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ABSTRACT: Expansive soils shrink and swell with wetting and drying. The shrink-swell capacity of expansive soils
can result in differential movement beneath foundations. The Geotechnical Investigation notes that the soil near the
surface of the site is expansive in nature and provides methods to minimize the expansive soil impact on foundations.
This paper will discuss about the problems in foundation due to expansive soil & its remedies.
INTRODUCTION
Expansive soil, also called shrink-swell soil, is a very common cause of foundation problems. Depending upon the
supply of moisture in the ground, shrink-swell soils will experience changes in volume of up to thirty percent or more.
Foundation soils which are expansive will “heave” and can cause lifting of a building or other structure during periods
of high moisture. Conversely during periods of falling soil moisture, expansive soil will “collapse” and can result in
building settlement. Either way, damage can be extensive.
Expansive soil will also exert pressure on the vertical face of a foundation, basement or retaining wall resulting in
lateral movement. Shrink-swell soils which have expanded due to high ground moisture experience a loss of soil
strength or “capacity” and the resulting instability can result in various forms of foundation problems and slope failure.
Expansive soil should always be a suspect when there is evidence of active foundation movement.
In order to expansive soil to cause foundation problems, there must be fluctuations in the amount of moisture contained
in the foundation soils. If the moisture content of the foundation soils can be stabilized, foundation problems can often
be avoided. I will be following up on this concept a bit later.
II. CAUSE OF EXPANSION
Soils are composed of a variety of materials, most of which do not expand in the presence of moisture. However, a
number of clay minerals are expansive. These include: smectite, bentonite, montmorillonite, beidellite, vermiculite,
attapulgite, nontronite, illite and chlorite. There are also some sulfate salts that will expand with changes in
temperature. When a soil contains a large amount of expansive minerals it has the potential of significant expansion.
When the soil contains very little expansive minerals it has little expansive potential.
When expansive soils are present they will generally not cause a problem if their water content remains constant. The
situation where greatest damage occurs is when there are significant or repeated moisture content changes.
III. GENERAL FOUNDATION DESIGN CRITERIA
For satisfactory performance, the foundation of any structure must satisfy two independent design criteria. First, it must
have an acceptable factor of safety against bearing failure in the foundation soils under maximum design load. Second,
settlements during the life of the structure must not be of a magnitude that will cause structural damage, endanger
piping connections or impair the operational efficiency of the facility. Selection of the foundation type to satisfy these criteria depends on the nature and magnitude of dead and live loads, the base area of the structure and the settlement
tolerances. Where more than one foundation type satisfies these criteria, then cost, scheduling, material availability and
local practice will probably influence or determine the final selection of the type of foundation.
The Geotechnical Investigation indicates that no adverse foundation-related subsurface and groundwater conditions
would be encountered that would preclude the construction and operation of the proposed structures. The site can be
considered suitable for development of the proposed structures.
A. SHALLOW FOUNDATIONS
The Geotechnical Investigation has provided guidance for the detailed design of the foundations of the proposed
structures. Shallow foundation construction will utilize this data.
B. DEEP FOUNDATIONS
Compressive soils have been determined to constitute a consideration in the design of foundations. The
recommendations of the Geotechnical Investigation will be utilized in the detailed design of all foundations.
C.CORROSION POTENTIAL AND GROUND AGGRESSIVENESS
Corrosively tests will be conducted to determine whether the site soils are either noncorrosive or corrosive for buried
steel based on the chloride content and pH values.
IV. DAMAGE IN FOUNDATION DUE TO EXPANSIVE SOIL
The most obvious way in which expansive soils can damage foundations is by uplift as they swell with moisture
increases. Swelling soils lift up and crack lightly-loaded, continuous strip footings, and frequently cause distress in
floor slabs.
Because of the different building loads on different portions of a structure's foundation, the resultant uplift will vary in
different areas. As shown in Fig. 1, the exterior corners of a uniformly-loaded rectangular slab foundation will only
exert about one-fourth of the normal pressure on a swelling soil of that exerted at the central portion of the slab. As a
result, the corners tend to be lifted up relative to the central portion. This phenomenon can be exacerbated by moisture
differentials within soils at the edge of the slab. Such differential movement of the foundation can also cause distress to
the framing of a structure.
CONCLUSION
On the basis of the present study, the following conclusions aremade:
1. Foundation on expansive soil with proper studyof the expansive soil and measures can be safe.
2. Fly ash or lime can reduce the expansion of the soil.
3. Fiber reinforcement also can be a good alternative in case of foundation in expansive soil.