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ESE 60016 © Imperial College London
IMPERIAL COLLEGE LONDON
BSc and MSci EXAMINATION 2022
For internal students of Imperial College London
Taken by students of Geoscience
This paper is also taken for the relevant examination for the Associateship of the
Royal School of Mines
ESE 60016 GEOLOGICAL & COASTAL ENGINEERING
Monday 16 May 2022 from 11:00 BST
Duration: 90 Minutes
Total Marks: 100
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Page 2 of 5 ESE 60016 © Imperial College London
SECTION A (40%)
Answer ALL questions
1. (i) Explain how the point load strength test is performed. How might it be used
in combination with other site data to guide the selection of excavation
method for in-situ rock masses? (5 marks)
(ii) In a quarry rock blast, explain the mechanisms responsible from the moment
of detonation through fragmenting the rock and producing a blast pile on the
quarry floor. Hint: your answer should include strength of rock in relation to
the type of stress waves generated. (5 marks)
2. A horizontal cylindrical tunnel is to be bored with its axis at 300 m depth in rock
with an average overburden density of 2,600 kg/m
3
. Assume the tunnel is
contained within a very thick horizontal bed of massive limestone and that the
rock mass strength can be assumed to be the same as the intact strength of the
limestone.
The region falls within a strike-slip tectonic regime with Maximum Horizontal
stress,
H
and Minimum horizontal stress,
h
striking E-W and N-S respectively.
The in-situ stress ratios are given as
H/
v
= 1.5 and
h/
v
=0.6. The Unconfined
Compressive Strength of the limestone is 25 MPa.
(i) If the tunnel is running North-South, calculate the compressive (hoop) stress
in the mid roof and in the mid sidewall positions and explain why or why not
there is likely to be shear failure when considering each of these positions if
there is no support. (8 marks)
3. A rock revetment has been designed in accordance with the Van der Meer
equations to permit only an acceptable amount of damage for a given 100-year
design condition. This design is based on a local source of limestone with a rock
density of 2.50 t/m
3
. The design mass for the individual pieces of armourstone,
M50 is 8 t and a specified grading is 6-10 t armour.
The contractor has discovered a source of gabbro with similar shape
characteristics and with a density of 3.2 t/m
3
but the block sizes available in the
quarry are such that they can only supply armourstone in the range 3 to 6
tonnes.
(i) Assume for this calculation that the seawater has the same density as fresh
water. Using the alternative density rock source, i.e. the gabbro, calculate
the M50 required to give an identical stability to the original design and
thereby discuss if the smaller available grading of denser armour will give
greater, less or about the same stability. (7 marks)
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Page 3 of 5 ESE 60016 © Imperial College London
4. The accompanying figure (Fig. Q4) is a diagram used to explain quantitatively
the results from rock blasting using two different blast designs, one for
armourstone production and one for aggregates production. Three size
distributions from a particular quarry (Quarry A) have been idealised in the form
of the Rosin Rammler equation, as given in Fig. Q4.
(i) Explain the terms BBSD and IBSD. Describe how the BBSD can be rapidly
assessed for real blast piles. (3 marks)
(ii) Assume 20,000 tonnes of rock are to be blasted in Quarry A. To be clear
with the definition of armourstone in this question, blocks of 1 tonne or
heavier are designated to be of sufficient size to be called armourstone.
Using the coefficients given in the accompanying Fig.Q4 for each BBSD
curve, or otherwise, determine the total armourstone yield (in tonnes) in the
“armourstone blast”. Compare this with the armourstone yield (in tonnes) in
the “aggregates blast”. (4 marks)
(iii) Aggregates between 10 and 60 mm are especially useful and are produced
in the blast from Quarry A without the need for crushing. Determine how
much greater the yield of 10-60 mm aggregates (in tonnes) will be in the
aggregates blast than in the armourstone blast using the blast curves shown
in the accompanying Fig.Q4. (4 marks)
(iv) An investigation of joint spacing in a potential quarry site (Quarry B) has
determined that the IBSD can be estimated using the Rosin Rammler
coefficients, D
50
= 0.5 m, nRRD = 2.00. Discuss the suitability of this quarry
site for the supply to a breakwater project that requires delivery in the
proportion 20% armourstone (pieces heavier than 1 tonne) and 80% for
rockfill. (4 marks)
Fig. Q4
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Page 4 of 5 ESE 60016 © Imperial College London
SECTION B (60%)
Answer TWO questions (from the four to choose from)
5. Tunnel construction projects for highway, rail and water supply are a major
recipient of government revenues for infrastructure projects in developed and
developing countries that have mountainous terrains to traverse.
Describe the role that a geologist’s skills will play in helping to complete such
tunnelling projects, and how these skills combine with the civil engineer’s
systematic methods, tools and skills to design a safely excavated and supported
structure for the tunnelling contractor. (30 marks)
6. Steep and gentle slopes in outcrops of rock masses are ubiquitous in nature’s
landscapes. For man-made highways, open pits and quarries, geological
engineers assess the cut slope faces that will provide an acceptable level of
protection from risk of slope failure.
(i) In rock slope stability design, explain what is meant by
(a) kinematic stability analysis
(b) limit equilibrium analysis, and
(c) describe a scenario for which a two-dimensional limit equilibrium
analysis can guide the main design decisions regarding drainage and
bolting requirements.
(5 marks)
(ii) A highway is to traverse a ridge of sedimentary rocks but is not going fully
over the top and will have substantial cuttings as it reaches the highest
section. You are given the highway orientation azimuth and the discontinuity
data for dip and dip direction from the geological structural mapping of ample
surface outcrops along the route of the highway. You are presented with the
task of finding the maximum safe slopes for cut slope faces on either side of
this highway. The task addresses the general case, taking account of plane,
wedge and flexural toppling failure, given the prior knowledge that the
bedding and two dominant joint sets are well-represented throughout the
region and without much angular variation.
(a) Present a detailed step-by-step description of the stereo-net methods
you would use to complete your task. Your presentation should include
sketches and any assumptions you will need to make. (20 marks)
(b) Explain which type of failure mechanism is likely to be most problematic
if there are steep bedding planes striking with a direction almost parallel
to the road’s azimuth. (5 marks)
PAPER CONTINUES ON NEXT PAGE
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Page 5 of 5 ESE 60016 © Imperial College London
7. The design of rubble mound coastal structures built out of quarried rock was for
many decades based on an empirical formula by Hudson which is still widely
used and sometimes extended to concrete unit rubble mound structures,
especially breakwaters. The formula was improved upon by the Van der Meer
equations in the 1980’s.
(i) Write down the Hudson formula, listing and defining all its variables.
Describe the experiments and data analysis Hudson would have needed to
perform to create his formula. (7 marks)
(ii) Show how Hudson’s formula can be rearranged to define the Stability
Number, N
s
in terms of two dimensionless numbers, and how this in turn
sets the armour characteristics needed for the wave height of the design
storm for a given coastal site. (7 marks)
(iii) For rock armour structures, outline the key improvements that were
introduced in the Van der Meer equations that led to greater confidence in
the reliability of a breakwater design compared with the Hudson formula.
Explain why two equations were needed. (8 marks)
(iv) In the 1970’s and 1980’s a great many breakwaters suffered failures, most
notably, the Sines Breakwater in Portugal. Discuss the difference between
structural stability and hydraulic stability of rubble mound coastal structures.
Explain the likely cause for the several deep-water breakwater failures
during these two decades and how modern 21
st
century design practices
have lessened the likelihood of such failures taking place. (8 marks)
8. Phase II of the Environmental Improvements at Lyme Regis completed in 2007,
together with Phase IV, completed in 2014, have been heralded in the local
press as tremendous successes for the economy of the town, despite the
disruption during construction.
(i) Describe the processes and mechanisms that were responsible for the
coastal and landslide problems addressed by Phase II and explain how the
type of design solution for the foreshore protection was arrived at and tested.
(10 marks)
(ii) For the Phase IV works to the East of Lyme Regis, outline the motivation
and objectives of this works phase, the solutions adopted, and why you think
possible alternative solutions using rock armour were not chosen.
(15 marks)
(iii) Briefly discuss the evidence that the 2008 landslide closely follows a hybrid
failure mechanism, one that combines translational sliding on a plane of low
shear strength with rotational slip due to lack of cohesive strength in the
overlying mudstone. (5 marks)
END OF EXAMINATION
