Geotechnical Engineering Cheat Sheet
The core ideas of Geotechnical Engineering distilled into a single, scannable reference — perfect for review or quick lookup.
Quick Reference
Effective Stress Principle
Terzaghi's fundamental principle stating that the mechanical behavior of soil (strength and compressibility) is governed by the effective stress, which equals the total stress minus the pore water pressure. Only the stress carried by the soil skeleton (grain-to-grain contact) controls deformation and strength.
Bearing Capacity
The maximum pressure that a foundation soil can support without undergoing shear failure. It depends on soil shear strength, foundation geometry, depth of embedment, and groundwater conditions. Engineers apply safety factors to the ultimate bearing capacity to obtain an allowable bearing capacity for design.
Consolidation
The time-dependent process by which saturated fine-grained soils (clays and silts) decrease in volume under sustained loading as excess pore water pressure dissipates and water is squeezed out of the soil voids. Terzaghi's one-dimensional consolidation theory provides the mathematical framework for predicting settlement rates.
Shear Strength of Soil
The resistance of soil to shearing stresses, described by the Mohr-Coulomb failure criterion as a function of cohesion and internal friction angle. Shear strength governs the stability of slopes, bearing capacity of foundations, and lateral earth pressures on retaining structures.
Lateral Earth Pressure
The horizontal pressure exerted by soil against a retaining structure. It is classified into three states: at-rest (K0), active (Ka, when the wall moves away from the soil), and passive (Kp, when the wall moves into the soil). Rankine's and Coulomb's theories provide methods for calculating these pressures.
Slope Stability
The analysis of natural and man-made slopes to assess their susceptibility to failure (landslides). Methods include limit equilibrium approaches (such as the method of slices by Bishop, Janbu, or Spencer) and finite element methods. The factor of safety is the ratio of available shear strength to the shear stress required for equilibrium along a potential failure surface.
Soil Compaction
The process of mechanically densifying soil by reducing air voids to improve its engineering properties, including strength, stiffness, and resistance to erosion. The standard and modified Proctor tests determine the maximum dry density and optimum moisture content for a given compactive effort.
Liquefaction
A phenomenon in which saturated loose granular soils lose their shear strength during cyclic loading (typically earthquakes), causing the soil to behave like a liquid. The rapid buildup of excess pore water pressure reduces effective stress to near zero, triggering ground failure.
Permeability (Hydraulic Conductivity)
A measure of how easily water flows through soil, governed by Darcy's law. It depends on grain size, void ratio, and soil structure. Permeability is critical for analyzing seepage through dams, dewatering excavations, and predicting the rate of consolidation.
Pile Foundations
Deep foundation elements that transfer structural loads through weak or compressible surface soils to stronger strata at depth. Piles resist loads through end bearing (tip resting on hard stratum) and skin friction (shaft resistance along the pile length). Design methods include static analysis, dynamic formulas, and pile load tests.
Key Terms at a Glance
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