The effects of suction history on the cyclic behavior of unsaturated road base filling materials

doi:10.1016/j.enggeo.2020.105775

Engineering Geology

Volume 276, October 2020, 105775

https://doi.org/10.1016/j.enggeo.2020.105775 Get rights and content

Highlights

•
The cyclic behavior of CTAs under various suction history is investigated.
•
The permanent axial strain of CTAs decreases with the maximum suction history.
•
The effect of drying-wetting cycles on permanent strain is found to be significant.
•
The effect of suction history on the resilient modulus is limited.

Abstract

Road base is usually subjected to cyclic traffic loadings as well as environment loads. Evidence shows that excessive permanent deformation of the road base may occur under the action of traffic loads and the complicated suction history induced by climate change. Currently, how the suction history of road base affects its long-term deformation remains unclear. To gain a deep understanding of the long-term deformation of road base, cyclic loading tests were conducted on the road base aggregates (mixture of crushed tuff aggregates and clay fines) under controlled suction and suction histories. A large-size soil-water characteristic curve (SWCC) test apparatus was designed and manufactured for the water retention test of the large-size specimen, and the large-diameter cyclic triaxial testing system (LDCTTS) was upgraded with the unsaturated control system to control the matric suction and suction history during the cyclic loading test. Test results show that the permanent axial strain of the mixture has a negative correlation with the current suction and maximum suction history. The effect of drying-wetting cycles on the permanent axial strain is significant. The permanent axial strain decreases with drying-wetting cycles at the drying path, while increases with drying-wetting cycles at the wetting path. The resilient modulus increases significantly with the current suction magnitude while is independent of the suction history.

Introduction

The road base is an important component of the pavement structure, which plays a key role in bearing upper traffic loadings and transferring them to the subgrade. The road base is usually exposed to the atmosphere, and the road base layers are generally in unsaturated conditions. Studies show that the matric suction in the road base layers can reach 100 kPa (Heath et al., 2004), and the seasonal changes of moisture content lead to the complicated suction histories of the road base layers (Bicalho et al., 2015a; Bicalho et al., 2015b; An et al., 2017). The existence of matric suction can improve the cyclic behavior of road base under cyclic traffic loadings (Inam et al., 2012; Ishikawa et al., 2014; Cao et al., 2017). The invasion of fines into the road base through muddy pumping from the subgrade or particle breakage can magnify the influence of suction on the road base performance (Duong et al., 2013; Ebrahimi et al., 2015; Ngo et al., 2017).

To study the effect of moisture content on the road base performance, Cerni et al. (2012), Cao et al. (2017) and Cao et al. (2018) investigated the cyclic behavior of road base filling materials under cyclic loadings in optimum moisture content and saturated moisture content, and it was found that the specimen in full saturation presented larger permanent strain and lower resilient modulus than that in optimum moisture content. Gabr et al. (2013) conducted the large-diameter cyclic triaxial tests on the crushed concrete aggregate and concluded that the resilient modulus and permanent strain of the aggregate depended on both the moisture content and applied cyclic stress. Duong et al. (2013) had done the large-scale cyclic triaxial test on the materials of the interlayer between the subgrade and ballast of an ancient railway in France, and the test results showed that the invasion of fines would increase the permanent axial strain in nearly saturated condition while decreasing the permanent axial strain at the lower water content due to the existence of suction. Rahman and Erlingsson (2016) further revealed that the resilient modulus presented an upward trend following the increasing of water content until the optimum water content, and then showed a downward trend above the optimum moisture content. Trinh et al. (2012) conducted a series of cyclic tests on the fouled-ballast in ancient railway track substructure, and the results suggested that the lower moisture contents in samples led to higher shear strength and lower permanent strain. These researches have revealed the significant effect of moisture content on the cyclic behavior of the road base filling materials, while the suction in the specimens is not measured or controlled in these tests which hinder the study of the cyclic behavior of the road base under the framework of unsaturated soil mechanics.

To investigate the effect of matric suction on the cyclic behavior of the aggregates, Azam et al. (2015) conducted the water retention test on recycled clay masonry and concrete aggregate by the filter papers and hanging water column method to obtain the soil-water characteristic curves (SWCC). Then a series of cyclic loading tests on the aggregate were conducted by the large-diameter triaxial test apparatus at different water content, and an equation was proposed to predict the permanent strain of the aggregate at different suction based on the cyclic testing results and SWCC. Ekblad and Isacsson (2006) improved the triaxial testing system with a high-capacity suction probe for unsaturated unbound granular materials to measure the suction directly, and testing results showed that the resilient modulus of the coarse materials decreased slightly when brought close to saturation, while would respond with a substantial loss upon increased water content when fines content was high. By applying the axis-translation method, Craciun and Lo (2010) improved the large-diameter triaxial test apparatus with the suction controller system, which was proved to be effective in conducting the cyclic tests on unsaturated coarse grain materials. Ishikawa et al. (2014) upgraded the large-diameter triaxial tests by adopting the hydrophilic microporous membrane filters instead of the ceramic disks to shorten the equilibrium time in the samples. Ahmadinezhad et al. (2019) combined the hanging water column method and axis-translation method to control suction in the coarse-grained soils and the merit of this method was illustrated through the comparison of soil shear modulus obtained by constant-suction tests and constant-water content test. Ng et al. (2017) carried out cyclic tests on specimens under different matric suction to study the change of shear modulus and damping ratio of the road base with suction. Test results revealed that the increase of matric suction could increase shear modulus and decrease the damping ratio.

The drying-wetting effect and the suction history of road base filling materials may have a considerable effect on its cyclic behavior under the traffic loads. Currently, few researches have been presented to study the effects of suction history on the dynamic behavior of road base filling materials. Testing on clay and silt through the regular-size triaxial test apparatus have shown that the suction and suction history have significant effects on the resilient modulus and the permanent strain of the soil under the cyclic loadings (Banerjee et al., 2020; Ng and Xu, 2012; Goh et al., 2014; Guney et al., 2007; Han and Vanapalli, 2016). However, the influence of the suction history on the cyclic behavior of the road base filling materials remains unclear. Therefore, it is necessary to investigate the effects of suction history on the cyclic behavior of the road base fillings to grasp a deep understanding of the long-term performance of the road.

In the present study, the water retention test was firstly conducted on the crushed tuff aggregates mixed with fines by the large-size SWCC testing apparatus; then the large-diameter triaxial testing apparatus was upgraded with an unsaturated testing module and the cyclic loading tests were conducted on the unsaturated mixture under controlled suction and suction history. The long-term behavior of road base under cyclic traffic loads and different suction paths were revealed.

Section snippets

Testing materials

The crushed tuff aggregates (CTAs) is a major source of road base filling materials on the southeast coast of China. Tuff is a kind of volcanic rock with the characteristics of high porosity, lobed, and complex composition (Wyering et al., 2014). To simulate the road base filling materials fouled by fines, CTAs were mixed with Kaolin clay at a relatively low mass ratio of 3% (Duong et al., 2013). Fig.1 shows the gradation curves of CTAs, Kaolin clay, and the clay-CTAs mixture. The clay-CTAs

Permanent axial strain

Series 1 tests were carried out to study the effect of current suction on the permanent axial strain and resilient modulus of the mixture subjected to cyclic traffic loading. Fig. 9 shows the permanent axial strain εp 1 versus the loading cycles N under different current suction (s = 0 kPa, 30 kPa, 60 kPa, and 90 kPa) and two cyclic stress amplitudes (q^ampl = 60 kPa and 100 kPa). εp 1 increases at a high rate at the beginning of tests, and then tends to increase slowly at a low constant rate

Discussions

The road base filling materials may be fouled by fines due to the mud pumping from the subgrade during the life span of roads, which would change the mechanical and hydraulic properties of the road base. The in-situ measurement shows that the road base can experience a complicated suction history during its service time (Blight, 1997; Bicalho et al., 2015a, Bicalho et al., 2015b, An et al., 2017; An et al., 2018). Systematic research on the long-term behavior of road base materials under cyclic

Conclusions

To better grasp the long-term deformation of road base under cyclic traffic loads and complicated suction histories, the water retention test has been conducted on the clay-CTAs mixture to test the soil-water characteristic curve (SWCC), then a series of cyclic loading tests under different suction histories have been conducted by the large-diameter cyclic triaxial tests. The effects of current suction, maximum suction history, drying-wetting cycles on the cyclic behavior of unsaturated road

Declaration of Competing Interest

None.

Acknowledgements

The authors wish to acknowledge the support of the National Key Research and Development Plan of China (Grant No. 2016YFC0800200), the National Natural Science Foundation of China (Grant Nos. 51778571, 51978611), Program of International Science and Technology Cooperation (Grant No. 2015DFA71550).

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View full text

The effects of suction history on the cyclic behavior of unsaturated road base filling materials

Highlights

Abstract

Introduction

Section snippets

Testing materials

Permanent axial strain

Discussions

Conclusions

Declaration of Competing Interest

Acknowledgements

Soil Dyn. Earthq. Eng.

Comput. Geotech.

Comput. Geotech.

Eng. Geol.

Soil Dyn. Earthq. Eng.

Eng. Geol.

Constr. Build. Mater.

Transport. Geotech.

Soils and foundations

Build. Environ.

Eng. Geol.

Soils Found.

Soils Found.

Soils Found.

Eng. Geol.

Soils and foundations

J. Volcanol. Geotherm. Res.

A constitutive model for partially saturated soils

Géotechnique

D698-12e2 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 ft-lbf/ft3 (600 kN-m/m3))

D5084-16a Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter

D2487-17e1 Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)

D3999 Standard Test Methods for the Determination of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial Apparatus