Effect of freeze-thaw cycles on shear strength of unsaturated bentonite modified clay
Introduction
Ningxia Hui Autonomous Region is located in the northern of China's Loess Plateau, which is the arid-semi-arid region of the northwest China. It is dry with little rainfall and extreme winter. The average annual minimum temperature is −28.4 °C, and the sub-zero temperature can last for about 107d (Dong et al., 2018), and the maximum freezing depth is 1.3m or more (Zheng et al., 2006). In Ningxia, previous studies have shown that the rises height of capillary water in clay was more than 2.0m (Xue, 2012). This serious frost-heave and freezing damage after freeze–thaw cycles often cause deformation of the roadbed, slip of the slope, crack and uplift of the lining (Zhao et al., 2015). Therefore, the study of freeze–thaw cycle damage on clay in Ningxia should be taken seriously.
From the microscopic point of view, the migration of capillary water is the main source of water supplement during the freeze-thaw process (Lu et al., 2017; Xu et al., 2016; Ghanbarian and Hunt, 2017; Watanabe and Osada, 2017; Bing et al., 2015). In the area of capillary water migration, only the part of clay which near the groundwater is saturated (Sr>85%). The middle and upper zone of clay are in an unsaturated state which are unsaturated soils. Therefore, as shown in Fig. 1, soil freeze-thaw zone can be divided into three parts. Since there is little rain during winter in Ningxia, only groundwater is considered as the source of water supply. In zone-I, it is unsaturated clay, which is far from the groundwater level, and there is no groundwater recharge during the freeze-thaw cycles, so it is a non-water supplement freeze-thaw region. In zone-III, it is saturated clay that recharged by groundwater during freeze-thaw process, and which is a freeze-thaw problem of saturated soil. Unsaturated soil, especially in zone-II, which has a larger frost-heave property and a higher proportion in the freeze-thaw zone. The freeze-thaw deformation in zone-II is the main component of foundation freeze-thaw deformation, and it is the significant part to research the freeze-thaw effect of clay, so the freeze-thaw deformation of unsaturated soil in the water supplement area (zone-II) should be considered seriously and firstly.
In order to understand the effects of freeze-thaw cycles on the physical and mechanical properties of clay, domestic and foreign scholars have conducted a series of researches in this area. Previous studies suggested that under the condition of freeze-thaw cycles, the strength and cohesion of soil showed a decreased trend, while the internal friction angle increased exponentially (Zhou et al., 2014; Wang et al., 2018; Viran and Binal, 2018). Watanabe et al. (Watanabe and Kugisaki, 2017) performed one-dimensional freeze-thaw test on describing the effects of macro-pores on the formation of frozen soil layers in unsaturated soils. Those results revealed that large pores in the soil can prevent the formation of frozen soil layers. Meanwhile, Steiner et al. (2017) have elaborated the freezing rate and shear strength will be influenced by altering and forming between capillary water and ice crystals. Some studies (Gao et al., 2016; Zhang et al., 2019) pointed that the cohesion and friction angle after freeze-thaw cycles of the clay decrease with the increase of water content and salt content, increase with the increase of dry density and degree of compaction.
According to present studies (Ghazavi and Roustaie, 2010; Ghazavi and Roustaei, 2013; Zaimoğlu et al., 2016; Aldaood et al., 2014a, 2014b; Orakoglu and Liu, 2017; Roustaei et al., 2015), many scholars have added new materials (additives) to enhance the freeze-thaw resistance of soils. Ghazavi et al. (Ghazavi and Roustaie, 2010; Ghazavi and Roustaei, 2013) verified the enhancement of geotextile layer on soil strength characteristics under the condition of periodic freeze-thaw cycles through unconsolidated and undrained triaxial compression test. The test results showed that the addition of geotextiles can effectively enhance the peak strength of the soil under periodic freeze-thaw and reduce the adverse effects of freeze-thaw process. Geotextile layer as a permeable material can transfer the water in the soil pores to the soil layer beyond the depth of the frozen soil, which can effectively reduce freeze-thaw damage. From the perspective of environmental protection and sustainable development, Zaimoğlu et al. (2016) incorporated the secondary product poultry feathers into high-plastic clay, after performed a series of triaxial and freeze-thaw cycles tests, the effect of randomly dispersed chicken feathers on the freeze-thaw cycles of high-plastic clay was studied. The results revealed that feathers can provide a acceptable resistance to slip at the interface between soil particles. Under different lateral pressure conditions, the deviatoric stress increases obviously with the increase of feather incorporation. Aldaood et al., 2014a, 2014b conducted a series of tests on open and closed freeze-thaw cycles. The tests verified that with the increase of cycles, the moisture content of samples increased, which make a decrease in the durability and strength of samples. During the open-system, the water supply and the appropriate gypsum content will have a significant impact on the strength of the soil, the addition of lime will increase the efficiency of samples on water absorption. Orakoglu et al. (Orakoglu and Liu, 2017) found that different added materials would lead to different properties of mixed samples, because different added materials would change the fracture mode of soil fracture surface. The results showed that the moisture content of soil can be effectively reduced by adding appropriate proportion of basalt and glass fiber to samples, and the yield strength can be improved under the condition of freeze-thaw cycles. Roustaei et al. (2015) studied the effect of polypropylene fiber on freeze-thaw characteristics of fine-grained soil, which shown that the reduction of elastic modulus and cohesion in freeze-thaw cycles can be effectively improved by adding polypropylene fiber, the fiber component increased the toughness and plasticity of samples, and also reduced its internal friction angle.
With the development of the economy, foundation engineering in seasonally frozen soil region is developing fast. In previous studies, the use of different additives in soil reinforcement has significant on reducing the freeze-thaw effect of soils. In order to investigate better materials to reduce the effects of freeze-thaw cycles in soils. In this study, bentonite will be used as an additive to study the cyclic freeze-thaw characteristics of clayey soil under limited water supply. Bentonite is a nonmetallic mineral with montmorillonite as its main mineral component. It has characteristics of expansion when mixed with water, and shrinkage when lost water, intensity deformation in different moisture content and outstanding ion exchange properties, which has been applied in soil reinforcement, soil impermeability improvement and soil water retention. Cui et al., 2010, 2018 carried out an experimental study on the improvement of sand permeability by combining bentonite and cohesive soil. Studies have shown that the combination of bentonite and clay can significantly reduce the permeability of sand, bentonite can effectively improve the compressive strength of clay, in a certain range, increasing the increment of bentonite can enhance the liquid limit, plastic limit, unconfined compressive strength (Wen et al., 2016). Bentonite grouts can effectively improve the engineering properties of granular soils (El Mohtar et al., 2015; Yoon and El Mohtar, 2015).
In comparative with traditional external additives, there are limited studies on the effect of freeze-thaw cycles on strength characteristics of unsaturated bentonite modified clay. In order to fill the gap of research in this area and reduce the impact of freeze-thaw damage, based on previous research experience and theoretical analysis, an orthogonal test scheme was designed based on the content of bentonite, dry density and saturation. Through visual analysis, variance analysis and regression analysis and other methods to find some conclusions which are beneficial to reduce the freeze-thaw effect of cohesive soil by compare with the unreinforced clay.
Section snippets
Test materials
The clay that used in this test was taken from the southern region of Ningxia. The soil samples were air-dried and sieved using 2 mm sieve. Only soils passing through 2 mm sieve was taken as samples. The basic physical and mechanical parameters of the cohesive soil are shown in Table 1, while the major chemical components are shown in Table 2. The main mineral components and XRD are shown in Fig. 2. The particle size distribution diagram is shown in Fig. 4. The bentonite used in the test is
Method for preparing samples
In this test, the dry density, saturation, and bentonite content were used as factors to design the L9 (34) orthogonal test scheme. The factors and levels are shown in the follows, where e is the error column. The orthogonal test scheme is shown in Table 4.
According to the test plan, specimens of natural clay were mixed with different saturation, dry density and content of bentonite. Then, mix them evenly, put them in a sealed bag, and place them in a moisturizing dish for not less than 24 h to
Results and discussion
The test program and cohesion test results are listed in Table 5, and the increment of cohesion are listed in Table 6. It can be seen from Table 6 that with the effect of freeze-thaw cycles, the cohesion shows a decrease trend, and the first freeze-thaw cycle has the greatest influence on cohesion and friction angle of specimens, and gradually stabilized after 7th freeze-thaw cycle. The maximum of change has reached to 24.84 kPa. Similar results were reported by Wang et al. (2018).
where: c is
Conclusion
In this study, according to the one-dimensional freeze-thaw test method that maintains the saturation before and after freeze-thaw cycles, the strength characteristics and freeze-thaw effects of bentonite modified clay under limited water supply conditions are studied. The function laws are analysed, and the relationship model among the strength characteristics and saturation, dry density, bentonite content and freeze-thaw cycles is established. The results are as follows:
- •
Before samples go
Author statement
All data, models, and code generated or used during the study appear in the submitted article.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The project is supported by Scientific research project of higher education in Ningxia (NGY2018027)
References (36)
- et al.
Impact of freeze–thaw cycles on mechanical behaviour of lime stabilized gypseous soils
Cold Reg. Sci. Technol.
(2014) - et al.
The effect of magnesite calcination conditions on magnesia hydration
Miner. Eng.
(2000) - et al.
Improving unsaturated hydraulic conductivity estimation in soils via percolation theory
Geoderma
(2017) - et al.
Freeze–thaw performance of clayey soil reinforced with geotextile layer
Cold Reg. Sci. Technol.
(2013) - et al.
The influence of freeze–thaw cycles on the unconfined compressive strength of fiber-reinforced clay
Cold Reg. Sci. Technol.
(2010) - et al.
Effect of waste tire cord reinforcement on unconfined compressive strength of lime stabilized clayey soil under freeze–thaw condition
Cold Reg. Sci. Technol.
(2012) - et al.
Electrokinetic and thermodynamic characterization of lime-water interface: physical and rheological properties of lime mortar
Construct. Build. Mater.
(2017) - et al.
Effects of freeze–thaw cycles on a fiber reinforced fine grained soil in relation to geotechnical parameters
Cold Reg. Sci. Technol.
(2015) - et al.
Performance and micro-structural development of MgO–SiO2 binders under different curing conditions
Construct. Build. Mater.
(2017) - et al.
Simultaneous measurement of unfrozen water content and hydraulic conductivity of partially frozen soil near 0°C
Cold Reg. Sci. Technol.
(2017)
A filtration model for evaluating maximum penetration distance of bentonite grout through granular soils
Comput. Geotech.
Experimental study on shear strength characteristics of sulfate saline soil in ningxia region under long-term freeze-thaw cycles
Cold Reg. Sci. Technol.
Laboratory investigation on tensile strength characteristics of warm frozen soils
Cold Reg. Sci. Technol.
Effect of long-term soaking and leaching on the behaviour of lime-stabilised gypseous soil
Int. J. Pavement Eng.
Cyclic freeze–thaw as a mechanism for water and salt migration in soil
Environmental Earth sciences
Study on the improvement of sand soil impermeability by the combination of bentonite and clay soil
Water-saving irrigation.
Freeze-thaw deformation characteristics of compacted loess in winter irrigation area under insufficient water supply
J. Ningxia Univ. (Nat. Sci. Ed.)
The relationship between winter temperature changes and atmospheric circulation anomalies in Ningxia
Sci. Technol. Eng.
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