ظرفيت باربري پي هاي سطحي واقع بر خاك چسبيده

چكيده انگليسي :

Bearing Capacity of Shallow Foundations on Geogrid Reinforced Cohesive Frictional Soil Fattah Vahid fattahvahid@yahoo com Date of Submission March 13 2011 Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Dr M A Rowshanzamir mohamali@cc iut ac ir AbstractUsing geosynthetics for improving the performance of shallow footings have been studied by many investigatorsduring last two decades Amongst available geosynthetic materials geogrids have more usage in reinforcing soilsbecause of their rigidity and high tensile strength Reinforcing geogrid layers transfer footing loads to the supportingsoil in a deeper and wider area Thus the reinforcements cause an increase in the soil bearing capacity as well as adecrease in the footing settlement In the present investigation bearing capacity of shallow footings on reinforcedcohesive frictional soils has been studied In this context footing model load tests have been carried out on a sandysoil as well as four cohesive frictional soils Thus the influence of cohesion as an effective parameter on the soilreinforcement efficiency and bearing capacity of footing has been studied Also the effect of variables such as thedepth of first reinforcement layer the length of reinforcement layer the vertical spacing and number ofreinforcement layers on the footing bearing capacity have been studied As a result the optimum amounts ofvariables have been offered for obtaining the maximum bearing capacity Then the soil cohesion effect on theoptimum parameters has been assessed Another beneficial aspect of soil reinforcement is the reduction of thefooting settlement which is due to the soil stiffness increasement This subject has also been investigated fordifferent reinforcement conditions Basing on the footing model load tests it was found that by increasing fine fraction of the supporting soil i e increasing the soil cohesion in a fixed compaction percentage the bearing capacity increased while thereinforcement efficiency decreased It was also observed that changing the type of adding clay to the testing sand changing clay mineralogy had no significant effect on the reinforcement efficiency In the tests that supporting soilwas reinforced only with a single layer of geogrid an optimum embedment depth was obtained in which the footingbearing capacity reached to a maximum value This depth was found to be 0 25B in this investigation B the footingmodel width This depth increased with increasing the cohesion and reached to 0 35B for cohesive frictional soils In the tests with a geogrid layer in the optimum depth increasing the reinforcement length caused an increase in thebearing capacity but this increase was negligible for the reinforcement lengths greater than a critical value Thecritical length was found to be about 4B for the sandy soil while it was around 3B for the cohesive frictional soils This result indicates that any cohesion increase in the reinforced soil causes a decrease in the reinforcement criticallength The results showed that regardless of the soil type the optimum vertical spacing of reinforcement layers wasfound to be 0 35B In addition the model tests showed that in a cohesive frictional soil the bearing capacity goes upby increasing the number of layers up to four layers For reinforcement layers more than 4 layers there was nosignificant increase in bearing capacity Moreover an enhancement in the stiffness of the reinforced supporting soilswas noticed i e the stiffness increased up to 3 5 times in the reinforced sandy soil and 2 1 times in one of thereinforced cohesive frictional soils with the optimum reinforcement geometry This result clearly indicates that thesoil reinforcement may significantly decrease the footing settlement The settlement decrease was found to be morepronounced in the greater bearing pressures Key Words Bearing Capacity Cohesive Frictional Soil Geogrid Stiffness Settlement

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ظرفيت باربري پي هاي سطحي واقع بر خاك چسبيده - اصطكاكي مسلح به ژئوگريد

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