Surveying is a critical part of a development project.  When advances occur in surveying technology, those designing and constructing projects enjoy the benefits of increased efficiencies.

Currently, High Definition Surveying (HDS) 3D Laser Scanning is among the newest technology being deployed in the surveying field. HDS technology collects thousands of topographic shots per second, increases design workflow and improves safety for surveyors in the field.

HDS is a much different process than what surveyors used years ago.  During the first 200 years of America’s history, not much changed with the equipment or techniques that were utilized to measure properties or to layout construction work.  However, the last 40 years have been filled with many advances in surveying technology.

Enter the 1970s and electronic measuring devises enabled us to quickly, accurately and more safely perform our everyday field tasks. Field computers allowed us to collect data and stake out for construction with increasingly less manual calculations and paper work. The late ‘80’s brought us the early stages of practical GPS applications allowing us to measure distances of several miles in a fraction of the time it took with our conventional surveying equipment. Through the ‘90’s and the early part of this millennium, our total stations and GPS equipment improved, as did the techniques that we perfected. Small gyro motors and reflectorless technologies in our “robotic” total stations allowed us to reduce the number of persons required to safely and efficiently run a survey crew. HDS is the latest technological advance to be utilized by the surveying industry.

HDS technology collects topographic information on projects where considerable detail, high accuracy, accessibility and safety are concerns. The HDS scanner utilizes a time-pulse laser to obtain literally thousands of 3D topographic shots per second. In about an hour’s time, and from a single instrument setup, the technology can collect millions of topographic points on detailed projects. Back at the office this wealth of data means less interpolation, better accuracy and quicker and more intelligent deliverables.

Another advantage of the HDS technology is that it is capable of capturing very detailed information. By increasing the density of the scan data, we can now, if desired, accurately measure power line sag, roof overhangs, bolt patterns, settlement plates, pipe worksand overhead features such as bridge and tunnel ceilings, etc. Scanner technology can be very useful in measuring and monitoring surfaces and features that are not safe to approach or occupy such as landslides, cliffs, building facades, river banks, chemical or electrical facilities, overhead wires and high traffic areas.

Hall & Foreman Inc., and the Prizm Group used HDS technology on a landslide site that occurred during the severe rain storms that hit Southern California during the 2004/2005 rainy season.  A slope failed on Inverness Drive, a residential street that connects hillside residents with the City of La Canada Flintridge. The intense rain caused two sections of the road to fall away, one 90-foot-long section and one 40-foot-long section, leaving the road impassable by any vehicles. (Image 1) The road is located on a steep slope surrounded by hills and valleys.  It was extremely difficult to access the areas of failure for investigation and surveying. The 3D laser scanning technology allowed the topographic survey to be performed in a timely manner without placing staff in danger.

The laser scanner was set up at five strategic locations enabling the team to collect literally millions of topographic points (known as point clouds) (Image 2) that defined the slide areas and the existing road surface.  A laptop computer connected to the scanner recorded unique X, Y, and Z coordinates for each of these topo points. Back in the office, laser scanning software was utilized to create sections, contours, topographic maps, and point elevations and other client requested deliverables. All maps and details were delivered in Autocad 2004 format.

At the beginning of the project, two design solutions were considered: mechanically stabilized earth slope repair and soldier pile retaining wall repair. The laser-scanned data and 3D software allowed the team to obtain accurate cross sections at any location as necessary to assist in the selection of the design solution and the design itself.  The selected design solution was the mechanically stabilized earth slope repair.  

Utilizing the HDS technology on this site provided a safe, accurate alternative to traditional survey methods and expedited the design solution. SLDT