How to Easily Calculate Embankment Volume with a Smartphone! The Latest Methods for As-Built and Earthwork Quantity Management Usable on Site

Table of Contents

• When is embankment volume calculation necessary?

• Traditional embankment volume calculation methods and their challenges

• Evolution of earthwork management through ICT technologies

• The latest method to easily measure embankment volume with a smartphone

• Benefits of using smartphone surveying for as-built management

• New technology supporting smartphone surveying: LRTK

• FAQ (Frequently Asked Questions)

When is embankment volume calculation necessary?

In civil engineering, "embankment (morido)" refers to the work of piling up soil and sand on site to form ground. In road construction or land development that involves embankments, accurately calculating the embankment volume (the amount of soil to be placed) is indispensable. For example, during the planning stage, you calculate how much soil must be brought in from elsewhere or how much of the excavated material (so-called cutting) can be reused for embankment, and based on that you set the overall project cost and schedule. After construction, as part of as-built management, volumes are measured to confirm that the embankment has been finished to the specified heights and shapes. Especially in public works, it is necessary to measure embankment thicknesses and volumes according to as-built management guidelines and to prove that construction standards have been met.

Calculating embankment volume is a routine task for construction stakeholders, but its importance is very high. If the estimated amount of soil is incorrect, shortages during the project can delay the schedule, or conversely, excess soil may require disposal, increasing effort and cost. After completion, if the volume is insufficient compared to the plan, the design may not meet stability requirements and the embankment faces higher risks of settlement or collapse. To prevent such troubles, embankment volumes must be calculated and managed accurately and quickly. So how are earthwork quantities actually calculated on site?

Traditional embankment volume calculation methods and their challenges

Traditionally, the average end-area method has been widely used to determine embankment volume. This method surveys cross-sections of the embankment at regular intervals, calculates the area of each cross-section, and computes volume by multiplying the average of adjacent cross-sectional areas by the distance between sections. For example, if you obtain cross-sectional areas at the start A and end B of an embankment section, multiplying the average of those two cross-sectional areas by the distance A–B gives an approximate embankment volume. The average end-area method has relatively simple calculation steps and has long been a basic technique on construction sites.

However, volume calculation by the average end-area method has several challenges. First is the time and labor required. To create cross-section drawings, survey staff must measure heights and widths on site using surveying instruments such as total stations and levels. Measuring multiple cross-sections requires both manpower and time, and calculating cross-sectional areas and volumes from the measured data is cumbersome, often involving manual calculations or area calculations in CAD. On fast-paced projects, it is practically difficult to perform such measurements and calculations one by one, so as-built verification tends to be done after construction or at milestone points.

Second is the issue of accuracy and coverage. The average end-area method relies on interpolation for parts between measured sections, so when the terrain is complex or has local irregularities, discrepancies from the actual volume can occur. The more cross-sections required, the more difficult and costly the surveying work becomes. Conversely, if cross-section intervals are made coarse, calculations become easier but the risk of overlooking or miscalculating volume increases. Adverse conditions such as rain or mud can also make surveying difficult. In short, with traditional methods it has been difficult to measure earthwork quantities over wide areas quickly and with high accuracy.

For small embankments, supervisors sometimes estimate by eye, e.g., "equivalent to X dump truck loads, so approximately Y cubic meters." However, such experience-based estimates are only rough and do not constitute objective proof. As described above, traditional earthwork calculation methods suffer from problems such as being time-consuming, requiring manpower and expertise, lacking real-time capability, and having limited accuracy. Therefore, the field has long desired a more efficient, easy-to-use measurement method.

Evolution of earthwork management through ICT technologies

In recent years, driven by the Ministry of Land, Infrastructure, Transport and Tourism's promotion of ICT construction and i-Construction, digital technologies have been introduced into earthwork management, causing major changes. A representative example is the use of 3D surveying technology. For instance, drone photogrammetry (UAV surveying), which photographs the entire site from above to create a 3D terrain model, is a revolutionary method that can acquire detailed shapes of embankments and cuttings over wide areas in a short time. By stitching many photos taken by a drone using software (SfM processing) to generate point clouds and contour models, volume calculations can be performed automatically at the push of a button. Ground-based laser scanning measurement has also become common. A tripod-mounted terrestrial LiDAR device can be rotated to acquire surrounding point cloud data and measure the as-built condition of embankments with high density. Using these advanced devices makes earthwork management far more efficient and precise compared to the era when cross-sections were measured by hand.

While ICT adoption has greatly advanced civil construction, there are also challenges and hurdles. For drone surveying, aviation law permissions and qualifications may be required, and flights cannot be conducted in strong winds or rain. Post-flight data processing requires specialized software and time. High-performance laser scanners are very expensive and require expertise to operate. Therefore, while these methods are effective for large-scale projects and periodic as-built inspections, using them for everyday small-scale surveying work comes with high barriers. Not all site personnel always carry drones or expensive equipment, and many feel that a more convenient, everyday measurement method is desired.

Against this backdrop, smartphone-based surveying technology has attracted attention in recent years. If you could measure earthwork quantities with a smartphone that everyone carries, field personnel could quickly understand the situation without relying on special equipment or specialist staff. So, can smartphones really measure embankment volumes? The next chapter looks in detail at the latest methods.

The latest method to easily measure embankment volume with a smartphone

With improvements in smartphone performance and advances in peripheral technologies, "surveying with a smartphone" is no longer a dream but a reality. The latest methods make use of smartphone sensors and cameras to capture the embankment shape in 3D and automatically calculate volume. There are two main approaches in these methods.

The first is to use the smartphone camera or LiDAR (laser ranging) function to obtain a 3D point cloud (digital terrain model) of the embankment surface. For example, some iPhone and iPad models have built-in LiDAR sensors; scanning the site with these can record piles of soil and surface irregularities as a collection of innumerable points (a point cloud). Even on devices without LiDAR, you can photograph the embankment from various angles with the smartphone camera and create a 3D model using photogrammetry techniques. By launching a dedicated app and walking around the embankment while holding up the phone, a terrain model is generated much like shooting a video.

The second point is to give the acquired point cloud or model an accurate scale (dimensions) and positional information. A 3D model obtained solely with a smartphone is generally generated at approximate real scale by the device’s internal sensors (gyros and AR functions), but over long scans or wide areas small drifts can accumulate, and the model’s global position may be unknown. What helps here is a high-precision GNSS (GPS) receiver that can be linked to the smartphone. Recently, compact GNSS devices that connect to smartphones and enable centimeter-class positioning have appeared. Attaching such a device to the smartphone allows the phone’s position to be tracked in centimeters during measurement, attaching high-precision latitude, longitude, and altitude to each point of the point cloud. As a result, the entire point cloud of an embankment obtained by smartphone fits into the public coordinate system, yielding 3D data with accuracy comparable to measured drawings. When the text refers to centimeter-level accuracy, it means cm level accuracy (half-inch accuracy).

Calculating volume from a 3D model obtained by smartphone 3D measurement is very easy. In a dedicated app or on a cloud service, if you specify a reference surface (for example, the designed finished elevation or the original ground surface), the software instantly computes the volume of the embankment above that plane. If you scan the terrain both before and after construction and compare the difference, the software can automatically calculate the volume added by embankment or the volume removed by excavation. What used to be volume calculations done manually with a calculator can now be completed by holding a smartphone over the site for a few minutes.

The advantages of this latest method are speed and ease. What used to take a surveying crew half a day to measure at one location can, in some cases, be completed by walking around with a smartphone for 10–15 minutes to acquire data, then simply checking the automatically calculated results. Because quantities can be grasped nearly in real time, you can immediately decide "how many m³ more are needed to meet the design" or "where to add more fill." Previously there was a time lag in the survey→calculation→result reflection cycle, but smartphone measurement allows you to check as-built and quantities while working and make on-the-spot adjustments to construction methods. This truly enables real-time construction management.

Benefits of using smartphone surveying for as-built management

3D data obtained with a smartphone is powerful not only for quantity calculation but also for as-built management. If you record the finished form of an embankment as a point cloud—a digital copy—you can later extract any required cross-sections or elevation data. Unlike the traditional approach of measuring only representative points, scanning the entire surface ensures there are no overlooked irregularities. Specifications such as "embankment thickness of ○ cm (○ in) or more" can be easily checked by examining the elevation at arbitrary points on the point cloud. The acquired as-built data can be visualized on a tablet or PC, making data sharing with clients and inspectors easy. Gradients and shapes that are hard to convey on paper drawings can be intuitively understood with a 3D model. Sharing via the cloud enables checking progress from the office without being on site.

Furthermore, combining smartphone survey data with design data enables automated pass/fail judgment of as-built conditions. For example, by preparing CAD or BIM 3D design models in advance and overlaying them with the smartphone-acquired point cloud, you can color-code deviations from design or numerically calculate excess or deficiency volumes. This makes it easy to see at a glance where embankments are lower/higher than design and clarifies where corrective action is needed. Traditionally, comparing design drawings and as-built conditions required experience and intuition, but digitization makes as-built inspection accessible to anyone. Applying AR (augmented reality) allows overlaying the design finished-line on the live embankment image on the smartphone screen, enabling visual confirmation of shortages or overfills while looking at the site. These benefits mean smartphone surveying contributes to quality assurance and prevention of rework. By obtaining accurate as-built data quickly, defects can be discovered and corrected on the spot, greatly reducing rework and inspection comments in later stages.

As described above, using smartphones for as-built and earthwork quantity management is a revolutionary method that simultaneously improves on-site productivity and quality. So what specific products and technologies realize this smartphone surveying? Next, we introduce notable smartphone surveying tools that have appeared recently.

New technology supporting smartphone surveying: LRTK

A representative example of high-precision surveying with smartphones is the platform called "LRTK" developed by Reflexia Corporation. LRTK is a next-generation surveying tool composed of a dedicated ultra-compact RTK-GNSS receiver, a smartphone app, and cloud services. By simply attaching a palm-sized receiver to an iPhone or iPad with one touch, the smartphone quickly becomes a centimeter-level positioning device (cm level accuracy (half-inch accuracy)). At about 125 g in weight and compact, it can be carried in a work uniform pocket and is convenient to take out and start surveying whenever needed.

Using LRTK allows you to fully enjoy the advantages of smartphone surveying discussed in this article. Starting positioning in the dedicated app displays the current position on the smartphone screen in real time, and with a single button you can record coordinates of any point. Altitudes are automatically converted to Japanese geodetic systems (including geoid heights), allowing you to confirm elevation values on the spot. In addition to point surveying, the app also has a function to perform 3D point cloud scanning simply by holding the smartphone and walking. Acquired point cloud data can be visualized immediately on the smartphone, enabling instant analysis such as checking embankment cross-sections or selecting arbitrary areas to measure volume. With one tap you can upload data to the cloud, and then view the site point clouds and photos from an office PC via a web browser. On the cloud you can overlay multiple point clouds to calculate volume differences, import drawing data to compare as-built conditions, and perform other advanced analyses.

The greatest feature of LRTK is its simplicity so that non-specialist surveyors can operate it. Unlike traditional surveying instruments, complicated settings are unnecessary; the smartphone's intuitive UI is designed so anyone can "measure," "view," and "share." Developed with the aim of a "one-person, one-device universal survey instrument," LRTK performs in every on-site scenario. In addition to embankment volume calculation, it can measure distances and areas, stake out positions according to design, visualize buried utilities in AR, and handle many other tasks with a single device. Its price is also far more accessible than traditional surveying instruments※, and because each worker can use their own smartphone, sites that previously waited for surveying can operate more smoothly (※While very inexpensive compared to traditional equipment, please contact us for specific pricing). By incorporating simple surveying with LRTK, as-built and earthwork quantity management is being dramatically streamlined, and the style of site operations is beginning to change. In an era where so much can be done with a single smartphone, why not introduce the latest technology to your site and experience its effects?

FAQ (Frequently Asked Questions)

Q. Can I really survey with just a smartphone? A. Yes, it is possible. Modern smartphones have high-performance sensors and cameras, and by combining appropriate apps and peripherals you can use them for surveying tasks. For example, attaching a small RTK-GNSS receiver to a smartphone allows you to obtain position information with cm level accuracy (half-inch accuracy), and you can scan terrain with the camera or LiDAR to obtain point cloud data. Using these technologies, surveying with sufficient accuracy can be achieved without relying on traditional surveying instruments.

Q. Is specialist knowledge or certification required? A. Smartphone surveying is designed to be easier to operate than traditional surveying instruments, and can be used without special certification. Anyone with basic smartphone skills can start measurements intuitively. Of course, basic surveying knowledge (such as coordinate systems and elevation reference concepts) makes it easier to utilize, but the device operation itself follows app instructions so there is little to worry about. However, for official surveys such as public survey deliverables, work must still be conducted under the supervision of certified personnel as before. Even in such cases, smartphone surveying can streamline site work while final verification is performed by certified staff.

Q. Is the accuracy sufficient compared to traditional methods? A. Surveying with a smartphone plus a high-precision GNSS can achieve horizontal errors on the order of several centimeters and vertical accuracy on the order of several centimeters to several tens of centimeters. This meets the accuracy requirements for typical civil surveying (for example, as-built management often allows tolerances on the order of ± several cm). Because smartphone surveying can capture wide areas at high density, even if point-wise errors exist they tend to average out and overall volume calculation accuracy can be very high. Since smartphone surveying captures surfaces rather than estimating volume from a few points, the theoretical accuracy of estimates is improved. However, appropriate operation is necessary to achieve higher accuracy. For RTK surveying, correctly receiving base station correction information and covering the embankment comprehensively with clear lines of sight during scanning are basic considerations that ensure high accuracy.

Q. In what ways is it inferior or superior compared to drone surveying or laser scanners? A. Smartphone surveying has a level of convenience that other methods do not. You do not need to obtain flight permissions or worry about weather like with drones, and you can perform measurements on the spot—this is a major strength. It also avoids the need to purchase expensive equipment and is suited for everyday short-duration surveys. On the other hand, for efficiently measuring very large areas at high density from above, drones or long-range laser scanners can be more effective. It’s a matter of using the right tool: drones are powerful for large-scale earthworks spanning several hectares, while smartphone surveying is more convenient and cost-effective for embankment checks of a few hundred square meters or daily progress measurements. Also, because smartphone surveying is conducted from the ground, it can work in places where drones have difficulty, such as under trees or under bridges.

Q. Besides surveying, how can smartphone survey data be used? A. Point cloud and survey point data obtained by smartphone can be applied to many purposes. If you store the as-built 3D data as construction management records, you can compare terrain changes later for maintenance. You can also use the point cloud to measure pavement thicknesses, slope gradients, estimate excavation volumes for buried objects, and other analyses. Using AR functions, you can display virtual stakes or lines on site based on acquired coordinates, overlaying design and as-built conditions for checks. Smartphone surveying is not just for "measuring"—it is a means to realize digital twinization of the site. By utilizing those data, you can optimize construction plans, streamline as-built inspection, and promote information sharing among stakeholders, broadly advancing site digital transformation (DX).

Q. I am worried about introduction costs. Can I start without expensive equipment? A. One of the attractions of smartphone surveying is its low introduction cost. Basically you can use your existing smartphone and, if necessary, prepare a small GNSS receiver adapter or an app, so initial investment can be greatly reduced compared to traditional surveying instruments or drones. Products like LRTK are cost-effective, and rather than purchasing multiple expensive dedicated machines, equipping field staff to measure with their own smartphones often yields better overall cost performance. Reducing the number of times you need to contract external surveying services also cuts expenses. You can start simply and gradually expand operations, which is another advantage of smartphone surveying.