Geotechnical Engineering

Our infrastructure is built either on or below ground, and may even be made of earth materials (for example earth dams or levees). Geotechnical engineers characterize the properties of earth materials and analyze soil and soil-structure systems to optimize their performance for anticipated loads. See Figure 2-6 for the geotechnical engineer’s viewpoint. Often it is said that there are four basic structural materials: wood, metal (chiefly steel), masonry (e.g., brick, concrete block), and concrete. Actually, all construction built here on Earth includes a fifth basic structural material – the earth beneath or around the building or other construction. Geotechnical engineers work closely with geologists to gather information about subsurface characteristics and with structural engineers to design the foundation for the overlying structure. A geotechnical engineer might be concerned with such activities as:

• Assessment: evaluating sites for constructability and risks, such as stability failures (e.g., landslides) or deformations (soft soil that excessively compacts)
• Analysis: modeling response of soil and soil-structure systems to future loads, e.g., earthquakes, and/or changes in environmental conditions, e.g., change in the level of the water table (soil properties are often sensitive to water content)
• Design: design of geotechnical systems to meet performance criteria; examples of geotechnical systems include foundation systems, retaining structures, pavement, tunnels, and earthworks such as dams, levees, landfills, and filled ground where construction will be built
• Monitoring: monitoring earthwork and foundation construction to verify analysis assumptions and quality control in the construction process
• Mitigation: stabilizing slopes and excavations, installing barriers to inhibit the movement of subsurface contaminants.

Geotechnical engineering has become an increasingly sophisticated field in recent years. (“Soil engineering” is what the field was usually called until a few decades ago). In the application shown in Figure 2-7, geotechnical engineering, in combination with the use of modern instruments and communication technology, is used to contend with the hazard of landslides. On this narrow ledge along the Pacific Ocean, where the roadbed has several times fallen down the cliff because of landslides, wires are embedded across the road to measure a fraction of an inch of extension if the road begins to stretch and slide toward the downhill side. Illuminated lights and a sign are then activated to warn drivers. A cell phone call is also automatically generated to notify state highway engineers.

Figure 2-6. The geotechnical engineer’s viewpoint. Geotechnical engineers look at a building site differently than the way we usually do, because most of us only visualize a building or other construction from the ground up. Geotechnical engineers study and field-measure the properties of the soil and rock layers beneath and around construction so that foundations, drainage, and underground construction such as pipelines, can be properly designed and constructed. illustration: RR

Figure 2-7. Geotechnical monitoring of landslide hazard, Highway 1, Devil’s Slide, California.

photo: RR