Vol. 11(22), pp. 296-305, 30 November, 2016 DOI: 10.5897/IJPS2016.4546 Article Number: 128344F61633 International Journal of Physical ISSN 1992 - 1950 Copyright ©2016 Sciences Author(s) retain the copyright of this article http://www.academicjournals.org/IJPS Full Length Research Paper Troubled roads: Application of surface geophysics to highway failures of the sedimentary terrain (Iruekpen- Ifon Road) of Edo State, Nigeria Ozegin K. O.1*, Adetoyinbo A. A.2, Jegede S. I.1 and Ogunseye T. T. 2 1 Department of Physics, Ambrose Alli University, Ekpoma Edo State, Nigeria. 2 Department of Physics, University of Ibadan, Ibadan, Nigeria. Received 2 August, 2016; Accepted 24 October, 2016 As part of effort to examine the factors responsible for highway failure in the sedimentary terrain, geophysical survey involving Very Low Frequency Electromagnetic (VLF-EM), Schlumberger Vertical Electrical Sounding (VES), and dipole-dipole electrical resistivity techniques were carried out along Iruekpen-Ifon highway. This was aimed at using surface geophysics to characterize and identify the factors responsible the for road failures along Iruekpen-Ifon highway. ABEM WADI instrument was used to obtain electromagnetic-Very Low Frequency (VLF) field data, while ABEM resistivity meter was used to obtain electrical resistivity field data. The VLF-EM data were interpreted using the VLF Graphic software, VELFAN 1.0 double plot of filtered real and filtered imaginary against distance. The VES data obtained were interpreted using IP 2 Win software. Geoelectric parameters were used to generate the Dar Zarrouk second order parameters. 2-D inversion modeling of the dipole-dipole data was carried out using ZONDRES window software. VLF-EM result suggested varying degree of conductivity in the area and the wide spread of clay/metallic ore and water in the study area. Results show that the topsoil generally varies in composition from clay to clayey and laterite with resistivity values varying from 89 to 400 Ωm and thickness between 0.2 and 4.0 m. The fractured layers composed of clay and compacted clayey sand which represents the recent alluvial deposits with resistivity values of 2 to 89 Ωm and the thickness between 1.5 and 11 m. The fresh water zone is characterized by low resistivity ranging from 0.5 to 23 Ωm, which is diagnostic of saline water saturated with clay formation, fresh water ingression, and marls. The values of co-efficient of anisotropy () range from 1.03 to 2.19. The relatively higher values of λ (1.30 to 2.19) suggest that the subsurface rocks in these areas are likely to be more intensely fractured and more permeable. The saline water saturated with clay formation, fresh water ingression, fracture and marls clearly limit the lithological contacts and enhance high swelling potential which might be responsible for the road pavement failures in the studied area. Key words: Highway, resistivity, troubled roads, Dar Zarrouk, anisotropy. INTRODUCTION A road is a thoroughfare, way, or route on land between such as cracks, surface deformation (rutting, etc.), two places, which in general has been paved or disintegration (potholes, etc.), surface defects (ravelling, otherwise, enhanced to allow travel by some etc.) on a road network is regarded as road failure. transportation. However, the presence of discontinuities Accordingly, roads are constructed with detailed UNIVERSITY OF IBADAN LIBRARY Ozegin et al. 297 information obtained from geological, geophysical and series of small polygons resembling an alligator’s skin geotechnical investigations of the construction site (Figure 1a). This could result from the fatigue effect of because information obtained play important role in the repetitive heavy truck loads or ageing in combination with design, stability, economical construction and exponential loss of pavement thickness. It can occur with maintenance of the roads. Such investigations are or without surface distortion and pumping. capable of delineating structures such as unconsolidated soil formations with varying resistivity and expansiveness, naturally occurring underground water channels which Rutting may expedite discontinuities. Degradation of many highway pavements is traceable to the surface water A rut is a longitudinal deformation at wheel tracks mainly ingress through cracks and joints. These have resulted to associated with shoving along the road (Figure 1b). This frequent motor accidents leading to loss of lives and is caused by heavy loads and high tyre pressure, properties in Nigeria. However, some major Nigerian subgrade settlement caused by saturation, poor highways are known to fail shortly after construction and construction methods, or asphalt mixtures of inadequate well before their design ages and this unfortunately has strength. become an embarrassing stigma to the road users and nation at large. Furthermore, one of the main consequences of many rackety vehicles on the Nigerian Chuck holes (Potholes) roads is due to its failure. It has been shown that vehicles wear down faster in less developed countries of Africa Potholes are irregularly shaped holes of various sizes. like Nigeria than is obtainable in civilized economies. This These most often result from wear or destruction of the is evident in secondhand vehicles that are shipped from wearing course, sometimes from the presence of foreign developed economies to Africa which are in most cases bodies in the surfacing (Figure 1c). They can also be here considered as new vehicles. caused by water penetrating the surface and causing the In particular, three main sections of the Iruekpen-Ifon base and/or subgrade to become wet and unstable. They highway have experienced recurrent failure after are small when they first appear. In the absence of rehabilitations. In recognition of the devastating effects of maintenance, they grow and reproduce in rows. these highway problems in recent years, it has become imperative to use surface geophysics to investigate these failed sections in order to identify the causes of the Ravelling failures along this highway. Surface geophysics provides economic, non-destructive and rapid tools for the This is progressive loss of pavement material. The detection of discontinuity in road network resulting in possible cause for ravelling could be separation of cracks, disintegration, bulges and depressions. There are bituminous film from aggregates through stripping caused numerous case studies all over the world showing the by deficiency of bonding or ageing of surface due to effectiveness of geophysical methods in the detection of variations in climatic and loading conditions (Figure 1d). It highway failures (Olorunfemi and Mesida, 1987; Adesida can also occur due to the inconsistent deformation of the and Omosuyi, 2005; Ozegin et al., 2007; Momoh et al., lower pavement layers. 2008; Ojo et al., 1990; Soupios et al., 2007; Akintorinwa and Adeusi, 2009; Ofomola et al., 2009); and the methods have been established to play complementary Shear failures (Block cracking) roles in geotechnical studies, besides the fact that they are less expensive and non-invasive. This is block cracking leading to chipping of pavement Road failure is an inevitable consequence of man’s surfacing and/or upheaval outside the tyre cracks with activities and a natural phenomenon as well. Road failure associated cracking. This could result from deficiency in can be of these patterns, namely, (i) Alligator cracking, (ii) cohesion and internal friction in pavement base structure Rutting, (iii) Chuck holes (Potholes), (iv) Ravelling, and due to ageing and fatigue (Figure 1e). (v) Shear failures (Block cracking). MATERIALS AND METHODS Alligator cracking Two geophysical methods were adopted; Very Low Frequency This is described by interconnected cracks forming a electromagnetic method and electrical resistivity method. ABEM *Corresponding author. E-mail: ozeginkess@yahoo.com. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License UNIVERSITY OF IBADAN LIBRARY 298 Int. J. Phys. Sci. Figure 1. (a) Alligator cracking; (b) Rutting at wheel path; (c) Potholes; (d) Ravelling; (e) Block cracking. WADI instrument was used to obtain electromagnetic-Very Low longitudinal conductance and resistivity  (-m) for the co-efficient Frequency (VLF) field data, while ABEM resistivity meter was used of anisotropy () in porous media). 2-D inversion modeling of the to obtain electrical resistivity field data. The use of electromagnetic dipole-dipole data was carried out using ZONDRES window method was preliminary survey along the three locations with software. It should be emphasized that 2 D Electrical Resistivity traverses measuring 210, 600 and 140 m, respectively. The EM- Tomography (ERT) is a method by which 2 Dimensional images of VLF data were interpreted using the VLF Graphic software, subsurface resistivity distribution are generated. Using this method, VELFAN 1.0 double plot of filtered real and filtered imaginary features with electrical properties differing from those of the against distance. For the electrical resistivity method, two surrounding material may be located and characterized in terms of techniques were used, namely, the Vertical Electrical Sounding electrical resistivity, geometry and depth of burial. (VES) using Schlumberger configuration with AB/2 (AB/2 = Current electrode spacing) varying from 1 to 100 m. A total of 42 VES stations were occupied, which include 10, 25 and 7 VES stations at Location and geological setting of the study area the three studied locations, respectively. 2-D Electrical Resistivity Tomography (ERT) using dipole-dipole configuration with inter The study area is bounded by Longitudes 5°50ʹ and 6°39ʹE and station separation (a) of 10 m, an expansion factor (n) that varied Latitudes 6°55ʹ and 7°37ʹN (as shown in Figure 2). The study area from 1 to 5 was also carried out. The VES data obtained were is underlain by the Imo Eusterine and Marine Shale which comprise interpreted using IP 2 Win Software and layer parameters such as grey-black shale at the basal region of the section of about 100 m, true resistivity and thickness were determined. The geoelectric graded upward into alternation of thin beds of fissile dirty-light shale parameters were used to generate the concept of Dar Zarrouk and gypsum of about 2 to 5 cm. The section passes on into light second order (Maillet, 1974) parameters (transverse unit resistance, yellow-brown sandy mudstone with lateral variation in faces from UNIVERSITY OF IBADAN LIBRARY Ozegin et al. 299 Iruekpen – Ifon road F igure 2. Geological and mineral resources map of Edo State, NGSA 2006. sandy mudstone to clay. The shale is generally hard at Uhonmora constitutes the Anambra Basin. Sedimentation in the Anambra and the section is more of shale and intercalation of gypsum and Basin, thus commenced with the Campanian-Maastrichtian marine shale towards the top of the section. However, the Ozalla section of and paralic shales of the Enugu and Nkporo Formations, overlain the Imo Shale does not have intercalation of gypsum bed with shale by the coal measures of the Mamu Formation (Reijers and Nwajide, rather it comprises mudstone, clay and shale (Plate 1). The two 1998). The fluviodeltaic sandstones of the Ajali and Owelli sections of Imo Shale in the study area exhibit similar unique Formations lie on the Mamu Formation and constitute its lateral characteristic of ferruginous nature within the sandy mudstone unit. equivalents in most places. In the Paleocene, the marine shales of This unique characteristic in the study area strengthening the the Imo and Nsukka Formations were deposited, overlain by the load carrying capacity of the lithology except for the area with tidal Nanka Sandstone of Eocene age. Down dip, towards the Niger faces variation from ferruginous sandy mudstone to clay. The Delta, the Akata Shale and the Agbada Formation constitute the mudstone is well laminated with imbedded clay clast (Obaje, 2009). Paleogene equivalents of the Anambra Basin. Sedimentation in the Lower Benue Trough commenced with the marine Albian Asu River Group, although some pyroclastics of Aptian-Early Albian ages have been sparingly reported (Ojoh, RESULTS AND DISCUSSION 1992). The Asu River Group in the Lower Benue Trough comprises the shales, limestones and sandstone lenses of the Abakaliki Formation in the Abakaliki area and the Mfamosing Limestone in The approaches adopted for data interpretation are of the Calabar Flank (Petters, 1982). The marine Cenomanian– two types, namely qualitative approach which involves Turonian Nkalagu Formation (black shales, limestones and visual inspection of Electromagnetic curves and siltsones) and the interfingering regressive sandstones of the Agala quantitative approach which involves depth calculation of and Agbani Formations rest on the Asu River Group. Mid-Santonian VES, dar Zarrouk parameters etc. The localities studied deformation in the Benue Trough displaced the major depositional axis westward which led to the formation of the Anambra Basin. are variously shown in (Plate 2a to c). Post-deformational sedimentation in the Lower Benue Trough, The purpose of Very Low Frequency – Electromagnetic UNIVERSITY OF IBADAN LIBRARY 300 Int. J. Phys. Sci. Plate 1. Geological setting showing beddings and faults of the rock exposures. Method (VLF – EM) is to qualitatively delineate the secondary parameters (longitudinal conductance (Si), conductive zones and non-conductive zones in the study transverse resistance (Ti), longitudinal resistivity (  ), L area. Graphic software, VELFAN 1.0 developed by Alberg Services Nigeria Limited (Geophysical Consulting transverse resistivity (  t ) and coefficient of anisotropy Services), in MATLAB graphical user interface was used (λ)) were determined from the layers’ resistivities and to plot the filtered imaginary and real Very Low thicknesses using the mathematical relations (Zohdy et Frequency- Electromagnetic curves. High positive values al., 1974): indicate presence of conductive subsurface structures while low or negative values are indicative of resistive n h formations, (Sharma and Baranwal, 2005). Si  i (1) The positive peak anomalies P1, P2, P3 and P4 on the i1 i filtered real curve, revealed vertical and/ or near vertical conductors (Figure 3a). n 2 In Figure 3b, the filtered real curve indicates Ti hi i (Ohm.m ) (2) conductors with positive peaks. P1, P2, P3, P4, P5, P6, i1 F1, F2 and F. These conductors are 80, 175, 212, 245, 380, 420, 500, 522 and 550 m from the starting station n h (zero mark) of the survey profile.   i (ρl=H/S) (3) L In Figure 3c, the positive peaks anomalies P1, P2, P3 , i1 si P4 and P5 indicated on filtered real curve, show locations of vertical and/or near vertical conductors. These n T anomalies are 42, 102, 143, 169 and 200 m from the t  i (ρt = T/H) (4) starting station (zero mark) of the survey profile. i1 hi Estimating Dar Zarrouk (D-Z) parameters from (VES) t results   (5)  L The analysis of the D-Z parameters longitudinal unit conductance (S), transverse unit resistance (T), also, The concept of Dar Zarrouk parameters were first longitudinal resistivity (ρt) provides a very convenient and introduced by Maillet (1974) to explain the problem of easily applicable solution to understand the geophysical non-uniqueness in the interpretation of resistivity depth behavior of saline and fresh water aquifers. (Maillet, sounding curves. As resistivities of clay with sand and 1947) termed the Dar Zarrouk (D-Z) parameters. The saline water interfere with each other, the data UNIVERSITY OF IBADAN LIBRARY Ozegin et al. 301 Plate a Plate b Plate c Plate 2. (a) Failed Section at Locality 1; (b) Failed Section at Locality 2; (c) Failed Section at Locality 3. interpretation becomes a difficult task. Such situation fresh and saline aquifers. requires the formulation of better analysis technique of The geoelectric parameters were used to generate the interpretation for the existing data to yield useful and concept of Dar Zarrouk second order parameters. The easily understandable solution to differentiate among coefficient of anisotropy (λ) has been shown to have UNIVERSITY OF IBADAN LIBRARY 302 Int. J. Phys. Sci. a b c Figure 3. (a) VLF-EM Curves in locality 1; (b) VLF-EM Curves in locality 2; (c) VLF-EM Curves in locality 3. UNIVERSITY OF IBADAN LIBRARY Ozegin et al. 303 Table 1. Dar Zarrouk parameters results. VES No. Total resistance (T) Total conductance (S) Co-efficient of anisotropy () 1 115.40 0.017 1.03 2 274.73 0.063 1.20 3 87.31 0.027 1.07 4 654.08 0.144 1.05 5 114.21 0.015 1.24 6 226.13 0.068 1.13 7 102.79 0.128 1.51 8 153.28 0.019 1.38 9 376.84 0.013 1.15 10 851.87 0.007 1.29 11 284.50 0.057 1.16 12 548.80 0.019 1.36 13 583.52 0.024 1.31 14 380.82 0.036 1.31 15 289.81 0.067 1.22 16 279.80 0.070 1.21 17 190.99 0.037 1.12 18 564.75 0.013 1.61 19 181.87 0.081 1.24 20 223.41 0.061 1.14 21 191.51 0.033 1.42 22 175.93 0.033 1.42 23 158.91 0.050 1.33 24 193.62 0.022 1.22 25 230.88 0.030 1.17 26 235.05 0.066 1.28 27 200.85 0.028 1.22 28 414.04 0.023 1.28 29 380.38 0.026 1.29 30 425.75 0.022 1.16 31 245.12 0.026 1.11 32 225.23 0.118 1.12 33 454.77 0.121 1.50 34 353.53 0.047 1.37 35 273.82 0.020 1.06 36 2212.63 0.008 1.53 37 1313.04 0.015 1.43 38 533.34 0.035 1.84 39 163.94 0.070 1.24 40 196.27 0.083 1.33 41 330.10 0.022 2.19 42 150.45 0.019 1.09 the same functional form as permeability anisotropy. intensely fractured and more permeable. These clearly Thus, a higher coefficient of anisotropy (λ) implies higher limit the lithological contacts and enhance high swelling - permeability anisotropy. The values of co-efficient of potential. anisotropy () ranges from of 1.03 to 2.19 (Table 1). The The dipole-dipole profiling involving the combination of relatively higher values of λ (1.30 to 2.19) suggest that horizontal profiling and vertical electrical sounding was the subsurface rocks in these areas are likely to be more adopted as a means of mapping vertical discontinuities UNIVERSITY OF IBADAN LIBRARY 304 Int. J. Phys. Sci. Fractured Saturated clay/marls Wet silty/clay a Fractured Sea water/moist Alluvium (clay interbeded) clay interbeded) b Mud stone/clayey Sand clay/ clayey sand/laterite Saline/Fresh water c Figure 4. (a) 2-D Modelling of Dipole-Dipole Data at Locality 1; (b) 2-D Modelling of Dipole-Dipole Data at Locality 2; (c) 2-D Modelling of Dipole-Dipole Data at Locality 3. typical of jointed, fractured and faulted zones. The dipole- are variously shown in Figure 4a, b and c. dipole field data were inverted to 2-D resistivity structure The dipole-dipole pseudo-sections and the 2-D using ‘ZONDRES for Window’ software. The dipole- resistivity structure at locality 1 are as shown in Figure dipole pseudo-sections and the 2-D resistivity structures 4a. The 2-D resistivity structure shows a subsurface UNIVERSITY OF IBADAN LIBRARY Ozegin et al. 305 sequence with very thin topsoil which is virtually REFERENCES unrepresented on the 2-D resistivity structure, a nearly Adesida A, Omosuyi GO (2005). Geoelectric investigation of Bedrock uniform weathered layer and nearly filled entire structure Structures in the Mini-Campus of The Federal University of with wet silty/clay and saturated clay/marls. The dipole- Technology, Akure, Southwestern Nigeria and the Geotechnical dipole pseudo-sections (field and theoretical) and 2-D Significance. Nig. J. Pure Appl. Phys. 4:32-40. resistivity structure at locality 2 (as shown in Figure 4b), Akintorinwa OJ, Adeusi FA (2009). Integration of geophysical and geotechnical investigation for a proposed lecture room complex at the shows a fracture/weathered basement, moist clay and Federal University of Technology, Akure, SW, Nigeria. J. Appl. Sci. alluvium that are predominately observe with depth 2(3):241-251. varying from 1 to 12 m. Figure 4c shows the dipole-dipole Maillet R (1974). The fundamental equations of electrical prospecting. pseudo-sections and 2-D resistivity structure profile at Geophysics 12(4):529-556. Momoh LO, Akintorinwa OJ, Olorunfemi MO (2008). Geophysical locality 3. 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The Southern part of the Benue Trough (Nigeria) From the engineering geophysical site investigation Cretaceous stratigraphy, basin analysis, paleo-oceanography and undertaken at the study areas (locations 1, 2 and 3), it geodynamic evolution in the equatorial domain of the South Atlantic. can be inferred that the possible causes of highway NAPE Bull. 7:131-152. Olorunfemi MO, Mesida EA (1987). Engineering Geophysics and its pavement failure in the studied highway are near-surface application in Engineering Site Investigation-(case study from Ile-Ife linear (geological) features such as lithological contact area). Nig. Eng. 22(2):57-66. beneath the highway pavements. This feature act as Ozegin KO, Azi SO, Isiwele DO (2007). Geophysical Investigation of zone weakness that enhances the ingression Oke-Agbe-Oyin Road Failure Using VLF and Double Dipole. J. Nig. Assoc. Math. Phys. 11:411-414. (accumulation) of water and hence leading to pavement Petters SW (1982). Central West African Cretaceous-Tertiary benthic failure portions at all the locations, which is secondary foraminifera and stratigraphy. Palaeontographica Abt. A 179:1–104. salinity. Marls and clay topsoils/sub-grade soils (with Reijers TJA, Nwajide CS (1998). Geology of the Southern Anambra characteristic low layer resistivity less than 100 Ωm) Basin. Unpublished Report for Chevron Nigeria Limited. Field Course Note. which are encased in alluvium have the tendency of Soupios PM, Georgakopoulos P, Papadopoulos N, Saltas V, absorbing water as a result of intense fracture hence Andreadakis A, Vallianatos F, Sarris A, Makris JP (2007). Use of exhibit high swelling potential and collapse under engineering geophysics to investigate a site for a building foundation. imposed traffic load stress which subsequently lead to J. Geophys. Eng. 4:94-103. Sharma SP, Baranwal VC (2005). Delineation of groundwater-bearing translational failure. This fracture could also be said to be fracture zones in hard rock area integrating VLF-EM and resistivity non-systematic and first order. This was majorly data. J. Appl. Geophys. 57:155-166. observed in failed portion 2. Excessive cut into the Zohdy AAR, Eaton GP, Mabey DR (1974). Application of surface conductive water absorbing clayey substratum geophysics to groundwater investigations: Techniques of water resources investigations of the United Geophysical Survey Book. (weathered layer) that is montmorillonite (clay that United States Government Printing Office, Washington DI, P 116. undergoes expansion and contraction by virtue of change in moisture contents) as observed at locations 1 and 3. Potential to degrade the pavement material is the presence of water (permanent or seasonal) in the road environment, may have a far more deleterious impact on the road formation than salts present in the water. This was visibly seen in location 2. Conflict of Interests The authors have not declared any conflict of interests. View publication stats UNIVERSITY OF IBADAN LIBRARY