Question 5 (a) The existence of moisture in soil significantly influences soil c

Question

Question 5 (a) The existence of moisture in soil significantly influences soil characteristics and behavior. (i) What are the two main water retaining mechanisms in soil? Discuss why fine grain soils have greater capability to retain water through those mechanisms? (3 marks) (i) What major changes happen to a soil mass when it passes the shrinkage limit during drying? (2 marks) (b) Your are a geotechnical engineer required to find a good site for a house construction project The client has recommended two sites with different soils (Soil A and Soil B) and it is your responsibility to select the most suitable site for the construction. Some basic properties of the two soils are given in Table 5.1 (i) Based on the data in Table 5.1, which site will you recommend for the house construction (site with Soil A or Soil B)? Justify your recommendation. (2 marks) Dry Initial moisture Soil Type Shrinkage Average Limit Particle Size Density (mm) content | (96, weight basis) 10 ! ( PD) (%, weight basis) 0.0015 0.1 1.0 1.6 40 15 Table 5.1 The two sites were subjected to heavy rain during construction and this caused the moisture content of Soil A to increase from 10% to 20% and Soil B from 15% to 35%. (ii) Calculate the volumetric swelling for each soil type after rainfall. (Hint: assume a 1 cm, initial soil volume for your calculations). (7 marks) (iii) Does your answer in (ii) support your initial decision in answer (0)? (1 mark) (Total marks for Question 5- 15)

Explanation / Answer

(a) (i) Answer:-

Two water retaining mechanism in soil:-

1. Osmotic mechanism

2. Absorption mechanism

Fine grained soil have less void. Due to this reason fine grained soil retained more water than sand. Because air do not enter into fine grain soil. Due to this reason water retained in fine grain soil.

(a) (ii) Answer:-

At shrinkage limit in drying process soil mass becomes hard because soil grain come together and packed each other. Soil grains are placed very close or tightly packed with minimum void ratio.At shrinkage limit color of soil mass changes to light color.

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