GERUSAN LOKAL DI SEKITAR DUA ABUTMEN DAN UPAYA PENGENDALIANNYA
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Flow in an open channel with a mobile bed is generally accompanied by a transport of sediments, which is a result of interaction between flow and sediment. An obstacle, such as pier or abutment, positioned in the flow, will locally alter the flow in the channel, causing erosion (scour) and possibly deposition in the vicinity of the pier or the abutment. More than one abutment is possibly installed with series positions in river. This group of abutment will exhibit a mutual influence on the hydraulic behavior and on scouring. Until now research on the single abutment was considered, however research using two abutments is extremely scarce. Research of scour around two abutments was conducted in Hydrology and Hydraulic Laboratory, PSIT Gadjah Mada University. Flow was clear-water scour and steady uniform flow. A tilting sediment recirculating flume with 10 m long and 60 cm wide was used. Flow is run in movable bed using sediment with d50=0.73 mm and s=2710 kg/m3. Two abutments were installed in the side of the channel. These were separated variously. Scour depth around the two abutments was measured using point gauge. Researches were also done for a horizontal ring-formed shield placed on the abutments prove to diminish the scour depth. Research results on scour at two abutments indicate that the scour depth of the front abutment is greater then the one of the rear abutment. Detailed results are: when the two abutments touch each other, the scour depth of the front abutment is not influenced; when the two abutments are separated, the scour depth of the front abutment begins to increase but eventually falls out. A maximum increase of scour of the front abutment, reach 30 % compared with the scour depth of a single abutment, is found when the separation of the two abutment, a/Dp, is about 3; When the two abutments are much separated, a/Dp≈12, the front abutment is not influenced; The scour depth of the rear abutment is always smaller then the one of the front abutment; The scour depth between the two abutments diminish rapidly and is negligible for a/Dp > 12 ; when ring-formed is placed on the abutment, scour depth of the front abutment is reduced reached 36,7 %.