Creating a Zero-Rework Site through Estimated Quantity Design

One of the factors that threatens productivity on construction sites is on-site rework (redoing work). Rework, which is a major cause of schedule delays and cost overruns, is often the result of human errors caused by insufficient information or quantity calculation mistakes during the design stage. Conversely, these issues are largely preventable with appropriate countermeasures.

One approach that has attracted attention as a key to minimizing rework is estimated quantity design. This method involves early estimation of earthwork volumes and material quantities and reflecting those estimates in design and cost estimation to reduce on-site quantity errors. If accurate quantities are understood during the planning stage, additional work and rework during construction can be greatly reduced. This article explains what estimated quantity design is, the effects it brings to the field, and concrete steps to carry it out accurately. It also touches on mechanisms to enhance the consistency between design and construction, its connectivity with ICT construction and as-built management, and finally highlights the importance of quantity design based on field surveying by introducing the “Simple Survey” function of the latest LRTK tool as an example.

What is estimated quantity design?

Estimated quantity design is, literally, a design approach based on “approximate quantities.” It involves calculating, by simple methods early on, the earthwork volumes for excavation and embankment and the quantities of materials to be used, and preparing design documents and quantity takeoffs using those estimated values. It is characterized by omitting or simplifying detailed final designs at the time of tendering and adjusting designs as needed during construction. In other words, rather than determining precise quantities from the outset, a provisional design quantity is set using standard cross-sections or averages from past projects, and then modified and finalized later to match field conditions.

This concept of estimated quantity design has recently been gaining attention as a measure to streamline estimating and design tasks. For example, in water and sewer pipeline works, some municipalities now provide only plan routes and standard cross-sections at the time of order and let contractors bid using estimated quantities calculated from pipe lengths. After contract award, the contractor performs detailed site investigations to determine the locations of buried utilities and ground elevations—site conditions—and then prepares accurate pipeline drawings and quantity tables. This reduces preconstruction design effort while enabling post-contract updates that reflect actual conditions, thereby decreasing unnecessary design changes and rework. Estimated quantity design is thus an initiative that aims to both streamline the entire procurement-and-construction process and prevent on-site rework.

The reality of quantity errors and rework on site

On construction sites, quantity errors—even minor calculation mistakes—can lead to serious rework. No matter how smoothly construction proceeds, mistakes in estimating required quantities will inevitably have consequences. The following are examples that actually occur on site:

• Errors in earthwork quantity estimation: Mistakes in calculating excavation or embankment volumes result in less or more soil than planned. If soil is lacking, additional soil delivery or re-excavation is required; if there is excess, costs rise due to disposal of surplus soil.

• Incorrect material order quantities: Errors in the number or quantities of required materials—such as rebar, formwork, or piping—lead to shortages on site and halt work. If additional procurement takes time, schedules slip and, in some cases, deadlines are affected.

• Unit misinterpretation: Basic mistakes such as misreading dimensional units—calculating in “mm” when it should be “m”—produce errors by orders of magnitude. Large quantity shortfalls or surpluses force a rework of construction plans.

• Inconsistencies between drawings and specifications: When quantities shown on design drawings and those in specifications conflict, uncertainty at the site can result in construction errors. For example, pipe lengths that differ between drawings and actual conditions may require additional fittings and work.

• Omissions in quantity aggregation: Some structures or work items may be overlooked during the design-phase quantity takeoff and thus omitted from estimates. When these missing quantities are discovered mid-construction, urgent design changes or additional orders become necessary.

When such errors are discovered, additional rework and schedule changes at the site are unavoidable. Equipment may need to be removed and reinstalled, or night work may be required to make up shortages, all adding unnecessary effort and cost. Rework that could have been prevented undermines staff morale and can damage trust with the client.

Effects of early quantity design

What benefits can be obtained by implementing quantity design thoroughly at an early stage? The main advantages include:

• Improved design accuracy: Calculating quantities with construction conditions and site context in mind raises the accuracy of design documents and enables plans without inconsistencies or omissions. Identifying quantitative contradictions before construction reduces the need for later drawing revisions.

• Stable cost and schedule: Accurate estimating based on quantities improves cost estimation accuracy. It prevents situations where “the budget is insufficient” or “the schedule is extended” after contract award, making it easier to proceed according to planned budget and timeline.

• Optimized resource use: Early awareness of earthwork balance and required material quantities enables adjustment of the cut-and-fill balance to minimize spoil disposal and imported fill. Materials can be ordered in appropriate amounts, reducing excess inventory and waiting losses.

• On-site construction efficiency: With accurate quantity information in advance, construction teams can proceed with well-organized work. Fewer unexpected redoes mean fewer interruptions and improved overall efficiency.

• Improved reliability and safety: Plans backed by quantity data increase trust from clients and stakeholders. Reduced uncertainty about whether things will go as planned leads to more realistic plans, which is also beneficial for site safety management. As a result, rework risk is greatly reduced and the site gains assurance.

Thus, carrying out quantity design appropriately at an early stage is a key factor not only in preventing rework but also in improving overall project quality and productivity. This aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of “front-loading” (thorough early-stage planning and stakeholder coordination), and careful quantity checks before construction are now emphasized across the construction industry.

Steps for accurate quantity design

Next, let’s confirm the basic steps to advance accurate quantity design.

• Conduct field investigations and surveys: Thoroughly investigate the target site to understand current conditions. Perform topographic surveys to digitize ground elevations and terrain shapes, and confirm the locations of buried utilities and existing structures. Conduct geotechnical investigations and stakeholder interviews as needed to accurately identify the assumptions used for quantity calculations.

• Prepare plan and cross-section drawings: Using field survey data, consider the layout of planned structures and earthworks. For roads or pipelines, determine the route on plan drawings and create longitudinal and cross sections at key locations to plot ground lines and design lines. This visually reveals cut-and-fill cross-sectional areas and dimensions of required structures. If applying standard cross-sections, verify that the shapes are practical for the actual terrain.

• Calculate quantities and volumes: Compute specific quantities from the prepared drawings. For earthwork, determine each cross-sectional area and compute section volumes using the average-end-area method to sum total earthwork. Extract concrete volumes for structures, rebar weights, pipe lengths, etc., from design drawings and aggregate them in spreadsheet software. Pay attention to unit conversions and coefficients (e.g., changes due to compaction) to ensure no quantities are omitted.

• Verify and adjust calculation results: Check the calculated quantities from multiple perspectives to ensure they are reasonable. Cross-check drawings and calculation results to confirm nothing was overlooked. For earthwork, review the cut-and-fill balance and, if there are large surpluses or deficits, consider revising the design plan. Also confirm consistency with other trades and uncover any design errors related to quantities. Problems found at this stage should be resolved by design revisions or additional investigations.

• Reflect results in design documents: Incorporate the finalized quantities into design documents and quantity takeoff sheets. Add quantity-based notes to plans and sections as needed, and prepare quantity tables and progress measurement sheets to share with stakeholders. Use the confirmed quantities to perform cost estimating and reflect the information in specifications and schedules. In this way, design information handed over to the site includes accurate quantity data, minimizing the risk of rework during construction.

Mechanisms to increase consistency between design and construction

To eliminate information gaps between the design and construction phases and ensure that work is executed according to design intent, mechanisms to strengthen consistency between design and construction are essential. One approach is to review the project delivery method itself. For example, in a design–build model where the same team or company handles both design and construction, the contractor’s know-how is reflected in the design, reducing mismatches such as “we can’t build it as drawn.” Having construction managers participate in drawing reviews from the design stage or conducting thorough precontract coordination among client, designer, and contractor (so-called front-loading) can also catch issues that would otherwise lead to rework during construction.

Another important mechanism is centralized digital management and sharing of design information. Historically, information loss occurred when paper drawings and quantity tables were exchanged, but now BIM/CIM—three-dimensional modeling that links design to construction data—is becoming more widespread. If contractors can directly use the 3D models of terrain and structures created at the design stage and apply them to ICT equipment’s machine guidance and as-built measurement, design data and the construction site become seamlessly connected. Storing drawings and quantity data on the cloud allows everyone to access the latest versions immediately when design changes occur, enabling consistent instructions. Additionally, AR (augmented reality) displays on tablets or smartphones let users overlay design models on the actual site view. Being able to visually check on site whether the work will finish “as designed” helps prevent mistakes due to misunderstandings and significantly closes the gap between design intent and construction execution.

Connectivity with ICT construction and as-built management

Digitizing quantity design dramatically increases compatibility with the currently promoted ICT construction (construction using information and communication technologies). If 3D terrain models and construction data prepared at the design stage are loaded into ICT machinery for machine control, the machines can automatically excavate or place fill to the design elevations and slopes. High-precision GNSS and sensor-equipped equipment can trace the progress quantity accurately without relying solely on the intuition of experienced operators, enabling achievement of the targeted quantities. The frequency of stake-out and surveying sessions that were traditionally performed manually is reduced, shrinking the opportunity for errors.

Quantity design data also proves powerful in post-construction as-built management (verification of final dimensions and shapes). Because design reference data is clearly quantified, point cloud data captured by drones or 3D laser scanners can be compared directly with the design model. Displaying surface differences as color maps makes even slight deviations in elevation or irregularities immediately obvious. For example, areas where embankment thickness falls below the standard can be detected instantly and corrected on the spot with additional work. Tasks that previously took half a day using tapes and levels can now be completed quickly with drone flights or mobile surveying. The Ministry of Land, Infrastructure, Transport and Tourism reports that surveying work time on ICT earthwork sites has been reduced by an average of over 30%, demonstrating marked improvements in efficiency and measurement accuracy for as-built inspections. Recording and reporting of measurement results can be semi-automated with software and shared with clients via the cloud to streamline approvals. By digitally linking quantity design through to ICT construction and as-built management, the system for ensuring construction quality and achieving zero rework becomes robust.

The importance of field surveying-based quantity design and LRTK’s Simple Survey

Finally, it must be emphasized that quantity design based on field surveying is crucial. Calculating quantities solely from desk-based design that diverges from actual site conditions is meaningless. Conversely, accurate field survey data can greatly reduce the risk of rework even with an estimated-level design. Surveying technology has also advanced so that measurement tasks that once required specialist survey teams can now be easily performed by site management personnel.

For example, using the Simple Survey function of LRTK (a compact, high-precision GNSS surveying device) enables fast and efficient surveying and measurement on site. This compact device, attachable to a smartphone, can obtain position coordinates with centimeter-level accuracy. With a single unit you can perform photo positioning (automatically recording high-precision location information with photos), AR display (overlaying design models and measurement results on the site view), cloud synchronization (instant cloud sharing of measurement data), and even monopod measurements (simple height measurements using a monopod) and on-the-spot volume calculations. Without waiting for a specialist survey crew, site staff can obtain sufficient surveying data themselves and immediately reflect it in design.

Introducing such modern tools dramatically speeds and simplifies feedback from field investigation to design. When actual site conditions are accurately reflected at the design stage, discrepancies in quantities that cause rework are unlikely to occur, approaching an ideal construction cycle with almost no rework. To maximize the benefits of estimated quantity design, data linkage between site and design is essential. In that context, user-friendly, high-precision Simple Survey tools like LRTK are a powerful ally in building zero-rework sites.