Construction Technology

Question 1

Types of Structural frames

Answer 1

• Concrete
• Timber
• Steel

Question 2

Types of foundation

Answer 2

Strip foundations- A concrete base that is poured to a minimum depth of 225mm, upon which the walls of the foundation are built up to the level of the ground floor. Used when setting a building on firm, level ground that has been properly prepared.

Trench fill foundations- Similar to strip foundations, but with the trench filled with concrete. Typically used on sites with clay soils or where tree roots are a problem.

Raft foundations- Large, flat slab of concrete used to spread the weight of a building over a larger area. Raft foundations are typically used on soft, weak or waterlogged ground.

Pile foundations: Used on sites where the soil is unstable, or where the building is particularly heavy. Pile foundations involve the use of long, steel or concrete columns that are driven deep into the ground to support the weight of the building.

Pad foundations: Similar to strip foundations but consists of isolated footings that support individual columns or stanchions. Typically used on lightweight structures or on sites with a shallow layer of topsoil.

Question 3

What is off-site manufacturing/ construction

Answer 3

Off-site construction is a construction procedure that involves the planning, designing, fabrication, transportation of fabricated building items and its assembling on the site.

Panelised (2D) construction- flat panel units used in the form of walls, floors or roof panes in order to create a complete structural shell. Built in the factory and transported to the site for assembling as a three-dimensional structure or to fit into an already on-site constructed structure. panel units can be made out of timber, insulated panels or light gauge steel or concrete.

Volumetric/ modular (3D) construction- three-dimensional units are produced in the factory and brought to the site and bolted together. The frames constructed can be either steel, timber or concrete. The modules can bought in different forms e.g. basic structural shell or with internal and external finishes and services.

Question 4

Benefits of OSM

Answer 4

Speed, high degree of precision, cost savings, greater quality control

Question 5

When is OSM suitable

Answer 5

Project has to meet tight deadlines, involves the construction of repetitive structures, space limitations on site, safety concerns.

Question 6

RIBA Plan of Work 2020

Answer 6

RIBA is a framework explaining how a construction project should be organised.
Split into 8 stages from 0-7:

Question 7

RIBA Stage 0

Answer 7

Strategic definition- Determining the best means of achieving the clients requirements, including undertaking early cost appraisals (which could be not build something new). QS involvement in reviewing budget as part of business case.

Question 8

RIBA Stage 1

Answer 8

Preparation and brief- Developing detail of the brief to make sure everything needed for the design phases is in place (undertaking feasibility studies). Agree budget and produce initial cost plan/ estimate (e.g. based on unit rate)

Question 9

RIBA Stage 2

Answer 9

Concept design- Getting a design concept that makes sure the look and feel for the building is in line with the clients requirements and budget. Cost plan update, e.g. ratio analysis.

Question 10

RIBA Stage 3

Answer 10

Spatial coordination- Spatially coordinate the design before the detail required for construction is added e.g. the spaces required for any building systems – such as structural and building services have been determined. Cost plan can be updated to elemental cost plan.

Question 11

RIBA Stage 4

Answer 11

Technical design- Developing the information required to manufacture and construct the building. Cost plan continue to be updated, with constant review against budget and analysis of design solution/ value engineering. Cost plan update to initially be updated with approximate quantities and developed to full BoQ with pre-tender estimate also produced. BoQ is then issued to tenderers to populate with rates and pricing document is then produced and negotiated to agree a contract sum.

Question 12

RIBA Stage 5

Answer 12

Construction and manufacturing- Constructing/ manufacturing the building. The QS main involvement begins in regard to managing the construction contract (undertaking duties detailed in contract administration) monitoring and managing costs (as per project finance/ commercial management duties)

Question 13

RIBA Stage 6

Answer 13

Handover- Closing out of defects and completing the handover tasks required to conclude the building contract (agree final account, undertaking analysis looking at final cost against initial budget, assessing lessons learnt)

Question 14

RIBA Stage 7

Answer 14

Use- When the building is in use, this lasts until the building reaches the end of its life

Question 15

Monitoring of MSE roof for loading

Answer 15

An automatic total station was installed on top of one of the precast concrete columns. Monitoring prisms were then installed throughout the precast structure which would feed information to the total station. Readings were taken automatically every hour to check if there was any movement in the structure.

This was required whilst the loading of the green roof took place due to previous deflection that had occurred on the structure

Question 16

what were some of the OSR issues, how were they resolved?

Answer 16

Due to the location of the roundabout, in the centre of London with utilities, tram lines etc. underneath, although scanning was undertaken unforeseen ground conditions with various obstructions (Thames water chamber) and utility clashes (BT cable) were common.

During the weekly construction progress meetings these were discussed and solutions identified. EWNs would be raised for this and I would chair the EWN section of the meeting where mitigating actions would be discussed and determined (lower of cable) to prevent cost and time impact on the programme.

Question 17

What is an IDR, what does it include?

Answer 17

IDR is an Independent Design Review which takes place a different stage of the design process. It involves multiple discipline engineers, project managers etc. from the business to come together and undertake a complete review of the design to date.
I attended the surrey quays 60% IDR which was undertaken at 60% completion of the design, some of the key elements reviewed included;
- review of site constraints e.g. existing retaining walls, station interface, trackside assets
- CDM plan overview and responsibilities
- Detail on safety procedures e.g. use of man safe harness system when accessing roof
- Whole life carbon modelling review
- Inclusive design considerations
- Acoustic modelling review
- Structural engineering model using BIM to review loading considerations, foundation arrangements etc.

Question 18

What is acoustic modelling?

Answer 18

Acoustic models used to predict a wide range of acoustic characteristics within rooms and spaces
- help with the shaping of rooms
- selection of acoustic finishes,
- placement of speakers

This is important for TfL projects that involve refurbishment/ building of new stations as we have minimum standards we must comply with in regard to the acoustic levels of our audio information.

Acoustic performance of wall and ceiling finishes therefore need to be considered, e.g. use of acoustic panels in ceilings can help absorb unwanted noise and improve clarity of sounds

Question 19

What is BIM?

Answer 19

BIM is a Building Information Modelling system which is capable of enabling designers to generate and optimise different 3D structural models. It helps them assess the structural integrity of buildings, simulate various load scenarios, and identify potential issues before the actual construction begins.
BIM enhances collaboration, provides enhanced visualisations, clash detection, improved cost estimation, sustainable design and efficient communication.

Question 20

Trial holes vs scanning

Answer 20

Trial holes involved penetrating the ground in different locations to analyse the ground conditions whereas the use of ultrasonic scanning uses a scanning tool which can assess ground conditions non-intrusively. The scanning was less time consuming, and came with less risk due the non-intrusive methodology. Whilst it came with slightly more direct costs the reduced risk and time resulted in overall cost savings.

Question 21

Construction methodology for ESS

Answer 21

The ESS location was surrounded by live tracks and therefore provided access constraints to the project. Access options were considered as part of the methodology review, my involvement in this was to review the costed programme and advise on cost savings based on a change to the construction methodology.
One option was to install an underpass, this would provide ease and safe access to the compound, however came with circa £500k of increased costs and a slightly increased programme duration. Even with the underpass weekend possessions would be required to undertake works with close vicinity to the tracks and therefore an additional number of possessions or a blockade would provide cost and programme advantages.

Question 22

Advantages and Disadvantages of concrete frames

Answer 22

Advantages;
- durable
- low maintenance
- does not rust, rot, or burn
- effective soundproofing material

Disadvantages;
- can be more expensive than other products
- heavy, which may present transportation challenges
- Cannot be stored once it is mixed as the cement reacts with water and the mixture hardens.

Question 23

Advantages and Disadvantages of timber frames

Answer 23

Advantages;
- light, and easy to work with,
- inexpensive,
- a natural resource
- good at absorbing sound inside a building

Disadvantages;
- cannot be easily used to build at height
- requires treatment and protection using chemicals often manufactured in energy-intensive processes.
- more susceptible to water damage, fire, decay, and termites.

Question 24

Advantages and Disadvantages of steel frames

Answer 24

Advantages; Strong and cost effective, quick to erect, which can lead to labour savings, suitable for prefabrication and mass production, reusable after a structure is disassembled. Additionally, steel binds well to concrete, meaning reinforced concrete can be used to provide deep foundations and basement, making it a very popular building material

Disadvantages; steel is made using an energy intensive process, exposure to the environment can damage the material and cause corrosion and it has high manufacture and maintenance costs.

Question 25

Precast vs In-situ concrete

Answer 25

Precast
- more control over quality
- not impacted by weather
- faster to manufacture providing cost savings

In-situ
- useful for constrained/ hard to access sites
- requires less heavy lifting equipment

Question 26

Site investigation considerations

Answer 26

• site access/ constrained site
• site type (greenfield/ brownfield)
• ground conditions (utilities, trams, unexploded ordinance)
• soil type
• topology
• third party interfaces/ public interface

Question 27

Concrete vs steel frames

Answer 27

• steel is lightweight and faster to erect which can come with financial benefits
• however concrete is naturally fire resistant and can be better for enclosed/ tight spaces such as underground as it can be poured in-situ

Question 28

How do design solutions impact the efficiency of a building / project?

Answer 28

• during the design stage value engineering can be used to find the optimal solution/ methodology/ materials to maximise efficiency
• the design stage can identify solutions such as smart technology/ improved insulation etc. to impact the buildings performance efficiency

Question 29

Typical site considerations

Answer 29

• access
• storage
• accommodation
• temporary services
• hoarding

Question 30

What are temporary works

Answer 30

Parts of the construction project needed to enable permanent works to be built (e.g. temporary services/ traffic’s management)

Question 31

What is meant by buildability?

Answer 31

The extent that the design of a building facilitates the ease of construction

Question 32

Construction methodology for new track

Answer 32

• site preparation (clearance of and trees/ bushes or anything else on the ground and level it out)
• install track drainage and any other utilities/ services
• lay the bottom ballast
• lay the sleepers
• install the rails
• lay the top ballast
• connect utilities/ services e.g. power/ signalling etc.

Question 33

What material finishes were looked at for the acoustics at Surrey Quays

Answer 33

• Acoustic tiles/ panelling with sound absorbing properties
• Acoustic spray plaster with sound absorbing properties
• Normal plaster board/ cladding or panelling
• With the sound absorbing materials the speaker placements could be amended as sound could be absorbed better

Question 34

How did I advise on the savings for the ESS construction methodology change?

Answer 34

I reviewed the estimate produced along with the programme and identified that a big cost driver was the underpass construction at £500k.

I discussed the methodology with the engineer raising the query on the necessity of the underpass if possessions would still be required and the feasibility of undertaking all the works through possessions.

Following confirmation from him that safe working could still be undertaken without the underpass, I worked with the planner to input this into the programme.

I then produced an optioneering paper advising the project lead on the two options for the construction methodology, and a table showing the cost and programme benefits of additional possessions vs the use of the underpass. Input was provided from the engineer in regard to confirming safe working and constructability using this method. It also identified the greater network impact of the increased possessions (in hours) for the project lead to make the final decision on whether the project cost & programme savings outweighed the additional network impact.

Question 35

How did I advise on the GPS bunds construction options?

Answer 35

I reviewed the two construction options submitted by the contractor (trial holes & non-invasive scanning).

I identified the cost of each which showed the non-invasive scanning had a lower cost due to less resources required, a programme review also showed it was a quicker option which came with cost savings.

I reviewed the risk profile of each with the scanning having a lower risk cost due to not being impacted by weather.

I produced an optioneering paper outlining the two methodologies, with input from the engineer in regard to the accuracy of the results from each. The scanning is due to have less ability for human error, however has not been used by tfL before, whereas the trail holes were a tried and tested method for the business.

I then produced a table showing a comparison of the cost, risk & programme which showed the benefits of the scanning.

I summarised this below, where I advised that based on the cost & programme benefits the scanning would be the most appropriate option.

Question 36

What is top down construction?

Answer 36

Builds the permanent structure members of the basement along with the excavation from the top to the bottom.
Construction sequence of top-down;
- Construct the embedded retaining wall (usually a
diaphragm wall).
- Construct piles. Place the steel columns where the
piles are constructed.
- Proceed to the first stage of excavation.
- Cast the floor slab of first basement level with the
opening to allow machines to be lowered to
excavate level below and for excavation material to
be removed.
- Proceed to the second stage of excavation; cast the
floor slab of the second basement level.
- Repeat the same procedure until the desired depth
is reached.
- Construct the foundation slab. Complete the
basement.

Question 37

What is bottom up construction?

Answer 37

Bottom-Up construction method is the conventional
construction method. In this method the base of the structure is constructed and subsequently moves up to the surface.

Question 38

Top down vs Bottom up construction

Answer 38

Top down
- Reduced construction duration
- Beneficial in areas where space is limited
- However requires greater coordination and planning to ensure each level is properly supported
- Can be more costly due to additional support required

Bottom Up
- Most common and familiar construction method
- Simpler method of construction
- Takes longer than top down and comes with more disruption.

On NLE we wanted to minimise programme & disruption as much as possible. 2 stations were to be built with a connecting tunnel. decision for one to be built bottom up to allow tunnel excavation to start whilst the other constructed top down, whilst the tunnel construction was ongoing