Slope Stability
Fills
Learning Objectives:
- Recognize and distinguish different types of slope failures, such as slides, slumps, and flows, that can occur in filled slopes.
- Understand the geotechnical factors affecting slope stability, including soil properties, water content, slope geometry, and external loading.
- Understand various construction methods for creating fills, including layer placement, compaction, and considerations for soil improvement.
- Slip plane is the surface of sliding.
- Sliding mass is the mass of soil within the slip plane and the ground surface.
- Slope is the angle of inclination of a slope to the horizontal.
- Layer Placement: Fills are constructed in layers, each compacted to achieve the desired density.
- Compaction: Adequate compaction is essential to enhance soil strength.
- Soil Improvement: Techniques like soil reinforcement or stabilization may be employed.
Slope Failure along Planar Surface:
Factor of Safety against slope instability,Available shearing resistance along slip surface
Mobilized shear force along slip surface,
English: Amanda Sweeney, Public domain, via Wikimedia Commons
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Solved Example: 9532-01
Which type of fill material is typically used in embankment construction for highways and railways?
A. Sand
B. Silt
C. Gravel
D. Peat
Correct Answer: C
Solved Example: 9532-02
Which factor does not influence the selection of fill material for a specific project?
A. Cost
B. Availability
C. Particle size distribution
D. Ambient temperature
Correct Answer: D
Embankments
Learning Objectives:
- Understand the concept of embankments in civil engineering and their role in raising the ground level for various applications, including road construction, railway infrastructure, dams, and flood protection.
- Learn about the different types of embankments, including road embankments, railway embankments, earth dams, and levees, and their specific purposes and design considerations.
Embankments are raised structures built from compacted earth or other materials to raise the ground level and provide support for various engineering purposes. They are common in civil engineering for applications such as road construction, dam building, and railway infrastructure.
Types of Embankments:- Road Embankments: Road embankments are built to raise the roadbed above the surrounding terrain. They provide a level and stable foundation for roadways, enabling safe and efficient transportation.
- Railway Embankments: Railway embankments serve a similar purpose to road embankments, elevating the tracks above the surrounding landscape. This minimizes grade changes and facilitates smoother rail travel.
- Earth Dams: Earth dams are embankments constructed to impound water, creating reservoirs for various purposes, such as water supply, flood control, and hydroelectric power generation.
- Levees: Levees are embankments built along rivers and water bodies to protect against flooding. They help contain rising water levels during periods of high flow.
Minninglow embankment by Richard Croft, CC BY-SA 2.0, via Wikimedia Commons
Solved Example: 9453-01
What is the primary purpose of an embankment in civil engineering?
A. To control stormwater runoff
B. To provide a stable foundation for structures
C. To create a barrier for erosion control
D. To raise the ground level for road or rail construction
Correct Answer: D
Solved Example: 9453-01
What material is commonly used for constructing embankments due to its stability and compaction characteristics?
A. Gravel
B. Sand
C. Clay
D. Loose soil
Correct Answer: C
Solved Example: 9453-01
What is the term used to describe the process of compacting layers of soil or other materials in an embankment to achieve a stable foundation?
A. Erosion control
B. Grading
C. Compaction
D. Slope protection
Correct Answer: C
Solved Example: 9453-01
In the design of embankments, what is the significance of the factor of safety?
A. It ensures compliance with environmental regulations
B. It measures the stability of the embankment against failure
C. It determines the embankment's aesthetic appeal
D. It assesses the cost-effectiveness of construction
Correct Answer: B
Solved Example: 9453-01
What role does a drainage system play in the construction of embankments?
A. It prevents soil erosion
B. It enhances the visual appeal of the embankment
C. It controls stormwater runoff and reduces the risk of saturation
D. It increases the structural load-bearing capacity of the embankment
Correct Answer: C
Solved Example: 9900-01
An embankment has a slope of 30$^\circ$ which was constructed with soil having C = 30 kN/m$^2$, $\phi$ = 20$^\circ$ and $\gamma$ = 15 kN/m$^3$. The height of the embankment is 20 m. Using Taylor's stability no 1/40, the factor of safety with respect to cohesion is:
A. 0.25
B. 2
C. 4
D. 1.5
Correct Answer: C
Solved Example: 9900-02
An embankment of 100 m$^3$ volume is to be constructed. A borrow area has a dry density of 17 kN/m$3$ if the embankment is to be constructed with a dry density of 16 kN/m$3$, then the volume (m$^3$) of soil required will be
A. 94
B. 106
C. 100
D. 90
\begin{align*} (V \times \gamma_d)_{\mathrm{borrow\ pit}} &= (V \times \gamma_d)_{\mathrm{embankment}}\\ (V \times 17) &= (100 \times 16)\\ V_{\mathrm{borrow\ pit}} &= 94\ m^3 \end{align*}
Correct Answer: A
Cuts
Learning Objectives:
- Identify the key elements involved in an excavation cut, including cut depth, slope ratio, and benching.
- Understand factors influencing slope stability, including soil type, moisture content, and slope angle.
A cut, also known as an excavation or an embankment cut, involves removing soil or rock material from a natural or existing slope to create a desired slope configuration. Cuts are commonly used to create level surfaces for infrastructure development, such as roads, foundations, and building sites.
Types of Cuts:- Bench Cuts: Often used in road construction, bench cuts involve creating horizontal platforms or benches at intervals on the slope, which act as natural or engineered terraces to improve stability.
- Sidehill Cuts: These are made on the side of a hill or slope and often require extensive excavation and slope stabilization measures.
- Toe Cuts: Toe cuts are made at the base of a slope to widen the slope's footprint and enhance stability.
Solved Example: 9452-01
In an embankment cut, what is the significance of the term "slope ratio"?
A. It determines the width of the embankment
B. It establishes the ratio of cut depth to horizontal distance
C. It measures the volume of the excavated material
D. It assesses the compaction of the embankment fill
Correct Answer: B
Solved Example: 9452-02
In an embankment cut, why is proper compaction of the excavated material essential?
A. To increase the cost-effectiveness of the project
B. To enhance the aesthetic appeal of the embankment
C. To prevent settlement and ensure stability
D. To control stormwater runoff
Correct Answer: C
Solved Example: 9452-03
For the soil shown below, the weight of the soil above the slip surface is most nearly:
A. 13100
B. 14130
C. 15990
D. 16780
\begin{align*} \tan 35^\circ &= \dfrac{AD}{BD}\\ BD &= \dfrac{AD}{\tan 35^\circ}= \dfrac{18}{\tan 35^\circ}= 25.71' \end{align*} \begin{align*} \tan 52^\circ &= \dfrac{AD}{CD}\\ CD &= \dfrac{AD}{\tan 52^\circ} = \dfrac{18}{\tan 52^\circ} = 14.06' \end{align*} \begin{align*} A(\Delta ABC) &= A(\Delta ABD) - A(\Delta ACD)\\ &= \dfrac{1}{2}(BD \times AD) - \dfrac{1}{2}(CD \times AD)\\ &= \dfrac{1}{2}(AD) (BD - CD)\\ &= \dfrac{1}{2}(18) (25.71 - 14.06) = 104.82\ \mathrm{sq.ft} \end{align*} \begin{align*} \mathrm{Weight\ of\ soil\ per\ ft.} &= A(\Delta ABC) \times \gamma\\ &= 104.82 \times 125 lb/ft^3\\ &= 13102.7\ \mathrm{lb/ft} \end{align*}
Correct Answer: A