تاثير چرخه هاي تر و خشك شدن و بارگذاري خارجي بر شاخص هاي تراكم پذيري خاك مزارع زير كشت نيشكر

چكيده انگليسي :

Effect of Wetting and Drying Cycles and External Loading on Soil Compactibility Indices of Sugarcane Field Soils Maryam Salehian Dastjerdi Saleh273@ yahoo com Mars 14 2011 Department of Agricultural Machinery Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Abbas Hemmat ahemmat@cc iut ac irAbstractIn nature soils could be compacted due to own weights external loads and internal forces as a result of wetting anddrying processes Intrinsic properties such as texture and dynamic properties such as water content wetting and dryingcycles and external loads are recognized as being important factors influencing soil compactibillity Soil compaction insugarcane fields usually occurs due to flood irrigations during intensive crop production as well as mechanized harvestingoperations by using heavy machinery in wet soils respectively Estimating the soil stress at its compaction threshold i e pre compaction stress pc and the soil sensitivity to excess compaction deformability coefficient CD or compressionindex CC when the applied stresses due to the field traffic exceed the pc can be useful to prevent soil compaction Theobjectives of this research were a to study the changes in pc and CD of coarse Sandy loam and fine silty clay textured soils with without wetting and drying cycles b to determine soil shear strength parameters of the soils c todetermine the relationship between the measured physical and mechanical parameters and d to obtain the waterretention characteristics curves for the soils Disturbed soil samples with coarse Sandy loam and fine silty clay texturedsoils were taken from the topsoil 0 20 cm layer of the sugarecane fields in Ahvaz province The compressive properties pc CD and CC of the two soils with or without wetting and drying cycles at two water contents of 0 9 plastic limit PL and 1 1PL and three preloads 0 100 and 200 kPa were obtained using plate sinkage test PST and confinedcompression test CCT Stress sinkage and stress strain curves were drawn for both PST and CCT respectively For eachcurve three different methods were considered to determine the pc These methods were 1 Casagrande method 2 maximum curvature and 3 intersection of virgin compression line VCL and x axis Soil shear strength parameters cohesion c and internal friction angle were measured using a direct shear box test Results showed that in PST themaximum and minimum values of pc were obtained with Casagrande and maximum curvature methods respectively InCCT the maximum values of pc were obtained with Casagrande method and the minimum values of pc were obtainedsometimes with maximum curvature method or with intersection of VCL and x axis When the soil texture changed fromsandy loam to silty clay the pc decreased about 5 5 and 27 in PST and CCT respectively With 5 cycles of wetting anddrying samples compared to no wetting and drying the pc increased by 27 5 and 23 in PST and CCT respectively When the water content increased from 0 9PL to 1 1PL the pc decreased by 13 5 and 27 in PST and CCT respectively With increasing the preload from 0 to 100 kPa and from 100 to 200 kPa this parameter was increased by 2 4 2 1 inPST respectively and by 2 3 and 1 8 in CCT respectively When the soil texture changed from sandy loam to siltyclay the CD in PST increased about 8 and Cc in CCT increased about 7 With 5 cycles of wetting and drying samplesthe CD in PST and Cc in CCT increased by 6 and 18 5 respectively When the water content increased from 0 9PL to1 1PL the CD and Cc increased and decreased by 3 5 and 13 respectively When the preload was increased from 0 to100 kPa and from 100 to 200 kPa the CD increased by 13 and 28 and the Cc decreased by 18 and 30 respectively The soil cohesion was increased and the internal friction was decreased with wetting and drying and when the watercontent increased from 0 9PL to 1 1PL When the preload increased from 0 to 100 kPa and from 100 to 200 kPa thecohesion was increased a

صالحيان دستجردي، مريم

تاثير چرخه هاي تر و خشك شدن و بارگذاري خارجي بر شاخص هاي تراكم پذيري خاك مزارع زير كشت نيشكر

تنش پيش-تراكمي , ضريب تغيير شكل پذيري , شاخص فشردگي , مقاومت برشي