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ENEN20002 Assignment 

DEPARTMENT OF INFRASTRUCTURE ENGINEERING

ENEN20002 Earth Processes for Engineering

Semester 1 (2022)

Assignment 3 – Basic soil behaviour and water in soil

Problem Description

A new airport has been proposed to be constructed at a site with ground condition as shown in
Figure 1.

Figure 1 Ground condition of the site
Part A

Soil samples have been retrieved from the top three soil layers of the site. All three soils are
fine grained soils with laboratory classification test results summarised below:

Table 1 Atterberg test results
Soil # Shrinkage
Limit (%)
Plastic Limit
(%)
Liquid Limit
(%)
Soil 1 10 21 53
Soil 2 10 15 34
Soil 3 17 23 74




Clay
6m
Hard Rock
500m 1000m 500m
6m
Soil 1
Soil 2
10m
10m
2 km Airport Runway
A B C
Soil 3
2m
Airport
Terminal
Soil 1
2m
Note: drawing not to scale
ρsat = 1600 kg/m3
Gs = 2.6

ρsat = 1800 kg/m3
Gs = 2.7
ρsat = 1700 kg/m3
Gs = 2.65




ENEN20002 Assignment 3 – 2022 (Semester 1) 2


1) Using the laboratory test results in Table 1, classify the three soils according to the
Unified Soil Classification System (USCS). 9 marks

2) Among the three soils, predict their volume change (swelling/shrinkage) with change
in water content in ascending order (lowest volume change to highest volume change).
Explain your ranking using the the results in Table 1. 6 marks

3) Through laboratory tests, the presence of two common types of clay minerals are
presence in the 3 soils (Montmorillonite and Illite). Comment on the possible type of
clay mineral for the three soils and explain your choice. 6 marks

Part B (40 marks)

The airport construction will involve a 2km long runway from point A to B, and an airport
terminal at point C. Taking into consideration the potential seasonal change from the wettest
to the driest, the water content variation with depth from ground surface to 12 m is summarised
in Table 2.

Table 2 Water content variation along depth
Depth, z
(m)
Water content at
extremely wet season, w
(%, dry weight basis)
Water content at extremely
dry season, w
(%, dry weight basis)
0 30 6
2 28 8
4 26 10
6 24 12
8 22 14
10 20 16
12 19 17
14 18 18

4) If the dry density for Soil 1 is ρd = 1400 kg/m3, determine the current water content
using the saturated density ρsat provided in Figure 1. In comparison to Table 2,
comment on whether the site is currently experiencing wet or dry season. 3 marks

5) Calculate the potential maximum vertical settlements of the ground at points A, B and
C with the seasonal change from wettest to driest.
a. Using phase relations, establish a generic set of equations to estimate the vertical
settlement for each depth interval. 10 marks
b. Plot the water content versus depth profile using the data provided in Table 2.
Determine the average water contents (both at extremely wet and dry season)
for the 7 equal layers of soil*. 16 marks
c. Using the generic equation from (a), determine the vertical settlements for each
soil layer and total vertical settlement at points A, B and C. 21 marks
Hint:
• *Determine the total vertical settlement by considering 7 equal layers of 2 m
thickness from z = 0 to 14 m
• Assume each soil layer is extensively long, and thus lateral movement of the soil
has been restricted by the surrounding soil.
ENEN20002 Assignment 3 – 2022 (Semester 1) 3

Part C
6) According to design specifications, the allowable maximum vertical slope (∆h/L) along
the length of the runway is 1/2000. ∆h is the elevation difference between any two
points along the length of the runway, and the L is the horizontal distance between that
two points. Evaluate the potential risk put on the runway by the extreme seasonal
change. 5 marks

7) If the allowable settlement for the airport terminal is 60 mm, evaluate the risk of damage
to the airport terminal during the extreme seasonal change in water content. 2 marks

8) If the shrinkage limit of Soil 2 increases to 17%, recalculate the total vertical settlement
at Point C. Comment on the effect of new shrinkage limit on the risk of damage for the
airport terminal. 10 marks

9) Based on the outcomes of Questions 6 to 8, comment on the effect of ground condition
on the construction and risk of damage for the airport. 2 marks



Teamwork and Reporting
o For this assignment, you will be working in the same group that you have been
allocated for your previous assignments.

o Each group needs to submit one team report fully addressing all the points
mentioned above. You will find guidance on report writing on the LMS in the
assignment area. The report should be less than 2000 words.

o You should submit only the soft copy of the document (word file) into the
TurnItIn link available on the LMS (No need to submit an excel sheet and the word
file should be a self-contained document).

o Each group should submit only one report using any of the group members LMS user
name (do not submit multiple copies from a group). You must use your group name
to name your soft copy (e.g. 1:15pm_Group1.docx).

o This assignment is due at 5 p.m., Friday, May 13, 2022. Late submissions received
after the due date without prior arrangement will receive a penalty of 5% per day
late.