Before a single shovel hits the dirt on a civil engineering project, extensive surveying and mapping work has likely taken place to gather critical spatial data about the site. Detailed topographic surveys, aerial photography, soil analyses, utility mapping, and other techniques come together to provide a comprehensive picture of existing conditions. This enables the civil engineer to thoughtfully design alignments, earthworks, drainage, and infrastructure that work in harmony with the natural and built environment. 

Advances in surveying technology over the past decades including GPS, LiDAR scanning, and high-resolution aerial photography have vastly expanded the civil engineer’s understanding of project sites. At the same time, computer-aided design (CAD), geographic information systems (GIS), and building information modeling (BIM) tools allow this mass of surveying data to be modeled and analyzed in powerful new ways. This leads to more intelligent project planning, more accurate quantity takeoffs, and designs optimized for constructability and cost-efficiency.

This article provides an overview of essential surveying and mapping techniques used in civil engineering today. It covers how survey data is collected in the field, processed in the office, and then leveraged to inform design decisions. Keep reading to understand how taking the time to thoroughly survey a project site ultimately saves time and headaches when it comes to building it.

Gathering Survey Data for Civil Projects

Performing an accurate field survey is the critical first step in the civil engineering design process. This provides the raw spatial data about site topography, geology, hydrology, and existing built structures. Several traditional and newer advanced surveying technologies are available for capturing different types of site data:

Traditional Surveying Methods 

Total Stations: Total stations remain a surveying workhorse for many engineering and construction tasks. This optical-mechanical instrument incorporates an electronic distance meter (EDM) and digital theodolite in a single robotic unit. The total station is positioned over a known survey control point and stabilized. The surveyor then aims the electro-optical sensor at a prism target set up at points requiring measurement. By firing the EDM’s laser at the prism and measuring the phase shift of the returned signal, the total station can calculate point positions in 3D space to within a few millimeters accuracy at ranges of up to 1,000 feet. These points are recorded digitally for later CAD and GIS mapping. The key advantages of total stations are high precision and fast data capture.

Global Positioning Systems (GPS): GPS technology has largely replaced traditional optical surveying for establishing accurate positioning data over broad areas. A GPS receiver uses triangulation of signals from multiple satellites to pinpoint latitude, longitude, and elevation coordinates within a few centimeters. For engineering surveys, high-precision static GPS surveys are used to create an accurate geospatial framework. This involves leaving a GPS receiver over a control point for an extended period to collect data. The raw data is then corrected at a computer workstation to achieve survey-grade accuracies. GPS is ideal for rapid topographic surveys, establishing survey control networks, and mapping large infrastructure.

Remote Sensing Technologies

In addition to “boots on the ground” surveying, many remote sensing technologies provide valuable high-level intelligence: 

Aerial Photography: Aerial photography from planes, helicopters, and drones provides detailed planar views of project sites. This helps civil engineers analyze the surrounding landscape, identify drainage patterns, and locate existing structures. Orthorectified aerial photos can be used as highly accurate base maps for design. Ongoing site photography is also useful for construction progress monitoring.

Satellite Imagery: Satellite imagery offers a bird’s eye view of project sites. While lacking the detail of aerial photography, it provides helpful regional context. Satellite data is also useful for preliminary site analyses when scoping potential projects in new areas. Services like Google Earth provide free satellite imagery that can supplement engineered surveys.

LiDAR: LiDAR (light detection and ranging) is a powerful remote scanning technology that uses pulsed laser light to capture incredibly detailed 3D data about site topography and features. LiDAR sends hundreds of thousands of laser pulses per second from aircraft-mounted scanners to map the landscape. Sophisticated LiDAR processing software filters the raw scan data into detailed digital elevation models as well as photorealistic 3D point clouds. LiDAR provides accuracy close to total station surveys over large areas in much less time.

Analyzing and Mapping Survey Data  

Once survey data is collected in the field, the next step is compiling it into formats usable for engineering design. This involves creating 3D computer models, maps, drawings, and data tables through CAD, GIS, and other software:

Creating Digital Elevation Models (DEM): DEMs portray the topographic elevations and contours of project sites. They are generated from total station or LiDAR survey data and used as base maps for design. Detailed DEMs help engineers plan appropriate road grades, situate drainage, calculate earthworks balances, and more.

Identifying Soil and Geological Conditions: Soil boring logs, test pit data, geophysical surveys, and other subsurface investigations inform the design of foundations, retaining walls, excavations, and more. This data comes together in geotechnical reports and maps.

Locating Existing Infrastructure: Any existing structures, utilities, and other built objects on site must be carefully surveyed and mapped. This prevents interference with new construction and helps plan connections to existing systems. Common tools include ground-penetrating radar, electromagnetic mapping, and cavity detection.

Applications for Planning Civil Projects

The insights derived from survey data analysis directly guide project planning and design:

Designing Alignments and Grades: Alignments and roadway grades are optimized based on surveyed topographic constraints. This balances earthmoving while maintaining appropriate slopes and sight distances.  

Calculating Earthwork Volumes: Accurate earthwork takeoffs require a quality DEM with precise elevations. Civil 3D and other programs can quickly calculate cut and fill volumes from survey surfaces.

Planning Drainage and Hydrology: DEM data enables watershed analysis for positioning drainage infrastructure. Surveyed wetlands, floodplains, and water bodies inform stormwater management plans.

Analyzing Construction Feasibility: Surveyed topography may reveal constructability issues like tight working space or difficult access that impact planning. Subsurface conditions indicate foundation requirements.

Integrating Survey Data with Design Software

Powerful engineering design software allows civil engineers to integrate field survey data for analysis and modeling:

Computer-Aided Design (CAD): CAD programs like Autodesk Civil 3D are the centerpiece of civil engineering design. Survey data populates its mapping, drawing, and modeling capabilities. Designs are generated directly from field measurements.

Geographic Information Systems (GIS): GIS platforms like ESRI ArcGIS help analyze spatial relationships in survey data. They enable advanced mapping and database capabilities to manage large survey data sets.

Building Information Modeling (BIM): BIM tools like Autodesk Revit utilize survey data to create comprehensive 3D models. All project elements down to terrain are virtually constructed before physical work begins.

Challenges and Limitations 

While surveying provides invaluable site data, there are also challenges civil engineers must plan for:

Data Accuracy and Precision: All measurements have some degree of error. Surveyors must diligently check and recheck data quality. Small mistakes can propagate and compromise downstream design work. 

Processing Large Data Sets: Advanced survey techniques like LiDAR produce immense point clouds with millions of data points. Compiling this into usable information requires expertise and computing power.

Staying Current with New Technologies: The rapid evolution of surveying hardware and software demands constant learning. Training and research are needed to leverage cutting-edge technologies.

Conclusion

Complete, accurate surveying is a prerequisite for high-quality civil engineering design and construction. The advent of new remote sensing and data processing technologies has opened up tremendous opportunities to model the physical world for infrastructure projects. However, human expertise remains essential for planning successful surveys, interpreting the data collected, and integrating it into design workflows. By embracing both emerging and time-tested surveying techniques, civil engineers can optimize project outcomes.