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Apr 30, 2024

Assignment Task

Objectives

After completion of this assignment students will have a complete understanding of bridge foundation design. This assignment will take students through the actual design process involved in the pile design, until the construction of piles. The assignment provides an opportunity for them to understand risks associated with designs and how engineers dealt with them, what engineering judgement need to be taken at various design stages and during construction. It also provides an opportunity for them to make their own engineering judgments. During this exercise students will have an opportunity to utilise related Australian Standards and TfNSW (RMS) design guidelines and other design literature. This assignment provides a step by step approach to bridge foundation design and will develop student’s critical thinking, analytical skills to solve a real engineering problem. This also provides an opportunity to work in a team environment and to take collective decisions.

Description of the problem

The attached bridge elevation and plan show the proposed bridge across the environmentally sensitive creek for Transport for New South Wales (TfNSW). The contract was awarded as design and built contract. The team consists of designer and contractor. The width of the bridge is 23.0m.

Bridge consists of three spans. Bridge is supported on two abutments at the embankment of the creek and two piers located within the creek. Bridge abutment consists of five numbers of cast-in-place bored piles of diameter 1050mm and connected by 1200mm wide and 1400mm deep capping beam. Bridge pier consists of portal frame supported by single cast-in-pace bored pile of diameter 1200mm at each column locations. Bridge is partially restraint in the longitudinal and transverse direction. Bridge abutments and piers are provided with scour protection. Piles will be constructed without permanent casing.

Boreholes BR-15 and BR-22 are provided with tender design documentations. After contract was awarded, two additional boreholes BR-18 and BR-19 were drilled. Four boreholes were available during detail design. Loading on piles for tender design and detailed design are tabulated in Table 1 and Table 2 respectively

Performance Requirements of Piles.

  • The pile should be socketed into competent rock,
  • Differential settlement between piles should be limited to 10mm,
  • The bridge should be stable for 1:2000 year ARI flood.

Questions

1. Based on design data provided during tender, you are required to design piles for tendering.

a. Estimate pile lengths for tender design by considering axial load only.

b. What pile lengths are you going to provide for estimating the tender pricing.

c. Please list at least three risks involved in your answer in Q1b.

d. Against risks identified in Q1c, please suggests mitigation measures for each risk.

2. Copy the table provided and evaluate the Average Risk Rating (ARR) and Geotechnical Strength Reduction Factor for piles in accordance with AS 2159 Clause 4.3.1. Please write down reasons for each rating on column provided in the table.

3. Based on design data provided for detailed design you are required to design piles for construction. Please use geotechnical strength reduction factor evaluated in Q2.

a. Calculate the required socket length.

b. Calculate the pile length.

c. Compare against tender design pile lengths in Q1c.

d. Can you agree with your risks/mitigation identified in Q1c&Q1d? Please justify your answer.

4. Understanding of construction specifications and preparation of construction drawings:

a. Please name the TfNSW QA Specification of construction of cast-in-place reinforced concrete piles without permanent casing.

b. Please tabulate the information you would like to provide for piling construction.

c. Please develop at least five design notes to be provided in the construction drawing.

5. How to manage design issues during construction: It was observed that during the construction of piles, encountered rock profiles were different to what was assumed in the detailed design drawing. Construction manager provided the following information to the design team.

a. What actions are you going to take to resolve above issues? Please note that you have very limited time since construction is in progress.

b. Are you going to revise your pile lengths, if so please provide new lengths and justify your answer.

c. To alleviate similar issues in future designs, what suggestions are you going to give to your design team?

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