Ch 2. Review Building Materials

The purpose of a foundation system is to safely transfer building loads to the ground.

true

Explain the difference between waterproofing and damp proofing. When is one or the other an appropriate choice for protecting a foundation from moisture?

-Waterproofing is to resist liquid pressure and prevent it from entering and damaging structure behind -Damp proofing is primarily for moisture proofing. -It depends on the severity of the water conditions

What is filling? Why is fill placed in lifts?

-any placing of earth materials -replace the soil that has been removed to input foundation -achieve optimal compaction and minimize future settlement.

Under what conditions would you use a watertight barrier instead of well points when digging below the water table?

A watertight barrier is desirable in situations where lowering of the water table would have serious detrimental effects on neighboring buildings, and is possible in situations where the bottom edge of the barrier lies in an impermeable stratum of soil below the water table.

In cold climates, how does the frost line affect the placement of shallow footings? What footing type is an exception to this general principle?

Foundations exposed to freezing temperatures can be lifted and damaged by soil that expands as it freezes or by ice lenses, thick layers of ice that form as water vapor migrates upward from the soil and is trapped under the footings. Thus footings must be placed below the frost line. In climates with little or no ground freezing, the thickened exes of a concrete slab on grade or spread footings can function as simple, inexpensive spread footings for one and two story buildings. Where footings must be deeper or floors are raised over a crawlspace or basement, concrete walls resting on strip footings provide support for the structure above.

Explain the differences among sand, silt, and clay, both in their physical characteristics and their behavior in relation to building foundations.

Physically: Sand varies from .0187 inches to .003 in diameter. Silt is smaller than .0029 inches but are roughly spherical like sand. Clay is also smaller than .0029 inches and are typically an order of magnitude. Clay is flat or plate shaped instead of spherical. Behavior: Clay is putty like when wet and hard when dry. silts are not sticky when wet and have little to no cohesiveness when dry. Behavior is related to shear strength which is the resistance to internal sliding. Sand is a coarse grained soil and when densely packed it makes it relatively difficult for particles to move past one another. Poorly packed then particles can move more easily past one another and less load can be supported. In clay and silt they are subject to a wider array of inter particle forces. As particle size decreases, surface area increases and the spaces between the particles called soil pores get smaller.

What is a test soil boring? Why is a test soil boring performed?

Soil Boring is a test where a tube is put in the ground to collect soils It is done to check the types of soil and ground conditions

If shallow foundations are substantially less costly than deep foundations, why do we use deep foundations?

We use deep foundations in situations where competent soil lies too far beneath the surface to be reached by shallow foundations.

What conditions might lead to the choice of a mat foundation for a building?

When bearing capacity of soil is low.

What soil conditions favor piles over caissons? What type of pile is especially well suited to repair or improvement of existing foundations and why?

When non-cosheive soils, subsurface water, or excessive depth of bearing strata make caisson impractical. Minipiles or helical piles are installed without hammering which avoids much of the vibration and noise associated with conventional pile installation. This makes these pile types good choices for work close to existing buildings or for the improvement of exiting foundations where excessive vibration could damage exiting structures or noise could disrupt ongoing activities. Their slenderness entails little or no soil displacement, minimizing the risk of disturbance to nearby foundations.

List and explain some cost thresholds frequently encountered in foundation design.

building below the water table- dewater site, strengthen slopes supper sys., waterproof foundation building close to an existing building - requires underpinning(temp braced structure of existing building) increase in column/wall load- height of a building determines depth of foundation

Explain the difference between a cohesion less soil and a cohesive soil.

cohesionless soil have a lower shear strength and the particles can move past one another more easily and rely primarily on internal friction for strength. cohesive soil has a higher shear strength and tend to be hard when dry and moldable or plastic when moist, higher liquid limit to sustain a higher moisture content before arriving at a flowable consistency because they tend to arrange themselves into more complex internal structures, called fabric that allows the particles to not slip past one another as easily.

Example of a cohesion less soil and a cohesive soil.

cohesionless soil: gravel or soil sand because they rely primarily on internal friction for strength and these coarse grained soil consist of relatively large mineral par tiles with little or no attractive or repulsive forces acting between them. cohesive soil: clay soils because they stick together rather than being frictional, they can have sufficient shear strength in the unconfined soil to prevent excavation walls form collapsing.

What is the nature of the most common type of foundation failure? What are its causes?

differential settlement is the most common type of foundation failure. Its causes are soil types, building loads, or structural systems carrying among different parts of a single building. This can lead to cracked walls, glass, distortion of the building frame, and sloped floors.

List two types of waterproofing and describe one possible advantage of each.

1) Liquid Applied Membrane - Easier to apply to shapes 2)Sheet Membrane - more consistent

List the components of a typical foundation drainage system and their functions.

Drainage mat is a manufactured sheet product, usually about 1/2 inch thick, made of a plastic egg-crate-like structure or some other very open, porous material. It is faced on the outside with filter fabric that allows water to pass easily but prevents fine soil particles from entering and clogging its drainage passages. Subterranean water that approaches the wall falls through th meat to perforated drain piping near the bottom of the foundation wall. The perforation in the pipes face downward so that as the water level in the soil rises, it enters the pipes at the lowest possible level.

De-watering of a construction site:

Is a process of lowering the water table within a construction site

On an unrestricted site, a deep excavation

Is often sloped back at an angle

Which of the following are properties, or characteristics, of a cohesive soil (clay)

Measurable shear resistance (can permit a 'vertical' excavation)

What is excavation sheeting used for? List three different types of excavation sheeting.

Sheeting may be by means of soldier beams and lagging, sheet piling, or slurry wall.