CHAPTER 1
INTRODUCTION
1-1. Purpose
basic information presented is broadly applicable to
the investigation and analysis of volume changes in
This manual presents guidance and information for
soils supporting these structures and methods for
the geotechnical investigation necessary for the selec-
minimizing potential soil volume changes. Guidance is
tion and design of foundations for heavy and light
also not specifically provided for the design of struc-
military-type buildings constructed in expansive clay
tures in areas susceptible to soil volume changes from
soil areas. The information in this manual is generally
frost heave and chemical reactions in the soil (e.g., oxi-
applicable to many types of structures such as resi-
dation of iron pyrite), although much of the informa-
dences, warehouses, and multistory buildings. Empha-
tion presented can be useful toward these designs.
sis is given to the maintenance of an environment that
encourages constant moisture conditions in the
1-3. Background
foundation soils during and following construction.
This manual is concerned with heave or settlement
Special attention must always be given to specific re-
caused by change in soil moisture in nonfrozen soils.
quirements of the structure such as limitations on al-
Foundation materials that exhibit volume change
lowable differential movement.
from change in soil moisture are referred to as expan-
a. The guidance and information provided in this
sive or swelling clay soils. Characteristic expansive or
manual can significantly reduce the risk of undesirable
swelling materials are highly plastic clays and clay
and severe damages to many structures for numerous
shales that often contain colloidal clay minerals such
expansive soil conditions. However, complete solutions
as the montmorillonites. Expansive soils as used in
for some expansive soil problems are not yet available;
this manual also include marls, clayey siltstones, sand-
e.g., the depth and amount of future soil moisture
-
stones, and saprolites.
changes may be difficult to predict.
a. Damages from differential movement. The differ-
b. This manual presents guidance for selecting eco-
ential movement caused by swell or shrinkage of ex-
nomical foundations on expansive soil to minimize
pansive soils can increase the probability of damage to
structural distress to within tolerable levels and guid-
the foundation and superstructure. Differential rather
ance for minimizing problems that may occur in struc-
than total movements of the foundation soils are gen-
tures on expansive soils.
erally responsible for the major structural damage.
1-2. Scope
Differential movements redistribute the structural
loads causing concentration of loads on portions of the
a. Guidelines of the geotechnical investigation and
foundation and large changes in moments and shear
analysis necessary for selection and design of military-
forces in the structure not previously accounted for in
type buildings constructed in expansive clay soil areas,
standard design practice.
as outlined in chapters 2 to 5, consist of methods for
the recognition of the relative magnitude of the swell-
b. Occurrence of damages. Damages can occur with-
in a few months following construction, may develop
ing soil problem at the construction site, field explora-
tion, laboratory investigations, and application of
slowly over a period of about 5 years, or may not ap-
methodology for prediction of volume changes in
pear for many years until some activity occurs to dis-
swelling foundation soils. Chapter 6 presents guidance
turb the soil moisture. The probability of damages in-
for selection of the type of foundation with structural
creases for structures on swelling foundation soils if
details of design procedures provided for reference.
the climate and other field environment, effects of
Chapters 7 to 9 discuss methods of minimizing founda-
construction, and effects of occupancy tend to promote
moisture changes in the soil.
tion movement, construction techniques and inspec-
tion, and considerations for remedial repair of dam-
c. Structures susceptible to damages. Types of
aged structures.
structures most often damaged from swelling soil
b. Guidance is not specifically provided for design
include foundations and walls of residential and light
of highways, canal or reservoir linings, retaining
(one- or two-story) buildings, highways, canal and
walls, and hydraulic structures. However, much of the
reservoir linings, and retaining walls. Lightly loaded
1-1
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