The Practical Power of Approximate Quantity Design Seen in Field Case Studies

Introduction: Can Quantity Design Change the Field?

On civil engineering sites, the approximate quantities calculated during the design phase are a critical factor that can determine the outcome of an entire project. If quantities such as the volume of earthworks, slope surface areas, and the lengths of water and sewer pipes are accurate, both owners and contractors can proceed with confidence. However, large errors in approximate quantities can lead directly to cost overruns, design changes, and even loss of trust among stakeholders. In fact, in recent years some local governments have begun trialing a “approximate quantity design method” that treats initial design quantities as provisional and finalizes them after contract award (https://www.pref.chiba.lg.jp/suidou/kyuusui/gaisansuuryou.html). This approach aims to simplify early-stage quantity calculations and speed up procurement, but it still raises the crucial question of how to ensure the reliability of the approximate quantities themselves. That is why there is an increasing demand for new technologies that improve the accuracy, speed, and trustworthiness of quantity design.

Recently, new technologies that dramatically improve the accuracy, speed, and reliability of quantity design have begun to be introduced on sites. How the “practical power” of approximate quantity design changes the field is explored in this article through case studies of land development, slope protection, and water/sewer projects.

Case 1: Earthwork Volume Accuracy in Development Planning Influences Procurement Decisions

This occurred during the planning stage of creating an industrial park in a suburban area. The client, a local government, aimed to balance cut and fill volumes as much as possible to avoid off-site disposal of surplus soil. However, there remained unease about the earthwork volume calculations produced by conventional methods. Because terrain had been inferred from a limited number of survey points, there was a risk of discrepancies between the estimated and actual cut-and-fill volumes. If a large amount of unexpected surplus soil occurred, additional disposal costs and extended schedules would be unavoidable. Faced with the procurement decision, the municipal official wondered, “Can we really rely on these quantities?”

The new method adopted to address this was detailed 3D surveying using drone photogrammetry and RTK-GNSS. The entire planned site was flown with drones to acquire high-precision point cloud data. The cut-and-fill volumes calculated from that point cloud were far more accurate than conventional estimates, differing by only a few percent from the initial plan. For example, whereas conventional methods raised concerns about errors exceeding 10% in earthwork volumes, drone surveying achieved as-built accuracy of ±5 cm and estimation errors within ±5% in some reported cases (Japan Federation of Construction Contractors, “Productivity Improvement Case Studies 2018”: https://www.nikkenren.com/sougou/seisansei/pdf/seisan_all_2018.pdf). With such high-precision quantity data, the municipality was able to proceed confidently with procurement as planned. As a result, no major design or contract changes occurred during construction, and the project progressed smoothly.

Case 2: Underestimation of Slope Spray Area → Mist Prevented by AR Visualization

In a steep-slope protection project, the initially designed sprayed concrete area had been underestimated. The design drawings simplified the slope geometry and therefore could not fully reflect the actual surface irregularities, meaning the real sprayed area might be larger than estimated. If materials had been prepared according to the design quantities, the site risked running short of materials mid-construction and leaving parts of the slope untreated.

This mistake was prevented in advance by using AR (augmented reality) on site. A construction manager held up a tablet and overlayed the designed sprayed-area model from the drawings onto live footage of the slope. Areas not covered by the design immediately became obvious. Previously, crews could only visually compare drawings with the field and were susceptible to subtle oversights, but the intuitive “visualization” provided by AR quickly revealed the quantity error. The team promptly revised the design and arranged for the additional materials needed. As a result, they were able to protect the entire slope as planned without rework or additional orders after construction began.

*AR (augmented reality): a technology that overlays digital information such as 3D models onto live camera views. In civil engineering, AR is increasingly used to visualize design drawings and the locations of buried utilities.*

Case 3: Point Cloud Analysis Helped Avoid Redesign of Water and Sewer Pipelines

In a planned renewal project for aging water and sewer pipelines in a certain municipality, hidden issues that could not be captured by conventional 2D drawings emerged. The initial design established routes for the new pipes based on old drawings, but discrepancies with actual site conditions raised the risk that design changes would be required during construction.

Point cloud analysis played a major role in resolving this issue. The team used laser scanners and high-precision photogrammetry to capture detailed 3D point cloud data of the terrain around existing pipelines, including inside manholes. They integrated the point cloud into a CIM (Civil Information Model) and overlaid the 3D model of the new pipeline for analysis. This revealed that, in certain sections, the initial design risked interference with existing structures. For example, point cloud data showed that another buried utility lay close to the planned route of a sewer pipe, meaning the designed depth would not provide adequate cover soil thickness.

Following this discovery, the design team revised the route and depth of the new pipeline at an early stage. If they had proceeded using only the old drawings, unexpected clashes or exposure of buried elements could have been discovered during excavation, potentially triggering extensive design changes and schedule delays. By running simulations based on point cloud data, they identified risks in advance and avoided redesign. This case strongly impressed stakeholders with the usefulness of digital technology.

In recent years, tools have also been developed that project the position information of underground buried objects collected in this way onto the field using AR, allowing anyone to easily confirm “invisible obstacles.” For example, a tablet-based buried-utility visualization system developed by Shimizu Corporation overlays drawings of underground lifelines such as water and sewer pipes at GNSS-determined positions, helping to prevent damage during excavation and improving construction planning efficiency (Cabinet Office “Michibiki” official site: https://qzss.go.jp/usage/userreport/shimz_170306_1.html). Combining point clouds and AR in this way can dramatically improve the accuracy and safety of underground infrastructure projects.

Technical Background: The New Norms in Quantity Design from Point Clouds, RTK, and BIM

The technologies underpinning the above cases that have attracted attention in recent years include point cloud data, high-precision positioning (RTK-GNSS), and BIM/CIM as digital infrastructures. Historically, estimating approximate quantities relied on dimensions from drawings and empirical rules. But now, deriving quantities directly from detailed, fully digitized site data is becoming the “new normal.”

Point cloud surveying technology (3D measurement using laser scanners or drone photogrammetry) captures the surfaces of terrain and structures as densely populated sets of points. This allows volumes and areas that were previously estimated by human judgment or inferred from a few survey points to be calculated directly from measured data. The accuracy and efficiency improvements over conventional methods have been dramatic: one construction DX article notes that “point cloud technology can reduce work time by up to 50% and improve surveying accuracy by more than tenfold” (from an explanatory article on construction DX). Point clouds can rapidly measure wide areas and cover all the information needed for quantity design, from earthwork volumes and slope geometry to the positional relationships of existing structures.

The spread of RTK-GNSS (real-time kinematic satellite positioning) has further accelerated point cloud utilization. Using an RTK-capable GNSS receiver allows point cloud data and photos captured on site to be given world coordinates (absolute coordinates), keeping measurement errors to within a few centimeters. This makes it possible to align design coordinates and on-site measurement data precisely. Applications such as comparing as-built models with point clouds to calculate differential earthwork volumes and accurately overlaying digital information on the field in AR are therefore enabled. In addition to expensive surveying equipment, products now exist that allow centimeter-level positioning and point cloud scanning simply by attaching a small GNSS receiver to a smartphone, making it easier to obtain high-precision data.

The advancement of BIM/CIM should not be overlooked either. BIM, born in the building sector, is a 3D model–based information management technology, and its civil counterpart is CIM. Creating 3D models from the design stage to automatically calculate quantities and costs and run construction simulations greatly improves project outlook. The Ministry of Land, Infrastructure, Transport and Tourism is promoting full adoption of BIM/CIM in public works and standardization of 3D design data with a target of 2025 (see: https://www.archifuture-web.jp/headline/480.html), and information sharing among stakeholders and rapid quantity updates during design changes are becoming the norm—things that were difficult with 2D drawings alone. While approximate quantities have sometimes been regarded as “just estimates,” combining BIM/CIM with point clouds and RTK now makes it possible to grasp quantities at the basic design stage with accuracy approaching that of detailed design. A new norm in quantity design is truly emerging.

The Value of “Accuracy” from Managers’ and Technicians’ Perspectives

Improving quantity design accuracy matters not only to field technicians but also to management. Accurate quantities are not merely numerical—they form the foundation that enhances the overall reliability of a project. Historically, when errors in design quantities led to budget overruns or schedule delays, considerable effort was required for adjustments, and stakeholders were consumed by negotiations and additional consultations. Conversely, if high-accuracy quantities are available from the conceptual stage, unnecessary rework can be prevented and project transparency improved. Given the chronic labor shortages in the construction industry, eliminating wasted rework and achieving reliable results with minimal effort makes improving quantity accuracy an unavoidable challenge.

What specific value does improved accuracy create? Let’s organize it from the perspectives of management and field technicians.

• Management benefits: Reduced overall project risk (avoiding budget overruns and schedule extensions), higher decision-making certainty during planning, easier accountability to clients and residents, and fewer internal adjustments when additional costs arise. Accurate quantities provide reliable data for managerial decisions and strengthen trust inside and outside the organization.

• Field technician benefits: Fewer extra tasks such as design changes and additional work orders so they can focus on core duties; improved construction quality (fewer mistakes due to correct material quantities); increased safety (construction proceeds as planned without unexpected shortages or excesses); and personal skill development (learning to use new technologies and acquiring digital-era expertise). Higher quantity accuracy makes on-site work easier and more rewarding for technicians.

Quantity design backed by accuracy is like a project’s “assurance of peace of mind.” For management it is a compass that stabilizes planning, and for field technicians it is a reliable tool to carry out safe, efficient construction.

Conclusion: Field Trust Begins with Quantity Accuracy

As we have seen, improving the accuracy of quantity design even at the approximate stage ultimately leads to smoother site operations and greater trust. Accurate earthwork volumes support appropriate procurement decisions in development planning, AR visualization prevents construction errors in slope work, and point cloud analysis avoids unnecessary redesign in pipeline projects. What these cases share is that improving quantity accuracy generates a sense of security on site and becomes the driving force that builds trust among stakeholders.

With technological advances, the era of accepting “small discrepancies because it’s just an estimate” is coming to an end. Rather, actively leveraging digital technology to secure high-precision quantity information from the early stages will become the new standard for construction projects. A focus on accuracy may seem unglamorous, but its cumulative effect builds substantial trust and supports the field. Field trust begins with quantity accuracy—keeping this in mind, we should continue pursuing robust, high-performing quantity design in our daily work. It is no exaggeration to say that the accuracy of approximate quantity design can determine a project’s success or failure.

Bonus: The First Step to Becoming a High-Performance Approximate Quantity Designer with LRTK

Even if you want to implement advanced quantity design, you may worry that specialized equipment and software are barriers. Against this backdrop, a recently introduced solution called LRTK has attracted attention as an easy way to realize simple surveying, point cloud acquisition, and AR proposals. LRTK consists of a small GNSS receiver that attaches to a smartphone and a proprietary app, turning a smartphone into a versatile high-precision surveying instrument. Even without specialized knowledge, you can walk around with your phone and scan surrounding 3D point cloud data in about a minute, automatically calculating earthwork volumes and areas with centimeter-level accuracy and checking results in the cloud. The acquired point clouds and 3D design models can also be displayed in AR on site and shared with stakeholders. For example, if you scan buried pipes in advance and project them in AR during construction, you can visualize invisible obstacles and proceed safely.

Using convenient tools like LRTK makes it possible to start practicing high-performance approximate quantity design today. Even on small sites, tasks that previously required outsourcing to surveying firms can be completed quickly in-house, enabling proposals and decisions based on high-accuracy quantity information. Digital technology is a tool; whether we master it as a weapon for the site is up to us. As a familiar first step, consider taking on smart quantity design using LRTK.