CIV E 381 Winter 2025 Lecture Notes

Flashcards created from CIV E 381 Winter 2025 lectures covering soil mechanics, pore pressure, effective stress, and related concepts.

Pore Pressure

The pressure exerted by a fluid within the pores of a material, often influencing the strength and behavior of soil.

Undrained Condition

A state in which the soil does not have time to drain excess pore water due to rapid loading.

Drained Condition

A state in which pore pressure can dissipate over time, allowing soil to behave more predictably.

Effective Stress Principle

The concept that the strength of soil is influenced by both the total stress acting on it and the pore water pressure.

Skempton's Parameter B

A measure of the efficiency with which applied stress is converted to pore pressure.

Compressibility

The ability of a material to decrease in volume under applied pressure; important in understanding pore pressure response.

Saturated Soil

Soil in which all pores are filled with water, affecting its strength and behavior under loading.

Unsaturated Soil

Soil that contains both water and air in its pores, displaying different mechanical behaviors compared to saturated soils.

Skempton's Parameter A

A parameter that describes the pore pressure response to shear stresses in soils.

Triaxial Test

A laboratory test used to measure mechanical properties of soil, involving applying pressures in three directions.

Consolidated Drained Test

A type of triaxial test where pore pressure dissipates during shearing, allowing effective stress to remain constant.

Consolidated Undrained Test

A triaxial test in which the sample is fully consolidated but undrained shearing is applied.

Mohr-Coulomb Failure Criterion

A model used to describe the failure of soil as a function of applied stress and pore pressure.

Residual Strength

The decreased strength of a soil after significant deformation has occurred, often due to shearing.

Peak Strength

The maximum strength a soil can achieve before failure occurs.

Critical State

A condition in which the soil undergoes continuous deformation without volume change; related to the critical void ratio.

Frictional Strength

The resistance to sliding between soil particles, influenced by effective stress.

Shear Strength

The ability of soil to resist shear forces, commonly measured through various testing methods.

Pore Pressure Response

The change in pore pressure within soil when subjected to stress, crucial for stability analysis.

Compressible Skeleton

The framework of solid soil particles that bear loads, typically incompressible within the context of soil mechanics.

Effective Stress

The force transmitted through soil skeletons, calculated as total stress minus pore pressure.

Lateral Earth Pressure

The horizontal pressure exerted by soil against retainment structures, important for wall design.

At-Rest Condition

A state where the soil is neither expanding nor contracting, often used to calculate initial horizontal effective stress.

Rankine's Active Earth Pressure

The lateral earth pressure experienced when soil behind a wall is allowed to move and fail.

Rankine's Passive Earth Pressure

The lateral pressure applied to a wall when soil is compacted against it, preventing failure.

Dilating Soil

Soil that expands when sheared, leading to a decrease in pore pressure and increased load-bearing capacity.

Contracting Soil

Soil that decreases in volume when sheared, causing increased pore pressure and reduced load-bearing capacity.

Porosity

The volume of voids in soil compared to the total volume, affecting water retention and strength.

Cohesion

The attractive forces between soil particles; contributes to strength in saturated clays.

Effective Angle of Friction

The angle that characterizes the frictional resistance of soil under effective stress conditions.

Normal Force

The component of force acting perpendicular to a surface, crucial in determining friction and shear strengths.

Shear Force

The component of force that acts parallel to a surface, causing deformation in soil.

Vane Shear Test

An in-situ test used to determine the undrained shear strength of cohesive soils.

Hydrostatic Pressure

The pressure exerted by a fluid at rest due to the weight of the fluid above it.

Stress Path

The trajectory of stress states experienced by soil during loading, consolidation, and shear.

Anisotropic Stiffness

A condition where stiffness varies in different directions, affecting how stress is transmitted through soil.

Soil Structure

The arrangement and organization of soil particles, influencing mechanical behavior and stability.

Shear Strength Envelope

The graphical representation of the relationship between normal stress and shear strength for various soils.

Soil Consolidation

The process by which soil volume decreases under load, primarily due to expulsion of pore water.

Capillarity

The ability of soil to retain water in its pores against gravity due to surface tension.

Void Ratio

Ratio of the volume of voids to the volume of solids in a soil sample, influencing behavior under load.

Permeability

The ability of soil to transmit water, an important factor in pore pressure and effective stress analysis.

Consolidation Rate

The speed at which pore pressure dissipates, often dependent on soil type and loading conditions.