| Summary: | One of the structural failure of soil caused by the earthquake is liquefaction. Liquefaction occurs in the layer of water-saturated loose sand due to receiving cyclic loading of earthquake vibrations that changes the nature of soil from solid to liquid state so that thes soil is unable to sustain the load of the building on or above it. To determine the effect of the load on the liquefaction potential experimental test was performed. An experimental study using a shaking table was performed using sample of sand which is from the sand of Kali Opak Pleret Yogyakarta. Earthquake parameters considered in this study include the earthquake maximum acceleration of 0,3g, 0,35g, 0,4g with duration of vibrating was for 32 seconds. Testing was done without load and load increase of 0,15 t/m2, 0,31 t/m2 and 0,46 t/m2. The value of relative density sand in the test ranged from 25 – 27 % accordance with the relative density in the field. Tool pore water pressure readings used in this study are pressure transducer and headmeter. Results evaluation of testing was done by comparing the pore water pressure and effective stress. Liquefaction would occur if the ratio of the increase in pore water pressure is more than one or equal to one (ru ≥ 1) otherwise if ru < 1 liquefaction would not occur. Based on the results of sieve analysis testing, sand of Kali Opak Pleret belongs to the zone of most susceptible to liquefaction. The same evident is shown from the observation with a stereo microscope, the shape of the sand particles tends to look round and almost uniformly, so it is liquefaction potential. Result testing using shaking table showed that the more is the load increase, the less is ratio of pore water pressure increase under the load. The highest ratio of the increase in maximum pore water pressure was obtained at testin without load with earthquake maximum acceleration of 0,4g is as much as 1,338 (pressure transducer I), 1,457 (pressure transducer II), and 1,379 (headmeter) and the lowest one is at the load of 0,46 t/m2 with earthquake acceleration of 0,3g. Over all potential liquefaction defence at load more than 0,22 t/m2 and at maximum load 0,46 t/m2, potential liquefaction suffering decrease between 41,90% - 53,10%. The high earthquake acceleration generates the higher ratio of increase of pore water preasure and the longer duration of liquefaction occurence. The maximum duration of liquefaction is 54 seconds (pressure transducer I), 43 seconds (pressure transducer II), 46 seconds (headmeter). The largest decrease occurred in the testing without load and earthquake acceleration of 0,4g is 4 cm while the smallest one occurred in the testing with a load of 0,46 t/m2 and earthquake acceleration of 0,3 g is 0,53 cm.
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