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Foundation in Expansive Soils


Quiz Questions

1.The type of damage you can expect from a swelling foundation soils can be:

Distortion and cracking of pavements and on-grade floor slabs
Cracks in grade beams, walls, and drilled shafts
Jams and misaligned doors and windows
Failure of steel or concrete plinths (or blocks) supporting grade beams
Lateral forces may lead to buckling of basement and retaining walls

True
False
2. Which one of the followings are design elements in foundation design:
The foundation should be constructed or taken to a depth to protect the structure against damage by swelling or shrinking soil.
The foundation should transmit the combined dead and imposed loads to the The foundation should provide protection from the freeze-thaw cycle of soil in cold climates and adequately resist any chemical or deleterious attack such as by sulfates and other harmful material in the soil.
The foundation should transmit the combined dead and imposed loads to the ground without causing settlements or damage the structure or reduce its overall usefulness.
All of the above
3.The following steps are taken in the decision process to properly select the foundation and superstructure.

Site and soil investigations
Study of topography
Drainage
Soil stabilization
Selection of the foundation and superstructure.

True
False
4. If practical, the foundation should be located on uniform soils subject to the least swelling or volume change. Discontinuities or significant lateral variations in the soil strata should be avoided. Special attention should be given to adequate compaction of filled areas, types of fill, and leveling of sloped sites.
True
False
5.Undeveloped sites generally do not need any subsurface exploration.
True
False
6.Substantial differential heave may occur beneath structures constructed on previously undeveloped sites where trees and other heavy vegetation reduce the transpiration of moisture. Construction of the foundation over the soil will tend to further increase soil moisture because of reduced evaporation of moisture from the ground surface.
True
False
7. Future irrigation of landscaped areas and leakage from future sewer and other water utility lines following development of the site may substantially increase soil moisture and cause a water table to rise or to develop if one had not previously existed. Filled areas may also settle if not properly compacted.
True
False
8.Borings should be spaced to define the geology and soil nonconformities. Spacings of 50 or 25 feet and occasionally to even less distance may be required when erratic subsurface conditions (e.g., soils of different swelling potential, bearing capacity, or settlement) are encountered. Initial borings should be located close to the corners of the foundation, and the number should not be less than three unless subsurface conditions are known to be uniform. Additional borings should be made as required by the extent of the area, the location of deep foundations such as drilled shafts, and the encountered soil conditions.
True
False
9.According to table 4-1 soils that have a liquid limit LL of less than 50 percent, Plasticity index PI less than 25 percent and natural soil suction less than 1.5 their classification for potential swell is:
Low
Marginal
High
10.The foundation soil may expand both vertically and laterally. The vertical movement is usually of primary interests, for it is the differential vertical movement that causes most damages to overlaying structures.
True
False
11.A slab constructed on the ground surface of a wet site may in time lead to downwarping at the edges after a long drought or growth of a large tree near the structure.
True
False
12.Edge uplift may occur following construction on an initially dry site (fig 5-3 b)
True
False
13.The foundation of the structure should be designed to eliminate unacceptable foundation and structural distress. The selected foundation should also be compatible with available building materials, construction skills, and construction equipments. The foundation should be designed and constructed to maintain or promote constant moisture in the foundation soils. For example, the foundation should be constructed following the wet season if possible. Drainage should be provided to eliminated ponded waters. Excavations should be protected from drying.
True
False
14.In preparation for construction, the foundation should always be provided with adequate drainage, and the soil properly prepared to minimize changes in soil moisture and differential movement. Existing trees and other heavy vegetation should be removed. New plantings of like items installed during post construction landscaping should not be located within a distance always from the structure ranging from 1 to 1.5 times the height of the mature tree.
True
False