The success of a construction project hinges on preliminary quantity design in the early stages (rough calculation of materials and earthwork volumes required). In civil and building works, surpluses or shortages and rework caused by quantity estimation errors can significantly affect construction accuracy and costs. This article explains in detail the common causes of quantity mistakes on construction sites, the basics of preliminary quantity design, and the key points to improve quantity accuracy. Focusing especially on earthwork (excavation, removal of soil, embankment and grading), let’s explore the secrets of preliminary quantity design for enhancing construction accuracy.

Typical Factors Leading to Construction Quantity Errors

First, let’s identify typical factors that cause quantity surpluses/shortages and re-estimation in construction. Below are the main causes that are likely to lead to construction quantity mistakes.

• Failure to reflect design changes: This occurs when design drawings or specifications are changed during the planning process but those changes are not reflected in the quantity calculations. It is caused by not sharing design changes with the estimating staff or lack of coordination.

• Human error (calculation/input mistakes): Simple mistakes that occur when quantities are picked up or calculated manually. Typical human errors include digit input mistakes, misuse of formulas, and misreading drawings.

• Omission of items within the estimate scope: Sometimes necessary items are simply not included. For example, missing the quantity for a certain process in the construction workflow or failing to include the soil volume for part of an area.

• Insufficient understanding of site conditions: When preliminary calculations rely on old drawings or inaccurate survey data, discrepancies with the actual terrain or ground conditions can lead to quantity surpluses or shortages.

• Inadequate checking system: If the results of quantity calculations are not double-checked by a third party or supervisor, oversights can go unnoticed. Without cross-checking by multiple people, mistakes are less likely to surface.

When these factors overlap, discrepancies arise between the initial quantity plan and actual construction volumes, causing additional work and changes in material procurement, and resulting in unnecessary rework. So why is preliminary quantity design so important?

Impact and Importance of Preliminary Quantity Design

Preliminary quantity design before construction starts has a major impact on the overall project plan. For example, by grasping early on the excavation and embankment volumes, and the required amounts of concrete and rebar, you can arrange appropriate budgets, schedules, equipment, and personnel. Conversely, if quantities are mistaken at this stage, the following problems may occur.

• Cost overruns or losses: Underestimating quantities can force later additional material purchases, leading to budget overruns. Overestimating quantities can result in excess inventory and wasteful orders, increasing costs.

• Schedule delays: If necessary soil or materials run out, the schedule must be rearranged for additional procurement or additional work. The greater the discrepancy from the initial plan, the more time will be spent on rearranging site operations.

• Reevaluation of the entire construction plan: Large quantity errors may force changes to construction procedures or methods. For example, large discrepancies in earth volumes may require reworking transport plans or revising the scale of structures.

The initial estimate acts as the project’s compass. Accurate preliminary quantities improve the reliability of subsequent detailed design and construction planning, and they become the assumptions shared among stakeholders. Therefore, performing high-accuracy quantity design at this stage directly contributes to smooth downstream processes and improved final construction accuracy.

Risks and Impacts Caused by Earthwork Quantity Errors

In particular, earthwork (excavation, embankment, grading, etc.) carries serious risks when quantities are misestimated. Earthwork uses a natural material—soil—so actual quantities are easily influenced by site-specific topography and soil properties. Below are typical risks and impacts from errors in earthwork quantity estimation.

• Miscalculation of spoil handling and fill amounts: If excavation volume is underestimated, a large amount of spoil (unwanted soil) may actually be produced, requiring additional disposal costs and hauling operations that were not originally planned. Conversely, overestimating excavation can lead to excessive arrangements for disposal sites or dump trucks, causing higher costs and inefficiency.

• Shortage of fill material: If the volume of soil needed for grading or embankment is underestimated, fill material shortages will occur during construction, forcing additional soil to be brought in from other sites or borrow pits. Procuring and transporting this soil takes time, resulting in schedule delays and additional costs. There are many site cases where work stopped because there was not enough backfill soil, causing the schedule to extend.

• Insufficient response to topographic changes: In grading works, plans are made to balance cut and fill. But if quantity errors upset that balance, you can end up with excess soil in some areas and shortages in others, requiring replanning. You may need to secure temporary storage for surplus soil to be removed later or find new sources to supply missing soil, complicating site management.

• Impact on heavy equipment and vehicle operation plans: Discrepancies in earth volumes affect the number of machines in operation and the round trips of dump trucks. Planned excavation that should finish in 5 days may take twice as long—10 days due to excess soil, or insufficient truck allocations may cause transport to fall behind. Such troubles affect not only construction accuracy but also safety management.

As shown, earthwork quantity errors ripple through costs, schedule, and safety. That is why preliminary earthwork quantities must be calculated carefully and as accurately as possible. The next chapter explains the basic methods for calculating earth volumes.

Basic Knowledge of Preliminary Earth Volume Calculation (Average Cross-Section Method and Trapezoidal Approximation)

In earthwork, classic methods have long been used to estimate rough volumes from terrain and section shapes. Representative techniques are the average cross-section method and calculation by trapezoidal approximation. These are basic techniques to grasp approximate earth volumes by hand even without advanced software or 3D models.

Average cross-section method: The simplest earth volume calculation method. Calculate the cross-sectional areas at the beginning and end of a segment (for example, cut and fill areas obtained from roadway or grading cross-sections), then multiply the average of those areas by the segment length to get the volume. The formula is V = ((A1 + A2) / 2) × L (A1 and A2 are the end cross-sectional areas, L is the segment length). This method, based on the intuitive idea of volume = average cross-sectional area × length, has been used for many years in civil works. Dividing the whole into finer segments and performing this calculation for each, then summing them, yields an overall preliminary earth volume.

Trapezoidal approximation: Essentially similar to the average cross-section method, but the cross-section or excavation shape is divided into several trapezoids or triangles to calculate areas and sum volumes. Even for complex cross-sections, if they can be decomposed into trapezoids (or triangles), area can be calculated from the top base, bottom base, and height. For example, an irregular polygonal cross-section can be approximated by decomposing it into multiple trapezoids and summing their areas to estimate volume. Mathematically, this relates to the trapezoidal rule, a numerical integration method, and can be applied manually if you know basic geometry.

These methods are only for rough estimates and simplify actual terrain, so errors relative to precise values will occur. However, as a reference before detailed design, they are very useful. Experienced site engineers often use an average cross-section approach mentally to get a rough sense of quantities. The important thing at the preliminary stage is to grasp overall volume quickly rather than pursue excessive precision. The next chapter covers points to complement this stage to avoid omissions.

Easily Overlooked Quantity Elements (Spoil, Imported Fill, Backfill, Topsoil Stockpile)

When calculating preliminary quantities, there are also elements that are easily overlooked. Here we organize the earthwork quantity elements to pay attention to. Accounting for these without omission leads to more accurate preliminary estimates.

• Spoil handling volume: Whether excavated unwanted soil (spoil) will be fully hauled off-site or partly reused on-site changes how it is treated. In particular, excavated ground tends to swell; compared to 100% of in-situ bank volume, excavated soil is generally considered to increase to about 110–120% (varies with moisture content and soil type). If this “bulking increase” is not accounted for, there is a risk of insufficient truck allocations or disposal site capacity.

• Volume of imported soil (backfill/fill material): When importing soil for backfill or embankment, that volume must be accurately estimated. This applies when excavated soil is not reused or on-site soil is insufficient. Imported soil generally reduces in volume when compacted (depending on compaction rates, it often reduces to about 85–95% of the in-situ soil volume). Therefore, to ensure the required backfill thickness, a slightly larger amount of soil should be prepared. Misestimating this may lead to shortages and emergency additional imports.

• Backfill cross-sectional area: The amount of backfill soil around structure foundations or after embedding pipes must not be overlooked. Excavated volume does not always equal backfill volume. Structures or pipes occupy volume underground, creating simple soil volume differences. Also, compaction during backfilling can cause the soil to settle and reduce the required soil compared to excavation. In trench works, backfill soil tends to be insufficient, so it is safe to secure spare soil in advance.

• Topsoil stockpile: In grading works, topsoil (surface soil rich in vegetation and organic matter) is often stripped and stored separately for later reuse in landscaping or final grading. If the topsoil stockpile volume is not included in the overall plan, problems such as “no place to store topsoil” or “excess backfill when topsoil is reused” may occur. Because topsoil volume changes with sieving and drying, it is important to estimate the storage yard capacity as well.

These elements are hard to read from simple shapes on drawings and are often missed by less experienced personnel. Since spoil handling costs and imported soil arrangements greatly affect construction costs, incorporating them into preliminary estimates from the start prevents later rework.

Improving Preliminary Accuracy Using As-Built Plans and Cross-Sections

To improve the accuracy of preliminary quantities, it is essential to make maximum use of accurate on-site information. By verifying and correcting with actual terrain data and survey results rather than relying only on drawings and desk work, you can calculate quantities that better reflect reality. Specific points are as follows.

Reference current survey drawings: The basic step is to refer to the latest survey maps and terrain drawings. Use drawings that reflect the current terrain elevations and site shape, not old materials or assumptions. For grading works, create an elevation difference map between the existing ground and the planned finished ground, and visualize cut and fill volumes with color coding or numerical display to easily identify quantity biases and anomalies.

Check with cross-sections and longitudinal sections: Elevation changes that are difficult to grasp on plan views can be verified with sections. Compare the design section (planned section) and the existing ground section at multiple locations and confirm the difference in cross-sectional area. The average cross-section method requires computing area per section. By deriving existing and design cross-sectional areas at key transects and cross-checking against preliminary volumes, you can correct local errors.

Consider geological and ground information: Ground hardness and the presence of bedrock also affect quantities. For example, rock excavation differs from topsoil or soft soils—actual excavation cross-sections may not match design (slopes may be irregular, or rock spalls may occur). Therefore, predict the depth of hard layers from borehole survey results and allow extra for rock portions as needed.

Utilize ICT and 3D data: If available, using a current 3D model generated from drone aerial photos or point cloud data from 3D laser scanners is an option. With these, you can compute the difference between the existing ground and the design ground on a computer and automatically calculate cut and fill volumes. Digitizing what used to be read from paper drawings reduces human error and improves accuracy.

As described, multiple layers of checks using current information significantly increase the reliability of preliminary estimates. Although this requires some effort, spending time up front to verify prevents rework that could be several times larger later.

Why High-Accuracy Preliminary Estimates Lead to Better Construction Accuracy, Cost Control, and Less Rework

As covered so far, increasing quantity accuracy in the early stages positively affects construction quality and efficiency. Let’s summarize again why high-accuracy preliminary quantities are so important from the perspectives of construction accuracy, cost control, and preventing rework.

• Improved construction accuracy: When quantities are accurate, it is easier to achieve the intended finished product on site. For example, if embankment heights and slopes are constructed according to prior quantities, the finished shape will conform to design accuracy. No quantity errors = ability to construct according to design intent, leading to stable quality of the as-built shape (the formed shape of the completed structure).

• Proper cost control: The more accurate the quantities, the smaller the variance between budget and actuals. Eliminating excess ordering and emergency purchases prevents wasteful spending and opportunity loss. Also, procurement and contracts based on proper quantities reduce disputes over additional claims or price reductions. As a result, the project can be run according to the financial plan set at the planning stage, contributing to profit preservation.

• Prevention of rework and reconstruction: Rework caused by quantity discrepancies is a major loss on site. For example, in earthwork, scenarios like “re-excavating and re-backfilling an area because there wasn’t enough soil” or “concrete left over and suddenly discarded” could have been avoided with accurate initial estimates. If preliminary estimates are reliable, design changes and rework can be minimized, shortening schedules and stabilizing quality.

Thus, taking the time to accurately determine quantities up front may seem like extra effort, but it is the best long-term cost-reduction measure, enabling smarter site management. High-accuracy preliminary quantity design is a project-wide “invisible reassurance.”

Differences Between Traditional Preliminary Methods (Spreadsheets/Sketches) and Using Point Cloud Models

With technological progress, methods for calculating quantities are also changing significantly. Here we compare traditional manual-centered preliminary methods with the increasingly common use of point cloud data and 3D models.

Traditionally, many engineers picked up dimensions from drawings and calculated quantities with hand calculations or spreadsheet software. They sketched on drawings, computed lengths and areas for each part, and entered numbers into Excel to compute volumes. For example, placing many paper cross-sections side by side, measuring areas on graph paper, or dividing shapes into trapezoids by hand while noting dimensions, then inputting the numbers into Excel. The merit of this approach is that the tools are simple and it can be done anywhere, but the downsides are that it is time-consuming and error-prone. Because humans process with eyes and calculators, a single digit error can drastically skew results, and complex terrain makes calculations cumbersome.

On the other hand, CAD, CIM (Construction Information Modeling), and point cloud data obtained by drone or laser scanner enable automated quantity computation. Specifically, digitize the existing terrain via point cloud scans or photogrammetry and overlay it with the digital design model to have the computer calculate volumes. This enables far higher accuracy in far less time than manual calculations. For example, what used to take half a day from field survey to office calculation can be completed in just minutes with point cloud data. In addition to calculations, 3D visualization makes it intuitive to see which areas have cut or fill and by how much, accelerating site decision-making.

However, new methods have caveats. 3D scanners and drones require specialized equipment and skills, and data processing may demand high-performance PCs and software. Weather and site environment can also affect operations. Therefore, immediate adoption on every site is not always feasible. But the barriers to these technologies are lowering: smartphone-based measuring devices and cloud services for automatic calculation are becoming available, making it possible for anyone to measure quantities quickly.

In short, traditional hand-based estimation is being streamlined and made more accurate by digital technologies. By combining traditional methods with modern tools according to site scale and purpose, more reliable quantity understanding and optimized construction planning can be achieved.

Using LRTK Point Cloud Scanning and Volume Calculation Features on Site

Finally, as an example of a modern tool, we introduce LRTK’s point cloud scanning and volume calculation features. LRTK is a system that attaches a compact high-precision GNSS receiver to a smartphone and performs three-dimensional surveying with a dedicated app. With this tool, anyone can easily walk a site to acquire high-density point cloud data, and immediately calculate earth volumes and areas from the acquired point cloud.

For example, if you scan a pile of spoil generated by excavation with LRTK, you can calculate its volume on the spot, enabling you to determine the number of dump trucks required immediately. What traditionally took a site survey and office calculation over half a day can be completed with a few minutes of scanning. Quickly grasping daily progress (earthwork volumes) speeds up construction management decisions such as reassigning equipment or revising truck allocations.

LRTK not only performs point cloud scanning but also has functions such as area measurement for ranges enclosed by multiple positioning points and on-site calculation of cut and fill volumes from elevation differences against reference heights. In short, with just a smartphone on site you can instantly verify required quantities. Because it does not necessitate specialized surveying instruments or advanced data processing—and can be operated by site staff—it is easily adopted for routine progress management and checks.

By aiming for high-accuracy preliminary quantity design and using the latest technologies as on-site aids, you can further improve construction accuracy and efficiency. If you want to “perform on-site surveying and earth volume calculation more easily,” consider adopting a smart surveying tool like [LRTK](https://www.lrtk.lefixea.com/). Accurate quantity control and prompt construction management can surely be realized on your sites as well.