ارزیابی تغییرات چگالی و شاخص دوام سنگ شیست تحت تاثیر سیکل‌های انجماد-ذوب

ﻫﻮازدﮔﯽ ﺳﻨﮓ در ﻣﻨﺎﻃﻖ ﮐﻮﻫﺴﺘﺎﻧﯽ دوام و ﻣﻘﺎوﻣﺖ آن را در ﻃﻮل زﻣﺎن ﺗﺤﺖ ﺗﺎﺛﯿﺮ ﻗﺮار ﻣﯽ دﻫﺪ. ارزﯾﺎﺑﯽ دوام و اﺳﺘﺤﮑﺎم ﺳﻨﮓ ﻫﺎ در اﺛﺮ ﺳﯿﮑﻞ ﻫﺎی اﻧﺠﻤﺎد- ذوب ﻓﺎﮐﺘﻮر اﺳﺎﺳﯽ ﺑﺮای ﺗﺤﻠﯿﻞ ﭘﺎﯾﺪاری ﺳﻨﮓ ﻫﺎی ﺑﺴﺘﺮ ﭘﺮوژه ﻫﺎی ﻣﻬﻨﺪﺳﯽ از ﻗﺒﯿﻞ ﺗﻮﻧﻞ، ﻣﻌﺪن و ﻧﻈﺎﯾﺮ آن اﺳﺖ. در اﯾﻦ ﻣﻄﺎﻟﻌﻪ ﺗﺎﺛﯿﺮ ﺳﯿﮑﻞ ﻫﺎی اﻧﺠﻤﺎد- ذوب ﺑﺮ روی ﺷﺎﺧﺺ دوام ﺳﯿﮑﻞ ﻫﺎی دوم و ﭘﻨﺠﻢ، ﭼﮕﺎﻟﯽ ﺧﺸﮏ و ﺣﺠﻢ ﺳﻨﮓ ﺷﯿﺴﺖ ارزﯾﺎﺑﯽ ﺷﺪه اﺳﺖ. ﺑﺪﯾﻦ ﻣﻨﻈﻮر، 13 ﮔﻤﺎﻧﻪ در دﯾﻮاره ﻏﺮﺑﯽ ﻣﻌﺪن اﻧﮕﻮران ﺣﻔﺮ و ﻧﻤﻮﻧﻪ ﻫﺎی ﻣﻮرد ﻧﯿﺎز ﺗﻬﯿﻪ و آﻣﺎده ﺳﺎزی ﺷﺪه اﺳﺖ. در ﮐﻞ، 75 ﺳﯿﮑﻞ اﻧﺠﻤﺎد- ذوب روی ﻧﻤﻮﻧﻪ ﻫﺎ اﻋﻤﺎل و در ﺳﯿﮑﻞ ﻫﺎی 40 ،15 ،7 ،0 و 75، آزﻣﺎﯾﺶ ﻫﺎی آزﻣﺎﯾﺸﮕﺎﻫﯽ از ﻗﺒﯿﻞ ﺷﺎﺧﺺ دوام ﺳﯿﮑﻞ ﻫﺎی دوم و ﭘﻨﺠﻢ، ﭼﮕﺎﻟﯽ ﺧﺸﮏ و اﻧﺪازه ﮔﯿﺮی ﺣﺠﻢ ﻧﻤﻮﻧﻪ ﻫﺎ اﻧﺠﺎم ﺷﺪه اﺳﺖ. ﺑﺮ اﯾﻦ اﺳﺎس، رواﺑﻄﯽ ﺗﺠﺮﺑﯽ ﺑﺮای ﻣﺤﺎﺳﺒﻪ ﺷﺎﺧﺺ دوام و ﭼﮕﺎﻟﯽ ﺧﺸﮏ ﻧﻤﻮﻧﻪ ﻫﺎ ﺑﻪ ازای ﺳﯿﮑﻞ ﻫﺎی اﻧﺠﻤﺎد-ذوب ﻣﺨﺘﻠﻒ اراﯾﻪ ﺷﺪه اﺳﺖ. ﻧﺘﺎﯾﺞ ﺑﻪ دﺳﺖ آﻣﺪه ﻧﺸﺎن دﻫﻨﺪه ﮐﺎﻫﺶ ﻧﻤﺎﯾﯽ ﺷﺎﺧﺺ دوام ﺳﯿﮑﻞ ﻫﺎی دوم و ﭘﻨﺠﻢ و ﭼﮕﺎﻟﯽ ﺧﺸﮏ اﺳﺖ. ﻫﻤﭽﻨﯿﻦ، ﺣﺠﻢ ﻧﻤﻮﻧﻪ ﻫﺎ ﺑﺎ اﻓﺰاﯾﺶ ﺗﻌﺪاد ﺳﯿﮑﻞ ﻫﺎی اﻧﺠﻤﺎد- ذوب، اﻓﺰاﯾﺶ ﯾﺎﻓﺘﻪ اﺳﺖ. ﻫﻤﭽﻨﯿﻦ، ﻣﺸﺨﺼﺎت ﮐﺎﻧﯽ ﺷﻨﺎﺳﯽ ﺳﻨﮓ ﺷﯿﺴﺖ ﻫﻢ ﺑﺎ اﺳﺘﻔﺎده از ﻣﯿﮑﺮوﺳﮑﻮپ ﭘﻼرﯾﺰان و آﻧﺎﻟﯿﺰ xrd ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. ﻧﺘﺎﯾﺞ اﯾﻦ ﻣﻄﺎﻟﻌﻪ ﻧﺸﺎن داد ﮐﻪ ﮐﺎﻧﯽ ﻫﺎی اﺻﻠﯽ ﺗﺸﮑﯿﻞ دﻫﻨﺪه ﺳﻨﮓ ﺷﯿﺴﺖ ﺷﺎﻣﻞ ﮐﻮارﺗﺰ، ﮐﻠﺴﯿﺖ، ﺑﯿﻮﺗﯿﺖ و ﮐﻠﺮﯾﺖ اﺳﺖ. در ﻧﻬﺎﯾﺖ، ﺑﺮای اﻋﺘﺒﺎرﺳﻨﺠﯽ ﻧﺘﺎﯾﺞ ﺑﻪ دﺳﺖ آﻣﺪه و ﺑﺮرﺳﯽ دﻗﯿﻖ ﺑﺎﻓﺖ ﻧﻤﻮﻧﻪ ﻫﺎ، ﺳﻨﮓ ﺷﯿﺴﺖ در ﺣﺎﻟﺖ ﺑﮑﺮ و ﭘﺲ از اﻋﻤﺎل 75 ﺳﯿﮑﻞ اﻧﺠﻤﺎد- ذوب ﺑﺎ اﺳﺘﻔﺎده از ﻣﯿﮑﺮوﺳﮑﻮپ اﻟﮑﺘﺮوﻧﯿﮑﯽ ﻣﻄﺎﻟﻌﻪ ﺷﺪ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن دﻫﻨﺪه ﻣﺘﺮاﮐﻢ ﺑﻮدن ﺑﺎﻓﺖ ﻧﻤﻮﻧﻪ ﻫﺎ ﻗﺒﻞ از ﻫﻮ ازدﮔﯽ ﺑﻮده ﮐﻪ در آن ﻓﺎﺻﻠﻪ ﺑﯿﻦ ﺳﻄﻮح ﺷﯿﺴﺘﻮزﯾﺘﻪ ﺧﯿﻠﯽ ﮐﻢ اﺳﺖ. ﺑﺎ اﯾﻦ ﺣﺎل، ﭘﺲ از اﻋﻤﺎل 75 ﺳﯿﮑﻞ اﻧﺠﻤﺎد- ذوب، ﻓﺎﺻﻠﻪ ﺑﯿﻦ ﻧﺎﭘﯿﻮﺳﺘﮕﯽ ﻫﺎ اﻓﺰاﯾﺶ ﯾﺎﻓﺘﻪ و ﺗﺮک ﻫﺎی ﺟﺪﯾﺪی در راﺳﺘﺎی ﻋﻤﻮد ﺑﺮ ﻣﺤﻮر ﻃﻮﻟﯽ ﻧﻤﻮﻧﻪ ﻫﺎ اﯾﺠﺎد ﺷﺪه اﺳﺖ.

Evaluating the variations of density and durability index of schist rock under the effect of freezingthawing cycles

Rock weathering affects its durability and strength in mountainous areas during the time. Evaluating durability and strength variations of rocks under freezing and thawing (FT) cycles is a key factor for stability analysis of bedrocks in engineering projects such as tunnel, mine and etc. In this study, the influence of FT cycles on second durability index, fifth durability index, dry density and schist rock volume has been evaluated. For this purpose, 13 boreholes have been drilled in western wall of Angouran mine and required samples have been prepared. In overall, 75 FT cycles have been conducted upon the samples and laboratory tests including durability index of second and fifth cycles, dry density and measurement of samples volume have been carried out in 0, 7, 15, 40 and 75 cycles of FT. On this basis, new equations presented and suggested to calculate durability index and dry density of samples in different FT cycles. The obtained results showed that durability index of second and fifth cycles and dry density both decreased exponentially. Also, volume of samples has been increased by increasing the number of FT cycles. In addition, mineralogical characteristics of schist rock have been studied by optical microscope and XRD analysis. Results of these analyses showed that Chlorite, Biotite, Calcite and Quartz are main constructive minerals of the schist rock. Finally, intact and weathered schist samples (after 75 cycles of FT) are studied by an electronic microscope to validate the results and evaluate the effect of weathering on the microstructure of specimen’s texture. Obtained results indicated that the texture of samples was dense before weathering in which spacing of the schistosity beddings was very low. However, after 75 cycles of FT, the discontinuity spacing was increased and new cracks were created in the body of samples perpendicular to the longitudinal axis.