Pile Classification and Analysis Assignment

1. Pile Classification by Material

List the types of piles classified based on the material used for construction.

• Timber Piles

  • Advantages: Renewable, lightweight, and easily driven into place.
  • Disadvantages: Prone to decay, limited lifespan, and strength.

• Concrete Piles

  • Advantages: High load-bearing capacity, durable, resistant to environmental factors.
  • Disadvantages: Heavy, expensive, and difficult to transport.

• Steel Piles

  • Advantages: High strength, easy to splice, can penetrate hard soils.
  • Disadvantages: Prone to corrosion, expensive, requires protective coatings.

• Composite Piles

  • Advantages: Combines benefits of different materials (e.g., steel and concrete).
  • Disadvantages: Complex design and higher costs.

2. Driven Piles in Clay and Sandy Soils

• In Clay:

  • May cause excess pore water pressure during installation, leading to temporary soil softening.
  • Settles over time due to consolidation, increasing pile capacity.

• In Sandy Soils:

  • Compacts the soil, increasing the bearing capacity.
  • Risk of soil heave or displacement during installation.

3. Collapsible Soil and Behavior Under Load

Definition: Collapsible soils are low-density soils (e.g., loess) that experience sudden volume reduction under moisture increase and loading.
Nature:

• When dry, the soil maintains strength.
• Under load and moisture, soil particles reorganize, causing settlement or failure.

4. Shallow Foundation vs. Deep Foundation

• Shallow Foundation:

  • Transfers load to near-surface soil layers.
  • Suitable for light structures and stable ground.

• Deep Foundation:

  • Transfers load to deeper, more stable strata.
  • Used for heavy structures or weak surface soils.

5. Negative Skin Friction

Definition: A downward drag on a pile caused by soil settlement relative to the pile.
Development: Occurs when surrounding soil consolidates due to applied loads, groundwater changes, or surcharge loading.

6. Calculations for Pile in Sand

Given:

• Pile dimensions: Length = 16 m, Cross-section = 400 mm × 400 mm.
• Soil parameters: Unit weight, γ = 18 kN/m³, φ = 30°.

a) Ultimate Point Load (Qp)

1. Meyerhof’s Method:
   Formula: Qp=Ap⋅qpQ_p = A_p cdot q_pQp=Ap⋅qp
   qpq_pqp: Point bearing pressure calculated from Meyerhof’s empirical relations.

2. Vesic Method:
   Requires: Es = 20.5 MN/m², μs = 0.3.

3. Janbu Method:
   Given: η` = 900.

b) Frictional Resistance (Qs)

• Formula:
  Qs=K⋅A⋅γ′⋅H⋅tan⁡(δ)Q_s = K cdot A cdot gamma` cdot H cdot an(δ)Qs=K⋅A⋅γ′⋅H⋅tan(δ).
• Given: $K=1.3$, $\delta =0.8\phi$.

c) Allowable Load Capacity

• Qallow=QuFSQ_{ ext{allow}} = frac{Q_u}{FS}Qallow=FSQu, where FS = 4.

7. Driven Pile in Layered Sand

Tasks:

1. Calculate the ultimate point load using Meyerhof’s method.
2. Compute ultimate frictional resistance QsQ_sQs with $K=1.4$, δ′=0.7φδ` = 0.7φδ′=0.7φ.
3. Determine allowable load QallowQ_{ ext{allow}}Qallow using FS = 4.

8. Driven Pile in Clay

Given:

• Outside diameter = 400 mm, Wall thickness = 6.35 mm.
• Top 10 m of clay = normally consolidated.
• Bottom clay layer: OCR = 2.

a) Net Point Bearing Capacity

• Use effective stress principles and pile geometry to calculate.

b) Skin Friction

• Apply methods for clay layers based on consolidation properties.

c) Net Allowable Pile Capacity

• Formula: Qallow=QuFSQ_{ ext{allow}} = frac{Q_u}{FS}Qallow=FSQu, where FS = 4.