�CONSTRUCTION TECHNOLOGY

Dr Adewale Abimbola, FHEA, GMICE.

www.edulibrary.co.uk

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Aim & Objectives

Aim: Types of Foundation

Objectives: At the end of the lesson, the students should be able to:

• Discuss types of foundation construction used for buildings.
• Design a pad foundation.
• Evaluate the foundation types used for buildings.

Substructure Design Principles

The main objective of foundation design is to:-

• Guarantee the secure and cost-effective transmission of structural loads to the subsoil, with minimal acceptable movement throughout both the construction phase and the expected lifespan of the building or structure.

Figure 1. Types of substructure failures (Ground & Water Ltd, 2021)

Types of Foundations

1. Raft foundation (Fig. 2).
2. Strip foundation (Fig. 3).
3. Trench fill foundation (Fig. 3).
4. Pad foundation (Fig. 4).
5. Pile foundation (Fig. 5).

Figure 3. Trench fill, and variations of strip foundation (University of the West of England, 2009)

Figure 4. Pad foundation (Heaton Manufacturing Ltd., 2023)

Figure 2. Raft foundation (LABC, 2023)

Figure 5. Pile foundation (Civil today, n.d.)

Raft Foundations

• The concrete raft foundation serves as a broad support for buildings, ideal for low load-bearing soil like loose sand or soft clays.
• It is preferred on poor or unstable ground due to its lower bearing pressure compared to strip foundations.
• Cost-effective when covering over half of the ground area, it minimises concrete usage and interference with subsurface water movement.
• Particularly suitable for areas with expected differential movements or subsidence.
• It requires design by a chartered civil or structural engineer.

Figure 6. Raft edge detail (Chudley and Greeno, 2016)

Figure 2. Raft foundation (LABC, 2023)

https://www.youtube.com/watch?v=gPm8MKxwFpc

Raft Foundation Design

• Steel reinforcement is lapped at least 450mm and provided with a minimum of 40mm concrete cover (LABC, 2023).
• To avoid damage from frost action or when building during cold weather, the minimum foundation depth should be 600 mm below the ground level.
• Use of damp proof course to prevent the passage of moisture to the inside of the structure. Also, a drained cavity/cavity drainage system and damp proof membranes can be used.

Figure 7. The position of DPC to resist moisture in raft foundation (NHBC, 2023)

Strip Foundation

• A strip foundation, situated under load-bearing walls, varies in width and depth based on the building load and ground characteristics.
• Stability and good bearing capacity of the underlying soil are crucial due to foundation design.
• Strip foundations for example require a minimum of 750mm depth in clay soils or 450mm in others. Most local authorities will require 1m deep.
• This economical choice allows for adaptation to sloping ground by 'stepping up' the strip foundations
• To avoid damage from frost action or when building during cold weather, the minimum foundation depth should be 450 mm below the ground level.

Figure 8. The position of DPC to resist moisture in ground beam foundation (NHBC, 2023)

https://www.youtube.com/watch?v=a5LfHmaH8O0

https://www.youtube.com/watch?v=QqHA_DkkTt8

Trench Fill Foundation

• Trench fill foundations offer a swift alternative to strip foundations, enhancing ground stability by minimising exposure.
• The construction speed reduces the need for extensive support structures, resulting in cost savings and improved safety.
• The concrete used stabilises the earth without risking collapses, making it a secure option for poor ground conditions.
• Additionally, the concrete's strength allows it to bridge minor soft spots, and the minimum thickness (T) for a trench fill foundation is 500 mm.

Figure 9. Foundation dimensions. (NHBC, 2023)

Figure 10. Trench fill foundation.

https://www.youtube.com/watch?v=J9MzxAzP1pY

Pad Foundation

• The fundamental foundation for columns in steel or reinforced concrete frame structures is the 'pad foundation’
• Comprising a typically square excavation filled with in-situ concrete.
• Embedded within the concrete are starter bars for reinforced concrete columns or holding down bolts for steel columns.

Mass Concrete Bases:

• Preferable Usage: Recommended whenever feasible.
• Scenario Suitability:
• Unstable excavations.
• Requirements for rapid and cost-effective construction.

Reinforced Bases:

• Appropriate in Conditions of:
• High water table.
• Adverse alterations in soil strata.
• Presence of buried services/structures.
• Thin soil strata.
• Existence of underground obstructions.

Figure 11. Types of pad foundation

https://www.youtube.com/watch?v=qDUGMIaSEnc

Pad Foundation

• Pad foundations are a type of shallow foundation, with depth below finished ground level less than 3m.
• Ground Condition Considerations:
• Risk Factors:
• Concrete vulnerability to:
• Ground or groundwater contamination.
• Effects of freeze/thaw cycles.
• Damage from vegetation.
• Soil Types Prone to Expansion:
• Silts, chalks, fine sands, and certain clays.
• Expansion risk during freeze. Soil freezes to a depth of 450mm.
• Pads on susceptible soils placed at 500mm below ground level.

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Potential solutions to mitigate against pad deformation include:

• Increased Thickness (D > B/2):
• Ensure pad thickness (D) is greater than half the column base dimension (B/2).
• Minimum thickness BS 8004: 150 mm, but consider a minimum of 300 mm.
• Steel Reinforcement (Bottom of Foundation):
• Incorporate steel reinforcement at the foundation's bottom.
• Enhances structural integrity and load-bearing capacity.
• Sulphate Salts Presence:
• Use sulphate-resisting cement in pad concrete to mitigate potential deterioration.

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Pad Foundation – Calculate the size of the pad

Pad Foundation – Calculate the size of the pad

Pad Foundation – Calculate the size of the pad

Pad Foundation – Calculate the size of the pad

Self-assessment Task

Pile Foundation

• Piles are vertical foundation elements designed to transfer loads from superstructures.
• Functions:
• Load Transfer:
• Transmit loads through weak, compressible strata or water to stable bedrock.
• Channel loads onto stiffer, less compressible soils or rock.
• Uplift Load Support:
• Handle uplift loads for tall structures facing overturning forces (e.g., winds, waves).
• Marine Structure Considerations:
• Endure lateral loads from berthing ships and wave impacts.
• Versatile Applications:
• Support retaining walls, bridge piers, abutments, and similar structures.

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Figure 12. Pile foundation (Jamal, 2017)

Pile Foundation - Classification

Load Bearing Piles

• The "soil mechanics approach" calculates a pile's capacity by considering two primary components: skin friction and end resistance.
• Piles are categorized based on the predominant component: friction piles emphasize skin friction, while end-bearing piles rely on support from hard substrates.

Components:

• Skin Friction:
• Predominant in friction piles.
• Arises from frictional forces along the pile's surface with the surrounding soil.
• End Resistance:
• Predominant in end-bearing piles.
• Occurs when the pile rests on hard, incompressible material like rock.

Figure 13. Pile foundation (Tomlinson and Woodward, 2008)

Pile Foundation

Pile Cap

• A pile cap is a reinforced concrete structural element that connects and distributes loads from the superstructure to a group of piles.
• Purpose:
• To transfer and distribute loads evenly across multiple piles
• To provide a stable connection between the superstructure and foundation
• To enhance the overall stability and load-bearing capacity of the foundation system

Pile Beams

• A pile beam is a horizontal structural member that spans between and connects multiple pile caps or individual piles.
• Purpose:
• To distribute loads laterally across a series of piles
• To provide additional rigidity to the foundation system
• To resist lateral forces and moments in the foundation

Figure 14. Pile cap and pile beams. (UK Helix, 2023)

Pile Classification According to BS 8004

• 1. Large Displacement Piles:
• Definition: Solid-section or hollow-section piles with a closed end, either driven or cast-in-place, displacing the soil (Cranston, 2021). Usually over 600 mm in diameter.
• Examples:
• Timber (round or square section, jointed or continuous).
• Precast concrete (solid or tubular section in continuous or jointed units).
• Prestressed concrete (solid or tubular section).
• Steel tube (driven with a closed end).
• Steel tube driven and withdrawn after placing concrete.

Figure 15. Displacement piles (Engineers Today, 2012)

Watch driven piles

Pile Classification According to BS 8004

• 2. Small-Displacement Piles:
• Definition: Driven or jacked into the ground with a relatively small cross-sectional area (Cranston, 2021). Usually less than 600 mm in diameter.
• Examples:
• Rolled steel H- or I-sections.
• Pipe or box sections driven with an open end (soil enters the hollow section).
• Precast concrete (tubular section driven with an open end).
• Prestressed concrete (tubular section driven with an open end).
• Steel H-section.
• Steel tube section (driven with an open end, soil removed as required).
• Steel box section (driven with an open end, soil removed as required).

Figure 16. Displacement piles (Superior Foundations, 2023)

Pile Classification According to BS 8004

• 3. Replacement piles are created through various drilling methods, where soil is removed before inserting a substitute material. Techniques include:
• Bored and Cast-in-Place:
• Concrete is placed in a hole drilled using rotary auger, baling, grabbing, airlift, or reverse-circulation methods.
• Tubular Insertion:
• Tubes are placed in a hole drilled as described above, filled with concrete as necessary.
• Precast Concrete Units:
• Preformed concrete elements are placed in a drilled hole.
• Injection Techniques:
• Cement mortar or concrete is injected into a drilled hole.
• Steel Sections:
• Steel sections are placed in a drilled hole.

Figure 17. Replacement piles. (Ougan Technology, 2020)

Watch CFA Piles

Watch cast-in-place piles

Pile Classification According to BS 8004

• 4. Composite piles leverage the strengths of different materials and categories, providing tailored solutions for specific foundation requirements.
• Composite piles result from combining units of different categories:
• Combining Different Types:
• Formation: Units from various categories (large-displacement, small-displacement, or replacement) are combined.
• Timber and Precast Concrete Joint:
• Process: Jointing a timber section to a precast concrete section creates a composite pile.
• H-Section Attachment:
• Process: A precast concrete pile may have an H-section jointed to its lower extremity for added strength and support.

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Figure 18. Composite piles. (CTech-LLC, n.d.)

Self-assessment Task

Case Study: Multi-Use Sports Development on Former Industrial Site. The proposed development will include the following buildings and facilities:

1. A multi-use sports hall with an open floor area of 40 metres by 20 metres.
2. An attached building containing:
• Changing rooms, showers, a gym, and a fitness suite.
• A reception area designed for public access, including space for vending machines and customer seating.
• Dedicated teaching and meeting rooms to accommodate schools, local sports teams, and business groups, allowing the complex to be hired for various events.

Location: Reclaimed brownfield land previously used for paint manufacturing and storage (1950s).

Ground Conditions: Mixed fill layers from remnants of solid concrete ground floor, remnants of basement structures, and potential contamination from historical industrial use.

Task:

Discuss and Evaluate (advantages and disadvantages) any three types of foundation that can be used for the buildings.

Reference/Bibliography

Chudley, R. and Greeno, R. (2016) Building construction handbook. 11^th edn. London: Routledge.

CTech-LLC (n.d.) Retrofitting of marine structures. Available at: https://ctech-llc.com/en/applications/marine-structures/ (Accessed: 17 November 2023)

Designing Buildings Ltd. (2023) Sheet piles. Available at: https://www.designingbuildings.co.uk/wiki/Sheet_piles (Accessed: 17 November 2023)

Engineers Today (2012) How to install pile to foundation. Available at: https://engineerstoday.blogspot.com/2012/04/how-to-install-pile-to-foundation.html (Accessed: 17November 2023)

Ground & Water Ltd (2001) The g&w guide to… foundation design. Available at: https://groundandwater.co.uk/blogs/the-gw-guide-to-foundation-design/ (Accessed: 08 November 2023)

Heaton Manufacturing Ltd. (2023) Pad foundations: types and uses. Available at: https://heatonmanufacturing.co.uk/pad-foundations/ (Accessed: 08 November 2023)

Jamal, H. (2017) Types of piles based on load transfer, installation methods and materials. Available at: https://www.aboutcivil.org/types-classification-of-piles.html (Accessed: 31 October 2023)

LABC (2023) Raft foundation basics. Available at: https://www.labc.co.uk/news/raft-foundation-basics (Accessed: 08 November 2023)

NHBC (2023) NHBC standards. Available at: https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/nhbc-standards-2023-complete-compressed.pdf (Accessed: 09 November 2023)

Ougan Technology (2020) Fully cased drilling with oscillator. Available at: https://www.ougangroup.com/en/news/detail_675.html (Accessed: 17November 2023)

UK Helix (2023) Can You Use Grade Beams with Screw Piles? Available at: https://www.ukhelix.com/can-you-use-grade-beams-with-screw-piles/ (Accessed: 29 September 2024)

Superior Foundations (2023) Driven piles. Available at: https://www.superiorfoundationsllc.com/our-services/driven-piles/ (Accessed: 17November 2023)

Tomlinson, M. and Woodward, J. (2008) Pile design and construction practice. 5^th edn. Oxon: Taylor & Francis.

University of the West of England (n.d.) Types of foundation. Available at: https://environment.uwe.ac.uk/geocal/foundations/fountype.htm#:~:text=Raft%20foundations%20have%20the%20advantage,loads%20over%20a%20larger%20area. (Accessed: 09 November 2023)

University of the West of England (2009) Evolution of building elements. Available at: https://fet.uwe.ac.uk/conweb/house_ages/elements/section1.htm (Accessed: 08 November 2023)

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