A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions

 

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dc.contributor.advisor Moyo, Pilate
dc.contributor.author Stehle, Hermann Theodor
dc.date.accessioned 2019-02-05T06:40:24Z
dc.date.available 2019-02-05T06:40:24Z
dc.date.issued 2018
dc.identifier.citation Stehle, H. 2018. A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/29282
dc.description.abstract South Africa is considered a water-scarce country and this fact alone stresses the absolute need to preserve its water resources. As time goes by, the ageing of dams in South Africa is becoming an increasingly important factor to consider from a dam safety perspective. When considering concrete dams, Alkali Aggregate Reactions (AAR) which is the collective term referring to the potential chemical reactions between the cement and the coarse aggregate in the concrete, are a major cause of ageing. AAR causes internal swelling of concrete leading to stresses that eventually manifest on a macroscopic level as inter alia cracks, deformation and opening of horizontal construction joints. Although the effect of AAR expansion on arch dams is complex, certain behavioural phenomena have been identified as typical indicators of swelling concrete. These are well covered by literature. This thesis aims to compare the structural behaviour of concrete arch dams in South Africa that are subjected to swelling due to AAR. Three arch dams, namely Hartebeeskuil Dam, Poortjieskloof Dam and Thabina Dam (all located in different climatic regions), were identified and their behavioural patterns were investigated by using visual techniques along with the interpretation of instrumentation results. The typical instrumentation results that were used for interpretation purposes included geodetic surveying results, crack width gauge results, in situ stress measurement results and trivec measurement results. Poortjieskloof Dam, the oldest of the three dams, showed permanent upstream displacement trends of both flanks, but the centre of the arch showed a downstream displacement trend. Both flanks show swelling towards the abutments and rising crest levels are evident throughout the length of the dam wall. The dam wall was cracked quite severely on the downstream face and the horizontal joints showed clear separation. The most recent displacement trends suggest that the rate of AAR is decreasing. Hartebeeskuil Dam, the second oldest of the three dams, showed permanent upstream displacement trends throughout the length of the dam wall. Both flanks show swelling towards the abutments and crest levels at both flanks show some settlement. The central section of the arch show rising crest levels. The results of in situ stress measurements carried out in 1999 showed that the downstream section of the arch is experiencing tensile stresses while the upstream section of the arch is mostly experiencing compressive stresses. The cracking patterns on both the upstream and downstream faces seem to agree with these findings. The results generally seem to suggest that the AAR mainly occurs on the upstream side of the arch and that the effective arch has become thinner due to the tension zone on the downstream side. The most recent displacement trends suggest that the rate of AAR is not showing any signs of decreasing. Thabina Dam, the youngest of the three dams, showed permanent upstream trends of the right flank while the central region and left flank of the arch showed downstream trends. The flanks have moved permanently towards each other and the crest levels have increased throughout the length of the arch section. The most recent trends show increasing rates of strain especially in the vertical (z) and tangential (y) directions. More recently the entire arch has started showing upstream displacement trends. These may indicate the onset of a swelling mechanism in the concrete, most likely AAR, but extensive testing is required to prove this.
dc.language.iso eng
dc.subject.other Civil Infrastructure Management and Maintenance
dc.title A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions
dc.type Master Thesis
dc.date.updated 2019-01-31T12:36:39Z
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Engineering and the Built Environment
dc.publisher.department Department of Civil Engineering
dc.type.qualificationlevel Masters
dc.type.qualificationname MSc (Eng)
dc.identifier.apacitation Stehle, H. T. (2018). <i>A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions</i>. (). University of Cape Town ,Engineering and the Built Environment ,Department of Civil Engineering. Retrieved from http://hdl.handle.net/11427/29282 en_ZA
dc.identifier.chicagocitation Stehle, Hermann Theodor. <i>"A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions."</i> ., University of Cape Town ,Engineering and the Built Environment ,Department of Civil Engineering, 2018. http://hdl.handle.net/11427/29282 en_ZA
dc.identifier.vancouvercitation Stehle HT. A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions. []. University of Cape Town ,Engineering and the Built Environment ,Department of Civil Engineering, 2018 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/29282 en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Stehle, Hermann Theodor AB - South Africa is considered a water-scarce country and this fact alone stresses the absolute need to preserve its water resources. As time goes by, the ageing of dams in South Africa is becoming an increasingly important factor to consider from a dam safety perspective. When considering concrete dams, Alkali Aggregate Reactions (AAR) which is the collective term referring to the potential chemical reactions between the cement and the coarse aggregate in the concrete, are a major cause of ageing. AAR causes internal swelling of concrete leading to stresses that eventually manifest on a macroscopic level as inter alia cracks, deformation and opening of horizontal construction joints. Although the effect of AAR expansion on arch dams is complex, certain behavioural phenomena have been identified as typical indicators of swelling concrete. These are well covered by literature. This thesis aims to compare the structural behaviour of concrete arch dams in South Africa that are subjected to swelling due to AAR. Three arch dams, namely Hartebeeskuil Dam, Poortjieskloof Dam and Thabina Dam (all located in different climatic regions), were identified and their behavioural patterns were investigated by using visual techniques along with the interpretation of instrumentation results. The typical instrumentation results that were used for interpretation purposes included geodetic surveying results, crack width gauge results, in situ stress measurement results and trivec measurement results. Poortjieskloof Dam, the oldest of the three dams, showed permanent upstream displacement trends of both flanks, but the centre of the arch showed a downstream displacement trend. Both flanks show swelling towards the abutments and rising crest levels are evident throughout the length of the dam wall. The dam wall was cracked quite severely on the downstream face and the horizontal joints showed clear separation. The most recent displacement trends suggest that the rate of AAR is decreasing. Hartebeeskuil Dam, the second oldest of the three dams, showed permanent upstream displacement trends throughout the length of the dam wall. Both flanks show swelling towards the abutments and crest levels at both flanks show some settlement. The central section of the arch show rising crest levels. The results of in situ stress measurements carried out in 1999 showed that the downstream section of the arch is experiencing tensile stresses while the upstream section of the arch is mostly experiencing compressive stresses. The cracking patterns on both the upstream and downstream faces seem to agree with these findings. The results generally seem to suggest that the AAR mainly occurs on the upstream side of the arch and that the effective arch has become thinner due to the tension zone on the downstream side. The most recent displacement trends suggest that the rate of AAR is not showing any signs of decreasing. Thabina Dam, the youngest of the three dams, showed permanent upstream trends of the right flank while the central region and left flank of the arch showed downstream trends. The flanks have moved permanently towards each other and the crest levels have increased throughout the length of the arch section. The most recent trends show increasing rates of strain especially in the vertical (z) and tangential (y) directions. More recently the entire arch has started showing upstream displacement trends. These may indicate the onset of a swelling mechanism in the concrete, most likely AAR, but extensive testing is required to prove this. DA - 2018 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2018 T1 - A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions TI - A comparative study on the structural behavior of concrete arch dams subjected to swelling due to aggregate sllica reactions UR - http://hdl.handle.net/11427/29282 ER - en_ZA


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