Faculty o Physical Sciences - University of Nigeria

INTEGRATING SOME GEOTECHNICAL AND GEOPHYSICAL

METHODS IN ASSESSING FREQUENT BUILDING COLLAPSE IN

AKPUGO, NKANU WEST L.G.A., ENUGU STATE, NIGERIA

Digitally Signed by: Content manager’s

DN : CN = Weabmaster’s name

O= University of Nigeria, Nsukka

OU = Innovation Centre

ORJI ANN N.

Faculty of Physical Sciences

Department of Geology




UNA, CHUKU OKORO

PG/M.SC/12/6460

: Content manager’s Name

Weabmaster’s name

a, Nsukka




INTEGRATING SOME GEOTECHNICAL AND GEOPHYSICAL METHODS IN

ASSESSING FREQUENT BUILDING COLLAPSE IN AKPUGO, NKANU WEST L.G.A.,

ENUGU STATE, NIGERIA.

A PROJECT SUMMITTED TO THE DEPARTMENT OF GEOLOGY, FACULTY OF

PHYSICAL SCIENCES, UNIVERSITY OF NIGERIA,NSUKKA, IN PARTIAL

FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF

SCIENCE

BY

UNA, CHUKU OKORO

PG/M.SC/12/64604

APRIL, 2014

TITLE PAGE

INTEGRATING SOME GEOTECHNICAL AND GEOPHYSICAL METHODS IN

ASSESSING FREQUENT BUILDING COLLAPSE IN AKPUGO, NKANU WEST L.G.A.,

ENUGU STATE, NIGERIA.

CERTIFICATION

The work embodied in this project is original and has not been submitted in full or part for any

other degree or professional qualification for this or any other university.

UNA, CHUKU OKORO

PG/M.SC/12/64604

APPROVAL PAGE

Mr Una, Chuku Okoro, a post graduate student of Department of Geology has satisfactorily

completed the requirements in research work for the degree of Masters of Science (M.Sc.) in

Geology with option in Engineering Geology

-------------------------------------------- -------------------------------------

----------

Dr Igwe Ogbonnaya Prof. O. P. Umeji

(Supervisor) (Head of Department)

--------------------------------------------

External Examiner

DEDICATION

This work is dedicated to God Almighty for his mercies and love in my life.

ACKNOWLEDGEMENT

I wish to express my profound gratitude to my supervisor, Dr Igwe Ogbonnaya for

making this research work a reality, I also want to appreciate Mr Okechukwu N and other

lecturers in the department of Geology University of Nigeria, Nsukka for the part they played in

making this work a success. I appreciate my colleagues ( Raph, Abiye, Nnamani, Reuben,

Tochukwu, Emma and Mallam Degree) for their efforts in making this masters programme a

reality. I wish to acknowledge the help of Engr Nwabueze of Civil Engineering Laboratory,

University of Nigeria, Nsukka and all the staff of Kabia laboratories limited Enugu.

I Will not fail to acknowledge my family members and my friend Stella for their support and

prayers during this period.

Finally, I thank the Almighty God for His favour, health and everything He has done for me.

ABSTRACT

Over the years, the people of Akpugo in Nkanu West L.G.A., Enugu State, South-East Nigeria

have suffered from frequent building collapse without knowing the cause. This study integrates

geotechnical and geophysical techniques to evaluate the factors responsible for this phenomenon.

Areas with cracked and non-cracked buildings were studied to assess the geotechnical properties

of the soils. Samples were taken at different locations and subjected to x-ray diffraction analysis

(XRD), grain size analysis, specific gravity, Atterberg limits, permeability, compaction and

triaxial tests. Electrical resistivity method was also used to delineate the geo-electrical layers and

to image the lateral variations of the sub-surface. Results revealed that problematic zone (areas

with cracked buildings) have low permeability (4.018– 7.016x10-7

m/sec), lower angle of

shearing resistance (10 – 14o), and medium to high plasticity index (25.1 - 38.33), while the Non-

problematic zone (areas without cracked buildings) have higher permeability (1.55 – 1.925 x 10-6

m/sec), higher angle of shearing resistance (15 – 18o), and low plasticity index (18.1 - 19.4). The

X-Ray diffraction results of the problematic zone revealed significant amount of smectite which

has a very high swelling and shrinkage potential. The presence of significant amount of smectite

in the soils of the problematic zone may be a strong factor in the structural problems. The

electrical resistivity profiling clearly delineated the boundary between the problematic zone and

non-problematic zone and showed that the problematic zone has lower resistivity values (2 –

25Ωm) while the non-problematic zone has higher resistivity values (20–170Ωm).

TABLE OF CONTENTS

Title Page …………………………………………………………………………… i

Certification ……………………………………………………………………….... iii

Approval …………………………………………………………………………… .. iv

Dedication…………………………………………………………………………… v

Acknowledgements………………………………………………………………….. vi

Abstract……………………………………………………………………………… vii

Table of Contents …………………………………………………………………… viii

List of Figures……………………………………………………………………… .. xi

List of Tables………………………………………………………………………… xiii

List of Appendices…………………………………………………………………… xiv

CHAPTER ONE: INTRODUCTION……………………………………………… 1

1.1 Preamble……………………………………………………………………… 1

1.2 Statement of Problem ………………………………………………………… 2

1.3 Aims and Objectives …………………………………………………………… 2

1.4 Study Area Description ……………………………………………………….. 5

1.4.1 Location ………………………………………………………………... 5

1.4.2 Climate …………………………………………………………………. 5

1.4.3 Relief and Drainage……………………………………………………. 5

1.4.4 Geology of the Study Area………………………………………………. 9

1.5 Literature Review……………………………………………………………… 11

CHAPTER TWO: POTENTIAL FAILURE/COLLAPSE MECHANISMS …… 14

2.1 Foundation Movement and Settlement of Soil………………………………… 15

2.2 Effects of Expansive Soil on Building…………………………………………… 15

2.3 Elastic Deformation……………………………………………………………… 16

2.4 Moisture Changes……………………………………………………………… 16

2.5 Movement Due to Creep……………………………………………………….. 17

2.6 Movement Due to Chemical Reaction………………………………………… 17

2.7 Design Faults and Poor Construction Practices………………………………. 18

2.8 Cracking Due to Vegetation…………………………………………………… 19

CHAPTER THREE: RESEARCH METHODOLOGY…………………………… 20

3.1 Field Mapping ………………………………………………………………… 20

3.2 Resistivity Survey……………………………………………………………… 21

3.3 X-Ray Diffraction (XRD) Analysis…………………………………………… 22

3.4 Geotechnical Analysis ………………………………………………………… 23

3.4.1 Grain Size Analysis… ………………………………………………… 23

3.4.2 Specific Gravity…………...…………………………………………… 23

3.4.3 Atterberg Limits…………………………..…………………………… 24

3.4.3.1 Liquid Limit…………………………………………………… 25

3.4.3.2 Plastic Limit…………………………………………………… 25

3.4.3.3 Plasticity Index………………………………………………… 26

3.4.5 Compaction Test………………………………………………………… 26

3.4.6 Coefficient of Saturated Permeability…………………………………….. 27

3.4.7 Undrained Triaxial Test…………………………………………………… 28

CHAPTER FOUR: RESULTS AND DISCUSSION…………………………………… 30

4.1 Particle Size Distribution………………………………………………………… 30

4.2 Specific Gravity…………………………………………………………………… 32

4.3 Atterberg Limits…………………………………………………………………… 33

4.4 Permeability……………………………………………………………………… 36

4.5 Compaction Test………………………………………………………………… 36

4.6 Triaxial Shear Strength…………………………………………………………… 37

4.7 X-Ray Diffraction (XRD)………………………………………………………… 41

4.8 Electrical Resistivity……………………………………………………………… 44

4.8.1 Vertical Electrical Sounding (VES)………………………………………… 44

4.8.2 Electrical Resistivity and Induced polarization Profiling…………………… 49

4.9 Proposed Mechanism Of Frequent Building Collapse In Akpugo: Findings From

Integrating Geotechnical And Geophysical Methods …………………………….. 52

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS………………… 55

5.1 Conclusions………………………………………………………………………… 55

5.2 Recommendations………………………………………………………………… 56

References………………………………………………………………………………… 57

Appendices

LIST OF FIGURES

Figure 1: Map of Nigeria, Showing the Study Area…………………………………….... 3

Figure 2: Newly constructed building with major cracks…………………………………. 3

Figure 3: Collapsing Buildings in Akpugo ……………………………………… 4

Figure 4: Old and New Buildings without Cracks in Akpugo……………………………. 4

Figure 5: Map of the study area showing VES points, problematic and non-problematic

zones 9……………………………………………………………………………… 7

Figure 6: Topographic Map of the Study Area……………………………………………. 8

Figure 7: A 3D Topographical map of the study area……………………………………. 8

Figure 8: Geological map of southeastern Nigeria (modified from Akande et al, 2007)… 10

Figure 9: Particle Size Distribution curves of Soil Samples…………………………. .…… 31

Figure 10: Casagrande plasticity Chart of the Samples……………………………………… 35

Figure11: Mohr view plot of Location 1(Problematic zone)……………………………… 38

Figure 12: Mohr View plot of Location 2 (Problematic zone)……………………………….. 38

Figure 13: Mohr View plot of Location 3 (Problematic zone)……………………………… 39

Figure 14: Mohr View plot of Location 7 (Non- problematic zone)……………………… 39

Figure 15: Mohr View plot of Location 8 (Non- problematic zone)………………………. 40

Figure 16: XRD of Location 1(Most Problematic Zone)…………………………………… 42

Figure 17: XRD of Location 2 (Problematic Zone)………………………………………… 42

Figure 18: XRD of Location 3(Problematic zone)………………………………………. 43

Figure 19: Cracks on the Ground surface during the dry season due to Expansive clays… 43

Figure 20: VES of Problematic Zone…………………………………………………… 47

Figure 21: VES of the Non-Problematic Zone………………………………………….. 47

Figure 22: VES of Non-problematic zone……………………………………………… 48

Figure 23: Induced Polarization Model across the problematic and non-problematic zones. 51

Figure 24: Electrical resistivity profile across the problematic and non-problematic zones. 51

Fig. 25: Expansive soil most affected structural part of an engineering structure (a) wall

corners or end of wall (b) junction between the wall and floor (c) between the wall and

the roof slab (d) Corners of windows and doors………………………………………… 54

LIST OF TABLES

Table 1: Summary of Particle size distribution Results of the Study Area……………… 30

Table 2: Summary of Geotechnical results ……………………………………………… 33

Table 3: Plasticity According to Liquid Limit (after Bell, 2007)………………………… 34

Table 4: Apparent Resistivity values of the Study Area…………………………………… 46

LIST OF APPENDICES

Appendix 1: Compaction Test of Location 1





Appendix 6: Coefficient of Saturated Permeability of Location 1 and 8




Appendix 10: X-Ray Diffraction Data of Location 1(Problematic zone)

Appendix 11: Horizontal profiling data of the Study Area when “a” is 10






CHAPTER ONE

INTRODUCTION

1.1 PREAMBLE

Building collapse essentially refers to the structural failure of a building or failure to transmit

the weight of the structure to the ground evenly without any problem. This can also mean the

inability of the subsurface to carry the weight of the building where the weight surpasses the

allowable bearing capacity of the ground causing uneven settlement of the building. Loss of

lives, severe injuries and huge economic losses in millions of naira are mostly associated with

building collapse, (Ayedun, et al, 2012; Matawal, 2012)

Building collapse is one of the major disasters that occur frequently in different parts of

Nigeria and other countries in the world (Gambo et al, 2013). The incidence of building

collapses in Nigeria has taken an alarming dimension owing to the frequency of its occurrences.

It is on record that hardly a month passes by without a case of collapse building being recorded

(Kingsley, 2010). Each of these collapses carries along tremendous effect, socially,

economically, psychologically and environmentally, that cannot be easily forgotten by any of its

victim. While the rest of the World has advanced technologically and have been able to surmount

the present challenges we are facing, we are yet to address these problems holistically (Felix,

2012).

Major natural disasters like earthquakes, tsunamis, hurricanes and tornadoes are some of

the major causes of building collapse in developing and developed nations of the world. In West

Africa, especially in Nigeria, the menace of collapse building is most common in our major cities

like Lagos, Port-Harcourt, Ibadan, Kano, Abuja etc. It is however not limited to those big cities

even the rural areas share in the menace. The sad event is that the building failures in the rural

areas are not reported like the once in the big cities. It is therefore a difficult task to track down

the complete record of building collapse in Nigeria. Worse more the exact number of casualties

is never known or reported (Augustine 2012).

In Nigeria, the common causes of building collapse have been traced to bad design, faulty

construction, use of low quality materials, hasty construction, foundation failure, lack of proper

supervision, ineffective enforcement of building codes by the relevant Town Planning

Authorities, lack of proper maintenance e.t.c. (Folagbade, 2001 and Badejo, 2009).

1.2 STATEMENT OF PROBLEM

A building, once properly constructed is expected to be in use for a very long time. Over

the years, the people of Obinagu Uwani in Akpugo, Nkanu West L.G.A. Enugu State,

Southeastern Nigeria (Fig. 1) have suffered from building collapse without knowing the real

cause. Buildings are built and major cracks appear after sometime (Figs 2), these cracks

eventually cause the building to collapse (Fig. 3), but in some areas, the buildings don’t have

cracks (Fig. 4). The real cause of the cracks are not known by the people, some believe it is

ancestral curse, while others believe it is a problem from the soil and some believe is from the

root of trees.

1.3 AIMS AND OBJECTIVES

The following are the reasons for this work:

1 To investigate the cause of building collapse in Akpugo.

2 To determine the boundary between the problematic zone and the non-problematic zone.

3 To determine the shear strength parameters of the soils.

Fig. 1: Map of Nigeria, Showing the Study Area.

Fig. 2 Newly constructed building with major cracks

Fig. 3: Collapsing Buildings in Akpugo

Fig. 4: Old and New Buildings without Cracks in Akpugo

A B

1.4 STUDY AREA DESCRIPTION

1.4.1 LOCATION

Akpugo lies within latitude 6o17 and 6

o20 North of the equator and longitudes 7

o35 and

7o38East of Greenwich meridian and spans an approximate area of about 25km

2 (Fig. 5 ). The

mapped area under study is accessible, with lots of tarred and untarred roads that were of great

advantage in the course of this work. The main access routes include Enugu - Agbani road,

Amagunze - Akpugo road and Nara - Akpugo road.

1.4.2 CLIMATE

The study area lies within the tropical rain forest region of Nigeria. It has two distinct

seasons, the rainy and dry. The rainy season begins from April and ends October, while the dry

season begins in November and ends in March. Records of rainfall showed high values within

the months of May to early August when there is a rainfall break and resumes in late August to

end of October with higher values. There is virtually little or no rainfall from November to

March. Average annual rainfall is between 1875mm and 2500mm and an average annual

temperature of about 27oC, the pressure range is from 1010 to 1012.9 millibars (Moanu and

Inyang, 1975).

1.4.3 RELIEF AND DRAINAGE.

The study area has a general elevation ranging from 110 to 150 meters above mean sea

level. It is a part of the low-lying undulation of the Cross-River plain which form part of the

scarp lands of the Southeastern Nigeria (Kogbe, 1989). The drainage pattern is both structurally

and topographically controlled. The area is drained mainly by rivers and streams (Fig.5). The

two major rivers in the area are river Nyaba and Atavo river. The streams ooze out from between

the contact of sandstone and shale units and they include Nkpume Utukpa stream, Uhuakpa

stream and Akpa stream. The drainage pattern in the study area is dendritic, It may be related to

inequalities in rock hardness, structural controls, geologic and geomorphological evolution of the

drainage basin (Figs 6 and 7).

Fig. 5: Map of the study area showing VES points, problematic and non-problematic zones

Profile line

Fig. 6: Topographic Map of the Study Area.

Fig. 7: A 3D Topographical map of the study area

1.4.4 GEOLOGY OF THE STUDY AREA.

The study area is underlain by the following geological formations, the Asu River Group,

Eze Aku Formation and Awgu Formation (Fig. 8). The Asu River Group is the earliest recorded

marine sediments consisting of bluish grey to brown shale and sandy shale, fine-grained

micaceous sandstones and dense blue limestone (De-Swardt and Casey, 1963; Reyment, 1965).

The sediments of the Eze Aku Formation consist of hard grey to black shales and siltstones with

frequent facies changes to sandstone or sandy shale (Reyment,1965). The Awgu Formation

which is the main geologic formation seen that outcropped at Akpugo consists of bluish grey,

well-bedded shales with intercalations of fine-grained sandstones and thin often marly shelly

limestones. The beds are rich in ammonites and other mollusks (Kogbe, 1981).

Fig. 8: Geological map of southeastern Nigeria (modified from Akande et al, 2007)

1.5 LITERATURE REVIEW

Individual opinions differ radically from one another on the professional to blame for

building collapse. The cause of building collapse also differs from one place to another based on

the geological, geotechnical and architectural views.

Sharma and Pant (I960); Suresh, (1979); and Tarsem,( 2010) Said that the existence of

vegetation, such as fast growing trees in the vicinity of compound walls can sometimes cause

cracks in walls due to expansive action of roots growing under the foundation.

Wang (1973) demonstrated that clay mineralogy of rocks and soils are the controlling ingredient

of engineering behaviour of rocks and soils which leads to building collapse.

Abeyesekera et al (1978) described shale as a notoriously unpredictable material in which a

number of failures have been reported involving settlement and shear failure in compacted

embankment.

Ometar (1987) attributed the cause of building collapse to a neglect of real professionals advice

whereby the owner prefer to build the house either with half-baked professionals or the use of

artisans and labour as a means of direct labour contract.

Oyewande (1992) observed that building failures are attributed to the following causes: design

faults (50%), faults on construction site (40%) and product failure (10%)

Roddis (1993) considered failure as occurring in building components when they can no longer

be relied upon to fulfill their principal functions. He distinguished between defect and failure

in buildings. Defect is deflection in a building causing certain amount of cracking or distortion

while excessive deflection that results in serious damage to partitions, ceilings and floor finishes

is referred to as building failure. A distressed building exhibits defects in its components,

noticeable as weakened foundation, cracks in floors, walls, and roofs.

McCarthy (1999) noted that there is therefore a need to carry out soil surveys to ascertain the

compressibility or consolidation potentials as well as the bearing strength of the soil of a

particular site. Movements often result in sand and clayey sites because there are too many voids

between their particles. Silt deposits are susceptible to collapse if exposed to excessive amounts

of water while clays shrink in the dry season only to swell during the wet season or in the

constant presence of water. The challenge in most cases is the human error of poor monitoring.

In Nigeria, the common causes of building collapse have been traced to bad design, faulty

construction, use of low quality materials, hasty construction, foundation failure, lack of proper

supervision, ineffective enforcement of building codes by the relevant Town Planning

Authorities, lack of proper maintenance, extraordinary loads, use of unqualified contractors e.t.c.

(Bamidele, 2000; Folagbade, 2001; and Badejo, 2009)

Chinwokwu (2000) said that natural occurrences such as rainfall, temperature and pressure result

into building collapse. When there is a heavy downpour of rain, there is a possibility that one or

more buildings (completed or uncompleted), somewhere, would carve in.

Uzokwe (2001) observed that the cause of a building failure is unique to each building but

summarized the various causes of building collapse as due to the quality of the blocks used,

quality of concrete used, poor compaction and consolidation of foundation soil, weak soil.

Akwwi and Al-kharasheh (2002) reported that the swelling and shrinkage potential of soils are

affected by mineralogical constituents and surrounding environments cause building collapse. .

While Akinpelu (2002) categorized the following as major causes of structural failures:

environmental changes, natural and man-made hazards; improper presentation and interpretation

in the design.

Buildings fail through mainly ignorance, negligence and greed (Bolaji, 2002).

Fadamiro (2002) said that design deficiencies also come under calculation errors, bearing

support problems, deformation, secondary stresses, elastic cracking, temperature and shrinkage

problems, detailing and drafting problems, errors in assumed loading, changes and alterations in

existing buildings, all contributing substantially to building structural failures, disasters and may

finally lead to building collapse.

Manasseh and Agbede (2004) observed that shales of the Lower Benue Trough contain

significant amount of smectite, illite, kaolinite and montmorillonite. Obiora and Umeji (2004)

confirmed this mineralogy in some shale units of Lower Benue Rift.

Ayininuola and Olalusi (2004), `identified two types of failure in building, which are cosmetic

and structural types. Cosmetic failure occurs when something has been added to or subtracted

from the building, thus affecting the structures' outlooks. On the other hand, structural failure

affects both the outlook and structural stability of the building.

Bazant and Verdure (2007) attributed building failure to either natural or man-made phenomena.

A natural phenomenon may consist of earthquakes and typhoons while man-made phenomena

consist of disasters which may be borne out of man’s negligence mainly in areas such as soil

type, building design and planning for extra ordinary loads and stress from strong winds and

earthquake for tall buildings, foundation works, quality of building materials, strict monitoring of

craftsmen and quality of workmanship. Different soil types pose varying problems for built

foundations and the structural integrity of an entire building.

Amadi et al . (2012). Said that building collapse are due to under design, improper supervision,

poor quality construction, poor funding, use of sub-standard construction materials and absence

of geo-technical investigation and engagement of non-professionals (quacks).

Expansive soils pose the greatest hazard in regions with pronounced wet and dry seasons.

CHAPTER TWO

POTENTIAL FAILURE/COLLAPSE MECHANISMS

The scientific method relies on a process of postulation and verification. Many scientific

endeavours have floundered as a result of failing to consider alternative postulates and gathering

only information which supports a particular point of view Rao(2005). The purpose of this

chapter is to identify all the potential triggers, sequences of events and failure/collapse

mechanisms. Failures are not always related to geotechnical problems. If there are no apparent

ground movements, failures are most likely due to defective design of structures (Hulme, et al.,

1993). Principal causes of building collapse are as follows:

a) Foundation movement and settlement of soil

b) Effects of expansive soils on buildings

c) Elastic deformation,

d) Creep,

e) Moisture changes,

f) Chemical reaction,

g) Design faults/lack of proper supervisor

h) Vegetation.

2.1 FOUNDATION MOVEMENT AND SETTLEMENT OF SOIL

Shear cracks in buildings occur when there is large differential settlement of foundation

either due to unequal bearing pressure under different parts of the structure or due to bearing

pressure on soil being in excess of safe bearing strength of the soil or due to low factor of safety

in the design of foundation (Arora, 2008).

2.2 EFFECTS OF EXPANSIVE SOILS ON BUILDINGS

Buildings constructed on shrinkable clays (also sometimes called expansive soils) which

swell on absorbing moisture and shrink or drying as a result of change in moisture content of the

soil, are extremely crack prone and special measures are necessary to prevent such buildings

from collapsing. Effect of moisture variation generally extends up to about 3.5 m depth from the

surface and below that depth it becomes negligible. Effect of soil movement can be avoided or

considerably reduced by taking the foundation 3.5 m deep and using moorum, granular soil or

quarry spoil for filling in foundation trenches and in plinth. Variation in moisture content of soil

under the foundation of a building could be considerably reduced by providing a waterproof

apron all round the building. Use of under-reamed piles in foundation for construction on

shrinkable soils has proved effective and economical for avoiding cracks and other foundation

problems (Sharma and Pant I960; Wang, 1973; Suresh, 1979; Oyewande, 1992; Arora, 2008;

and Tarsem, 2010).

2.3 ELASTIC DEFORMATION

Structural components of a building such as walls, columns, beams and slabs, generally

consisting of materials like masonry, concrete, steel, etc, undergo elastic deformation due to load

in accordance with Hook's law, the amount of deformation depending upon elastic modulus of

the material, magnitude of loading and dimensions of the components. When walls are unevenly

loaded with wide variations in stress in different parts, excessive shear strain is developed which

causes cracking in walls and possible collapse of the building. When a beam or slab of large span

undergoes excessive deflection and there is not much vertical load above the supports, ends of

beam/slab curl up causing cracks in supporting masonry. If two materials, having widely

different elastic properties, are built side by side, under the effect of load, shear stress is set up at

the interface of the two materials, resulting in- cracks at the junction(Sharma and Pant I960;

Suresh, 1979; Arora, 2008; and Tarsem, 2010).

2.4 MOISTURE CHANGES

Most of the building materials have pores in their structure in the form of intermolecular

space. These materials expand on absorbing moisture and shrink on drying. These movements

are reversible, that is Cyclic in nature and is caused by increase or decrease in the inter-pore

pressure with moisture changes, extent of movement depending on molecular structure and

porosity of a material. Initial shrinkage occurs in all building materials that are cement/lime

based such as mortar, masonry and plasters. (Suresh, 1979; McCarthy, 1999; Arora, 2008; and

Tarsem, 2010).

2.5 MOVEMENT DUE TO CREEP

Some building items, such as concrete, brickwork and timber, when subjected to

sustained loads not only undergo instantaneous elastic deformation, but also exhibit a gradual

and slow time-dependent deformation known as creep or plastic strain. The latter is made up of

delayed elastic strain which recovers when load is removed, and viscous strain which appears as

permanent set and remains after removal of load. The amount of creep in steel increases with rise

in temperature (Sharma and Pant I960; Abeyesekera et al (1978) Suresh, 1979; and Tarsem,

2010).

2.6 MOVEMENT DUE TO CHEMICAL REACTION

Certain chemical reactions in building materials result in appreciable increase in volume

of materials, and internal stresses are set up which may result in outward thrust and formation of

cracks which will lead to building collapse. The materials involved in reaction also get-

weakened in strength. Commonly occurring instances of this phenomenon are: sulphate attack on

cement products, carbonation in cement-based materials, and corrosion of reinforcement in

concrete and brickwork, and alkali-aggregate reaction. Soluble sulphates which are sometimes

present in soil, ground water or clay bricks react with tricalcium aluminate content of cement and

hydraulic lime in the presence of moisture and form products which occupy much bigger volume

than that of the original constituents. This expansive reaction results in weakening of masonry,

concrete and plaster and formation of cracks. For such a reaction to take place, it is necessary

that soluble sulphates, tricalcium aluminate and moisture, all the three have to be present.

These chemical reactions result in unequal settlement of foundation and cracks in the

superstructure and possible collapse of the building with time. Sharma and Pant I960; Suresh,

1979 and Tarsem, 2010).

2.7 DESIGN FAULTS AND POOR CONSTRUCTION PRACTICES.

Before a building is constructed, it is crucial that the designer must first consider the

environmental conditions existing around the building site. It is also very important to do

geotechnical investigations to determine the type of foundations, the type of concrete materials to

be used and the grade of the concrete depending on chemicals present in ground water and

subsoil. It is critical for the structural designer and architect to know whether the company

proposed to carry out the construction has the requisite skills and experience to execute their

designs. Complicated designs and inadequate skills of the contractor will ultimately cause poor

construction of the building and eventually collapse. Very often, the building loses its durability

on the blue print itself or at the time of preparation of the specifications for concrete materials

and various other related parameters. The construction industry has in generally fallen prey to

non-technical persons most of whom have little or no knowledge of correct construction

practices. There is general lack of good construction practices either due to carelessness, greed,

negligence or ignorance. Or worst still, a combination of all these. For a healthy building, it is

absolutely necessary for the construction agency and the owner to ensure good quality materials

and good construction practices. All the way to building completion, every step must be properly

supervised and controlled without cutting corners. (Bamidele, 2000; Folagbade, 2001; Badejo,

2009; Oloyede et al 2010 and Amadi et al . (2012).

2.8 CRACKING DUE TO VEGETATION

Existence of vegetation, such as fast growing trees in the vicinity of compound walls can

sometimes cause cracks in walls due to expansive action of roots growing under the foundation.

Roots of a tree generally spread horizontally on all sides to the extent of height of the tree above

the ground and when trees are located close to a wall; these should always be viewed with

suspicion. (Sharma and Pant I960; Suresh, 1979; and Tarsem, 2010).

CHAPTER THREE

RESEARCH METHODOLOGY

This study integrates some geotechnical and geophysical techniques to evaluate the

factors responsible for frequent building collapse in Akpugo. Areas with cracked and non-

cracked buildings were studied to assess the geotechnical properties of the soils. Samples will be

taken at different locations and subjected to x-ray diffraction analysis (XRD), grain size analysis,

specific gravity, Atterberg limits, permeability, compaction and triaxial tests. Electrical

resistivity method will also be used to delineate the geo-electrical layers and to image the lateral

variations of the sub-surface. To achieve the purpose of this study, the author will compare the

geotechnical and geophysical results of the problematic zone soils (areas with cracked buildings)

to that of the non-problematic zone soils (areas without cracked buildings)

3.1 FIELD MAPPING

A detailed field mapping of the area was carried out using a base map of the area on a

scale of 1:25,000 as well as other field mapping equipment such as compass and Global

Positioning system (GPS). The field mapping involved description, measurement and sampling

of outcropping sections along the stream channels as well as location of major cracked and

collapsed buildings. The types of lithologies were carefully examined and noted at different

locations as well as GPS values of the locations. Rock samples were collected with the aid of

geologic hammer and the samples collected were accurately labeled at the location it was

collected. The rock samples were studied megascopically before they were taken to the

laboratory for geotechnical analyses.

3.2 RESISTIVITY SURVEY

After the first field mapping, it became necessary for a geophysical mapping to be carried

out in order to obtain subsurface information. The electrical resistivity method that was

carriedout consists of three(3) vertical electrical soundings (VES) to determine the electrical

resistivity and delineate the subsurface vertical geoelectric sections of the geologic materials and

one(1) horizontal profiling to determine the horizontal variations of the rock units. The

Schlumberger array was implored for the VES , while Wenner array was used for the horizontal

profiling..

The field equipment for this study are

1 Terrameter SAS(Self Averaging System) 1000

2 Four electrodes, two of them for sending current into the ground and the other two for

measuring potential difference.

3 Four cables for connecting the ABEM Terrameter SAS 100 with the electrodes.

4 Four hammers for forcing the electrodes into the ground.

5 Measuring tapes

6 A 12volt car battery as the power source.

In this configuration, the four electrodes are positioned symmetrically along a straight

line, the current electrodes on the outside and the potential electrodes on the inside. The

distances between the current electrodes and the potential electrodes were equally spaced. To

change the depth range of the measurements, the current electrodes and the potential electrodes

were displaced outwards together. The profiling covered a distance of 270m and the electrode

spacing used were 10m, 20m, 30, 40m, 50m and 60m to get a better depth. The apparent

electrical resistivity and induced polarization data of the various surveys were inverted with

RES2DINV© software by means of a Least-squares inversion (Loke et al., 2003) and model

refinement. The resistivity models resulting from the inversion are presented as blocks (Genelle

et al, 2012)

RES2DINV© software was used to generate a two dimensional (2-D) resistivity model for the

subsurface which can be referred to as Electrical Imaging Surveys (Edwards 1977; Dobrin and

Savit, 1988; Kenma et al, 2000).

3.3 X-RAY DIFFRACTION (XRD) ANALYSIS.

The XRD analysis was done in the XRD laboratory of Centre for Energy Research and

Development, Obafemi Awolowo University,Ile-Ife. Shale and clay samples were collected from

the problematic zone as shown on the map (Fig. 5). The samples were sun dried and pulverized.

The pulverized sample was placed in the sample holder of the XRD machine, then the sample

placed in the diffractometer and illuminated with x-rays of a fixed wave-length, the intensity of

the reflected radiation was recorded using a detector (Bish and Reynolds, 1989; Moore and

Reynolds, 1997). The pattern shown on the detector was analyzed using the search and match

method. The database of Centre for Energy Research and Development, Obafemi Awolowo

University,Ile-Ife contains several well known compounds which were used to match the

unknown compounds in the sample.

3.4 GEOTECHNICAL ANALYSIS

The following geotechnical analyses were carried out on the samples collected at the study

area, to determine their geotechnical properties. Grain size analysis, specific gravity, Atterberg

limits, coefficient of saturated permeability, compaction test and undrained triaxial test

3.4.1 Grain size analysis

This test was done on the soil samples to determine quantitative distribution of the different

particle sizes.

The samples for the experiment were sun dried and gently disaggregated without breaking the

grains; the weight of the sample was obtained, then the sieves to be used were cleaned and the

weight of each was obtained. The BS sieves 4.75mm, 2.36mm, 1.18mm, 0.600mm, 0.425mm,

0.300mm, 0.212mm, 0.150mm and 0.075mm were used for this analysis. The sieves were

arranged to have the largest (sieve 4.75mm) at the top of the stack and the least sieve(0.150mm)

at the bottom. The pan was placed below the sieve 0.150mm and the soil sample was carefully

poured into the top sieve and covered with the cap cover. The sieve stack was placed in the

mechanical shaker and allowed to shake for 10 minutes, then the sieve stack was removed from

the shaker and each sieve including the pan was weighed and recorded with the soil sample

retained in it. Particle size distribution curve was plotted for each of the samples.

3.4.2 Specific Gravity

Soil samples were oven dried at 1050C for 24 hours and used to run this test. Apparati included

a thermometer for temperature measurements, weighing balance and a large pycnometer bottle.

Approximately 500 grams of each specimen was weighed and the operations were as follows:

Weight of empty pycnometer bottle = W1

Weight of oven dried soil + pycnometer bottle = W2

Weight of pycnometer bottle + soil + distilled water = W3

Weight of pycnometer bottle + distilled water only = W4

Weight of dry soil, Ws = W2 – W1

Weight of distilled water = W4 – W1

Weight of water having the same volume as that of soil solids = (W4 –W1) – (W3 – W1)

By definition and by Archimedes’ principle,

Weight of soil solids

G =

Weight of water of volume equal to that of solids

= (W2 – W1) / (W4 – W1) – (W3 – W2)

= (W2 – W1) / (W2 – W1) – (W3 – W4)

Recall that (W2 – W1) = Ws

Therefore, Ws

G =

Ws – (W3 – W4)

3.4.3 ATTERBERG LIMITS

Atterberg limits also referred to as Consistency limits, comprise of

Liquid Limit, LL

Plastic Limit, PL

Plasticity Index, PI

3.4.3.1 Liquid limit

About 200grams of sun dried pulverized samples all passing 0.425mm (No 36BS Sieve)

were mixed with distilled water to a stiff consistency and a portion of it placed in the liquid limit

cup of the liquid limit device, and then the surface smoothened. A groove was made with the

Casagrande grooving tool, on the specimen cup. The handle of device was turned at a specified

rate of about two rotations per second until the sides of the groove just closed. The number of

blows required to close the groove to about one-half of an inch (2.5cm) was recorded. A portion

of the sample was then taken from around the groove for water content determination. The

operation was repeated four times at different consistencies. The specimen was prepared at such

consistencies that the number of blows was between 11 and 48. The moisture content was plotted

against the number of blows on a graph paper. The best fitting line was drawn and the moisture

content corresponding to 25 blows was taken as the liquid limit (British Standard, 1975; Arora,

2008). This operation was carried out on the clay and shale samples.

3.4.3.2 Plastic limit

The same material utilized for the liquid determination was air dried for a while, and

kneaded with fingers, then rolled between the palms. Further rolling was done on a flat glass

plate to form a thread of about 3mm (⅛ inches) in diameter. The specimen was kneaded together

and rolled out again. The process continued until the thread crumbled when it was about 3mm

diameter. At this stage, the moisture content of the material was determined. The entire

procedure was repeated and the average value of the moisture content was taken as the Plastic

limit of the material. (Lambe 1951; British Standard, 1975; Arora, 2008) This operation was

carried out on the clay and shale samples

3.4.3.3 Plasticity index

The Plasticity Index was calculated from the liquid and plastic limits values as follows

Plasticity Index = Liquid Limit – Plastic Limit

3.4.4 Compaction Test

Soil particles passing through the ¾ inches sieve were used. 6kg of the specimen were

weighed out. Water weighing 6, 8, 10, and 12% of the specimen was measured out, and each

thoroughly mixed with the weighed out specimen. The water percentages were chosen from a

trial test that showed that a parabolic curve was produced when the dry density of the material

was plotted against corresponding moisture.

The soil samples were shared into five approximately equal parts. After compaction, the weight

of the material in the mould was determined, and a portion of the material collected from top and

bottom for water content determination.

The maximum dry density (MDD) and the optimum moisture content (OMC) of each of the

compacted samples were determined from a plot of dry densities versus corresponding moisture

content. The following relationships were used for the calculation

ρ

Pd =

1 + W

where Pd is the dry density of material

ρ is the bulk density of the compacted material

W is the water content

The procedure followed those of Lambe (1951) and BS (1975).

3.4.5 Coefficient Of Saturated Permeability

Constant-head method was used in this experiment.

Equipment

a) Permeameter mould

b) Detachable collar

c) Dummy plate

d) Drainage base, having a porous disc

e) Drainage cap, having a porous disc with a spring attached to the top

f) Compaction equipment\

g) Constant-head water supply reservoir

h) Vaccum pump

i) Constant-head collecting chamber

j) Stop watch

k) Large funnel

l) Thermometer

m) Weighing balance, accuracy 0.1g

n) Filter paper

Experiment procedure

The collar of the mould was removed. The internal dimensions of the mould were measured and

weighed, with dummy plate to the nearest gram, Little grease was applied to the inside of the

mould and about 2.5kg of the soil sample from a thoroughly mixed wet soil in the mould. The

soil was compacted at the required dry density, using a suitable compacting device.

The collar and the base plate were removed, and the excess soil level was trimmed with the top

of the mould, the outside of the mould and the dummy plate was cleaned, and the mass of the

soil was measured. A small specimen of the soil was taken in a container for the water content

determination. The porous discs (stones) were saturated and placed on the drainage base, and a

filter paper was kept on the porous disc. The dummy plate was removed and the mould with soil

was placed on the drainage base, after inserting water in between. The edges of the mould were

cleaned and grease was applied in the groove around them. Drainage cap was fixed using

washers after placing a filter paper and a porous disc. The water reservoir was connected to the

outlet at the base and allowed to flow upwards till it had saturated the sample, the the reservoir

was disconnected from the outlet at the bottom after the empty portion of the mould was filled

with de-aired water, without disturbing the soil. The constant-head reservoir was connected to

the drainage cap inlet. The stop cock was opened and the water was allowed to flow downward

so that all the air was removed. The stop cock was closed and the water was allowed to flow

through the soil till a steady state was attained, water was collected flowing out of the base in a

measuring flask for a convenient time after the stop watch was started. This was done three more

times keeping the time interval the same. The difference of the head(h) in levels between the

constant-head reservoir and the outlet in the base was measured.(Arora,2008)

3.4.6 Undrained triaxial test

This test was done to find the shear of the soil by undrained Triaxial Test.

Apparatus for the preparation of the sample.

a) 37.5mm internal diameter and 75.0mm height sample tubes

b) Rubber ring

c) An open cylindrical section fitted with a small rubber tube

d) Stop clock

e) Moisture content test apparatus

f) Dial gauge, accuracy 0.01mm

Experimental Procedure

The sample was placed on the compression machine and a pressure plate was placed on the top.

Care was taken to prevent any part of the machine or cell from jogging the sample while it was

being setup. The cell was properly setup and uniformly clamped down to prevent leakage of

pressure during the test, making sure the sample was properly sealed with its end caps and

rings(rubber) in position and that the sealing rings of the cell are also correctly placed.

The pore water pressure measurement device was attached to the specimen through the pressure

connections and the proving ring dial gauge was set to zero. The sample is sheared by applying

the deviator stress by the loading machine. The proving ring readings were taken corresponding

to axial strains. Upon completion of the test, the loading was shut off. Using the manual control,

all additional axial stress was removed. The cell pressure was then reduced to zero, and the cell

was emptied (Arora, 2008).

The values obtained were plotted as Mohr circles from where Mohr envelopes were drawn to

obtain the strength parameters of cohesion (C) and angle of shearing resistance (Φ).

CHAPTER FOUR

RESULTS AND DISCUSSION

4.1 PARTICLE SIZE DISTRIBUTION.

The soil samples were classified based on Unified Soil Classification System, the

samples collected from the problematic zone(location1- 3) in Akpugo falls within the SILT-

CLAY soils under the general classification, while the samples collected from the Non-

problematic zone (location 4-8) falls within the Well-Graded Sands. The results of the particle

size distribution are summarized in table 1, while Fig. 9 shows the Particle Size Distribution

curve of Soil Samples.

Table 1: Summary of Particle size distribution Results of the Study Area.

Sample

Number

Clay/Silt

(%)

Fine grained

sands (%)

Medium

grained sands

(%)

Coarse

grained sands

(%)

Gravel

(%)

Zone

Location 1 97 3 - - - Problematic



Location 4 15 5 73 7 - Non-Problematic



Location 7 11 4 56 26 3 Non-Problematic

Location 8 8 8 58 25 1 Non-Problematic

Fig. 9: Particle Size Distribution curve of Soil Samples

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1

location 1

location 2

location 3

location 4

location 5

location 6

location 7

location 8

4.2 SPECIFIC GRAVITY

The results of the specific gravity of the tested samples are shown in table 2. The specific

gravity of the soil samples is within the range of 2.50 to 2.58. Shakoor and Brook (1987) stated

that specific gravity is a reflection of the densities of the materials in each sample exclusive of

the permeable void they contain. Thus, the low values of the Gs of the tested samples could be

attributed to the clay minerals they contain, which have Gs values between 2.56 and 2.74, and

the feldspars, which later weather to give the clay minerals, with Na – Ca – Felspar and K –

Felspar Gs ranges between 2.54 and 2.76 (Emesiobi, 2001)

There is no difference in the specific gravity values of the samples at the problematic

zone and samples collected from the Non problematic zone. Soils containing organic matter and

porous particles may have specific gravity values below 2.0 and Soils having heavy substances

may have values above 3.0 (Jegede, 1998).

A comparison of specific gravity values of rock aggregates that serve well in

construction project with the samples revealed that the sandy soil samples are slightly below the

range, while the shale samples have a slight higher specific gravity which could be as a result of

possible heavy metals or higher silt content in the shale.

Table 2: Summary of Geotechnical results Location

Number

Specific

gravity

LL PL PI Permeability

(m/sec)

MDD

(kg/m)

OMC

(%)

C

(kpa)

Angle of

shearing

resistance

(o)

Zone

Location 1 2.52 36 8.9 25.1 4.018 x 10-7

1.79 11.3 32.13 10 Problematic

Location 2 2.50 55 16 39 7.016 x 10-7

1.94 12.8 36.54 12 Problematic

Location 3 2.54 37 9.1 27.9 6.502 x 10-7

1.85 10.7 35.67 14 Problematic

Location 4 2.56 29.7 10.7 19 1.55 x10-6

1.80 5.7 15.76 17 Non-problematic

Location 5 2.58 28.6 10 18.6 1.925 x 10-6


Location 6 2.56 30.1 10.9 19.2 1.608 x 10-6


Location 7 2.55 30.3 10.9 19.4 1.745 x 10-6


Location 8 2.57 27.6 9.5 18.1 1.830 x 10-6


4.3 ATTERBERG LIMITS

The results of the Atterberg limits test carried out on the soil samples are summarized in

table 2. The results showed that Liquid Limits (LL) of the Problematic zone ranges from 36 - 55,

while that of the Non problematic zone is 27.6 - 30.3, Plastic Limits (PL) of the problematic zone

is 8.9 - 16, while that of the non-problematic zone is 9.5 - 10.9. The Plasticity Index (PI) of the

problematic zone is 25.1 - 39, while that of the Non problematic zone is 18.1 - 19.4. Sowers and

Sowers (1970) noted that P1>31 should be considered high and indicates high content of

expansive clay, most probably mortmorillonite. On the basis of LL and PI values, the

problematic zone samples are classified as inorganic clays of high plasticity while the non-

problematic zone samples are classified as inorganic clays of low plasticity (Fig. 10). A soil with

PI >31 is described as highly plastic (Table 3) and such a soil usually has the ability to retain

appreciable amount of total moisture in the diffuse double layer, especially by means of

adsorption. High plasticity materials are usually susceptible to high compressibility (Sowers and

Sowers, 1970). An increase in plasticity of material also decreases its permeability and hydraulic

conductivity (Sowers and Sowers, 1970). Increase in PI denotes loss in strength, plastic soils

decrease in load bearing capacity as moisture increases (Emesiobi, 2002). Obiora and Umeji

(2004) observed the dominance of expansive minerals such as smectite > illite > kaolinite in the

Abakaliki shale, Ezeaku and Awgu Formations. The volume changes due to humidity variations

can result in either swelling or shrinking. These changes can have significant impact on

engineering structures such as light buildings and roads ( Fouzan and Muawia, 2013). This could

possibly explain the mechanism of cracks formation in Akpugo.

Table 3: Plasticity According to Liquid Limit(after Bell, 2007)

Description Plasticity Range of Liquid Limit

Lean or Silty Low Plasticity <35

Intermediate Intermediate plasticity 35 – 50

Fat High Plasticity 50 – 70

Very fat Very High plasticity 70 – 90

Extra fat Extra High Plasticity >90

Fig. 10: Casagrande plasticity Chart of the Samples

4.4 PERMEABILITY

The permeability test result conducted on the soil samples revealed lower values for the

problematic zone and slightly higher values for the non-problematic zone. The problematic zone

has lower permeability because its high clay content, while the Non problematic zone has higher

permeability because of its lower clay content (Craig, 2004). The coefficients of saturated

permeability of the samples are summarized in table 2. Infiltration capacity of soil depends on

the permeability, degree of saturation, vegetation and amount and duration of rainfall (Todd,

1980).

The implication of the result is that problematic zone is water-logged during the rainy

season because of low permeability values. In general, the foundation soil in the area could be

regarded as a poor to fair foundation soil due to poor drainage abilities. The higher the drainage

of a foundation soil, the lesser the pore water pressure, the greater the effective stress and better

the load carrying capacity of the soil (Arora, 2008)

4.5 COMPACTION TEST

Compaction test seeks to simulate the right combination of moisture (optimum moisture

content) and load (compactive effort) on a soil that would result in increased density (maximum

dry density) of such soil; thus improving its appropriateness in construction projects. The

maximum dry densities (MDD) values at their corresponding optimum moisture content (OMC)

obtained from the samples are summarized in table 2. The result revealed that OMC is higher in

the shale samples than in the sand samples. This agrees with Arora (2008) that OMC in higher in

fine grained soils and lesser in coarse grained soils. Principally a decrease in MDD is an

indicator of soil weakness (Eltaif and Gharaibeh, 2008).

4.6 TRIAXIAL SHEAR STRENGHT

The results of undrained triaxial test are summarized in table 2. The shale sample at the

problematic zone has lower cohesion and lower angle of internal friction compared to the shale

sample from the Non problematic zone. This result indicates lower shear strength for the

problematic zone and perhaps, bearing capacity loss, which makes the area a weak site for

engineering projects. The Mohr circle plots of the samples are shown in Figs. 11, 12, 13,14 and

15.

Blyth and de Feritas (1984) postulated that the strength of any rock or soil where

permeability prevents the draining of water in the voids would be reduced by any increase in

hydrostatic pore pressure that develops within them, when loaded. On this account of poor

drainage qualities of shales, all compacted samples are likely to experience shear reduction at the

peak of rains or moisture influx if heavily loaded. Increasing the compaction effort, however,

may result in increased strength.

Fig. 11: Mohr view plot of Location 1( Problematic zone)

Fig. 12: Mohr View plot of Location 2 (Problematic zone)

Fig. 13: Mohr View plot of Location 3 (Problematic zone)

Fig. 14: Mohr View plot of Location 7 (Non- problematic zone)

Fig. 15: Mohr View plot of Location 8 (Non- problematic zone)

4.7 X-RAY DIFFRACTION (XRD)

X–ray diffraction analysis was carried out on the soil samples, to aid in the identification

of clay minerals. The X-ray diffraction analysis revealed that Smectite and Kaolinite occurred as

major clay minerals in the study area (Figs 16, 17 and 18). The problematic zone revealed

abundant of Smectite clay mineral, while the Non problematic zone revealed abundant of

Kaolinite clay mineral. Smectite expand about 300% their original volume when drained

(Farmer, 1973), the swelling of smectite during the rainy season and subsequent shrinkage

during the dry season causes differential settlement of the buildings and results in cracking and

collapse of buildings in the area(Arora, 2008). Uduji et al, (1996) observed that Cracks resulting

in the collapse of some buildings in Awgu-Okigwe area have been observed and attributed to

tension resulting from heaving shrinkage of the soils.

In general, these clay minerals are formed from weathering of different rock types and

under specific climatic conditions. Smectites and Illites are derived from weathering of basic

volcanic rocks. Kaolinite is derived from nearly all types of igneous, metamorphic and

sedimentary rocks if rainfall is frequent and water flow and hydrolysis are sufficiently strong

under tropical to subtropical climate (De Visser, 1991). The implication of the presence of these

minerals in the soils indicates high compressibility, high plasticity index and low strength

characteristics. To further support the XRD result, expansive clay soils in the field can be easily

recognized in the dry season by the deep cracks, in roughly polygonal patterns, in the ground

surface (Fig. 19a and 19b). The zone of seasonal moisture content fluctuation can extend, this

creates cyclic shrink/swell behavior in the upper portion of the soil column, and cracks can

extend to much greater depths than imagined. On buildings, the effects of expansive clays are

seen as the major cracks that lead to building collapse in the study area.

Fig. 16: XRD of Location 1(Most Problematic Zone)

Fig. 17: XRD of Location 2 (Problematic Zone)

Fig. 18: XRD of Location 3(Problematic zone)

Fig. 19. Cracks on the Ground surface during the dry season due to Expansive clays

A B

4.8 ELECTRICAL RESISTIVITY

4.8.1 VERTICAL ELECTRICAL SOUNDING (VES)

VES was used to delineate the vertical geo-electrical layers of the subsurface of the study

area; it helped to understand the lithologies of the subsurface and also to identify fractures in the

area.

The VES carried out at the problematic zone (Fig. 20) revealed four (4) geo-electrical layers. The

first layer extents from the top to a depth of about 1 m with apparent resistivity range of 26.52 –

12.775 Ω m and it was classified as the topsoil. The second geo-electrical layer extended from a

depth of 1 - 12m, with apparent resistivity range of 6 – 4 Ω m. The third layer extended from a

depth of 12 - 26m, with apparent resistivity range of 7 – 4 Ω m. The fourth layer which extended

from a depth of 26 – 150 m with apparent resistivity range of 2 – 0.5 Ω m. The very low

resistivity values at the problematic zone indicates that the area is saturated and rocks are mainly

clays and shales based on Palacky (1987) and Reynold (1998) resistivity classification of rocks

which was also confirmed by Sowers and Sowers(1970).

The gap between the third and fourth layers is an evidence there is a major fracture (Fig. 20)

between the layers, which serves as a good drainage to the area, but because of the poor

permeability of the area, poses a serious problem to the engineering structures in the area,

especially the residential buildings.

The VES of the Non-problematic zones (Figs 21 and 22) showed higher resistivity

values. Fig. 21 revealed five (5) geo-electrical layers with alternating increasing and decreasing

resistivity values. The first layer extended from the surface to a depth of about 0.1m with

apparent resistivity value of 28.597 Ω m, the second layer extended from a depth of 0.1 - 1.5 m

with electrical resistivity range of 99.01 – 167.75 Ω m. The third layer extended from depth of

1.5 – 3.5 m, with apparent resistivity range of 18.92 – 74.159 Ω m. The fourth layer extended

from a depth of 3.5 – 20 m with apparent resistivity range of 101.54 – 419.3 Ω m. the fifth layer

extended from a depth of 20 – 150 m with apparent resistivity range of 22.001 – 57.534 Ω m.

These resistivity values suggest mainly sand stones and silt stones based on resistivity

classification of rocks (Sowers and Sowers, 1970; Palacky, 1987 and Reynold, 1998)

VES 3(Fig. 22) revealed four (4) geo-electrical layers. The first layer extended to a depth

of 0.4 m from the surface, with apparent resistivity range of 142.88 – 169.2 Ω m. the second

layer extended from a depth of 0.4 – 7 m, with apparent resistivity range of 50.249 – 94.543 Ω

m. The third layer extended from depth of 7 – 50 m, with apparent resistivity range of 16.163 –

44.441 Ω m. The fourth layer extended from a depth of 50 – 150 m, with apparent resistivity

range of 6.69 – 9.83 Ω m. The resistivity values suggest mainly sand stones and silt stones based

on resistivity classification of rocks (Sowers and Sowers, 1970; Palacky, 1987 and Reynold,

1998). The decreasing resistivity values could suggest decrease in the shear strength of the earth

materials in that area.

Table 4: Apparent Resistivity values of the Study Area.

AB/2

(m)

MN

(m)

VES I

Apparent

Resistivity(Ω m)

VES 2

Apparent

Resistivity(Ω m)

VES 3

Apparent

Resistivity(Ω m)

1.5 1 28.597 26.52 169.2

2 1 167.75 19.001 142.88

3 1 99.01 12.775 94.543

5 1 74.159 6.5356 94.124

8 1 73.904 4.6256 80.484

10 1 67.176 4.1692 72.805

15 1 40.656 5.2941 50.249

15 7 56.735 5.1411 67.736

20 7 42.96 6.1432 44.441

30 7 26.522 7.1069 18.423

40 7 27.446 2.7437 16.7

50 7 33.618 5.8973 16.163

50 28 18.92 3.0549 19.436

75 28 101.54 5.3798 18.515

100 28 419.3 11.824 8.9901

150 28 57.534 1.0584 9.8344

200 28 25.344 1.0134 7.2787

200 28 22.001 0.501 6.6856

Fig. 20: VES of Problematic Zone

Fig. 21: VES of the Non-Problematic Zone

1 10 100 1000

10

100

1000

4

10

5

10

A K PU G O V ES I

App

aren

t R

esis

tivity

(oh

m-m

)

Spacing (m)

PA K I ST A N C O U N C I L O F R E SE A R C H I N W A T E R R ESO U R C ES 1

100 1000

4

10

5

10

6

10

0.01

0.1

1

10

100

Dep

th (

m)

R esistiv i ty (ohm -m )

Fig. 22: VES of Non-problematic zone

4.8.2 ELECTRICAL RESISTIVITY AND INDUCED POLARIZATION (IP) SURVEY.

Electrical resistivity quantifies how strongly a given material opposes the flow of electric

current, while induced polarization (IP) is a measure of a delayed voltage response in earth

materials or it indicates the ability of rocks to briefly hold an electrical charge after the

transmitted voltage is turned off. To produce an IP effect, fluid-filled pores must be present,

since the rock matrix is basically an insulator. The IP effect becomes evident when these pore

spaces are in contact with metallic-luster minerals, graphite, clays or other alteration products

(Griffiths and Barker, 1993).

The IP model across the problematic (VES 2) and non-problematic zone (VES 3) showed

low chargeability with a relatively higher chargeability at an offset distance of about 190m along

the profile line which is also the inferred boundary between the problematic and the non-

problematic zones (Fig. 23). This is chargeability anomaly in areas with higher especially at

depths between 15.9 and 28.7m with chargeability range between 152 to 400 Msec, indicating

high metallic content materials.

The greatest limitation of the resistivity sounding method is that it does not take into

account horizontal changes in the subsurface resistivity. A more accurate model of the

subsurface is a two-dimensional (2-D) model where the resistivity changes in the vertical

direction, as well as in the horizontal direction along the survey line (Loke, 2000).

Resistivity tomography (ERT) for the profile line carried out along VES II and VES III revealed

a relatively high resistivity (50 Ω m) at an offset distance of about 190 m, and a steady increase

from there to the end of the profile line (270 m). Therefore, the author inferred that the boundary

between the problematic zone and the Non problematic zone is at the offset of 190m along the

profile line (Fig. 24), The arrow shows the boundary between the problematic and the non-

problematic zones. Previous works revealed that sand stones have higher resistivity values

compared to shales (Sowers and Sowers, 1970; Dohr, 1975; Palacky, 1987). This implies that the

Non problematic zone has higher shear strength compared to the problematic zone. This was

further confirmed during the field study, that the residential houses from the 190m offset of the

profile line do not have any crack on the walls.

Fig. 23: Induced Polarization Model across the problematic and non-problematic zones.

Fig. 24: Electrical resistivity profile across the problematic and non-problematic zones.

4.9 PROPOSED MECHANISM OF FREQUENT BUILDING COLLAPSE IN AKPUGO:

FINDINGS FROM INTEGRATING GEOTECHNICAL AND GEOPHYSICAL

METHODS

This research work presents an approach to investigate the phenomenon of major cracks

and subsequent building collapse in Akpugo. Geophysical and geotechnical methods were used

together in order to evaluate these cracks and identify the reasons that led to the emergence of

such phenomenon. These cracks on the walls in Akpugo can normally occur due to a geological

or physical event or due to the nature and properties of the subsurface material (Fouzan and

Muawia, 2013). It was intended to use two different techniques at a time, compare, and integrate

the outcome of the results. The results of geophysical method revealed that the problematic zone

has lower resistivity values, while the non-problematic zone has higher resistivity values. The

geotechnical results showed lower permeability, angle of shearing resistance and higher

plasticity and fines content, while the non-problematic zone revealed higher permeability, angle

of shearing resistance, lower plasticity and fines content. The geophysical and geotechnical tests

showed good agreement. The results showed that the cracks on the walls were mainly caused due

to the nature of the soil in the area, which is considered as a high-risk soil type and classified

within expansive soil groups (Sowers and Sowers, 1970; Bell, 2007 and Arora, 2008). The

subsurface formation of the problematic zone contained excessive fines with high percentage of

highly plastic clay materials as revealed by particle size distribution, vertical electrical sounding

(VES) and x-ray diffraction.

Akpugo is in the tropics, which has two major seasons (wet and dry season). The water

content of the expansive soils in the area increases during the wet season and decreases during

the dry season. Smectite clay mineral in the soil adsorbs much water during the wet season and

swells/expands, while it shrinks/decreases during the dry season. The phenomenon of swelling

and shrinking causes the cracks on the soils and the walls in the study area. According to Arora

(2008), these cracks may travel deep into the ground with a maximum width usually limited to

20mm. The soils do not support foundation of structures and thus, heavy damage may occur to

buildings, roads, runways, pipeline and other structures built on such soils if proper preventive or

safety measures are not adopted (Arora, 2008).

The above mechanism might majorly be the cause of frequent building collapse in the study

area. During the rainy season, the soils becomes wet, and they expand as their water content is

increased causing structures built on them to experience cracking and damage due to differential

heave. Also, a crack occurs during the dry season due to shrinkage of the soils when they

become dry, thereby causing differential settlement of the structures built on them (Arora, 2008;

Fouzan and Muawia, 2013). The damage can be prevented to a large extent if the characteristics

of the expansive soil and the active zone are properly assessed and suitable measures are taken in

the design, construction and maintenance of structures built on the soil.

During swelling of the expansive soil, they push up parts of the engineering structures

constructed on them as the soils take the shape of a dome and cracks develop on them. The parts

of the structure most affected are the foundations, walls, floors and slabs. The footing wall is

pushed outward and it causes the cracking of the end wall of the building (Fig. 25A) Also,

Cracks occur at the junctions between the walls and the floor slab (Fig. 25B) and also between

the wall and the roof slab (Fig. 25C) because movements are restricted at these points. Cracking

also occurs at the corners of the windows and door openings (Fig. 25D) because of diagonal

cracking of the walls.

Fig. 25: Expansive soil most affected structural part of an engineering structure (a) wall corners

or end of wall (b) junction between the wall and floor (c) between the wall and the roof slab (d)

Corners of windows and doors

A B

D C

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

5.1 CONCLUSIONS

The geotechnical results obtained from the study area revealed that the soils in the

problematic zone have medium to high plasticity, most probably, due to its content of expansive

clay mineral as revealed by the X-Ray diffraction which showed presence of significant amount

of smectite. The results of the non-problematic zone revealed lower plasticity of the soils while

the electrical resistivity results showed mainly saturated clays/silts at the problematic zone and

sands at the non-problematic zone. The electrical resistivity profile revealed the boundary

between the problematic zone and non-problematic zone. The presence of significant amount of

smectite which has a very high swelling and shrinkage potential in soils of the problematic zone

is the main cause of building collapse in the study area. The geotechnical and geophysical results

agreed, showing that integrating two or more techniques should be adopted more in scientific

studies for better results.

5.2 RECOMMENDATIONS

The following recommendations by the author, arise from the findings of this research.

1 Strong and rigid foundations: the foundation is made strong and rigid to withstand heave.

Because the structures are rigid, uniform settlements would occur.

2 Flexible structures: structures are made flexible so that they change shape depending

upon the heave. Thus the effect of differential heave is not felt.

3 Stabilization of the soil to increase its shear strength is required before erecting a

building at the problematic zone. Application of hydrated lime to swelling soils is a

common treatment that is usually effective in preventing or reducing expansion. In this

method the sodium in the clay is replaced with calcium, thereby reducing the ability to

swell

4 Relocation to the non-problematic zone for the people living in the problematic zone

because many of them cannot afford the options above.

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APPENDICES


Appendix 10: X-Ray Diffraction Data of Location 1(Problematic zone)

2θ d values I int I max. I rel. I corr. FWHM

16.66 5.32193 141 6.8 31.1 40.9 0.280

16.80 5.27783 190 9.1 41.9 54.9 0.280

17.19 5.15818 52 2.5 11.5 14.7 0.280

17.55 5.05189 65 3.1 14.2 17.9 0.280

25.60 3.47898 454 21.7 100.0 100.0 0.285

31.73 2.81988 34 1.6 7.4 6.8 0.289

31.82 2.81223 104 5.0 22.8 21.0 0.289

32.27 2.77382 257 12.3 56.7 52.0 0.289

33.30 2.69030 131 6.3 28.8 26.1 0.289

33.77 2.65381 196 9.4 43.2 39.1 0.289

34.10 2.62891 282 13.5 62.0 55.9 0.289

34.55 2.59587 236 11.3 52.0 46.7 0.289

34.85 2.57458 220 10.5 48.5 43.5 0.289

35.25 2.54620 274 13.1 60.3 53.8 0.289

35.50 2.52885 303 14.5 66.8 59.5 0.289

35.89 2.50213 249 11.9 54.9 48.7 0.289

36.14 2.48562 147 7.0 32.4 28.7 0.289

36.34 2.47233 240 11.5 52.9 46.8 0.289

37.09 2.42400 337 16.1 74.2 65.4 0.288

37.46 2.40074 275 13.1 60.5 53.1 0.288

37.88 2.37521 221 10.6 48.6 42.6 0.288

38.34 2.34737 283 13.5 62.3 54.4 0.287

38.67 2.32857 246 11.8 54.2 47.3 0.287

39.03 2.30792 101 4.8 22.2 19.3 0.287

39.07 2.30553 107 5.1 23.6 20.5 0.286

39.43 2.28495 173 8.3 38.1 33.0 0.286

40.00 2.25405 245 11.7 54.0 46.7 0.286

40.65 2.21925 75 3.6 16.5 14.2 0.285

41.14 2.19408 183 8.8 40.3 34.6 0.284

41.65 2.16843 142 6.8 31.4 26.9 0.284

42.39 2.13225 81 3.9 17.8 15.2 0.283

43.72 2.07061 79 3.8 17.3 14.7 0.282

44.01 2.05740 124 5.9 27.4 23.2 0.281

44.67 2.02855 94 4.5 20.6 17.4 0.280

45.02 2.01359 111 5.3 24.4 20.6 0.280

45.26 2.00357 52 2.5 11.4 9.6 0.279

45.73 1.98388 81 3.9 17.7 14.9 0.279

46.19 1.96521 47 2.3 10.4 8.8 0.278

46.41 1.95631 49 2.3 10.8 9.0 0.278

46.61 1.94860 116 5.5 25.5 21.3 0.278

48.21 1.88738 62 3.0 13.6 11.3 0.276

49.01 1.85844 40 1.9 8.7 7.2 0.275

49.28 1.84919 48 2.3 10.5 8.7 0.275

49.80 1.83101 32 1.5 7.0 5.8 0.275

65.31 1.42870 26 1.2 5.7 4.6 0.279

65.59 1.42329 44 2.1 9.7 7.7 0.279

66.12 1.41313 50 2.4 11.1 8.9 0.281

66.60 1.40413 140 6.7 30.9 24.6 0.282

Continuation of X-Ray Diffraction Data of Location 1(Problematic zone)

2θ d values I int I max. I rel. I corr. FWHM

67.25 1.39208 191 9.1 42.1 33.5 0.285

67.49 1.38766 213 10.2 47.0 37.4 0.286

67.92 1.37994 160 7.7 35.3 28.0 0.287

68.17 1.37560 176 8.4 38.8 30.8 0.286

68.60 1.36790 210 10.0 46.2 36.7 0.280

69.38 1.35457 228 10.9 50.3 39.9 0.280

69.57 1.35122 243 11.6 53.4 42.4 0.280

69.75 1.34814 262 12.5 57.7 45.7 0.280

70.16 1.34132 355 17.0 78.1 61.9 0.280

70.55 1.33482 265 12.7 58.4 46.3 0.280

70.86 1.32976 297 14.2 65.5 51.8 0.280


Distance(m) a (m) Resistivity(Ω m) IP (Msec)

15 10 5.6811 5.72

25 10 6.2419 -0.54

35 10 5.0721 -3.67

45 10 5.7725 0.6

55 10 5.0311 -1.94

65 10 5.0246 15.6

75 10 6.0612 2.29

85 10 6.4881 12.7

95 10 8.4418 3.33

105 10 10.883 19.7

115 10 15.207 -1.97

125 10 17.671 3.68

135 10 13.075 -13.7

145 10 15.469 -5.64

155 10 12.422 4.63

165 10 15.528 -10.8

175 10 19.375 7.5

185 10 25.105 4.74

195 10 50.345 7.54

205 10 55.705 3.61

215 10 76.003 6

225 10 90.695 7.09

235 10 77.159 16.8

245 10 109.07 10.1

255 10 70.818 20.1

Appendix 12: Horizontal profiling data of the Study Area

when “a” is 20


30 20 5.3953 1.84

40 20 4.9992 -8.76

50 20 5.7037 -0.74

60 20 5.87 -3.39

70 20 6.981 31.9

80 20 6.9739 36.1

90 20 9.1054 104

100 20 6.9036 -38.8

110 20 12.284 13

120 20 14.395 24.3

130 20 11.825 -23.6

140 20 10.904 23.3

150 20 13.142 -36.5

160 20 16.113 37

170 20 14.058 12.6

180 20 15.795 5.56

190 20 22.574 6.56

200 20 23.095 14.8

210 20 23.137 39.6

220 20 21.372 76.8

230 20 25.996 18.9

240 20 27.228 48.7


when “a” is 30


45 30 5.5838 -8.19

55 30 7.328 36.4

65 30 7.5929 35.4

75 30 7.9326 110

85 30 7.0936 57.7

95 30 8.2533 44.3

105 30 13.829 68.6

115 30 12.632 20.5

125 30 13.678 51.8

135 30 10.809 3.96

145 30 10.667 34.2

155 30 10.018 -1.34

165 30 10.226 -91.6

175 30 12.868 -29

185 30 15.341 9.29

195 30 21.341 51

205 30 16.313 194

215 30 13.367 -15.8

225 30 23.207 144


when “a” is 40


60 40 15.897 136

70 40 9.338 80

80 40 8.208 63

90 40 10.051 71.2

100 40 8.6077 10.9

110 40 13.425 49.1

120 40 9.8798 -1.82

130 40 13.582 74.8

140 40 11.527 80.6

150 40 13.651 84.6

160 40 7.6067 -60

170 40 9.8974 34.6

180 40 15.324 45.8

190 40 16.518 508

200 40 24.301 102

210 40 29.745 151


when “a” is 50


75 50 10.839 87.2

85 50 6.4176 20.5

95 50 11.564 55.9

105 50 7.7967 -37.5

115 50 14.698 69.3

125 50 12.263 48.7

135 50 11.335 51.4

145 50 9.6962 35.3

155 50 9.41 57.7

165 50 20.289 144

175 50 10.669 268

185 50 14.057 98.3

195 50 5.2633 1186


when “a” is 60


90 60 7.1483 -1.83

100 60 12.774 69.7

110 60 12.003 59

120 60 15.296 88.1

130 60 11.535 39.4

140 60 13.029 73.9

150 60 5.6202 1069

160 60 21.277 208

170 60 15.36 158

180 60 35.848 231

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