This document discusses various engineering aspects of expansive soils and the damage they can cause to structures. Some key points made include: - Expansive soils containing clay swell when moist and shrink when dry, causing foundations and slabs to heave and crack. - Common signs of expansive soil damage include sidewalk and slab lifting, cracking of structural elements like corners, and differential movement between heavy and light elements. - Proper drainage, symmetric landscaping, and pier and grade beam foundations can help mitigate expansive soil movement and damage over time.

1. J. David Rogers
SOME
ENGINEERING
ASPECTS OF
EXPANSIVE
SOILS
J. David Rogers

2.  Expansive soils cause billions of dollars in real
property damage to structures in the United States
each year. The only peril causing greater loss is that
illustrated here: dry rot of wood elements. Never
allow moss to grow on a shingle roof! Dry rot and
expansive soils damage are typically uninsured perils.

3. Part 1
RECOGNITION OF
FEATURES
COMMONLY
ASSOCIATED WITH
EXPANSIVE SOILS
FOUNDATIONS

4. Expansive Soils
 Expansive soils are
those containing
sufficient quantities
of clay, which tend
to swell when they
absorb moisture and
shrink when they
lose moisture
 A pattern of
polygonal
desiccation, or
“shrinkage cracks”,
results, as seen at
left.

5.  Sidewalk heave is a common manifestation of
expansive soils foundations.
 Excessive watering, leaky irrigation systems,
and/ or poor drainage often accentuates this
problem.

6.  Poor drainage
adjacent to slabs and
flatwork is a common
problem is expansive
soils-related damage
 Difficult to solve in
flat-lying flood plains

7.  Telltale signs of expansive soils behavior
include lifting of lighter structural elements, as
opposed to heavy elements, such as
chimneys. Edge lift at corners and shear
cracking near corners is also common.

8.  Not all structural distress is ascribable to expansive soils action.
 The employment of dissimilar materials within wood frame
structures also leads to differential performance
 The most common problem is cross grain shrinkage of timber
elements (typically shrinks 6% in cross grain direction)

9.  Many homes in California, Colorado, and Texas
are constructed on isolated piers and/or piers
and grade beams to better resist seasonal
heave and shrinkage.

10.  Perimeter heave is common tendency during the first
decade after construction, before soil moisture
equilibrates beneath the structure. This is sometimes
termed “edge curl”.

11.  Soil moisture can be drawn through soil by
temperature and pressure-induced flux, sketched
above. This can cause pseudo settlement of
perimeter foundation elements, due to tilt.

12. Typical
Foundation
Damage –
Interior
isolated
piers
 Isolated interior piers tend to perform poorly if
external sources of free moisture finds their way
into the home’s crawl space, as shown here.

13.  Variances in framing loads acting on foundation
elements limits the amount of heave that can
occur.
 Heavy loads resist heave and uplift, while
lighter loads cannot resist, leading to
differential heave

14.  The perimeter of drilled pier-supported
structures may settle when soil moisture levels
decline significantly about the perimeter of the
structure, as sketched here. This commonly
occurs during extended drought periods.

15.  A common problem with lightly loaded
structures on expansive soils is differential
heave, caused by water ponding on the shady
side of such structures, leaky water lines, or
natural varainecs in soil moisture content.

16. Past Land Use
 A seemingly unlimited
number of factors can
affect differential heave,
aside form asymmetric
structural loads
 These include factors
such as rotting of old tree
root balls, shown here
 These create pockets of
high soil moisture
content, causing
differential heave

17.  A common cause of differential heave is asymmetric
landscaping practices, shown here
 Allowing more water to penetrate the soil on one side
of a structure than the other inevitably leads to
differential performance and damage. The worst
problems are usually caused by leaky water lines,
sprinkler control boxes, or hose bibs