Engineering Structural Strength Properties of Lateritic Soil-Cement Mix for Road Pavement Stability

Qualitative construction materials in highway pavement prompted addition of cement at different proportion of 2 - 10% to lateritic soils for enhanced performance. Engineering geological tests were performed on the soil-cement mixture to determine their highway pavement suitability for durable road construction. Furthermore, modelling of the strength characteristics of the mixture presents the correlation between the structural properties and cement mix. Thus, increase in soil-cement California bearing ratio (CBR) and unconfined compressive strength (UCS) values with higher cement mix of 8%, revealed enhanced soil improvement. The soil strength is also affected by the curing period. Better quality strength characteristics obtained decreases pavement thickness with reduced cost in road construction. Relationship between the soil strength properties and cement mix content are represented by polynomial model. This reveals stronger bearing capacity of soil cement mix cured in 14 days with R2 ≥ 0.8. The lateritic soil cement mix at 8% cement content could serve as highway subbase and base construction materials. Cement mix having positive effects on soil geotechnical properties are indication of its effectiveness in enhancing volume stability of different soils. Prolong curing time is essential for compacted soil cement mix for enhanced geotechnical engineering properties and to improve the quality of lateritic soil used as road construction materials. Thus, cement-stabilized lateritic soil reduces cost of road construction, its persistent failure, human and environmental losses

Geophysical and geostatistical reserve estimates of migmatite-gneiss deposits from parts of southwestern nigeria

The plan for durable rock base road construction and other civil engineering works necessitated this study to establish the thickness and quantify migmatite-gneiss deposits. This intends to facilitate its exploitation and proffer specific details for diverse applications. Comprehensive geological field mapping, laboratory density measurements and geoelectrical resistivity were employed for the resource quantification. The extent of migmatite-gneiss deposits and its contacts with other rock types were identified. Seventeen (17) fresh migmatite-gneiss rock samples collected from different rock outcrops were taken to the laboratory for measurement of their density. Schlumberger vertical electrical sounding (VES) technique with a total of forty-two sounding stations were employed across the area with electrode spread (AB/2) ranging 1 - 200 m. The average density of the deposits is 2.70 ± 0.10 g/cm3. Three to five geologic layers characterized the area subsurface sequence. Thick fractured rock layer across the area would facilitate the exploitation of the deposits as construction aggregates. Basement topographical highs at northeastern, northwestern and southeastern parts serve as the best zones viable for mining. The basement resistivity (> 3000 Ωm), resistivity contrast, reflection coefficient values and high transverse layer resistivity (ρT) (> 500 Ωm) corroborate the freshness of the deposits. The average thickness of the deposit is 29.3 m, though, thicker at northeastern and northwestern parts of the area where the deposit is fresh and less weathered. The study area occupies a total area of 71,300,000 m2 with volume of the deposits calculated as 2,089,090,000 m3. Distantly-spaced data points of the variogram reveal high degree of variability with respect to locations. The estimated migmatite-gneiss resource tonnage of 5,640,543,000 tonnes shows prospects for sustainable large scale mining as construction aggregates and diverse applications of economic purposes using open pit coupled with underground mining for deeper sections of the migmatite-gneiss deposit

Nijerya'nın güneybatı temel kompleks bölgesinde yüzeye çıkan granit kayaların doğal radyoaktivite ve radyolojik tehlikelerinin yerinde değerlendirilmesi

Radioactive emission (gamma ray) emanating from rock materials constitutes threats to humans and their environment. Hence, the natural radioactivity and radiological hazard indices of some granite gneiss outcrops with their residual soils from two different localities within the Southwestern Basement Complex of Nigeria were assessed using Gamma-ray spectrometry. The study aimed at determining the natural radiation levels of granite gneissic rocks and associated radiological threats to people living in the study area from gamma ray exposure. Data were collected along six geophysical traverses of 200 m each with station spacing of 5 m using the portable hand-held Gamma-ray Spectrometer. The results of weighted mean values of the elemental and activity concentrations for 40K, 238U, and 232Th are 2.00 ± 1.43%, 3.13 ± 0.90 ppm, 12.32 ± 4.99 ppm and 629.28 ± 447.29, 38.58 ± 11.02, 49.96 ± 20.23 respectively. The obtained mean concentration ratios of 1.32 for U/Th and 2.14 for Th/U were higher than 0.26 and lower than 3.5 global standard ratios respectively. The increase in activity concentrations and concentration ratio may have suggested the enrichment of radioactive minerals in the granite gneissic rocks. The annual outdoor and indoor effective doses of gamma ray exposure for people living in the study area were below the world permissible standard of 1 , thus, the area is radiologically safe. However, increase in estimated mean of AGDE and ELCR; 525.620 and 1.273 above the world permissible standards of 300 and respectively does not translate to significant radiological threats. Therefore, control measure by constant monitoring of the radioactivity levels of the area and rocks should be practiced.Kaya materyallerinden kaynaklanan radyoaktif emisyon (gama ışını) insanlara ve çevresine tehdit oluşturur. Bu nedenle, Nijerya'nın Güneybatı Temel Kompleksi'nde iki farklı bölgeden yüzeye çıkan granit kayalar ile bunların kalıntısı olan toprakların doğal radyoaktivite ve radyolojik tehlike endeksleri Gamma-ray spektrofotometre kullanılarak değerlendirilmiştir. Bu çalışmada, granit yapıdaki kayaların doğal radyasyon düzeylerinin ve bağlantılı radyolojik tehlikelerin çalışma alanında yaşayan ve gama ışınına maruz kalan insanlar üzerindeki etkilerinin belirlenmesi amaçlanmıştır. Veriler, taşınabilir Gamma-ray Spektrometresi kullanılarak her biri 200 m’lik altı jeofizik travers boyunca 5 m’lik istasyon aralığı ile toplanmıştır. 40K, 238U ve 232Th için temel ve aktivite konsantrasyonlarının ağırlıklı ortalama değerlerinin sonuçları sırasıyla %2.00 ± 1.43, 3.13 ± 0.90 ppm, 12.32 ± 4.99 ppm ve 629.28 ± 447.29, 38.58 ± 11.02, 49.96 ± 20.23 dir. Elde edilen U/Th (1.32) ve Th/U (2.14) ortalama konsantrasyon oranları, sırasıyla, genel standart oranları olan 0.26’dan yüksek ve 3.5’tan düşüktür. Aktivite konsantrasyonları ve konsantrasyon oranlarındaki artış, yüzeye çıkan granit kayalarda radyoaktif minerallerin zenginleştiği anlamına gelebilir. Çalışma alanında yaşayan insanlar için gamma ışını maruziyetinde uygulanan yıllık dış ve iç etkili dozları dünyanın izin verilen 1 standardının altında olduğundan, alan radyolojik olarak güvenlidir. Bununla birlikte, AGDE ve ELCR'nin tahmini ortalamaları olan 525.620 ve 1.273 x10-3 değerlerindeki artışın, izin verilen 300 ve 0.29 x10-3 standart miktarların üzerinde olması da ciddi radyolojik tehditler anlamına gelmemelidir. Bu nedenle, alanın ve kayaların radyoaktivite seviyesinin sürekli izlendiği kontrol önlemleri tatbik edilmelidir

GEOTEHNIČKO ISPITIVANJE PUCANJA KOLNIKA – UZROCI I MOGUĆA RJEŠENJA ZA ODRŽIVU KONSTRUKCIJU PROMETNICA U SUPSAHARSKOJ AFRICI

Engineering geological investigation of some unstable and stable sections of the Ibadan-Iwo-Osogbo highway was undertaken to unravel the intrinsic reasons responsible for continuous pavement failure along this road. Eighty disturbed and forty undisturbed soil samples were collected at different depths from twenty test pits of six selected failed sections (FS) and two stable sections (SS). Road construction analysis was done on these soil samples using standard methods. Liquid limit (22 - 64% and 32 - 40%), plasticity index (13 - 41% and 12 - 18%) and percentage fines (47 - 59% and 32 - 41%) indicated fair to poor and fair to good subgrade materials of FS and SS respectively. Medium to high plasticity and high clay content of soils of FS are indicative that the soils possess medium to high swelling potential. The activity of clay in soils of FS was approximately 0.3 – 1.2 and classified as inactive to normal clay. High linear shrinkage (> 10%), low compacted density and predominance of fines in soils of FS caused the instability. Exposure to excessive moisture led to strength reduction of the soils. Triaxial compression showed cohesion (72.6 - 127.0 kN/m2) and internal friction (12.7° - 33.3°) indicating moderate to good shearing strength of the soils. A coefficient of compressibility of 0.1 – 0.5 kN/m2 indicated incompetency of the soils for road construction and the coefficient of consolidation was 0.01 – 0.30 m2 /year. The subsoil of the FS is impervious with a relatively low coefficient of permeability, indicative high saturation in the region. Thus, the pavement failure was caused by water absorbing clayey soil, poor geotechnical parameters of the soils and a poor drainage network.Kako bi se otkrili razlozi neprekidnoga lomljenja i pucanja kolnika duž ceste Ibadan-Iwo-Osogbo, napravljena su inženjerskogeološka istraživanja i nestabilnih i stabilnih odsjeka ceste. Uzeto je 80 poremećenih i 40 neporemećenih uzoraka tla s različitih dubina iz 20 testnih bušotina smještenih na 6 razlomljenih i 2 stabilna odsjeka. Načinjena je analiza konstrukcije ceste uporabom tih uzoraka i standardnih metoda. Vrijednosti granice tekuće faze (22 – 64 i 32 – 40 %), indeks plastičnosti (13 – 41 i 12 – 18 %) te postotak finoće (47 – 59 i 32 – 41 %) uputili su na solidan do loš stupanj za razlomljene i solidan do dobar stupanj za stabilne odsjeke. Srednji do velik indeks plastičnosti i znatan udio gline u tlu na razlomljenim dijelovima pokazali su kako takvo tlo ima srednji do visok potencijal bubrenja. Glina u tim tlima imala je aktivnost 0,3 – 1,2 te je klasificirana kao neaktivna do stabilna glina. Velik iznos linearnoga skupljanja (>10 %), mala gustoća (kompakcija) i prevladavanje sitnozrnatoga detritusa uzrokom je nestabilnosti. Izloženost velikoj vlazi uzrokovala je smanjenje čvrstoće tla. Trosna kompresija uputila je na koheziju (72,6 – 127,0 kN/m2 ) te unutarnje trenje (12,7 – 33,3 o ) pokazujući umjerenu do dobru smičnu čvrstoću takva tla. Koeficijent kompresibilnosti (0,1 – 0,5 kN/m2 ) uputio je na nepogodnost tla za gradnju prometnice, kao i koeficijent konsolidacije (0,01 – 0,03 m2/god). Tlo je ispod razlomljenih odsjeka nepropusno s relativno malim koeficijentom propusnosti te visokim (regionalnim) zasićenjem. Dakle, lomovi su uzrokovani apsorpcijom vode u glinovito tlo, a time i slabim geotehničkim parametrima, odnosno slabom drenažom

Engineering geological evaluation of some rocks from Akure, Southwestern Nigeria as aggregates for concrete and pavement construction

The importance of rocks and rock aggregates cannot be overemphasized in construction and concrete design globally. This study evaluated the physical and mechanical characteristics of fine grained granite, porphyritic granite, quartzite, granite gneiss, migmatite gneiss and charnockite from ten different locations in Akure for their suitability as construction materials. Field observation, water absorption, specific gravity, shape indices, aggregate impact value (AIV), aggregate crushing value (ACV), Los Angeles abrasion value (LAAV), compressive strength, tensile strength and petrography of the selected rocks were evaluated. The field studies indicate fresh outcrops with little signs of weathering. Porphyritic granite shows a higher water absorption value >1%, suggestive of its unsuitability as foundation materials in water logged areas. The higher flakiness and elongation indices of porphyritic granite, quartzite and migmatite gneiss are detrimental to the higher workability and stability of mixes. AIV (14.79–23.52%), ACV (18.32–28.93%) and LAAV (25.22–34.55%) showed that granite, granite gneiss and charnockite have good soundness and hardness with greater resistance to wear. Higher strength values of all the rocks were found to be satisfactory for use in the production of aggregates for civil constructions. Petrographic analysis revealed similarities in the compositions of the rocks, with quartz being the dominant mineral. The results show that all the rock types possess the required quality standards for use as construction aggregates in highway pavements and foundations. Some of the aggregates (GG1, GG2, GF, GC, MG1, CK1 and CK2) are also suitable for bituminous mixes. Quartzite should be avoided in load bearing masonry units due to its lower strength values. The most suitable rocks proven as road and building stones are fine grained granite, granite gneiss and charnockite because of their low water absorption, low flakiness and elongation indices, low abrasion values, higher strength values (tensile strength and unconfined compressive strength) and sound petrographic characters. Thus, adequate knowledge of rocks and rock aggregates is crucial in order to prevent continuous structural failure around the globe and make the environment friendlier

Land satellite imagery and integrated geophysical investigations of highway pavement instability in southwestern Nigeria

The high global numbers of road accidents due to bad roads and the failure of other engineering structures have necessitated this study, particularly as road transport accounts for a higher percentage of cargo movement in African countries. The geophysical investigation was carried out on six failed and two stable sections along the Ibadan-Iwo-Osogbo highway to examine the geological factors responsible for highway failure in the area. A Landsat ETM+ (Enhanced Thematic Mapper Plus) imagery of the study area and its environs was acquired and processed for lineaments analyses. Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity methods involving Schlumberger Vertical Electrical Sounding (VES) and 2-D imaging using a dipole-dipole array were utilized. Lineaments were identified across failed localities. Lateral magnetic variations in the near-surface geological materials characterized the study area. The 2-D VLF-EM models generated showed conductive zones corresponding to fractured zones of conductive clay materials within the basement rocks. Subgrade soils below the highway pavement along the failed sections are typical of incompetent clayey and sandy clay/clayey sand formations with resistivity values between 20–475 Ω∙m. In comparison, the subgrade soil beneath the stable sections has moderate to high resistivity values of 196–616 Ω∙m. 2-D resistivity structures across the failed segments identified low resistivity water-absorbing clay and lithological contacts. Water absorbing, clay enriched subgrade soils and the identified near-surface linear conductive features are the major geologic factors, and poor drainage network resulted in the highway failure. Remote sensing and geophysical investigations of the geological sequence and structures underlying the highway should be carried out before construction to effectively complement the routine geotechnical studies to ensure the sustainability of road infrastructure

GEOLOGICAL AND LITHOLOGICAL MAPPING OF PART OF IGARRA SCHIST BELT USING INTEGRATED GEOPHYSICAL METHODS

Integrated geophysical techniques involving magnetic and radiometric data were used to investigate the subsurface geometry of Igarra schist belt in Precambrian basement complex of southwestern Nigeria which falls within the latitude range of 7° 1635.6” to 7° 1736.0’ North and longitude range of 6° 0534.1” to 6°05’44”East, with a view to interpret the geology of part of Igarra schist belt and estimate the depth to basement of magnetic source in the area. Six profiles were established with the objective of delineating the metasediments and its structural attributes, and geophysical measurements were made at 5m intervals along these profiles. The results of magnetic datasets were presented as maps and profiles of varying magnetic intensities and the causative rock types. Qualitative interpretation of the magnetic data using Reduction to pole, Analytical signal, first vertical, horizontal and tilt derivatives, upward continuation filters shows what has been interpreted as the signature of a near-vertical fault, trending along a NE-SW and NW-SE direction while radiometric datasets gave geochemical rates of U, Th and K as well as the effect of water contents on the rocks present within the study area. Qualitative and quantitative interpretation of individual magnetic anomalies and geological knowledge of the survey area yielded information on the depth of the geological features (e.g. rock contact, faults or fractures), structure and magnetic properties of rock units. 3D Euler deconvolution and Average radial spectrum were adopted to estimate the depth of the magnetic sources which ranges from - 92.895m to 73.95m; -115.45m to 57.44m and 63m to 44.1m; 88.2m to 81.9 m respectively. The Igarra schist belt has evolved different episodes of orogenies and the metasediments were formed from low grade regional metamorphism of argillaceous sediments such as shales or sediments of varying composition

IMPROVED MAGNETIC DATA ANALYSES AND ENHANCEMENT TECHNIQUES FOR LITHOLOGICAL AND STRUCTURAL MAPPING AROUND AKURE, SOUTHWESTERN NIGERIA

This study employs improved magnetic data analyses and enhancement techniques to map and interpret the lithological and structural features around Akure and its environs. Several forms of filtering processes were performed to improve and enhance the Total Magnetic Intensity (TMI) data and other reduced data that were later produced. The analysed results of the upward continuation to 500 m and 1 km revealed the attitudes of deepseated basement rocks and anomalous structures with regional trend of NW-SE direction, as well as depth of structures that ranged beyond 1 km. On the other hand, derivatives images revealed lineaments/faults: F1-F’1, F2- F’2, F3-F’3 (minors) and F4-F’4 trending NNE-SSW, N-S, NE-SW, minor (ENE-WSW and E-W) and NW-SE respectively. Based on magnetisation contrast, four amplitude zones were revealed on the Analytic Signal (AS) image, which include very high zone as migmatite complexes; intermediate zone as migmatite/gneiss and charnockite complexes; fairly low zone as granite-gneiss and granite complexes, and low zone as quartzite ridge/ complex. The large causative bodies delineated from the pseudo-gravity revealed density of about 0.133 g/cc in susceptibility. The total depth estimate to top of magnetic sources ranged from 53 m to 1.98 km for shallower and deeper sources respectively. This study, therefore, suggests different rock types of varying mineralogical compositions, tectonic framework and structural deformations that led to change in intensity of rocks in the study area