Experimental Study on Stiffness of Weakly Bonded Sand at Low Confining Stress

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Experimental Study on Stiffness of Weakly Bonded Sand at Low Confining Stress

ارائه دهنده: Provider: Fatemeh Moradi

اساتید راهنما: Supervisors: Dr mohamad maleki

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr abas qadimi-Dr meysam zarinfar

زمان و تاریخ ارائه: Time and date of presentation: 2023

مکان ارائه: Place of presentation: Electricity department, seminar 1

چکیده: Abstract: Steep slopes and cliffs formed in cementitious sands are often either a geological hazard or an engineering challenge; Although at the harder end of cement-sand slopes (i.e. sandstone), the behavior of materials is expressed by the principles of rock mechanics, at their weaker end, the behavior of cement-sand is not completely similar to soil or rock. In these cases, it is often not clear whether the adhesive element of the material can be trusted or not. Studies have shown that there are soils in nature that contain a small percentage of cement. The effect of soil cementation can be best observed and understood from various experiments on soils with low cement percentage; Because such soils may have aspects of the behavior of cement and non-cement soils; Despite the many studies that have been done on sandy soils with additives, most of these studies are aimed at stabilizing the soil and finding an optimal percentage for the additive; While weak cement soils, depending on the type and amount of cement material in them, have significant strength, which in many cases may meet the needs of the project; In this research, sandy soil in a weakly cemented state was investigated; Also, the optimal moisture percentage and standard density were not used to consider the soil in a natural state. For the tested soil, Firuzkoh silica sand (sand 161) was used, and for cementing the soil, lime, whose chemical characteristics are mentioned in the text, was used with 0, 1, 3, and 5 percent, as well as 5 and 10 percent kaolinite clay which was prepared from Laljin city of Hamadan was also used in the samples. The triaxial test was used to check the strength and stress-strain behavior of the soil, and the pressure plate test was used to check the suction in the soil. To better examine the results of the triaxial test, the test was performed with a strain rate of 0.1 mm/min. The results showed that by adding lime to the soil, even at the rate of 1%, cement bonds are established between the soil grains and increase the soil strength. The fracture of the base soil under the triaxial device is in the form of a barrel, but with the addition of lime as a cement material to the soil, the brittleness increases and the fracture of the sample reaches from the barrel state to the 45 degree failure state. The bonds formed by lime in the soil are broken in the deviatoric stress below 150 kPa and the axial strain below 2%, and the strength is supported by the sand grains; The important point in this case is that the stiffness of the soil decreases with the increase of confining stress, and since the stiffness has an inverse relationship with soil settlement, the possibility of soil settlement increases at higher confining stresses. It should be noted that the distortion in the samples can be seen in confining stresses of 50 and 100 kPa, and is not visible in low confining stress, such as 25 kPa. In fact, the bonds formed in the confining stress are able to resist. By examining the SWCC diagram obtained from the pressure plate test, it was found that the base soil has low suction without the presence of lime, but when lime is added to the soil as a cement material, it creates a bond between the soil grains and the same issue It does not allow water to leave the soil and creates suction in the soil, which is about 100 kPa