Pile Foundation Basics

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Questions and Answers

What can potentially damage concrete piles in organic soils?

Heavy machinery movement

Acid formation from organic materials (correct)

High moisture content

Temperature fluctuations

What is a primary disadvantage of using concrete piles in marine environments?

Vulnerability to freezing

Difficulty in installation

Abrasion from wave action (correct)

Limited load-bearing capacity

Which of the following does NOT affect the selection of piles?

Length of the pile (correct)

Availability of construction materials

Soil type

Environmental conditions

Which method is used to determine the ultimate bearing capacity of a pile?

Dynamic Analysis Signup and view all the answers

What is a characteristic of driven piles compared to bored piles?

Greater load capacity Signup and view all the answers

Which type of piling technique involves replacing the soil?

Replacement piling Signup and view all the answers

What does static analysis for load capacity of pile include?

Stress-strain relationships Signup and view all the answers

What type of pile is used primarily to resist tensile forces?

Anchor pile Signup and view all the answers

What is primarily considered when evaluating the efficiency of a pile group?

Characteristics of pile, spacing, and total number of piles Signup and view all the answers

Which factor does NOT contribute to the efficiency of a pile group?

Temperature variations in soil Signup and view all the answers

What is the bearing capacity factor (Nc) used in the calculation for the load capacity of the group?

9 Signup and view all the answers

In the provided example, what is the total load capacity (Q) of the pile group calculated to be?

1367 kN Signup and view all the answers

Which settlement influences the efficiency of the pile group after pile driving?

Consolidation settlement after dissipation of excess pore pressure Signup and view all the answers

What is one of the primary reasons for the need for a pile foundation?

Very large design loads Signup and view all the answers

What is the maximum load capacity for timber piles under usual conditions?

450 kN Signup and view all the answers

Which of the following statements regarding steel piles is false?

Steel piles have a maximum load capacity of 1000 kN. Signup and view all the answers

What is the optimum length for prestressed concrete piles?

18 - 25 m Signup and view all the answers

Which type of pile is formed by tensioning high strength steel prestress cables?

Concrete piles Signup and view all the answers

What is a major disadvantage of steel piles?

Vulnerability to corrosion. Signup and view all the answers

What type of construction allows for concrete piles to have high load capacities and resistance to bending?

Precast reinforced concrete Signup and view all the answers

How are cast in place concrete piles formed?

By drilling a hole and filling it with concrete. Signup and view all the answers

What indicates that the ultimate load has been reached during pile testing?

The settlement continuously increases at a constant load. Signup and view all the answers

How is the load released after reaching the ultimate load in pile testing?

In increments of 1/6 of the total load. Signup and view all the answers

What is the required condition for holding the load constant in pile testing according to IS code?

Until the settlement is 0.1 mm for 5 minutes. Signup and view all the answers

In a group of closely spaced piles, what is a key factor affecting bearing capacity?

Soil resistance may overlap between piles. Signup and view all the answers

Which statement is true regarding the bearing capacity of friction pile groups?

The total bearing capacity can be less than the product of individual friction values. Signup and view all the answers

What happens to the load carrying capacity of combined friction and end bearing piles?

Only the capacity of the frictional portion is reduced. Signup and view all the answers

What approach is used to estimate the bearing capacity of a group of friction piles?

Multiplying the individual pile capacity by the number of piles and a reduction factor. Signup and view all the answers

When increasing the load during pile testing, how long should the load be held when the working load is reached?

For 24 hours before unloading. Signup and view all the answers

Study Notes

Need for Pile Foundation

Necessary for structures with very large design loads.
Essential when soil conditions are poor at shallow depths.
Utilized in sites with constraints, e.g., property lines.

Timber Piles

Made from tree trunks, installed with the small end as a point.
Maximum length is 35 m; optimum length ranges from 9 to 20 m.
Typical maximum load: 450 kN; optimum load range: 80 - 240 kN.
Advantages: High availability, easy to work with.
Disadvantages: Susceptible to decay and low durability.

Steel Piles

Practically unlimited maximum length, with an optimum range of 12 to 50 m.
Load capacity depends on maximum allowable stress and cross-sectional area.
Common shapes include rolled HP shapes and pipe piles.
Closed-end piles can be filled with concrete post-installation.
Advantages: High load capacity and efficient under hard driving conditions.
Disadvantages: Vulnerable to corrosion; can be damaged by obstructions.

Concrete Piles

Types include precast, prestressed, cast in place, and composite constructions.
Precast piles designed to resist bending during transport and lateral loads.
Prestressed piles use tensioned high-strength steel cables.
Max lengths: 10 - 15 m for precast and 20 - 30 m for prestressed.
Load capacity varies: 900 kN for precast, 8500 kN for prestressed; optimum: 350 - 3500 kN.
Advantages: High load capacities and corrosion resistance.
Disadvantages: High initial costs, handling difficulties, susceptible to soil-induced damage.

Composite Piles

Combination of materials, taking advantage of both timber and concrete properties.

Installation Techniques

Displacement Piling: Earth is displaced as piles are driven in.
Replacement Piling: Soil is removed to make space for piles.

Classification by Load Transfer

End Bearing Piles: Transfer loads directly to the soil.
Friction Piles: Load is supported through friction along the pile's surface.
Tension Piles: Designed to resist upward loads.
Compaction Piles: Used for ground improvement.
Anchor Piles, Fender Piles, and Dolphins: Specific functions related to stabilization and marine applications.

Factors Affecting Pile Selection

Load carrying capacity assessed through methods like static analysis, dynamic analysis, and pile load testing.
Established through correlation with field tests (SPT, CPT, etc.).

Pile Load Testing

Determines settlement and ultimate bearing capacity.
Initial or routine tests involve applying incremental loads.
Failure load reached when settlement exceeds a specific percentage of pile diameter, followed by recovery measurements.

Efficiency of Pile Group

Closely spaced piles may experience overlapping soil resistance.
Total bearing capacity of a group may differ from the sum of individual piles.
Efficiency of group depends on factors like characteristics, spacing, and number of piles, calculated using efficiency factor (ηg).

Pile Spacing Considerations

Affects overlapping stress distribution and foundation costs.
Influences settlements from various causes, such as soil consolidation and groundwater level changes.

Example Calculation

A pile group of 9 piles in soft clay with specific parameters illustrates load capacity estimation based on bearing and adhesion factors, underscoring practical applications of theoretical concepts in pile foundation design.

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Description

Explore the essential concepts of pile foundations, including their need for large design loads and suitability in poor soil conditions. This quiz covers various types of piles, particularly timber piles, detailing their specifications and limitations. Test your understanding of pile foundations and their applications in construction.