ABSTRACT
This project work was carried out at
Ireukpen-Ozalla Road Axis Ekpoma, Esan-West Local Government Area Edo State.
Using seismic refraction prospecting method to examine the cause(s) of the
persistent failure of the road. An ABEM TERRALOC MARK-6 Seismometer was used as
the recording instrument and twelve geophones as wave detectors in series with
one another. The geophones were spread at predetermined distances and the
impact of a sledge hammer on a flat plate served as the source of generating
seismic waves. The “SERCOM1” software was employed in the interpretation of the
field result for the forward and reversed shooting respectively. From which the
subsurface reveals two layers of velocities, which are 980ms-1 and
1283ms-1 for the forward shooting, 851ms-1 and 1276ms-1
for the reversed shooting respectively. The investigation also shows that at
twenty three metres (23 m) from the surface of the forward shooting, clay
deposit could be discovered. And even at thirteen metres (13 m) from the
surface of the reversed shooting clay deposit could also be encountered. The
form of road failure identified in this study is due to subsidence associated
with clayey material and the delineated clayey water absorbing sections which
are major geologic factors responsible for road failure in the area.
CHAPTER ONE
MEANING AND BASIC APPLICATION OF GEOPHYSICS
1.1 INTRODUCTION
It is to be noted that the
geophysical method of prospecting and delineation of anomalous zone in the
subsurface extend its wide application to buried material (both of economic and
non economic values) (Ozegin, K.O. et al., 2007). Also geological factors are
not often considered as precipitators of road failure even though the highway
pavement is founded on the geology (Momoh et al., 2008).
Seismic method has successfully help
in the search and exploitation of the subsurface. In particular, seismic
refraction method is commonly used to get detailed information of the
subsurface lithology, geologic setting (mapping), locating refracting
interfaces separating layers of different seismic velocity, subsurface mapping,
lithological boundary differentiation, engineering geophysics and static
correction.
It is sad to note, that, the
perennial or incessant failure and poor rehabilitation work on these roads has
become a very common phenomena and a source of concern. Generally, in seismic
refraction surveying technique, the method uses seismic energy that returns to
the surface of the Earth after travelling through the ground along refracted
ray paths. The vast majority of refraction surveying is carried out along
profile lines which are arranged to be sufficiently long to ensure that
refracted arrivals from target layers are recorded as first arrivals for at
least half the length of the line. It involves putting the first geophone
relatively far away from the shot point, and the shot and detector are on the
same line. Consequently, the ABEM TERRALOC MARK-6 were used. And a hand held
hammer was used to generate the source energy.
Many factors causes road failure,
these include;
Geogical,
geomophological/geotechnical, road usage, poor or bad construction practices
and maintenances. The influence of geology and geomorphology in the design and
construction phases may not have been adequately considered. The problem could
also be as a result of inadequate knowledge of the characteristics and behavior
of residual soils and not putting the bearing capacity of rocks in relation to
vehicular traffic into consideration. Furthermore, the geological factors in
road failure covers the nature of soils (i.e. laterite) the near surface
geological sequence, existence of geological structure like cavities, ancient
stress, channels and shear zones, near surface geological sequence. Sometimes
there is the presence of some concealed subsurface geological structure as well
as rock weakness or deficiency. One or more of the aforementioned factors has
been noticed to have contributed in some of our highway and rail track
failure. For the purpose of
information, geomorphological factors are concerned or related to topography
and surface/subsurface drainage systems. Also, subsurface geologic sequence and
concealed geological structure can be mapped by geophysical method, hence its
relevance (Ozegin et al., 2007).
1.2
LOCATION OF STUDY AREA
The study area lies along the
Iruekpen-Ozalla Road, in Esan-West Local Government Area, Ekpoma, Edo State, Nigeria.
It has its headquarters in the town of Ekpoma, with an area of 502km2
and a population of 125,842 people, according to the 2006 national census. The
study area is located on 614411211N, 60813611E
as obtained from a reliable geographical positioning system (GPS) meter. The
Local Government Area is bounded on the South by Orhionmwon Local Government
Area, on the East, by Esan Central Local Government Area (L.G.A), on the West
by Uhumwonde and on the North by Owan West L.G.A. The people of the local government
are basically subsistent farmers and petty traders.
It is thickly forested with a
moderate temperature between 200C to 300C and a climate
which is predominately rainforest characteristics by two seasons, that is, dry
and wet season. Its topography is generally undulating (Ewanlen, T.A., 2010).