Soil Investigation of a Collapsed Building Site in Jos, Nigeria

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SSRG International Journal of Recent Engineering Science Volume 8 Issue 5, 1-5, Sep-Oct, 2021
ISSN: 2349 – 7157 /doi:10.14445/23497157/IJRES-V8I5P101 © 2021 Seventh Sense Research Group®
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Research Article
Soil Investigation of a Collapsed Building Site in
Jos, Nigeria
Timothy Danjuma1, Mbimda Ali Mbishida2, Ephraim Maude Haruna3, Benjamin Yusuf Mailafiya4
1,2,4 Department of Building Research, Nigerian Building & Road Research Institute (NBRRI) North-Central Zonal Office Jos,
Plateau State, Nigeria
3Department of Road Research, Nigerian Building & Road Research Institute (NBRRI) North-Central Zonal Office Jos,
Plateau State, Nigeria
Received Date: 18 August 2021
Revised Date: 23 September 2021
Accepted Date: 05 October 2021
Abstract – This investigation was conducted on soil samples
collected from a site of the collapsed building in Jos,
Nigeria, with the aim to serve as a reference document to
Engineers, Designers, and Builders in the building
profession. Two test pits of 0.4m x 1.2m located within the
premises of the collapsed building were excavated at a depth
of 0.6m, 1.0m, and 1.2m, at which samples were collected at
each depth. The Soil Investigation was drawn in such that
only vital tests that will provide the parameters required for
the desire and construction of the foundation were carried
out. These tests conducted include: Sub-soil investigation,
sieve analysis using the wet sieving procedure, Atterberg
limit test in order to classify the soil according to the Unified
Soil Classification System, and shear strength using triaxial
compression test, which was further used to determine the
soil bearing capacity. The results obtained shows that the
soil has slight to medium expansion and compressibility with
poor drainage. The shear strength parameters obtained from
trial pits MAE 2 at 1.0m yielded the least angle of internal
friction of 60 with high cohesion values of 150N/m2. The
highest cohesion values obtained were from test pit 1, which
suggests that the soil contains an appreciable amount of clay
and silt fractions. The allowable/safe bearing value was
found to be 234.5 KN/m2, which suggests that the soil is
cohesive, consisting of clayed materials.
Keywords — Soil, Bearing capacity, Shear strength,
Atterberg limit
I. INTRODUCTION
Building collapse is a global phenomenon but more
prevalent in the developing countries. Between 2011 and
2012, high incidences of building collapse were recorded in
Nigeria, with the highest in Lagos (60%), followed by Abuja
(20%), Port Harcourt (10%), and others (10%). The
frequency of its occurrence though reduced, is of great
concern to every Nigerian, especially stakeholders in the
built environment [1].
Buildings are primarily used for living, working, and storage.
They can be categorized them into three broad types. The
first is the monumental structures which comprise the
religious buildings like Churches and so on, city halls, and
sports arenas. The second is the institutional structures
represented by the more usual kind, such as a block of flats,
tertiary institutional buildings for academic and
administrative purposes. The third group comprises the
industrial structures represented by the ordinary small-scale
industrial types [2].
The site of the collapsed building is located along
Gero Road Bukuru, Jos South Local Government Area of
Plateau State, Nigeria (the savannah vegetation belt of
Northern Nigeria). The collapsed building was constructed to
provide accommodation for teaching and learning for the
pupils of the Bukuru community of Jos. The collapsed
building is a 1-storey building viz; ground floor and first
floor with a courtyard surrounded by existing adjourning
classrooms and neighbouring houses. The Building Structure
includes a hall, laboratory, and five (5) classrooms with a
narrow single loading corridor at the first-floor level.
Bordering the site eastwards, west, and southwards are
buildings constructed with either laterite blocks or sandcrete.
Lying north is an access road. As a result of many years of
weathering, and decomposition in a tropical environment, the
soil on the site has transformed into laterite soil. The
underlying rock seems to have decomposed, leaving a
relatively hard material that has a grave texture mixed with
some clayey materials.
It was reported that this building collapse was the third
incident that occurred in that community in the span of two
(2) years. As such, this paper is intended to investigate the
soil on which the said structure was build upon, and hence
serve as a reference document to Engineers, Designers, and
Builders in the building profession. The recommendations
will also help to reduce the rate and severity of building
collapse, especially in that particular community and the
nation at large.

Timothy Danjuma et al. / IJRES, 8(5), 1-5, 2021
2
PLATE I: The Partially collapsed areas
Source: field survey
II. MATERIALS AND METHOD
The investigation was conducted on soil samples
collected from the site of the school. Two test pits of 0.4m x
1.2m located within the premises of the school were
excavated. Burrow Pit 1 was at a coordinate of 9.7977N and
8.8635E. Burrow Pit 2 was at a coordinate of 9.9799N and
8.8638E. A summary of the detailed borehole drilling is
given in Table 4. There was continuous sampling with
inspection for logging purposes throughout the depths of the
test pits. The pits were dug manually to a depth of 0.6m,
1.0m, 1.2m. Samples were taken at these depths (by driving
in the sampler) in a polythene bags and plastic tins so as to
preserve the natural moisture content of the samples.
The Soil tests were conducted in accordance with
standards [3]. Field logging was in line with the international
format. Results for the test are presented in tabular form.
A. Materials and Equipment
The material used includes the soil sample dug from the
site, while the equipment used includes the following,
Compaction Rammer, Compaction mold, Electronic top-
loading Balance, Semi-Automatic Digital Cone
Penetrometer – BS:1377, Spatula, Sieve Brush, Aluminum
Scoop, Glass Plate, Moisture Content Tin, and Laboratory
Oven.
B. Method
a) Sieve Analysis through the Wet Sieving Procedure
Firstly, the specimen to be used for the simple dry
sieving analysis was obtained from the original sample
obtained from the site by riffling, or by subdivision using the
cone-and-quarter method. The specimen was placed on a tray
and was allowed to dry overnight, in an oven maintained at
105-110 °C [4]. Thereafter, it was allowed to cool and was
weighted.
The dried soil sample was then placed in the topmost
sieve and was shaken long enough that all particles smaller
than each aperture size could pass through. The whole nest of
sieves with receiving pan was placed in the shaker, the dried
soil was placed in the top sieve, which was then fitted with
the lid, and the sieves were securely fastened down in the
machine. The sand retained on each sieve is transferred to a
weighed container. Any particle lodged in the apertures of
the sieve was carefully removed with a sieve brush, the sieve
being first placed upside-down on a tray. These particles
were added to those retained on the sieve. The masses
retained (Ms1, Ms2, etc.) were recorded against the sieve.
b) Atterberg Limit Test
The Atterberg limit tests, which were basically
moisture contents at different limit levels, were carried out to
determine the plastic and liquid limits of the fine grain soil.
Engineering properties of the soil were correlated to those
limits and were used to classify the fine soil according to the
Unified Soil Classification System. The test was performed
in accordance with the recommendations of [5].
c) Shear strength of the soil using triaxial compression test
Shear strength is defined as the maximum shear stress that
the soil may sustain without experiencing failure. Shear
strength is a critical parameter in geotechnical projects. It is
needed to derive the bearing capacity, design retaining walls,
evaluate the stability of slopes and embankments, etc. [6].
The triaxial test is highly versatile; a variety of stress and
drainage conditions can be employed. The cylindrical soil
specimen is enclosed within a thin rubber membrane and
placed inside a triaxial cell. The cell is then filled with a
fluid. As pressure is applied to the fluid in the cell, the
specimen is subjected to a hydrostatic stress. Drainage from
the specimen is provided through the porous stone at the
bottom, and the volume change was measured [7].
II. RESULTS AND DISCUSSION
Table 1 presents the borehole drilling
details, which include the sampling depth excavated, pit size,
drilling method, and type of sampling.
Table 1: Borehole Drilling Details
Test
Pit
No.
Sampling
Depth
Excavated
[m]
Pit Size
[m]
Drilling
Method
Type of
Sampling
1
0.6, 1.2
0.4X1.2
Manual
Undisturbed
2
1.0, 1.5
0.8X1.2
Manual
Undisturbed
A. Sub-Soil Investigation
Details of the strata encountered during boring showed
little variation in test pit 1 and 2, and are given on the bore-
hole log. The detailed descriptions are summarized as
follows:

Timothy Danjuma et al. / IJRES, 8(5), 1-5, 2021
3
a) Top Soil
The top is dark grayish sandy soil, which is certainly not
suitable for any engineering foundation works. It is shallow,
ranging from 0 to 0.30m. A loamy soil layer with some
gravel was visible in the boreholes from the topsoil to 0.30m
depth. At the depth, the soil was moist and reddish in color
and of a medium dense structure.
b) Lower Soil Stratum
At the bottom of the borehole [0.6m – 1.5m], the stratum
consists of red iron oxide color and is moist. At 0.5m, water
was encountered in test pit 1. The topsoil is a principal of a
medium sandy nature with some gravel and fine material in
both test pits.
Generally, the test pits tended to reveal the existence of a
profile of bedrock or decomposing rock material.
B. Atterberg Limit Test
Table 2 shows the results of the Atterberg limit tests
performed on the soil samples.
Table 2: Result of the Atterberg Limit Test
Sample No
LL
(%)
PL
(%)
PI
(%)
NMC
(%)
MAE (Pit1) @
0.6m
35
31
4
25.2
MAE (Pit 1)
@1.5m
35
27
8
22.45
MAE (Pit 2)
@1.0m
31
19
12
22.6
MAE (Pit 2)
@1.5m
36
30
6
21.0
Plasticity Index was obtained from the two limits;
PI =LL – PL (%) ... 1
Where PI = Plasticity Index
LL = Liquid Limit
PI = Plastic Index
From Table 2 using the Unified Soil Classification
System (USCS) [8], the soil samples could be said to fall
within the clayey sand (SC) group. Since the plot of LL
against PL was above line A of USCS chart, it shows that the
soil is composed of inorganic clays of medium plasticity.
These soils generally have slight to medium expansion and
compressibility with poor drainage.
C. Shear Strength Parameters
Table 3 showed high values of cohesion 'c' which may
subsequently increase the value of the bearing capacities of
the soil.
Table 3: Shear Strength Parameters
LOCATION
Shear Strength Parameters
Cohesion, c
(KN/m2)
Angle of Shearing
Resistance Ø (0)
MAE1 (Pit1) @0.6m
120
22
MAE1 (Pit1) @1.5m
200
22
MAE1 (Pit 2) @1.0m
150
6
MAE1 (Pit 2) @1.5m
150
25
The triaxial test is one of the most versatile and
widely performed geotechnical laboratory tests, allowing the
shear strength and stiffness of soil and rock to be determined
for use in geotechnical design. Advantages over simpler
procedures, such as the direct shear test, include the ability to
control specimen drainage and take measurements of pore
water pressures. Primary parameters obtained from the test
may include the angle of shearing resistance ϕ΄, cohesion c΄,
and undrained shear strength cu, although other parameters
such as the shear stiffness G, compression index Cc, and
permeability k may also be determined [7].
The shear strength parameters obtained for the soil
samples collected at 0.60m, 1.0m, and 1.5m depths are
presented in Table 3. Samples collected from trial pits MAE
2 at 1.0m yielded the least angle of internal friction of 60 with
high cohesion values of 150N/m2. The highest cohesion
values obtained were from test pit 1, which suggests that the
soil contains an appreciable amount of clay and silt fractions
[1]. The values were used as indices for the determination of
the bearing capacity factors Nc, Nq, and Ny, respectively.
D. Soil Bearing Capacity
Undisturbed specimens were extracted from the depth of
0.60m and 1.5m for triaxial tests in test pit 1 and at a depth
of 1.0m and 1.5m in test pit 2. Laboratory extrusion of
undisturbed specimens for the triaxial tests showed low
recovery of the soil at 1.5meters for both pit 1 and 2,
possibly because of their nature which was either
decomposed rock mineral or sand with some gravel.
Based on the Mohr-Coulomb failure envelope [7, 9]
obtained from the triaxial shear test, the values of soil
cohesion, c, and angle of internal friction, were obtained and
used to obtain the internal bearing capacity of the soil in
accordance with rigorous bearing capacity formulae for
square and strip footings, with partial safety factors of 1.25,
1.50 and 1.75 for unit weight, angle of internal friction and
cohesion, respectively, with a global load Safety factor of
3.0. The undisturbed specimen from 1.5metres depth was
used to compute. The bearing capacities were computed
based on the rigorous process using the first principle to
yield the equation:
Qult = (1 + 0.3𝐵
𝐿).c. Nc + γ. z. Nq + (1 - 0.2𝐵
𝐿). γ . B . Nγ …2
Where:

Timothy Danjuma et al. / IJRES, 8(5), 1-5, 2021
4
Nq = eπ.tan.ø .tan2(π
4 + ø
2 );
Nc = (Nq – 1) cot ø;
Nγ = 1.5 (Nq – 1) tan ø
Known as bearing capacity factors, while:
c is the cohesion in KN/m2
γ is the soils unit weight in KN/m3
z = Df is the depth of foundation in meters
B and L are the lateral dimensions in meters, which
for square footings, B = L, and applying other
factors, gives the Terzaghi equation for square
foundations as:
Qult = 1.3cNc+ γ. z. Nq +0.4γBNγ … 3
Based on partial safety factors of 1.25, 1.50 and
1.75 on γ, ø, and c, respectively, and a load factor F = 3.0,
the computations of ultimate, qult; safe, qs; and allowable, qall,
bearing capacity can be made based on:
Øs = tan-1(tan ø
𝑓ø ); qall = qs
𝐹 … 4
Table 4: Bearing Capacity Factors: Nc, Nq, and Ny
PI
T
Dep
th
M
Factors For Ultimate
Bearing Capacity
Factors For Safe
Bearing Capacity
Ø
Nq
Nc
Ny
Øs
Nq
s
Ncs
Nys
1
0.6
22.
0
7.8
2
16.
88
4.1
3
15.
1
3.9
8
11.
04
1.2
1
1.5
22.
0
7.8
2
16.
88
4.1
3
15.
1
3.9
8
11.
04
1.2
1
2
1.0
6.0
1.7
2
6.8
1
0.1
1
4.0
1.4
3
6.1
9
0.5
0
1.5
25.
0
10.
66
20.
72
6.7
5
17.
3
4.9
0
12.
54
1.8
2
Ø in Degrees
Taking ground water-table on the ground surface for
the worst conditions based on a nominal footing width of
1.0metre, the unit weights based on measurements are as
follows:
Table 5: Bearing Capacity Factor Values (KN/m2)
PI
T
Dept
h
M
Average
Densities
Average Unit
Weights
γsat,
KN/
m2
C,
KN/
m2
℮b,
g/c
c
℮b,
g/c
c
γb,
KN/
m2
γb,
KN/
m2
1
0.6
1.9
5
1.5
6
19.13
15.30
21.81
120
1.5
2.0
1.8
20.50
17.66
22.81
200
9
0
2
1.0
2.0
2
1.6
3
19.82
15.99
21.81
150
1.5
1.9
2
1.5
9
18.84
15.60
20.81
150
An average saturated unit weight, γsat, of 21.81
KN/m2 was adopted for all computations.
Table 6: Bearing Capacity Factor Values (KN/m2)
PIT
Depth
M
Bearing Capacity Values, KN/m2
qult
qs
qall
1
0.6
2709.4
1011.7
337.2
1.5
4549.4
1702.2
567.4
2
1.0
1349.1
703.5
234.5
1.5
4264.7
1474.9
491.6
From the table, the least allowable bearing capacity obtained
for the site is 234.5 KN/m2, which is adopted as the design
allowable bearing capacity to be used for all foundation
computations.
IV. CONCLUSION AND RECOMMENDATION
The following conclusions were drawn from this
investigation:
I. Based on the result of the Atterberg limit test
obtained and using [5], the soil tested is composed
of inorganic clays of medium plasticity. These soils
generally have slight to medium expansion and
compressibility with poor drainage.
II. For pad foundation practice, it is recommended that
the footing levels should be of a minimum depth of
1.5m below the natural ground. However, what was
measured on site was less than 1.5m.
III. The allowable/safe bearing capacity obtained from
the site is 234.5 KN/m2, which should have been
adopted as the design allowable bearing capacity to
be used for all foundation computations, but that
was not used.
IV. The soil at the site seems to be made up of ground.
V. Lastly, it is strongly recommended that the design
and construction of the future superstructure at the
site should be carried out in accordance with good
engineering practice as embodies in recognized
codes of practice such as the British Standard
institutions BS 6031: 1981, Code of Practice for
Earthworks and BS 8004: 1986, Code of Practice
for Foundation.
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