AbstractHydraulic fracturing in a core of embankment dams is one of the biggest threats to dam engineers affecting the safety of the dams. There have been many researches on hydraulic fracturing mechanism by different researchers in present and past where they have based their researches on classical approach of hydraulic fracturing where hydraulic fracturing is based on the tests and experiments conducted in intact boreholes and have concluded that the hydraulic fracturing is said to be initiated when the tensile strength of the soil is exceeded by circumferential tensile stress induced by applied or acting water or hydraulic pressure. This classical approach has completely ignored the effect of initial or existing cracks in the dams. Since, the typical value so the tensile strength of soil is very small or almost negligible, this research has studied hydraulic fracturing mechanism in embankment dam with viewpoint of fracture mechanics. The reason behind this theory is that the fracture mechanics considers the effect crack parameter (initial length crack) and applied force which is hydraulic pressure in this
case. This research has presented a laboratory experimental procedure for hydraulic fracturing tests. In this research, modified triaxial test is presented, by which an applied fluid pressure, required to induce hydraulic fracture at the tip of an initial crack in soil samples, is measured. Three different soil samples are experimented in order to compare the differences on their findings in terms of hydraulic fracturing. Fracture toughness (𝐾𝐼𝐶) which is also an indicator of soil’s resistance to fracturing of the soil samples are calculated by using an equation of linear elastic fracture mechanics (LEFM). Here the mechanism of risk of hydraulic fracturing in fill dams is then discussed based on the obtained results. This research finds the fracture toughness of
tested clay are very small for disturbed soil and all the dams including well designed and constructed dams, have a potential risk of hydraulic fracturing it is because the fracture toughness of the soil is very small to resist against water pressure. So as a
countermeasure, a filter zone which works as a crack stopper of a crack propagation, puddling clay in an embankment can also work as a crack stopper in embankment dam. The experimental results indicate reflects the exact same performance happening in real
and in a theoretical model environment. The experimental result obtained herein are compared with the past research on fracture toughness of clay and found the results agreeing with just two research projects.
|Date of Award||2022|
|Supervisor||Samson Ngambi (Supervisor) & Adegoke Olubanwo (Supervisor)|