�BUILDING SURVEYING IN CONSTRUCTION

Dr Adewale Abimbola, FHEA, GMICE.

www.edulibrary.co.uk

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Aim & Objectives

Aim: Modern Methods of Construction: Foundation, External Wall, and Roof.

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

• Describe modern methods of foundation construction used for residential housing.
• Discuss the impact of the modern construction methods on current and future repair and remedial work.

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 10. 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 8. Foundation dimensions. (NHBC, 2023)

Figure 9. Trench fill foundation.

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

Self-assessment Task

In modern foundation construction, raft foundations are ideal for _______ load-bearing soil, while trench fill foundations enhance ground _______ during construction. Strip foundations require a minimum depth of _______ mm in clay soils, whereas the minimum thickness for a trench fill foundation is _______ mm. Strip foundations can adapt to sloping ground by _______ up. To prevent frost damage, the minimum foundation depth should be _______ mm below ground level. In raft foundations, steel reinforcement should be lapped at least _______ mm. A _______ proof course is used to prevent moisture passage in raft foundations. Trench fill foundations are particularly suitable for _______ ground conditions, while strip foundations are typically situated under _______ walls. Raft foundations require design by a _______ civil or structural engineer. The concrete used in trench fill foundations helps stabilise the _______ without risking collapses. Strip foundations' width and depth vary based on building _______ and ground characteristics.

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damp poor 750mm load-bearing chartered 500 mm 450 mm low stability 450 mm stepping load earth

Fill in the blanks with the appropriate words or phrases:

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

1. Describe any two modern methods of foundation construction used for residential housing.
2. Discuss their impact on current and future repair and remedial work.

Additional Reading

• Impact on current and future repair and remedial work of the specified modern methods of foundation construction:

Raft Foundation:

• Provides more uniform load distribution, potentially reducing differential settlement issues

• May require specialised techniques for localised repairs due to its integrated nature

• Future remedial work might involve careful cutting and reinforcement to maintain structural integrity

• Potential for improved performance in areas with soft or variable shallow soils

• May necessitate comprehensive ground investigation to ensure proper design and performance

Strip Foundation:

• Generally allows for easier access to localised areas for repairs

• May require reinforcement in areas with poor ground conditions

• Future remedial work might involve underpinning or extending depth if settlement occurs

• Potential for differential settlement in variable soil conditions

• Repairs may be needed if foundation depth is insufficient to protect against frost heave

Trench Fill Foundation:

• Offers reduced excavation work compared to traditional strip foundations

• May present challenges in ensuring consistent foundation levels during construction

• Future repairs might involve careful consideration of load distribution if localised issues occur

• Potential for improved performance in areas with deeper frost penetration

• May require specialised techniques for remedial work in confined spaces

Pad Foundation:

• Allows for targeted repairs to individual pads without disturbing the entire foundation

• May require careful monitoring of differential settlement between pads

• Future remedial work might involve additional pads or connecting beams if soil conditions change

• Potential for improved adaptability to varying ground conditions across a site

• Repairs may be needed if pad sizing or spacing is found to be inadequate over time

Pile Foundation:

• Often requires specialised equipment and expertise for both initial construction and future repairs

• May present challenges in diagnosing and addressing issues with deep-set piles

• Future remedial work might involve additional piles or pile caps to address settlement or changing loads

• Potential for improved performance in areas with poor surface soil conditions

• Repairs may be complicated by the need to maintain existing structural loads during work

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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