Al-Rafidain University Collage Civil Engineering Department Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil /

Lecture 1

Introduction to Soil and

Most of the civil structures rest on the soil, so the life of these structures depends on the soil and its behaviour under the loads. The behaviour of soil under the loads depends on the various properties of soil. The different soil properties can be determined by studying soil mechanics. 1.1 Soil

The word “Soil” is derived from the Latin word “Solum” which has different meanings to different professions as: ① In agronomy: the term means the upper layer of the earth that may be plowed; specifically, the loose surface material of the earth in which plants grow. ② In : the term means the materials, which are produce from weathering of rocks and cover the upper layer of earth’s crust. ③ In civil engineering: the term means, uncemented inorganic material, composed of solid particles, produced by the disintegration of rocks. The void space between the particles may contain air, water or both.

Since ancient ages, engineers have been handling as an engineering material for various construction projects. Construction of the Egyptian pyramids, Iraqi ziggurats, Roman aqueducts, and China’s Great Wall.

In civil engineering, soil is used as (Figure 1-1): ① A constructional material (fill materials) such as earth dams, embankments, slopes, railways, highways, and airports. ② To supports loads from the foundations of buildings.

Lecture 1: Introduction to Soil and Soil Mechanics 1

Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

Figure (1-1): Use of Soil in Civil Engineering

1.2 Soil Mechanics

Soil Mechanics is one of the youngest disciplines of civil engineering involving the study of the physical and mechanical properties of soil. The first definition of soil mechanics has been coined by so-called "father of soil" "Dr. Karl Terzaghi", Karl Terzaghi coins the term of "Soil Mechanics" in (1925), and define the soil mechanics as following: Soil Mechanics is the application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks regardless of whether or not they contain an admixture of organic constituents. Definitions ① engineering: is a branch of soil engineering dealing with the application of principles of soil mechanics to the design and construction of foundations for various structures. ② Geotechnical engineering: is a broader term and refers in total to all engineering problems involving soil and/or rock as foundation material and construction material. Geotechnical engineering involves the application of soil mechanics, rock mechanics, and engineering geology to engineering problems including soils and rocks.

Lecture 1: Introduction to Soil and Soil Mechanics 2

Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

1.3 Applications of Soil Mechanics in Civil Engineering

Soil mechanics has vast applications in many fields of civil engineering works. Some of the important applications are as under:

① Foundations: The loads from any structure have to be transmitted to a soil through the foundation for the structure. Thus, the type, and details of which can be decided upon only with the knowledge and application of the principles of soil mechanics. ② Underground and Earth-retaining Structures: Underground structures such as pipe lines, and tunnels and earth-retaining structures such as retaining walls can be designed and constructed by evaluating the forces exerted by the soil on these structures. This requires application of the principles of soil mechanics. ③ Slopes and Excavations: Slopes is not horizontal surface, there is a component of weight of the soil, which tends to move it downward and thus cause instability of slopes. This requires study the stability analysis in soil mechanics. Likewise, excavations require the knowledge of ; deep excavations may need supports (bracing). These supports should be designed to resist the lateral forces exerted by the soil. This requires knowledge of theories of lateral earth pressure only in soil mechanics. ④ Embankments and Dams: The construction of embankments and earth dams where soil itself is used as the construction material requires a thorough knowledge of the engineering behaviour of soil especially in the presence of water. Knowledge of seepage analysis as well as compaction characteristics for achieving maximum unit weight of the soil is essential for efficient design and construction of embankments and earth dams. ⑤ Pavement Design: A Pavement is a hard crust placed on soil for providing a smooth a strong surface on which vehicles can move. Pavements depend more on the subgrade soil for transmitting the traffic loads. The design of pavements depends on swelling and shrinkage of sub-soil and frost action. Consideration of these factors is necessary and one cannot do without the knowledge of soil mechanics.

Lecture 1: Introduction to Soil and Soil Mechanics 3

Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

1.4 Uniqueness of Soil

Soil unlike others civil engineering materials such as concrete, steel, brick, ect. The soil problems as a material can be considered unique because: ① Stress-Strain relationship of soils is not linear. This makes the stress-strain properties analysis of soil mass is difficult.

Non-Linear Stress Stress Linear

Strain Strain ② Soil is not elastic material and the behaviour of soil depends on the elastic and plastic properties. Soil is Elasto-Plasto material.

Elastic

Stress Stress Elastic-Plastic

Strain Strain ③ Soil behaviour strongly depends on pressure, time, and environments conditions. Soil properties are controlled by changing in pressure and presence of water. ④ Soil is not homogenous material; this means the soil properties may be different from location to other. ⑤ The nature of soil is complex (Figure 1-2). Soil composed of particles with wide range in sizes, shapes, and grading. Soil mass is three phase system, the pours between its solid particles filled with water and air. Because of these particulate natures of soil, the development of mathematical models to describe and predict the soil behaviour of soil is a difficult.

Lecture 1: Introduction to Soil and Soil Mechanics 4

Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

Sand particles Clay particles

Soil System (solids, water, air) Soil particles Shapes of soil particles Figure (1-2): The Nature of Soil ⑥ Most soils are very sensitive to disturbance and the properties measured by a laboratory test may be unlike that of the in situ soil. ⑦ Soil mass cannot be seen entirely and its properties evaluated based on small sample.

Lecture 1: Introduction to Soil and Soil Mechanics 5

Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

1.5 Example of Soil Mechanics Problems

Engineers have to deal with many challenging soil mechanics problems even at present, as well as in the past. A famous building illustrates the problems of soil mechanics is leaning Tower of Pisa. This famous building illustrates historical soil mechanics problems. The (56 m) high tower at Pisa, , leans about (3.9 m) at top toward the south. The construction of the tower started in (1173) and was completed in (1372). It was reported that the tower started to sink unevenly after the construction progressed to the third floor in ( 1178) and more floors were built up to accommodate for the tilt. The lean is due to differential settlement of the foundation soil. In March ( 1990), the tower was closed to the public due to the possibility of collapse in the near future. Engineering remediation procedures were discussed to stop further leaning.

Lecture 1: Introduction to Soil and Soil Mechanics 6

Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

An early attempt was made to put heavy load (800 metric tons of lead counterweight) on the north side of the tower foundation to compensate for the larger settlement on the south. A more drastic measure was taken later to extract soil mass (38 m3) under the north side of the foundation soil by angled auger holes so that the north side experienced extra settlement. In December 2001, the tower was reopened to the public and

has been declared stable for at least another 300 years.

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Al-Rafidain University Collage Civil Engineering Department Soil Mechanics Lectures for Third Year Students By Dr. Ahmed Al-Adly Ph. D Civil / Geotechnical Engineering

Dr. Karl von Terzaghi

(October 2, 1883 – October 25, 1963)

An Austrian civil engineer and geologist, founder and guiding spirit of soil mechanics, outstanding engineering geologist, and preeminent foundation engineer. Is generally recognized as a Father of Soil Mechanics. His early professional life was spent in search for a rational approach to earthwork engineering problems. His efforts were rewarded with the publication in 1925 of his

famous book on soil mechanics, this publication is now credited as being the birth of soil mechanics.

Terzaghi was the first to make a comprehensive investigation of the engineering properties of soils; he created most of the theoretical concepts needed for understanding and predicting the behavior of soil; and he devised the principal techniques for applying scientific methods to the design and construction of foundations and earth structures. To commemorate Terzaghi’s great work, the American Society of Civil Engineers (ASCE) created the Terzaghi’s lecture and the Terzaghi Award.

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