Geological Behavior (GBR)

One of the most common problem faced by geotechnical engineers is slope stability assessment. The predictions of slope stability in soil or rock masses is very important for the designing of reservoir dams, roads, tunnels, excavations, open pit mines, and other engineering structures. It is the importance of slope stability problem that has reasoned alternate methods for evaluating the safety of a slope. This study reviews the existing methods used for slope stability analysis. These methods are divided into five different groups which are; (a) Limit equilibrium method, (b) Numerical simulation method, (c) Artificial neural network method, (d) Limit analysis method, and (e) Vector sum method.

Electrical resistivity survey was conducted around Students’ Hostels in FUPRE to delineate prolific aquifer for potable water to serve the teeming population of staff and students. Five vertical electrical soundings (VES) using Schlumberger electrode configuration with a maximum current electrode spread of 300m were employed for data acquisition. WINRESIST software was employed to execute the iteration and inversion processes of computing resistivities, depths and thicknesses of the various layers and the curve types. Results indicate that the area is characterized by 4 distinct geoelectric layers inferred differently at the VES locations. Two potential groundwater aquifer zones are delineated. The unconfined shallow aquifer zones found at VES 1, 3, 4 and 5 locations have shallow overburden depth ranging between 3.7-19.3m and coarse-grained sand columns with thicknesses ranging between 2.8-17.7m while the confined deep aquifer zone found at VES 2 location coincides with deep overburden layer at a depth of 42.6m and coarse-grained sand column with appreciable thickness of 19.1m. These results suggest that boreholes for sustainable groundwater supply around the Students’ Hostels should be sited at VES 2 location and screened at a depth ≥40.0m. However, aquifers at VES 1, 3, 4 and 5 have potentials for groundwater but are vulnerable to contamination. It is recommenced that electrical resistivity and hydrogeological surveys should be conducted at different locations in FUPRE, before any borehole(s) are drilled, to delineate the appropriate aquifer for potable groundwater supply and to avoid possible contamination.

A combination of geoelectric and hydrogeologic concept was used in the assessment of groundwater vulnerability in fractured aquifers of Oju and environs. The study area is underlain by the sediments of the Asu River Group, Southern Benue Trough Nigeria. A total of twenty-seven (27) Vertical Electrical Sounding (VES) was carried out within the study area. Geoelectric parameters (layer, resistivity and thickness) of the overlying layers across the study area were determined and used to evaluate the vulnerability of the underlying aquifers. Three charts were compared using geo-electrically derived models; LC (Longitudinal Conductance), GLSI (geoelectric layer susceptibility indexing) and GOD (groundwater occurrence, overlying lithology and depth to the aquifer. Results obtained from LC revealed that the study area fell within the moderate category, GLSI showed that aquifer vulnerability were categorize within negligible to low category and GOD fell within low to moderate category. On the average, groundwater within the study area is considered moderate vulnerable to groundwater contamination.

The assessment of terrestrial background ionizing radiation levels within fossil fuel and gas dispensing environments to evaluate the radiological risk around Warri metropolis has been conducted using a digilert 200 Nuclear Radiation monitor meter and a GPS. The GIS monitoring of the BIR levels was carried out between September and December 2018 by delineating the city into eight zones using GIS mapping. The measured average exposure rates ranged from 0.006mRh-1(0.50 𝑚𝑆𝑣𝑦-1) to 0.026mRh-1(2.19𝑚𝑆𝑣𝑦-1) with an overall mean value of 0.015±0.004mRh-1 (1.26±0.32 𝑚𝑆𝑣𝑦-1). The estimated mean outdoor absorbed dose rate for the regions ranged from 116.60±40.38nGyh-1 in Jeddo region to 148.9±49.63nGyh-1 in PTI region and a mean of 129.82±32.98𝜂Gyh-1.The AEDE evaluated is 0.16±0.04 𝑚𝑆𝑣𝑦-1 while the ELCR value is 0.56±0.014µ𝑆𝑣𝑦-1. The estimated dose to organs testes receiving the highest organ dose of 0.10 𝑚𝑆𝑣𝑦-1 while the liver receives the lowest dose to organ of 0.06 𝑚𝑆𝑣𝑦-1. The GIS mapping of the examined facilities revealed that radiation levels in 38 of the 61 sampling locations (62.3%) exceeded the global ambient permissible level of 13.0 𝜇Rh-1 (1.0 𝑚𝑆𝑣𝑦-1) reported by UNSCEAR, therefore the measured values are adjudged high and the environment radiologically impaired. But, these may not cause any short- team health risk to the fuel/gas attendants and attendees in these stations. The obtained estimated excess lifetime cancer risk indicates low chances of contracting cancer and the radiation doses to the adult organs investigated is insignificant.

The study was carried out in-situ using a Radalert 100 nuclear radiation monitor and a geographical positioning system (GPS). Five facilities were investigated at the rig site which included the rig site host community as well as the camp site for the oil workers at Ekapkamreh town. Ten 10 sampling locations were evaluated at a total of 60 study points. The values obtained range between 0.115±0.018 (µSv/hr) and 0.299±0.040 (µSv/hr) for the rig site environment, 0.111±0.006 (µSv/hr) and 0.337±0.031 (µSv/hr) for field logistic base (offices and workshops), 0.114±0.011 (µSv/hr) and 0.312±0.021 (µSv/hr) for components of the mud circulation section. Also, the radiological concentration of the Chemical Store ranged between 0.126±0.019 (µSv/hr) and 1.181±0.104 (µSv/hr), while the radiological values obtained from other facilities within the rig site ranged from 0.155±0.026 (µSv/hr) and 0.249±0.026 (µSv/hr). Radiation readings obtained for soil ranged from 0.149±0.05 (µSv/hr) to 0.219±0.025 (µSv/hr) and 0.114±0.039 (µSv/hr) to 0.219±0.051 (µSv/hr) respectively at the host community and camp site. Most of the results obtained showed that the general environment of the rig site is slightly above the permissible absorbed dose rate threshold of 0.15(µSv/hr) recommended by the United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in 2009. However, the exposure rates exceed the standard background level of 13µR/hr (coequal to 0.13µSv/hr). There is high tendency for the industry workers to be exposed to radiation with time.

Jalan Sungai Hitam in the Sandakan Peninsula traverses a flat to gently undulating terrain of low hills and ridges surrounded by broad alluvial flats. Recent slope cuts expose bluish to dark grey mudstones of the Garinono Formation containing pebble to boulder sized, angular to rounded, blocks of sandstone and other rock types. Slump-mud flows have occurred at most of the slope cuts; the failed materials characterized by desiccation cracks and fissures. Soil index properties, including consistency limits and grain size analyses, indicate that the mudstones have a medium to high swell potential. X-ray diffraction analyses show the clay minerals present to be kaolinite, illite and randomly interstratified illite-montmorillonite (a swelling clay mineral). The mudstones are thus sensitive to atmospheric wet-dry cycles with repeated swelling and shrinkage giving rise to the desiccation cracks and fissures, The cracks and fissures reduce the shear strength of the mudstones and allow for the infiltration of rainwater which initiates the slump-mud flows. It is concluded that earthworks in areas of the Garinono Formation in eastern Sabah need to consider the presence of swelling clay minerals; an occurrence that can be inferred from evaluating soil index properties.

In this paper, we explored the relationship between the stream-length gradient index over the Kiulu River upstream and its respective landform. The knickpoints derived from stream-length gradient index detected sudden drop in elevation that may be associated with recent tectonic activity over NW Sabah. To illustrate the changes in the stream profile, two knickpoints, F1 which coincided with historical earthquakes, and F2 which showed peak anomaly are selected. The landform over knickpoint F1 showed river diversions whereas the landform over knickpoint F2 showed deep ponding. Both field sites, however showed consistent alternation between rapids and ponding forming a step-like landform where the inferred normal fault is oriented at N40E. The stretched landform over the Kiulu river sites supports an extension setting that may be associated with gravity-sliding tectonics over NW Sabah.

The study of the earth mass movement has long been regarded as one of the most important and interesting aspect of engineering geology and geotechnical engineering, which the designers and planners from the private and public sectors address when implementing the initial stage of urban and rural development projects. This involves highways and infrastructures construction and land use planning among the others. Failure to appreciate the problems relating to mass movements of earth material could lead to damage of man made structures and even the loss of lives. These studies focused on the mass movement in Bundu Tuhan to Kundasang highway area approximately 84 km to 96 km from Kota Kinabalu city, Sabah, one of the most vulnerable to mass movements occurrence in west coast of Sabah. It is bounded by longitude line E 116o 31.592’ to E 116o 36.183’ and latitude line N 06o 00.269’ to N 05o 57.610’. The main objectives of this study are; 1) to map and locate the landslides in the study area; and 2) to study the mechanism and the influence of geological factors causing the mass movement. Geology of the study area and its surrounding is hosted mainly by three sedimentary rock formations: Trusmadi Formation (Palaeocene to Eocene age), Crocker Formation (Late Eocene to Early Miocene age) and Pinousuk Gravel (Upper Pleistocene to Holocene age). These three geologic formations dissected by numerous geological lineaments structural produced by a complex tectonic history of multi phase folding and thrust, normal and reverse faulting. These tectonic setting reduce the physical and mechanical properties of the soil and produced intensive displacement in substrata resulting in intensive high degree of weathering processes. The weathered materials are weak and cause sinking, subsidence and sliding due to high pore pressure subjected by both shallow and deep groundwater. Evaluation 10 boreholes data in study area indicated that the groundwater table in study area is shallow and range 1.9 meter to about 11.3 meters. The groundwater in study area fluctuate drastically even within short period. Sand and gravel layer with variable thickness defined the major shallow aquifers within the top weathered materials while the highly fracture sedimentary rocks defined the major deep aquifers. Most of the aquifer within top unconsolidated weathered material is under unconfined condition. Most of significant aquifers within the sedimentary rocks are sandstones. The sandstones generally fracture and contain coarse sediments, which increase the permeability. Geologic and geotechnic evaluation of the study area indicates that the mass movement take place when slope materials are no longer able to resist the force of gravity. These decrease the shear resistance resulting mass movement, which is due to internal and external factors. Internal factors involve some change in either physical or chemical properties of the rock and soil. External factors involve increase of shear stress on slope, which usually involves a form of disturbance that is induced by man. The triggering mechanism in the study area most likely involves heavy rainfall causing water saturation of the slope material and loss of cohesion along rapture planes. The sheared shale, bedding and fault planes, and opening fractures are all structural weaknesses, which acting as pathways for water seepage, hastening the weakening and eventual mass movement in the study area. Development planning has to consider these hazards in order to counter their effect. An environmental management program should be implemented to prevent these losses. Geological and geotechnical studies will play a vital role in ground stability assessment that critical in public safety.

Slope stability assessment using modified D-Slope method is been conducted on five (5) rock slopes from Sandakan, Sabah. D-slope method comprises of G-Rating determination and Potential Instability. G-Rating includes 17 parameters of field observation and laboratory analysis to assess the slope condition. Kinematic analysis is used for Potential Instability analysis to determine the type of failures for each slope. This later is to determine the level of slope’s risk: No Risk, Low Risk, Moderate Risk or High Risk. Based on the results of G-Rating, only slope C1 and C2 have value more than 0.4 while other slopes have less than 0.4 which indicates stable slopes. Based on kinematic analysis, slope C1 and C3 experienced wedge failures, slope C4 with toppling failure, slope C5 with wedge/planar failures and no failure shown for slope C2. D-slope analysis indicates that slope C1 is considered as Low Risk with mitigation suggestions of stream system inspection and vegetation on exposed area of the slopes, while other slopes (C2, C3, C4 and C5) have no suggestion for mitigation as been assessed as No Risk.

The Beris Dam is founded on a sequence of thick bedded to massive conglomerate and gritstone with some sandstone and mudstone, mapped as the Semanggol Formation of Triassic age. Portable shear box tests on polished surfaces of a sandstone, and a conglomerate, core yield friction angles of 18.0o and 20.8o, respectively. These friction angles are comparable with residual friction angles of between 17.5o and 19.0o determined in field and laboratory tests on sheared mudstone surfaces of the Semanggol Formation at the Muda Dam. Apparent cohesion values determined in the portable shear box tests result from the restricted normal displacement test conditions and should not be considered in shear strength calculations.