1. Overview

As the basis and premise of engineering construction, earthwork calculation plays an important role in railway, highway, hydropower engineering, port, urban planning and other engineering construction. Accurate calculation of yard volume is of great significance in resource allocation, estimation of project cost, accelerating project progress and improving project quality. In traditional, earthwork calculation is mainly performed by using single point measurement through total station, GNSS-RTK, etc., which not only consumes time and money, but also there is a large error between calculation results and the reality. With the promotion and popularization of 3D laser scanning technology, there is a trend showing the rapid and diversified development for acquisition of 3D point cloud data, which has the characteristics to get quickly and effectively the point cloud data with high-density and high-precision of accumulation surface, offering a new way for accurate earthwork calculation.

2. Current Situation of Earthwork Calculation

At present, the data acquisition methods used in earthwork calculation mainly include traditional measurement, UAV photogrammetry, static laser scanning, UAV onboard LiDAR scanning and mobile vehicle/backpack LiDAR scanning. Each acquisition method has its own advantages and disadvantages and is only suitable for earthwork calculation in a certain scene. 

Comparison Table on Collection Methods of Field Data for Earthwork Calculation

3. Application Scenarios of Earthwork Calculation by Using SLAM Technology

Simultaneous Localization and Mapping (hereinafter referred to as SLAM) Technology is not only able to locate its own position and pose through repeatedly observed environment features during movement in unknown environment and locations, but also it can build an incremental map of the surrounding environment through 3D data obtained according to its own position, achieving the purpose of simultaneous localization and mapping. SLAM allows to make position and navigation independently without depending on GNSS. It is suitable for the acquisition of 3D point cloud data with high density of accumulations in all indoor and outdoor scenes. The volume of the accumulations can be measured quickly and accurately by combining with methods of earthwork calculation, like irregular net of triangulation, grid method, cross section method and so on.

3.1 Checking Inventory of Grain Reserves in Granary

During checking the inventory of grain reserves in granary, it is required to measure the volume of grain quickly and accurately. In traditional, the volume of grain is calculated by using the data volume formula after measuring the length, width or diameter according to the shape of grain accumulation. In this way, there is a large error of volume of grain reserves because the above lengths are measured roughly. With the application and development of information technology in the field of grain, how to measure accurately the volume of grain is an urgent problem.

Complete and continuous point cloud data can be obtained when collection personnel walk around a grain accumulation with the SLAM 100, which can be used in calculation of the volume of grain reserves during checking inventory indoor to establish visual 3D information file of grain accumulations. The volume of grain accumulations can be calculated accurately, effectively improving the efficiency of checking inventory of grain reserves.

3.2 Coal mine stripping quantity inventory

In mining, the calculation of excavation quantity is a basic work of mining engineering. With the great importance of excavation quantity in the project cost and scheme selection, its accuracy is related directly to the economic benefits of the production enterprises. As a result, it is particularly important to calculate the earthwork quantity quickly, simply and accurately by using the on-site measurement data. At present, earthwork excavation quantity for many open-pit mine is still calculated through cross section method parsed artificially and irregular net of triangulation method of DTM after using GNSS-RTK to measure points. In this way, although it is allowed to avoid the situation that the result of actual measurement is inconsistent with the actual terrain caused by data loss of slopes, steps, scarps and so on. But calculation of mine excavation quantity is a cyclical repetition work. With the expansion of production and mining field, usually GNSS-RTK can't be fixed at the bottom of coal mine, for which it is unable to guarantee the efficiency and precision of data measured. It will affect the accuracy of excavation quantity calculation and ultimately affect the efficiency of production enterprises. 

In the above scenarios, SLAM technology is allowed to make full use of its characteristics of localization and navigation independently. With its advantage to obtain quickly and accurately the point cloud data, it can achieve 3D visual display of coal heap excavation quantity and calculate accurately the excavation quantity.

3.3 Landscaping Engineering Earthwork Calculation

Landscaping engineering occupies a very important position in urban landscaping construction planning, which plays a very important role in improving the overall landscape and standardizing the spatial layout. To achieve thorough landscaping rectification construction, a scientific and reasonable construction scheme is required to be formulated according to the actual situation of the region. However, the accuracy of earthwork calculation has a great influence on the rationality of the construction scheme. At present, the main earthwork calculation methods include:

①Earthwork construction estimation, provides important support for the temporary construction of the whole project according to the actual situation of earthwork terrain construction to directly assess the amount of earthwork needed for the construction.

②Earthwork figure geometric formula calculation, evaluates the amount of earthwork through scientific geometric calculation formula by regarding the amount of earthwork needed for engineering construction as a geometric pattern.

③Earthwork section calculation usually is applied in the calculation of long and narrow earthwork according to the section data collected by GNSS-RTK.

④Earthwork contour line calculation, set corresponding contour interval for adjacent sections. The sections are obtained along the direction of earthwork contour line.

Among the above methods, ① and ② estimates the earthwork quantity according to experience, while ③ and ④ calculates the earthwork quantity based on point measurement in field. There are large errors no matter which the above calculation is applied. What's worst, the sighting condition and GNSS signals are poor in gardens because of vegetation and serious occlusion, making it difficult for field operation.

Free from the limitation of sighting conditions and GNSS signals, SLAM technology can be applied in landscaping engineering earthwork calculation, allowing the collection personnel to get easily the point cloud data when walk through the woods. Terrain points can be obtained after rectifying, denoising and classifying the point cloud, and then earthwork quantity can be calculated accurately by combining with irregular net of triangulation method of DTM.

3.4 Sand Quantity Calculation of Sand Carriers

In projects of reclaiming land from the sea by building dykes, sand is not only the main building material, but also the main part of the construction cost. Therefore, the accuracy of sand quantity calculation affect directly the profits and loss of projects. For traditional manual calculation, there are relatively large errors affected by measurement instruments, human factors and calculation methods. How to calculate accurately the sand quantity of sand carriers is an urgent problem to solve. The existing calculation is to use a static scanner to scan the sand piles, and then calculate the sand quantity after splicing and thinning data later. The results are correct by using this kind of calculation. But there are two following shortcomings: ①low efficiency of data collection; ②collection of point data affected by instability of static scanner resulting from ships sloshing in the water.

SLAM technology is not affected by hull shaking. When a sand carrier is unloaded and full loaded, SLAM100 can be used by collection personnel to walk around the cabin of sand carriers to get corresponding point cloud data respectively. The sand quantity can be acquired after calculating the difference between the point cloud models of the two periods.

3.5 Earthwork Calculation of Site Leveling Projects

Site leveling projects refer to the transformation of the original landform of the engineering site according to the construction needs. By using the results of topographic survey, earthwork calculation can be calculated precisely and then balance the quantity of filling and digging, allowing to select construction manpower and machinery in a reasonable way. Site leveling projects is the reliable basis for controlling the site construction scheme, and the key to affect the project cost and investment, practically relating to all aspects of project construction. Due to the defects of traditional measurement methods to collect data in field, there are relatively large errors in earthwork calculation of site leveling projects no matter which calculation method is applied. Consequently, it is of great particularly importance to get high-precision data which can improve high precision in project construction, to create higher economic profits.

Collection personnel can get the site point cloud data quickly by walking around the site with SLAM100. At the same time, automatic measurement of non-contact Light Detection and Ranging(LiDAR) solves problems to get data in the places difficult to reach, like slopes, platform steps and so on. It really achieves to copy 3D realistic sites. Terrain points of sites can be acquired after working of coordinate transformation and classification. Balance of filling and digging can be calculated by selecting reasonably earthwork calculation methods according to the terrain characteristics.

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