ﺑﺮرﺳﯽ و ﻣﻘﺎﯾﺴﻪ وﯾﮋﮔﯽﻫﺎي ﻣﻘﺎوﻣﺘﯽ ﺧﺎكﻫﺎي ﻣﺎﺳﻪاي ﺑﺎ ﺗﻐﯿﯿﺮ درﺻﺪ رﻃﻮﺑﺖ و ﻣﺸﺨﺼﺎت ﺑﺨﺶ رﯾﺰداﻧﻪ

Investigating and comparing the resistance characteristics of sandy soils with changing the percentage of moisture and fine-grained characteristics

در ﻃﺒﯿﻌﺖ، ﺧﺎك ﻣﺎﺳﻪاي ﺑﻪ ﻧﺪرت ﺑﻪ ﺷﮑﻞ ﺗﻤﯿﺰ و ﺧﺎﻟﺺ ﻣﯽﺑﺎﺷﺪ و اﻏﻠﺐ داراي ﻣﻘﺎدﯾﺮ ﻣﺨﺘﻠﻔﯽ رﯾﺰداﻧﻪ اﺳﺖ. اﻧﺘﻈﺎر ﻣﯽرود ﮐﻪ ﺣﻀﻮر رﯾﺰداﻧﻪ در ﺧﺎك ﻣﺎﺳﻪاي ﻋﻤﻠﮑﺮد ﻣﻘﺎوﻣﺖ ﺑﺮﺷﯽ و اﺗﺴﺎﻋﯽ ﺧﺎك ﻣﺎﺳﻪ را ﺗﺤﺖ ﺗﺄﺛﯿﺮ ﻗﺮار دﻫﺪ؛ ﻟﺬا در ﺗﺤﻘﯿﻖ ﺣﺎﺿﺮ ﺑﺎ ﯾﮏ اﯾﺪه ﺟﺪﯾﺪ در ﺳﺎﺧﺖ ﻧﻤﻮﻧﻪ ﻫﺎ، رﻓﺘﺎر ﻣﻘﺎوﻣﺘﯽ و اﺗﺴﺎﻋﯽ ﻣﺨﻠﻮط ﻣﺎﺳﻪ ﺗﺮﮐﯿﺐ ﺷﺪه ﺑﺎ رﯾﺰداﻧﻪ ﺑﺎ اﺳﺘﻔﺎده از دﺳﺘﮕﺎه ﺑﺮش ﻣﺴﺘﻘﯿﻢ ﮐﻮﭼﮏ ﻣﻘﯿﺎس ﺑﺎ دو ﻧﻮع رﯾﺰداﻧﻪ ﺳﯿﻠﺖ و رس و در ﭼﻬﺎر درﺻﺪ رﯾﺰداﻧﻪ ﻣﺘﻔﺎوت 30 ،20 ،10 و 40 و در ﺳﻪ ﺗﺮاﮐﻢ ﻧﺴﺒﯽ 60 ،30 و 90 درﺻﺪ و ﺑﺎ دو درﺻﺪ رﻃﻮﺑﺖ ﺑﻬﯿﻨﻪ و اﺷﺒﺎع، آﻣﺎده و ﺗﺤﺖ ﺗﻨﺸﻬﺎي ﻗﺎﺋﻢ 1 ،0,5 و 1,5 ﮐﯿﻠﻮﮔﺮم ﺑﺮ ﺳﺎﻧﺘﯿﻤﺘﺮ ﻣﺮﺑﻊ ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺘﻨﺪ. ﻧﺘﺎﯾﺞ اﯾﻦ ﺗﺤﻘﯿﻖ ﻧﺸﺎن ﻣﯽدﻫﺪ ﮐﻪ اﻓﺰاﯾﺶ ﻣﻘﺪار رﯾﺰداﻧﻪ ﻣﻨﺠﺮ ﺑﻪ ﮐﺎﻫﺶ ﻣﻘﺎوﻣﺖ ﺑﺮﺷﯽ ﺧﺎك ﻣﺎﺳﻪاي ﻣﯽﮔﺮدد و رﯾﺰداﻧﻪ رﺳﯽ ﻣﻘﺎوﻣﺖ ﺑﺮﺷﯽ ﺧﺎك ﻣﺎﺳﻪ را ﺑﯿﺸﺘﺮ ﮐﺎﻫﺶ ﻣﯽدﻫﺪ. ﻫﻤﭽﻨﯿﻦ اﻓﺰاﯾﺶ درﺻﺪ رﯾﺰداﻧﻪ ﭼﻪ از ﻧﻮع ﺳﯿﻠﺖ و ﭼﻪ از ﻧﻮع رس ﺳﺒﺐ ﮐﺎﻫﺶ اﺗﺴﺎع و زاوﯾﻪ اﺗﺴﺎع و ﻫﻤﭽﻨﯿﻦ زاوﯾﻪ اﺻﻄﮑﺎك داﺧﻠﯽ ﺧﺎك ﻣﺎﺳﻪاي ﻣﯽﮔﺮدد؛ اﻟﺒﺘﻪ رس ﻧﺴﺒﺖ ﺑﻪ ﺳﯿﻠﺖ ﭘﺎراﻣﺘﺮﻫﺎي ﻣﺬﮐﻮر را ﺑﯿﺸﺘﺮ ﮐﺎﻫﺶ داده اﺳﺖ. ﭘﺎراﻣﺘﺮ ﭼﺴﺒﻨﺪﮔﯽ ﻧﯿﺰ ﺑﺎ اﻓﺰاﯾﺶ رﯾﺰداﻧﻪ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ و اﻟﺒﺘﻪ در ﻣﺨﻠﻮط رﺳﯽ ﭘﺎراﻣﺘﺮ ﭼﺴﺒﻨﺪﮔﯽ ﺑﺎ اﻓﺰاﯾﺶ رس، ﺑﯿﺸﺘﺮ اﻓﺰاﯾﺶ ﯾﺎﻓﺘﻪ اﺳﺖ. ﻫﻤﭽﻨﯿﻦ ﻧﺮخ ﺗﻐﯿﯿﺮات ﭘﺎراﻣﺘﺮ ﭼﺴﺒﻨﺪﮔﯽ ﺑﺎ اﻓﺰاﯾﺶ درﺻﺪ رﯾﺰداﻧﻪ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ.

In nature, sandy soils are rarely clean and often contain some clay and silt. These fines grain have a significant effect on the resistance and dilation behavior of sandy soils. Therefore, in this study, resistance and dilation behavior of sand mixture with fine grains such as silt and clay using a small scale direct shear test have been studied. Tests are conducted on specimens of sand with various fine content ranging from 0 to 40%, density of 30, 60 and 90 percent and the samples are subjected to three normal stresses 0.5, 1.0 and 1.5 kg/cm2 with two percent of optimum and saturation moisture. The test results show with increase in percentage of fine grains, the shear strength of sandy soil decrease and with increase in percentage of clay the shear strength decreases further. Also, dilation angle and angle of friction decreases with increase fine grains content and cohesion parameter increases with increase fine grains, Of course, it more increases with increase clay content and the rate of change of the cohesion parameter increases with increasing fine-grained percentage.