Bearing Capacity and Pile Types Quiz

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Questions and Answers

What is the value of the Nγ factor for a pile in soil with a friction angle of 10 degrees according to IS 6403:1981?

1.22 (correct)

5.39

2.65

0.45

Which factor influences the N factor for piles according to IS 6403?

The diameter of the pile only

The method of construction and soil type (correct)

The length of the pile only

The environmental conditions only

What is the estimated safe load capacity of a driven pile with a factor of safety of 2.5 in a uniform sand with a friction angle of 40 degrees?

Approximately 48.03 kN/m2

Approximately 10.88 kN/m2

Approximately 271.76 kN/m2

Approximately 109.41 kN/m2 (correct)

At what depth should the water table be located for it to affect the pile's safe load capacity significantly?

At ground level Signup and view all the answers

What is the diameter of the pile in the example provided?

300 mm Signup and view all the answers

What is the formula for calculating the ultimate bearing capacity for driven piles in granular soils according to Tomlinson's / Berezantsev’s Method?

qpu = σ' Nq Signup and view all the answers

Which condition leads to a reduction in the angle of shearing resistance of sand when driving piles?

When φ is greater than 40° Signup and view all the answers

What is the maximum tip or point bearing resistance for piles, as stated by Berezantsev?

11000 kN/m² Signup and view all the answers

For dense sand, what is the limiting value for point end bearing according to Mayerhof (1976)?

50Nq tan φ kN/m² Signup and view all the answers

What is the Ki value range for driven piles in loose to dense sand with φ between 30° and 40°?

1 to 2 Signup and view all the answers

In the context of the ultimate bearing capacity formula, what does Ap represent?

Area of the pile tip Signup and view all the answers

Which of the following factors is NOT included in the ultimate bearing capacity equation for piles in granular soil?

Pore water pressure Signup and view all the answers

According to Murthy (2001), how does the angle of internal friction affect the bearing capacity factors Nq and Nγ?

They change based on the angle of internal friction Signup and view all the answers

What does the variable $c_u$ represent in the context of pile foundations?

Undrained cohesion in the embedded length of pile Signup and view all the answers

Which type of soil consistency corresponds to an undrained cohesion ($c_u$) of 0-12.5 kPa?

Very soft Signup and view all the answers

In the ultimate load capacity equation for piles in clay, what does $q_{pu} = c_u N_c$ signify?

Undrained cohesion multiplied by bearing capacity factor Signup and view all the answers

What is the purpose of the reduction factor α in pile design?

To modify undrained cohesion to account for pile type Signup and view all the answers

Which bearing capacity factor ($N_c$) is recommended for circular and square piles according to Skempton?

9 Signup and view all the answers

In driven piles within sandy soils, what could be a typical range for the earth pressure coefficient ($K_i$)?

1 to 2 Signup and view all the answers

How far must a pile penetrate into the bearing stratum according to design standards?

At least 5D Signup and view all the answers

What aspect of pile foundations does the $Q_u$ equation illustrate for piles in clay?

Sum of base and shaft resistances Signup and view all the answers

What factor is primarily affected by the angle of shearing resistance when using driven piles in sand with an angle greater than 40 degrees?

Dilatancy effect reduces the angle Signup and view all the answers

What is the maximum base or tip bearing resistance specified for piles?

11000 kN/m² Signup and view all the answers

In granular soils, which of the following factors does NOT influence the Nq factor for piles?

Soil moisture content Signup and view all the answers

Using Mayerhof's method for dense sand, what is the limiting value for point end bearing?

50Nq tan φ kN/m² Signup and view all the answers

What does the variable 'D' represent in the equation for bearing capacity in granular soils?

Diameter of the pile Signup and view all the answers

Which coefficient is NOT a part of the equation for bearing capacity of piles in granular soil?

θ Signup and view all the answers

What effect does driving piles into sand have on the angle of shearing resistance at angles greater than 40 degrees?

Reduces the angle Signup and view all the answers

For loose sand, what is the limiting value for point end bearing according to Mayerhof?

25Nq tan φ kN/m² Signup and view all the answers

In the context of bored precast and cast in situ concrete piles, which parameter primarily affects the Nq factor?

Type of soil Signup and view all the answers

What does the variable 'q pu' represent in relation to driven piles in sand?

Ultimate bearing capacity Signup and view all the answers

What is the maximum permissible settlement for the pile group design described?

40 mm Signup and view all the answers

Which parameter is used to determine negative skin friction in single piles within cohesive soils?

Perimeter of the pile Signup and view all the answers

What factor is used to ensure safety against bearing failure in the design?

2.5 Signup and view all the answers

What is the primary consideration when aggregating negative skin friction for a pile group?

The higher value from different equations for negative skin friction Signup and view all the answers

Which of the following describes the condition of the soil with an undrained cohesion of less than 12.5 kPa?

Very soft Signup and view all the answers

What is the unit weight of the saturated soil used in pile foundation design?

20 kN/m³ Signup and view all the answers

Which equation is used for computing negative skin friction in cohesive soils for pile groups?

Fng = cu Lc Pg + γLc Ag Signup and view all the answers

What represents the total load a pile group can carry based on the design conditions provided?

Working load plus negative skin friction Signup and view all the answers

What is the compression index of the sub-soil in the pile design example?

0.10 Signup and view all the answers

What is the unconfined compressive strength of the sub-soil indicated in the data?

70 kN/m² Signup and view all the answers

Study Notes

Bearing Capacity Factors

Nγ factor is relevant for general shear failure and varies by soil nature, type of pile, L/D ratio.
IS 6403:1981 provides values for Nγ based on φ degree, ranging from 0 (0.00) to 50° (762.89).

Pile Types and References

IS:2911(Part1/Sec1):2010 covers driven piles, while IS:2911(Part1/Sec2):2010 addresses bored piles.
Driven piles: precast and cast in situ concrete.
Bored piles: also precast and cast in situ.

Safe Load Capacity Calculation

Example indicates calculating safe load for a driven pile with parameters like length, diameter, soil unit weight, and factor of safety (F.O.S).
Formula: ( q_{pu} = \sigma' N_q \phi + 40° ).

Shearing Resistance and Safety

For driven piles in sand, φc relates to in situ angle of shearing resistance. If φ > 40°, driving reduces effective shearing resistance.
Maximum point bearing resistance is capped at 11,000 kN/m².

Mayerhof's Limitations

Limit values for point end bearing:
- For dense sand: ( q_{pul} = 50N_q \tan(\phi) )
- For loose sand: ( q_{pul} = 25N_q \tan(\phi) )

Pile Load Capacity in Granular Soils

Total load capacity ( Q_u ) calculation for granular soils incorporates:
- Effective pressure at the pile tip.
- Contribution from skin friction from layers surrounding the pile.
For driven piles in sand, Ki varies from 1 to 2; for bored piles, from 1 to 1.5.

Pile Load Capacity in Clay Soils

Ultimate load ( Q_u ) is derived from base and skin resistance:
- Formula: ( Q_u = q_{pu} A_b + f_s A_s ).
- Undrained cohesion at the base impacts the bearing capacity.

Negative Skin Friction

Cohesive soils: calculated via the perimeter of the pile and undrained cohesion.
Cohesionless soils: utilizes lateral earth pressure coefficient and soil weight for calculations.

Pile Group Dynamics

Negative skin friction for groups considers the number of piles and overall perimeter.
Ultimate load capacity is adjusted by factoring in negative skin friction.

Cone Penetration Testing

For heterogeneous soil, ultimate point bearing utilizes average cone resistance values to determine load capacity.

Settlement and Design Considerations

Total compressive load, acceptable settlement, and factor of safety against bearing load are critical components in pile design.
Example designs need to factor in existing soil conditions, adherence factors, and corrosion standards.

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Description

Test your knowledge on bearing capacity factors, pile types, and safe load capacity calculations. This quiz explores key guidelines such as IS 6403:1981 and IS:2911 standards related to driven and bored piles. Understand the nuances of shearing resistance and safety in foundation engineering.