounted power unit with mould blade in the front. It can adjust into an angledozer and can tilt the mould blade about a central swivel point. It can excavate up to 300m deep on level ground. It also acts as a towing tractor.
  • Scrapers – this machine has a scraper bowl which cut and collect soil where stripping ang ground levelling are required. It should operate in downhill if possible and have smooth roads.
  • Tractor Shovels – there are sometimes called loaders. It scoops up fine materials, maneuver into a position, and loose the load into a position. It can carry out bulldozing, loading activities, and excavating.

Task 3: Relate the specification of plant, materials and methods evidence for P4 to the constraints on the project evidence for P3.

As per with normal plans and projects, construction also have certain parameters in plans, methods and materials to be used. These are all govern with scope and limitations. These limitations are also called constraints that gives restriction to the full use of a certain material or method to secure its safety and long-term efficiency. Plants or the equipment machinery and construction apparatus like hand tools, powered tools, bulldozers, etc. are really efficient to use during construction but over using them will put the workers to risk, that’s why proper training about its use and limits should be done before the actual construction of the project. For materials, referring to any wood and timber, steel, concrete or other reinforced materials etc. poor materials can be dangerous to use, while good materials but overworked one is also dangerous for public construction. That’s why setting and knowing the limits or constraints is really important. Same at methods, there are a hundred of methods to be used in construction but like materials, these methods also have limits and conditions. Following the systems or methods conditions may help the workers work safely, fast and better. Knowing the right method or course of action in a certain plan will always give positive outcome than not knowing other better option to do the project. All of the plants, materials and methods are the ace of cards of construction. Without them it is not possible to build great buildings and infrastructures, you need plants to make the constructing easier, and you need the materials to build a framework and actual buildings and you need methods to execute the project in the best way or course possible. These makes these three construction terms related. Without the three of this constructing a project will be a real hard problem.

 

Task 4: Evaluate the relationship between demand, provision and funding of infrastructure projects. You will need to refer to the actual projects which they have chosen or another two.

To construct a certain project, biddings or funding is one of the biggest factors what, when and how the building is to be build. What are the materials, when and where will the construction take place and how will it be constructed? It should be part of the planning phase. Knowing the demand of the structure also helps in making the project possible. Is it really a need to construct? What is its purpose. The provisions to be given by the contractors and the engineering offices should contain all information that will be needed for the legal construction of infrastructure in a site. The demand of certain infrastructures or projects will ask the engineering offices or contractors for a plan to construct, while the provisions make it legally allowed to be constructed and the funding makes it possible to be done. Without demand, you cannot plan to build, without provision you can’t start the construction legally, and lastly without the funding, your project will just be a plain plan and will never come to actual construction. Sometimes the government makes comparable projects before actually constructing one. For example, building a public school or a hospital. What is more demanded and needed, what project will cost more and what project will be smarter to build first. For example, the Alder Hey hospital Project in England, the demand of hospital emergency services are increasing. Now that the demand has been identified the legal provision or contract is now required for the construction of Alder Hey hospital Project. The parameters and design should be carefully discussed or stated such that the benefits and use, structural and architectural design and occupancy of the project is emphasized. Last is the funding. How would it be funded, is it sustainable and how does it represent the value of money and why. Here also comes the bidders and contractors who will submit revised design fitting to the standards of the project without sacrificing the budget.

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