ABSTRACT Karst problems often result in unexpected additional building costs and the proper under... more ABSTRACT Karst problems often result in unexpected additional building costs and the proper understanding of karst terrains is therefore important for geotechnical engineer. The karst terrain is developed from the dissolution of carbonate rock. Groundwater flow through carbonate rock enhances the dissolution of carbonate minerals which can cause the development of subsurface cavities or voids. The subsurface cavities and uneven depth of bedrock make foundation design very difficult in karst terrain. A subsurface characterization and grouting case study are presented for the Yongweol-ri site, South Korea. In the project area, mortar was injected into subsurface cavities for consolidation and/or grouting purposes. The subsurface cavities were imaged using electrical resistivity and borehole camera (BHTV) before and after mortar injection. In addition, the resistivity changes of mortar specimens were studied in the laboratory simulating various field conditions. The injected mortar was imaged as anomalies exhibiting lower resistivity than the surrounding rocks. A comparison of the pre- and post-grouting resistivity provided detailed information of the subsurface cavities plus the areas which have been occupied by the mortar after consolidation. Also, BHTV field test confirmed the presence of the mortar in the subsurface cavities. The results obtained from this study showed that electrical resistivity imaging can be a useful tool for detecting and evaluating changes in subsurface resistivity due to the injection of the mortar. From the laboratory analysis, it is confirmed that mortar is a good material for grouting and ground stability hazard management.
Abstract Exploration carried out along lineaments identified by aerial photo interpretation in ha... more Abstract Exploration carried out along lineaments identified by aerial photo interpretation in hard rocks had revealed the existence of deep weathered and fractured zones capable of yielding up to 45,000 litres of groundwater per hour. Integrated studies of aerial photo interpretation followed up by hydrogeological and geophysical surveys was conducted in Hindupur taluk of Anantapur district in Andhara Pradesh for identification of groundwater potential zones for drinking water and for sugarcane development. Aerial photos of scale 1:63,000 were used covering an area of 1,600 km 2 . A number of lineaments running in NW-SE and NE-SW direction were identified using aerial photo interpretation. The studies have indicated a high density in lineaments in Dharwar rocks in Pennar and Jayamangali river basins and moderate to poor density of lineaments in granitic gneisses in Kushavathi and Chitravathi river basins. Fluvial deposits (alluvium), valleyfill deposits and pediment zones were also deciphered. Field checks during surveys along lineaments led to drilling of exploratory borewells. The drilling results indicated that the lineament zones are highly productive for construction of borewells, the maximum discharge being 45,000 litres per hour and the minimum being 9,000 litres per hour. Groundwater is mainly confined to weathered, fractured and fissured granites, gneisses and schists. Analysis of the lithologs indicated and increase in discharge in the fissured and fractured zones and at the contact of the different formations. The result of surveys along lineaments gives an insight into exploitation of groundwater along lineaments by means of borewells ranging in depths of up to 60 metres.
Groundwater is a natural resourceof the earth that sustains and supports domestic, agricultural a... more Groundwater is a natural resourceof the earth that sustains and supports domestic, agricultural and industrial activities. It is distributed fairly and evenly throughout the world and over half of the world’s population depends on groundwater for drinking water supplies. Its usage is increasing due to rapid population growth, high rate of urbanization, industrial growth and agricultural utilizations. This has resulted to rapid depletion of groundwater which leads to water stress and degradation of these resources. The situation is further worsened by inadequate information on groundwater resource which has been and is still a big obstacle to the proper management of these resources. Remote sensing and GIS techniques have emerged as very effective and reliable tools in the assessment, monitoring and conservation of groundwater resources. The purpose of this paper was to identify and delineate groundwater potential zones in Lake Chala Basin in Kenya using Remote sensing and GIS. In th...
Lake Chala is a transboundary fresh water resource with no surface water inflow or outflow and is... more Lake Chala is a transboundary fresh water resource with no surface water inflow or outflow and is located in the southwestern part of Kenya on the Kenya-Tanzania border. The lake catchment area is bound by longitudes 37 0 41’ E and 37 0 43’ E and latitudes 3 0 18’ S and 3 0 20’ S. The Lake has a surface area of 4.2 km 2 and lies within a surface catchment area of about 16.23 km 2 , which falls within a semiarid region frequently facing severe water scarcity especially during periods of prolonged drought. The major economic activities in this area are agriculture, horticulture and animal husbandry which account for about 75-80% of household income. Due to reliance on rain fed agriculture, water scarcity has often had negative impact on the people and there is need to tap the lake water for irrigation purposes. As such, water samples were collected on the Kenya and Tanzania sides from eleven (11) sites in March 2011 and subjected to analysis for chemical characteristics. Ten of the wa...
A geo-electrical investigation was carried out in Lake Chala Watershed in Kenya to determine the ... more A geo-electrical investigation was carried out in Lake Chala Watershed in Kenya to determine the groundwater potential of the area. The Vertical Electrical Sounding using schlumberger configuration with a maximum current electrode spread varying from 250 320m and potential electrode spread of 25m was utilized to provide information of the aquifers and subsurface lithology. A total number of 50 VES were carried out. The data obtained were interpreted by computer iteration process. Interpreted results revealed four to six distinct subsurface layers which comprised of top soil (clay, sandy clay soil intercalated with silt, sand and gravel), highly weathered ryholite, and moderately weathered basalt volcanic ash, highly weathered fractured basalt, weathered basalt, slightly fractured dry and fresh basalt and basalt basement rock layers. The results showed that the auriferous layer was composed of highly weathered fractured basalt, moderately weathered basalt & volcanic ash and weathered...
Arus-Bogoria geothermal prospect encompasses several features of geological significance that are... more Arus-Bogoria geothermal prospect encompasses several features of geological significance that are indicators of possible geothermal potential. These include surface manifestations, such as fumaroles, steam jets, mud pools, hot springs, spouting geysers, and high rate of micro-seismic activity of about 500 earthquakes recorded within a period of three months in comparison to other geothermal fields and prospects along the Kenya Rift Valley (KRV). A comparison of the results of gravity surveys undertaken between 2005 and 2006 for geothermal resource evaluation of Arus and Lake Bogoria geothermal prospects, to results of micro-seismic monitoring undertaken in 1985 during the Kenya Rift International Seismic (KRISP 85) Project was undertaken to map the existence of heat source(s). The results indicate that the heat source is due to a series of north-south trending dyke injections occurring at depths of ~3 – 6 km in the vicinity of the Arus steam jets. Most of the seismic activity is pro...
Earthquakes in Kenya are likely to be concentrated along the Kenya Rift Valley due to the slow di... more Earthquakes in Kenya are likely to be concentrated along the Kenya Rift Valley due to the slow divergent movement of the rift and hydrothermal processes within the geothermal fields. This implies slow but continuous radiation of seismic energy which relieves stress in the subsurface rocks. It is therefore unlikely that the Kenya rift poses significant earthquake hazard in Kenya. On the contrary, the NW-SE trending rift/shear zones such as the Aswa-Nyangia fault zone and the Muglad-AnzaLamu rift zone are more likely sites of major earthquakes in Kenya and the East African region. These rift zones have been the sites of a number of strong earthquakes in the past such as the Mw = 7.2 southern Sudan earthquake of May 20, 1990 and aftershocks of Mw = 6.5 and 7.1 on May 24, 1990; the 1937 Ms = 6.1 earthquake north of Lake Turkana close to Kenya-Ethiopian border, and the 1913 Ms = 6.0 Turkana earthquake, among others. We have attempted to determine the source parameters of the May 20, 1990...
Kenya has had a seismic station since 1963 as part of the World Wide Standardized Seismograph Net... more Kenya has had a seismic station since 1963 as part of the World Wide Standardized Seismograph Network (WWSSN). In 1990, the University of Nairobi in collaboration with GeoForschungsZentrum (GFZ) started to build up a local seismological network, the Kenya National Seismic Network (KNSN), which operated for about ten years between 1993–2002. This, however, experienced a myriad of problems ranging from equipment breakdown, vandalism and lack of spares. Kenya is seismically active since the Kenya rift valley traverses through the country from north to south bisecting the country into eastern and western regions. In the central part, the Kenya rift branches to form the NW-SE trending Kavirondo (Nyanza) rift. The Kenya rift valley and the Kavirondo (Nyanza) rift are the most seismically active where earthquakes of local magnitude ( M l ) in the order of ⩽2.0–5.0 occur. Furthermore, historical records show that earthquakes of magnitudes of the order of M l ⩾ 6.0 have occurred in Kenya. S...
The Lake Bogoria basin, here in referred to as the study area, is located in the greater Baringo-... more The Lake Bogoria basin, here in referred to as the study area, is located in the greater Baringo-Bogoria basin (BBB), about 100 km to the north of Menengai geothermal prospect on the floor of Kenya Rift Valley (KRV). It is bound by latitudes 0 00’ and 0 30’N and longitudes 3545’E and 3615’E within the rift graben. The study area is characterized by geothermal surface manifestations which include hot springs, spouting geysers, fumaroles/steam jets and mud pools. The area is overlain by Miocene lavas lavas, mainly basalts and phonolites, and Pliocene to recent sediments and pyroclastics such as tuffs, tuffaceous sediments, superficial deposits, volcanic soils, alluvium and lacustrine silts. The terrain is characterized by extensive faulting forming numerous N-S ridges and fault scarps. Gravity and magnetotelluric (MT) surveys were undertaken in the area to determine the heat source, characterize the geothermal reservoir, and evaluate the geothermal resource potential of the basin. Gra...
ABSTRACT Karst problems often result in unexpected additional building costs and the proper under... more ABSTRACT Karst problems often result in unexpected additional building costs and the proper understanding of karst terrains is therefore important for geotechnical engineer. The karst terrain is developed from the dissolution of carbonate rock. Groundwater flow through carbonate rock enhances the dissolution of carbonate minerals which can cause the development of subsurface cavities or voids. The subsurface cavities and uneven depth of bedrock make foundation design very difficult in karst terrain. A subsurface characterization and grouting case study are presented for the Yongweol-ri site, South Korea. In the project area, mortar was injected into subsurface cavities for consolidation and/or grouting purposes. The subsurface cavities were imaged using electrical resistivity and borehole camera (BHTV) before and after mortar injection. In addition, the resistivity changes of mortar specimens were studied in the laboratory simulating various field conditions. The injected mortar was imaged as anomalies exhibiting lower resistivity than the surrounding rocks. A comparison of the pre- and post-grouting resistivity provided detailed information of the subsurface cavities plus the areas which have been occupied by the mortar after consolidation. Also, BHTV field test confirmed the presence of the mortar in the subsurface cavities. The results obtained from this study showed that electrical resistivity imaging can be a useful tool for detecting and evaluating changes in subsurface resistivity due to the injection of the mortar. From the laboratory analysis, it is confirmed that mortar is a good material for grouting and ground stability hazard management.
Abstract Exploration carried out along lineaments identified by aerial photo interpretation in ha... more Abstract Exploration carried out along lineaments identified by aerial photo interpretation in hard rocks had revealed the existence of deep weathered and fractured zones capable of yielding up to 45,000 litres of groundwater per hour. Integrated studies of aerial photo interpretation followed up by hydrogeological and geophysical surveys was conducted in Hindupur taluk of Anantapur district in Andhara Pradesh for identification of groundwater potential zones for drinking water and for sugarcane development. Aerial photos of scale 1:63,000 were used covering an area of 1,600 km 2 . A number of lineaments running in NW-SE and NE-SW direction were identified using aerial photo interpretation. The studies have indicated a high density in lineaments in Dharwar rocks in Pennar and Jayamangali river basins and moderate to poor density of lineaments in granitic gneisses in Kushavathi and Chitravathi river basins. Fluvial deposits (alluvium), valleyfill deposits and pediment zones were also deciphered. Field checks during surveys along lineaments led to drilling of exploratory borewells. The drilling results indicated that the lineament zones are highly productive for construction of borewells, the maximum discharge being 45,000 litres per hour and the minimum being 9,000 litres per hour. Groundwater is mainly confined to weathered, fractured and fissured granites, gneisses and schists. Analysis of the lithologs indicated and increase in discharge in the fissured and fractured zones and at the contact of the different formations. The result of surveys along lineaments gives an insight into exploitation of groundwater along lineaments by means of borewells ranging in depths of up to 60 metres.
Groundwater is a natural resourceof the earth that sustains and supports domestic, agricultural a... more Groundwater is a natural resourceof the earth that sustains and supports domestic, agricultural and industrial activities. It is distributed fairly and evenly throughout the world and over half of the world’s population depends on groundwater for drinking water supplies. Its usage is increasing due to rapid population growth, high rate of urbanization, industrial growth and agricultural utilizations. This has resulted to rapid depletion of groundwater which leads to water stress and degradation of these resources. The situation is further worsened by inadequate information on groundwater resource which has been and is still a big obstacle to the proper management of these resources. Remote sensing and GIS techniques have emerged as very effective and reliable tools in the assessment, monitoring and conservation of groundwater resources. The purpose of this paper was to identify and delineate groundwater potential zones in Lake Chala Basin in Kenya using Remote sensing and GIS. In th...
Lake Chala is a transboundary fresh water resource with no surface water inflow or outflow and is... more Lake Chala is a transboundary fresh water resource with no surface water inflow or outflow and is located in the southwestern part of Kenya on the Kenya-Tanzania border. The lake catchment area is bound by longitudes 37 0 41’ E and 37 0 43’ E and latitudes 3 0 18’ S and 3 0 20’ S. The Lake has a surface area of 4.2 km 2 and lies within a surface catchment area of about 16.23 km 2 , which falls within a semiarid region frequently facing severe water scarcity especially during periods of prolonged drought. The major economic activities in this area are agriculture, horticulture and animal husbandry which account for about 75-80% of household income. Due to reliance on rain fed agriculture, water scarcity has often had negative impact on the people and there is need to tap the lake water for irrigation purposes. As such, water samples were collected on the Kenya and Tanzania sides from eleven (11) sites in March 2011 and subjected to analysis for chemical characteristics. Ten of the wa...
A geo-electrical investigation was carried out in Lake Chala Watershed in Kenya to determine the ... more A geo-electrical investigation was carried out in Lake Chala Watershed in Kenya to determine the groundwater potential of the area. The Vertical Electrical Sounding using schlumberger configuration with a maximum current electrode spread varying from 250 320m and potential electrode spread of 25m was utilized to provide information of the aquifers and subsurface lithology. A total number of 50 VES were carried out. The data obtained were interpreted by computer iteration process. Interpreted results revealed four to six distinct subsurface layers which comprised of top soil (clay, sandy clay soil intercalated with silt, sand and gravel), highly weathered ryholite, and moderately weathered basalt volcanic ash, highly weathered fractured basalt, weathered basalt, slightly fractured dry and fresh basalt and basalt basement rock layers. The results showed that the auriferous layer was composed of highly weathered fractured basalt, moderately weathered basalt & volcanic ash and weathered...
Arus-Bogoria geothermal prospect encompasses several features of geological significance that are... more Arus-Bogoria geothermal prospect encompasses several features of geological significance that are indicators of possible geothermal potential. These include surface manifestations, such as fumaroles, steam jets, mud pools, hot springs, spouting geysers, and high rate of micro-seismic activity of about 500 earthquakes recorded within a period of three months in comparison to other geothermal fields and prospects along the Kenya Rift Valley (KRV). A comparison of the results of gravity surveys undertaken between 2005 and 2006 for geothermal resource evaluation of Arus and Lake Bogoria geothermal prospects, to results of micro-seismic monitoring undertaken in 1985 during the Kenya Rift International Seismic (KRISP 85) Project was undertaken to map the existence of heat source(s). The results indicate that the heat source is due to a series of north-south trending dyke injections occurring at depths of ~3 – 6 km in the vicinity of the Arus steam jets. Most of the seismic activity is pro...
Earthquakes in Kenya are likely to be concentrated along the Kenya Rift Valley due to the slow di... more Earthquakes in Kenya are likely to be concentrated along the Kenya Rift Valley due to the slow divergent movement of the rift and hydrothermal processes within the geothermal fields. This implies slow but continuous radiation of seismic energy which relieves stress in the subsurface rocks. It is therefore unlikely that the Kenya rift poses significant earthquake hazard in Kenya. On the contrary, the NW-SE trending rift/shear zones such as the Aswa-Nyangia fault zone and the Muglad-AnzaLamu rift zone are more likely sites of major earthquakes in Kenya and the East African region. These rift zones have been the sites of a number of strong earthquakes in the past such as the Mw = 7.2 southern Sudan earthquake of May 20, 1990 and aftershocks of Mw = 6.5 and 7.1 on May 24, 1990; the 1937 Ms = 6.1 earthquake north of Lake Turkana close to Kenya-Ethiopian border, and the 1913 Ms = 6.0 Turkana earthquake, among others. We have attempted to determine the source parameters of the May 20, 1990...
Kenya has had a seismic station since 1963 as part of the World Wide Standardized Seismograph Net... more Kenya has had a seismic station since 1963 as part of the World Wide Standardized Seismograph Network (WWSSN). In 1990, the University of Nairobi in collaboration with GeoForschungsZentrum (GFZ) started to build up a local seismological network, the Kenya National Seismic Network (KNSN), which operated for about ten years between 1993–2002. This, however, experienced a myriad of problems ranging from equipment breakdown, vandalism and lack of spares. Kenya is seismically active since the Kenya rift valley traverses through the country from north to south bisecting the country into eastern and western regions. In the central part, the Kenya rift branches to form the NW-SE trending Kavirondo (Nyanza) rift. The Kenya rift valley and the Kavirondo (Nyanza) rift are the most seismically active where earthquakes of local magnitude ( M l ) in the order of ⩽2.0–5.0 occur. Furthermore, historical records show that earthquakes of magnitudes of the order of M l ⩾ 6.0 have occurred in Kenya. S...
The Lake Bogoria basin, here in referred to as the study area, is located in the greater Baringo-... more The Lake Bogoria basin, here in referred to as the study area, is located in the greater Baringo-Bogoria basin (BBB), about 100 km to the north of Menengai geothermal prospect on the floor of Kenya Rift Valley (KRV). It is bound by latitudes 0 00’ and 0 30’N and longitudes 3545’E and 3615’E within the rift graben. The study area is characterized by geothermal surface manifestations which include hot springs, spouting geysers, fumaroles/steam jets and mud pools. The area is overlain by Miocene lavas lavas, mainly basalts and phonolites, and Pliocene to recent sediments and pyroclastics such as tuffs, tuffaceous sediments, superficial deposits, volcanic soils, alluvium and lacustrine silts. The terrain is characterized by extensive faulting forming numerous N-S ridges and fault scarps. Gravity and magnetotelluric (MT) surveys were undertaken in the area to determine the heat source, characterize the geothermal reservoir, and evaluate the geothermal resource potential of the basin. Gra...
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Papers by Josphat Mulwa