Module code: CIVE5975M01
Page 1 of 5
Module Title: Foundation Engineering
© UNIVERSITY OF LEEDS
School of Civil Engineering
Semester One 2021/22
Calculator instructions:
• You are allowed to use a calculator or a computer calculator in this assessment.
Dictionary instructions:
• You are allowed to use your own dictionary in this assessment and/or the Spell Checker
facility on your computer.
Assessment Information:
• There are 5 pages to this online assessment.
• You will have 6 hours to complete the assessment.
• This assessment is worth 70% of the overall module mark.
• Question A, which is in five parts, is worth 40 marks. The questions in Section B are
worth 20 marks each
• Candidates are expected to make reasonable assumptions about any data not provided
in the questions. In such cases, any assumed information must be stated clearly in the
answers provided.
• It is anticipated that this assessment should take about 3 hours to complete
• The deadline for submission of your assessment is between: 09:00 to 15:00 on
Wednesday 12 January 2022 (UK time).
• Please submit your assessment to the ‘Exam Submission’ area on the module’s Minerva
page.
• Please include your Student Identification Number (SID) in the title of your submission.
• Please number every page of your submission in consecutive order.
• If there is anything that needs clarification or you have any problems, please email
civil@leeds.ac.uk and we will respond to you as quickly as possible within normal
working hours UK time (9:00-17:00 hours, Monday-Friday). Remember to include your
student name, ID and the full module details (module code and title).
• You must not discuss or share the content of or answers to this assessment, with any
fellow students, any staff or other contacts outside the school or the University’s
professional services. School contacts available to you are in the bullet point above.Module code: CIVE5975M01
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Section A
1.
Attempt this entire question. Each part is worth 8 marks.
(a) Figure A1a is a cross section of an existing two-storey brick house built about 1930.
The Figure shows the foundations and underlying geological profile. It is proposed to
build a single storey brick extension attached to the existing house as indicated on
Figure A1a. Briefly describe the issues to be addressed when designing the
foundations for the extension. Suggest appropriate foundations for the extension
giving reasons for your choice.
Figure A1a The soil and soil property profiles and location of the extension relative to the
existing house (note the foundations for the extension are not shown)
[8 marks]
(b) A new four-storey building is to be built adjacent to an existing three-storey building.
The concrete foundations for the existing building are 0.9m wide with the formation
level at 0.6m below ground level as shown on Figure A1b. Figure A1b also shows the
location of the new building and its foundations, and the geological profile. Estimate
the additional settlement of the existing building due to the construction of the new
building.
Figure A1b Cross section showing the soil profile and the location of the existing and new
foundations
[8 marks]Module code: CIVE5975M01
Page 3 of 5
(c) It is proposed to pre-consolidate a 3m layer of alluvial clay underlain by dense sand
prior to developing the site. The coefficient of volume change of the clay, mv, varies
with depth, z, from the top of the alluvial clay such that [mv = 0.1 – 0.01z] m2 /MN.
Calculate the settlement of the alluvial clay assuming:
i. Vacuum consolidation;
ii. or a 3m thick layer of engineered fill.
[8 marks]
(d) A concrete floor of a shed used to store de-icing salt has cracked leading to pollution
of the groundwater. An investigation showed that the floor was made of 150mm thick
10m by 10m lightly reinforced concrete slabs cast onto 0.5m of compacted sand and
gravel. The compacted sand and gravel is underlain by sand with an SPTN60 value of
15. This sand layer is 5m thick and is underlain by weathered sandstone. A forensic
investigation showed that the unit weight of the salt was 12.5kN/m3 and the height of
the stockpile varied from a maximum height of 5m in summer when the salt was stored
to zero at the end of the winter after the salt had been used. The shed is 10 years old
and has been used to store de-icing salt throughout that period. Estimate the
settlement of the floor and comment on whether that is the reason for the cracking.
[8 marks]
(e) Piles are to be used as anchors for ships tied up to a quay wall. Calculate the lateral
resistance of the 0.5 diameter 5m long concrete pile shown in Figure A1e. The piles
are installed in engineered fill, which is formed of coarse-grained soil. The river level
is 2m below ground level. Assume the unit weight of the engineered fill above the
ground water level is 16kN/m3 and, below the ground water level 19kN/m3 . The
angle of friction of the fill is 35o .
Figure A1e Cross section of a quay wall showing the location of the 5m long 0.5m diameter
anchor pile
[8 marks]Module code: CIVE5975M01
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Section B
2.
A 20m diameter, 10m high oil tank is to be built as part of a tank farm. The tank weighs 238
tonnes when empty. The site is underlain by 5m alluvial clays. The alluvial clays are
underlain by sand, which has an SPTN60 value of 25. Prior to construction, the 0.3m thick
layer of topsoil will be removed. The top soil will be replaced with a 1m thick compacted
gravel platform with a geogrid layer to allow access for the construction vehicles and form
the foundation for the oil tank. The alluvial clay is 10m thick and is underlain by dense sand
and its properties are given in Table B2. The ground water level is at 1m below the original
ground surface.
The integrity of the tank will be tested by filling it with water. This will have to be carried
out in stages to allow the clay to consolidate thus preventing failure during filling.
(a) Determine the maximum level of water at the end of the first stage of filling.
(b) Determine the settlement at the end of the first stage of filling.
(c) Determine the time for the settlement to occur at the end of the first stage of filling.
(d) Suggest three methods to accelerate the construction programme.
Unit weight
16kN/m3
Undrained shear strength
15kPa
Vertical coefficient of consolidation
1.5m2 /yr
Coefficient of volume compressibility
0.9m2 /MN
Table B2 The properties of the alluvial clays
[20 marks]
3.
0.3m diameter cfa piles will be used to support the slurry tank shown in Figure B3. The
ground level around the building will be raised by 2m using coarse grained engineered fill
after the tank is built so that the new ground level is level with the top of the tank. Assume
that the walls and floor of the concrete tank are 0.2m thick and the density of the slurry is
1100kg/m3 .
(a) Produce a diagram showing the forces acting on the pile group and calculate the
maximum load on the pile group.
(b) Determine the number and length of piles using a global factor of safety of 2.
Figure B3 Cross section showing the soil profile and location of tank (note the piles are not shown)
[20 marks]Module code: CIVE5975M01
Page 5 of 5
END
4.
A 15m high, 8m diameter steel grain silo sits on a square reinforced concrete slab, which
rests on firm to stiff clay. The slab is 2m deep with the formation level at 1.5m below ground
level. Details of the ground conditions are given in Table B4. The mass of the silo including
the weight of the foundation is 45 tonnes. The silo stores grain with a density of 790kg/m3 .
The maximum wind load produces a horizontal force of 30kN acting at 10m above ground
level.
(a) Determine the maximum and minimum contact stress between the base of the
foundation and the soil.
(b) Check that the concrete slab would provide a stable foundation that satisfies Design
Approach 1 Combination 1.
Unit weight
18kN/m3
Undrained shear strength
0.7σv’
Coefficient of consolidation
1.5m2 /yr
Coefficient of volume compressibility
0.5m2 /MN
Ground water level
1m bgl
Table B4
Soil profile and properties
[20 marks]
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