CVE20004 Geomechanics
Task
Instructions to Students:
This final assessment assignment will contribute 60 per cent towards your overall mark, which must be completed and submitted within the fixed 24 hour period (stated above).
This final assessment assignment consists of a mix of numerical and short descriptive type questions. When answering the descriptive questions, make sure that your answers are well thought out, detailed, and covers what the question is actually asking. Please don’t fill your answer with random and irrelevant details from the notes. For the numerical type questions, you must show all working to justify your answer and incorporate diagrams if appropriate. Please also make your interim and final answers clear by using highlighting and/or underlining.
This assignment will be marked out of a total of 100 marks. All questions carry different marks, as indicated.
Your submission document that you upload to Canvas should be a single pdf and it must be presented in the same order as the assignment questions. Please check your submission document is complete before uploading to Canvas. Once the assignment deadline has closed, no further assignments will be accepted.
When uploading your submission through Canvas, it is strongly recommended that you leave plenty of time for your document to upload fully. It must be accepted within the 24 hour assessment window.
Important Note: This final assessment assignment is strictly an individual task. As you have a full day to complete this assignment (i.e., which is essentially an open book test), please resist the temptation to share any work or answers with others before the due date. This is plagiarism. I will be making an extra effort to detect any form of copying or collusion amongst student submissions. Understand that it is very easy to detect plagiarism for some questions, especially those numerical type questions when groups of students all make the same wrong assumptions / interpretations or simple miscalculations.
Question One
For the igneous rock Granite, explain what it is, how it is formed, and what it could potentially turn into through the various stages of the rock cycle. The purpose of this question is for you to demonstrate your knowledge and understanding of the rock cycle and the relationships between different types of rocks. Please note that there are several possible and acceptable answers for this question. (4 marks)
Question Two
Provide a brief discussion response (limited to 300 words) to only one of the topics listed below.
• In geological terms, how did the Dandenong Mountain range form or evolve? In your answer, be sure to discuss when and how this geological formation took place, the type of rocks likely to be found in this area today, and any immediate impact this event had on the surrounding landscape.
or
• In geological terms, how did the suburbs of Port Melbourne and Fishermans Bend form or evolve? In you answer, be sure to discuss when and how this geological formation took place, the type of geological deposits likely to be found in this area today, and any immediate impact this event had on the surrounding landscape. (8 marks)
Question Three
From data collected during a geological survey, you find the following for a given sedimentary rock layer:
• An apparent dip of 21.1 degrees was measured at a bearing of 5 degrees, and
• An apparent dip of 25.3 degrees was measured at a bearing of 88 degrees.
If the direction of true dip was approximated to be 53 degrees, estimate the magnitude of the true dip. Also comment on whether you believe this approximated direction of true dip was accurate or not. (8 marks)
Question Four
A cylindrical undisturbed sample of clay (20 cm long) was retrieved using a tube with a 10 cm internal diameter. The wet and dry mass of the sample were each measured at 2.985 kg and 2.487 kg respectively. Assuming the specific gravity of the clay particles is 2.65, draw and label an appropriate soil model to describe the soil and then (from first principles) calculate the following:
(a) Values for VS, VW and VA (with appropriate units).
(b) Moisture Content.
(c) Void Ratio.
(d) Degree of Saturation. (8 marks)
Question Five
The sieve analysis results for two soils (A and B) are summarised in the table below.
The initial dry mass was recorded at 1,000 grams for each sample (A and B). This initial dry mass was recorded before either sample was prepared for the mechanical sieve analysis.
For soil B, the Atterberg limits were determined to be: Liquid Limit = 60 % and Plastic Limit = 40 %.
For each soil (A and B):
(a) Calculate and tabulate the percent passing at each sieve aperture.
(b) Plot the particle size distribution curve.
(c) Classify according to AS1726-2017.
Notes:
1. Blank particle size distribution plots are available via Canvas.
2. Show all relevant working and ensure that you fully justify your final soil classification result.
Question Six
Two steel sheet pile walls (7 m apart) were driven into a fully saturated clayey sand layer. One side of the sheet pile wall extends 8 m into the clayey sand layer, while the other sheet pile wall only extends 6 m. The soil between the two sheet piles was then excavated to a depth of 5 m from the surface. An impervious sedimentary rock layer exists beneath the clayey sand layer and is located 4 m directly beneath the base of the deeper sheet pile and 2 m beneath the base of the shorter sheet pile. This should reveal an approximate true dip angle of 30 degrees for the impervious rock layer described. Assume: (i) the strike direction for the sedimentary rock layer and the direction of the sheet pile walls to be the same, (ii) the width of the sheet piles is negligible, and (iii) permeability of the clayey sand layer to be 4.0 x 10-4 cm/sec.
Draw an appropriately sized diagram to scale detailing the geological layers, the two sheet pile walls, and the excavation. Then,
(a) Sketch an appropriate flow net for water entering the excavation, and
(b) If the two sheet pile walls and excavation is 175 m long, calculate the required pump capacity (in m3 per day) to maintain a dry excavation (Ignore the end effects of the excavation in your calculation). (10 marks)
Question Seven
For the loaded area and sewer location shown below, calculate:
(a) The change in vertical stress on the sewer at point A if the sewer is 2 m deep, using the influence value chart and formula ∆σv = q × I.
(b) The change in vertical stress on the sewer at point B if the sewer is 2 m deep, using Newmark’s chart.
Notes:
1. Point A is on the sewer line and located at a tangent offset distance of √8 m from the corner of theloaded area as shown below.
2. Point B is on the sewer line and is located at a distance of √8 m from point A as shown below.
3. You can download blank copies of both charts via Canvas (Modules\Useful Charts and Documents). (10 marks)
Question Eight
For the soil block below, which is subject to various external normal and shear stresses, draw a scaled Mohr circle that represents this soil block and apply the method of poles to answer the following:
(a) Determine the magnitudes of the major and minor principal stresses.
(b) Draw and label the major and minor principal planes on your Mohr circle.
(c) Determine the magnitude of the normal stress and shear stress acting on the inclined plane AA.
(d) On the soil block diagram below, draw in the directions (and label) the normal stress and shear stress acting on the inclined plane AA.
(e) Determine the angle (θ) of the inclined plane for when the shear stress is a maximum value. (10 marks)
Question Nine
The following results were obtained from a consolidated drained triaxial test on three identical saturated sandy clay specimens.
(a) Draw the Mohr-Coulomb failure envelope for the soil tested and estimate the soil’s effective strength parameters. It is recommended that you do this accurately on graph paper using a scale of 1 cm = 20 kPa (A4 sheet in landscape view).
(b) Estimate the angle of the inclined plane where failure occurred on the soil specimen.
(c) If a further identical soil specimen was tested via an unconsolidated undrained triaxial test, and the cell pressure and pore pressure were measured at 200 kPa and 120 kPa respectively at failure.
Determine:
(i) The effective principal stresses at failure on the sample.
(ii) The effective stresses acting on the critical inclined plane at failure.
(iii) The total principal stresses at failure on the sample.
(iv) The undrained shear strength parameter, cu. (10 marks)
Question Ten
A strangely shaped flexible footing is proposed, as shown below. The shape is essentially a large rectangle (12 m x 9 m) that incorporates a smaller rectangular cut out. The footing is to be founded at ground surface over a deep uniform layer of medium dense sand and loaded to 200 kPa (shaded area only).
If the modulus of elasticity and Poisson’s ratio of the sand is 25 MPa and 0.35 respectively, estimate the immediate settlement at Point A. (8 marks)
Question Eleven
If a rigid concrete footing (2 m x 3 m) is to be founded at a depth of 1.5 m and loaded to 4,000 kN, estimate the following:
(a) The immediate settlement.
(b) The average consolidation settlement based on a 2:1 load spread and by dividing the consolidating layer into five appropriately thick layers. Provide a brief reason for your selected layer thicknesses.
(c) The time for 90 % consolidation to occur.
For the clay layer, a one-dimensional consolidation test was performed on a sample that was retrieved from a depth of 4 m (i.e., 4 m from the surface). At this location, the clay was found to have a natural void ratio of 0.56 and deemed to be over-consolidated as the pre-consolidation pressure was estimated at 95 kPa. The compression indices were measured at cc = 0.17 and cs = 0.03, and the coefficient of volume consolidation was measured at 0.8 m2/yr. Also, saturated unit weight = 19.5 kN/m3 and modulus of elasticity = 3,000 kPa.
For the sand layer, the dry unit weight = 18 kN/m3, saturated unit weight = 21 kN/m3, Poisson’s ratio = 0.35, and modulus of elasticity = 30,000 kPa.
Please ensure that you show full working to support your answers. (12 marks)
