ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
48th Ghana Institution of Engineers (GhIE) Annual Conference, Sunyani,
Brong-Ahafo, Ghana, March 2017
GHANA’S NATURAL RESOURCES AND SUSTAINABLE DEVELOPMENT –
THE ROLE OF THE ENGINEER
The Story of a 9-Storey Building Foundation Design for a
Hotel in the Airport Area of Accra
B. D. Atarigiya, P. Amankwah, I. Osei, N. K. Allotey, J. Oddei, & W. Albert-Viala
[Engineering Service Provision Company Ltd.]
REFEREED PAPER
Abstract
In light of the recent collapse of buildings in Ghana, and also the protection of professional integrity, it
has become imperative to exercise great caution in the design and review of engineering works, especially
when dealing as a third party consultant. This paper narrates the story of the review of a 9-storey
building design that ended up in a total overhaul of the whole design; i.e., from the architectural concept
to the entire structural and MEP design of the building. The paper focusses mainly on the geotechnical
design of the building foundation since this was a critical part of the redesign, and almost cost the review
design engineer significant embarrassment.
Background
The recent collapse of various structures in Ghana, notably the Achimota Melcom disaster in 2012 has
resulted in loss of property, and most importantly, the loss of human lives. The reasons for these collapses
are varied, including, poor building design, use of inferior construction materials, ignorance, poor regulatory
oversight, unethical behaviour, and also poor/wrong design by built environment professionals. The story of
this hotel building rests greatly on the latter two factors.
The story about this design project started when the building owner wanted to secure a building permit to
start construction of the proposed hotel. The owner was required to come along with “the” structural
engineer (firm) to the Metropolitan Authority to defend the structural drawings, along with a host of other
professionals. The owner contacted our firm (i.e., ESPCo) to represent him. The building owner’s reason
was that the structural engineer who designed the building was not currently available in the country. Our
office informed him that we could only be in a position to do so, if we were provided with the structural
drawings, and were given the opportunity to review them in detail. The building owner agreed to our
request, and that is how our involvement in this project started.
In conducting our review, many inconsistencies in the drawings were noted, examples of which are:
 Inadequately sized columns
 Foundation designs not addressing the geotechnical findings of low bearing capacity
 Lack of any form of ground improvement measures in the foundation drawings
 No sign of seismic ductile detailing
 Some poorly designed beams spanning long lengths with limited supports at the roof level, etc.
These inconsistencies prompted the call for a thorough review of all other designs, and also the need for a
reconnaissance field visit. Upon the field visit, it was noted that the proposed hotel (9-storey) with a
basement was to be placed in a confined area, with 3-storey buildings already constructed on the adjacent
sides of the facility. The space between the existing walls of the adjacent buildings and the plan area of the
proposed building were noted to very be small, some sides even being less than the required width of 3 m.
Considering the findings from the geotechnical investigation report, it was noted that there was the presence
of collapsible soils in the upper 5 - 6 m with an associated high groundwater level. This pointed to the
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ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
possibility of the instability of excavated unprotected slopes below the ground level. At this point, it was
clear that the problem being faced was bigger than rectifying inconsistencies in the structural drawings and
defending it for a permit. Apart from the identified structural and geotechnical issues, later on, while setting
out, the contractor noted that location of the building on the provided area was also wrong. Furthermore, the
mechanical and electrical services designs were noted to be totally flawed. In short, this whole saga later led
to the architectural, structural, geotechnical, mechanical and electrical redesign of the entire building.
In regards to the geotechnical design of the building foundation, the original geotechnical report
recommended shallow foundations below the basement level, i.e., greater than 4 m. The report noted weak
soils composed of collapsible soils with low SPT to about 6 m, and underlain by medium dense decomposed
schist. Furthermore, the report stated that the SPT-N values at 9 m from the two boreholes were 40 and 60,
respectively, and showed a sharp increasing trend pointing to the change from a weathered intermediate
geomaterial type of ground medium to that of firm rock.
Preliminary Foundation Design
Raft Foundation with Basement
The initial foundation choice provided for the building was a raft foundation at about 4 m below the ground
level, with a one-storey basement. Taking into account the adjacent structures and the collapsible soil to a
depth of 6 m, it was decided that there was the need to conduct slope stability analyses to determine the
stability of the proposed excavations. Slope/W (GeoSlope Inc, 2008), a commercial slope stability analysis
programme was used for the analysis. It showed that the excavations were going to be very unstable. Figure
1 shows the output results from Slope/W, showing a factor of safety (FoS) of as low as 0.391, which is less
than the limiting acceptable value, which differs in various jurisdictions, but generally falls between the
range of 1.2 – 2, depending on the type of soil, project size, importance, and risk (WSDOT, 2005).
Figure 1. Slope Stability Analysis
Considered Foundation Alternatives
Due to the instability that would be caused by the foundation excavations, and its impact on adjacent
structures, the raft foundation with the basement was found not to be viable. The option of a raft foundation
without a basement, with the provision of shoring and side bracing, was also considered. This option was,
however, discontinued since it required ground improvement to a significant depth, which was considered
not cost-effective. The only option available was thus to consider the use of deep foundations. Two options
were examined.
 The use of micropiles. This was investigated to quite an extent, but was not continued since the
limited load carrying capacity, rendered the number and length of piles to be on the high side, thus
making the option also not cost-effective.
 Eventually, the final option chosen was the use of conventional bored concrete piles. This was to
be combined with a raft foundation. The cost-benefit analysis of this option was noted to be the
best, and also easily constructible.
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ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
Preliminary Piled Raft Foundation Design
Based on availability and costing, 600 mm augured concrete piles were selected for the project. This section
of the paper only details the background to the preliminary piled raft design, and does not detail the design
itself. This is because, as would be noted below, the design had to be redone due to some totally unforeseen
reasons. This is explained below.
Based on the initial geotechnical report (SPT-N values), an initial length of 10 m was chosen for the
design. The take-down gravity and seismic loads from the structure however showed this length to be
somehow insufficient.
At this stage, since the initial geotechnical investigation was not done by our firm, it was decided that an
additional confirmatory geotechnical investigation be requested for. In this regard, it was agreed to sink two
percussion boreholes to a depth of 10 m to confirm the subsurface condition. The test results showed the
upper 6 m to be consistent with the initial geotechnical report. However, to our dismay and astonishment
there was significant difference in the subsurface condition from 8 m onwards. Whereas, the initial
geotechnical investigation pointed to the presence of increasingly dense weathered rock material at this point
onwards, the confirmatory tests showed the ground condition at this level to be medium dense silty sand.
This new revelation raised eyebrows since the new subsurface conditions could not support the structure,
and as such, there was a need sink the piles far deeper. This resulted in a lot of disagreement between the
geotechnical engineer who performed the confirmatory tests, our firm, the piling contractor, the general
contractor, and the building owner.
A compromise was later reached between all parties that required each party to contribute towards footing
the bill for a third confirmatory percussion borehole. As the design engineers, we were required to closely
monitor this test, to ensure that what the geotechnical engineer provided was truly the ground condition at
the project site. It was also agreed that this percussion borehole be sunk until there was strong resistance to
penetration, signifying the presence of hard/strong ground conditions. The results of this third borehole
confirmed that results obtained by the additional two confirmatory boreholes, thus endorsing the work of the
geotechnical engineer. It must be said that our firm has a long standing working relationship with this
geotechnical engineer, and events up till this point almost marred this long standing relationship.
In summary, it became clear to the entire team that the results of the initial geotechnical investigation were
inaccurate. The lesson to be learnt from this unfortunate incident is that it is advisable to proceed with a lot
of caution when adapting third party data/information for one’s own work!
Pile Raft Foundation Design
General
Based on the second confirmatory geotechnical investigation, 15 m piles were initially investigated. This
was, however, increased to 17.5 m. A pile cap of 1 m depth was also adopted for the pile raft design.
The undrained cohesive strength parameters for the different soil layers were estimated based on SPT – Cu
correlations obtained from the Canadian Foundation Engineering Manual (CFEM, 2006). The values of
unconfined compressive strength (qu) for the weak decomposed rock (intermediate geomaterial) were
obtained from the result of qu tests conducted on similar rocks from two other project sites within the Airport
area. For these sites, they showed the weathered rock material to have very low RQDs (between 10 – 30)
representing poor rock, with an associated qu of between 7 - 9 MPa. The pile input parameters for both the
axial and lateral responses were computed using the approach provided by the API guideline (API, 2014)
These values were used to estimate the required pile axial and lateral load-deformation parameters and
also associated pile capacity parameters. The axial and lateral pile analyses were conducted with
commercial program, ALLPILE (CivilTech, 2011). The program ALLPILE analyzes provide both the axial
and lateral pile load-deformation response and also provides the respective pile load capacities. The
programme is able to consider different types of piles, including: drilled shafts, driven piles auger-cast pile,
steel H and pipe piles, tapered piles, etc. Figure 2 below shows an interface of the ALLPILE program.
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ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
Figure 2. ALLPILE Interface
Source: (AllPile, 2011)
Axial & Lateral Pile Analysis
The axial response of the pile was computed assuming the pile to mobilize strength through both side
friction and end-bearing. The top 3 m of the pile was not accounted for in the side friction computations.
In the axial direction, under gravity loading, the factor of safety (FS) for compression loading was taken
as 2.5 for both side friction and tip resistance. Under seismic loading a FS of 2 was used for both
components.
For the horizontal direction, the piles were assumed to be fixed at the pile head due to the rigid nature of
the pile cap. Based on IBC (2012) recommendations, the ultimate lateral load was taken as the load at 25
mm deflection. It is important to note that the computed deflections, moments and shears take into account
the 2nd order P-delta effects due to the supported axial loads being part of the pile analysis. Also, the pile
capacities include an increased pile resistance contribution due to the presence of the pile cap.
Some summary plots from the ultimate analysis of the pile are shown in the figure below. In addition,
Table 1 provides a summary of the results obtained from analysis.
ALL-PILE
ALL-PILE
CivilTech Software
www.civiltech.com
CivilTech Software
www.civiltech.com
Licensed to
Vertical Load vs. Total Settlement
Licensed to
Concrete poured into drilled hole.
Diameter is limited to 24in (61cm).
FOUNDATION PROFILE & SOIL CONDITIONS
5000
0
FOUNDATION PROPERTIES
Depth
0.0
Width-cm
60
A'-cm2
2827.4
SOIL PROPERTIES
Per.-cm
I'-cm4
E -MPa
W -kN/m
188.5
636172.5
20683
6.673
Depth
0.0
 -kN/m3

C-kN/m2
k-MN/m3
e50 %
Nspt
8.1
0.0
20.0
17.2
1.48
4
Concrete (rough)
Depth
from
Ground-m
0
4500
2
4000
Loose-Medium reddish brown lateritic Fil
2
4
4.0
8.1
0.0
5.0
8.1
0.0
30
64.1
0.98
8
0.69
15
0.66
16
Compression Load, Qdw -kN
Depth
from
Ground-m
4
Firm moist greyish sandy Clay
6
70
147.8
6
Firm moist greyish sandy Clay
7.0
9.5
8
0.0
90
164.2
8
Medium dense yellowish brown grey sandy
9.5
10
9.5
0.0
120
383.3
0.44
31
0.36
43
0.29
86
0.18
150
0.18
200
0.18
300
10
Medium dense yellowish brown grey sandy
12
12
12.5
10.1
13.5
10.1
0.0
160
568.0
Hard yellowish brown greyish sandy Silt
14
0.0
220
788.8
14
14.5
10.3
15.5
10.3
17.5
10.3
0
500
24.8
3000
2500
2000
1500
1000
Hard yellowish brown greyish sandy Silt
16
3500
16
Very weak decomposed sandy silt Schist
18
17.5
0
1000
24.8
0
1500
24.8
500
18
Very weak decomposed sandy silt Schist
Weak decomposed sandy silt Schist
20
0
20
22
22
24
24
26
26
28
28
0.0
0.5
1.0
1.5
2.0
30
Batter Angle=0
Figure
3a. Soil
CivilTech
Software
Characteristics
(Pile diameter not to scale)
Layering
Surface Angle=0
and
Side
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
Total Settlement, X -cm
Total
30
2.5
CivilTech
Software
Friction
Side
Tip
Figure 3b. Vertical Load Deformation Curves
Figure 1
4
Figure 1
10.0
ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
ALL-PILE
CivilTech Software
www.civiltech.com
Licensed to
PILE DEFLECTION & FORCE vs DEPTH
Single Pile, Khead=5, Kbc=2
Depth (Zp)
from
Pile T op-m
0
DEFLECTION, yt -cm
-5.00
0
MOMENT -kN-m
+5.00
-1000
0
SHEAR -kN
+1000
-500
0
+500
G-kN/m3
Phi
C-kN/m2
k-MN/m3 e50 %
8.1
0.0
20.0
17.2
1.48
Loose-Medium reddish brown lateritic Fil
2
Depth (Zp)
from
Pile T op-m
0
2
4
6
yt=0 at 6.7-m
St=0 at 0.2-m
8.1
0.0
30
64.1
0.98
Firm moist greyish sandy Clay
8.1
0.0
70
147.8
0.69
Firm moist greyish sandy Clay
9.5
0.0
90
164.2
0.66
Medium dense yellowish brown grey sandy
8
9.5
0.0
120
383.3
0.44
Medium dense yellowish brown grey sandy
10
12
4
6
8
10
12
10.1
0.0
160
568.0
0.36
Hard yellowish brown greyish sandy Silt
14
10.1
0.0
220
788.8
0.29
Hard yellowish brown greyish sandy Silt
10.3
0
500
24.8
0.18
Very weak decomposed sandy silt Schist
16
18
T ip yt=-4.93E-16
T op yt=2.5E+0
Max. yt=2.5E+0
T op St=0E+0
T op Moment=-557.0
Max. Moment=557.0
T op Shear=221.0
Max. Shear=221.0
10.3
0
1000
24.8
0.18
Very weak decomposed sandy silt Schist
Last Section: E -MPa=20683
10.3
0
1500
24.8
0.18
Last Section: I'-cm4=636173
Weak decomposed sandy silt Schist
14
16
18
20
20
22
22
24
Figure 4. Summary of Ultimate Lateral Load Analysis Plots
24
26
26
28
28
Table 1. Summary of Axial & Lateral Pile Loading Results
30
AxialCivilTech
Load Results
Software
30
ValueFigure
(kN)
2
Ultimate Compression load
5300
Allowable Compression load - Gravity
2000
Allowable Compression load – Seismic
3000
Ultimate Uplift load
3000
Allowable Uplift load - Gravity
1200
Allowable Uplift load - Seismic
1700
Lateral Load Results
Value (kN)
Ultimate Lateral load (at 25 mm deflection)
370
Allowable Lateral load (half ultimate – IBC 2012)
240
Structure-Pile-Soil-Interaction Analysis
Based on the axial and lateral load-deformation responses, the effective vertical and horizontal pile
stiffnesses were computed. These were then entered into the CSI SAFE analysis programme to conduct the
structure-pile-soil interaction analyses. The foundation action forces (i.e., gravity and seismic action forces),
raft pile cap geometry, load cases and combinations were exported from CSI ETABS building analysis
programme to SAFE. Additional overburden soil surcharge was applied to the model where required, and
modulus of subgrade reaction springs were also placed under the raft foundation, in addition to the lateral
and axial pile springs computed from the ALLPILE analysis. Pile group effect was considered in the
analysis in an overall manner by reducing the axial and laterally computed pile stiffnesses.
From the various analyses, it was noted that the gravity load case impacted considerably piles within the
vicinity of the highly loaded columns. On the other hand, the seismic load combinations were observed to
highly impact the columns within the vicinity of the core walls. In fact, the seismic load cases were the cases
in which it was very difficult to satisfy the required maximum pile load limits. From the optimization
analysis conducted, a total number of 103 – 600 mm augured concrete bored piles were observed to be
required.
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ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
Figure 5a. Vertical Pile Forces for Building
Portion A under Gravity Loading
Figure 5b. Horizontal Pile Forces for Building
Portion B under Seismic Loading
Conclusions
This paper has provided a summary of the design of a piled raft foundation for a 9-storey hotel building in
the Airport area of Accra. The design had been provided by a team of earlier professionals. A preliminary
review of the design showed a number of flaws in virtually all the required disciplines that needed to be
rectified. Particularly significant was the foundation design that needed to redesigned. Among the options
considered, a piled raft foundation with concrete bored piles was chosen.
The initial design of the piled raft foundation had to be redone since the initial geotechnical investigation
was found to be incorrect. This led to some level of mistrust developing between the various project team
members. Upon carrying out a second confirmatory field boring, it became clear that the initial geotechnical
results had been cooked. This unethical behaviour was both surprising and astonishing, and could have led
to a totally wrong foundation design, that would have resulted in the hotel building experiencing overly
large settlements. The following lessons have been learnt by our engineering firm from this experience:
 It is important (even crucial) to undertake a confirmatory geotechnical assessment when in doubt
about any findings from a third-party consultant.
 Pragmatic stakeholder discussions are critical in projects of this nature, especially when project
cost can be significantly affected.
 The review of a third party consultant’s project documents is very critical in order to achieve
project goals and to avert any discrepancies, so as to safeguard the Client’s investments.
 No matter the rules governing engineering practice, there would certainly be some criminal
elements who would flout the ethical requirements of the profession.
References
API RP-WSD (2014), Recommended Practice for Planning Design and Construction of Fixed Offshore
Platforms, Working Stress Design, American Petroleum Institute, Houston, TX, US.
CFEM (2006) Canadian Foundation Engineering Manual, 4th Edition, Canadian Geotechnical Society,
Bitech Publishers, Vancouver, BC, Canada.
CivilTech (2011), AllPile Ves. 7, Pile Design and Analysis Software, CivilTech Software, US.
CSI ETABS (2015). Structural software for building analysis and design, 2015 Version, Computers &
Structures International, Berkeley, CA.
CSI SAFE (2012). Concrete slab and foundation design software, 2012 Version, Computers & Structures
International, Berkeley, CA.
GeoSlope Inc, (2008) Slope Stability Modeling with Slope/W 2007 Version, An Engineering
Methodology, 3rd Edition, Geo-Slope International Ltd., Calgary, AB, Canada.
WSDOT (2005) Chapter 10 - Slope cut design, Geotechnical Design Manual, M46-03, Washington State
Department of Transportation, Seattle, Washington, US.
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ATARIGIYA, AMANKWAH, OSEI, ALLOTEY, ODDEI & ALBERT-VIALA
Contact details
Brendan D. Atarigiya
ESPCo
# 5 Mankralo Close, East Cantoments, Accra
Tel: (+233) 020 9461321
Email: brendanatarigiya@live.com
Phillip Amankwah
ESPCo
# 5 Mankralo Close, East Cantoments, Accra
Tel: (+233) 020 9461321
Email: pamankwa@espco-gh.com
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