Soil Mechanics
Weightage = 50%
Question 1 (20 Marks)
A square footing, 2 × 2 m resting on a soil mass. The footing carries a load of LAST FOUR DIGITS OF YOUR STUDENT ID in KN.
(For example if student ID is 21369572, the load on the footing for this student is 9572 KN)
Determine the vertical stress increase due to load on footing at a depth of 1, 2, 5, and 10 m using;
(a) Boussinesq method under the centre of the footing (15 Marks)
(b) Approximate method under the centre of the footing (5 Marks)
Question 2 (20 Marks)
An undisturbed soil sample was tested in a falling head permeameter. The results were;
Initial head of water in stand pipe = 1750 mm
Final head of water in stand pipe = 735 mm
Duration of the test = 331 seconds
Sample length = 100 mm
Sample diameter = 100 mm
Standpipe diameter = 5mm
Determine the saturated hydraulic of soil in m/sec. Also comment on the type of soil it is. (10 Marks)
Question 3: (Marks 20)
- Estimate the immediate settlement of a concrete footing 2 m × 2 m in size, if it is founded at a depth of 1.5 m in a silty sand whose elastic modulus is 16000 kPa. Footing is expected to transmit a stress of 370 kPa. Assume reasonable values of Ipand μ from the lecture slides. (Marks 10)
- A layer of clay 7.5 m thick underlies a proposed new building. The existing overburden pressure at the center of layer is 190 kPa and the stress due to new building increases the pressure by 167 kPa. Assume coefficient of consolidation, mv= 0.185 m2/MN and compression index, Cc = 0.34. Estimate the consolidation settlement.
Question 4: (20 Marks)
A standard proctor test was carried out on Oxford clay and following data was collected. Analyse the data, plot compaction curve (Dry density v/s moisture content), and determine Maximum dry density and Optimum moisture content for the soil. Suggest how you compact this soil in the field if you are a site engineer. (10 Marks)
| Test number | 1 | 2 | 3 | 4 | 5 |
| Mass of mold + base (m1) – kg | 4.408 | 4.408 | 4.408 | 4.408 | 4.408 |
| Mass of mold + base + soil (m2) – kg | 6.237 | 6.357 | 6.663 | 6.446 | 6.271 |
| Volume of mold (V) – m3 | 9.37×10-4 | 9.37×10-4 | 9.37×10-4 | 9.37×10-4 | 9.37×10-4 |
| Density of soil (ρ) – kg/m3 | |||||
| Weight of empty container – g | 45.2 | 45.2 | 45.2 | 45.2 | 45.2 |
| Wet weight of soil + empty container – g | 73.3 | 89.3 | 82.3 | 80.1 | 89.2 |
| Dry weight of soil + empty container – g | 72.6 | 85.1 | 78.1 | 75.8 | 81.4 |
| Moisture content (w) – % | |||||
| Dry density of soil (ρd) – kg/m3 |
Question 5: (20 Marks)
- Plan geotechnical site investigations for the Housing development. Client for the project intends to build a housing scheme in the shaded area shown in figure below. Housing scheme consists of series of two storey homes and 4 blocks of 5 storey flats.
Task 1:
Carryout desk study for the site and find required information about the project, determine the quality and uniformity of the soil at the site. In addition determine the depth of the bedrock. (5 marks)
Task 2:
Based on the information obtained in task 1 plan site investigations for the housing scheme. (10 marks)
- Number of boreholes/test pits and their depths and locations
- The in-situ tests and their depths.
- Type of samples collection and their depths
Task 3:
Discuss with references why you think your design is optimum. (5 mark)
Figure 1: Location of the site.