Retaining Walls Flashcards
What causes soil to accumulate vertical load?
Gravity and the elasticity of the soil
What does vertical pressure in soil create?
Lateral (horizontal) earth pressure
What can happen in the absence of a structural element resisting horizontal pressures?
A mass of soil can become unstable and suffer catastrophic displacements
What does a naturally stable slope rely on to resist lateral destabilizing forces?
Inherent friction and cohesion
What is often a limitation of naturally stable slopes?
Lack of adequate horizontal space
What is the primary function of retaining walls?
To hold back earth where there is not enough space for a stable slope
How do retaining walls impact space utilization?
They create a near flat surface at grade level
What costs are affected by the use of retaining walls?
Cost of primary construction and cost of secondary features such as drainage elements
What effects are minimized by vertical separation created by retaining walls?
Noise and pollution effects of traffic
Fill in the blank: A naturally stable slope relies on _______ and cohesion.
friction
What are cantilever walls?
Cantilever walls rely on bending strength of the wall stem to provide lateral resistance.
How do anchored walls function?
Anchored walls use cables or other stays anchored in the rock or soil behind it. Anchors are expanded at the end of the cable, either by mechanical means or often by injecting pressurized concrete (grout), which expands to form a bulb in the soil. Anchors must be placed behind the potential failure plane (Rankine) in the soil.
What are mechanically stabilized earth (MSE) systems?
MSE systems transmit lateral forces to the soil using geogrids, which derive strength from the friction mobilized between the geogrid and the soil. The designer must consider that the geomembranes can only develop the required resistance through the length located behind the potential failure plane (Rankine) in the soil.
What is the principle behind gravity walls?
Gravity walls rely on simply the weight of the wall to have adequate stability against sliding and overturning against horizontal forces.
What are semigravity walls?
Semigravity walls have a moderate amount of reinforcement.
How do counterfort walls develop lateral resistance?
Counterfort walls have ribs on the retained earth side and develop lateral resistance via tension in these ribs.
How do buttressed walls develop lateral resistance?
Buttressed walls have ribs (buttresses) on the side opposite the retained earth and develop lateral resistance via compression.
What factors influence the selection of a retaining wall system?
Location geometry most often dictates the selection of a retaining wall system.
Why have segmental retaining walls gained favor?
Segmental retaining walls have gained favor over poured-in-place concrete walls or treated-timber walls because of lower cost, easier installment, and better environmental implications.
When might MSE walls be inappropriate?
In many situations—especially cuts—MSE may not be the most appropriate wall type due to additional excavation and shoring required for installation, making them uneconomical and difficult to construct.
What is the typical tilt degree that causes an increase in lateral forces for retaining walls?
A tilt of about 10 degrees causes a 20% increase in lateral forces.
What is a common cause of shifting in retaining walls?
Shifting is usually caused by repeated cycles of freeze and thaw.
What causes bowing in retaining walls?
Bowing is caused by excessive lateral forces behind the wall, usually due to water buildup.
