All questions of Pile Foundation for Civil Engineering (CE) Exam

Protection Piles for Structures

The piles that are used for protecting structures from ships and floating objects are known as protection piles. They are designed to absorb the energy of an impact from a vessel or floating object to prevent damage to the structure.

Types of Protection Piles

There are several types of protection piles that can be used to protect structures from ships and floating objects. These include:

1. Anchor Piles: These piles are used to anchor ships and boats in place. They are typically driven deep into the ground to provide a secure anchor point for vessels.

2. Fender Piles: These piles are designed to absorb the impact of a vessel or floating object. They are typically made of durable materials such as steel or concrete and are placed around the perimeter of a structure to provide a cushion against impacts.

3. Compaction Piles: These piles are used to reinforce the ground beneath a structure. They are typically driven deep into the ground to provide additional stability and support.

4. Batter Piles: These piles are installed at an angle to provide additional support and stability to a structure. They are typically used in areas with high water flow and strong currents.

Conclusion

In conclusion, protection piles are an important part of any structure that is located near water. They help to prevent damage from ships and floating objects and provide additional stability and support to the structure. There are several types of protection piles available, each with its own set of advantages and disadvantages. It is important to carefully consider the specific needs of your structure when choosing the appropriate type of protection pile.

Safe Load Test for Determining the Load Carrying Capacity of an Under-reamed Pile



The load carrying capacity of an under-reamed pile, which is a type of deep foundation, can be determined through various tests. However, the most commonly used method is the safe load test. This test is conducted to evaluate the performance and strength of the pile under load and to ensure that it can safely support the design load.



Explanation:


The safe load test involves applying a gradually increasing load to the pile until it reaches its ultimate capacity or a predefined limit state. The test is typically performed in two stages: the initial loading stage and the main loading stage.



Initial Loading Stage:


During the initial loading stage, a small load is applied to the pile to remove any residual air or water pressure in the soil. This ensures that the load is transferred directly to the pile and not to the surrounding soil.



Main Loading Stage:


In the main loading stage, the load applied to the pile is increased incrementally until the desired load is achieved or the pile reaches its ultimate capacity. The load is usually applied using hydraulic jacks or reaction frames, and the settlement of the pile is measured at each load increment.



Load-Settlement Curve:


The load-settlement curve obtained during the safe load test provides valuable information about the behavior and load carrying capacity of the under-reamed pile. The curve typically exhibits three distinct regions:

1. Elastic Region: In the initial stages of loading, the pile undergoes elastic deformation, and the settlement is directly proportional to the applied load.

2. Plastic Region: As the load increases, the pile enters the plastic region, and the settlement rate starts to increase at a faster rate. This indicates that the soil surrounding the pile is undergoing plastic deformation.

3. Ultimate Load Region: At a certain point, the pile reaches its ultimate load capacity, and the settlement increases rapidly. This signifies that the pile is nearing its failure state.



Safe Load Determination:


The safe load carrying capacity of the under-reamed pile is usually determined based on the allowable settlement criteria specified in the design code or project specifications. The load at which the settlement exceeds the allowable limit is considered the safe load capacity of the pile.



Therefore, the safe load test is used to determine the load carrying capacity of an under-reamed pile by gradually applying loads and measuring the corresponding settlements. The test provides valuable information about the behavior and performance of the pile, ensuring that it can safely support the design load without excessive settlement.

Understanding the Dynamic Formula in Soil Mechanics
The dynamic formula is a method used to estimate the bearing capacity of soils under dynamic loads. Its effectiveness varies depending on the soil type involved.
Why Dynamic Formula is Valueless for Clay Soil
- Nature of Clay Soil:
Clay soil exhibits plasticity and cohesion, making it fundamentally different from granular soils like sand. Its strength is heavily influenced by water content and can change dramatically with moisture variations.
- Low Shear Strength:
The dynamic formula relies on the assumption of constant shear strength, which is not applicable to clay. The undrained shear strength of clay can be highly variable, particularly under dynamic loading conditions.
- Sensitivity to Loading:
Clay soils are sensitive to loading rates. The dynamic formula does not account for the time-dependent behavior of clay, which can lead to inaccurate predictions of stability and load-bearing capacity.
- Risk of Failure:
Under dynamic loads, clay can experience significant deformation or failure, which is not accurately captured by the dynamic formula. This risk is particularly pronounced in saturated or soft clay conditions.
Conclusion
Given these characteristics, the dynamic formula becomes ineffective for clay soils. Accurate assessments of clay's behavior under dynamic loads require alternative methods, such as effective stress analysis or empirical data that considers its unique properties. Thus, option 'C' is indeed the correct answer.

Understanding Ultimate Bearing Capacity (Qup)
The ultimate bearing capacity (Qup) is a critical concept in geotechnical engineering, referring to the maximum load a soil can support before failure occurs. The static formula for Qup incorporates various stress components acting on the soil.
Components of the Static Formula
The correct answer, option 'B', states that Qup is equal to Rf + Rp. Here's a breakdown of these components:
- Rf (Effective Overburden Pressure):
- This is the vertical stress exerted by the weight of the soil and any additional loads above the foundation.
- It reflects the contribution of the soil's weight to the overall bearing capacity.
- Rp (Additional Pressure from Loads):
- This represents the extra stress induced by structural loads, such as buildings or other constructions resting on the ground.
- It accounts for the additional forces that can affect the soil's stability and strength.
Together, these components provide a comprehensive view of the stresses acting on the soil, leading to a more accurate assessment of its bearing capacity.
Why Option B is Correct
- The other options (A, C, D) include terms that do not represent the correct relationship in the calculation of Qup.
- Option B effectively combines the two critical stress components (Rf and Rp) that govern the soil's ability to support loads.
By understanding this formula, engineers can design foundations that are safe and effective, ensuring longevity and stability in construction projects.

Introduction:
Under reamed piles are a type of foundation piles that are bored into the ground to provide support for structures. They have a unique design feature called under reaming, which creates a bulb-shaped enlargement at the base of the pile. This enlargement increases the bearing capacity of the pile and enhances its load-carrying capacity.

Explanation:
Under reamed piles are normally bored as cast-in-situ piles. This means that they are constructed on-site by drilling a hole into the ground and then filling it with concrete. There are several reasons why cast-in-situ piles are preferred for under reamed piles:

1. Flexibility of Design: Cast-in-situ piles allow for flexibility in design. The size, shape, and depth of the under reamed bulb can be customized based on the specific soil conditions and load requirements of the structure. This flexibility is not easily achievable with pre-cast or steel piles.

2. Quality Control: Cast-in-situ piles offer better quality control. The entire installation process can be closely monitored to ensure that the pile is constructed in accordance with the design specifications. Any issues or deviations can be addressed and rectified immediately, resulting in a more reliable foundation system.

3. Seamless Connection: Cast-in-situ piles provide a seamless connection between the under reamed bulb and the shaft of the pile. This ensures a smooth transfer of loads from the structure to the underlying soil. In contrast, pre-cast or steel piles may have joints or connections that can be potential weak points and compromise the overall stability of the foundation.

4. Cost-effectiveness: Cast-in-situ piles are generally more cost-effective compared to pre-cast or steel piles. The materials required for cast-in-situ piles, such as cement, aggregates, and reinforcement, are readily available and relatively inexpensive. The construction process is also simpler and requires less specialized equipment.

5. Adaptability: Cast-in-situ piles can be easily adapted to suit site-specific conditions. The borehole can be adjusted as necessary to accommodate any encountered obstructions or changes in soil properties. This adaptability is crucial in situations where unforeseen challenges may arise during the construction process.

In conclusion, under reamed piles are normally bored as cast-in-situ piles due to their flexibility of design, quality control, seamless connection, cost-effectiveness, and adaptability. These advantages make cast-in-situ piles the preferred choice for constructing under reamed piles in various soil conditions and structural requirements.

Maximum Design Load for Precast Concrete Piles

The precast concrete piles are generally used for a maximum design load of about 80 tonnes. This is an important consideration in the design and construction of foundations for various structures.

Reason for Maximum Design Load

- The maximum design load of 80 tonnes is determined based on the structural capacity of the precast concrete piles.
- This load limit ensures that the piles can safely support the weight of the structure and any additional loads that may be imposed on them during their service life.

Factors Influencing Maximum Design Load

- The type and quality of the concrete used in the precast piles play a significant role in determining their maximum design load.
- The dimensions and shape of the piles also influence their load-bearing capacity.
- Soil conditions at the site where the piles will be installed are another factor that affects the maximum design load.

Importance of Following Maximum Design Load

- Exceeding the maximum design load of precast concrete piles can lead to structural failure, compromising the stability and safety of the entire structure.
- Adhering to the specified load limit ensures the longevity and durability of the foundation system.

In conclusion, understanding and adhering to the maximum design load of precast concrete piles is crucial for the successful construction of stable and safe structures.

History of Pile Driving

Introduction: The practice of driving piles into the ground has been an essential part of construction for thousands of years. Pile driving is a technique used to create a foundation for structures by driving long, slender objects deep into the ground.

Romans: The Romans were the first to use pile driving to construct their famous aqueducts, which were used to transport water from distant sources to their cities. They used wooden piles to support the weight of the aqueducts and prevent them from collapsing.

Modern Pile Driving: Modern pile driving techniques have evolved significantly since the time of the Romans. Today, pile driving is done using heavy machinery such as pile drivers, which use hydraulic or pneumatic power to drive steel, concrete, or wooden piles into the ground.

Benefits of Pile Driving: Pile driving is a crucial part of construction because it provides a stable foundation for structures. Piles help to distribute the weight of a structure evenly, preventing it from sinking or shifting over time. Additionally, pile driving is a cost-effective solution for building on unstable or uneven ground.

Conclusion: In conclusion, the art of driving piles into the ground was first established by the Romans. Pile driving has evolved significantly since then, and today it is an essential part of construction in many industries. Pile driving provides a stable foundation for structures and is a cost-effective solution for building on unstable or uneven ground.

Compaction Piles
Compaction piles are used to compact loose granular soil by densifying the soil through vibratory methods. This process helps to improve the soil's load-bearing capacity and reduce settlement potential. Here are some key points about compaction piles:

How Compaction Piles Work
- Compaction piles are installed by driving a steel casing into the ground to the desired depth.
- The casing is then filled with aggregate material, such as crushed stone or gravel.
- A vibrating probe is inserted into the casing, which compacts the surrounding soil as it is withdrawn.

Benefits of Compaction Piles
- Improves the stability and strength of the soil.
- Reduces settlement and potential for uneven foundation movement.
- Cost-effective solution for improving soil conditions in construction projects.

Application of Compaction Piles
- Commonly used in areas with loose or granular soil that require increased density for structural support.
- Ideal for foundations of buildings, bridges, roads, and other structures on unstable soil conditions.

Conclusion
Compaction piles are an effective solution for compacting loose granular soil to enhance the soil's load-bearing capacity and reduce settlement risks. They are a cost-effective method for improving soil conditions in construction projects.

Factors affecting the spacing of piles in under-reamed pile foundation:
- Nature of the ground: The spacing of piles in under-reamed pile foundation depends largely on the nature of the ground. If the soil is loose or weak, closer spacing of piles is required to distribute the load effectively and prevent settlement. In contrast, if the soil is firm and stable, wider spacing of piles may be sufficient.
- Type of pile: Different types of piles, such as bored piles or driven piles, have varying load-bearing capacities and behavior in different soil conditions. The type of pile used will influence the spacing required to support the structure adequately.
- Load acting on the pile: The magnitude and distribution of the load that the pile foundation needs to support also play a crucial role in determining the spacing of piles. Higher loads or unevenly distributed loads may necessitate closer spacing of piles to ensure structural stability.
In conclusion, the spacing of piles in under-reamed pile foundation is primarily influenced by the nature of the ground and the type of pile being used. These factors, along with the load acting on the pile, need to be carefully considered during the design phase to ensure the foundation's effectiveness and longevity.

The answer is a) Converse Labarre formula.

Understanding Negative Skin Friction
Negative skin friction occurs when the soil surrounding a pile settles or moves downward, exerting a downward drag force on the pile itself. This phenomenon is critical in the analysis and design of pile foundations.
Key Concepts of Negative Skin Friction:
- Definition: Negative skin friction is the resistance that develops between a pile and the surrounding soil, primarily due to the downward movement of the soil.
- Causes: It can be caused by factors such as:
- Soil consolidation
- Excavation of adjacent areas
- Changes in water table levels
- Weight of additional structures or fills placed around the pile
- Impact on Pile Behavior:
- Results in additional load on the pile, which can lead to:
- Increased settlement
- Altered load distribution
- Potential structural failure if not accounted for in design
- Importance in Design: Engineers must consider negative skin friction during the design phase of pile foundations to ensure stability and safety. This involves:
- Conducting soil analysis to predict potential movement
- Designing piles with sufficient capacity to withstand additional loads
- Mitigation Strategies: To minimize the effects of negative skin friction, techniques may include:
- Using larger-diameter piles
- Increasing pile embedment depth
- Implementing soil stabilization methods
In summary, understanding negative skin friction is essential for civil engineers to ensure the integrity of pile foundations in varying soil conditions. Proper assessment and design adjustments can significantly enhance the performance of these structures.

Under-reamed pile foundation is most suitable for seasonal moisture change type of condition.

Explanation:
Under-reamed pile foundation is a type of pile foundation in which the pile base is enlarged by forming a bulb or bell-shaped enlargement at the bottom. This enlargement increases the bearing capacity of the pile and improves its resistance against vertical and lateral loads.

Reasons for suitability:

1. Seasonal moisture change:
Under-reamed pile foundation is particularly suitable for areas where the moisture content in the soil varies significantly with seasonal changes. These variations can cause the soil to expand or contract, leading to differential settlement and potential damage to the structure. The under-reamed bulb acts as a counterbalance to the expansive or contractive forces exerted by the soil, reducing the risk of differential settlement.

2. Increased bearing capacity:
The bulb-shaped enlargement at the bottom of the pile significantly increases the bearing capacity of the pile. It provides a larger contact area with the soil, allowing the load to be distributed over a larger area. This is especially beneficial in soil conditions with lower bearing capacity, such as cohesive soils.

3. Resistance against lateral loads:
Under-reamed pile foundations also offer improved resistance against lateral loads. The bulb acts as a stabilizing element, increasing the lateral stiffness of the pile and reducing the deflection under horizontal forces. This is particularly important in areas prone to high wind or seismic activities.

4. Cost-effective:
Under-reamed pile foundations can be a cost-effective solution in areas with seasonal moisture change conditions. By preventing differential settlement and reducing the risk of structural damage, they can minimize the need for costly repairs and maintenance in the long run.

In conclusion, under-reamed pile foundations are most suitable for areas with seasonal moisture change conditions due to their ability to counteract differential settlement, increased bearing capacity, improved resistance against lateral loads, and cost-effectiveness.

Efficiency of Pile Group

The efficiency of pile group refers to the ability of the group of piles to resist the load or pressure applied to it. The efficiency depends upon various factors, some of which are discussed below:

1. Characteristics of Pile

The characteristics of the pile are one of the most important factors that affect the efficiency of the pile group. The following characteristics of the pile need to be considered:

- Length of pile
- Diameter of pile
- Material of pile
- Type of pile
- Pile spacing

2. Spacing of Pile

The spacing of the pile is another important factor that affects the efficiency of the pile group. The spacing should be such that it can distribute the load uniformly over the pile group. If the spacing is too close, then the piles will interfere with each other and may result in a reduction in the load-carrying capacity of the pile group. On the other hand, if the spacing is too wide, then it may result in excessive soil movement and a reduction in the load-carrying capacity of the pile group.

3. Bearing Capacity of Soil

The bearing capacity of the soil is another factor that affects the efficiency of the pile group. The soil should have a suitable bearing capacity to resist the load applied by the pile group. If the bearing capacity of the soil is low, then it may result in excessive settlement and a reduction in the load-carrying capacity of the pile group.

Conclusion

In conclusion, the efficiency of the pile group depends upon the characteristics of the pile and the spacing of the pile. The bearing capacity of the soil also plays a significant role in determining the efficiency of the pile group. Therefore, it is essential to consider all these factors while designing and constructing pile groups to ensure an efficient load-carrying capacity.

Dynamic formulae are best suited for Coarse grained soil.

Coarse grained soil refers to soil particles that are larger in size, such as sand and gravel. These types of soils have a relatively low water-holding capacity and less cohesion between particles compared to fine grained soils.

Dynamic formulae are empirical relationships used to estimate soil properties based on the results of dynamic tests, such as the Standard Penetration Test (SPT) or the Cone Penetration Test (CPT). These tests involve driving a metal rod or cone into the ground and measuring the resistance encountered. The results of these tests, combined with other factors such as the soil type and groundwater conditions, can be used to estimate various soil properties.

Coarse grained soils are typically more granular and have larger void spaces between particles compared to fine grained soils. This allows for better penetration of the dynamic testing tools and provides more accurate measurements of soil resistance. The dynamic formulae have been developed and calibrated based on the behavior of coarse grained soils, and therefore, they are best suited for this type of soil.

On the other hand, fine grained soils, such as clay and silt, have smaller particles and tend to be more cohesive. The cohesive nature of these soils can affect the results of dynamic tests, leading to less accurate estimations of soil properties using dynamic formulae. Furthermore, the small particle size and high water-holding capacity of fine grained soils can impede the penetration of dynamic testing tools, making it difficult to obtain reliable measurements.

In conclusion, dynamic formulae are best suited for coarse grained soils due to their granular nature, larger void spaces, and better penetration characteristics. These formulae provide a useful tool for estimating soil properties in this type of soil, which is commonly encountered in civil engineering projects.

The correct answer is option 'C', which states that piles can be classified into 8 types. Let's discuss each type in detail:

1. End bearing piles:
- End bearing piles transfer the load of the structure through the pile tip to a firm stratum below.
- These piles are used when the upper soil layers are weak and cannot bear the load of the structure.
- Examples include driven piles and bored cast-in-situ piles.

2. Friction piles:
- Friction piles transfer the load of the structure through skin friction along the pile shaft.
- These piles are used when the soil layers along the pile shaft have sufficient frictional resistance to support the structure.
- Examples include driven piles and bored cast-in-situ piles.

3. Cohesion piles:
- Cohesion piles rely on the cohesive properties of the soil to transfer the load of the structure.
- These piles are used when the soil has high cohesion and can support the structure.
- Examples include bored cast-in-situ piles and drilled displacement piles.

4. Tension piles:
- Tension piles are used to resist uplift forces in structures subjected to pulling forces.
- These piles are designed to withstand tension and are installed to counteract uplift forces.
- Examples include bored cast-in-situ piles and driven piles with anchor heads.

5. Compaction piles:
- Compaction piles are used to improve the soil's bearing capacity by densifying loose or weak soils.
- These piles are driven into the ground to compact the soil and increase its strength.
- Examples include precast concrete piles and steel sheet pile walls.

6. Sheet piles:
- Sheet piles are used as retaining walls to provide lateral support and prevent soil or water from encroaching on a structure.
- These piles are interlocked and driven into the ground to form a continuous barrier.
- Examples include steel sheet piles and vinyl sheet piles.

7. Bored piles:
- Bored piles are constructed by excavating a hole in the ground and filling it with concrete or reinforcing material.
- These piles are commonly used in deep foundation systems and can be installed using various methods.
- Examples include bored cast-in-situ piles and drilled displacement piles.

8. Micro piles:
- Micro piles, also known as mini piles or pin piles, are used in limited access areas or areas with restricted space.
- These piles are smaller in diameter compared to traditional piles and can be installed using specialized equipment.
- Examples include micropiles with steel reinforcement and grout injection piles.

In summary, piles can be classified into 8 types: end bearing piles, friction piles, cohesion piles, tension piles, compaction piles, sheet piles, bored piles, and micro piles. Each type serves a specific purpose and is selected based on the soil conditions and structural requirements of the project.

C) Qug = Qup + Qus