Impact of Geographical Information Systems on Geotechnical Engineering

Over the last four decades Geographical Information Systems (GIS) have emerged as the predominant medium for graphic representation of geospatial data, including geotechnical, geologic and hydrologic information routinely used by geotechnical and geoenvironmental engineers. GIS allow unlimited forms of spatial data to be co-mingled, weighted and sorted with any number of physical or environmental factors. These data can also be combined with weighted political and aesthetic values to create hybrid graphic products capable of swaying public perceptions and decision making. The downside of some GIS products is that their apparent efficacy and crispness can also be deceptive, if data of unparalleled reliability is absorbed in the mix. Disparities in data age and quality are common when compiling geotechnical and geoenvironmental data. Despite these inherent shortcomings, GIS will continue to grow and evolve as the principal technical communication medium over the foreseeable future and engineers will be forced to prepare their work products in GIS formats which can be widely disseminated through the world wide web. This paper presents the historical evolution of GIS technologies as it relates to the impact in geotechnical engineering, concluding with four case histories on the application of this emerging technology. INTRODUCTION AND BACKGROUND Origins of Remote Sensing In 1904 the U.S. Geological Survey began using terrestrial photogrammetry to aid its topographical mapping of remote mountainous regions in Alaska. In 1907 German inventor Alfred Maul began placing gyroscopically stabilized Rolliflex cameras in rockets. By 1912 his system was able to propel a 41 kg payload to altitudes of 2600 feet to make aerial oblique images. The first aerial photo imaged from a manned aircraft in the United States was in November 1910, when Oroville Wright took a newspaper photographer aloft near what is now WrightPatterson AFB. During the First World War (1914-18) aerial photography became a commonplace tool for military reconnaissance, initially limited to observation of enemy positions and movements. Both sides soon learned that aerial images could be exploited to discern remarkable detail about military conditions and disbursements, and this discovery naturally led to the rapid development of camouflage and concealment techniques that had been unimaginable a few years previous. Development of sophisticated aerial cameras began during the war, with the first multiple lens aerial cameras being developed by the USGS in 1916. Between 1918-20 Sherman Fairchild developed an aerial camera with a focal plane shutter, which became the industry standard for several decades thereafter. In 1924 Fairchild completed an exquisite map of New York’s five boroughs with sufficient resolution to discern individual cars on Fifth Avenue and summertime crowds on Coney Island (Brandt, 1990). The 1920s saw the emergence of aerial mapping as a significant engineering tool, beginning with the U.S. Geological Survey (USGS) mapping of Santo Domingo and Haiti in 1920. The first topographic map derived from aerial imagery appeared the flowing year (Reelfoot Lake quadrangle in Tennessee-MissouriKentucky). Aerial photos began to be used for timber inventory purposes in 1923, for railroad alignments in heavily forested areas in 1924, for locating highways and tunnels as early as 1924, for petroleum exploration and geologic mapping by 1926, and route surveying for locating pipelines and transmission lines by 1929. The stereo-autograph was developed in Germany and initially brought to America by the USGS in 1924. By 1927 the USGS had developed a protocol using stereophotogrammetry to create topographic maps, and this technology gradually eclipsed plane tabling as the primary means of map construction over the succeeding decade, using their Multiplex Aeroprojector. The U.S. Soil Conservation Service instituted a nationwide program to inventory soils in beginning in 1933, which succeeded in covering the continental 48 states and territories by 1941. After the Second World War the USGS began to photograph the continental United States to develop 7.5 minute (1:24,000 scale) and 15-minute (1:62,500 scale) orthophoto-derived topographic maps. This first generation of photos were imaged between 1946-49, and the initial series of 7.5-min. maps were released between 1947-59. Less inhabited regions, such as mountains and forests, were covered by the larger scale 15-minute maps. In 1956 the USGS began imaging a second series of aerial photos across the metropolitan areas experiencing rapid post-war growth, such as portions of New York, Texas and California.