ارزيابي رفتار تراكم پذيري و تغيير حجم خاك هاي ماسه اي سيمانته

Investigating the Compressibility and Volume Change Behaviour of Cemented Sands

چكيده- بيشتر مطالعات آزمايشگاهي با موضوع بررسي و تبيين رفتار مكانيكي خاك ها ي س يماني شده در گذشته بر ارزي ابي ويژگي هاي مقاومت برشي اين مصالح استوار بوده است. در اين پژوهش سعي شده است كه خصوصيات تراكم پذيري و تغيير حجم و تحكيم ايزوتروپ بررسي شود. بنابراين ماسه ريز و بد دانه بند ي (K خاك هاي ماسه اي سيماني شده در شرايط تحكيم يك بعدي ( 0 شده سواحل بابلسر به عنوان مصالح پايه و گچ و سيمان پرتلند به عنوان عامل سيماني كننده استفاده شده است. نمونه ها با تراكم ها ي 1 ساخته شدند. دستگاه تحك يم ادومتر ب راي ارزي ابي ويژگ ي ها ي / 1 و 5 /0 ،0/ 50 و 70 درصد و درصد سيمان هاي 5 ، نسبي 30 تراكم پذيري يك بعدي و سلول سه محوري براي بررسي خصوصيات تغيير حجم ايزوتروپ استفاده شد. با انجام آزما يش ها ، رفتار و K تغيير حجم و تراكم پذيري خاك ماسه اي سيماني شده ارزيابي شد. از موارد بررسي شده تنش تسليم باندهاي سيماني در شر ايط 0 فشار ايزوتروپ در تراكم هاي نسبي و درصدهاي سيمان مختلف است. نتايج اين پژوهش نشان مي دهد كه تراكم نسبي خاك، درصد و نوع عامل سيماني كننده به شدت خصوصيات تغيير حجم خاك هاي سيماني شده را تحت تاثير قرار مي دهند. با ازدياد تراكم نسبي و درصد سيمان، سختي خاك سيماني شده افزايش يافته و به عبارتي ديگر بر مدول حجمي و فشار لازم براي خردشدگي باندها افزوده مي شود.

Abstract: Most of previous researches on cemented soils, concern about their shear strength. However, in present study the main issue is investigating compressibility of cemented sandy soils during one dimensional and isotropic compression loading conditions. The soil used in present study is fine and poorly graded sand from the shores of Caspian Sea (in the city of Babolsar located in North Iran). Gypsum and Portland cement are used as the cementing agents. Gypsum cemented samples were tested under completely dry condition; however, samples cemented with Portland cement were tested in saturated state. Indeed, a back pressure of 15 kPa was applied for about one hour to receive a Skempton B value of 0.9 more for the samples. The specimens were made in three relative densities of 30, 50 and 70 and cement contents of 0.5, 1 and 1.5 percent. All the samples were cured for seven days in a humid room under a constant temperature to gain their strength before the tests. Oedometer tests were used for one dimensional compression (K0 condition) and triaxial apparatus cell with a diameter of 100 mm was used for the isotropic compression tests. The pressure was applied in increments of 50 kPa during the tests. Compressibility and volume change of cemented samples was investigated during the tests by considering e-Ln(pʹ) curves for all samples. Yield stress, bulk modulus and normalized stress of cemented matrix have been analyzed and effect of cement type, cement content and relative density on these properties have been investigated. Results showed that the mentioned parameters affect compressibility behaviour of cemented sand, for example bulk modulus and yield stress, increase with relative density and cement content. Cement type was another important factor in compressibility of cemented sand. For specimens with gypsum cementation, yield stress, bulk modulus and stress of cemented matrix were more than those with Portland cement. Also stress of cemented matrix increased with cement content and decreases with relative density. According to the results of experiments, a mathematical formulation suggested for calculation of yield stress in cemented soil and also bulk modulus. Moreover, new equations are presented to determine stresses in both cemented bonds and uncemented matrix of cemented soil. These equations are based on the critical state theory for uncemented matrix and a normalized framework for calculation of the stress in cemented bonds. Based on this framework, stress of cemented bonds can be predicted based on the yield stress and volumetric strain in cemented soil. As a result, stress-strain relation of soil can be determined during isotropic compression loading conditions.