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CEGEG0031 ADVANCED SOIL MECHANICS

COURSEWORK 3 (30%)

Individual report

Deadline: 15 January 2024 Monday 23:59am, via Moodle

With a maximum 2500 words* (excluding figures, graphs, tables, references and appendices), write an essay to describe the recent advances in the geotechnical stability analyses and illustrate its usage using the slope stability analysis as an example. Reference should include “Sloan, S.W. (2013) Geotechnique 63(7), 531-572” and other relevant papers. The report must consist of the following sub-sections:

1. List and compare the core principles and major differences between the conventional (a) Upper and (b) Lower Bound limits calculations, and (c) Limit Equilibrium calculations. [15%]

2. Describe and compare the core principles and major differences between (a) this numerical Finite-Element Limit Analyses (FELA) proposed by Sloan (2013), including its Upper and lower bounds formulations, optimisations and the strength reduction techniques, (b) other popular displacement-based elastoplastic FEM analyses adopting a constitutive model. [15%]

3. Register and download an academic licence of the 2-dimensional Optum G2 software based on the method proposed by Sloan (2013). Describe in detail each input and each step you adopted to set up a numerical model, in order to calculate the maximum bearing stress at failure to the foundation at edge of a saturated slope. The foundation has width B = 20m, it is situated on top of a 45o clay slope of H = 30m height, see Figure on page 2. (Note this is the same slope geometry as that in CW2 Question 1b).

The soil properties are: undrained shear strength Cu = 400kPa and saturated unit weight γsat = 20kN/m3 . (You could assume the dry unit weight γdry = 18kN/m3 , Young’s modulus of the soil could be assumed 15MPa, if needed, and NO factored strength is needed.)

What is the estimated bearing stress at failure? Also apply various strategies to refine and improve the accuracy of the prediction. [30%]

4. Perform a parametric comparative study to investigate how much: undrained shear strength Cu, unit weights of the soil γ, and width of foundation B, etc. would possibly affect the maximum bearing stress. Which factor has the most significant impact to the estimation to the maximum bearing stress? Are the results reasonable? [20%]

5 If drainage occurs in the long term, illustrate your steps to calculate the maximum bearing stress? You may assume peak friction angle is 40o , critical state friction angle is 35o . [10%]

The report must include introduction and conclusion*, and other appropriately used supplementary information e.g. figures, references, and appendices. The presentation of all these contribute to 10% of the total mark as a general presentation of your report. [10%]

Please write down the total word count immediately after the conclusion. There would be a penalty, according to UCL rules, if word count exceeds 2500 (excluding figures, graphs, reference and appendices), no allowance this time. Please also submit your G2x file to moodle.

Figure: Geometry of the slope from CW2 Question Q1(b)

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Note There were a lot of youtube tutorials about Optum G2, please ensure you watch these tutorials before your own work and meeting with me.

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Marking criteria:

Exemplary (90%-100%): Fulfilled all the required tasks with an exceptional level of insight, thoroughness, and originality. Comprehensive yet clear and concise. Impeccable English and presentation.

Outstanding (80%-89.99%): Fulfilled all the required tasks to a very high standard with no significant error but may be lacking slightly in some aspects of secondary significance (e.g. conciseness or some minor presentation flaws).

Very Good (70%-79.99%): Shows an understanding of the problem and how to solve it. Got everything right except for a few minor errors, inaccuracies or presentation flaws.

Good (60%-69.99%): Good understanding of the problem and how to solve it. Got most of the results right but made a few mistakes or showed some slight misunderstandings. Good overall presentation but may be lacking in a few places.

Satisfactory (50%-59.99%): Shows a Satisfactory understanding of the problem and solves a significant fraction of it correctly but may contain some serious mistakes or misunderstanding. Presentation acceptable but can be poor in places.

Fair (40%-49.99%): Most requirements attempted but shows limited understanding of the problem or detailed knowledge. Contains mistakes, misunderstandings, or irrelevant material. Organisation and expression and presentation inadequately poor and standard or presentation.

Fail (0%-39.99%): Very limited understanding of the question asked and how to answer it. Some marginally relevant material and limited content but badly organised with frequent errors and misconceptions. Serious weaknesses in presentation. Also applies to submissions that are most completely irrelevant, messy or missing altogether, or submissions showing clear plagiarism.