1

CLAY MINERALS &

GEOTECHNICAL PROBLEMS

Faculty of Engineering – Civil Eng. Department

By: Amira Abdallah Youssef Ibrahim

To: Dr. Salah Shata

2

Clay Minerals

Definition

Clay refers to naturally occurring material composed primarily of fine-

grained minerals, which is generally plastic at appropriate water

contents and will harden when fired or dried.

The minerals found in clay are generally silicates less than 2 microns

(one millionth of a meter) in size, about the same size as a virus. Clays

are very abundant at the earth's surface; they form rocks known as

shales and are a major component in nearly all sedimentary rocks. 1

Importance

Clay contributes many benefits to the physical, chemical and biological

properties of soil. It increases the soil’s cation exchange capacity,

enhances waterholding capacity, provides elasticity, acts as a binding

agent for the non-clay components, and reduces nutrient loss through

leaching. The buffering capacity of soil (resistance to change in pH) is

enhanced by clay, which means that growers do not have to apply

lime as often. Clay is an essential component of a productive soil. It

plays a vital role

in holding plant

nutrients and

water. Without

it, successful

crop production

would be in

jeopardy.2

1 -INTRODUCTION TO THE PROPERTIES OF CLAY MINERALS Stephen Guggenheim Department of Geological Sciences University of Illinois at Chicago 2- Clay Minerals: Their Importance and Function in Soils by Tucker, M. Ray.

3

Types of Clay minerals :

There're four

basic types of clay

minerals .3

Kaolinite: This clay mineral is the weathering

product of feldspars. It has a white, powdery appearance. Kaolinite is named after a locality in China called Kaolin, which invented porcelain (known as china) using the local clay mineral. The ceramics industry uses it extensively. Because kaolinite is electrically balanced, its ability of adsorb ions is less than that of other clay minerals.

Illite: Resembles muscovite in mineral

composition, only finer-grained. It is the weathering product of feldspars and felsic silicates. It is named after the state of Illinois, and is the dominant clay mineral in midwestern soils.

Chlorite: This clay mineral is the

weathering product of mafic silicates and is stable in cool, dry, or temperate climates. It occurs along with illite in midwestern soils. It is also found in some metamorphic rocks, such as chlorite schist.

3 Journal of Natural Resources and Life Sciences Education

4

Vermiculite: This clay mineral has the

ability to adsorb water, but not repeatedly. It is used as a soil additive for retaining moisture in potted plants, and as a protective material for shipping packages.

Smectite: This clay mineral is the

weathering product of mafic silicates, and is stable in arid, semi-arid, or temperate climates. It was formerly known as montmorillonite. Smectite has the ability to adsorb large amounts of water, forming a water-tight barrier. It is used extensively in the oil drilling industry, civil and environmental engineering (where it is known as bentonite), and the chemical industry.

5

Engineering Characteristics

Changes in soil water content or solution chemistry of clayey soils induce swelling pressures sufficiently large to fracture and damage structures and roads.4

Swelling process

Clay minerals, such as smectites and mixed-layer illites, can expand in volume up to 20 times their original volume through adsorption of layers of water between their unit cells. Such 2:1 clay minerals are particularly prone to swelling because there is no hydrogen bonding between the octahedral layers of the unit cells.

Swelling is known to occur in three steps. In the first step, referred to as crystalline swelling, layers of

Jones Jr., F.O. 1964. Influence of Chemical Composition of Water on Clay Blocking of Permeability. J 4

Pet Technol 16

6

water enter the interlayer space in the clay mineral, resulting in an increase in the C spacing of the clay mineral in steps. The size of these steps is observed to be approximately equal to the diameter of the water molecule

The next stage in swelling is referred to as hydration swelling. This is thought to occur through the hydration and dehydration of ions entering the interlayer region. Several theories have been proposed to explain the observed repulsive hydration force observed in the presence of different cations.

Finally, when the interlayer spacing is ≈ 50 Å or so, free swelling occurs. This is driven primarily by the balance between electrostatic and van der Waals forces between the layers of clay. In this stage of swelling, the clay layers are sufficiently far apart that very little mechanical integrity exists in the clay. Such clay minerals are liable to be dispersed in the flowing fluid and to plug pore throats.

Shrinkage

Shrinkage is the rate at which the body

shrinks during drying and firing .

Moist clay begins to shrink as soon as it is

taken out of its plastic storage bag and comes

into direct contact with the air. Water is

drawn out of the clay until it reaches the

moisture content of the surrounding

atmosphere.

7

Effects of swelling and shrinkage on Structures

Foundation Damage 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.5

DAMAGE TO FOUNDATIONS FROM EXPANSIVE SOILS J. David Rogers, Robert Olshansky, and Robert 5

B. Rogers

8

Road damage (Asphalt cracks)

Mud flow & Debris flow

9

Engineering Solutions For Geotechnical Problems

Pile Foundations

A pile is basically a

long cylinder of a

strong material such

as concrete that is

pushed into the

ground to act as a

steady support for

structure built on the

top of it .

Types of Piles due to depth

Material used in piles

10

Piles Foundation

Driven Piles

Micro piles

Concrete Piers

Helical Piers

Helical Piers

11

12

Concrete Piles

Micro Piers

13

Other Solutions :

14