| Summary: | Damage of the concrete pavement commonly occurs because subgrade deformation . Ununiform deformation of the subgrade form a cavity between subgrade and pavement . Nailed slab system used on pavement that was built on expansive soil . Nail slab system supported by concrete small pile that is fused to the concrete slab . Small pile made a good contact between pavement and subgrade to avoid cavity bettwen them. Value of the modulus of subgrade reaction be required for analysis of nailed slab system. Equivalent modulus of subgrade reaction is modulus of subgrade reaction that considering the influence of pile. Vertical displacement of the pile followed by vertical displacement of the surrounding soil. There was small difference between the vertical displacement of the pile and vertical dicplacement of the surrounding soil. These small value cause the frictional resistance on interaction between soil and pile can not be fully mobilized .
Tested in the laboratory on scaled nail slab system. Eksperiment was modeled in test box measuring 1.5 x 1.5 x 1.5 m3 . Plates with diameters of 3� was used in eksperiment. The pile variations was 10cm , 15cm , and 20cm and 2 cm in diameters. Nailed slab system was also calculated use Hardiyatmo (2011) method and modeled by the computer program (Plaxis 8.5). Parameters used were obtained from the testing of physical and mechanical properties of the soil . The dry density of sand used was 1.9 gr/cm3, the friction angle was 32.23ο, and the value of modulus of elasticity was 17000 kN/m2. Modulus of elasticity of the concrete used to create a test object was 21000000 kN/m2 . The result of laboratory test and computer modeling was compared. Computer modeling followed by using plate diameter 76 cm , 100 cm , and 125 cm forl approach the behaviora of nailed slab system on big scale. Approach of the difference between vertical displacement of the pile and surrounding soil ( δ0 ) obtained using computer modeling results. Mobilized frictional resistance can be determined by calculating the pile displacement factor ( α ) multiplied by 100 . Mobilized friction resistence expressed in percent ( % ) .
The results of test in laboratory showed modulus of subgrade reaction more greater with increasing of the length of pile. Comparison of modulus of subgrade reaction shows the largest difference in the value of the increase in modulus of subgrade reaction was 9.80 % . The largest difference of modulus of subgrade reaction was 6.60 % . Frictional resistance mobilized at the plate with a diameter of 7.6 cm with 10cm , 15 cm , and 20 cm pile long , respectively was 23.8 % , 36.9 % , and 43.9 % . Frictional resistance mobilized on the use of 76 cm diameter plate with 100 cm , 150 cm , and 200 cm pile long , respectively for 18.5 % , 30.1 % , and 38.2 % . The Ratio of δ/δ0 gets smaller with increasing of vertical displacement of the plate .Pile displacement factor ( α ) greater with increasing of pile vertical displacement.
Keyword : modulus of subgrade reaction, mobilized friction, plaxis
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