Week 7 Challenge
Answer
Question no 1 :
Fixing the number of piles in deep foundations for a flyover in Delhi requires careful consideration of various loads and factors. Here's a step-by-step guide:
1. List all loads acting on the flyover:
- Dead load (self-weight)
- Live load (traffic)
- Wind load
- Seismic load (earthquake)
- Soil pressure (from surrounding soil)
2. Calculate load combinations as per IRC 6:
- Combine dead load, live load, and wind load
- Combine dead load, live load, and seismic load
- Combine dead load, live load, and soil pressure
3. Determine the required pile capacity:
- Calculate the total load on each pier or abutment
- Divide the total load by the allowable pile capacity (based on soil conditions and pile type)
4. Factors affecting the number of piles and depth:
- Soil conditions (type, density, and strength)
- Pile type (e.g., bored, driven, or helical)
- Pile diameter and length
- Spacing between piles
- Load distribution and transfer mechanisms (e.g., pile caps, footings)
- Settlement and deflection criteria
- Construction constraints (e.g., access, noise, and vibration)
5. Differences in wall-type abutment and pier (free and fix):
- Wall-type abutment: Requires more piles due to higher lateral loads and moment resistance
- Pier (free): Requires fewer piles due to lower lateral loads and moment resistance
- Pier (fix): Requires more piles due to higher lateral loads and moment resistance, similar to wall-type abutment
Question no 2 :
Fixing the diameter of a well in deep foundations for a river bridge in Delhi requires careful consideration of various loads and factors. Here's a step-by-step guide:
1. List all loads acting on the well:
- Dead load (self-weight)
- Live load (traffic)
- Wind load
- Seismic load (earthquake)
- Water pressure (from river)
- Soil pressure (from surrounding soil)
2. Calculate load combinations as per IRC 6:
- Combine dead load, live load, and wind load
- Combine dead load, live load, and seismic load
- Combine dead load, live load, and water pressure
- Combine dead load, live load, and soil pressure
3. Determine the required well diameter and depth:
- Calculate the total load on each well
- Consider the bearing capacity of the soil and the required factor of safety
- Use empirical formulas or numerical analysis (e.g., finite element method) to determine the required well diameter and depth
4. Factors affecting the diameter and depth of the well:
- Soil conditions (type, density, and strength)
- Water table level and fluctuations
- Scouring and erosion potential
- Pile or well spacing and layout
- Load distribution and transfer mechanisms (e.g., pile caps, footings)
- Settlement and deflection criteria
- Construction constraints (e.g., access, noise, and vibration)
5. Differences in wall-type abutment, fixed and free pier:
- Wall-type abutment: Requires larger well diameter and depth due to higher lateral loads and moment resistance
- Fixed pier: Requires larger well diameter and depth due to higher lateral loads and moment resistance
- Free pier: Requires smaller well diameter and depth due to lower lateral loads and moment resistance
Additional factors to consider:
- Hydrodynamic forces (e.g., river currents, waves)
- Environmental factors (e.g., water quality, aquatic life)
- Geotechnical conditions (e.g., soil liquefaction, settlement)
Question no 3 :
Free standing length in a pile system refers to the length of the pile shaft that extends above the pile cap or foundation level and is not laterally supported. It's an important consideration in pile design as it affects the pile's stability and resistance to lateral loads.
To determine the free standing length, you can follow these steps:
1. Identify the pile type (e.g., bored, driven, helical)
2. Determine the pile diameter and material properties
3. Calculate the pile's slenderness ratio (L/r, where L is the length and r is the radius of gyration)
4. Check the pile's stability against buckling and lateral loads using applicable code clauses and formulas
Applicable code clauses from IRC and IS codes:
IRC:
- IRC:6-2017, Section 3.2.3: "Pile foundations"
- IRC:6-2017, Section 3.2.4: "Pile design"
- IRC SP 114
IS:
- IS:2911-2010, Section 5.2: "Pile foundations"
- IS:2911-2010, Section 5.3: "Pile design"
- IS:456-2000, Section 6.2: "Columns and pile caps"
- IS: 875-1987: "Code of practice for design loads (other than earthquake) for buildings and structures"
- IS: 1893-2016: "Criteria for earthquake resistant design of structures"
QUESTION NO 4 :
The impact of free-standing length on the full length of the pile:
- Increases the risk of buckling and lateral instability
- Reduces the pile's vertical and horizontal capacity
- Affects the pile's settlement and deflection behavior
Rough estimate of the number of piles required for an abutment:
- Height (H) = 5 m
- Width (B) = 12 m
- Vertical capacity (P) = 250 tonnes
- Horizontal capacity (H) = 35 tonnes
Assuming a typical pile diameter (D) = 1.0 m
- Vertical load per pile (P/pile) = P/number of piles = 250/number of piles
- Horizontal load per pile (H/pile) = H/number of piles = 35/number of piles
Using the Tributary Area Method:
- Tributary area per pile (A/pile) = (B x H) / number of piles = (12 x 5) / number of piles
- Vertical load per pile (P/pile) = A/pile x soil pressure (approx. 100 kPa) = (12 x 5) / number of piles x 100 kPa
Solving for the number of piles:
- Number of piles = (250 tonnes / (12 x 5) x 100 kPa) x (35 tonnes / (12 x 5) x 100 kPa) ≈ 4-6 piles
QUESTION NO 5:
Failures in deep foundations and their remedies as per codal provisions:
1. Inadequate bearing capacity:
- Remedy: Increase pile diameter or depth, or use a different pile type.
- Code reference: IS 2911-2010, Section 5.2.1
2. Insufficient lateral resistance:
- Remedy: Increase pile diameter or depth, or add lateral support.
- Code reference: IS 2911-2010, Section 5.3.1
3. Pile buckling:
- Remedy: Increase pile diameter or reduce free-standing length.
- Code reference: IS 2911-2010, Section 5.2.3
4. Pile settlement:
- Remedy: Increase pile length or diameter, or improve soil conditions.
- Code reference: IS 2911-2010, Section 5.2.2
5. Pile material failure:
- Remedy: Use higher-strength materials or improve construction quality.
- Code reference: IS 456-2000, Section 6.2.1
6. Inadequate pile spacing:
- Remedy: Increase pile spacing or use a different pile configuration.
- Code reference: IS 2911-2010, Section 5.2.4
7. Scouring or erosion:
- Remedy: Use scour protection measures or improve foundation design.
- Code reference: IRC:6-2017, Section 3.2.3.2
Construction parameters to be taken care of before planning a deep foundation:
1. Soil investigation and testing
2. Pile type and material selection
3. Pile diameter and length determination
4. Pile spacing and layout
5. Foundation design and analysis
6. Construction techniques and equipment
7. Quality control and assurance
8. Safety considerations
9. Environmental factors (e.g., water table, soil contamination)
10. Adjacent structures and potential impacts