تاثير افزودن طولاني مدت مواد آلي به خاك بر ظرفيت باربري و مقاومت برشي خاك

چكيده انگليسي :

Effect of Long Term Incorporation of Organic Matters into a Soil on its Load Support Capacity and Shear Strength Nahid Aghilinategh Nahidaghili 85@yahoo com January 4 2008 Department of Agricultural Machinery Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Abass Hemmat ahemmat@cc iut ac irMorteza Sadeghi sadeghimor@cc iut ac irAbstract Water content and organic matter are recognized as being important factors influencing soilcompactibility Sustaining soil organic carbon SOC is of primary importance in terms of improving thephysical and mechanical properties of soils in arid and semi arid regions The pre compaction stress andcompression index obtained from Log stress strain curve of a confined compression test are often usedas criteria for determination of load support capacity and suseptibility to compaction of a soil Theobjectives of the research reported here were to 1 characterize the soil physical properties andconsistency limits shirnkage limit SL plastic limit PL liguid limit LL and 2 obtain pre compactionstress compression index cohesion and angle of internal friction of a silty clay loam soil under long term seven years application of organic matters compost sewage sludge farm yard manure at three rates 25 50 and 100 t ha and one inorganic fertilizer combination 250 urea kg ha and 250 ammoniumphosphate kg ha These mechanical properties were determined at at two gravimetrical water contents WCs 17 1 and 20 9 db on remolded soil samples The experimental designs were consisted of 1 factorial design organic manure type organic manure rate and 2 orthogonal contrasts i control withinorganic fertilizer treatment and ii control and inorganic fertilizer with factorial group in a completelyranomized design with three replications Plate sinkage test PST and confined compression test CCT were used for determination of the pre compaction stress and compression index In this research Threedifferent models were fitted to log stress sinkage data for PST and log stress strain data for CCT withprogramming in Matlab software After fitting the models to the data the pre compaction stress wereobtained using three methods consisted of i cassagrand ii Maximum curvature and iii intersection ofvirgin compression line with x axis Soil shear strength was obtained using direct shear test Theremolded soil sample was preloaded by a stress of 00 kPa for 30 min The result showed that there was asignificantly linear and positive relationship between SOC and SL PL LL or friability index FI PL SL whereas the relationship with the soil bulk sensity BD was significantly negative The soil texture andplastic index PI LL PL were not affected by adding organic matter to the soil The application ofinorganic fertilizer increased all measured parameters while the increase was not significant for PL andSL as compared with the control The soil BD varied from 1 03 to 1 37 Mg m 3 The lowest BDs wererecorded in 100 Mg ha 1 sewage sludge and compost treatments whereas it was the highest in inorganicfertilizer treatment The PL varied from 19 to 30 d b With one percent increase in SOC the FI wasincreased by 3 9 The Casagrande s method showed highest values of pre compaction stress whereasmaximum curvature and intersection of compression line with x axis showed the lowest values at twowater contents for both PST and CCT The results showed that the pre compaction stress values fororganic matter added treatments were increased 1 to 3 and 1 to 3 5 times as compared to control treatmentfor PST and CCT respectively With an increase in SOC the compression index was significantlyincreased at 17 1 WC whereas at 20 9 WC the SOC did not have any significant effect oncompression index The effect of SOC on angle of internal friction was not significant By increasingWC the angle of internal friction significantly decreased Also with increasing SOC cohesion decreasedat 17 1 WC whereas it increased at 20 9 WC The decrease in pre compac

عقيلي ناطق، ناهيد

تاثير افزودن طولاني مدت مواد آلي به خاك بر ظرفيت باربري و مقاومت برشي خاك

pst , شاخص خردشوندگي