How 3D Models Change Preliminary Quantity Estimation

Definition of Preliminary Quantity Estimation and Its Role in Civil Engineering Work

Preliminary quantity estimation refers to the design process in the early stages of a civil engineering project in which the quantities required for construction (e.g., earthwork volumes, volumes and areas of structures) are roughly calculated. At this stage, approximate quantities are derived from plan layouts, standard cross-sections, and other preliminary drawings before detailed drawings and construction plans are available. The quantities obtained from preliminary quantity estimation are used to determine the project scale and to estimate preliminary construction costs, serving as important inputs for evaluating the feasibility of the plan and securing budgets.

In the flow of civil engineering design—from conceptual planning to preliminary and detailed design—preliminary quantity estimation plays a particularly important role in the early planning and budgeting phases. For example, in earthworks or road projects, having an early understanding of how much cut-and-fill is required, and how much pavement area or number of structures will be needed, makes it easier to forecast overall project costs and schedules. Recently, some local governments have trialed a “preliminary-quantity procurement method” that uses these preliminary quantities to advance construction contracting earlier, increasing the demand for higher accuracy and reliability in quantity estimation during the initial design stages.

Challenges of Traditional 2D-Based Design

Traditional civil engineering design relied on 2D drawings (plans, profiles, cross-sections) on paper or CAD to plan projects and derive quantities from those drawings. For roads and site development, it was common to generate cross-sections at regular intervals and calculate earthwork using the average cross-section method based on those sections. However, this 2D-based design approach has several known limitations.

• Insufficient reflection of terrain undulations and complex shapes: When cross-sections are taken every tens of meters, small depressions or rises between those sections are averaged out and not reflected in the calculations. Real terrain changes continuously, but 2D drawings can only represent it with points and lines, so the information inevitably becomes coarse.

• Cumbersome quantity calculation work: Measuring lengths and areas on drawings and summing volumes by segment relies heavily on manual work and is time-consuming. Designers often repeat calculations for each section in spreadsheet software, which is a major burden. As calculation processes become more complex, the risk of human error also increases.

• Inefficient response to design changes: If the plan layout or vertical alignment is changed, cross-sections must be redrawn and quantities recalculated. This makes it difficult to quickly review plans or compare multiple alternatives, reducing flexibility in the design phase.

• Effort required for information sharing and consensus building: Because it is necessary to cross-reference plan, profile, and cross-section drawings to grasp the site image, explaining design intent to the client or contractor takes time. Finished forms are hard to intuit from 2D drawings alone, which can lead to inconsistencies with the terrain or oversights.

Thus, traditional methods had limits in accuracy and workflow efficiency for early-stage quantity estimation, often contributing to design changes or contract modifications during construction.

Concrete Benefits of Introducing 3D Models

In recent years, the use of 3D models has attracted attention. Introducing 3D models into design brings many benefits that were not achievable with conventional 2D design. Specifically:

• Quantity estimation that faithfully reflects terrain: In 3D models, the existing ground and planned ground can each be represented as surface data (meshes or TINs), and earthwork volumes can be calculated directly from their differences. Because large areas of terrain are handled continuously, fine undulations are reflected in the quantities. For example, by setting a finer mesh size, locally overlooked depressions can be included in calculations, dramatically improving the accuracy of earthwork estimation.

• Automation and acceleration of quantity calculations: If a model is created in specialized civil 3D CAD software, quantities such as volumes, areas, and lengths are automatically aggregated by the software. This greatly reduces manual measurement and hand calculations and can dramatically shorten the time required to produce numerical estimates. In one large project, a task that previously took four people seven days was completed by two people in one day using a 3D point cloud model, demonstrating significant speed gains for both design and construction.

• Flexible response to design changes and comparative evaluation of multiple options: If alignment or elevation is modified in the model, quantities are recalculated immediately. It becomes easy to quickly compare earthwork and quantities for different design options, facilitating rapid selection of optimal plans and quick adaptation to changes. This broadens the scope of evaluation in the design phase and helps produce more economical and rational plans.

• Higher consistency in design and reduction of errors: Because terrain, structures, and ancillary facilities can be represented integrally in 3D, interferences and inconsistencies among design elements are easier to detect in advance. For example, interactions between roads and drainage pipes or between retaining walls and soil can be visualized in the model to prevent issues that are hard to notice on 2D drawings. As a result, rework and corrections during construction are reduced, improving quality.

• Improved visual clarity and facilitation of consensus building: Sharing a 3D completion image simplifies explanations to clients and local residents and can accelerate consensus building. Complex structures can be intuitively understood by showing the model on a tablet, and if the model is used during construction, workers and operators can share a spatial understanding of the finished form. Performing schedule simulations or virtual construction on the model also helps in safety planning and optimizing construction procedures.

• Institutional support: The Ministry of Land, Infrastructure, Transport and Tourism is promoting i-Construction and making the use of BIM/CIM a standard, so design and estimating using 3D models are expected to become mainstream. In fact, the guidelines for civil engineering quantity calculation specify 3D data-based calculation methods (such as TIN differencing of point clouds and the prismoidal method), and software vendors have implemented features to support these methods. Technological advances have lowered the barrier to adopting 3D design, and what was once limited to some large projects is now becoming a realistic option for a wide range of sites.

Changes in Quantity Design by Major Work Types: Earthworks, Pavement, Revetments, Slopes, etc.

Next, let’s look at how quantity calculation methods change for major civil work types when utilizing 3D models.

Earthworks (Fills and Cuts)

The impact of 3D model introduction is particularly significant in earthworks. By comparing 3D surface models of existing and planned ground, cut and fill volumes can be accurately calculated together. Unlike the average cross-section method, 3D models do not miss undulations between measurement points and allow complete capture of total earthwork, enabling more accurate estimation of spoil disposal volumes and the quantities of fill material to procure. Adjusting design elevations to simulate earthwork balance is also easy, enabling rapid optimization such as effective use of on-site soil and minimization of exported material.

Pavement

In pavement design for roads, parking lots, etc., 3D models make calculating areas and thicknesses smooth. By creating the 3D shape of the pavement surface and base on the road model, the accurate pavement area including curves and grades can be obtained automatically. Quantities that were previously estimated as length × width on plan view can now be precisely calculated by the model, including widening sections and complex intersection geometries, ensuring required asphalt and base material volumes are fully accounted for. When alignment or width changes occur, updating the model instantly re-aggregates quantities, minimizing the need for re-measurement work associated with changes.

Revetments

For river and coastal revetment works, 3D design greatly improves shape understanding and quantity accuracy. For example, modeling a riverbank in 3D allows accurate estimation of fill volumes and the number of revetment blocks required along curves and slopes. Sections that could only be represented as representative cross-sections in 2D can be expressed as continuous structures in the model, enabling consistent quantity calculations along the length. This allows precise estimation of block counts, concrete placement volumes, and sheet pile lengths, aiding material procurement planning from the design stage. Adjusting revetment alignment to fit complex terrain is also easy in 3D space, allowing pre-checks of how the structure will fit the actual site.

Slopes

In slope works for developed land or roadside slopes, capturing slope geometry in 3D ensures accurate calculation of required materials. Modeling the finished shape of cut slopes allows instant measurement of their surface area, enabling correct estimates for seed spraying or slope covering. Work that previously involved summing slope lengths for each cross-section can be computed for the entire slope at once in the model, preventing calculation errors or omissions. Adjusting lines such as the slope crest and slope toe visually to match the terrain allows rational consideration of fill slope height settings and bench (terrace) placement. Consequently, quantities of retaining structures and reinforcement materials can be properly understood, enhancing the reliability of construction planning.

Data Management with an Eye from Design Through Construction and Maintenance

The benefits of 3D model use extend beyond the design stage. Seamlessly carrying the created digital data through the construction and maintenance phases and using it consistently can bring further efficiency and quality improvements.

• Smooth handover to construction: The 3D models created during design can be used as-is in construction. Traditionally, contractors had to recreate construction data from 2D drawings, but sharing the design model simplifies data linking to machine control and surveying instruments. Referencing the model on-site can reduce batter board work and enable real-time confirmation of as-built form, directly contributing to labor-saving and sophistication through ICT construction.

• Use for as-built management and quality inspection: During and after construction, point cloud data captured by drone photogrammetry or terrestrial LiDAR can be overlaid with the design 3D model and used for as-built quantity estimation and progress control. Visualizing differences between design and measured values in 3D (e.g., color-coded) makes it easy to detect excesses or shortages early and simplifies as-built inspection. For example, in excavation work, scanning the post-construction terrain to automatically calculate cut volumes and immediately evaluating differences from design volumes facilitates early consideration of contract changes or additional procurement, speeding on-site responses. The as-built 3D data can be stored and used as electronic delivery data, reducing the burden of creating traditional paper-based inspection documents.

• Data use in maintenance: The 3D data of completed structures is a valuable information asset during maintenance. If the as-built model saved at handover is kept as baseline data, it can be compared with future point cloud surveys during periodic inspections to understand aging changes or quantitatively evaluate damage after disasters. Adding attribute information (material type, construction year, etc.) to the 3D model and linking it with maintenance systems or GIS allows it to function as a digital ledger. Consistently using and updating data from design through construction to maintenance realizes a “digitally connected” workflow where project information remains useful throughout the lifecycle.

Practicality for Small-Scale Projects and Municipal Design Work

So far we have discussed the advantages of 3D model use, but you may think it is only feasible for large projects or specialist firms. However, recently the environment for using 3D models in small-scale projects and local government design work is becoming more accessible, and applications are spreading to everyday tasks.

On the software side, intuitive 3D CAD and cloud services for civil design have become widespread, enabling basic terrain and design model creation even without specialized knowledge. Free software and low-cost tools have emerged, making adoption feasible for budget-limited projects. On the hardware side, the cost of drone aerial photography and terrestrial laser scanning has fallen, and in some cases, simple measurement methods using tablets or smartphones to capture 3D site data are now available.

In practice, municipal authorities have reported cases where small road improvements or local dam works successfully introduced 3D design experimentally, achieving richer deliverables and shorter design periods. Even small design teams can improve efficiency and accuracy by partially implementing 3D (e.g., modeling only the terrain and main structures). The key is to start digitalization at a scale appropriate to the project. For example, creating a 3D model of the existing terrain first and calculating earthwork volumes can be a small initial step that clearly demonstrates the difference from traditional methods.

Thus, 3D technology is not a special tool reserved for large projects but a powerful means to update everyday design work and can be applied across projects of all sizes.

Implementation Benefits of Simple 3D Surveying with LRTK

Finally, we introduce simple 3D surveying using LRTK, a technology that makes 3D model utilization even more accessible. No matter how advanced design technology becomes, accurate on-site terrain and structure data are essential for high-accuracy quantity estimation. Traditionally, high-precision 3D surveying required expensive laser scanners and specialized operators, making adoption difficult for small sites. LRTK (Lightweight RTK) is a groundbreaking solution that greatly lowers that barrier.

LRTK is a surveying system consisting of a pocket-sized RTK-GNSS receiver that can be attached to a smartphone and a dedicated app, enabling centimeter-level positioning by anyone. RTK-GNSS corrects the smartphone’s position information to obtain high-precision coordinates. In addition, by linking with the smartphone’s built-in LiDAR scanner or camera to scan the surroundings, site geometry can be recorded as 3D point cloud data. What once required specialized equipment can now be achieved with just a smartphone and a small device, symbolizing the "democratization of 3D surveying".

Introducing LRTK on-site offers many benefits. First, the low cost is a major advantage: there is no need for expensive specialized equipment, and a smartphone plus a relatively inexpensive receiver is sufficient, dramatically reducing initial investment. Second, its portability and mobility are excellent; the pocket-sized device allows walking the site while measuring, making it useful for small mountain-area projects or cliff sites where large machinery cannot be brought in. Third, the ease of operation is notable—non-specialist personnel can complete precise surveys by following app prompts and pushing a button, making it an intuitive, universal surveying tool without complex setup or expert knowledge. Furthermore, real-time data sharing and immediate analysis are possible: data can be uploaded to the cloud on-site and shared with office colleagues for quick review. Automatically calculating volumes from captured point clouds to immediately grasp earthwork quantities on-site supports rapid decision-making.

By using LRTK, on-site acquisition of 3D data—which traditionally required significant time and effort—becomes dramatically easier, enabling preliminary quantity estimation using 3D models for projects of all scales. Incorporating high-accuracy existing 3D data from the early design stage improves the precision of earthwork and structure layout, directly enhancing design reliability and reducing rework. LRTK is expected to be a key technology supporting the transformation of preliminary quantity estimation through 3D model utilization. Going forward, leveraging such easy 3D surveying tools will further accelerate the digitalization and sophistication of civil engineering design work.