*3.1.2. Swelling-shrinkage behavior of clay*

properties. This is because most physical and mechanical behaviors can be explained by the soil's physico-chemical and microstructural properties. In general, clay is an unwanted material because it creates significant engineering problems. Unlike other minerals of the same size, clay forms mud when mixed with water. Clay has plasticity and can be shaped into dough, and when cooked it turns into a solid with great strength increments. Clay generally shows a volume increase when wet, and when it is dried, its volume decreases, which creates many cracks.

In geotechnical engineering, it is important to identify a clay type, as the type directly affects the important properties of clay, such as Atterberg's limits, hydraulic conductivity, swellingshrinkage, settlement (compression) and shear resistance. Atterberg's limits, known as consistency limits, define the relationship between ground particles and water and the state of the soil relative to varying water contents. With increasing moisture content, clay changes from solid state, to semisolid state, to plastic state and to liquid state, which is given in **Figure 7**. In **Figure 7**, the clay-water mixture shows a total volume reduction, which is equivalent to the volume of water lost around the liquid and plastic limits, as the clay transitions from liquid to dry, and if the decrease in water content continues, no reduction in volume is observed. This limit value is called the shrinkage limit. Therefore, the shrinkage limit is the moisture content at which the soil volume will not reduce further if the moisture content is reduced. The plastic limit is the moisture content at which the soil changes from a semisolid to a plastic (flexible) state. The liquid limit is the moisture content at which the soil changes from a plastic to a viscous fluid state [19]. In geotechnical engineering, the liquid and plastic limits are commonly used. These limits are used to classify a fine-grained soil, according to the Unified Soil

Water is a problem in geotechnical engineering, such as water in voids in the ground mass, flowing in pores, or in the pressure or stress that water creates in the pores. Clay plays an important role in the emergence of water problems, especially on fine soils, and these

**3.1. Physical and mechanical behavior of clay**

90 Current Topics in the Utilization of Clay in Industrial and Medical Applications

Classification system, AASHTO system or TS1500 (Turkey).

*3.1.1. Hydraulic conductivity properties of clay*

**Figure 7.** Water content-volume relationship of soils.

The effect of swelling-shrinkage on fine-grained soils is often seen as a problem in geotechnical engineering applications. Shrinkage behavior in clay soils is effective in reducing the strength in a slope and a foundation's bearing capacity. Shrinkage is usually visible from evaporation in dry climates, reduction of groundwater and sudden arid periods. Swelling can be seen due to rising water. These volume changes are harmful to heavy construction and road coverings. Swelling occurs when the inflation pressure is greater than the pressure from the covering or structure. The material damage from the swelling-shrinkage of soils is more likely to occur in the United States due to greater water pressure, floods, typhoons and earthquakes [4].

Jones and Holtz [20] estimated that shrinking and swelling soils cause approximately \$2.3 billion in damage annually to small buildings and road surfaces in the United States. This amount of damage is twice the amount of damage incurred from floods, earthquakes and hurricanes. Krohn and Slosson [21] estimated that swelling soils cause approximately \$7 billion in damage each year. According to Holts and Hart [22] 60% of 250,000 newly constructed


**Table 1.** Hydraulic conductivity of soils [19].

homes incur minor expansive soil damages and 10% incur significant expansive soil damage each year in the United States. Coduto [2] noted that expansive soils caused \$490,000 in damage to a building over a 6-year period. The estimated annual cost due to significant structural damages, such as cracked driveways, sidewalks and basement floors, heaving of roads and highway structures, condemnation of buildings; and disruption to pipelines and other utilities in Colorado, is \$16 billion, according to AMEC [23].

soil particles. These interactions are divided into friction strength and cohesion strength [2]. When the clay soils are subjected to shear, the volume change in the drainage shear depends on the environmental pressure, as well as the stress history of the soil. In addition, loading on clay soils does not allow water to escape from the pores, and thus, this creates excess water pressure. If the loading does not cause failure, the excess water pressure is dampened, consolidation occurs and volume change is observed. The long process of this volume change in the clays is due to very low hydraulic conductivity. Determination of the shear strength of the clay is performed by a direct shear test, triaxial compression test, vane test and standard penetration tests [4]. **Figure 9** presents the relationship between the shear stress and normal stress for a typical shear strength test and triaxial compression test. After the failure envelope

The Importance of Clay in Geotechnical Engineering http://dx.doi.org/10.5772/intechopen.75817 93

is drawn, the cohesion (c) and internal friction angle (f) are obtained.

**Figure 8.** The graph of a typical test for consolidation test by oedometer.

**Figure 9.** The graph of a typical test for shear strength test by triaxial compression test.

Swelling pressure depends on the type of clay mineral, soil structure and fabric, cation exchange capacity, pH, cementation and organic matter. Any cohesive soil can involve clay minerals, but montmorillonite or bentonite clay minerals are more active regarding swellingshrinkage. Swelling is calculated by swelling experiments with chemical and mineralogical analysis, soil indices and some empirical formulas from soil classifications. The shrinkage limit is determined from a laboratory test or approximate calculation recommended by Casagrande. Properties of clay improve with chemical additives such as cement, lime, limefly ash, cement-fly ash, calcium chloride and so on. [24].

Structures transfer loads to the subsoil through their foundations. The imposed stress from the structure compresses the subsoil. This compression of soil mass leads to a decrease in the volume of the mass, which results in the settlement of the structure, and this should be kept within tolerable limits. Therefore, settlement (compression) should be estimated before construction. The settlement is defined as the compression of a soil layer due to the construction of foundations or other loads. The compression is seen in deformation, relocation of soil particles and expulsion of water or air from void spaces. In general, the soil settlement under load falls into three categories: immediate or elastic settlement, which is caused by the elastic deformation of dry soil or moist and saturated soils without change in the moisture content; primary consolidation settlement, which is the result of a volume change in saturated cohesive soils because of the expulsion of water occupying void spaces; and secondary consolidation settlement is the volume change under a constant effective stress due to the plastic adjustment of soil fabrics [19]. The consolidation settlement is seen when a structure is built on saturated clay or the water level is permanently lowered. Simultaneously, consolidation settlement is seen under its own weight or the weight of soils that exists above the clay. The consolidation settlement of clay takes a long time, and the reason for this is the low hydraulic conductivity and slow drainage of clay. Settlement of the soil is determined by one-dimensional consolidation (odometer) and hydraulic consolidation (Rowe). In experiments, the vertical loads and void ratios are recorded. Afterwards, the relationship between the pressure and void ratio is determined from the measured data. These data are also useful in determining the consolidation coefficient. The consolidation coefficient is determined by the root of time method and the log-t method. **Figure 8** shows the relationship between the void ratio and stress for a typical odometer test for consolidation.

#### *3.1.3. Shear strength behavior of clay*

The shear strength of soils is one of the most important aspects of geotechnical engineering. The strength of the soil provides safety for geotechnical structures. The bearing strength, slope stability and bearing wall of the bases are influenced by the shear strength of the soils. Failure in the soils occurs in the form of shear. If the stresses in the soil exceed the shear strength, failure occurs. The shear failure of the soil depends on the interactions between the soil particles. These interactions are divided into friction strength and cohesion strength [2]. When the clay soils are subjected to shear, the volume change in the drainage shear depends on the environmental pressure, as well as the stress history of the soil. In addition, loading on clay soils does not allow water to escape from the pores, and thus, this creates excess water pressure. If the loading does not cause failure, the excess water pressure is dampened, consolidation occurs and volume change is observed. The long process of this volume change in the clays is due to very low hydraulic conductivity. Determination of the shear strength of the clay is performed by a direct shear test, triaxial compression test, vane test and standard penetration tests [4]. **Figure 9** presents the relationship between the shear stress and normal stress for a typical shear strength test and triaxial compression test. After the failure envelope is drawn, the cohesion (c) and internal friction angle (f) are obtained.

**Figure 8.** The graph of a typical test for consolidation test by oedometer.

homes incur minor expansive soil damages and 10% incur significant expansive soil damage each year in the United States. Coduto [2] noted that expansive soils caused \$490,000 in damage to a building over a 6-year period. The estimated annual cost due to significant structural damages, such as cracked driveways, sidewalks and basement floors, heaving of roads and highway structures, condemnation of buildings; and disruption to pipelines and other utili-

Swelling pressure depends on the type of clay mineral, soil structure and fabric, cation exchange capacity, pH, cementation and organic matter. Any cohesive soil can involve clay minerals, but montmorillonite or bentonite clay minerals are more active regarding swellingshrinkage. Swelling is calculated by swelling experiments with chemical and mineralogical analysis, soil indices and some empirical formulas from soil classifications. The shrinkage limit is determined from a laboratory test or approximate calculation recommended by Casagrande. Properties of clay improve with chemical additives such as cement, lime, lime-

Structures transfer loads to the subsoil through their foundations. The imposed stress from the structure compresses the subsoil. This compression of soil mass leads to a decrease in the volume of the mass, which results in the settlement of the structure, and this should be kept within tolerable limits. Therefore, settlement (compression) should be estimated before construction. The settlement is defined as the compression of a soil layer due to the construction of foundations or other loads. The compression is seen in deformation, relocation of soil particles and expulsion of water or air from void spaces. In general, the soil settlement under load falls into three categories: immediate or elastic settlement, which is caused by the elastic deformation of dry soil or moist and saturated soils without change in the moisture content; primary consolidation settlement, which is the result of a volume change in saturated cohesive soils because of the expulsion of water occupying void spaces; and secondary consolidation settlement is the volume change under a constant effective stress due to the plastic adjustment of soil fabrics [19]. The consolidation settlement is seen when a structure is built on saturated clay or the water level is permanently lowered. Simultaneously, consolidation settlement is seen under its own weight or the weight of soils that exists above the clay. The consolidation settlement of clay takes a long time, and the reason for this is the low hydraulic conductivity and slow drainage of clay. Settlement of the soil is determined by one-dimensional consolidation (odometer) and hydraulic consolidation (Rowe). In experiments, the vertical loads and void ratios are recorded. Afterwards, the relationship between the pressure and void ratio is determined from the measured data. These data are also useful in determining the consolidation coefficient. The consolidation coefficient is determined by the root of time method and the log-t method. **Figure 8** shows the relationship between the void ratio and stress for a typi-

The shear strength of soils is one of the most important aspects of geotechnical engineering. The strength of the soil provides safety for geotechnical structures. The bearing strength, slope stability and bearing wall of the bases are influenced by the shear strength of the soils. Failure in the soils occurs in the form of shear. If the stresses in the soil exceed the shear strength, failure occurs. The shear failure of the soil depends on the interactions between the

ties in Colorado, is \$16 billion, according to AMEC [23].

92 Current Topics in the Utilization of Clay in Industrial and Medical Applications

fly ash, cement-fly ash, calcium chloride and so on. [24].

cal odometer test for consolidation.

*3.1.3. Shear strength behavior of clay*

**Figure 9.** The graph of a typical test for shear strength test by triaxial compression test.

### **3.2. Physico-chemical and microstructure behavior of clay**

For the determination of the physico-chemical and microstructural properties of clay soils, X-ray diffractometer (XRD) and scanning electron microscope (SEM) are commonly conducted. In addition, to determine the physico-chemical properties and structure of the soils, a pH test, electrical conductivity, cation exchange capacity, helium pycnometer, mercury intrusion porosimetry (MIP), surface area analysis (SSA), Brunauer-Emmett-Teller (BET) method or likewise, zeta potential and wavelength dispersive X-ray fluorescence test and Differential Thermal Analysis (DTA) are conducted. The pH value indicates the degree of H+ or OH− ions present. The change in pH affects the soil-water relations. Low pH indicates flocculation, and high pH indicates dispersion. The electrical conductivity of clay is defined by its ion number and type. Cation exchange capacity is a measure of isomorph displacement capacity. Isomorph displacement is when other ions of equal or different valence to those of the ions are left. This change emerges from the unbalanced electrical charge for every change. To prevent this imbalance, the cations in the environment enter the edges of the clays and between the blocks.

a high level of magnification. Soil specimens that are magnified up to 1,000,000 times enable the evaluation of differences in the surface by imaging the surface structures. The changes in the microstructural development of soils play a significant role in the behavior of soils. In particular, these parameters could lead to a better understanding of the engineering properties of compacted soils. The SEM images of typical clays are present in **Figure 12**. Thus, flocculated

The Importance of Clay in Geotechnical Engineering http://dx.doi.org/10.5772/intechopen.75817 95

Surface area analysis (SSA): The specific surface area is affected by grain-size distribution and the types and amounts of different clay minerals. Specific surface area is affected by the physi-

and dispersed structures are observed in the soil samples.

**Figure 11.** The pore size distributions for typical clay from the MIP tests.

**Figure 12.** The SEM images of typical clay for different magnification (a. 1000×, b. 10,000×, c. 35,000×).

cal and chemical properties of soils.

X-ray diffractometer (XRD) analyses: The mineralogical composition of soils is critical due to its significant influence on soil behavior; the soils are affected at first degree, especially by physical, chemical and mechanical properties of clay and by the mineral content. In geotechnics, it is important to find the type of minerals present in clay, as well as their proportions to understand the mechanical behavior. The XRD curve for typical clay is displayed in **Figure 10**. The X-ray diffraction patterns of clay show a mineralogical composition of montmorillonite, anorthite, quartz, calcite and silica.

Mercury intrusion porosimetry (MIP) analyses: In geotechnical engineering, the pore-size distributions for clay significantly influence the geotechnical behavior of soil. The pore-size distributions for typical clay from the MIP tests are displayed in **Figure 11**. This figure shows the relationship between incremental intrusion and pore-size diameter.

Scanning electron microscope (SEM): The microstructure of soils, especially clays, is observed using a versatile, analytical and ultrahigh-resolution field-emission SEM. An SEM provides

**Figure 10.** The XRD curve for typical clay.

a high level of magnification. Soil specimens that are magnified up to 1,000,000 times enable the evaluation of differences in the surface by imaging the surface structures. The changes in the microstructural development of soils play a significant role in the behavior of soils. In particular, these parameters could lead to a better understanding of the engineering properties of compacted soils. The SEM images of typical clays are present in **Figure 12**. Thus, flocculated and dispersed structures are observed in the soil samples.

Surface area analysis (SSA): The specific surface area is affected by grain-size distribution and the types and amounts of different clay minerals. Specific surface area is affected by the physical and chemical properties of soils.

**Figure 11.** The pore size distributions for typical clay from the MIP tests.

**3.2. Physico-chemical and microstructure behavior of clay**

94 Current Topics in the Utilization of Clay in Industrial and Medical Applications

anorthite, quartz, calcite and silica.

**Figure 10.** The XRD curve for typical clay.

For the determination of the physico-chemical and microstructural properties of clay soils, X-ray diffractometer (XRD) and scanning electron microscope (SEM) are commonly conducted. In addition, to determine the physico-chemical properties and structure of the soils, a pH test, electrical conductivity, cation exchange capacity, helium pycnometer, mercury intrusion porosimetry (MIP), surface area analysis (SSA), Brunauer-Emmett-Teller (BET) method or likewise, zeta potential and wavelength dispersive X-ray fluorescence test and Differential Thermal Analysis (DTA) are conducted. The pH value indicates the degree of H+ or OH− ions present. The change in pH affects the soil-water relations. Low pH indicates flocculation, and high pH indicates dispersion. The electrical conductivity of clay is defined by its ion number and type. Cation exchange capacity is a measure of isomorph displacement capacity. Isomorph displacement is when other ions of equal or different valence to those of the ions are left. This change emerges from the unbalanced electrical charge for every change. To prevent this imbalance, the cations in the environment enter the edges of the clays and between the blocks.

X-ray diffractometer (XRD) analyses: The mineralogical composition of soils is critical due to its significant influence on soil behavior; the soils are affected at first degree, especially by physical, chemical and mechanical properties of clay and by the mineral content. In geotechnics, it is important to find the type of minerals present in clay, as well as their proportions to understand the mechanical behavior. The XRD curve for typical clay is displayed in **Figure 10**. The X-ray diffraction patterns of clay show a mineralogical composition of montmorillonite,

Mercury intrusion porosimetry (MIP) analyses: In geotechnical engineering, the pore-size distributions for clay significantly influence the geotechnical behavior of soil. The pore-size distributions for typical clay from the MIP tests are displayed in **Figure 11**. This figure shows

Scanning electron microscope (SEM): The microstructure of soils, especially clays, is observed using a versatile, analytical and ultrahigh-resolution field-emission SEM. An SEM provides

the relationship between incremental intrusion and pore-size diameter.

**Figure 12.** The SEM images of typical clay for different magnification (a. 1000×, b. 10,000×, c. 35,000×).
