Onsite Verification of BIM Models

[edit] Introduction

On-site verification of BIM models is the process of comparing constructed work on a construction site with the federated building information model used for design, coordination and construction planning. It is an increasingly important aspect of construction quality management, helping to ensure that completed work conforms to design intent and project requirements.

While clash detection and model coordination processes are now widely established within the construction industry, verification of physical construction against digital models has traditionally been undertaken through manual inspections, surveys and quality audits, often towards the end of a project phase. Advances in digital technologies are enabling verification activities to be carried out more frequently and earlier in the construction process.

[edit] Need for on-site verification

Construction projects can be affected by discrepancies between coordinated design models and completed work. Such discrepancies may result in rework, programme delays, increased costs and operational issues.

Examples include:

• Structural elements installed outside specified tolerances.
• Mechanical, electrical and public health (MEP) services installed in locations that differ from the coordinated model.
• Misalignment of structural grids between floors.
• Openings and penetrations that do not correspond with coordinated design information.
• Equipment installations that affect access, maintenance or operational requirements.

Many of these issues may not be identified during model-based clash detection because the design models themselves remain coordinated. Problems arise when the physical construction deviates from the agreed design information.

[edit] Methods of on-site verification

A range of techniques may be used to verify constructed work against BIM models.

[edit] Manual measurement and visual inspection

Traditional verification methods rely on physical measurement tools, inspection checklists and construction drawings. These methods remain widely used and can be effective, but they may be time-consuming and dependent on the experience of the inspector.

[edit] Survey-based verification

Verification using total stations, GNSS equipment and other surveying technologies can provide high levels of accuracy and is commonly used for setting out and checking critical structural elements. This approach generally requires specialist equipment and trained personnel.

[edit] Reality capture and point clouds

Reality capture techniques such as laser scanning and LiDAR can generate detailed point clouds representing existing conditions. These datasets can be compared with BIM models to identify deviations and assess compliance with design requirements. Such methods can provide comprehensive records of completed work but may require significant processing and specialist expertise.

[edit] Augmented reality model visualisation

Augmented reality (AR) systems can overlay BIM models onto the physical environment using mobile devices or head-mounted displays. This enables site personnel to compare modelled and constructed elements in real time and identify potential discrepancies before subsequent work proceeds.

The achievable accuracy of AR-based verification varies depending on the technology used, calibration methods, site conditions and positioning systems. Accuracy should therefore be assessed on a project-specific basis rather than assumed to meet a fixed tolerance.

[edit] Key stages for verification

Verification is generally most effective when undertaken before subsequent construction activities conceal completed work or make corrective action more costly.

Typical verification stages include:

• Checking structural and service penetrations before concrete pours.
• Verifying installed assemblies against design information before closure or concealment.
• Inspecting ceiling voids and service risers before enclosure.
• Checking the alignment and tolerances of façades and long-span elements.
• Verifying complex building services installations and specialist systems.

[edit] Relationship with CDM 2015

The Construction (Design and Management) Regulations 2015 (CDM 2015) require projects to be planned, managed and monitored so that construction work is carried out safely and effectively.

Although CDM 2015 does not specifically require BIM-based verification, documented verification processes can support project management, quality assurance and information management objectives. They may also assist in demonstrating that construction work has been carried out in accordance with design information and project requirements.

[edit] Digital verification technologies

The increasing availability of digital surveying, reality capture and visualisation technologies has expanded the range of tools available for on-site verification.

These technologies can support earlier identification of construction deviations, improve communication between project participants and provide more comprehensive records of completed work. Their use is particularly beneficial on projects with complex geometry, extensive building services coordination, stringent tolerance requirements or significant operational constraints.

However, the effectiveness of any verification process depends on the quality of the underlying project information, the competence of personnel undertaking the checks, and the procedures established for managing and resolving identified issues.

[edit] Benefits and limitations

[edit] Benefits

Potential benefits of on-site BIM verification include:

• Earlier identification of construction errors.
• Reduced rework and associated costs.
• Improved quality control and assurance.
• Enhanced coordination between disciplines.
• Better documentation of completed work.
• Improved confidence in as-built information.

[edit] Limitations

Potential limitations include:

• Initial investment in equipment and software.
• Training requirements for site personnel.
• Dependence on the accuracy and completeness of BIM data.
• Data processing and management requirements.
• Variable accuracy depending on technology and site conditions.

[edit] Related articles on Designing Buildings

• Building information modelling BIM
• Federated building information model
• Clash avoidance
• BIM co-ordinator
• Project information model PIM
• Common data environment
• Industry Foundation Classes IFC
• Construction Operations Building Information Exchange COBie
• BIM maturity levels
• CDM