تاثير رطوبت، آهك و تر و خشك شدن بر فشردگي پذيري و مقاومت برشي خاك

چكيده انگليسي :

041 Effect of Water Content Lime and Wetting and Drying on Soil Compressibility and Shear Strength Rasoul Hasan Zahraei rh zahraei@yahoo com Janu 20 2013 Department of Agricultural Machinery Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Abbas Hemmat ahemmat@cc iut ac ir AbstractIn nature soils could be compacted due to own weights external loads and internal forces as a result of wettingand drying processes At any time soil will have an specific compressive strength as a result of its texture andstructure internal processes such as cementing and previous external compressive pressure like loaded wheeltraffic 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 compactibility Soilcompaction in fields usually occurs due to flood irrigations during intensive crop production as well asmechanized harvesting operations by using heavy machinery in wet soils Soil strength is measured in terms ofthe maximum stress that can be applied before the occurrence of the substantial increase in soil compression Estimating the soil stress at its compaction threshold i e precompaction stress pc and the soil sensitivity toexcess compaction compression index Cc when the applied stresses due to the field traffic exceed the pc canbe useful to prevent soil compaction The soil strength is termed precompaction stress pc at which the soildeformation changes from reversible behavior elastic to the irreversible behavior plastic On the other hand due to soil is not an elastic and resilient matter at each loading and unloading cycles a permanent deformationoccurred in soil By limiting the load below pc the risk of additional soil compaction can be minimized One ofthe natural characteristics of the soils in arid and semi arid regions is having high calcium carbonate lime content There is little information on the effect of lime and soil hardening under wetting and drying cycles oncompaction strength of calcareous soils in Iran Therefore the objectives of this research were to study theeffects of lime percentage under wetting and drying cycles on soil load bearing capacity precompaction stress and shear strength and to determine the relationship between these two soil strength values In this research asilty loam soil with very low carbonate content was used Then soils with different carbonate percentages 10 30 and 50 were prepared In order to the soils to regain their natural structure first the soils were kept at fieldcapacity for two months and then kept in laboratory conditions for ten months Then each pot was slicedthrough into two parts The top part was used for samples without wetting and drying cycles and the bottompart was used for samples with wetting and drying cycles Then the soil was wetted to desirable water content 0 7PL 0 9PL and 1 1PL In samples without wetting and drying process and without any preload the half potwas used directly for loading whereas for the samples with preload 200 kPa the soil from the half pot wastransferred to metal cylinder with minimum disturbance Stress sinkage and stress strain curves were drawn forplate sinkage test PST and confined compression test CCT respectively For each curve three differentmethods were considered to determine the pc These methods were 1 Casagrande method 2 maximumcurvature and 3 intersection of virgin compression line VCL and x axis Soil shear strength parameters cohesion c and Internal friction angle were measured by using a direct shear box test The effects ofcarbonate wetting and drying cycles water content and preload on precompaction stress and shear strengthwere studied using a factorial experiment in a randomized complete block design with three replications Resultsshowed that in PST the maximum and minimum values of pc were obtained with Casagrande and maximumcurvature methods respectively In CCT

حسن زهرائي، رسول

تاثير رطوبت، آهك و تر و خشك شدن بر فشردگي پذيري و مقاومت برشي خاك

تنش پيش تراكمي , شاخص فشردگي , چرخه هاي تر و خشك شدن , كربنات كلسيم