Evaluation of rock property variability

ABSTRACT

Rocks are natural geo-materials, whose properties are affected by many spatially-varying factors, such as the properties of their parent materials, weathering processes, and discontinuity conditions. Engineering properties of rocks therefore vary spatially and exhibit significant variability. To evaluate rock property variability, an extensive literature review is performed in this study to collect data reported in literature for igneous, sedimentary and metamorphic rocks during the last several decades. The typical ranges of rock property data, mean values and coefficient of variations of rock properties are evaluated and summarized. These typical ranges of rock properties can be used as guidelines for approximation when rock property data are not available at a project site. Furthermore, they can be used as prior knowledge when developing Bayesian framework for quantifying the variability of rock properties at a specific project site.     

Stream energy distribution below Eleyele Dam in Southwestern Nigeria

Expressing the rate of energy dissipation either within a basin or in a downstream manner is important in understanding occurrence and association between various morphological variables. This study focuses on the downstream variation in stream power and its relationship with morphological variates along the main channel of River Ona, Ibadan, Nigeria. River Ona stretches for 20.5 km downstream of Eleyele Dam. Twenty‐seven (27) points were sampled along this stretch. The 27 points were averaged into nine (9) reaches. At each cross‐section, channel characteristics were observed and measured. These include: width (W), depth (D), velocity (V), slope (S), Cross‐sectional area (A), discharge (Q), total stream power (TSP), specific stream power (SSP), width‐depth ratio (W/D), hydraulic radius (R) and wetted perimeter (P). This study confirmed that the influence of a dam present upstream of a river channel significantly alters the behaviour of slope and this in essence affects the distribution of energy along the river channel. Slope produces a logarithmic relationship with increasing distance downstream (Y = ‐32.79‐0.70InS, r = 0.70, r2 = 0.49, p < 0.05) while there was no significant relationship between Q and distance downstream.     

Continuous permeability predictions in heterogeneous reservoirs using Vshale and microstructure calibrated free-fluid models (a combined study of a Niger Delta field and the tight gas sandstone of the southern North Sea)

The well-established free-fluid model from NMR technique provides continuous permeability values that closely match with core permeabilities better than most theoretical models especially when it is core calibrated for field specific use. However, only few wells have NMR logs in a field while marginal fields may not have any due to economic reasons. This study explored means of achieving one of the overriding objectives of most marginal field operators, which is to reduce the overall cost of production to the attainable minimum. The free-fluid model was modified into two simple and cost-effective models in order to optimize its applicability to predict permeability in the absence of NMR data. The two new models, which were developed for the single and double porosity systems analyzed in this study, consist of calibration parameters that can be empirically determined to account for variation in reservoir quality based on the rock type profile per field. A non-matrix parameter, α, was introduced into the model derived for tight gas sandstone being regarded as a double-porosity formation. This inclusion represents the permeability contribution of natural fractures or any crack-like pores to the different flow units. By using the alternative version to the known free-fluid model, continuous permeability curves that match experimental results were predicted without NMR logs.     

South Africa’s soft power and the diplomacy of nuclear geopolitics

GeoJournal - From when it was reaccepted into the international community in the early 1990s, South Africa has made significant contributions towards the construction of new international regimes...     

Modelling of malaria incidence in Akure,Nigeria: negative binomial approach

The connections between malaria incidence and climate variability have been studied in recent time using some mathematical and statistical models. Many of the statistical models in literature focused on time series approach based on Box–Jenkins methodology. However, fitting time series model based on the Box–Jenkins methodology may be challenging. Most malaria incidence data are count and are over-dispersed. In this study, negative binomial models were formulated for fitting malaria incidence in Akure—one of the epidemic cities in Nigeria. In particular, negative binomial models were formulated for each of the number of outpatient individuals, number of inpatient individuals and mortality count as a function of some climate variables. It was found that an increase in minimum temperature and relative humidity at lag 1 significantly increased the chance of malaria transmission and thereby leads to an increase in the number of inpatient and outpatient individuals, as well as the total number of malaria cases. The minimum temperature, rainfall amount and relative humidity of the study area have a significant impact on the increase of number of inpatient and outpatient individuals while mortality count depends on the total number of reported malaria cases. The findings from this study is to offer in-depth understanding on climate-malaria incidence linkages in Akure, Nigeria.

     

Quantifying the EEJ current with ground-based ionosonde inferred vertical E × B drifts in the morning hours over Ilorin,West Africa

The relationship between the ground-based inferred vertical E × B drifts, Vz, and the magnetic equatorial electrojet current during the year of solar minima was presented. Both the diurnal and seasonal Vz variations are positively directed during the daytime and negative at nighttime. The evening time pre-reversal enhancement occurs around 19:00 LT. The fairly strong linear relationship between the electrojet current strength and Vz exhibited higher correlations during the daytime (06:00–16:00 LT). The maximum morning time proxy parameter described by E = [d (ΔH _ILR)/dt]_max in the morning hours, indicating the east-west electric field in the EEJ, corresponds reasonably well with the E × B drift and, hence, can be used as a proxy parameter for representing Vz in the morning hours. The daytime EEJ magnitude seasonal changes are connected with a change in conductivity emerging from the action of turbulence and divergence of momentum flux. These waves above the dynamo region are suggested to lead to partial counter electrojet during the equinoctial months.     

An Overview of the Use of Rockbolts as Support Tools in Mining Operations

Geotechnical and Geological Engineering - Historically, the idea of designing and installing rockbolts in rockmasses can be traced back to the construction of the Snowy Mountain hydroelectric...     

Geospatial analysis of land-use change processes in a densely populated coastal city: the case of Port Harcourt,south-east Nigeria

This study examines the pattern and processes of land-use change in a densely populated coastal city in the oil-rich Niger Delta region of Nigeria for 27?years using remote sensing and Geographic Information Systems. The results indicate that between 1986 and 2013, settlement/bare surface, mangrove forest/wetland and water body increased at 0.84% per year, 0.05% per year and 0.10% per year, respectively, while arable land/secondary vegetation and natural forest loss at 0.47% per year and 0.52% per year, respectively. This implies that intensity of change varies temporally. The implications of these changes include loss of valuable environmental goods and services, alteration of the food chain and increased impacts of climate change–related disasters. It is recommended that steps be taken to slow down the rate of land-use change in the study area to reduce its impact on the environment and social well-being.     

Empirical Estimation of Uniaxial Compressive Strength of Rock: Database of Simple,Multiple, and Artificial Intelligence-Based Regressions

Geotechnical and Geological Engineering - Empirical relationships for estimating Uniaxial Compressive Strength (UCS) of rock from other rock properties are numerous in literature. This is because...