�SITE INVESTIGATION

Dr Adewale Abimbola, FHEA, GMICE.

www.edulibrary.co.uk

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Aim & Objectives

Learning Outcomes and Assessment Criteria

P3 – Describe the pre-design studies carried out and types of information collected for a given construction site.

Site Investigation

Definition

• It involves the systematic gathering of data and the thorough assessment of the characteristics of the site, all aimed at facilitating the planning and construction of a solid foundation for a building or structure.

Its Purpose:

• Assessing the appropriateness of the site for the intended needs of the project.
• Implementing cost-effective foundation design strategies.
• Anticipating potential construction challenges.
• Safeguarding the client's investment by mitigating the impact of ground conditions on the long-term structural integrity.
• Ensuring the construction of secure and functional structures for end-users.

Site Investigation

Site Investigation

The common causes of structural damage to buildings include:

Site Investigation & Classification

Types of Site Investigation:

1. Investigation of sites for new construction projects.
2. Investigation of defects, failures, or safety concerns in existing structures.

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Site Classification: Compact & Extended

1. Compact: sites to contain buildings, bridges, dams, docks and airfields
2. Extended: sites covering a long narrow strip of land for roads, railways, tunnels, sewers, pipe and transmission lines, and coastal defence.

Site Investigation

• 1. Investigation of Sites for New Construction Projects
• Large information required and economic solutions involved:
• Ground Water Condition.
• Site Topography.
• Environmental Impact.
• Utilities and Infrastructure.
• Site Accessibility.
• Surrounding Land Use.
• Archaeological and Historical Considerations.
• Geological and Seismic Activity.

Site Investigation

Three Stages of Site Investigation or Pre-design Studies

Stages of Site Investigation

1. A clue of the desk study:

• Extent of detailed study:

Table 1. Types of information useful for desk studies (Geotechnique.info, 2004)

Table 2. Sources of maps and photographs (Geotechnique.info, 2004).

Stages of Site Investigation

• Clayey soils like London Clay and Gault Clay pose potential structural challenges due to their tendency to experience significant subsidence, with depths exceeding 1 m.
• For London clay, which often contains excessive soluble sulphates, the use of sulphate-resistant cement is recommended.
• In areas with trees, their root which may reach down to 5 m are capable of desiccating soil.
• Chalk and limestone are prone to dissolution features caused by acidic contaminants/surface water. The dissolved zone becomes infilled with loose soils which, if inundated, will become unstable and subside if built upon.
• Variability in Alluvial Deposits: Alluvial deposits tend to exhibit greater variability in lithology and lower compaction compared to other sedimentary deposits.
• Diverse Deposits: It's essential to recognise that all deposits vary in terms of thickness and geotechnical properties. The extent of site investigation should be tailored to the expected diversity of ground conditions.

Stages of Site Investigation

• Details of coal, iron deposits, limestone, sands and gravels, and other deposits of economic importance on geological maps may indicate evidence of mining. https://www.welshcoalmines.co.uk/Photo.htm
• The presence and concentrated network of utilities can potentially pose safety hazards to drilling personnel. Service documentation maintained by utility providers, such as gas, electricity, telephone, and water supply companies, needs to be studied.
• Soil Survey Records: Focusing on surface deposits, typically up to depths of around 1 m. https://www.ukso.org/static-maps/soils-of-england-and-wales.html
• Meteorological records: planning around bad weather conditions which may impact the operation of earthmoving equipment, etc. https://www.ventusky.com/
• River authority records: Archive information regarding historical flooding events and associated data. E.g. Section 19 report (Under Section 19 of the Flood and Water Management Act 2010).
• Published and unpublished geological records are available for a wide variety of areas from University libraries, journal papers, professional bodies, etc.
• Borehole data from site/soil investigation. https://www.bgs.ac.uk/map-viewers/geoindex-onshore/

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Self-assessment Task

Stages of Site Investigation

2. Site Reconnaissance/walk-over Survey:

• It involves physically surveying the site, commonly referred to as 'walking the site.' This step serves several purposes:
• Gathering additional insights into the geological features and potential construction challenges.
• Evaluating accessibility for investigation equipment and machinery.
• Determining the positions of existing buildings, boundaries, obstructions, and their relevance to the initial desk study.
• Documenting nearby properties and their potential influence on the proposed project.
• Local Investigations: This phase encompasses the examination of local archives related to the site and engaging with residents to gather valuable information about the site's history and characteristics; and previous mining activities.
• Information on the prevailing type of foundation in the area.

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Stages of Site Investigation

2. Site reconnaissance/walk-over survey:

• Observe signs of land movement, particularly susceptibility to landslips.
• Evaluate site accessibility for transportation purposes.
• Identify distinctive vegetation features, such as uncommon green areas, reeds, rushes, and willow trees, which can indicate wet ground conditions.
• Make a note of springs and seepages and incorporate them into the site plans.
• Gather historical data regarding past instances of flooding in the vicinity through local inquiries.
• Pay attention to indications of active soil erosion caused by surface water, including the presence of gullies.
• Inspect structures located on or near the site for any damage, making sure to capture photographic evidence of issues like cracks or deviations from vertical alignment. This documentation is essential to mitigate potential future claims from neighbouring properties.

3. Methods of Site Exploration

• The site investigation leads to the development of a soil testing and evaluation program, tailored to the specific requirements of different contract sizes, whether they are small, medium, or large in scale.
• For Small Projects: Small-scale works typically involve conducting trial pits, which can extend to depths of up to 4 metres.
• For Medium to Large Projects: Medium to large-scale projects may require more extensive exploration, involving boreholes that can reach depths of up to 30 metres.
• For Very Large Projects (e.g., Dams): Demand a comprehensive approach that combines deep boreholes, trial pits, and in-situ examinations performed from tunnels and shafts.

Stages of Site Investigation

• Soil is broadly classified into five categories:
• Granular soil (e.g. sands or gravels)
• Cohesive soil (e.g. clays)
• Organic soil (e.g. peats)
• Fill or made ground
• Rock

Stages of Site Investigation

Table 3. Types of laboratory and insitu tests (Building Research Establishment Ltd,1995)

Size Range of Grains

• In the British Soil Classification System, soils are classified into named Basic Soil Type groups according to size, and the groups further divided into coarse, medium and fine sub-groups.

Aids to Size Identification

Soils possess several physical characteristics that can be used as aids to size identification in the field.

A handful of soil rubbed through the fingers can yield the following:

• SAND (and coarser) particles are visible to the naked eye.
• SILT particles become dusty when dry and are easily brushed off hands and boots. https://www.youtube.com/watch?v=4xPxJomy0U8
• CLAY particles are greasy and sticky when wet and hard when dry and must be scraped or washed off hands and boots.

Stages of Site Investigation��3. Methods of Site Exploration�

Stages of Site Investigation

3. Methods of Site Exploration

• Borings: All borings placed sufficiently close together to prevent false deductions concerning the uniformity of horizontal strata. Approx. borehole position is usually at distances 15 metres apart in either direction.
• Depth depends on the type of loading.
• Three main factors govern the depth of exploration:

I. Depth to which the soil is significantly stressed:

• Depends on type of foundation, intensity of loading and the shape and size of the foundation structure

Figure 1. Location plan of boreholes (Chudley and Greeno, 2016)

Usually depths of:

1.5b is considered for road and airfields, 2.7b is considered for strip foundation, 1.4b for rafts foundation, 1.5b for pads foundation.

(Where b is the width of the structure).

Stages of Site Investigation

3. Methods of Site Exploration

• Borings:

I. Depth to which weathering is likely to affect the soil:

• Seasonal changes in moisture content and has been known to affect some soils down to a depth of 1.5 metres.

III. The depth at which impermeable strata occur: This applies to water-conserving structures such as reservoirs, where an impermeable stratum is essential and must be located.

Soil samples:

• Disturbed soil samples where the natural structure and properties of the subsoil are disturbed. Gotten from boreholes and trial pits.
• Undisturbed soil samples obtained using coring tools which preserve the natural structure and properties of the subsoil.

Research the following boring methods: hand auger, mechanical auger, light cable percussion borings, rotary boring, piston samplers, and sampling shells.

Self-assessment Task

Describe the pre-design studies carried out and types of information collected for a given construction site:

• Desk Study,
• Site Reconnaissance,
• Soil Investigation.

Reference/Bibliography

Building Research Establishment Ltd (1987) Site investigation for low-rise building:procurement. Digest 322.

Building Research Establishment Ltd (1995) Site investigation for low-rise building: direct investigations. Digest 411.

Carter, M. and Bentley, S. P. (2016) Soil properties and their correlations. 2^nd edn. John Wiley and Sons.

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

Geotechnique.info (2004) Chapter 3: The desk study and walk-over survey. Available at: http://www.geotechnique.info/SI/SI%20Book%20Chapter%203.pdf (Accessed: 31 October 2023)

Southern Testing Ltd (2023) Geological and geotechnical hazards in south east england: part 2 solution features in chalk. Available at: https://www.southerntesting.co.uk/blog/geological-and-geotechnical-hazards-in-south-east-england-part-2-solution-features-in-chalk/#:~:text=Solution%20features%20(or%20dissolution%20features,%2C%20if%20inundated%2C%20will%20subside. (Accessed: 31 October 2023)

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