Nowadays, using biopolymer as a ground improvement method has become very popular. However, since biopolymers are organic and degradable, their long-term effect is not fully known. In this study, the ...effects of biopolymers on the mechanical behavior of kaolin clay were investigated through a comprehensive program of experiments. Two types of biopolymer, i.e. xanthan gum and guar gum were chosen to investigate the effect of biopolymer type. For this purpose, specimens were prepared using standard Proctor energy at four different water contents (25%, 30% 35% and 40%) with 0.5%, 1%, 1.5% and 2% biopolymer inclusions. The specimens were cured for 1 d, 7 d, 28 d and 90 d. Moreover, some of the specimens were kept in the curing room for 3 years to observe the long-term effect of the biopolymers. At the end of the curing periods, the specimens were subjected to unconfined compression test, and scanning electron microscopy (SEM) analysis was performed to observe the mechanism of strength improvement. The results revealed that the unconfined compressive strength (UCS) of the specimens treated with biopolymers increased in all biopolymer inclusion levels and water contents up to a 90-d curing period. For specimens containing xanthan gum, the maximum strength increase was observed at 25% water content and 2% xanthan gum with 90-d curing. The strength increased 5.23 times induced by xanthan gum addition when compared to the pure clay. Moreover, the increase in strength reached 8.53 times in specimens treated with guar gum. Besides, increasing water content caused more ductile behavior, thus increasing the axial deformation.
•Xanthan gum and guar gum biopolymers were used to stabilize kaolin clay.•Unconfined compression tests were conducted on stabilized specimens at various water content.•Micro structure was studied by SEM pictures to explain strength gaining mechanism.•Biopolymer treated specimens were cured up to 3 years.
•Cement and waste bottle strips were used to improve strength of kaolin.•Unconfined compression tests were conducted on stabilized specimens at various plastic bottle strip content.•Energy absorption ...capacity and brittleness index of PBS-cement treated kaolin were determined.•Regression models were obtained for estimation unconfined compressive strength of treated kaolin.
In this study, the potential usage of wastewater bottle strips produced from polyethylene terephthalate (PET) as a reinforcing material for strength properties of cement stabilized clay was investigated. For this purpose; unconfined compression strength tests were conducted to determine the parameters affecting the strength properties of cement stabilized-reinforced clay. Four different ratios of cement (0, 3, 6, and 9%) were used for clay stabilization and waste bottle strips obtained by cutting from waste pet bottles were used for reinforcement. Considering that the waste bottle strips behave similar to the fiber material; cement stabilized-reinforced clay samples were prepared with the ratios of 0, 0.5, 1.0, 1.5, and 2.0%, which are generally used as reinforcement ratios for soil. The specimens were stored in the curing room for 1, 7, 28, and 90 days until testing. Test results were evaluated according to cement content, water bottle strip ratio and curing time parameters. The experimental results showed that the optimum water bottle strip ratio for maximum strength gain ranged from 1 to 1.5%. It was also observed that the plastic strips and cement used for soil improvement also changed the strength-deformation behavior of the kaolin clay. Besides, the augmentation in cement inclusion level and curing period increased the strength of kaolin clay.
Partial or complete replacement of soils by industry waste materials is becoming more prevalent due to its benefits including environmental considerations and improvements in engineering properties ...of soils. Geotechnical properties of EAF-slag-admixed soils are rarely studied in the literature, and beneficial outcomes are not well known. In this scope, the effect of electric arc furnace (EAF) slag inclusion on the geotechnical properties of clay soils was evaluated within an experimental framework. Clay soil was replaced with EAF slag at varying ratios of 30%–50%. Atterberg limits tests, Proctor tests, California bearing ratio tests, shear box tests and hydraulic conductivity tests were conducted to obtain the extensive mechanical properties and the strength parameters of the EAF-slag-admixed clays. It is primarily shown that with the addition of EAF slag, the liquid limit of the soil decreased and the maximum dry density, CBR value and shear strength increased. The presence of slag had a minor contribution on the permeability of the admixed soils. Although 50% of EAF slag was introduced to the clay, the soil mixture was still at an impermeable range. Generally, using EAF slag as a stabilizing material improved the geotechnical properties of clay soils.
This study focuses on the performance of fibers, improving the resistance to liquefaction in loose sands, medium sands, and dense sands in Izmir, Turkey. A systematic testing schedule consisting of ...cyclic triaxial tests was held under stress-controlled and undrained conditions on saturated sand specimens with and without fiber reinforcements. The major parameters having effects on the dynamic behavior such as fiber content, fiber length, and relative density on the liquefaction behavior and the excess pore water pressure developments of specimens with and without fibers were investigated. If the fiber content or the fiber length was increased in the specimens, higher number of loading cycles was needed in order to experience the liquefaction of sands. The reinforcement effect in medium-dense specimens was found to be apparently distinctive compared to loose specimens. The curves of pore water pressures and shear strains were achieved for the fiber-reinforced sands. The boundaries of pore water pressure curves presented in the literature on the clean sands were utilized in comparison with the pore water pressure curves of fiber-reinforced sands of this study. As a conclusion, the results presented in this study are useful to develop insight into the behavior of clean and fiber-reinforced sands under seismic loading conditions. Based on the test results, it was found that the number of loading cycles had a strong impact on the excess pore pressure generation.
Turkey is in an active earthquake zone. Recently, Izmir city was shaken by a major earthquake in October 2020. The earthquake caused extensive structural damage and more than 100 casualties. ...Therefore, the analysis of the dynamic response of local soils in this region is of great importance. In this study, the shear modulus and damping ratio of natural silts obtained from Izmir province are determined. A total of 29 cyclic triaxial tests and 12 tests with pre-loading were performed to establish a general framework for understanding the behavior of local silt soils before and after an earthquake. Besides the effect of an earthquake, the characteristic behavior of Izmir silts of different levels of plasticity was also investigated and significant changes were observed. In addition, the effect of void ratio, effective confining pressure, plasticity, and shear stress amplitude of the pre-loading stage on the dynamic characteristics of the low plasticity silts were investigated. It is understood that after seismic action, changes in the small strain behavior of silts are remarkable.
Soil improvement methods using environmentally friendly additives have gained popularity with increased environmental awareness. In the future, environmentally friendly polymers can be preferred in ...the stabilization of many geotechnical applications like the base of roads, landfills, and sub-base of foundations. This means the mechanical properties of these eco-friendly polymers should be investigated in detail. For this purpose, changes in the mechanical properties of specimens treated with different polymer types under freeze–thaw action were investigated. Three types of polymers which are xanthan gum, guar gum, and anionic polyacrylamide polymer were used to improve the strength properties of kaolin clay. The specimens were prepared in 3 different anionic polymer contents and 4 different biopolymer content. After 7, 14, and 28-day curing periods specimens were subjected to 5 and 10 cycles of freezing–thawing to observe freeze–thaw action by conducting unconfined compression tests and the control specimens were directly subjected to unconfined compression tests after the curing period. Regarding the outcomes obtained, both synthetic and biological polymer use induced strength gain. Guar gum which is a biological polymer is the most effective that improves the strength by around 8 times than pure clay. This increment ratio varied between 2 and 3.5 times in polyacrylamide polymer, which is a greater strength increase than in previous studies. In addition, curing time has no significant effect on strength gain in anionic polyacrylamide-contained specimens. It was also observed that freezing–thawing caused a drastic reduction in strength by around 5 to 60%, however, the anionic polymer is the most resistant to freeze–thaw considering the strength loss. As a result, eco-friendly polymers are suitable in regions exposed to freeze–thaw action between the seasons.
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•The efficiency of polyacrylamide polymer (PAM), guar gum and xanthan gum was compared.•Guar gum stabilization induced the greatest increase in strength.•PAM is the most resistant to freeze–thaw considering the strength loss.•Guar gum is more effective than xanthan gum and PAM under freezing-thawing.•Microscopic interactions between clay and polymers were investigated.
In this study, unconfined compression tests have been performed to investigate the effect of freeze–thaw cycles on strength properties of kaolin reinforced with fibers. Kaolin was mixed with ...bentonite in percentages of 10, 30, and 50 in terms of the dry mass of soil. Bentonite admixed kaolin specimens were prepared at optimum moisture contents and reinforced with varying fiber contents. The specimens were subjected to 0, 1 and 5 freeze–thaw cycles. It was found that, fiber inclusion to soil improved the mechanical properties of the soil; the peak strength increased by the existence of fibers and the strength loss after the peak strength decreased. It was also seen that the increment of the plasticity index required more fiber content to achieve a similar amount of compressive strength with the specimens that had a lower plasticity index. The unconfined compressive strength of unreinforced specimens decreased with increasing the number of freeze–thaw cycles, whereas reinforced specimens showed better performance and the strength reduction decreased with the optimum amount of reinforcing content. The lowest values of compressive strength are obtained after the 5th cycles of freezing-thawing of the specimens.
The propeller jet generated by a ship's propeller during berthing and unberthing from quays initiates sediment transport and causes scouring around the quay structures. Investigating the flow area ...caused by ship propeller jets at quays and piers is important in terms of determining the local scour at the seabed. In this study, the water jet formed by ship's propellers and sediment movements on the seabed were investigated. While medium sand is typically used as the sediment type in literature, fine-grained sand and silt were used as base materials in this study. As a result of the experiments conducted with a three-dimensional flow velocity measuring device (ADV), the measured three-dimensional velocity components and the propeller efflux velocity coefficients were redefined. By examining the time dependent scour graphs of silt and sand, their scour rates were compared, and time scales were obtained from graphs. Silt was observed to have a significantly slower scour rate compared to sand. Contrary to the findings in the literature, despite silt having a smaller median particle diameter than sand, the maximum scour depths of silt were found to be less than those of sand under the same experimental conditions. Based on the results of this study and previous studies, two equations were proposed to quantify the scour depth for sand material, and silt and sand-clay mixtures.
•Usage of silt as a seabed material.•Observation of time dependent scour development with bathymeter maps.•Investigation and comparison of scour time scales of silt and sand.•Calculation of propeller seabed-scour for sand, silt and clay-sand mixture.
This paper examines the strength characteristics of Portland cement-treated fat and lean clays (CH and CL) under the conditions of freeze–thaw cycles. Specimens of natural clays were mixed with ...Portland cement in different percentages of 5% and 10%, in terms of the dry mass of soil using two different water contents of 30% and 50% for CH type of clay soil and 20% and 30% for CL type of clay soil to represent different consistencies and workability of soils. Besides, a group of cement free specimens was prepared and/or a group of specimens was not subjected to freeze–thaw cycles for comparison reasons. All specimens were cured for 7 and 28days in a humidity controlled room at a constant temperature. After curing, specimens were subjected to a maximum of five cycles of closed-system freezing and thawing. Unconfined compression tests and ultrasonic pulse velocity tests were conducted on the specimens. The results of unconfined compression tests were evaluated in terms of water–cement ratio, curing period and the number of freeze–thaw cycles. Consequently, the compressive strength increased with the cement content increment of the clay specimens. While the specimens with highest cement content showed brittle behavior before freeze–thaw tests, they manifested less brittle behavior after freeze–thaw tests. The highest strength values were obtained in the specimens with low water contents. The compressive strength decreased as the freeze–thaw cycles increased, but cement treatment partially prevented the strength loss in freeze–thaw conditions. Generalized equations of strength development were assessed considering the total water–cement ratio and curing time effects for fat and lean clays that were subjected to 0, 1, and 5cycles of freeze–thaw tests. In this way, this study showed that clay water–cement ratio hypothesis can be used to analyze the strength development of clays at different freeze–thaw cycles. It was observed that a linear correlation existed between the ultrasonic pulse velocity and the unconfined compression strength values. Furthermore, the plasticity index of the specimens subjected to 5 freeze–thaw cycles showed a decrement for the clay which was highly plastic in its native condition. Finally, with this study it is proven that cement treatment techniques can be preferred to enhance the freeze–thaw durability of fat and lean clay soils.
•Cement treatment reduces the effects of freezing–thawing.•Untreated soil samples could hardly survive the effects of freeze–thaw cycles.•Generalized strength relationships are proposed.•UPV tests are performed.
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