What Are Geotechnical Structures?

Geotechnical structures are engineered systems that use soil, rock, or the interaction between earth materials and structural elements to carry loads, retain earth, control water, or create usable space below or at the ground surface. The category includes retaining walls, embankments, dams, tunnels, excavation support systems, and deep foundations. Their design depends on the mechanical properties of the surrounding ground, the geometry of the structure, and the loads it must sustain over its service life.

Unlike conventional structural elements made of homogeneous materials such as steel or concrete, geotechnical structures involve earth materials whose properties vary spatially, change with moisture and stress, and can only be estimated through sampling and testing. This inherent variability is managed through careful site characterization, conservative safety factors, and systematic instrumentation programs that monitor performance during and after construction. The field draws on soil mechanics, rock mechanics, hydraulics, and structural engineering in combination.

Retaining Systems

Retaining systems hold back soil or rock to create elevation differences required for roads, railways, building sites, and waterfront facilities. Gravity walls rely on their own mass to resist overturning and sliding forces. Cantilever retaining walls use a structural toe slab to develop resisting moments from the soil beneath. Sheet pile walls and soldier pile systems are embedded vertically in the ground and may be anchored by tiebacks or ground anchors when they are too tall to act as cantilevers alone. Mechanically stabilized earth (MSE) walls, developed in the 1960s by Henri Vidal, reinforce a compacted fill with layers of geosynthetic or metallic strips to create a composite mass that behaves as a gravity structure. The South Carolina DOT Geotechnical Design Manual classifies retaining structures by their primary mechanism of resistance and sets out design requirements for each type.

Embankments and Earthen Dams

Embankments are compacted fills built above existing ground to carry roads, railways, or waterways, or to impound water as earthen dams. Their stability depends on the shear strength of the fill and the native foundation soils, the pore water pressures generated during and after construction, and the long-term seepage regime through and beneath the structure. Earthen dams require a low-permeability core, often composed of compacted clay, flanked by more permeable shell zones and filter layers that prevent internal erosion. Monitoring programs using piezometers, settlement gauges, and inclinometers track performance throughout the life of the structure. Failures in embankment dams, such as the 1976 Teton Dam collapse, have driven refinement of seepage and internal erosion analysis methods. The USACE Geotechnical Engineering manual series provides detailed design guidance for these structures.

Tunnels and Underground Structures

Tunnels and other underground openings require the surrounding ground to carry loads that a conventional structural system would otherwise resist. Soft-ground tunneling relies on techniques such as earth pressure balance (EPB) shield machines and compressed air to stabilize the tunnel face, while rock tunneling makes use of the inherent strength of the rock mass, supplemented by rock bolts and shotcrete applied immediately after excavation. The New Austrian Tunneling Method (NATM) formalizes the principle of allowing controlled deformation to redistribute stresses before applying the final lining. Cut-and-cover construction, used extensively for urban transit systems, requires temporary excavation support through sheet piles or secant pile walls, followed by cast-in-place concrete structure. As the Virginia Tech geotechnical engineering research group notes, the interaction between the excavation sequence, support installation timing, and ground response governs final structural performance.

Applications

Geotechnical structures have applications in a wide range of disciplines, including:

• Highway and railway embankment and cut slope construction
• Flood control levees and earthen dam construction
• Underground transit tunnels and utility corridors in urban areas
• Basement excavation support for high-rise buildings
• Offshore and coastal protection structures
• Mine waste containment and tailings dam engineering
• Waterfront bulkheads and port infrastructure