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Research Papers: Polar and Arctic Engineering

Study on Mechanism of Freeze-Thaw Cycles Induced Changes in Soil Strength Using Electrical Resistivity and X-Ray Computed Tomography

[+] Author and Article Information
Xiaoliang Yao, Fan Yu

State Key Laboratory of Frozen Soil Engineering,
Northwest Institute of Eco-Environment
and Resources,
Chinese Academy of Sciences,
Lanzhou 730000, China

Lili Fang

Department of Civil Engineering,
Sichuan College of Architectural Technology,
Deyang 618000, China

Jilin Qi

School of Civil and Transportation Engineering,
Beijing University of Architecture
and Civil Engineering,
Beijing 100044, China

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received May 26, 2015; final manuscript received November 7, 2016; published online February 16, 2017. Assoc. Editor: Lizhong Wang.

J. Offshore Mech. Arct. Eng 139(2), 021501 (Feb 16, 2017) (9 pages) Paper No: OMAE-15-1041; doi: 10.1115/1.4035244 History: Received May 26, 2015; Revised November 07, 2016

In this study, freeze-thaw cycles were conducted on samples of a fine grained soil from the Qinghai–Tibetan plateau which had been prepared with different dry unit weights. During freeze-thaw cycles, electrical resistivity was measured. The soil samples were also scanned by X-ray computed tomography (CT) before and after freeze-thaw cycles. Unconsolidated and drained (UD) triaxial compression test was performed to obtain the apparent friction angle and cohesion. Changes in the arrangement and connections between soil particles were analyzed so as to investigate the mechanisms of changes in the strength parameters. The electrical resistivity increased in all samples, regardless of the different original dry unit weights, which implies that in all cases the arrangement of soil particles became more irregular and attached area between soil particles was increased. These changes contributed to the increase of apparent friction angle. On the other hand, the CT scans indicated that, depending upon the original dry unit weight, freeze-thaw cycles induced strengthening or deterioration in particle connections, and thus apparent cohesion was increased or decreased. With three freeze-thaw cycles, changes in microstructure of soil samples led to increases or decrease in both the apparent friction angle and cohesion.

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Figures

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Fig. 1

Grain size distribution of fine grained soil from the Qinghai–Tibetan Plateau

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Fig. 2

Procedure followed when performing freeze-thaw cycles tests

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Fig. 3

Apparatus used for freeze-thaw cycles tests

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Fig. 4

The stress–strain curves for dry unit weight of 16.0 kN/m3: (a) before freeze-thaw and (b) after one freeze-thaw cycle

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Fig. 5

The stress–strain curves for dry unit weight of 18.3 kN/m3: (a) before freeze-thaw and (b) after one freeze-thaw cycle

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Fig. 6

The Mohr–Column failure envelopes for dry unit weight of 16.0 kN/m3: (a) before freeze-thaw and (b) after one freeze-thaw cycle

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Fig. 7

The Mohr–Column failure envelopes for dry unit weight of 18.3 kN/m3: (a) before freeze-thaw and (b) after one freeze-thaw cycle

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Fig. 8

X-ray CT scanning of soil sample: (a) location of the three scanned layers in the soil sample and (b) location of the 2-mm wide concentric rings in each scanned layer

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Fig. 9

Tomographical intensity in the three layers after one freeze-thaw cycle for the soil sample at dry unit weight of 18.3 kN/m3

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Fig. 10

Changes in shear strength parameters versus freeze-thaw cycles: (a) changes in apparent cohesion and (b) changes in apparent friction angle

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Fig. 11

Hysteretic curve of saturation degree versus matric suction

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Fig. 12

Deformation versus time curves during freeze-thaw cycles: (a) for the soil samples with dry unit weight of 16.0 kN/m3 and (b) for the soil samples with dry unit weight of 18.3 kN/m3

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Fig. 13

Relationship between CT damage index and dry unit weight change ratio at different freeze-thaw cycles

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Fig. 14

Changes in CT damage index versus apparent cohesion at different freeze-thaw cycles: (a) for the soil samples with a dry unit weight of 16.0 kN/m3 and (b) for the soil samples with a dry unit weight of 18.3 kN/m3

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Fig. 15

Images of X-ray computed tomography with dry unit weight of 16.0 kN/m3: (a) before freeze-thaw and (b) after one freeze-thaw cycle

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Fig. 16

Images of X-ray CT with dry unit weight of 18.3 kN/m3: (a) before freeze-thaw and (b) after one freeze-thaw cycle

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Fig. 17

Changes in electrical resistivity during the freeze-thaw cycles: (a) for the soil sample at a dry unit weight of 16.0 kN/m3 and (b) for the soil sample at a dry unit weight of 18.3 kN/m3

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Fig. 18

Changes in electrical resistivity versus freeze-thaw cycles

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