University of Nairobi Department of Real Estate and Construction Management
BCM 112 CIVIL ENGINEERING CONSTRUCTION I
DR. NYAMBANE OSANO
[email protected] 2013
BCM 112 – CIVIL ENGINEERING CONSTRUCTION I
OSN - Lecture Notes
TABLE OF CONTENTS 1
OVERVIEW ....................................................................................... 1 1.1
COURSE DESCRIPTION AND OUTLINE
1
1.2
PREREQUISITE
1
1.3
STUDENT LEARNING OUTCOME
1
1.4
TEACHING METHODOLOGY AND TECHNIQUES
1
1.5
REQUIRED TEXT BOOKS
2
2
INTRODUCTION TO SOIL MECHANICS ............................................. 3 2.1
DEFINITION OF SOIL
3
2.2
SOIL MECHANICS AND GEOTECHNICAL ENGINEERING
3
3
SOIL FORMATION ............................................................................ 5 3.1
DEFINITION
5
3.2 3.2.1 3.2.2 3.2.3
WEATHERING INTRODUCTION PHYSICAL WEATHERING CHEMICAL WEATHERING
5 5 5 5
3.3
TYPES OF SOILS
6
3.3.1 3.3.2 3.3.3 3.3.4 3.3.5
SANDY SOIL SILTY SOIL CLAY SOIL PEATY SOIL SALINE SOIL
6 6 6 6 7
4
SOIL PROPERTIES ........................................................................... 8 4.1
INTRODUCTION
4.2 4.2.1 4.2.2 4.2.3
SOIL PHYSICAL PROPERTIES
SOIL TEXTURE SOIL STRUCTURE SOIL POROSITY
8 8 9 11
4.3
SOME USEFUL TERMS AND ASSOCIATED SYMBOLS
11
4.4 4.4.1 4.4.2 4.4.3 4.4.4
PHASE RELATIONSHIP PHASE DIAGRAM VOID RATIO (E) MOISTURE CONTENT (WATER CONTENT) (W) POROSITY (N)
12 12 13 13 13
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4.4.5 4.4.6 4.4.7 4.4.8 4.4.9 4.4.10 4.4.11 4.4.12
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SPECIFIC VOLUME (V) RELATIVE DENSITY (SPECIFIC GRAVITY) (GS) DEGREE OF SATURATION (SR ) AIR CONTENT (A) DENSITY OF SOLIDS (ΡS) BULK DENSITY (Ρ) SATURATED DENSITY (ΡSAT) DRY DENSITY (ΡD)
13 14 14 15 15 15 15 15
SOIL INVESTIGATIONS / EXPLORATION ....................................... 16 5.1
PURPOSE OF SOIL EXPLORATION
16
5.2 5.2.1 5.2.2 5.2.3
PLANNING AN EXPLORATION PROGRAMME RECONNAISSANCE OF THE AREA PRELIMINARY SITE INVESTIGATION DETAILED SITE INVESTIGATION
16 16 16 17
5.3 5.3.1 5.3.2
METHODS OF EXPLORATION TEST PITS BORINGS AND SAMPLING
17 17 17
5.4
FIELD IN-SITU TESTS
19
5.5
GEOPHYSICAL METHODS
19
5.6
LABORATORY METHODS
20
6
BEARING CAPACITY OF SOILS ....................................................... 21 6.1
INTRODUCTION
21
6.2
COMMON TYPES OF SOILS AND THEIR BEARING CAPACITY CHARACTERISTICS
21
6.2.1 6.2.2 6.2.3 6.2.4 6.2.5
ROCK GRAVEL SAND CLAY SILT
21 21 21 21 22
6.3 6.3.1 6.3.2 6.3.3
DESIGN PRINCIPLES FOUNDATION TYPE METHODS OF ASSESSING SOIL PROPERTIES DISPLACEMENT AND SETTLEMENT OF FOUNDATIONS
22 22 23 24
7
SHEAR STRENGTHS AND EFFECTIVE STRESSES ............................. 25 7.1
INTRODUTION
25
7.1.1 7.1.2
SHEAR STRENGTH IN SOILS THE MOHR – COULOMB FAILURE CRITERION
26 26
7.2 7.2.1
DETERMINATION OF SHEAR STRESS PARAMETERS DIRECT SHEAR TEST
29 30
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SOIL COMPACTION ........................................................................ 34 8.1
INTRODUTION
34
8.2 8.2.1 8.2.2
THEORY OF COMPACTION GENERAL VARIATION IN COMPACTION CURVE
34 34 35
8.3
LABORATORY COMPACTION TESTS
36
8.4 8.4.1 8.4.2 8.4.3
FIELD COMPACTION COMPACTION FIELD CONTROL OF COMPACTION SPECIFICATION OF THE FIELD COMPACTED DENSITY
37 37 38 39
9
LATERAL PRESSURES AND RETAINING WALLS .............................. 40 9.1
INTRODUTION
40
9.2
CATERGORIES OF EARTH PRESSURE
41
9.2.1 9.2.2 9.2.3
AT REST EARTH PRESSURE ACTIVE EARTH PRESSURE PASSIVE EARTH PRESSURE
41 41 42
9.3 9.3.1 9.3.2
CALCULATING LATERAL EARTH PRESSURE COEFFICIENTS AT REST COEFFICIENT ACTIVE AND PASSIVE COEFFICIENT
42 42 43
9.4
EARTH PRESSURE DISTRIBUTION
46
9.5 9.5.1
APPLICATIONS RETAINING WALLS
47 47
10
ROAD DESIGN ................................................................................ 48
10.1
ROAD PAVEMENT
48
10.2
FACTORS INFLUENCING DESIGN OF THE PAVEMENT
48
10.3
ROAD CONSTRUCTION MATERIALS
48
10.4
PAVEMENT DESIGN PHILOSOPHY (CRITERIA)
48
10.5 10.5.1 10.5.2
PAVEMENT TYPES FLEXIBLE PAVEMENTS RIGID PAVEMENTS
48 48 49
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OVERVIEW
1.1
COURSE DESCRIPTION AND OUTLINE
This course is an intr oductory part of Civil Engineering, which focuses on soil Mechanics. The Course Outline in summarized below; a) Soil properties, Soil investigation, methods adopted in soil investigation. Various types of soils; b) Load bearing capacity of soils and foundations; c) Shear Strengths and effective stresses, d) Soil compaction e) Lateral Pressures and Retaining Walls f) Road design
1.2
PREREQUISITE
None
1.3
STUDENT LEARNING OUTCOME
Upon successful completion of this course, the students should acquire the following knowledge: a) Developed competence in the principles of soil mechanics and application in engineering practice. b) Ability to list the relevant engineering properties of soils and their characteristics and describe the factors which control these properties. c) Ability to identify common situations when the soil becomes a factor in an engineering or environmental problem. d) Ability to apply basic analytical procedures to obtain the engineering quantity desired and understand their limitations.
1.4
TEACHING METHODOLOGY AND TECHNIQUES
This course relies on lectures and Power Point presentation by the lecturer. Worked examples will be offered. Students will then be required to contribute to discussions based on the explanations and will need to read the corresponding section in the assigned textbook.
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1.5
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REQUIRED TEXT BOOKS a) Modern Geotechnical Engineering, CBS Publishers & Distributors, New Dheli b) Geotechnical Engineering (Basics of Soil Mechanics), S. Chand & Company Ltd, New Dheli c) Foundation Engineering Handbook, CBS Publishers & Distributors, New Dheli.
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2 2.1
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INTRODUCTION TO SOIL MECHANICS DEFINITION OF SOIL Soil is the relatively loose mass of mineral and organic materials and sediments found above the bedrock, which can be relatively easily broken down into its constituent mineral or organic particles.
Fig. 2.1: Soil layers
Soil consists of layers of minerals constituents of variable thickness, which differ from the parent materials in the morphological, physical, chemical and mineralogical characteristics, as shown in Fig. 2.1. It is thus a natural product of weathering of rocks and decomposition of organic matter. It is an accumulation of individual particles that are bonded together by mechanical or attractive means, the strength of the bonds being a small fraction of the mineral particles. The particles may range from colloidal size to small boulders. Soil can also be referred to as regolith, or loose rock material.
2.2
SOIL MECHANICS AND GEOTECHNICAL ENGINEERING Soil mechanics is a branch of engineering mechanics that describes the behaviour of soils. Soil mechanics provide the theoretical basis for analysis in geotechnical engineering. Geotechnical Engineering is the branch of civil engineering concerned with the engineering behaviour of earth materials. It uses principles of soil mechanics, rock mechanics and engineering geology to investigate subsurface conditions and materials, determine the relevant physical/mechanical and chemical properties of the materials, evaluate stability of natural slopes and man-made soil deposits, access
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risks posed by site conditions, design earthworks and structure foundations and monitor site conditions, earthwork and foundation construction. A typical geotechnical engineering project begins with a review of project needs to define the required material properties. Then follows a site investigation of soil, rock, fault distribution and bedrock properties on and below an area of interest to determine their engineering properties. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place. Investigations can include the assessment of the risk to humans, property and the environment from natural hazards such as earthquakes, landslides, soil liquefaction, debris flows and rock falls. A geotechnical engineer then determines and designs the type of foundations, earthworks and pavement subgrades required for the intended man-made structures to be built. Foundations are designed and constructed for structures of various sizes such as high-rise buildings, bridges, medium to large commercial buildings, and smaller structures where the soil conditions do not allow code-based design. Foundations built for above-ground structures include shallow and deep foundations. Retaining structures include earth-filled dams and retaining walls. Earthworks include embankments, tunnels and sanitary landfills. Geotechnical engineering is also related to coastal and ocean engineering. Coastal engineering can involve the design and construction of wharves (structures on the shore of harbour where ships may dock to load and unload cargo or passengers) and jetties (structures that projects into a body of water to influence the current or tide or to protect a harbour or shoreline from storms or erosion).
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SOIL FORMATION
3.1
DEFINITION Soil formation is the process by which soil is created. The formation of soil happens over a very long period of time. Soil is formed from the weathering of rocks and minerals.
3.2
WEATHERING
3.2.1
Introduction Weathering is the process of breaking down rocks. Weathering occurs in situ or “with no movement”, and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity. Two important classifications of weathering processes exist – Physical and Chemical Weathering
3.2.2
Physical weathering Involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure, without any change in chemical condition. The soil formed due to physical weathering will be cohesionless (sand and gravel). In summary, the physical agencies causing mechanical weathering of rocks are; (i) Daily and seasonal temperature changes. (ii) Flowing water, glaciers and wind, which produce impact and abrasive action on rock. (iii) Splitting action of ice. (iv) Growth of roots of plants in rock fissures and to a minor degree burrowing activities of small animals like earthworms.
3.2.3
Chemical weathering Chemical weathering changes the composition of rocks by decomposing the parent minerals, transforming them into new compounds such as clay silica particles, carbonates and iron oxides. The (i) (ii) (iii) (iv)
decomposition of rock is the result of the following reactions; Oxidation Carbonation Hydration Leaching
i)
Oxidation
Within the weathering environment, oxidation of a variety of metals occurs. The most commonly observed is the oxidation of Fe2+ (iron) and combination with oxygen and water to form Fe3+ hydroxides and oxides such as goethite, limonite and hematite. This gives the affected rocks a reddish-brown coloration on the
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surface which crumbles easily and weakens the rock. known as ‘rusting’.
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This process is better
ii) Carbonation Carbonation of rock material is caused by carbon dioxide in the presence of water. Limestones are very much affected by carbonation. iii) Hydration Mineral hydration is a form of chemical weathering that involves the rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral. When rock minerals take up water, the increased volume creates physical stresses within the rock. For example iron oxides are converted to iron hydroxides and the hydration of anhydrite forms gypsum. Another example of hydration is the chemical decomposition of mineral fieldspar in granite to form kaolite. iv) Leaching Leaching is the process in which percolating water washes out water-soluble salts from the soil. Soil produced by chemical weathering of rocks will be cohesive (silt and clay).
3.3
TYPES OF SOILS
3.3.1
Sandy Soil This soil type has the biggest particles; and the bigger size of the particles in a soil the better is aeration and drainage of the soil. This soil is granular and consists of rock and mineral particles that are very small. Sandy soil is formed by the disintegration and weathering of rocks such as limestone, granite, quartz and shale. Sandy soil is easier to cultivate if it is rich in organic material, but then it allows drainage more than is needed, thus resulting in over-drainage and dehydration of the plants.
3.3.2
Silty Soil Silty soil has much smaller particles than sandy soil so it’s smooth to the touch. When moistened, it’s soapy slick. When you roll it between your fingers, dirt is left on your skin.
3.3.3
Clay Soil Clay soil has the smallest particles among the three so it has good water storage qualities. It’s sticky to the touch when wet, but smooth when dry.
3.3.4
Peaty Soil Peaty soil is dark brown or black in color, soft, easily compressed due to its high water content, and rich in organic matter. Peat soil started forming over 9,000 years ago, with the rapid melting of glaciers. This rapid melt drowned plants quickly and died in the process. Their decay was so slow underwater that it led to the accumulation of organic area in a concentrated spot.
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3.3.5
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Saline Soil The soil in extremely dry regions is usually brackish because of its high salt content. Known as saline soil, it can cause damage to and stall plant growth, impede germination, and cause difficulties in irrigation. The salinity is due to the buildup of soluble salts in the rhizosphere—high salt contents prevent water uptake by plants, leading to drought stress.
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SOIL PROPERTIES
4.1
INTRODUCTION Soil is comprised of minerals, soil organic matter, water, and air. The composition and proportion of these components greatly influence soil physical properties, including texture, structure, and porosity, the fraction of pore space in a soil. In turn, these properties affect air and water movement in the soil, and thus the soil’s ability to function. Although soil organic matter comprises a relatively small portion of soil, typically only 1–4%, it plays a key role in many soil processes
4.2
SOIL PHYSICAL PROPERTIES
4.2.1
Soil Texture Soil texture can have a profound effect on many other properties and is considered among the most important physical properties. Texture is the proportion of three mineral particles, sand, silt and clay, in a soil. These particles are distinguished by size, and make up the fine mineral fraction (Table 4.1).
Table 4.1: Diameter and approximate size of four soil particles. Soil Particle
Diameter (mm)
Approximate Size
Gravel
>2.0
●
Sand
0.05 – 2.0
•
Silt
0.002 – 0.05
.
Clay
