Physico-chemical study of groundwater in the Northeast of Kara region (Togo)

Groundwater is a major source of drinking water for people in the Kara region. This study aims at improving the knowledge of groundwater and to determine the processes responsible for groundwater mineralization in this region using hydro-chemical methods and multivariate statistical analysis. 47 water samples taken from the wells in the crystalline basement aquifer were analyzed. Chemical analyses were made on these samples according AFNOR methods to determine hydro-chemical characteristics. The hydro-chemical study showed that the waters in the region have an average temperature of 28.7 °C. They are acid to slightly basic, with a pH ranging between 5.7 and 7.87, but for the most part neutral. The waters are weakly to moderately mineralized, which confirms the well-known chemical characteristic of basement groundwater. However, high conductivity values were found in the waters in some localities. The highest value was measured at Broukou (1083 μS.cm-1). Groundwaters in this region belong to a variety of hydro-chemical facies in relation to the type of geological reservoir. Four hydro-chemical facies were identified. The most dominant is the calcic and magnesian bicarbonated facies (85%) followed by the sodic-potassic bicarbonated facies (8.5%). The sodic-potassic chlorinated facies (2.1%), calcic and chloride (2.1%) and calcic-magnesian sulfated facies are poorly represented in these waters. Major ions which are the cause of the waters mineralization come from rock weathering, hydrolysis of silicated minerals such as anorthite in plagioclase and the decomposition of ferromagnesian minerals such as biotite and amphibole. The contribution of soil leaching and pollution due to anthropic activities is not negligible.Keywords: Groundwater, Kara region, hydrochemistry, weathering, hydrolysis, basement complex

ASSESSMENT METHODOLOGY OF PERMEABILITY IN A GRANITIC AQUIFER IN A PILOT BASIN IN THE SOUTH OF SARDINIA (ITALY)

Groundwater circulation in fractured hard rocks aquifer (HRA) is an essential element in the fields of water supply, environment and geotechnics. The fracture properties, as orientation, size, abundance, and quality, influence the circulation of water. The geometry of the fractures makes the hydrogeological environment anisotropic and heterogeneous. Hence, defining the geological model is fundamental to understand spatial variability of permeability, and to define hydrogeological features of the aquifers. The present work aimed to develop a methodology to assess the permeability on crystalline rocks. As a pilot site, the Masoni Ollastru River basin (12,5 km2) in the South of Sardinia was considered. The reconstruction of the fracture network required a multiscale characterisation using field measurements and digital photogrammetry. The fractures field survey consisted in recording the features of discontinuities. The digital photogrammetry workflow produced a high resolution DEM (5m), orthophotos, digital stereo pairs, and a lineaments map. For each 11 geomechanical stations, the set of joints was characterized and the permeability was calculated applying the Darcy’s cubic law (three dimensional Darcy’s law or only cubic law) for each set. Spatial distribution of fracture properties was evaluated to approach the heterogeneity of the medium. For this purpose, two different scenarios in the geological conceptual model were evaluated: the first one concerns a stratiform aquifer with a sub-horizontal and sub-vertical fissured layer in the paleo-weathering profile of the granites; the second one regards valley incision by differential erosion determined by structural features (fractures density). The layer of unconsolidated alterite above the granitic paleo-weathering profile is thin and seems to represent the deeper level where the rocks are less weathered and fractured. Probably, the significant erosion of the large part of the saprolite is related to an uplift after Pliocene time. The permeability calculated with the cubic law was in a range of 10-8 to 10-2 m/s; the highest values are conditioned by the fractures aperture in the surface. According to the geological conceptual model, density and aperture of fractures decreases with depth, thus also permeability. The applied multi-phase methodology with a multiscale approach allowed to provide a hydrogeological conceptual model in a HRA

Drilled well yield and hydraulic properties in the Precambrian crystalline bedrock of Central Finland

Siirretty Doriast

The reliability of rock mass classification systems as underground excavation support design tools

This thesis examines the reliability of rock mass classification systems available for underground excavation support design. These methods are sometimes preferred to rational methods of support design particularly if detailed information required for the latter mentioned methods is lacking. The classification approach requires no analysis of any specific failure mechanisms or the forces required to stabilise unstable rocks, yet, the support measures thus designed are considered to deal with all possible failure mechanisms in a rock mass.Amongst the several rock mass classification methods developed for application in underground excavation engineering, two have stood out. These are known as rock mass rating (RMR) and tunnelling quality index (Q), introduced by Bieniawski (1973) and Barton et al. (1974), respectively. Over the years, the two methods have been revised and updated so as to improve their reliability as support design tools, yet the two methods are know to have limitations and their reliability has long been a subject of considerable debate. Nevertheless, attempts to assess their reliability in a systematic manner have been limited. Further, some practitioners in the field of rock engineering continue to use these methods as the sole methods of support design for underground rock excavations. The objective of thesis, therefore, is to contribute to a better understanding of the reliability of the two classification methods.This study considered that the reliability of the RMR and Q methods can be assessed by comparing their support predictions with those derived by other applicable methods and also with the actual support installed. Such an assessment can best be carried out during excavation of an underground opening because representative data can be collected by direct observation of the as-excavated ground conditions and monitoring the performance of the support installed. In this context, the geotechnical data obtained during the construction of several case tunnels were reviewed and the two classification methods were applied. The effectiveness of their support predictions was then evaluated against the potential failures that can be predicted by some of the applicable rational methods. Since the rock masses intersected in the case tunnels are jointed, mostly the structurally controlled failure modes were analysed. The support measures predicted by the two methods were compared with each other and with the actual support installed in the case tunnels. Further, the RMR and Q vales assigned to the case tunnels were correlated to observe any relationship between the two.The study showed that the RMR and Q predicted support measures are not always compatible. In some circumstances, the two methods can either overestimate or under estimate support requirements

Hydraulic properties of the table mountain group (TMG) aquifers

Philosophiae Doctor - PhDResearch findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers

Hydraulic properties of the Table Mountain Group (TMG) aquifers

Philosophiae Doctor - PhDResearch findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers