Introduction
Engineering geology applies geological knowledge to construction and infrastructure safety; environmental geology applies it to understanding and mitigating human impact on, and hazards from, the geological environment — together forming one of the most directly society-relevant branches of the subject.
1. Engineering properties of rocks and soils
Before any construction project, the mechanical properties of the local rock and soil must be assessed: strength (resistance to failure under load), compressibility (how much a material deforms under sustained load, critical for foundation settlement calculations), and permeability (relevant both to groundwater management, point 4, and to slope/foundation stability, since water pressure within a material significantly reduces its effective strength). These properties vary enormously between different rock and soil types, and even within a single formation, making direct site-specific testing essential rather than relying on generic, tabulated values alone.
2. Site investigation for dams, tunnels, roads, and foundations
Site investigation systematically reduces geological uncertainty before construction, typically combining surface geological mapping, subsurface exploration (boreholes, test pits), geophysical surveying (Chapter 6), and laboratory testing of collected samples. Different structures raise different critical geological questions: dams require particular attention to foundation strength and, especially, to reservoir and foundation permeability (to prevent excessive water leakage or seepage-induced failure); tunnels require assessment of rock strength, fracture/joint patterns (Chapter 4, since these control both stability and potential water inflow), and gas hazards; roads and foundations require good understanding of local soil bearing capacity, compressibility, and slope stability specifically along the intended route or site.
3. Slope stability, landslides, and geological hazards
Slope failure occurs when the forces driving downslope movement (primarily gravity, often significantly increased by water saturation adding weight and reducing internal friction) exceed the forces resisting it (primarily the material’s internal shear strength). Contributing factors include slope angle, rock/soil type and structure (particularly the orientation of any bedding planes, joints, or faults relative to the slope face), water content, and external triggers such as earthquakes or human excavation. Understanding this driving-versus-resisting-force framework allows engineering geologists to identify specific high-risk slopes in advance and to design appropriate mitigation measures (such as drainage improvements, slope regrading, or retaining structures).
4. Groundwater and contamination
Groundwater moves through interconnected pore spaces and fractures in subsurface rock and soil (an aquifer, if sufficiently permeable and productive to be a useful water source), and can become contaminated by pollutants introduced at or near the surface (from sources such as landfills, agricultural runoff, or industrial discharge) that subsequently infiltrate downward and are then transported, sometimes over considerable distances, by the natural groundwater flow itself. Because contaminated groundwater can be extremely difficult, slow, and costly to remediate once contamination has occurred and spread, understanding local subsurface permeability and groundwater flow direction in advance is essential specifically for effective contamination prevention, not merely eventual remediation after the fact.
5. Waste disposal, environmental impact, and hazard mitigation
Selecting appropriate waste disposal sites (for both ordinary and hazardous waste) requires careful geological assessment to minimise the risk of groundwater contamination described above — favouring locations with naturally low-permeability subsurface geology (to help contain any leachate) and appropriate additional engineered barriers, well away from any actively used aquifer. Broader environmental impact assessment for any significant construction or resource-extraction project should systematically consider its full range of potential geological consequences, including altered groundwater flow, increased erosion, and slope destabilisation, alongside standard hazard mitigation measures such as early warning systems, appropriately zoned and restricted land-use planning, and engineered protective structures.
6. Earthquake-related engineering considerations
Earthquakes release stored elastic strain (Chapter 4’s elastic deformation) suddenly along a fault, and engineering considerations specifically for earthquake-prone regions include appropriately assessing local seismic hazard (typically informed by known regional fault activity and historical earthquake records), designing structures able to withstand the expected ground motion levels (a discipline generally termed seismic or earthquake engineering), and specifically recognising and managing soil liquefaction risk — a phenomenon where water-saturated, loose granular soil temporarily loses its shear strength and behaves like a liquid under the intense, rapid shaking of a strong earthquake, a well-documented and historically significant cause of severe structural damage even where the shaking itself was not otherwise extreme.
Key Takeaways
- Engineering properties (strength, compressibility, permeability) of rock and soil vary significantly even within a single formation, requiring direct site-specific testing rather than generic assumed values.
- Site investigation combines mapping, subsurface exploration, geophysics, and lab testing, tailored to the specific critical questions raised by the particular structure being planned (dam, tunnel, road, or foundation).
- Slope stability is governed by the balance between gravity-driven driving forces and material shear-strength resisting forces, with water content and structural discontinuities as major contributing factors.
- Groundwater contamination can travel far from its source via natural flow and is far easier to prevent (through advance geological understanding) than to remediate after it has occurred.
- Earthquake engineering must specifically address both expected ground-shaking intensity and the distinct risk of soil liquefaction in water-saturated, loose granular soils.