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CEGEG0031 ADVANCED SOIL MECHANICS
COURSEWORK 2 (30%)
Individual report
Deadline: 13 January 2025 Monday 12:00 noon, 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. By sketching relevant diagrams, define (a) Upper and (b) Lower Bound solutions, and (c) Limit Equilibrium analyses. Compare their differences whether and how each of them satisfy (i) compatibility, (ii) equilibrium and (iii) material properties.[10%]
2. For the Upper bound mechanism shown in Figure 1, draw the velocity diagram for a unit velocity of the 45o wedge (black arrow). (a) Derive the value of bearing stress qat failure for a long slope with a foundation at its crest. The soil properties are undrained shear strength Cu = 200kPa and unit weight γ=20kN/m2. The dimensions and the weights of soil blocks per metre length of the slope (W1 and W2) are given for your convenience. [15%]
Figure 1
3. For the same 45 o slope of 30mheight with 20m foundation at the crest of the slope (Figure 2), propose one lower bound mechanism with 1 discontinuity line, and calculate bearing stress q of the foundation by drawing two Mohr circles diagrams. [Cu = 200kPa and γ=20kN/m2.] Mark clearly in your Mohr Circle diagrams and the Figure the major principal stress direction and Pole point of each zone, and the rotation of principal stress direction across discontinuity. List the potential limitations of your Lower bound calculation. [15%]
4. 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) the displacement-based elastoplastic FEM analyses adopting a constitutive model. [10%]
Figure: 2
5. 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 setup a numerical model, in order to calculate the maximum bearing stress at failure to the foundation at edge of a saturated slope (Figure 2). [Use undrained shear strength Cu = 400kPa and saturated unit weight γsat = 20kN/m3. (You may 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.)]
By applying various strategies to refine and improve the accuracy of the prediction, what is your best estimate of the bearing stress at failure? [15%]
6. Perform a parametric comparative study to investigate how sensitive (a) undrained shear
strength Cu, (b) unit weights of the soil γ, and (c) width of foundation B, would affect the maximum bearing stress. Which parameter has the most significant impact to the maximum bearing stress? [15%]
7. If drainage occurs in long term, what might happen to your slope, if the peak friction angle is 40o, critical state friction angle is 30o. By performing a parametric study on values of peak and critical state effective friction, comment on the stability of the slope. [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). Please also upload to Moodle a zip file of all clearly labelled G2x files.
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.
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 maybe 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.