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(2) Soil Mechanics
| Question | Answer |
|---|---|
| Earth Pressure | Occurs from forces adjacent to a soil mass or from within the soil mass itself. |
| Lateral Earth Pressure | Horizontal pressure against a retaining structure, such as a retaining wall, basement wall, or foundation. |
| Active Lateral Earth Pressure | Horizontal pressure exerted by soil against a retaining structure when the soil is in state of failure and is pushing against the structure. |
| Passive Lateral Earth Pressure | Horizontal pressure compressively exerted into soil at the front of a retaining structure when the soil behind the structure is in a state of rest and is being pulled away from the structure. |
| At-Rest Lateral Earth Pressure | Horizontal pressure exerted by soil against a retaining structure when the soil is neither in a state of failure nor in a state of rest. |
| Gravity Wall | A high-bulk structure that relies on self-weight. |
| Buttress Wall | Depends on compression ribs between the stem and the toe to resist flexure and overturning. |
| Counterfort Walls | Depends on tension ribs between the stem and the heel to resist flexure and overturning. |
| Cantilever Walls | Resist overturning through a combination of the soil weight over the heel and the resisting pressure under the base. |
| Stress States | The distributions of forces acting on the soil particles that make up a soil element. |
| Total Stress | Refers to the total force acting on soil particles, including the weight of the soil itself and any external loads. |
| Effective Stress | The difference between the total stress and the pore water pressure. |
| Pore Water Pressure | The pressure of the water within the soil pores, which can increase of decrease depending on changes in moisture content or external loading. |
| Shear Stress | The force acting parallel to a surface within the soil, which can cause the soil to deform or fail. |
| At-Rest Soil | Completely confined soil that cannot move. |
| Failure Surface | Theoretical model used to describe how a retaining wall will fail under pressure. |
| Surcharge | Additional force applied to the exposed upper surface of a retained soil. |
| Strip Load | Load of finite width and infinite length applied to a soil element. |
| Consolidation | A decrease in void fraction |
| Immediate Settling | Occurs immediately after a structure is built and typically occurs in sandy soils. |
| Primary Consolidation | Occurs due to the extrusion of water from the void spaces in clayey soils. |
| Secondary Consolidation | Occurs due to plastic readjustment of the soil grains, taking place at a much slower rate in clayey soils. |
| Normally Consolidated Soil | Soil in which the present load has never been exceeded. |
| Compaction | The process of increasing the density and stability of soil by reducing the volume of air present in the soil. |
| Soil Compaction is done for three reasons. | Improving load-bearing capacity. Reducing settling. Improving drainage capacity. |
| Consolidation | Process by which soil settles and compresses over time under its own weight. |
| Vibratory Plate Compactors | Commonly used for compacting granular soils such as sand and gravel. |
| Tamping Rammers | Used for compacting granular soils, but they use a more forceful impact. They are typically used for compacting in tight spaces or around obstructions. |
| Smooth-Wheeled Rollers | Used for compacting a wide range of soils, including cohesive soils (such as clay) and granular soils. Use their own weight to compress the soil beneath a smooth drum. |
| Pneumatic Rollers | Use rubber tires filled with air to compact the soil. They are typically used for compacting cohesive soils and for finishing work on asphalt and concrete surfaces. |
| Sheepsfoot Rollers | Used for compacting cohesive soils such as clay. These machines have a drum with protruding "feet" that penetrate, knead, and compact the soil. |
| Optimum Moisture Content (OMC) | Is the moisture content at which a soil or other material can be compacted to its highest possible density under a given compaction method. Always taken for dry unit weight, not saturated or total unit weight. |
| Proctor Compaction Test | Involves compacting a soil sampled using a specified number of blows from a hammer of specified weight dropped from a specified height. |
| Modified Proctor Compaction Test | Similar to the standard Proctor compaction test, but the number of blows and the weight of of the hammer are different. The test is typically used for soils with higher maximum dry densities and for pavement design. |
| California Bearing Ratio (CBR) Test | Involves compacting a soil sampled using a specified number of blows. Is a measure of the strength of the soil and is used in pavement design. |
| Vibrating Hammer Compaction Test | Involves compacting a soil sample using a vibrating hammer with a specified frequency and amplitude. The test is used for soils that are difficult to compact using the Proctor test. |
| Kneading Compaction Test | Involves kneading a soil sample using a rolling device with a specified weight and number of passes. The test is used for cohesive soils that are difficult to compact using the Proctor test. |
| Static Compaction Test | Involves compacting a soil sample using a specified weight and applying pressure for a specified duration. The test is used for soils that are easily compacted. |
| Standard Proctor Test (Proctor Compaction Test) | Used for soils with a maximum particle size of 20 mm. The test involves compacting a soil sample in a mold, using 25 blows from a 5.5 lbf hammer falling 12-in to impart a total compactive energy of 12,375 ft-lbf/ft^3. |
| Modified Proctor Test (Modified Compaction Test) | Used for soils with larger maximum particle sizes, up to 75 mm. Uses 25 blows from a 10 lbf hammer falling 18-in to impart a total compactive energy of 56,250 ft-lbf/ft^3. |
| Field Compaction | Refers to the process of compacting soil, asphalt, or concrete to increase its density and strength. |
| Tamping | Involves using a handheld or mechanical tamping device to compact the soil or other material. This is commonly used for small areas or around obstacles where larger machinery cannot fit. |
| Vibratory Compaction | Uses a vibrating plate or roller to compact the material. The vibrations help to settle the particles in the soil or other material, resulting in increased density. |
| Impact Compaction | Involves dropping a heavy weight onto the soil or material to compact it. This is commonly used for road construction and other large-scale projects. |
| Roller Compaction (proofroll) | Uses a heavy roller to compress the material. This is commonly used for asphalt and concrete construction. |
| Dynamic Compaction | Involves dropping a heavy weight from a height onto the soil or material to create a shock eave that compacts the material. This is commonly used for large-scale projects such as landfill construction. |
| Preloading | Involves placing a heavy load on the soil or material for an extended period. This is commonly used for soil stabilization or to prepare a site for construction. |
| Nuclear Gauge Method | Is a nondestructive testing technique used for a measuring the moisture, density, and thickness of materials such as asphalt, soil, and concrete. |
| Sand Cone Method | Can be used to find the in situ density and unit weight of soils. Includes filling a hole with a known amount of sand to find the volume of the hole and then calculating the density of the sample excavated from the hole. |
| Relative Compaction (RC) | Compares the density or unit weight of compacted soil in the field to the maximum density or unit weight obtainable in a lab. It is the percentage of the maximum value determined in the laboratory. |
| Bearing Capacity | The ability of soil to support foundation loads without shear failure. Determines the adequacy of a soil layer's resistance to settlements under vertical loads. |
| Allowable Bearing Capacity (Net Allowable Bearing Pressure/Safe Bearing Pressure) | Is the net pressure in excess of the overburden stress that will not cause shear failure or excessive settlements. |
| Terzaghi Bearing Capacity Theory | For shallow foundation that predicts shear failure along known planes and is derived from level strip footings with footing depths of Df < B. |
| Meyerhof Model Bearing Capacity Theory | Includes correction factors for footing shape, eccentricity, load inclination, and foundation depth. Takes shear strength of soil above the footing into account so the benefit of surcharge is included. |
| Hansen Model Bearing Capacity Theory | Considers footings depth, shape, and load inclination. |
| Vesic Model Bearing Capacity Theory | Closely follows the Meyerhof and Hansen models but addresses the concern that local shear failure leads to lower bound estimates of ultimate bearing capacity. |
| Frost Depth | The depth below the ground surface above which water in the soil will freeze and create frost heave. |
| Frost Heave | A phenomenon that occurs when moisture within soil freezes and expands, which can damage foundations and other structures in contact with the expanding soil. |
| Footing | An enlargement at the base of a load-supporting column or wall that is designed to transmit forces to the soil. |
| Spread Footing (Individual Column Footing/Isolated Footing) | A footing used to support a single column. |
| Continuous Footing (Wall Footing/Strip Footing) | A long footing supporting a continuous wall. |
| Combined Footing | A footing carrying more than one column |
| Cantilever Footing | A combined footing that supports a column and an exterior wall or column. |
| Eccentric | When one side of a footing has more applied weight than the opposite side of the footing, so the load is not symmetrical. |
| Zone of Influence | The area of the horizontal plane enclosed by the influence boundaries. |
| Schmertmann's Method | Used to estimate the immediate elastic settlement of the under the footing. |
| Influence Chart | Typically used to visually represent the effects of different factors or actions on the soil or rock underneath a structure, often in terms of stresses, stains, or displacements. |
| Vertical Strain Influence Factor | Is a parameter often used to assess the deformation behavior of soil or rock under loads or stresses. It helps determine how vertical strain, or change in vertical dimension, distributes within the soil of rock due to external loadings. |
| Peak Strain Influence Factor | Indicates the maximum level of strain that a soil or rock mass will experience under a certain applied load. |
| Angle of Internal Friction | Maximum slope for cuts in a cohesionless drained sand. |
| Taylor's Slope Stability Chart | Used to determine the maximum slope angle for cohesive soils. |
| Method of Slices | Involves breaking the sloped soil into segments of equal width. |
| Overall Stability Calculation | Is an iterative, guess and check procedure using a summation of forces from each slice within the failure zone. |
| Test Methods to Determine Cohesive Properties of Soils | Bishop, Janbu, Spencer (All consider the tangential force that is a result of the weight of the soil mass at the base of the shear plane) |
| Bishop Method | Also considers the lateral force of the adjacent soil mass |
| Janbu Method | Satisfies only horizontal force equilibrium, as opposed to moment equilibrium. |
| Spencer Method | Considers both normal and shear interslice side forces as well as moments. Theoretically more rigorous than the other methods. |
| Pore Water Pressure | The result of the buoyant force exerted by water in the soil mass. |
| Hydrostatic Conditions | Pressure head is equal to the distance between the point of interest and the free groundwater surface (phreatic surface) |
| Gravity Retaining Walls | Utilized for short unsupported heights. They are constructed with plain concrete or stone masonry and depend primarily on their height for stability. |
| Cantilever Retaining Walls | Used to retain higher unsupported soils and are generally made of reinforced concrete that consists of a thin reinforced concrete stem, a base slab, and an optional key. They depend on the primarily on the weight of the retained soil above the base slab. |
| Sheet Pile Walls | Are very thin and depend on passive earth pressure against the embedded portion of the piles and anchor tension pull-out resistance, if utilized, for stability. |
| Coulomb Theory | Takes into consideration all of the above angles when calculating the earth pressure coefficient; therefore, it provides a more accurate value for the earth pressure coefficients. |
| Rankine Theory | Neglects the friction between the soil and the wall, assumes the back of the wall is vertical, and it takes into account the back-slope angle. |
| Retaining Walls | Are designed by assigning initial dimensions based on experience and then using trial-and-error adjustments of the assumed dimensions to satisfy the stability requirements. |
| Shallow Foundations | Spread Footings, strip footings, combined footings, and mat/raft foundations, are generally supported on shallow soils with the foundation level located a few feet below the ground surface. |
| Deep Foundations | Extend deep into the ground to transfer the structural load to the deeper competent soils, bypassing the shallow weaker soils. |
| Intermediate Foundations | Shallow foundations supported on improved soils. |
| Primary Consolidation | Excess pressure transfers to the clay skeleton, causing a continuous reduction in volume over time. |
| Secondary Compression | Occurs after the excess pore pressure is dissipated and the soil particles undergo readjustment, reorientation, and sometimes crushing. |
| Final Compression Readings | Are used to create a consolidation curve, which will be utilized to estimate the primary consolidation settlement. |
| Normally Consolidated (NC) Clay | The present effective overburden pressure is equal to the maximum pressure the soil has been subjected to in the recent past. |
| Overconsolidated (OC) Clay (Preconsolidated Clays) | The present effective overburden pressure is less than the stress the soil has seen in the recent past. |
| Slope Stability | The potential for a slope in soil to withstand movement under given loading conditions. |
| Average Degree of Consolidation | The present of target settlement relative to the full primary consolidation settlement. |
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