Geotechnical Analysis for Reopening a Mine for Potash Extraction

LO1 Review rock types,their formation and civil engineering

LO2 Explore and classify soils to current codes of practice.

LO3 Analyse soil properties determined by geotechnical procedures.

LO4 Produce a proposal to address identified geotechnical weaknesses and problems.

Assignment Brief and Guidance

It is necessary to reopen a mine under the sea to extract potash. There is a flat area on the site near to the beach which was used in the past as a logistic center for the mine to bring in supplies and export the potash inland. This area is only about 4 m above mean sea level. The soil below this area is mainly soft sand with some made ground and some ridges of clay. A short distance inland from this area there are some steep rocky hills and two abandoned quarries. You have just started working with this company and are part of the team that is making preparations for developing the mine and the logistics area.

1. State the three main classes of rock and outline the main features of their formation
2. Give one example of how each type of rock is used in construction
3. Briefly outline the Bowen Series of rock classification and indicate to what extent this can explain the weathering characteristics of rocks
4. What are the most important mechanical characteristics of rocks used in the following situations:

i) as foundations for roads

ii) as facings for structures

iii) as aggregate for concrete HNC/HND Construction and the Built Environment 3

iv) as building stone.

1. Outline where soil is used as a construction material and compare this with alternative materials that could be used such as in a dam
2. Explain the difference in strength between rock mass and the same material taken out of a quarry
3. How is this shown in the RQD assessment of rock strength?
4. Analyze case studies involving tunneling and the problems posed by the discontinuous nature of rock mass

1. Briefly explain what a brownfield site is and how this differs from other sites.
2. How would you approach a ground survey in a brown filed site and show how this might differ from a ground survey on other sites.
3. Explain the difference between a disturbed and an undisturbed soil sample
4. Outline the laboratory tests that can be done only on undisturbed samples
5. Outline how soils are classified
6. How is plasticity used in the classification of soils?
7. Discuss the sampling of soil in situ giving an example of the measurement of bulk density and also of shear strength.
8. Discuss the relative merits of in situ testing and laboratory
9. Evaluate how much soil sampling is needed in a soil survey on a site and what are the dangers of too little or too much sampling?

a) Outline briefly how you would measure the following from an in-situ sample:

• soil moisture content
• bulk density and
• specific gravity

b) Outline briefly a method of measuring shear strength in-situ and one method used in the laboratory. Discuss the limitations of this test with respect to the type of soil under test

c) Briefly outline how soil compressibility is measured in the laboratory and discuss the importance of time in this measurement.

d) Outline the principle behind the California Bearing Test

e) State how the liquid limit and the plastic limit are measured in the laboratory and state the results we obtained from the laboratory tests carried out.

f) The following results were obtained during a test of the liquid limit of a clay rich soil. Calculate the liquid limit and compare the reliability and reproducibility of this test to the standard test for plastic limit. Cone penetration Moisture content

Address the problem of keeping the logistic area dry even during the highest tides. Occasionally tides as high as 7m above mean sea level area experienced here when there is a Spring tide (a very high tide) together with a strong on shore wind.

1. Outline your solution and
2. Outline what the geotechnical weaknesses are within the logistics area
3. Briefly suggest the site survey needed
4. Show what foundations are needed to support and protect the area.