3D Models Changing Preliminary Quantity Estimation Design

Definition of Preliminary Quantity Estimation Design and Its Position in Civil Engineering Work

Preliminary quantity estimation design refers to the design process in the early stages of a civil engineering project that roughly calculates the quantities required for construction (e.g., earthworks volumes, volumes and areas of structures). At this stage, rough quantities are obtained based on plan drawings and standard cross-sections before detailed drawings and construction plans are available. Quantities obtained from preliminary quantity estimation design are used to determine project scale and to calculate preliminary construction costs, serving as important decision materials for assessing the feasibility of plans and securing budgets.

In the flow of civil engineering design, as projects progress from conceptual planning to preliminary and detailed design, preliminary quantity estimation design plays a particularly important role in the early planning and budgeting phases. For example, in land development or road planning, knowing early on how much earth needs to be cut or filled, and how much pavement area or structure quantity will be required, makes it easier to forecast overall project costs and schedules. In recent years, some municipalities have trialed an “order-by-preliminary-quantity” approach that advances construction contracting early using these preliminary quantities, so improving the accuracy and reliability of quantity estimation at the early design stage is increasingly demanded.

Issues with Conventional 2D-Based Design

In conventional civil engineering design, plans were developed using 2D drawings on paper or CAD (plan views, longitudinal profiles, cross-sections), and quantities were derived from those drawings. For example, in roads or housing development, it was common to create cross-sections at regular intervals and calculate earthwork volumes using the average cross-section method from those sectional areas. However, several issues have been pointed out with this 2D-based design.

• Insufficient reflection of terrain undulation and complex shapes: When cross-sections are taken every several tens of meters, fine depressions and rises between those sections are averaged out and not reflected in the calculation results. 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 section by section relies heavily on manual work and takes time. It is necessary to repeat calculations for each section using spreadsheet software, placing a heavy burden on designers. The more complex the calculation process, the higher the risk of human error.

• Inefficient response to design changes: If plan layouts or longitudinal gradients are changed, cross-sections must be redrawn and quantities recalculated. It is difficult to quickly review plans or compare multiple alternatives, which reduces flexibility in the design phase.

• Effort required for information sharing and consensus building: Because it is necessary to cross-reference plan, longitudinal, and cross-sectional drawings to grasp the site image, it takes time to explain design intent to clients and contractors. It is also difficult to intuitively grasp the completed form from 2D drawings alone, leading to mismatches with the actual terrain and oversights.

Thus, conventional methods had limits in the accuracy of quantities and work efficiency in early design stages, which sometimes led to design or contract changes during later construction stages.

Specific Benefits of Introducing 3D Models

In this context, the use of 3D models has attracted attention in recent years. Introducing 3D models into design brings many benefits that cannot be achieved with conventional 2D design. Specifically:

• Quantity estimation that faithfully reflects terrain: In 3D models, existing ground and planned ground can each be represented as surface data (meshes or TIN), and earthwork volumes can be calculated directly from their differences. Because broad areas of terrain are handled continuously, fine irregularities are reflected in the quantities. For example, if mesh sizes are set finely, local depressions that were often overlooked in the past can be included in calculations, dramatically improving the accuracy of earthwork estimation.

• Automation and acceleration of quantity calculations: If models are created in dedicated civil 3D CAD software, the software will automatically aggregate quantities such as volumes, areas, and lengths. This significantly reduces manual measurement and hand calculation, dramatically shortening the time required to generate numbers. In one large site, a measurement and calculation task that previously required four people working seven days was completed by two people in one day by using a 3D point cloud model, demonstrating major speed improvements that benefit both design and construction.

• Flexible response to design changes and comparison of multiple alternatives: If alignment or heights are modified in the model, quantities are recalculated instantly. It is easy to quickly compare earthwork and quantities for different design options, enabling rapid selection of the optimal plan and quick follow-through on changes. This broadens the scope of exploration in the design stage and facilitates more economical and rational planning.

• Consistent design and error reduction: Because terrain, structures, and ancillary facilities can be represented integrally in 3D, interferences and inconsistencies between design elements can be discovered in advance. For example, conflicts between roads and drainage pipes or between retaining walls and the ground can be visualized in the model, preventing problems that are hard to notice in 2D drawings. As a result, rework and corrections during construction are reduced and quality is improved.

• Improved visual clarity and facilitation of consensus building: Sharing completion images in 3D makes it easier to explain to clients and local residents, speeding up consensus building. Complex structures can be intuitively understood by showing the model on a tablet, and if models are used during construction, craftsmen and operators can share a spatial image of the completed form. Additionally, conducting schedule simulations or virtual construction on the model helps examine safety planning and optimize construction procedures.

• Institutional support: As part of promoting i-Construction, the Ministry of Land, Infrastructure, Transport and Tourism is moving to make BIM/CIM utilization a principle, and design and estimation using 3D models are expected to become mainstream. In fact, civil engineering quantity calculation guidelines specify quantity calculation methods using 3D data (e.g., point cloud TIN differencing and prismoidal methods), and software vendors have implemented functions to support these methods. Technological innovation has lowered the barriers to introducing 3D design, and what was once limited to some large projects has now become a realistic option for a wide range of sites.

Changes in Quantity Design by Major Structure Type: Earthworks, Pavement, Revetment, Slopes, etc.

Next, let us look at how quantity calculation approaches change by major work type in civil engineering when utilizing 3D models.

Earthworks (Filling and Cutting)

The effects of introducing 3D models are particularly significant in earthworks. By comparing 3D surface models of existing and planned ground, cut and fill volumes can be calculated accurately in one operation. Unlike the average cross-section method, which can miss irregularities between survey points, you can fully grasp total earth quantities without omission, allowing you to more accurately estimate the amount of surplus soil to be disposed of and the amount of fill material to procure. It is also easy to simulate earthwork balance by fine-tuning design heights, enabling rapid optimization studies such as effective use of on-site excavated soil and minimization of exported soil.

Pavement

In pavement design for roads and parking lots, 3D models make area and thickness calculations smooth. If you create the three-dimensional shapes of the road surface and base on a road model, the software can automatically calculate the accurate pavement area including curves and gradients. Quantities that were conventionally estimated from plan length × width can now be accurately reproduced by the model even for widening areas and the complex shapes of intersections, so required asphalt quantities and base material volumes can be fully accounted for. When alignment or width changes occur due to design changes, updating the model immediately reaggregates quantities, minimizing the need for re-take measurement work caused by changes.

Revetment

In river and coastal revetment works, 3D design greatly improves shape comprehension and quantity accuracy. For example, modeling a river levee in 3D allows accurate estimation of fill volumes and the number of revetment blocks required along the curvature and slope of the river. Sections that could only be represented by typical cross-sections in 2D drawings can be expressed as continuous structures in the model, enabling consistent quantity calculation along the length. This makes it possible to accurately calculate quantities such as the number of revetment blocks, concrete placement volume, and the length of steel sheet piles, aiding material procurement planning from the design stage. Adjusting revetment alignment to complex terrain is also easily examined in 3D space, allowing pre-checks for fitting with the actual terrain.

Slopes

In slope works for developed land or roadside slopes, capturing slope shapes in 3D ensures accurate calculation of required materials. If the finished shape of a cut slope is modeled, its surface area can be measured instantly, enabling correct estimation of areas for seed spraying or surface protection. Work that previously required summing slope lengths by section can be computed in one operation on the model, preventing calculation errors or omissions. Visual adjustment of crest and toe lines to fit the terrain also makes it easier to rationally consider height settings for fill slopes and bench (terrace) placement. This allows accurate identification of quantities for required retaining works and reinforcement materials, increasing the reliability of construction planning.

Data Management Aimed at Seamless Handover from Design to Construction and Maintenance

The benefits of 3D models are not limited to the design stage. By seamlessly carrying digital data forward into construction and maintenance phases and using it consistently, further efficiency and quality improvements can be expected.

• Smooth handover to construction: 3D models created during design can be used as-is in the construction phase. Previously, contractors had to recreate construction data from 2D drawings, but sharing the design model makes it easy to link data to machine control systems and surveying equipment. Referring to the model on site can reduce batter board work and enable real-time confirmation of as-built forms, directly contributing to labor savings and sophistication through ICT construction.

• Use for as-built management and quality inspection: During and after construction, point cloud data obtained by drone photogrammetry or terrestrial LiDAR can be overlaid on the design 3D model and used for as-built quantity grasping and progress management. Visualization such as color-coding differences between design and measured values in 3D is easy, enabling early detection of excess/deficit and simplifying as-built inspections. For example, in excavation works, scanning the post-construction terrain to automatically calculate cut volumes and instantly evaluating differences from design volumes is possible. This enables early consideration of contract changes or additional procurement as needed, speeding site response. As-built 3D data can be saved and used as electronic deliverables, reducing the burden of preparing traditional paper inspection documents.

• Data use for maintenance: 3D data of completed structures are valuable information resources in the maintenance stage. If the as-built model at handover is stored as baseline data, future periodic inspections can compare new point cloud surveys to grasp aging changes, or quantitatively evaluate post-disaster deformations. Moreover, if attribute information (materials, construction year, etc.) is attached to the 3D model, it can be linked with maintenance systems or GIS to function as a digital ledger. By consistently utilizing and updating data from design through construction and maintenance, a “digitally connected” workflow is realized in which information remains useful throughout the project lifecycle.

Practicality for Small-Scale Projects and Municipal Design

So far we have described the advantages of using 3D models, but you might think this is only feasible for large projects or specialized firms. However, nowadays environments for using 3D models in small projects and local government design work are being established, and application to everyday tasks is expanding.

On the software side, intuitive civil 3D CAD and cloud services have become widespread, allowing basic terrain and design models to be created without specialized knowledge. Free software and affordable tools are also available, making adoption easier for budget-limited projects. On the hardware side, the cost of drone aerial photography and terrestrial laser scanning has decreased, and in some cases simple surveying methods such as capturing 3D data in the field with tablets or smartphones are now possible.

In fact, there are reports of local governments that manage small road improvements or erosion-control dam works having trialed 3D design and achieved enhanced deliverables and shortened design periods. Even small design teams can improve efficiency and accuracy by partially implementing 3D (for example, modeling only the terrain and primary structures). The key is to start digitalization at a manageable scale according to project size. For example, taking the small step of first creating a 3D terrain model of existing conditions and calculating earthwork quantities will let you experience the differences from conventional methods.

Thus, 3D technology is not a special tool only for large projects, but a powerful means to update everyday design work that can be used across projects of all scales.

Implementation Benefits of Simple 3D Surveying Using LRTK

Finally, we introduce simple 3D surveying using LRTK, a technology attracting attention for making 3D model utilization even more accessible. No matter how advanced design techniques become, accurate field terrain and structure data are essential for high-accuracy quantity estimation. Historically, high-precision 3D surveying required expensive laser scanners and specialist operators, making adoption difficult for small sites. LRTK (Lightweight RTK) is a revolutionary solution that significantly lowers this barrier.

LRTK is a surveying system composed of a pocket-sized RTK-GNSS receiver that can be attached to a smartphone and a dedicated app, enabling centimeter-level positioning (cm level accuracy (half-inch accuracy)) that anyone can perform easily. RTK-GNSS corrects the smartphone’s position information to obtain high-precision coordinates. Additionally, by linking with a smartphone’s built-in LiDAR scanner or camera to scan the surroundings, site shapes can be recorded as 3D point cloud data. What previously required specialized equipment is now achievable with just a smartphone and a small device, making LRTK a technology that truly symbolizes the “democratization of 3D surveying.”

Introducing LRTK on site brings many advantages. First, the ability to start at low cost is a major benefit. There is no need to procure expensive dedicated equipment; you can introduce the system with just a smartphone and a relatively inexpensive receiver, drastically reducing initial investment. Next, portability and mobility are excellent: a pocket-sized device can be carried around the site to take measurements, making it useful for small mountain-area projects or cliff sites where large machinery cannot be brought in. The ease of operation is also noteworthy; even surveyors without special training can complete precise surveying by following the app’s on-screen instructions and pressing buttons. With intuitive operation that requires no complex equipment settings or specialist knowledge, it becomes a versatile surveying tool that anyone can use. Furthermore, real-time data sharing and immediate analysis are possible: measured data can be uploaded to the cloud on the spot and shared with office colleagues for immediate review. Automatic volume calculation from acquired point clouds to instantly grasp earthwork quantities can be realized on site, supporting rapid decision-making.

By utilizing LRTK, field 3D data acquisition—which previously required considerable time and effort—becomes dramatically easier, making preliminary quantity estimation design using 3D models practical for projects of all scales. Incorporating high-precision existing-condition 3D data from the early design stage improves the accuracy of earthworks and structure placement, directly enhancing design reliability and reducing rework. LRTK is therefore expected to be a key technology supporting the transformation of preliminary quantity estimation design through 3D model utilization. Going forward, the digitalization and sophistication of civil engineering design work will accelerate further as such easy-to-use 3D surveying tools are also leveraged.